Summer 2021 Systems Guide

Guide Selfbuild

THIS ISSUE: SYSTEMS GUIDE

102 energy assessment

104

VENTILATION

122

RENEWABLES

112

HEATING & HOT WATER

100 OVERVIEW / 118 HEAT EMITTERS 126 GOING OFF GRID / 128 FIRST HAND EXPERIENCE IN CO DOWN SU MMER 2021 / SE L F B U IL D / 9 9

SYSTEMS GUIDE / OVERVIEW

Warm and cosy There are electrical and mechanical components that make your home warm (usually in the form of central heating), cosy (heating, lighting) and healthy (regulating indoor air quality through ventilation and the building fabric). In this guide we are focusing on ventilation, heating, and on site electricity supply.

image: Freepik.com 10 0 / S E L FB U IL D / SU MMER 2 0 2 1

Guide Selfbuild

hese days, we have become increasingly reliant on mechanised systems to help bring comfort into our homes. Despite the rising awareness of passive houses, this is likely to remain the case, especially as we turn more and more to alternative technologies for our heating, hot water and electricity, writes Patrick Waterfield.

T

Dr Patrick Waterfield is an energy consultant based in Belfast.

Many years ago I was invited on a study tour to Denmark, to view (and review) an energy efficient house sponsored by the makers of a window company. The house was very highly mechanised and controlled, with automatic opening windows as well as mechanical ventilation, motorised solar shading, a heat pump providing hot water as well as heating, plus solar water heating tubes and also photovoltaic panels.

It was very impressive, but the overwhelming feeling I came away with was of a huge maintenance liability. It made me resolve to make my own selfbuild, which I was planning at the time, less reliant on mechanised systems.

While more mechanisation generally means better control, it also means more maintenance and access requirements, which need to be taken into account in planning your build.

Accepting that some level of mechanised systems will be needed for your home, you must plan for them at the very start of your project. They may be among the last things you install in your build, but cannot be left as an afterthought in your design process. This is one of the things you must plan for at the very start, as these choices will have a knock-on effect on how you insulate and build your house.

Some systems will require very good airtightness, such as

PV panels and heat pump in County Cork new build

mechanical ventilation with heat recovery. Most will have to be factored into your floor plans as they will, in all likelihood, require at least part of a utility room, if not an entire plant room.

You will have to set aside space for all of the service runs – piping and ducting routes will have to be laid out as efficiently (i.e. short and with a minimum of bends) as possible, the units will have to be given a space in the home, enough room around them for maintenance access and the

controls carefully thought out so they are user friendly.

Also important is the fact that system choices will influence your interior design scheme.

Think of the difference between radiators and underfloor heating, or a mixture of both. Where will the controls go? Each solution will have a visual impact.

It is not possible to cover absolutely every combination and permutation of building fabric and fit-out – especially with a self-build. No two are the same.

So the aim of this guide is to give you an idea of what options are open to you.

The bottom line is, choose what systems will make your house comfortable. As with all things self-building, do your research at the design stage to increase your chances of success. Identify potential suppliers, obtain quotes and discuss issues as early as possible with your chosen suppliers/installers.

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SYSTEMS GUIDE / ENERGY ASSESSMENT

Energy

assessment There are two basic things to take into account when you choose your systems: the regulations and how much energy your house will actually need.

Regulations

The statutory regulations to be aware of are the building regulations enforced by building control, as well as planning requirements which are overseen by the local authority planning offices.

NZEB

The energy efficient house To build yourself an energy efficient house means making sure it does not require much energy to run on a daily basis. To achieve this, your architectural designer will adopt a fabric first approach, whereby each element of the building fabric (the layers that make up your walls including windows and doors, ground floor, roof) is well insulated and airtight.

In the regulations you will see minimum requirements for U-values.

This measurement is the most common one in use to show how much heat is lost through a building element, taking into account each layer.

The lower the value the better the energy efficiency; units are Watts per square metre Kelvin (W/sqmK) and the calculations will often be carried out by an insulation provider, or an energy consultant/assessor – or you can do it yourself – there are software packages commercially available or you could knock out a spreadsheet using the basic equations.

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Strict carbon emission factors and energy requirements mean that for new builds, and even for major renovations, your choice of heat source may be limited in ROI – usually coming down to heat pump, or gas boiler with photovoltaics (PV) – or a biomass boiler. Oil boilers are still possible but, all else equal, would require more PV, for example, to balance the carbon emissions.

In any case, in ROI and in NI, both gas and oil boilers for new builds are set to be phased out in the next few years. Centralised mechanical ventilation, meanwhile is fast becoming a de facto requirement to meet the regulations.

Indeed in 2019 in ROI, Parts F

(ventilation) and L (energy) were revised to tighten up the energy requirements – this has had the seemingly modest effect of increasing the minimum energy rating from an A3 to an A2 but, in practical terms, it has greatly limited your options in relation to central heating and ventilation systems. It also introduced a requirement to upgrade major renovation projects to a B2 energy rating.

All new buildings in ROI now need to be built to the Nearly Zero Energy Building (NZEB) standard, which is defined as a house that performs very well from an energy point of view (low utility bills) and one that gets a significant amount of the energy it still requires from renewable sources, onsite or nearby. This will further limit your options for systems, depending on your building fabric choices.

In NI, technical booklets F1 and K deal with energy (domestic) and ventilation respectively. And while the requirement for NZEB is also in place, the standard has not yet been published and the current requirement is simply to achieve

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Information gathered by Patrick Waterfield and Astrid Madsen.

the carbon dioxide emissions target – but keep an eye out for forthcoming developments.

Your energy assessment (see below) will check compliance with the building regulations.

Other regulatory requirements

In most cases, planning permission is not required to make system changes in an existing house. But, if there are external elements, such as solar panels, there may be a need to apply for permission (e.g. if they are visually obtrusive). In NI too, if you have a listed building, you may need listed building consent via the planning authority – in ROI, a similar requirement may apply to a protected structure.

You will of course require planning permission for a new build in both NI and ROI and you may come across restrictions, especially if you are considering the likes of a wind turbine.

Still, in the case of existing homes, in NI your Building Control inspector will have to oversee any changes to combustion (boilers, stoves) appliances. In ROI there is no such requirement but, in a new build scenario, the building regulations may limit your options considerably.

Energy Assessment

Alongside compliance calculations, the first step to choosing the right system for your home is to assess what your energy demand will be. Here are the basic concepts to help you wade through the options.

Demand

In order to know what you need from your systems, you will need to

check what your electricity, space heating, hot water and ventilation requirements actually will be. There are two determining factors: how much heat loss there will be from the house and how much energy you will use on a daily basis.

Heat loss will depend on how, and where, the house will be built.

A national or other average can be used for energy use, or your needs can be calculated based on the surface area, appliances, lighting, number of people, times of occupancy, etc.

These calculations will determine the demand, which will then in turn determine system sizing. Both of these are specialist jobs. The supplier of, say, a heat pump, will be able to carry out a calculation to identify the appropriate size of equipment based on the heat requirement of your proposed fabric.

Undersizing your systems to save on the upfront costs isn’t a good idea as it will make them work harder, which can lead to higher energy use and shorter lifespan.

Energy rating and airtightness The building regulations in both NI and ROI require that, at the end of the build, you submit an airtightness test result and the energy rating of the property.

Much like the rating on a domestic appliance, the building energy rating scores the home on a scale of A to G, with A being the best.

The common procedure, therefore, is to carry out a preliminary energy assessment at the start of the build to ascertain what energy rating the property should have. This is done to show compliance with the building regulations anyway,

using SAP (Standard Assessment Procedure) in NI and DEAP (Dwelling Energy Assessment Procedure) in ROI. As this is mostly a modelling exercise, with the assessor using data from the construction drawings to confirm the preliminary energy rating, there should be no surprises as to what rating you get at the end (subject to any changes made along the way).

The airtightness test, on the other hand, is an actual evaluation of how well the house was built from the point of view of minimising air flow through the fabric. The good news is, with the correct design and construction drawings, you should pass the test without a problem. But only as long as the site procedures are in place to make sure that the construction drawings are followed to the letter.

Also, crucially, any perforations in the airtightness layer made on site, due to perforations for cabling/piping, errors or a change in layout for example, must be patched up correctly. This is why, on commercial buildings, you will often find an airtightness inspector employed during the build. In a self-build, this is a role the foreman must take on.

If either the building energy rating or the airtightness test fall below the minimum requirements, costly remedial work will have to take place.

Also, if your compliance relies on a very low air permeability which is not achieved even with remedial measures, then alternative (and potentially even more costly) measures may be required.

Note also that a mechanical heat recovery ventilation system relies on an airtight building to achieve its optimum operation and efficiency – a “leaky” building will unbalance the system and make it less efficient thus

increasing actual heating energy loads and costs (see Ventilation section).

Calculation methods

Note that sizing calculations are not the same thing as the calculations made within SAP or DEAP, the methodologies behind proving compliance with the building regulations and behind the energy rating of your home.

SAP and DEAP will estimate the energy consumption and carbon emissions from your design, based on proposed wall, roof and floor make-ups, window and door specifications and how heating, hot water and ventilation will be provided, with account taken of renewables/ low-to-zero-carbon technologies.

The estimate is based on certain assumptions of occupancy patterns, comfort temperature etc, so may not be exactly the same as you get in reality.

Also, importantly, SAP and DEAP don’t take into account plug-in appliances. More significantly, for the self-builder at the design stage, these methodologies are not sizing tools – they won’t tell you what output your heating system needs to be. For that you need an energy consultant or detailed input from the system provider.

Last point to note, if you are thinking of building your house to the PassivHaus standard, a German methodology that is popular in Ireland to design low energy buildings, know that they have their own software package called PHPP. The PassivHaus Planning Package will model the house in much the same way as DEAP and SAP, though in greater detail and using more stringent standards.

SU MMER 2021 / SE L F B U IL D / 1 0 3

SYSTEMS GUIDE / VENTILATION

Ventilation systems All homes need fresh air, and a ventilation strategy is what will supply it.

Words: Andrew Stanway If we want our homes to have fresh, clean air that circulates to remove stale smells from kitchens and bathrooms, smoking and other pastimes and also removes moisture so the place doesn’t drip with condensation, some sort of ventilation is necessary in every home.

Traditionally, people opened windows and put up with draughty air leaks to achieve this but as building regulations have changed to make homes almost airtight in an effort to conserve heat, these simple methods are no longer suitable.

Minimum Requirements

All ventilation systems must explicitly demonstrate, for building control purposes, that they comply with the building regulations. This can be done by following technical guidance documents/booklets or by means of independent assessment of the technology or approach.

In ROI, recent developments in the building regulations have resulted in continuous mechanical ventilation systems becoming a de facto requirement. In large part this is because your house must achieve an airtightness rating of 5 m3/(h.sqm) at 50 Pascals, or below, as per Technical Guidance Document F, known as Part F. In theory, you can still install

10 4 / SELF BUIL D / SUMM ER 2021

intermittent fans in bathrooms, utilities and kitchens and use window and wall vents to take air in (natural ventilation). Where the design air permeability falls in the range 3 to 5 m3/ (h.sqm) Part F gives give the minimum total equivalent area of background ventilators, which is now much greater than it used to be, meaning more draughts and reduced comfort, with greater heat loss.

However, the main problem is that if you have relied on natural ventilation and your actual tested air permeability falls below 3 m3/(h.sqm), then Part F requires that “appropriate additional measures [are] implemented to ensure adequate ventilation”.

No calculations or suggestions for specific remedial measures are given

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Ventilation Types Natural ventilation

with intermittent fans was the traditional ventilation strategy.

It consists of extract fans in wet rooms that come on for a short period when a room is in use, often triggered manually or by Typical wall vent

– you would have to show a methodology or calculation on how you propose to deal with it. So, having achieved a good level of airtightness, which would normally be a good thing, you may have to retroactively add ductwork and a centralised unit, or figure out how to add bigger vents without compromising your heating system – all at a redesign cost and headaches on site.

This means a whole house mechanical ventilation system, such as MVHR or CMEV (see next section), is best suited to providing the correct airflow.

In NI, the minimum airtightness requirement for new builds is 7 m3/(h.sqm) at 50Pa, though a figure in the range of 2 to 4 m3/(h.sqm) is recommended with MVHR. Where natural ventilation is proposed, a greater

a light switch, and will typically stay on for a short period of time after the use of a room.

Fresh air is supplied into every room by means of an opening, commonly a vent in the wall or window. The amount of air extracted by fans and the size of opening in rooms is governed by the regulations.

The size and use of the room or dwelling is taken into account.

This setup causes uncontrolled air flows.

Passive stack ventilation can be used in place of extract fans, though you will need to show that the system is designed and installed to the appropriate standards.

Positive input ventilation, meanwhile, consists of a fan supplying fresh air, which forces stale air out of existing gaps.

Again, any method will need to prove compliance with the current building regulations.

Continuous mechanical extract ventilation

area of permanent background ventilators is required where the design air permeability is lower than 5 m3/(h.sqm) in order to guard against inadequate ventilation. Again, the issue arises that you will not know the actual air permeability until the house is built and you get the airtightness test done.

(CMEV) consists of extract points in wet rooms (bathrooms, kitchens, utility rooms, etc.) that continuously extract air from these spaces. This in turn creates a negative pressure and pulls air from the rest of the house.

Inlets in habitable spaces (bedrooms, living rooms, etc.)

Mechanical ventilation with provide fresh air through trickle heat recovery (MVHR) removes vents or wall vents. CMEV stale air from inside a house and Fibre cement can example

by Cedral Endurance systems either be aThrutone central exhausts it to the outside while fan (centralised) located in recovering heat from it to preheat an attic or other space in the the incoming, fresh, air. dwelling and ducted to the wet It consists of an air handling rooms or less commonly, have (ventilation) unit, usually in the extract fans in the wet rooms loft or in a plant room, which themselves (decentralised) like has ducting to supply fresh air traditional intermittent fans but to each living area and other continuously running. ducting that collects stale, moist, warm air from wet areas and returns it to the unit. There, most of the heat is recovered and recirculated into the house along with fresh air. If there’s no difference in the air temperature between inside and out then no heat is recovered.

The efficiency of MVHR systems depends on the airtightness of the building fabric – if cold air is leaking into the Example of DCV wall mounted extract unit: the Aereco BXC, aereco.ie building and/or warm air leaking out, then the system will not perform to its maximum potential It is common for CMEV systems and the energy savings will not to incorporate something be realised. called demand control. These A maximum air permeability are generically known as DCV of 2 to 3 m3/(h.sqm) at 50Pa systems. Structurally the same (about 0.1-0.15 air changes as CMEV they have in addition per hour at normal pressure) is a control strategy that allows recommended – though even them to change the flow of air lower is better. The PassivHaus into and out of the dwelling standard requires 0.6 ach at in response to the indoor air 50Pa, equivalent to about 0.03 quality. This can provide some ach at normal pressure. The additional benefits on indoor air MVHR will then be able to provide quality and energy savings over the requiredCedar ventilation efficiently. shingle roof covering a fixed system.

Heat Recovery Ventilation

Paul Lindsay photography

S U MM E R 2 0 2 1 / S E L FB UI L D / 105

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Phone: 091 739442 Email: proair@proair.ie Website: www.proair.ie

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Guide Selfbuild

So if you’re hoping MVHR will remedy your cold bridging, condensation or make up for poor insulation, you’ll be disappointed. These things must be treated at source and are in fact a prerequisite to get right prior to installing MVHR. Remember too that MVHR is not the same as air conditioning.

The modern way to do air conditioning is to serve one room with a heater /cooler unit which is connected to its own external unit. This is known as a split system. Split air conditioners re-circulate the same air continuously in the room and bring in no fresh air whatsoever.

This can lead to an unhealthy situation, so much so that few split air conditioning systems are installed nowadays without having MVHR in tandem with it.

By continuously replacing the air, and filtering it, MVHR actually supplies clean, healthy, fresh air.

However, there are now technical solutions to this dilemma. As many new, especially self-built, homes have so much glass, with its attendant

huge solar gains, people are demanding the advantages of both MVHR and air conditioning.

Such systems are now available.

Discuss this with a good ventilation company.

Note that if you are installing an MVHR system then you should have the cooker hood extract fitted with a pressure sensitive damper. This means that you only unbalance the system and compromise the airtightness for the short time you are cooking.

If you want to totally preserve the airtightness and make use of heat from cooking, you can install a re-circulation hood with a carbon filter to take out maximum dirt and some smells.

The MVHR extract point adjacent to the cooker will deal with the remainder of smells and the moisture. If this is your strategy, you need to make sure the MVHR system is not undersized and has lots of reserve for boost.

Some MHVR systems can cope with air from a cooker hood circulating back to the central unit, though fouling of ducts

and heat exchanger surfaces introduce an extra maintenance requirement.

Similarly, know that a wood burning stove above a certain size will need to have its own, dedicated, air supply from the outside. Also, one of the effects of MVHR is to have a slight equalising effect on the temperature throughout the building. If this is not what you want then the installation will need to be planned to give heat priority to certain areas.

Design & installation of mechanised systems All centralised mechanical systems need to be designed and installed correctly, and it’s vital to get the details sorted out right from the planning stage.

And it really is all about detail.

By definition, ducts have to be placed somewhere and their routes carefully planned to get

MVHR with built-in heat pump Especially for houses with very low heating/ cooling requirement, a hybrid MVHR system including heat pump powered heating and/ or cooling can provide the ventilation and conditioning in one system.

The heat pump increases the efficiency of the system by using the return air as the low temperature heat source for the heat pump which then boosts it up to a higher temperature. This is often referred to as an exhaust air heat pump. See project p128.

For about 400-460W of electrical consumption, up to 1-2kW of extra heat output can result. If the air needs cooling, the coolant circuit is reversed.

How much? does it cost you

n very ventilatio For heat reco tween omewhere be s w llo a to d e ne ro/ n thousand eu two and seve llation, unit and insta e th r fo g in rl ste e. This your house siz depending on equates to 30 per around £25/€ square meter

Information compiled by Astrid Madsen

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ADVIE06_SB_v1

© GettyI mages

END OF THE BALANCING ACT

THE FIRST NSAI CERTIFIED DEMAND CONTROLLED VENTILATION SYSTEM Ventilation doesn’t have to be a balancing act. Aereco has achieved Ireland’s first Agrément certification for Demand Controlled Ventilation.

A system that self balances and automatically adjusts to the needs of a home, securing indoor air quality and energy savings.

The National Standards Authority of Ireland (NSAI) Agrément provides a pathway that has significantly simplified the commissioning and validation process of Aereco systems.

Aereco is committed to constantly innovating and improving the performance of their systems. Along with the recent release of their control indicator as part of the updated regulations for Part F, Aereco is reaffirming this commitment.

For more information: www.aereco.ie air on demand

Guide Selfbuild

the result you want.

While this can mean having to lose ceiling height, an open web joist in the intermediate floor will allow ducts to run not only between but through them, greatly increasing your options for routes. The upper floor (unless spaced to the roof pitch) will usually have a roof void above to serve for duct runs, while vertical connection can often be achieved via cupboards or may need purpose-built risers. These routes need careful thought to ensure correct levels of ventilation to each zone of your home.

A good solution is to locate the unit in a storage area within the house and serve the rooms above up through and on the walls. In this way, you keep away from the cold loft space and add to the overall efficiency.

Noise

Suppliers will usually assure you that their systems are silent but the challenge is getting the design and installation right. If you use ducting that is too small in diameter then the unit has to work harder to get enough air through it and has to run at a

higher speed to do the job. This will result in excessive noise and indeed cost more to run. These systems generally have at least two, maybe three speed settings allowing normal operation and also higher air change rates to purge moist air, for example. The system will naturally make more noise on the higher settings. If you are particularly concerned about noise from the central unit it can be placed on acoustic

mounts. Just make sure it is not undersized.

Ducting

Aereco V4A acoustic whole-house fan, aereco.ie

This is where most people make their biggest mistakes. And because, by definition, most of the ducting is hidden it’ll cost a lot to get access to remedy these problems. Quality control and careful attention to installation detail is the secret here.

Everything must be done to ensure there’s no air, or moisture, leakage round the connections. Don’t skimp on quality ducting. The best companies also have all kinds of accessories to increase aerodynamic performance which makes everything quieter and more efficient. Don’t think of your ducting as simply a lot of ‘tubes’ that take air from one place to another. There’s much more to it than this.

Ducting should be designed

by a professional who understands the relationship between airflow velocity and acoustics. A well sized and designed system will mean the air flows gently through the duct and the unit is under no pressure. Most people won’t be able to hear the system in this situation.

Air handling unit Given this is the most expensive part it’s tempting to try to save on it.

But this would be a mistake because better units are more efficient and thus cost less in the long run. It is best to buy from a reputable supplier rather than a cheaper online option.

For any centralised mechanical system, where you put the air handling unit is of supreme importance so that you minimise the duct runs and get them inside the insulation envelope as much as

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SYSTEMS GUIDE / VENTILATION

possible. This is because the air temperature where the ducts run will affect the temperature of the air that enters your rooms and, hence, your comfort. Reputable manufacturers/ventilation suppliers will advise you on all of this so it is important to contact them early.

Insulation

Regulation guidance documents state that you must insulate your ducting where it passes through unheated areas such as voids and lofts. This is correct, but the trick is not to have it passing through cold voids. If this is unavoidable, the insulation should be foil-backed and at least 50mm thick. All efforts should be made to install the duct within the insulation and airtight envelope, in a purpose designed service cavity. A well thought out strategy for the duct runs will ensure that the inside of these ducts will be continuously clean and dry, even those that take wet air away from bathrooms and kitchen.

Fire safety

Something that may not immediately come to mind. When you take ducting through walls and ceilings you break the fire rating of that structure. This has to be reinstated by using proper fire break (stopping) products that are made for the purpose. Again, good designers know all about this.

Supply and extract registers

These are usually located on ceilings, but walls can also be a good option.

The air from a wall grill is pushed across the ceiling 11 0 / SELF BUIL D / SUMM ER 2021

Aereco BXC bathroom extract unit with DCV humidity sensor, aereco.ie

and then gently drops into the room before returning to the extract in an adjacent bathroom or kitchen. When using ceilings, it is important to have the register deep in the room so the air traverses as much of the room as possible on its way to the extract.

Larger areas may need more than one supply register.

Extract registers should be positioned reasonably close to the sources of waste air (e.g. showers, cookers etc.). Don’t forget also that when air enters a space some needs to get out, while air trying to leave needs to be replaced by incoming air – in other words rooms must not be airtight internally. When doors are open this is not an issue of course. But when they are closed, especially when the room is carpeted, you can end up effectively air-sealing the room. To avoid this, doors can be undercut by about 5mm – this should provide sufficient air

transfer route for most average sized rooms. This under-cut is more important between bedrooms and adjacent ensuites.

Controls

The control panel (unless wireless – in which case don’t lose it!) should be located somewhere convenient within the habitable part of the house so that settings can be changed and a check made on service/maintenance (e.g. filter change) periods.

Commissioning for all ventilation systems Commissioning happens when the installation is complete. The process involves checking that the volume of air supplied to the rooms and the rate of extraction from the wet rooms are correct and abide with the pre-specified

settings. It also ensures that the switches and general operation of the system is functioning as designed and manufactured.

Once these checks have been conducted, the installation will have to prove compliance with Technical Guidance Document F (ROI) / Technical Booklet K (NI). The installer has to supply a Balanced Commissioning Report to Building Control in order to have the house passed. In NI, this is only acceptable if prepared by a BPEC approved engineer – usually a representative of the company supplying the system. It is recommended that the end user is present.

At this point the handover commissioning certificate is filled in to match readings from each diffuser, and ensure that insulation, sound attenuators and the airtightness of any exposed duct is correct. The end user receives the handover of all operation and maintenance

Guide Selfbuild

manuals and is shown how to use the system.

The checks are carried out by a competent person using a calibrated (INAB or equivalent), anemometer, a device measuring airflow and velocity. It is important to ensure that the anemometer is suitable for low-volume and low-velocity measuring, and has a current calibration certificate. If there are discrepancies between the actual and specified airflows, they can be adjusted through the termination diffusers (on a branch system) or at the manifold.

Once the registers have been set they should not be moved unless by the installer, for example in response to concerns regarding adequacy of air flow.

Changes to the building regulations in ROI in 2019 mean that your installation will be technically subject to an independent assessor verifying that your installer has installed and commissioned the system properly, to the design provided (see Opinon piece).

What about maintenance?

Where filters are used, in systems such as MVHR, they need replacing every six to 12 months depending on usage and location. With the better units this is usually a DIY job. Note that the central unit should be located such that it is accessible, especially at the point where the filters are extracted and replaced. It is important that your supplier can offer at least a three yearly deep service to check and clean the ducts too.

Additional information: Patrick Waterfield, Ciaran King and David McHugh.

OPINION

Certification of ventilation systems in ROI In the latest iteration of Part F in the Republic, the technical guidance document says that all mechanical ventilation systems must be independently verified. But what does that actually mean in practice on self-builds, asks David McHugh.

In 2019 new building regulations came into force in ROI to ensure ventilation systems are designed and installed correctly, and independently checked.

For the purposes of the buying public and indeed the industry, this is a welcome development, even if it may take years to fully implement. There are too many sad stories of bad indoor air quality even after spending thousands on a supposedly state of art system. Then there are the stories that go ‘I got a great deal on my ventilation system’.

Yes, but does it actually work the way it should?

The independent verifier is meant to check that it does, but that person only verifies the flow rates presented and checks that they co-relate with the design provided. S/he then reports back to the client to let them know whether it’s a Pass or a Fail, very much as with the airtightness test. It is not the verifier’s function to adjust the system to try and achieve compliance.

The National Standards Authority of Ireland (NSAI) has been tasked with the development of this scheme. They run an accreditation and training regime for would-be verifiers, which is still at the early stages.

The hope would be that the existing network of airtightness testers would adopt this function. This would help to make the scheme more cost effective, as both jobs could be done on the same visit.

The problem for now is that currently, there are only 18 registered verifiers in the country and this means that only little more than a third of houses can be verified.

This sounds like bad news, but within a few short years it would be hoped that with over 100 verifiers in the field, that ventilation systems would cease to be under-sized and would be achieving balance by exhausting roughly the same amount of air they take in.

The safest way now for self-builders to ensure their ventilation system will work as intended is to pay a good advisor, that is an architectural designer, engineer or similar, who will follow the rules and ensure all others do the same.

David McHugh is the Chairman of the Residential Ventilation Association of Ireland and the Director of ProAir Systems

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Space heating and hot water Your home will have a basic need for hot water, and another for some form of space heating.

What is ing? central heat space

g refers to Central heatin stem describing a sy heating only, rally nt r or water ce of warming ai oms ro t it to differen then sending as s, pe ork of pi through a netw of e tic ac e old pr opposed to th . om ro by at room generating he

11 2 / S E L FB U IL D / SU MMER 2 0 2 1

Most buildings in Ireland will have an appliance, or multiple appliances, that will generate heat for space heating and/or hot water. Most systems, such as boilers and heat pumps, will fulfil both functions. This heat is then distributed through a network of heat emitters (usually in the form of radiators or underfloor heating), and through pipework for hot water.

Depending on the system you choose, your hot water network is likely to include a hot water cylinder – for the average house a capacity of at least 200 litres is recommended, or 300 litres if you have solar water heating (and no separate solar storage). Be aware that more physical space is needed for these larger tanks.

A combi boiler generates hot water instantaneously, sometimes with a very small storage capacity, thus removing the need for a hot water cylinder and freeing up space, which can be a big consideration in smaller dwellings and in renovation projects.

In the case of space heating, the system generally requires a water supply. The exception is when the heat emitter generates the heat on the spot, e.g. plugand-play electric underfloor heating mats for bathrooms, or electric radiators.

Heated air can also come through your centralised ventilation ducts (though this would generally provide top-up levels of heat only) or via a fully ducted warm air heating system (though these are rare in houses in this part of the world).

District heating, which supplies heat to homes and businesses in a network similar to your water or electricity supply, is rarely available in Ireland. That said, ROI’s first large scale district heating scheme was launched in Tallaght earlier this year and the

Cloughjordan eco-village in Co Tipperary, which is a cluster of sustainable self-builds, also has such a system in place.

But, in all likelihood, for your existing home or new build project you will have to look at how you will heat your house through a standalone system, designed for your own specific fabric surface area and needs.

Heating systems are made most efficient by controlling the room temperatures individually, at specific times.

Means of generating heat

There are three main means of generating heat, for hot water and space heating.

The first is by burning fossil fuels, usually in the form of an oil or gas fired boiler. This option is losing favour because of the resulting carbon emissions and greater difficulty in complying with building regulations.

The second is by using

Guide Selfbuild

Fresh water supply

Stoves

t, ways a thing of the pas Chimneys are in many eful car uire req and ld bui to as they are expensive e they do not compromis attention to make sure taken e hav ves Sto g. ldin bui the airtightness of the g d flame fires increasin their place, with gas fire the t hou wit ect eff me fla ea in popularity to provid t, as nowadays homes hassle, or the added hea any top up in heating ted tend to be so well insula omfortably hot. can make the room unc

electricity, usually in the form of a heat pump. The supply will normally come from the grid but it could be electricity you generate on site through a standalone renewable system (see p122) – or a combination of both. Electric heaters can be used as standalone systems if the house is so well insulated and airtight there is barely any space heating need.

Finally, there is the option of burning biomass, which usually translates to wood in the form of logs or pellets. A wood burning stove in your main living area will allow you more easily to heat that part of the house while reducing unnecessary heating in other areas – and a back-boiler will mean that hot water is being produced at the same time.

Solar energy can be harvested as a top up to any of these systems (see p124), and there are alternative eco-fuels such as biodiesels and RNG (renewable natural gas) in development as well. v

Low carbon technologies

Another way of looking at your options is to look at it from the point of view of choosing low or zero carbon technologies, collectively referred to as LZCs. In addition to renewables (solar, wind, hydro, see p124) there are technologies which are very low carbon, such as biomass (wood pellets, logs – renewable over a certain period of time) and others which are more efficient than conventional options and thus result in lower carbon emissions – examples are heat pumps (air, ground, water) and combined heat and power (simultaneous generation of electricity and heat).

Renewables are almost zero carbon in operation – a very small amount will usually result from controls, pumps, etc. The second group is very low carbon also, with a small amount resulting from transportation and drying/processing of the

Fresh water usually comes from the mains, which could be from a group water scheme depending on where you are. Some self-builders may choose to dig a well if the underlying site geology allows.

In the case of mains water, if the pressure is low you may need a pump to increase water pressure which can then negate the need for pumped electric showers. The water will come treated for the likes of bacteria but may have a lot of limescale, which can be reduced by passing it through a treatment tank.

In the case of wells, a submersible pump is likely and the water needs to be monitored for e-coli and other possible contamination, and treated with a choice of UV, osmosis and other filtering options. Limescale removal may also be necessary.

Pumps and treatment units are often located in a shed; water tanks in the roof space are much less common nowadays, as more systems are able to rely on mains pressure.

In most cases water is fed back to the house to feed the heating/ plumbing side of things in the first instance, then a separate network feeds the fresh water (potable) taps. Rainwater harvesting or limescale treatment will require a third network feeding e.g. wcs, in the case of the former or, for the latter, washing machines, wcs and possibly the hot water, as limescale corrodes the elements within the hot water cylinders.

When planning the layout of your house try to cluster “wet” rooms such as bathrooms, wcs, utility rooms and kitchen either horizontally or vertically (or both) as this will limit the length of pipework needed (reducing capital and labour costs) and also reduce heat loss from “dead legs” – hot water that has cooled and is run off to drain until it is at the right temperature – another source of inefficiency.

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fuel.

The third group cannot be termed zero carbon as these technologies rely on electricity (which, unless generated via on-site renewables, will incur some carbon emissions) or, in the case of CHP, gas (biomass CHP exists but not generally at domestic scale). However, they are deemed to be low carbon as they significantly leverage the efficiency of the fuel, resulting in lower energy use and emissions.

Fossil Fuels

In NI, oil and gas boilers are still commonplace in new builds as the building regulations do not particularly restrict their use.

In ROI, obligations in relation to energy use mean that using fossil fuels is only possible if you are also installing renewable energy sources, which in a Plant room with preinsulated hot water tank (far end), blue water tank for fresh water pump and ventilation unit (right).

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domestic setting would normally mean photovoltaics to balance the carbon emissions (see p102).

In existing homes, where mains gas is available, many oil boilers have been replaced with gas boilers in recent years – kW for kW oil is more polluting than gas and, depending on global and national economics, may be more expensive. Oil also requires the oil storage tank to be filled periodically.

However, both options are on the way out for new dwellings in both ROI and NI. Still, there are various advantages to gas boilers. One is the relatively low capital cost to install the system. The most popular type, the combi boiler, also does not require a hot water cylinder as the boiler heats hot water on demand (oil-fired combi boilers are also available).

A larger family may require a

larger boiler so, again, the energy requirements of the specific home will need to be calculated before a full comparison of heating systems can be made.

However, fossil fuel boilers work on the principle of heating water to a high temperature, which takes up a lot of energy as well as generating high levels of carbon emissions.

Combined heat and power (CHP) units produce heat/ hot water and electricity simultaneously, are very efficient, and run mainly on gas. CHP is mostly a commercial technology but there are (as yet still fairly expensive) micro models available for the home.

The latest development is the fuel-cell CHP, which uses a lot less gas as it converts it to hydrogen; the hydrogen is then put through the fuel cell to generate electricity and heat.

The premise is that fuel cell

Guide Selfbuild

micro-CHP is more efficient than installing two separate systems, e.g. a standalone electricity generating system such as photovoltaic panels plus a hot water and space heating system such as a heat pump or boiler.

A key difference between fuel cell CHP and conventional CHP (which combines a gaspowered boiler with a Stirling engine) is that, in the fuel cell, the fuel is not combusted. While simplifying the system and the overall environmental impact this reduces the availability of recoverable heat. However, the economics of fuel cell CHP systems is less dependent on thermal output as the electrical

“

fabric heat losses, we are on the cusp of a massive change in the way we heat our buildings, breaking a pattern of burning fuels in our dwellings that has evolved since Neolithic times.

As mentioned previously, heat pumps are becoming more and more common in new builds in ROI in particular, but also in NI, as energy/carbon regulations are tightened up and as we approach the time when fossil fuel systems are no longer allowed in new buildings. In homes built before 2011, grants from the Sustainable Energy Authority of Ireland are available in ROI to install a heat pump, as long as the house meets minimum airtightness and

need to find a location away from the main approach to the house and also one that doesn’t impair views.

An alternative system is to lay piping coils in the ground (or water if you have a suitable lake/river) and use it as the low temperature heat source. The advantage is a higher average source temperature, especially when you need it most, but a disadvantage would be additional cost and land requirement.

Small air source heat pumps can also be found integrated into hot water cylinders, to provide hot water separately from heating.

This may allow the main heat pump to operate more efficiently

...an advantage of installing a gas boiler is the relatively low capital cost but in ROI you would probably have to complement it with PV panels.

generation is very efficient (over 50 per cent). Heat recovery can then raise overall efficiency to around 85 per cent.

Electricity

Electric heating used to be a big “no no” as it was considered more expensive (it still is per kW) and less environmentally friendly than other fuel/energy sources. But as the electricity grid increasingly relies on renewables, mostly in the form of wind power, that argument holds less sway than it used to.

And with heat pumps, already about 300 per cent efficient and improving all the time, plus lower

insulation requirements.

Most domestic heat pumps these days are air-to-water types. That is, you harness low temperature heat from the air, boost it up through the refrigeration circuit, then pass the heat to water which then circulates around the house via pipework/radiators or underfloor arrays (see Heat Emitters p122).

An air source heat pump should be close to the house to reduce heat loss from pipes but far enough (at least a couple of feet) to allow good air circulation and, ideally, such that the prevailing wind takes its cool airstream away from the house.

Also, unless you particularly want to make a feature of it, you will

and to be sized for heating only, thus reducing its capital cost (though, naturally, the cylinder with integrated heat pump will be more expensive than an ordinary cylinder).

The hot water only option might also be considered with certain other combinations such as a biomass main boiler, which you may not want to have to fire up in the summertime.

Sizing Heat Pumps

You may wish to size your system to cope with a worst case scenario, e.g. a cold start in mid-winter, in which case it may be somewhat oversized during

How heat pumps work A heat pump takes low grade (low temperature) heat from a large reservoir (the ground, water or the outside air) and converts it to higher temperature heat for use in the

building.

It does this by transferring the low grade heat to a heat transfer fluid, which passes through a compressor thus raising its temperature and the resultant heat is then passed to water for use in the heating system and/or for domestic hot water.

Once the fluid has given up its heat to the water it goes through an expansion valve and is thus cooled, ready to absorb more low-grade heat.

The electrical energy needed to carry out this process is significantly less (typically a third to a quarter) than the increase in heat energy. If this sounds like magic it’s not quite – simply a consequence of the physical properties of the heat transfer fluid and its ability to gain and release heat when going through compression and expansion cycles.

Think of a fridge, which takes heat out of the inside of the appliance and rejects it at the back – a heat pump works on the same principle but in reverse.

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SYSTEMS GUIDE / S PA C E H E A T I N G & H O T WA T E R

Biomass

Another option for reducing your carbon footprint and helping to achieve building regulations compliance is biomass. This generally means either logs or wood pellets and is most commonly used in room-heater stoves, though biomass boilers can also be used as primary heating sources.

Multi-fuel stoves that can burn turf and coal are available but, as these two fuels are being phased out, wood burning stoves have taken over. Note that research from the Environmental Research Institute at University College Cork shows that burning peat, coal and even wood, releases small particles (PM2.5) harmful to human respiratory 11 6 / S E L FB U IL D / SU MMER 2 0 2 1

Photography Paul Lindsay

normal operation. Alternatively, if you have secondary heating, such as wood burner, you may be able to reduce the size of your main heat source.

Whereas boilers are available in a huge range of sizes and can be closely tailored to your heating requirements, heat pumps come in a more limited range of sizes, say, 7kW, 11kW, 15kW. You may find that your heat loss rate is just over the output of one model – do you take a chance and go for that model, or do you pay the extra for the next size up? The answer, incidentally is don’t skimp on the heat pump – it will have to work a lot harder and will not be as efficient.

A better idea is to revisit your fabric and reduce your heat requirement. Don’t forget also that if the heat pump is to provide hot water as well as heating it will need to be sized accordingly, bearing in mind that hot water for consumption is produced at a higher temperature than that for space heating.

A biomass stove as the central source of heating in a County Down self-build

health.

Logs or pellets?

Logs are cheaper but require more intervention/maintenance, bringing the fuel to the stove/ boiler and the removal of ash.

Pellet-systems can be more easily automated and produce less ash, though are more expensive to buy and require closely controlled temperature and humidity conditions for storage.

Biomass in the form of wood logs is a practical and obvious solution for self-build sites that also cultivate woodland.

Biomass systems tend to be a lot bulkier than gas- or oil-fired systems – bear this in mind when sizing and locating boilers/ stoves. Consider the route through the house to and from a room heater, especially a log burner, for bringing in fuel and taking out the ash.

Logs need to be well seasoned (dried) and stored in dry conditions, in order to burn well and efficiently. For convenience, they should be stacked somewhere close to the house, with a rainproof cover but open or slatted sides to allow the wind to pass through and

remove moisture. Newly cut logs fewer) periods which is more should be stored like this for at efficient. Again, you will need to least a year before being used, allow space for the buffer tank. though kiln-dried logs can be used immediately.

You should then have a place Stoves with back boilers are also inside the house – somewhere an option to heat up radiators around the stove would be and top up the hot water ideal – where the logs can dry cylinder, but clearly only provide out further and reach room additional heat when the stove is temperature and be ready to lit – on the other hand, you may hand when needed. as well be raising hot water while Wood pellets can be used heating the space. However, the for stoves or boilers but, for heat from the stove itself could the latter, the volume of pellets be intense and again, could lead required means a ventilated, dry to overheating in a well insulated shed is necessary, with a hopper home. for auto feeding.

If the hot water cylinder is Most pellet stoves will located above the stove, such include a hopper into which you can empty a full bag of pellets, which will then be used as needed. Pellet stoves have in-built ignition systems and some can even be timecontrolled to come on automatically.

Biomass boilers mon are more com work best when linked Wood pellets r ea they are cl ne to a buffer tank – a for stoves as er si ea d e fuels an large tank that stores than alternativ y an ly rd eight, ha hot water produced by handle (less w to to ed ne ts the boiler and circulates the pelle ash) although it around the heating be kept dry. system. In this way the boiler can fire for longer (but

Back boilers

Wood Pellets

Guide Selfbuild

Information gathered by Patrick Waterfield and Astrid Madsen.

that the flow and return pipes are as short and vertical as possible, you may be able to dispense with a pump. A wider bore of pipe (ca 28mm) is needed so that natural thermal buoyancy can allow the heated water to rise up to the tank, with the cooler return water then falling back to the boiler.

Note the flow pipework needs to maintain a continuous upward angle for the thermal buoyancy to be effective.

An added advantage is that, if the pipes are plumbed directly into a standard vented cylinder, you do not need any additional safety valves etc. Otherwise (and

generally for radiators) a pumped circuit will be needed.

Fuels of the Future

Hydrogen is an eco-friendly alternative to oil or gas in that, when you burn it, the only byproduct is water. There are two potential sources of hydrogen, the most eco-friendly being electrolysis of water which, if energised from a renewable source such as wind power, is carbon free at both the point of manufacture and use.

Hydrogen isn’t yet available as a fuel source, but it is a strong future contender as an alternative fuel for boilers. In Ballymena, County Antrim there are in fact efforts underway to ramp up investment in hydrogen on the back of the UK Budget announced in March 2021.

Meanwhile, developments are under way regarding biokerosene, which can supplement (replace or be added to) home heating oil.

Biogas is another alternative for boilers and transport.

Produced after organic materials (plant and animal products) are broken down by bacteria in

an oxygen-free environment, a process called anaerobic digestion, biogas contains both energy (gas), and valuable soil products (liquids and solids).

After biogas is captured, it can produce heat and electricity for use in engines, microturbines, and fuel cells. Biogas can also be upgraded into biomethane, also called renewable natural gas or RNG, and injected into natural gas pipelines or used as a vehicle fuel. Bord na Móna is currently preparing a proposal for a renewable gas facility on Cúil na Móna Bog in County Laois.

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SYSTEMS GUIDE / HEAT EMITTERS

Heat emitters The choice of heat emitters is usually between radiators and underfloor heating, but there are alternatives to consider. Remember too that temperature controls will be your most effective partner in reducing energy use.

Installation of underfloor heating pipes

Heat emitters refer to the part of the space heating system that makes the room warm. Everyone will be familiar with radiators, and in new builds underfloor heating is now commonplace.

But there are other options including trench heaters (which tend to be used in commercial settings, blasting air form the floor or above; these can be used in residential settings too), skirting heaters which are skirting boards that double up as radiators (these can be “wet” i.e. piped with water, or electric), and storage heaters and fan coil radiators.

A lower cost type of heating for a kitchen is to install a plinth heater rather than full skirting heating, although in an energy efficient home the kitchen wouldn’t generally be a room that needs such a top up.

Depending on your energy assessment and heating strategy, some of these specialist heat emitters may be especially useful if you don’t think you will need a heat pump or boiler for your space heating needs.

Radiators

Radiators refer to panels that

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emit heat through a mixture of convection and radiation. The materials of choice used to be steel but nowadays aluminium has gained favour, especially in the context of low temperature

Guide Selfbuild

Photgraphy: Paul Lindsay

condensation on the inside of windows with well-designed and well-installed double (or triple) glazing and adequate ventilation.

So the best location is on a wall perpendicular to the window wall – or possibly on both sides for a large room.

Towel radiators tend to have a lower output and can be either connected to the central heating system (pipework) or standalone (electric) and thermostatically and/or time controlled.

Underfloor heating

heating systems such as heat pumps.

Radiators mostly rely on convection to get the air to move around the room and heat it evenly. Finned radiator designs allow for better convection – radiation will only heat the area immediately adjacent. Better insulated houses will require smaller radiators, though condensing boilers (and heat pumps) will need them to be bigger, as they run at lower temperatures.

Sizing is important, which refers to the size in Watts of the radiators you need to meet the space heating needs of that room, as calculated in your energy assessment (see p102). Know that most rule of thumb methods will oversize the radiators to make sure the system runs smoothly, although this clearly costs more in the form of larger radiators. It

is not so long ago that plumbers sized radiators but nowadays, an energy assessor is usually brought on board to do the energy calculations to know what heating demand each room will have. This is especially important in the context of securing a grant in ROI for an existing home (built before 2006).

On the age-old question of where to site radiators, you should avoid putting them beneath windows – especially if you favour full length curtains. In past times, with thermally poor single glazing, a radiator beneath the window was seen as a means of combatting condensation (though, of course, much of the heat was lost straight through the glazing).

But that was then and this is now – these days we are more interested in energy efficiency – and we don’t tend to get

Underfloor heating consists of a network of pipes, usually filled with hot water, which is located under the floor covering, usually within a screed. Underfloor heating pipes can however also run in walls or skirting boards.

Underfloor heating mats are electric and are most common in small areas that need sporadic heating such as bathrooms.

Underfloor heating is well suited to heat pumps as it operates at a lower temperature.

That is, you need less energy to boost the heat up to the running temperature of the system than you would with a boiler. Whereas a boiler will produce water at around 70-80 degC, an underfloor heating system will run at around 40 degC – any higher and you’ll have problems with the screed cracking.

Fortunately, the large area of the floor compared to the average radiator means you can get enough useful heat out of it even at that lower temperature.

Floor coverings and response time

There are two things to consider with underfloor heating. The first is the choice of floor covering. If

you favour a carpet on your floor, know that the carpet and underlay will act as a very effective insulation blanket and you won’t get much heat coming into the room.

The floor covering of choice for underfloor heating is tiles or, at a pinch, solid timber flooring laid directly onto a power-floated or self-levelled screed. If tiling, make sure your adhesive layer is continuous (no voids) which is more robust as well as allowing better heat transfer.

The second aspect to consider is response time, or how long it takes the system to bring the house to comfort temperatures and conversely how long it takes for the heat to die down.

The quickest response system is air-based heating – of the order of minutes. Radiators are medium response – depending on the fabric maybe inside an hour.

Underfloor systems take several hours to build up heat in the floor and for that heat to permeate into the room.

And, once it does, it keeps coming out of the floor even after the room has reached a comfortable temperature. So underfloor systems tend to be run continuously to trickle heat into the house at a slow rate. This is fine in a very well-insulated fabric, though is still not very controllable.

For these reasons too, amongst others, underfloor heating is not normally seen on the first floor. It doesn’t sit as well on an intermediate timber floor and, assuming a conventional layout with daytime areas on the ground floor and night time areas upstairs, the heat requirement and occupancy patterns of the bedrooms don’t favour the long response times. Unless again the house is very well insulated and doesn’t require much energy to keep the bedrooms at a constant temperature. Plus, you’re more S U MM E R 2 0 2 1 / S E L FB UI L D / 119

SYSTEMS GUIDE / HEAT EMITTERS Information gathered by Patrick Waterfield and Astrid Madsen.

likely to want a carpet there.

A heat pump can feed radiators, though they will need to be oversized compared to normal boiler-based rules of thumb and will still tend to run at a higher temperature than the underfloor circuits. All this needs to be considered in the sizing and choice of system.

Heating controls

Controls are often overlooked but are actually the key to delivering low cost heating and hot water. If your space heating generator (e.g. heat pump or boiler) also produces domestic hot water, this should be provided on a dedicated pumped circuit, controlled on a separate channel on the programmer.

As in all other walks of life, you need to start with reducing demand – there isn’t much you can do with the hot water settings but you can control the space heating.

In a new build this means pondering what your comfort temperature is. Of course the

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lower the temperature you set rooms to, the lower the energy demand. Bedrooms are usually considered comfortable at 18degC and living areas at 21degC but this is very much subjective.

To control the heat output, at the bare minimum radiators will have a valve that can turn the individual radiator on or off.

Most will have thermostatic valves (TRV) which allow you to choose a level of heat – the TRV reacts to the room temperature to turn the radiator on and off to keep the room at a steady level.

The exception is the radiator in the area where the room thermostat is located – this should not have a TRV fitted as the two thermostats will end up fighting each other. TRVs should ideally be positioned to the side of the supply pipework rather than directly above it as otherwise it will be influenced by the heat from the pipes and not just the room.

But in new builds, you will have a much greater level of control than this. This is because heat pumps combined with

underfloor heating will have integrated systems to control the room temperature, either individually or in zones. These systems integrate controls to maximise efficiency – thermostat settings for rooms or zones within the house and maybe weather compensation for overall control.

The thermostats will usually be on the wall and/ or controllable from a central device (and maybe through an app on your phone/tablet/PC) – though in the case of underfloor heating the best place to sense the temperature is actually the floor itself. If you wait until the heat has got into the room it will have had time to build up in the floor.

Room thermostats should be located in a representative part of the house which is not subject to high heat gains (e.g. kitchen, or in direct sunlight) or draughts (i.e. not too close to outside doors).

If you have a large house, or very different occupancy patterns in different areas (e.g. upstairs and downstairs) you

Manifold or teed?

For any network of pipes you will be presented with the option of looping the pipes into one or multiple zones (traditional teed off system) or have each set come back to the central manifold.

Controlling rooms individually with a manifold system will lead to higher cost in terms of pipework but this may provide an easier way to balance the system and of course allows you to fine tune the settings.

“Wet” underfloor heating systems adopt the manifold approach, which will require a dedicated location and space – ideally fairly central. That could be in a porch, utility room, dedicated cupboard , maybe even under the stairs unless you had other uses in mind for that area, or if you favour open risers.

might consider a multi-channel programmer allowing you to separately control two or more heating zones.

You may even then start exploring the world of home automation, which will allow you to control not only heating and ventilation but other home systems such as lighting, entertainment, security and automated doors (garage, gates).

With artificial intelligence now integrated in our phones and smart home devices, more automation is on the horizon – all of which usually requires a good broadband connection. See the projects on pages 20 and 72 for examples of how to integrate home automation in your project.

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SYSTEMS GUIDE / R E N E WA B L E S

Renewable Energy Renewable energy technologies refer to energy harvested from the environment, such as the sun, wind, and the movement of water, as their supply is constantly replenished.

Words: Patrick Waterfield

Renewables are very attractive to self-builders, who tend to have a penchant for ecofriendly solutions. The main drawback for most is that, while renewables are constantly replenished, they are not always available in sufficient quantity when the energy is needed. In that case some type of storage may be used (see p126).

Nearly zero and low carbon technologies are more readily controllable and can be brought online when needed, which means renewables are often used in dual systems.

Solar water heating

Solar thermal panels/tubes harvest energy from the sun to heat up your hot water. As the intensity of the sun is lower in winter, a backup is required to top up the system and this can take the form of a boiler or a heat pump. There are two main types of solar water heating collector: tubes and flat panels.

In homes built before 2006,

Solar thermal panels (tubes) for generating hot water

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grants from the Sustainable Energy Authority of Ireland are available in ROI to install solar thermal systems.

An absorber surface (matt black/selective coating) heats up on impact of solar radiation and, in most cases, imparts heat to a heat transfer fluid, which rises to a manifold where the heat is passed to water.

In the tube type the absorber surface is contained within a vacuum, which makes the heat collection more efficient, especially in colder, higher latitudes. Tubes are also more efficient over a range of orientations, especially if not due south, though flat plate types perform equally well overall if oriented due south.

If you have a choice of orientation you might consider your usage/draw-off patterns.

If your array faces more to the east you will harness the morning sun but the heated water may not be available first thing. With a westerly facing array (and well insulated storage) you may have a better

Guide Selfbuild

“

Photovoltaic cells convert light (photo) into electricity (volts)...’

Solar inverter, part of the kit you will need to install with your PV panels

chance of an early morning solar shower, depending on your evening draw-off patterns.

The hot water cylinder will contain a number of coils to help it heat the water within; there are usually at least two, which includes one to connect to the boiler or heat pump and another to the solar thermal panels, and generally a back-up standalone immersion (electric) heater if all else fails.

Try to locate your hot water cylinder reasonably close to the solar array, as this will minimise heat loss from pipework. The hot water cylinder will need to be sized to allow for adequate storage of solar hot water during periods of high solar gains, especially if draw-off/usage is during different periods, unless you are opting for separate solar storage, in which case even more space will need to be found. A roof void would be a suitable

place.

Solar water heating is fairly straightforward in that you know what you are going to do with the output from the system and there is usually a fairly regular demand for hot water in the home.

However, as there will not always be sufficient sunshine when you need it and, as mentioned already, you will need a back-up system usually provided in any case via the main space heating heat generator – boiler or heat pump.

With the output mainly provided during the summer, when the heating system is not otherwise running, it should be relatively easy to avoid doubling up on supply which would, effectively, waste the “free” solar heat.

However, you still have the additional capital cost of the solar system which is only doing the same job as could be done,

even during the summer, by the boiler/heat pump? Will the cost saving in avoided electricity, gas or oil (or biomass) usage pay for the solar thermal system?

Frankly it is unlikely.

Of course there is merit in harnessing carbon free energy and it will help meet the regulatory targets. In the case of a super insulated home with no central heating system but just a wood-burner (with back boiler), a solar thermal array makes perfect economic sense as you have no competing options – you wouldn’t want to fire-up the

wood-burner in summer just for hot water!

Photovoltaics

Photovoltaic cells convert light (photo) into electricity (volts).

They are arguably the most straightforward of the renewable technologies as they have no moving parts and the output can (generally) be exported to the grid.

Even though currently in ROI there is no payment made for this, plans are underway to

S U MM E R 2 0 2 1 / S E L FB UI L D / 123

F RE REE UNI I QU IN CO NITI ES A SE L RV CO ERV ICE NS IC

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Guide Selfbuild

resistance (immersion) heater in your hot water cylinder (though this is arguably not such a good use of electricity as a premium energy type) or you can link it up to domestic battery storage. This is becoming a more attractive option, especially in conjunction with electric vehicles.

Small scale wind 5kW domestic wind turbine

introduce a Microgeneration Support Scheme from July of this year, which would introduce a feed in tariff. While in NI you’re likely to get paid for exported electricity, it will be at an often considerably lower rate than the supply tariff. In homes built before 2011, grants from the Sustainable Energy Authority of Ireland are available in ROI to install PV panels.

For this reason, as well as ongoing reductions in unit price, PV is often seen as the optimum way to meet the regulatory carbon target, especially if proposing a gas or oil-fired boiler.

PV comes in one of two basic forms, crystalline and thin film. Crystalline types, which can be monocrystalline or polycrystalline, require silicon cells to be grown and are thus expensive, though are more efficient than thin film types.

The thin film types, which include (non-crystalline) amorphous silicon and also non-silicon (cadmium telluride) options, are slightly less efficient (though improving all the time) but cheaper than crystalline silicon.

PV panels do not project much above the line of the roof pitch – and, indeed, can be flashed-in flush with the roof-covering in a new build situation. There are also PV tiles/shingles on the market which may provide a more aesthetic option, though at a considerable cost premium.

Note that as with solar water heating, if you have no suitable roof orientation (anywhere from east to west via south is fine, though north should be avoided) the panels can be ground mounted. This may give you freedom of orientation but possibly greater risk of overshadowing.

Don’t forget to leave a suitable route for cabling from the PV array to the inverter(s) and thus to the main consumer unit.

Grid connection is not the only option for PV – you can use it to power dedicated (e.g. low voltage) circuits, or a

This is a less obvious option for most people, unless in a rural location where the wind resource may be greater and planning restrictions lighter. Buildingmounted turbines enjoyed a brief flurry of popularity some years ago but seem to have gone quiet more recently. So we are talking mast-mounted models, which would need a certain amount of land around them (and not too many close neighbours) to address issues of safety, nuisance, etc.

Assuming you have the

land and no other obvious obstructions, the next step is to access a wind energy atlas such as the SEAI’s which will show the average wind resource at different heights above ground at your approximate location.

An average wind speed of at least 5m/s is generally recommended for wind power viability – the atlas will tell you if you have that and at what height, which will determine the size of mast and may impact on planning permission.

Generally with wind, the economics become more favourable the bigger you go, though a domestic machine is likely to be somewhere between 2.5kW and 15kW, rotor diameter and hub height increasing in proportion.

Micro hydro

Again, this will not be for everyone – a nearby watercourse with a reliable seasonal flow of water is required. You will certainly need planning permission and probably an abstraction license due to the number of other bodies that may have a vested interest in the watercourse up- or down-stream.

However, if you have the resource and can get over the regulatory hurdles, a micro-hydro system can produce enough electricity for all end uses (appliances and lighting) in the average home. Grid connection is possible though you will need either an induction generator or a grid-tied inverter, both of which will of course increase the capital cost. Alternatively, domestic battery storage would be an option.

A heat pump may be a more straightforward alternative if you have a stream, but again will require consultation with relevant bodies.

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SYSTEMS GUIDE / GOING OFFGRID

Cutting loose The pandemic has focused selfbuilders’ minds on the already popular topic of going off grid, meaning no electricity, gas, water or sewerage connections. But how feasible is it to totally disconnect, asks Patrick Waterfield.

The prospects of freedom from utilities, a more sustainable lifestyle and overall greater independence, especially in times of economic and societal uncertainty, hold a strong appeal.

Out of necessity, many rural houses in Ireland already have no mains sewerage connection, relying on septic tanks/mini water-treatment units and percolation areas.

Furthermore, enough water falls on this island to cater for our needs. Given a sufficient catchment area, storage and treatment/filtration, rainwater harvesting is a tried and tested method. On most rural sites there is also the possibility of drilling a well.

Many houses, again mostly in rural areas, have no connection to a mains gas supply with LPG and oil tanks widely available.

So for this article we shall focus solely on going off grid for electricity.

How off grid do you go?

“

‘...going off grid means not only not importing mains electricity but, also, not being able to export excess generation to the grid.’

12 6 / S E L FB U IL D / SU MMER 2 0 2 1

From a purely economic viewpoint, a remote location may favour an off-grid approach due to the potentially high cost of providing an electricity supply where one does not already exist. We could be talking tens of thousands of pounds/euros which would buy a considerable amount of on-site generation and storage.

Technically speaking, going off grid means not only not importing mains electricity but, also, not being able to export excess generation to the grid.

This will have an impact on the economics (although the price for “spilled” generation has not tended to be very favourable to date, low in NI and non-existent in ROI) and, more significantly perhaps, you will have no backup if your system fails.

A halfway step towards going off grid might therefore be providing all your electricity needs on site but still having connection to the grid. In this way you would still have the security of supply of a mains connection should you need it and would be able to spill your excess generation back to the grid. Note that equipment would be needed to effect a smooth switchover between on-site and grid supply and that various standing charges may apply for provision of supply even if you don’t use it.

Set up

Planning regulations permitting, a combination of photovoltaic (PV) panels, wind turbine and domestic battery storage, possibly linked into electric vehicle charging, could provide all the electricity needs for a well-designed house that incorporates things like low wattage appliances.

Cost wise, £30k/€40k would be a reasonable ballpark for a 5kWp PV system with 10kWh battery capacity and 11kW LPG-fired generator, such as would serve a medium-tolarge home with 5,000kWh electricity consumption per year.

The notional analysis shown here assumes this level of consumption.

Guide Selfbuild

issue!) would be low, probably less than 50 per cent.

Planning permission is never guaranteed to be straightforward with any build and going off grid is only likely to complicate things further. Make sure you understand the rules very clearly and consult with the planning authority at an early stage – be open and clear about your proposals. Consult with neighbours too to make sure they are on your side.

Also, it may be more difficult to get insurance for an off-grid property.

What we can all do

Bear in mind that typically only about 1,250 to 1,350 kWh of solar output would be used directly, the rest would be via battery or generator (the more of one, the less of the other). You could up the size of the PV array and batteries, to roughly 10kWp and 20kWh, to reduce the load on the generator but this would raise the overall cost to about £50k/€60k.

The reason for the generator is that off grid makes the most sense in a remote location where the cost of a new grid connection could be substantial. In this context, running the generator is unlikely to annoy neighbours.

The same might not be said for an urban/suburban setting, where grid connection is advantageous.

In a grid-connected system, any excess generation from the panels in summer would be exported to the grid and, in NI, you would be paid for. Though at a lower rate than for power imported, thus allowing the PV to

operate at full output at all times.

The generator or grid connection is needed to avoid having to oversize the PV and batteries to cover worst case conditions, which would not only increase costs but also require powering down of the PV system (and resultant “lost” generation) in summer/good weather.

To avoid running a generator at all, though it would be prudent to have one just in case, you would need about 30kWp of panels and 90kWh battery capacity to cover all your needs, which could cost around £135k/€150k all in.

Hurdles

On a very basic practical level, will you be able to get a mortgage or other loan to build a new off-grid house? Most of the High Street lenders would probably pass, though those already involved with self-build loans might be more approachable.

You might find, however, that the maximum percentage of loan to end value (another thorny

Installing a small amount of renewables, e.g. solar thermal or PV panels, is a good option for most of us, especially if there are grants available as is the case for most existing homes in ROI. Beyond that, we are all guilty of using energy, and water, when we don’t really need to. Flicking a switch or turning a tap is just too

easy! Cutting your shower time by just one minute can not only reduce water consumption but also up to £120/€135 per year on energy costs for a family of four.

Decoupling from wifi might be a step too far for many of us, especially those who work from home or have teenage kids.

However, increasingly these days, holiday companies are promoting off grid properties as a way of taking a break from the trappings of everyday modern life.

Interestingly, there is already a growing body of off-gridders in the UK, some 75,000 people, who are saving up to 90 per cent of their energy and water usage, and spending less than half in utility bills than the average family home.

Statistics aren’t available for Ireland but all in all, even if the full off grid dream is cost prohibitive here, adopting elements of an off grid mindset, even permaculture, can no doubt help us de-stress and minimise our impact on the environment.

“

... off-griders in the UK are spending less than half in utility bills than the average family home.

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BUILDING METHODS GUIDE / BUILDING THE DREAM

The bundle Choosing between the myriad of options for heating, hot water and ventilation is confusing at best. Self-builder Brian Corry, who’s on a mission to build an eco house, explains that is precisely why he relied on professional advice to come to a decision. In the end, he and his wife Karen chose an innovative system that combines all three.

Reality very quickly sets in once you have been granted planning permission to build your dream home. Chief among the most complex decisions Karen and I had to make early on, was how to heat our home, supply it with hot water and ventilate it correctly.

In the past, it was relatively straightforward to heat your home with a large, oil guzzling boiler and large radiators in every room – controlled by a simple on/off timer that never knew how warm or cold the house was (there certainly were no thermostats).

The house wouldn’t have been built with high levels of insulation and natural ventilation would have been the preferred method of injecting fresh air. This was done by boring four inch holes through the walls (typical in ROI) or having windows with integrated trickle vents (more typical in NI) causing your curtains to shift on a windy day.

A fireplace or two came in handy for the colder days and nights, as long as it was fed a steady stream of coal or turf. Not exactly good for the environment, your lungs or your pocket!

Ever stricter building regulations, especially in ROI (and soon to be in NI), have forced selfbuilders to think carefully about their choices, and in many ways have limited their options.

As with the motto, Reduce, Reuse, Recycle, the best kind of energy in the home is the one 12 8 / S E L FB U IL D / SU MMER 2 0 2 1

INTAKE Fresh Air

EXHAUST sale air

Brian Corry

Domestic hot water

EXTRACT sale warm air

INTAKE fresh air

SUPPLY fresh warm air with three temperature zones off HPV unit

you don’t need in the first place.

In building design this is called the “fabric first” approach. In other words maximise the energy efficiency of the house before you even look at what you need to heat it.

Even though we are building in NI and didn’t have to go down this route, we chose to heavily invest in insulation and airtightness to minimise the amount of heat we would need.

The fabric first approach is a

well proven method. My parents, for example, built a house back in 2012 that was near Passive House standard, which is a low energy building methodology that focuses on the fabric first. They didn’t quite have the confidence at the time to do away with radiators in every room, just in case, however in nine years they have never once been used.

Ventilation

Given the level of airtightness

20sqm underfloor heating in up to 2 zones

we plan to achieve, we knew we would go for a mechanised ventilation system to ensure a steady stream of filtered, fresh air. The most efficient system we came across was mechanical ventilation with heat recovery (MVHR) so that was on our musthave list from the start.

Researching suppliers, we found a heat recovery ventilation company that offered a system that combined ventilation with heating (see next section).

Guide Selfbuild

“

FIRST FLOOR

‘As with the motto, Reduce, Reuse, Recycle, the best kind of energy in the home is the one you don’t need in the first place.

ROBES

BATHROOM LINEN

BEDROOM 3

LANDING EN-SUITE

VOID BEDROOM 4

MASTER BEDROOM

GROUND FLOOR ENTRANCE LOBBY STORE UNDER STAIRS

STUDY

EN-SUITE CLOAKS

BEDROOM WC

KITCHEN UTILITY

DINING

LOUNGE SITTING ROOM

S U MM E R 2 0 2 1 / S E L FB UI L D / 129

BUILDING METHODS GUIDE / BUILDING THE DREAM

Of huge importance is designing and sizing the MVHR correctly to the specific layout of your home and the necessity to do so at the early design drawing stage so that ducts can be accommodated and hidden in the walls, ceilings and voids before the layout is finalised.

If we had tried to do this at a later stage it would have been a complete nightmare and led to costly and unsightly compromises. For example, the MVHR contractor found early on that we had left too little space in the plant room to actually fit the unit into. It was then dead easy to make the room 300mm wider and the next door bathroom 300mm smaller.

This is not something you would notice when built but would have been a costly error if we had discovered it too late.

Similarly, the freedom to plan the duct routes will lead to a cheaper install with fewer ducts, less bends and a more free flowing, quiet and efficient system.

Space heating and hot water

Working out the heat load requirement to heat the home was done as soon as we had our specifications finalised for the floor, wall and roof build up.

This step definitely requires an expert. After all, you wouldn’t dream of ordering a structural beam without first employing a structural engineer and the same goes for working out the heat loss calculations for each room.

Such granular detail is necessary given that the orientation of each room (e.g.

North facing) and the amount of glass (solar gain, less thermal performance than a wall, etc.) will each have an effect on the amount of heat required to heat it to a comfortable level.

We paid for a professional to 13 0 / SEL FB U IL D / SU MMER 2 0 2 1

SIDE VIEW

work out the calculations and it turned out that the heat load for each room was really very small.

So small, in fact, that installing a house wide heating system would have been a complete waste of money.

Instead, we looked at a system that would provide heating, hot water and mechanical heat recovery ventilation all in one, using an air to air heat pump as the primary source of heat generation.

The system was able to provide the small amount of heat we needed by warming the incoming fresh air and using the MVHR ducts to deliver it to each room. In addition, this system can heat a 300 litre unvented hot water cylinder with an electric immersion as back up.

This hot water cylinder has a third coil that can be connected to a solar thermal panel.

However, our intention for the future is to install photovoltaics (PV) and battery storage to reduce the electricity usage of the heat pump.

We have some electric heated towel rails in the bathrooms, and a small area of electrical underfloor heating in front of the large windows in the kitchen and living area. These will be sufficient to cope with the coldest of days. We have all heat

emitters integrated into the main heating controls.

Choosing this as our heating system meant we had to configure our ventilation ducts so that they would correspond to our heating zones. We have three heating zones, and therefore three sets of ductwork that feed back to the central ventilation unit; each of the three zones are then laid out in a tee’d configuration.

Cooling

Overheating can be a problem in many well insulated homes, particularly in south facing and heavily glazed rooms.

The solid timber build method we chose (see Spring 2021 edition) helps regulate the temperature inside, as it does not heat up or cool down quickly.

However, we do have a large south facing glazed area, so we will be adding a brise soleil to provide shading.

Our hybrid heating and ventilation system will also be set up so it can provide up to five degrees of cooling for hot summer days, by running the heat pump in reverse.

This cooling function comes at an additional cost but worth it, considering we didn’t have to invest in a standalone heating system and heat emitters. Then

again, if the brise soleil does its job, the cooling mode may turn out to be used just as much as my parents’ radiators. Only time will tell.

The bottom line

The overriding lesson throughout our journey was to work out what we wanted or needed as early as possible and have these details fed directly into the architect’s drawings.

Very few architectural designers have the skills and knowledge to provide this specialist advice to self-builders, but thankfully we found that any heating and energy efficiency consultants we came across were well practised working with them.

Making changes at the design stage saves a huge amount of redrawing and costly changes later on in the process. Every change has a knock on effect; some can be minor but others require entire areas to be redesigned.

Remember, professional input is critical in narrowing down the bewildering number of options available to you. Otherwise, you may find yourself quickly disappearing down a multitude of rabbit holes.

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