Euroheat Brochure by Rai Biswas

HOW TO AVOID

THE 5 COMMON MISTAKES

that will make your FLOOR HEATING system USELESS and IMPOSSIBLE to repair

www.euroheat.com.au

STOP,

Before you put the first pipe in… Hydronic floor heating systems are all the rage… and rightly so: The hydronic system lowers energy costs. It’s fully automated. And it gives your home a feeling of comfort, no matter what the temperature is outside. However, all this happens only if it is designed and installed properly. You see, several times a month we get calls from people who have a hydronic system… but it doesn´t work as the salesperson/architect/designer/builder/ installer promised. The client is cold, out of pocket, unhappy and paying a fortune in running costs … and the architect, builder and floor heating installer are scratching their heads trying to find out what went wrong (and who is responsible). Unfortunately, once a floor heating system is installed, it’s very difficult, and in most cases impos-sible, to fix: The “repair” would actually involve ripping up the concrete slab. Pulling down walls. Basically building the house all over again. And that´s why people with poorly designed floor heating systems have no other option than to turn the system off. And even though they paid tens of thousands of dollars for it, they have to find (and pay for) another way to

heat and cool their house. Getting the hydronic heating system right the first time is therefore essential… and that´s why I have written this guide for you. In the pages ahead, you’ll see the five most common mistakes made with hydronic floor heating systems and, most crucially, how to avoid them. As professional engineers and experienced installers, we’ve been designing and installing these systems for houses and commercial buildings in Western Australia for over 26 years (since 1992). The following tips are therefore only a snippet of what we had to learn over this time to make all our systems run… and run efficiently. And no matter if you decide to work on designing and installing your hydronic heating system with us or not, I hope these tips will help you make sure your floor heating works the way you want it to. Because once it´s installed, there is virtually no way to fix mistakes made at the beginning…

Phil Pacak Efficiency engineer Euroheat Australia (Perth)

Ph. 08 6468 8895 phil@euroheat.com.au

Mistake #1 Heat from the warm pipes doesn´t rise only upwards (the mistake of placing pipes into suspended slabs) Like you already know, hydronic floor heating works by circulating warm water through pipes installed in the floor. The heat from the water is soaked up by the concrete in the floor. And once the floor is warmer that the temperature of the air around it, it begins to pass the heat onwards.

3. Larger volumes of mass have greater surface areas, resulting in greater heat losses.

The essential fact is that heat doesn´t rise only up to the room above it… but the heat diffuses into every direction equally within the concrete.

I will show you the physics of how this happens…

Therefore: 1. The more concrete (or any other mass), the more energy is required to heat it up. 2. The greater the mass, the longer it takes to heat up.

257mm THICK HEATED SUSPENDED SLAB

This means it costs a lot to heat up a suspended slab. It takes a long time to do it. And a lot of the energy escapes to the sides and below and is therefore wasted.

Let’s compare two different floor constructions that include a hydronic floor system; a classic 3-course 257mm thick suspended slab, and a 50mm thick insulated screed on slab. We’ll assume that both the screed and the slab are of the same material and density (concrete), and subject to the same conditions to make the comparison fair.

50mm THICK HEATED SCREED WITH THERMAL INSULATION

Mistake #1

www.euroheat.com.au

How much more energy does the suspended slab need to heat up, compared to the screed?

requires 226.16kWh/8.0kW resulting in a heat-up time of 28.27hrs – again, 5 times longer than the screed.

If we assume a 100m² heated floor area, the suspended slab mass is 100m² x 0.257m thick = 25.7m³ = 61.68 tonnes of concrete. The screed on the other hand has a mass of 100m² x 0.05m thick = 5.0m³ = 12.00 tonnes of concrete. To raise the temperature from 15˚C to 30˚C, the suspended slab will require 226.16kWh of energy, yet the screed only 44.0kWh

But won’t a bigger heat source heat it up quicker? Yes, definitely… but after the initial heat-up the unit would be working at a fraction of its designed output, drastically reducing the efficiency and lifespan of the heat source. It would also cost multiple times more to install such a large heat source, and the cost of the energy input would be super high. It would be like driving a road-train to buy milk from the corner store.

So we can see the initial heat-up of the suspended slab alone requires more than 5x the energy, compared to the insulated screed – but take into account this does not factor in any additional heat losses from the suspended slab. How much longer will the suspended slab take to heat up, compared to the screed? This is determined by the maximum amount of energy that can be input into the system at any one time. For a moderately insulated building, a 100m² floor heating system would require a heat source of about 8.0kW capacity. The screed system requires 44.0kW hours of energy to rise from 15˚C to 30˚C, so 44.0kWh/8.0kW heat source, results in a heat up time of 5.5hrs (again, excluding any heat losses). The suspended slab, however,

257mm THICK HEATED SUSPENDED SLAB

But once the suspended slab is heated up, doesn’t it retain heat, and just need topping up? Yes… and no. If the building, and particularly the floor structure, were insulated super well, then yes, it would retain some heat and give it off to the internal environment. But most houses in Australia aren’t that well insulated… and most suspended slabs aren’t insulated well (generally not at all). What’s problematic is that it’s very difficult to insulate these suspended slabs well – because there are still so many thermal bridges for the energy to leak through. Let’s compare heat losses from the typical suspended slab to an insulated screed:

50mm THICK HEATED SCREED WITH THERMAL INSULATION

5 You can see the main difference between the two is there is much more heat escaping (especially downwards) from the heated suspended slab.

in all directions, even through adjoining building elements (conduction across solids), radically increasing the heat losses incurred.

But doesn’t heat rise? Yes, but this in only applicable in fluids, such as water and air. In solid objects, such as concrete, heat travels in every direction… and it travels the most to where it’s the coldest.

The detail shown above isn’t even that bad compared to other common building details/methods, where the energy loss is very severe.

So, as we can see above, the heat travels

Check some of the common heated slab energy loss situations out…

Thermal Bridge Through Exposed Edge Beam:

INTERNAL 20°C INTERNAL 20°C

EXTERNAL 7°C EXTERNAL 7°C

INTERNAL 20°C INTERNAL 20°C

Heat Emission and Leakage from Exposed Slab Soffit:

INTERNAL 20°C INTERNAL 20°C

EXTERNAL 7°C EXTERNAL 7°C INTERNAL 20°C INTERNAL 20°C

EXTERNAL 7°C

INTERNAL 20°C

www.euroheat.com.au

EXTERNAL 7°C

Mistake #1

INTERNAL 20°C

EXTERNAL 7°C INTERNAL 20°C

Thermal Bridge Through Slab to Balcony: From the examples shown it’s obvious that the two biggest issues with heating suspended slabs are: 1. Huge heat losses from exposed surfaces to the external environment, because the heat flow is stronger to where the mass is coldest (outside!). 2. Heat losses through conduction to other building elements such as walls or steel structures, which are difficult to avoid. All these wasteful heat losses greatly contribute to the running cost of the system. We can see this if we compare the approximate running costs for different situations. For a 100m² heated floor area, with a heat pump as the energy source, would cost per hour: ÌÌAverage-insulated building with insulated heated screed: $0.42/hr

ÌÌAverage-insulated building with heated suspended slab: $1.67/hr The suspended slab system cost 3.97 times more to operate (It would even be 50% cheaper to use aircon!)… And this is the difference between getting an $88 dollar monthly power bill for heating, and a $350 monthly power bill. So why is it commonly done like this in Australia (and no-where else in the world)? Most often the reasoning is “because it’s easier”, or “because it’s cheaper”. Both of these statements are true – it is easier and cheaper to ‘whack’ some pipes in a suspended slab – but the result is multiple times better if it’s done the right way. Many ‘enviro’ or ‘eco’ plumbers/contractors say “We’ve installed heaps of these into sus-pended slabs before!” And they are

7 right: Their system does heat the rooms above it a bit. But it also heats the bricks, walls and rooms below. On the sides. The garage. The pantry. The alfresco. The balcony. The air outside. And instead of having a system that is sustainable and energy-saving, they actually pay more in running costs than if they had installed a simple air-conditioning system. All because the heat they make ends up in other areas, and not the rooms they want to heat. We hear the same feedback over and over from people that have had heating installed into ‘normal’ Australian suspended slabs all the time: the floor is cool (at best not cold), and the running cost is sky high … and the physics (explained briefly above) confirms this outcome. What if the screed is poured directly on the top of a slab?

How to avoid mistake #1 The steps are simple: 1. Avoid putting heating into suspended slabs (unless you want an unhappy client). 2. The place to put the pipes is on top of a suspended slab and always only so in combination with an insulated screed or other well insulated system (such as diffusion plates or a dry system). This means a slightly larger initial investment, but only properly thought out and installed insulation will stop 50 - 90% of the heat from being wasted over the lifetime of the building. The cost of the wasted heat will definitely outweigh the cost of the insulation.

This doesn’t work. There MUST be thermal insulation between the screed and the slab, otherwise the screed and slab are bonded together and behave thermally as one thick mass.

“

www.euroheat.com.au

Mistake #2 “Hiding” the heat pump (a.k.a. try breathing with a plastic bag over your head) The warm water that circulates in the floor pipes is produced by a “heat pump”.

This is a good idea… until you understand the physics of how a heat pump works.

This is a machine of some size. It does some humming. And the a lot of the time, people think of hiding it somewhere: garage, store room, or even sometimes a ventilated roof space.

Because when you do, you´d never ever do what´s essentially the same as pulling a plastic bag over your head.

The thinking behind this is usually twofold:

The air/water heat pump is based on the principle that it collects low-value energy from the air, temporarily stores it, and turns it into high-value energy that is useful.

1. The heat pump is hidden from view, so it doesn’t stick out like a sore thumb, compromising the hard work put into designing an exceptional building. 2. The heat pump will be protected from the elements, saving it from water, corrosion, dust, and an early demise.

Let me explain …

For example, in winter it may be 10°C outside... To you and I, this is cold… but to the heat pump, this is a treasure trove of heat energy.

EXPANSION VALVE

REFRIGERANT / WATER HEAT EXCHANGER

HYDRONIC FLOOR HEATING SYSTEM

CIRCULATOR PUMP REFRIGERANT / AIR HEAT EXCHANGER COMPRESSOR

9 Picture a hydronic floor heating system is requesting heat… so the heat pump compressor turns on, compressing a batch of refrigerant that heats up to 40°C. Water from the hydronic system extracts this heat from the refrigerant, cooling it down to 35°C. The refrigerant is then decompressed (expanded), and becomes cold, say 5°C. The heat pump then moves this 5°C refrigerant in front of its fan, and the fan starts spinning. After a minute, the 5°C refrigerant in front of the fan has become 7°C refrigerant. And after another minute, it’s jumped up to 10°C. This is because the air is warmer than the refrigerant – the refrigerant is collecting heat from the air. Once again, this 10°C refrigerant is compressed, turning it into useful 40°C

15°C

refrigerant, ready for transfer to the hydronic system water… and this happens on continuous basis as long as there is call for heating. So we can see from the above process that low-value heat from the air is collected and made into high-value heat that can be used. We must remember that the higher the air temperature, the higher the efficiency of the heat pump, as it’s easier to collect heat from 20°C air than it is from 10°C air. This process is identical to an air conditioner condenser unit, and similar to how a fridge works (but in reverse). The heat pump is actually a complex piece of equipment that must be understood well to gain the most out of it - the explanation above is very simplified for our discussion here.

The heat 10°C pump needs to breathe…

2°C

Imagine the heat pump is enclosed in a garage. There are three walls, a roof, and a closed garage door. It’s 10°C outside, but 15°C inside the garage. The heat pump turns on and starts collecting heat from the 15°C air at a high efficiency, from the high air temperature available.

°C

Mistake #2

www.euroheat.com.au

But after 15 minutes it’s not 15°C in the garage anymore… it’s 10°C. The heat pump keeps going though, still producing heat, but at a lower efficiency. Another 15 minutes pass by, and it’s now 5°C in the garage. The heat pump is working harder and harder 15°Cto produce the 40°C heat. It’s still keeping up with the heat demand, but is now working twice as hard to do it (lower efficiency, higher running cost).

10°C

After 40 minutes of run time, it’s 2°C inside the garage, and the heat pump is working three times as hard to produce any heat. The efficiency has drastically reduced, costing more every minute it runs. Then someone comes home, and opens the garage door… The 2°C air from the garage spills out the open door and is replaced with 10°C 10°C outside air, and the efficiency once again increases, and the running cost decreases.

2°C

Just like getting a breath of fresh air after having a plastic bag over your head. Will a ventilated room provide enough air? We’ve now established that enclosing an air/water heat pump results in poor performance. And that it’s really important that an air/water heat pump (or airconditioner condenser) has 100% free air exchange with fresh external air always. Because it’s from this air that the heat pump collects heat energy. But what about enclosing an air/water heat pump in a ventilated room?

It’s only marginally better than completely enclosing it, as the majority of the same air recirculates within the enclosed space. Even an obstacle (such as a fence) closer than 1 metre from the face of fan can also result in mass air recirculation, decreasing the energy efficiency of the heat pump by up to 50%.

11 Compare the examples below of heat pumps outside with fences in front of them:

It’s clear that even outside, when there’s not completely free air circulation, that exhaust air from the heat pump gets sucked back

in – significantly reducing the heat pump’s efficiency.

www.euroheat.com.au

Mistake #2 Boreped que parundi tiusdae omnis dolent quibus molupis aut eturibusam es volent et rerferi buscian dipsus idelitis et aspiditiant ommol.

Any unit with air exchange should have the air exchange component positioned so it has 100% access to fresh air at all times. Units without air heat exchangers, such as water/water or ground/water heat pumps (i.e. water source or geothermal) can be positioned 100% internally. Do we need to protect the heat pump from rain, dust, sunlight etc.? You might think that covering or enclosing the unit in something will make it last longer, as it wonÂ´t become damaged by

rain, rust, dust, extreme sunshine etc. But good air/water units are designed for the outside environment: They actually make them for the outside. They are built to last in the conditions. Just like a car is made to run outside in rain and sunshine and does not need to be garaged at all times. Making the unit work harder by enclosing it will increase the wear on the heat pump parts more (especially the compressor and fan) than letting it rain on it.

How to avoid mistake #2 ÌÌTake care when you position the heat pump so that the exhaust air is not easily again sucked in as the supply air (short-circuiting). You can avoid this by positioning the heat pump in open area where there are no obstacles within 2 metres (minimum) in front of the exhaust fan.

ÌÌPlan the position of the heat pump when designing the building… otherwise it will probably end up shoved into a corner somewhere with poor air circulation. ÌÌIf the heat pump does need to be inside, within a plant room for example, use a purpose-built internal heat pump which is ducted.

Mistake #3 Forgetting “thermal comfort” when installing controllers and thermostats (in the wrong place) The reason we heat and cool our houses is to feel comfortable in them. Modern heating systems allow us to tell it what temperature we want to have in the room: The thermostat reads the temperature in the room. And the controller then increases or drops the heat coming from the heat pump to achieve and maintain it. That´s easy to understand and do, sure.

Here’s a short explanation why… On the surface the controls for the system are easy to set up: Decide on the time periods you want the rooms to have a certain temperature. Programme this into the controller. And when the thermostat finds out that the temperature has dropped below or exceeded the set temperature, it will turn the heating on/off.

But when you start setting the system up, you have to consider a lot of details that will The problem with this approach is huge: later decide if the occupants will actually feel comfortable This approach works with heating/cooling units that provide immediate warmth/ … because there’s a huge difference between the comfort of a room that´s being chill: Instant gas heaters. Air-conditioners. Electrical heaters. Etc. heated up by “blasts” of heat. And a room that has been heated up gradually and thoughtfully.

www.euroheat.com.au

Mistake #3

You turn these on, they heat up to 100 % and give out as much energy as possible as fast as possible. And when the thermostat tells them “that´s enough”, they switch off again.

towards the sun, the materials the house has been built from, the surroundings and a number of other factors that determine how quickly the room and the house will gain/lose/retain heat.

Technically, the room has been heated to the set temperature. You will see this temperature on the thermostat. So the occupants should be happy, right? But they’re not.

Only then can we decide how long to turn the heat pump on before the rooms need to be warm. And only this way will we actually be able to lower the energy costs and achieve thermal comfort:

The trouble is that “instant” heat is not as comfortable as “gradual” heat.

Only then will the system stop turning 100% on/100% off/100% on/100% off

You know this from your own experience outside: One day, you may feel hot, sweaty and uncomfortable. Another day, you will feel ok. But how is that possible, when during both days the temperature was exactly the same?

…but will (depending on the amount of heat in the room already), send 30% now, then drop to 17 %, then increase to 19%, then drop to 5% etc.

Outside, our “thermal comfort” is determined by humidity, sea breeze, shading, etc. Inside, the majority of thermal comfort is achieved by gradually heating the rooms up. And this is really the secret behind the natural and comfortably feeling of houses with hydronic floor heating: The occupants don´t get blasts of instant heat. But the rooms get heated up gradually. Just as we like the warm morning and afternoon sun rays more than the direct midday scorching heat. To achieve this thermal comfort however, we cannot just put in the thermostat controller and turn it on. We need to calculate the “temperature gradient”. This is a relatively complex mathematical calcula-tion based on the amount of glass in the room, it´s positioning

You don´t drive your car by starting up the engine, flooring the gas pedal and slamming on the brakes only after you get to your destination. This wouldn´t be the most efficient way to run your car. And neither is it for the heating your home. For the system to really work efficiently, the designer, architect and installer need to work over the floor plans. Do the calculations. And also place the thermostats and controllers in the right places… You see, if the thermostat “thinks” it’s cooler than it actually is, then it will keep heating, eventually overheating the building. On the other hand, if it thinks it’s warmer, it won’t heat enough, leaving the building cold and people uncomfortable.

15 The 5 most common thermostat positioning mistakes are… 1. Controls Floor Temperature Only: If the thermostat regulates only the floor temperature, and not the room temperature, then it can lead to over heating or under heating of the room, as the slab (floor) temperature DOES NOT equal the room temperature. 2. Hidden in Cupboard: The thermostat cannot get a read of the actual temperature of the room – it’s generally either warmer or cooler in the cupboard compared to the room, resulting in over/under heating of room. 3. In unheated area: Thermostat cannot get a good read of the room it’s heating… it’s reading the temperature of a part of the house that’s not even being heat... so it doesn’t actually control the comfort level. 4. In direct sunlight (or close to it), drafty area, or next to oven/stove/other heat source: Thermostat gets a ‘false’ reading, influenced by heat or chill from other sources. 5. For aircon, the sensor is often placed on the return air duct… But this is often not a true representation on the temperature experienced by the occupants in the room (the return air may be sucked only from the top layer of air in a room – not a good representation of the occupied zone lower down). Most importantly, it’s forgotten (or misunderstood) that the thermostat does not read only the air temperature… and that air temperature alone does not show the whole story of thermal comfort in a room. There’s air velocity, humidity, air temperature, and radiant temperature to consider - and also the metabolic rate and level of clothing worn by occupants in the room – but we won’t consider these here. In fact, right now, we’ll only consider air temperature and mean radiant temperature, because they have the largest impact on room comfort. So out of the two factors we’re discussing

– air temperature and mean radiant temperature – almost all HVAC designers and contractors only consider one: air temperature. Yet air temperature gives you, approximately, only one half of the story! For this reason, thermostats need to be positioned so that they receive an accurate radiant temperature reading of the room… this means exposing the front panel of the thermostat to the most frequently occupied area of the room… allowing it the get both a good radiant reading, and air tem-perature reading, of the room where people spend the majority of their time.

www.euroheat.com.au

Mistake #3

How to avoid mistake #3 1. If you just put the pipes in and stick a thermostat in each room, any system can heat up the house to the desired temperature… but you will have no guarantee you will actually feel comfortable in it. (Remember the example of sweaty/nice feeling outside during two days with the same temperature?) 2. For you to feel thermally comfortable in each of the rooms, fairly complex calculations need to be done. And the people doing them need to understand the effects of sunlight, positioning, building materials, neighbouring rooms etc. to work it out properly.

3. Take care to position thermostats out of direct sunlight: Ideally they’ll be around 1600mm above the floor in the room that’s being heated or cooled. Don’t forget to watch out for other sources of heat/chill that can affect the thermostat reading! 4. Choose a good thermostat: one that takes into consideration both the room air temperature AND the room radiant temperature - allowing it to regulate to room temperature accurately. Thermostats also need to be timeprogrammable, so they automatically turn on and off when desired by the occupants, and don’t excessively heat the room when not required.

Mistake #4 Forgetting that heat leaks (a.k.a. you wouldn’t keep water in a bucket full of holes) When moving and storing water in the garden, we know that we need to avoid holes in the hose or the bucket. Otherwise the water would leak. Disappear. And we´d be paying for water which we didn´t end up using. The same thing happens with heat too: When allowed, it will also leak. How?

Thermal energy always moves from hot to cold, and never the other way around: If you have produced heat, it will “look” for the coldest place in your house... And heat that up first. This is fine, if by doing this it heats up the furniture, walls and the whole room you are inhabiting. But it’s not if it first leaks to (for example) the uninsulated garage, ceiling, roof space, pantry or windows.

17 Obviously, installing the right type of insulation (which works as a thermal barrier) in the right positions helps prevent the flow of heat out during winter (and heat in during summer). So, where do the majority of heat losses happen in buildings? Generally they can be attributed to three areas: ÌÌGlazing: Heat escapes via both radiation passing through the glass outwards, and convection from warm internal air through the glass to the cold external air. It’s not practical or desirable to limit the amount of glazing to reduce heat losses in most buildings, so where possible, use double glazing with high R-value glass. ÌÌRoof: Heat from warm air under the ceiling escapes into the roof space (mainly through convection), and then through to the external environment. This type of heat loss is not a big problem when radiant heating is installed as the room air is not the main thermal energy carrier in this case, hence a lower air temperature is maintained under the ceiling in comparison to systems where air is heated (aircon). Insulating the ceiling and roof well with bulk or rigid insulation to mitigate heat losses in winter solves this issue. ÌÌThermal Bridges: These can be found in the floors, walls, windows and roof, where a building element directly connects the internal and external environments, allowing unhindered energy transfer between them (via thermal conduction). An example is un-broken window frames, where heat from inside only has to travel a short distance (not more than 100mm)

to the colder outside through the aluminium frame construction (a good heat conductor). What you must know about thermal bridges in connection to floor heating Out of the above, thermal bridges are the largest threat to floor heating efficiency. Let me explain… With traditional aircon systems, only the air in the room is heated… the building structure itself is not directly heated. The warmest air in the room gathers near the ceiling (losing vast amounts of energy to the roof space). The lower you get in the room, the lower the air temperature… so the coldest layer hangs out at the floor level (making it uncomfortable for occupants). This low layer air passes some of its heat to the slab, which then passes it on to the external environment. Because the air near the slab is already cool, and because the air is not a good energy carrier, the heat loss rate to the slab (and then outside) is relatively low.

“

Mistake #4

www.euroheat.com.au

It looks something like this:

25°C

35°C

25°C

25°C 15°C

15°C

15°C 15°C

Floor heating flips this situation on its head… BUT The floor structure is heated to a higher This is only applies to an insulated screed temperature than the air in the room and (or super well insulated slab). It looks emits ~55% of heat energy predominantly something like this: as thermal radiation, ~30% through the air 15°C convection, and ~15% via conduction to the structure and room furniture.

15°C

20°C

15°C

20°C

27°C

20°C

25°C 20°C

You can see the difference immediately... output can be as little as 25% radiation, The structural floor slab is still cool, but the 5% air convection, and 70% conduction to heated floating floor is warm (because of surrounding structures or the ground. the insulation between the slab and the This is because there is a direct link heated screed). The air temperature drops between the warm concrete slab, and the with increases in room height (resulting cold external environment. The majority 15°C in lower energy losses through the roof). of the heat is being sucked away outside The rooms radiant energy emitted from (where there is a high temperature gradient the floor is absorbed by the surrounding = high energy flow), instead of warming the structure and furniture, and re-emitted 15°C inside of the building. (balancing out the mean radiant room temperature). … So 70% of the energy that’s being sent to the slab doesn’t end up heating the A BIG difference is obvious in a heated room, but rather heating the air and structure slab, where thermal bridges ground outside! You can see that here: and heat losses have been ignored… the 20°C

20°C

15°C

27°C

25°C 20°C

Mistake #4

www.euroheat.com.au

15°C

20°C

15°C

27°C

25°C

15°C

The greatest heat losses from heated slabs are from the slab edge – either to the ground, or to adjoining structures – this is well known. Energy losses form the underside of the heated slab are the next major culprit. Examples of common thermal bridges from on-ground heated slabs: Exposed heated slab edge to sand/soil: Often it’s said that “WA has sandy soils that insulate”. Dry sand, however, has

a specific heat similar to concrete and aluminium (the amount of heat it can hold), and has thermal conductivity 10x that of polystyrene, 2x of plywood timber, and a quarter that of standard concrete. The thermal conductivity of soil is even higher when moisture is present (downpipes disposing water to underside of slab, overflowing soak-wells, high groundwater, leaking water pipes)… meaning the thermal conductivity can be equivalent to that of concrete.

Above you can see an indication of heat losses from an exposed heated slab edge to the atmosphere, conduction to the adjoining paving and window frame, and conduction to the footing and soil below. 70% of the heat from the floor is easily lost this way.

This is the most detrimental situation, as the heat flows away so aggressively that the floor heating system is rendered useless. The most common occurrences are when pools, in-situ concrete paving, cast-in planters, or other external concrete structures directly abut the heated slab.

Heated slab edge adjoins conductive structure:

ÂŠ 2018 Euroheat Australia Pty Ltd.

www.euroheat.com.au

Mistake #4

How to avoid mistake #4 1. To prevent these drastic heat losses, thermal breaks MUST be used. 2. Insulation to the underside of an on-ground slab is not required by the BCA/NCC in most climate zones – but we highly recommend it. In WA 25-50mm of polystyrene, or similar rigid insulation, is sufficient. 3. The BCA/NCC does however stipulate that on-ground slabs have at a minimum R1.0 slab edge insulation, extending the full vertical edge of the slab, or minimum of 300mm below the ground level. THIS IS IMPORTANT – it will save you the architect, the builder, and the client many headaches. 30mm of Extruded Polystyrene (XPS) or 25mm of Phenolic Foam is sufficient for this purpose. 4. Suspended slabs have by far the highest heat losses (see Mistake #1) – just one of the reasons we don’t recommend floor heating installation within a suspended slab. By BCA/NCC, suspended slabs require, in addition to slab edge insulation, insulation to underside/soffit. 5. The best result comes from an insulated screed system, as this eliminates energy leakages due to carelessness or unintentional mistakes. Often screeds are installed directly over a slab with no thermal insulation. However, this is a corner cutting approach ending with a poor result, as a huge amount of heat from the screed is drawn downwards by the concrete slab below. Remember, thermal energy in solid materials travels in all directions, not only upwards, and the heat flows most to where it is the coldest. A well installed screed heating system is thermally insulated from all other structures (such as walls, window frames and slabs below).

Mistake #5 Hydronic systems are not created equal (and while some will heat your building well, others will fail) Search the web for hydronic heating and the two most common phrases quoted are ‘hydronic heating is 30% more efficient than aircon’ and ‘water is a better heat conductor than air’.

aren’t true. They can be. The problem is, it is assumed that they apply to every system and building. That ALL hydronic systems are efficient, regardless how designed and constructed.

The problem isn’t that these promises

… and this is NOT true.

23 Since we design and install hydronic heating systems, we should be extolling only the virtues of the system.

4. Water flow rate too low – not enough energy being delivered to where it’s needed, leaving cold spots.

But we are the first ones to say that hydronic systems are good and suitable only sometimes:

5. Heat source over-sized – works at a low efficiency level and leads to early equipment failure.

Only when the system is designed and installed with knowledge, physical calculations, and care.

6. Floor heating pipe spacing inadequate – system cannot produce heat output as required.

You see, just because the principle is efficient, it doesn’t mean the system (or the building) is efficient by default.

7. Thermostat controller in wrong position or utilised for wrong function - over or under heating.

Regularly, efficiency is wiped out in a hydronic system from at least one, if not more, of these mis-takes:

8. Heat source installed in poor position works with low efficiency and leads to early equipment failure.

1. Floor heating pipes within too large a concrete mass – expensive to heat, long response time.

9. Poor design of heating loops – cold spots, poorly heated areas where higher thermal losses need to be covered (ie. near tall windows, high ceilings), overheated areas with solar gains.

2. Thermal bridges from heated slabs to unheated masses or external elements – heat escapes unintentionally, doubling or even tripling running cost, and extends heat-up time. 3. Uninsulated piping between heat source and the floor system manifold – heat is lost before it reaches its destination, increasing running cost and extending heat-up time.

10. Building heat losses not properly calculated. 11. Loops design not taking in consideration flooring type or furniture layout. 12. Poor installation – kinked pipes, unequal piping spacing, pipes surfacing on surface of slab.

Mistake #5

www.euroheat.com.au

These mistakes unfortunately happen a lot. It’s really easy to stuff it up. And usually impossible to fix. This comes from a unique characteristic of hydronic systems… The excellent results that come from a hydronic system – in terms of running efficiency and comfort – come from combining both a well-designed and well-executed hydronic system WITH a well-designed and well-executed building. This is because the hydronic system is integrated into the building itself. The two have to be in perfect harmony, working together… not working against each other… Because a well-designed hydronic system installed into a poorly executed structure ends in disappointment… the same as when a poorly designed hydronic system is installed in a well-designed structure. What you need to know about airconditioning and hydronic heating systems before selecting one The internet articles promise that hydronic heating is better than aircon. They say water is a better heat conductor than air. And that floor heating does not consume that much electricity. But is it true? Does water really transfer heat better than air? Water is certainly a better heat conductor than air… but people don’t swim in the warm floor heating water, but they do reside within the warm room. Because water has a higher ‘specific heat’, and hence can carry more energy than air, you can transfer more energy with less volume and power. For example,

with aircon, you may need to move 200 litres per second of air to transfer 2.5kW of energy…. But you can transfer the same 2.5kW of energy with 0.06 litres per second of water. This means less mechanical power is needed to move the energy (the pump for water will use a fraction of the power than that of the fan for the aircon). A beneficial by-product of this (difference in transferred volume) is there are lower energy losses from the smaller water pipe (e.g. 20mm diameter) compared to the large air duct (e.g. 300mm diameter), because of the smaller external surface area.

“

Just because the principle is effficient , it doesn’t mean the system is efficient by default.

Air & Water at 20°C and 100kPa

1000L of Air = 1m³ Density = 1.204 kg.m³ Specific Heat = 1.006 kJ/(kg.°C) = 1.21 kJ.°C = 0.000336 kW per °C per m³

Water can carry 3448x more energy than air at the same pressure and temperature.

Is hydronic heating really 30% more efficient than aircon? Is hydronic heating 30% more efficient than air? Yes – it can even be up to 50% more efficient. But, as with all sciences, there are many factors which influence the result. The 30% is generally quoted in reference to the room thermostat being set 2°C lower for radiant heating than air heating, whilst maintaining the same perceived comfort by the occupants. As a rule-of-thumb in the HVAC industry, it’s said that for every 1°C lower room temperature set, up to 15% running cost savings can be realised. So instead of 21°C with aircon, you can get away with 19°C with radiant, and still be comfortable. This is evident in some of the previous illustrations shown, where with aircon hot air collects at the ceiling level, and the heat escapes through the roof. The occupants also have cold feet and warm heads, which

1000L of Water = 1m³ Density = 998.19 kg.m³ Specific Heat = 4.18 kJ/(kg.°C) = 4172.43 kJ.C° = 1.159 kW per °C per m³

humans perceive as very uncomfortable. With floor heating, the savings are even greater if the water temperature utilised is very low (~35˚C), the building well insulated, and has high ceilings. But we have to make sure we’re comparing apples to apples here… If you compare a refrigerated type aircon in heating mode to hydronic floor heating (in-screed) with a heat pump, it’s a fair matchup. The condenser unit for the aircon works identically to a hydronic heat pump, only the heat is transferred to water instead of air. The main difference, if we keep it simple, is how the energy is distributed (air vs water) and utilised (or wasted with heat losses). In this instance, the hydronic floor heating would be much more economical to run compared to the aircon. If you compare the aircon and floor heating as above, however change the floor heating

25°C

www.euroheat.com.au

Mistake #5 15°C

15°C

15°C 15°C

from in-screed to in-suspended slab, then apples are being compared to oranges… The suspended slab would experience much higher unwanted heat losses (as explained in Mistake #1), meaning that the floor system would cost multiple times more to operate than aircon. Apples are also being compared to oranges when aircon is compared to a hydronic in-screed heating system with a gas boiler… The aircon condenser unit (and heat pump) can be assumed to have an efficiency of 300%. If electricity costs $0.25/kW, it

costs $0.083 per kW of heat produced. A condensing gas boiler can be assumed to have an efficiency of 95%. With gas costing $0.15/kW, it costs $0.158 per kW of heat produced. Now, if we take into account the overly simply and commonly quoted 15°C ‘hydronic is 30% more efficient’ – due to the method of energy distribution and consumption – we have a cost of $0.11/ kW. So, in this instance with a gas boiler as 20°C heat source, the running cost of aircon is 25% lower than a hydronic system (ignoring heat losses through ceiling from hot air, and lower level of comfort created by the 25°C aircon) 15°C

15°C

20°C

27°C

20°C

25°C

15°C

35°C

15°C

25°C

20°C

15°C

27°C

15°C

So be VERY careful when listening to “facts” about hydronic heating… from what we’ve seen and heard in WA over the past 15°C 26 years, 95% of installers don’t really understand the systems at all. Having said that, it’s not because they’re charlatans or liars… it’s because hydronic systems are 20°C much more than plumbing… 15°C

20°C

27°C

20°C

25°C 20°C

15°C

25°C

15°C

20°C

15°C

15°C 15°C

20°C

15°C

It requires a solid engineering knowledge and experience to get it right (that’s why hydronic systems are ALWAYS designed by ‘hydronic’ or ‘heating’ engineers in other countries)... It’s necessary to understand and integrate multiple disciplines to create a successful hydronic system.

What to do now to make sure your hydronic floor heating system really works The lowdown: While anyone can put in the pipes, install the thermostat and turn the heat pump on, only a few technicians and companies have the experience, technical education and knowledge to make the system actually as efficient as you want it to be. At Euroheat Australia, we’ve been designing and installing these systems for houses and commercial buildings in Western Australia for over 26 years (since 1992). As engineers specialised in sophisticated and cooling and heating systems, we don’t just calculate a building’s energy gains/ losses. We don’t just do ventilation. We don’t just do hydronic floor and wall systems. We don’t just do aircon. We don’t just open/close windows or blinds. Or just cool cellars. Or just heat pools. Instead, we will help you optimise the building design to reduce the required energy in the first place. We will then design every millimetre of the Phil Pacak system, install it and continually monitor &

optimise it. (The systems can completely integrate natural ventilation, floor heating/ cooling, aircon heating/cooling, pool heating, cellar cooling, tap hot water.) And we will make sure it all works together seamlessly, so that the occupants are comfortable all year round without having to do anything… and happy with the bills as well as the eco-footprint. I would like to say that clients marvel about the natural and non-artificial feel of the climate in their houses, but they don’t: They find the warm feeling in winter and cool in summer so natural (without rapid spikes of temperature or being blown hot/ cold air at them from vents) that they don´t notice they have a system doing this at all … and I suppose that is the ultimate compliment and sign of user happiness. If you’d like to create a similar climate in your buildings, perhaps we should meet in your office, for a quick, 15 minute chat. Over your current projects. And over ideas on how to make them more energy efficient. I promise no salesy pitching, just info on building physics, energy flows, thermal efficiency and how to use it all in seamlessly heating/cooling your buildings…

Efficiency engineer Euroheat Australia - Hydronic Systems & Building Engineers

Ph. 08 6468 8895 phil@euroheat.com.au

08 6468 8895 info@euroheat.com.au www.euroheat.com.au