Photovoltaic with Solar energy storage, augmenting heat pump to achieve Carbon Zero CIBSE ASHRAE London April 2012 by David Nicholson-Cole with help from Prof S Riffat, Dr B
Mempouo, Dr Chris Wood and David Atkins Department of Architecture and Built Environment University of Nottingham House solar-heated for the entire year: it is beyond zero-carbon, for both heating and hot water Hybrid retrofit; could be applied to existing houses Project from Aug 2009- present day
The Peveril Solar house in Nottingham is entirely solar heated, all year round, with more than carbon neutrality for heating and hot water. This is a hybrid retrofit, achieved on a British developer house. The house has good insulation, but was not built to passive house standard. The retrofit project has been going for two and a half years now, principally to apply interseasonal charging to a single house. It uses that heat to augment the ground source heat pump.
Carbon Zero Why do we want it? Climate change Long term, major risk
Energy shortage Short term, serious risk
What can we do? Design better buildings and
systems Teach others to do it
As academics at the University of Nottingham, the staff are committed to Sustainability. In much of our architectural design work in the school, we aim for Carbon Zero Design. My principal motivations are to retard Climate Change and to address Energy shortage. These two are likely to be causes of human conflict and loss of living space. What can we architects and engineers do to solve it? I believe that we should design better buildings and systems, and teach the next generation to do this too.
Carbon reducing tricks without special technology Simplify lifestyle Buy power from 100% renewable suppliers Yes! Feed in tariff Yes, financial incentive Plant trees Yes, but where? not being done enough Live off Grid? No, we cannot all do it Insulate and design better? Yes! Then follow with the Technology to reduce carbon emission Governments and people can use many ideas such as these to reduce carbon emissions. Carbon offsetting, or buying from renewable suppliers is good for those who cannot adapt buildings or create better ones. Feed in Tariffs are incentives to generate power and save energy. We can make more oxygen by planting more trees but is this being done? Can everyone live Off-Grid and store their own electricity, heat and water? This is impractical for the urban population. We must insulate buildings in cold climates and use bioclimatic design in hot climates. This will help, but there will still be a consumption of energy and carbon emissions. So I conclude that we do need TECHNOLOGY to reduce carbon emission.
Solar Energy
Amount of Solar Energy falling on the planet billions of GWhr/annum. It is Free! Catch it! • Ground Source heat pumps use stored Solar energy, not Magma • In Urban areas, direct solar heat cannot reach ground • Buildings can reach up and claw that energy down into storage Buildings and urban landscape shade the earth
Solar energy falls plentifully on the planet every day. As other forms of energy become more endangering to us, we must use the energy that is available free. Mostly, it falls in the wrong time of day or the wrong season when we do not need it. Logically, it needs to be stored. Ground source heat pumps use solar energy, but in urban areas, the buildings and trees can shield the ground. If too many buildings use ground source, it would be insufficient. Buildings can reach up and actively collect solar energy.
Peveril Solar house How do we do it? ‘Active House’ concept Using Technology and the Grid to balance
consumption and generation Highly applicable to Retrofit Yes, new houses should be Passivhaus
The Carbon Zero answer for the Peveril Solar house is to coordinate good Technology, using the Grid and the Ground as batteries, to make the house solar heated all year round. In the UK, we would mostly agree that new houses should be built to Passivhaus standard but there are millions of existing houses. This technological combination could be applied as a retrofit to houses with appropriate roofs and walls, making them an ‘Active House’.
Peveril Solar house Developer house 120m2, 2007 Brick-block, well insulated
Includes: • Vertical Elevator • Disabled kitchen • Light tube • PV panels • Thermal bottle-store • Efficient lighting • GS heat pump • Underfloor heating • Double glazing • Vegetable garden The house is an average British developer house, on a small plot. It has better-than-average insulation. The heat pump and underfloor heating and energy efficient lighting were included at the start, but the house was nowhere near Carbon Zero. The annual power consumption averaged 8,500 kWh in the first two years, one third of the average British house, but still too much.
Technology pentangle: Components The Grid PV roof 4kW
Sunbox 4 m2, 3 m3 Solar House 120 m2
The Earth
The Borehole Clay+Limestone 3600 m3
GSHP 2kW normal 6kW panic
This illustrates the technology pentangle. The house was built in 2007. The heat pump and borehole were installed at the time of construction. The PV was added in 2009, and the Sunbox was added in 2010. The PV roof generates electricity, the heat pump consumes electricity, but gets 75% of its heating requirements from the earth. The Sunbox makes the heat pump 30-40% more efficient. How? This will be explained.
Photovoltaic Roof 22 x 180W Sharp panels, 28 sqm = 3.96 kW, installed Oct 2009
Facing ESE Not ideal, but it’s good enough Shading from hill to south west
Generates 3,400 kWh annually Space available
Space available
3,400 kWh annually
The Photovoltaic roof is Grid connected, installed after the British Feed in Tariff was announced in twenty-09. This has limitations. The roof does not face south, and there is some shading from a hill, and the rules favour a maximum of 4 kilowatts. However, it produces enough in Summer and Equinox to meet the entire heating and hot water requirements of the heat pump, and more besides. This meets the objectives of the research project.
Heat pump - Ground Source Heat pump: Swedish IVT
Greenline C6 with integrated water tank
6 kW nominal output, power
consumed about 2.2 kW Has ‘additional heat’ option if it cannot get heat from ground Annual power consumption in 2008 was 4,800-5,600 kWh/year depending on weather, for this house size & parameters With Solar Augmentation, the heat pump is running at approx 2,700 kWh/ year
The heat pump is a Swedish IVT Greenline. It includes a water tank in one compact vertical cabinet. The normal annual power consumption for this size of house would be 5,200 kWh. The 2.2 kW heat pump has an ‘additional heat’ mode, working with its immersion heater if it cannot get enough heat from the earth.
Borehole Warm medium is 2 vertical boreholes, 48 metres deep (equivalent to 15 storeys) Manifold in the car space Soil is dense ‘Marl’ (glacial Clay-Rock mixture) Vertical boreholes are easy to recharge with solar heat if soil is good No garden space for horizontal ‘slinkies’ or collector These could not easily be solar charged
The heat pump uses two boreholes, forty eight metres deep and five metres apart. There was no space in the garden for a horizontal loop. The process of solar charging works best if it is stored vertically, to prevent heat escaping to the atmosphere. The cost was reasonable, using a lightweight drilling rig. The soil is perfect for solar storage, as it is a dense mixture of Clay and Rock.
Borehole Twin 48m boreholes Upper part affected by seasonal change -
less useful Not fully stable until 5-18m down
Active Volume 3,600 m3 Active Mass 6,800 tonnes Thermal capacity of active volume is 1750 kWh/ºK This is approximate Depends on how far heat goes in one season,
rate of heating, conductivity
Twinning of Holes is better for Solar
Charging
Space between, reduces loss, nurses the
added heat
The boreholes resemble two large bottles. Assuming that the active volume has a radius of about 3.6 metres around the pipes, the volume is assumed to be [3,600] thirty six hundred cubic metres, with a thermal capacity of [1,750] seventeen hundred and fifty kWh/ºK. There is a benefit in using a twin borehole. It would normally be wrong to cluster the boreholes, but with solar charging, the heat is nursed in the space between the holes.
Charging Principle 1 Without charging, deep ground
temperature falls
Reaches a new stasis, lower than in the
first year of operation Too deep to recover in one summer
Reduction in COP of heat pump COP worsens 3-4% with each degree C of
‘coolth’ in source
Let us put solar heat down NOW! • Every day! • Summer and Equinox sunshine • Even in winter!
Ground source energy is solar energy that has taken many years to reach the depths. A greedy house can suck energy out too quickly. In an urban area with many buildings, the Sun cannot reach the earth to restore energy levels. The deep earth gets progressively chilled over five to ten years. Each year, the borehole’s energy level is reduced if it cannot recharge. The COP of the heat pump can progressively worsen, leading the owner to believe that the heat pump is malfunctioning. Let us ask: why not put heat down, now? this year, every day whenever the sun shines? and even when it is not shining?
Charging Principle 2 Use Solar panel Can be flat plate or evacuated tube Can be Custom-designed Sunbox, as in the Surya models designed for this project, using recycled swimming pool panels, and mini-solarium design. Low temperature high volume flow seems to be most effective Future: could be PVT, PV with thermal loop behind glass Circulate glycol mixture Warmed liquid can be trickle fed into the ground loop Original design took ground loop through Sunbox (now replaced by trickle-feed) Sunboxes driven by Thermostat Delta-T >8 degs C or Real-T >21ºC The heat pump can be augmented with a solar collector to improve its efficiency and prevent the ground from chilling. A conventional panel could be used, as could evacuated tubes. On the Peveril Solar house, a custom designed sunbox has been hand-built, using recycled swimming pool panels. The control system uses a dual mode thermostat. It checks real temperature in the Sunbox and the Delta-T of the Sunbox and the ground loop.
Charging Principle 3 Summer - Interseasonal charging Heat pump dormant, doing hot water only Solar Sunbox pump depositing heat, every day,
equivalent to 1.15 kW. Triggered by delta-T or real-T
Equinox - Diurnial Heat pump working intermittently, as required,
drawing heat from Sunbox is there is a Delta-T Sunbox catches daytime heat on nice days for evening use
Winter - Realtime Heat pump busy much of the day - good Delta-T If enough heat up above, will divert some flow
to Sunbox and download it, equivalent to 1.8 kW but for shorter hours
Solar panels that heat a water tank reach stasis quickly in the Summer, and become unproductive. A solar panel that is heating the ground never reaches stasis, because the ground is infinitely large, and never gets ‘hot’ - the ‘energy bubble’ gets to 14ºC and then gets larger instead of hotter. The system has three modes of working, for Summer, Equinox and Winter. All are good and all will reduce the workload of the heat pump.
Surya Sunboxes
Design One
Both designs use the same
black poly-propylene chillers, each 1 m2 . 4 m2 face the sun, and for collecting from the air, the surface area is 8 m2.
First Design: Mar 2010-July 2011 Second Design: August 2011->
Design Two The black chillers in the Sunbox are an array of 4 polypropylene swimming pools panels 1 m2 each. 4 sqm are exposed to Sun, but a surface area of 8 sqm is exposed to warm air conditions. They work well in direct sunshine, despite being covered. They have a microclimatic enclosure around them, so that they work from warm air, even in Winter conditions on bright days, overcast sunny days. Warmed brickwork keeps them going long after Sunset on Summer nights.
Greenhouse effect Solar energy entering
transparent enclosure converting to heat because
wavelength changes and it does not reflect out again
Internal air temperature rises Basis for all greenhouses, global
warming, solar thermal panels
The Sunbox is using the Greenhouse Effect. It can warm up if there are bright or sunny conditions, even on Winter days. The black chillers work well in direct Summer sunshine, but the year consists of four seasons. The project’s aim was to maximise performance over the entire year, which requires an enclosure.
Surya Sunboxes First Design: 200mm deep solaria 1.1 cu metre volume Vertical front panel, glassy Metal reflectors above+ below 6mm polycarbonate walls
Design One
Second Design: 700mm deep solarium 2.8 cu metre volume Sloping front panel, matt Top reflectors only Multi-wall thin
polycarbonate Insulated detailing
Design Two
There are two designs. I called them ‘Surya’ after the Hindu Sun God. The first design was a pair of boxes - they worked excellently, achieving the aim of making the heat pump significantly more efficient. The second design builds on ideas for improvement devised by observing the performance of the first design. It is a unified volume, 2.5 times larger than the first design. It is highly insulated with thermal break construction. It has an insulated skin of polycarbonate with a matt finish, allowing more sunlight to enter, and losing less by solar reflection.
Solar cooker reflectors Concentrate additional solar
heat into the container
Millions of these in use in rural villages,
India+Africa
Reflectors are used on both the designs to
boost the performance on sunny days
Illustrations: Mark Aalf
The Design One had reflectors because their performance needed boosting in Winter months at low sun angles. There was an immediate improvement in performance but this was difficult to quantify. It coincided with the heating season and we do not have an un-mirrored sunbox to compare it with. The Design Two uses a top mirror externally, and the lower mirror is now internal.
Sunbox build Designed and built
entirely by DNC, the researcher and householder Scaffold, open ended time
limit Indoor plumbing too
Decisions Design continues to evolve
even while up there 3D Model every step
Precision metal and plastic - little
tolerance for errors Plumb and Square!
The system design and construction were entirely carried out during the winter of 2009-2010, and modified in 2011 and 2012. The system was 3D modelled on a computer, but many final decisions were made as the construction proceeded.
System: schematic Three possible system layouts Left, Peveril Solar house uses the simplest possible
circuit Right, a idea combining HW tank or heat exchanger with high performance solar panels This is the best layout
The original system layout, Left, was simply to TEE the loop from the solar Sunboxes onto the existing ground loop, with a diverting valve. High temperature collectors such as evacuated tubes, right, are more expensive and require a heat exchanger or water tank.
System: schematic layout 2010-2012
Schematic layout as of March 2012
Final System layout Plumbing and Electrics working since
Plumbing in airspace above the heat pump
May 2010 with solenoid valve No change in 2011 Modified in 2012, with parallel (trickle) circuit and tubes The electrics and plumbing are combined on this diagram. For the first two years, a solenoid valve was thermostatically activated to route the ground loop through the Sunbox and thus boost the COP directly. The plumbing and electrics have been modified in March 2012 to be a parallel circuit, trickling warm liquid into the ground loop. This was because the solenoid valve became unreliable, the Design Two overheated, and it became clear that a parallel circuit gives more reliability.
Technology pentangle:Performance (annual) The Grid PV roof 3,400 kWh
Sunbox 3,050 kWh Solar House
The Earth
The Borehole 12,000 kWh
These two are equal = Carbon Zero GSHP 2,700 kWh (5,200 kWh) No further need for ‘panic’ mode Saves 1,200 kWh / year
The components have performed well in the first years of testing. Before the project, the heat pump used 5,200 kWh/year. Since the sunboxes have been storing solar energy, the GSHP consumption has fallen to 2,700 kWh/year - less than the power generation of the PV roof.
Ground Temperature Deep Ground
temperature is key performance indicator Efficiency of GSHP related to warmth of source Ground temperature not fallen below 10.0º in two winters since Sunbox installed Ground does not get ‘hot’, but energy level expands to a larger sphere
Instal Sunbox
Graph of ground temps over three winters shows that it has a smoother curve and recovers quickly after the heating season
A key performance indicator is the temperature of the deep ground. The Winter of 2009 shows the ground reached a low of 4.8ºC. Since the Sunbox was installed, recovery was quick, and the curve is now smoother. The lowest ground temperatures in January 2011 and January 2012 were 10.0ºC, 5 degrees above the lowest temperature before installation. In summer, the ground has not gone above 14ºC. The additional energy put down seems to have had an expanding sphere of influence, rather than getting hotter.
Degree day <->Heating workload Red curve =heating requirements of any building in
Nottingham region, base 15.5º Blue curve = heating workload of GSHP Electrical consumption of Space heating only (omitting DHW and floor pump)
Instal Sunbox
Another key performance indicator is the electrical consumption of the heat pump (in blue), relative to the local heating requirements, expressed as degree days (in red). In the two winters of 2010-11 and 2011-12, the heat pump worked with less power consumption and fewer hours than the previous winter.
COP improvement? Heat pump electrical consumption saving is more than
40% annually The deep ground hints that there is approx 5 degrees of benefit in the cold season compared with previous year COP is assumed to improve by 3% / degree C - but improvement has been greater Heating requirement of 14,600 kWh is met by 2,700 kWh of electricity - suggests a virtual COP of >5. GSHP annual running time (FLEQ) is reduced from 2,100 to 1,200 hrs - saving approx 1,800 kWh The author surmises that much of the saving is by the heat pump never needing to use its ‘additional Heat’ mode, saving 1,200 kWh/yr
The electrical consumption and the annual running time of the heat pump have improved by more than 40%. Such an improvement in COP seems unlikely, but I observe that much of the improvement is based on the heat pump never needing additional heat mode, which saves 1,200 kWh/ year. It completes its heating tasks more quickly. The recent winter has also been less cold.
Addition of Tubes 2012 Evacuated tubes have been
added March 2012
Comparing: Commercial collector, high-
temperature, low volume circuit with Existing hand-crafted collector, high-volume, low temperature Tubes operate in ‘swimming pool circuit heating mode Both are based on parallel circuit Too early to judge! Very Intermittent operation Heat Exchanger required to
reduce intermittency Early indication is that Sunbox is far more effective An array of 15 evacuated tubes has been mounted on the roof, March 2012. I am comparing the performance of high-temperature low-volume collectors with the existing low-temperature high-volume collector. Tubes operate in a ‘swimming pool heating mode’, i.e. warming a very large mass. Early indications are that the hand crafted product is more efficient and does not suffer intermittency. Double, or perhaps 4 times the area of tubes would be needed to equal the Sunbox performance.
Website Research process and construction
process is recorded on a blog / website: http://chargingtheearth.blogspot.com/ Daily, weekly + monthly meter readings are stored on a web based spreadsheet: http://tinyurl.com/peveril-metering The project is continuing and evolving into the long term Data collected shows that the experiment has worked!
Data from this project is recorded every day, with weekly and monthly summaries. The blog website contains the ideas and the construction process, including some of the right and wrong decisions. Google for ‘chargingtheearth’ to find it. With more than two completed years of recorded data, it is possible to re-compute annual performance, every week - this is how we know that the house is Carbon Zero.
Solar thermal charging: will it happen? â&#x20AC;˘ The catalytic converter was invented in the 1950s, but took until the late 1990s to become a requirement. â&#x20AC;˘ Elisha Otis demonstrated the safety elevator in 1853, and died in 1861. It took until 1883 before the first Tall Building emerged Some inventions take time to be accepted! Will this technology become more commonplace? The catalytic converter for petrol engines was invented in the 1950s, but took until the 1990s for the catalytic converter to become mandatory. Elisha Otis demonstrated the safety elevator in 1853, but it took until 1883 for the first Tall Building to emerge in Chicago. With the small market share for ground source heat pumps, I expect 20-30 years for this to pick up.
Conclusion: GSHP with or without charging? GSHP expensive enough, you deserve to
have it perform better This should be considered with every GSHP, especially in urban area This Add-on could attract Renewable Heat Incentive Solar charging is a Defroster even if it does not actually ‘Heat’ the ground. Nota bene: Can be done with standard panels, not
sunbox Only possible if ground conditions permit Boreholes should be shallow and clustered, not deep and singular
Heat pumps are expensive so we wish them to perform efficiently. Large buildings have incidental heat gains which can be dumped underground. Houses have very small incidental gains, so could only use solar panels. The gain in performance of the heat pump is so palpable that solar or heat-gain charging should be the first choice, not an afterthought.
Scaling up the technology Hearst Tower in New York stores surplus
energy underground for later retrieval Power Tower in Linz is like a huge solar panel, with a PV solar facade, and 7 km of boreholes storing energy gains below ground Recent new Nottingham University buildings cool building by storing heat gains underground for later retrieval Researcher Nic Wincott has documented many examples in Sweden
On a much larger scale, I’m glad to see that new buildings under construction on Nottingham University campus are using incidental heat gains to charge underground boreholes, to boost their heat pumps. The Leed Platinum rated Hearst Tower in New York and the Power Tower in Linz both dump heat gains underground for later use. Cambridge researcher Nic Wincott has documented many examples in Sweden.
Scaling up the technology ď &#x2021; The principle can be applied to
larger buildings ď &#x2021; Authorâ&#x20AC;&#x2122;s postgraduate students applying it to very tall buildings for sites in New York and London: intermediate stores on mechanical floors
The principle of this technology can be scaled up even further. Numerous buildings and some district heating schemes in Sweden and Canada are using solar underground storage, notably Anneberg and Drakes Landing. Tall buildings can reach above the urban horizon and capture solar energy on facades. They would need local stores at intermediate floor levels, and local heat pumps. If ground source heat pumps are specified and if the ground conditions are good, I propose that they should also include solar earth charging.
Thankyou!
Architects of the future should ensure buildings have space on roof or facade for solar panels. Exploit the wonderful source of free clean energy right above our heads by burying it under our feet! Thankyou!