Solar earth charging - Sunboxes augmenting Ground Source Heat Pump to achieve Carbon Zero September 2011, SET 2011 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 Hybrid retrofit : it is zero-carbon, for both heating and hot water Project Aug 2009- present day The Peveril Solar house in Nottingham is entirely solar heated, all year round, with zero carbon output for heating and hot water. This is a hybrid retrofit, achieved on a typical British modern house. The house has good insulation, but was not built to passive house standard. The retrofit project has been going for two 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. We include it in all our teaching. In much of our architectural design work in the senior school, we aim for Carbon Zero Design. David’s principal motivations are to retard Climate Change and to address Energy shortage. Climate change is something we are all concerned about in the long term. Global energy shortage is likely to be a greater source of human conflict than any other cause. What can we architects and engineers do to solve it? David believes we should design better buildings and systems, and teach the next generation to do this too.
Carbon Zero Tricks 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 better? Yes! Then follow with
Governments and people can use financial tricks such as these. Carbon offsetting, or buying from renewable suppliers is good for those who cannot adapt buildings or create better ones. Feed in Tariffs are good incentives to generate power and save energy. Can we make more oxygen by planting more trees? There could not be enough trees or enough land to meet the emissions of the world’s growing population. Can everyone live Off-Grid and store their own electricity, heat and water? This is impractical for the urban population. Can we do it just by insulating buildings very well? This will help, but some climates are very hot, others are very cold, and there will still be emissions.
Peveril Solar house How do we do it? ‘Active House’ concept Using Technology and the Grid to balance
consumption and generation More applicable for Retrofit New houses should be Passivhaus
The Carbon Zero answer for the Peveril Solar house is to coordinate good Technology, and use the Grid as a battery, to make the house entirely solar heated all year round. This combination could be applied as a retrofit to any house with suitable adaptation. 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 still be used on any Active or Passive house.
Technology pentangle: Components The Grid PV roof 4kW
Sunbox 4 m2, 3 m3 Solar House 120 m2
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 the heating requirements from the earth. The Sunbox makes the heat pump 15-33% more efficient. How? This will be explained.
The house Developer house 120m2, 2007 Brick-block, well insulated Includes: • Vertical Elevator • Disabled kitchen • Light tube • 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. Note, that the average British house uses about 25,000 kWh / year.
Photovoltaic Roof 22 x 180W Sharp panels = 3.96 kW, October 2009
Facing ESE Not ideal, but it’s good enough Shading from hill to south west
Generated 3,330 kWh annually Space available
3,330 kWh annually
The Photovoltaic roof was installed from the moment that the British Feed in Tariff was announced, in 2009. This has limitations, as the roof does not face south, and there is some shading from a hill. It is Grid-connected and produces enough in Summer and Equinox to meet the entire heating and hot water requirements of the heat pump. This meets the objectives of the research project.
Heat pump - Ground Source Heat pump: Swedish IVT
Greenline C6 with integrated water tank
6 kWh nominal max. output,
power consumed about 2.2 kWh Has a ‘panic’ option if it cannot get heat from ground. Annual power consumption 4,800-5,600 kWh/year depending on design and installation and house size With Augmentation, the heat pump is running at approx 3,330 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 5,000 kWh. The 2.2 kW heat pump has a ‘panic’ mode of 6 kW, working with its immersion heater if it cannot get enough heat from the earth. In the first two years, it used this for over 220 hours per year, equivalent to more than 1,200 kWh.
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 No garden space for horizontal ‘slinkies’ 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 concept of solar charging depends largely on storing it vertically. 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 Assume upper part affected by
seasonal change - less useful Not fully stable until 15-18m 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
Twinning of Holes is better for Solar
Space between, reduces loss, nurses
the added heat
The borehole resembles two large merged 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 a bad thing, but with solar charging, the heat is nursed in the space between the holes.
Charging Principle 1 Without charging, ground
temperature falls, deep down Reaches a new stasis, lower than
in the first year of operation
Reduction in COP of heat pump COP worsens 3-4% with each
degree C of coolth in source
Put solar heat down NOW! • Every day! • Summer and Equinox sunshine
The heat in the borehole is solar heat that has taken many years to reach the depths. A greedy house can suck heat out too quickly. In an urban area with many buildings, the Sun cannot reach the earth to supply more heat. The deep earth gets progressively chilled over five to ten years. Each year, the borehole does not have enough Summer heat to restore its heat from its surroundings. The COP of the heat pump can get progressively worse, 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 PVT, the most efficient in future Can be Custom-designed Sunbox, as in the Surya models designed for this project, using recycled swimming pool panels, and greenhouse design. Circulate glycol mixture Can be trickle fed into the ground loop if small diameter pipes Entire ground loop can be ‘whooshed’ through panel if pipe diameter is large Sunboxes driven by Thermostat Delta-T >6 degs C or Actual-T >20ºC 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 built, using recycled swimming pool panels. The control system needs a dual mode thermostat. It checks actual temperature 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
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 most of the day - good Delta-T If enough heat up above, will divert flow up to Sunbox and
download it, equivalent to 1.85 kW
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, as the ground is infinitely large, and never gets ‘hot’ - it merely gets ‘warm’. The system has three modes of working, for Summer, Equinox and Winter, and all are good. The highest productivity is in the Equinox when there are sunny days, and the heat pump is providing a strong delta-T.
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 are an array of 4 polypropylene swimming pools panels 1 m2 each. They are useful because they have a 40mm entrance diameter, large enough to drive the entire ground loop directly through them. They work very well in direct sunshine. David decided to build a microclimatic enclosure around them, so that they would work from warm air, even in Winter conditions on bright days, or late into the night on Summer days.
Surya Sunboxes First Design: 200mm deep solariums 1.1 cu metre volume Vertical front panel Metal reflectors all sides Thick polycarbonate walls
Second Design: 700mm deep solarium 2.8 cu metre volume Sloping front panel Top reflectors only Multi-wall
polycarbonate Insulated skin
There are two designs. They are called ‘Surya’ after the Hindu Sun God. The first design was a pair of boxes - it has worked excellently, achieving David’s aim of making the heat pump significantly more efficient. The second design builds on the improvements that David devised by observing the performance of the Mark 1. It is a unified volume, 2.5 times larger than the first design. It is highly insulated with thermal break construction. It has a thinner skin of polycarbonate, allowing more sunlight to enter, and losing less by solar reflection.
Greenhouse effect Solar heat entering transparent
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 Sunboxes are using the Greenhouse Effect. They can warm up if there are bright or sunny conditions, even on Winter days. The black chillers work well without a box in Summer sunshine, but the year consists of four seasons. David wished to maximise performance over the entire year, which for him, requires an enclosure.
Solar cooker reflectors Concentrate additional solar
heat into the container
Millions of these in use in rural villages,
We only have 4 m2 and would like to have
8 m2 but do not have enough wall Reflectors are used on the Design One to boost the performance.
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 unmirrored sunbox to compare it with. The Design Two uses a top mirror externally, and the lower mirror is now internal.
System: schematic Three possible system layouts Left, Peveril Solar house uses the simplest possible Centre, a idea combining HW tank with high
performance solar panels Right, Solar thermal separate from heat pump This is the best layout
The system layout, Left, is simply to TEE the loop from the solar Sunboxes onto the existing ground loop, with a diverting valve. Other systems displayed are either too expensive or do not contribute to the COP of the heat pump.
System: detailed layout
Two way valve directs flow to Sunboxes or down to ground
Final System layout Plumbing and Electrics
Plumbing in airspace above the heat pump
working March 2010, Modified, finalised May 2010 No change required in 2011 The electrics and plumbing are combined on this diagram. A two way valve is thermostatically activated to add the sunboxes to the ground loop and thus boost the COP. During the recent rebuild of August 2011, no change was required. The plumbing and electrics work perfectly.
Technology pentangle:Performance (annual) The Grid PV roof 3,330 kWh
Sunbox 3,050 kWh Solar House
The Borehole 12,000 kWh
These two are equal = Carbon Zero GSHP 3,330 kWh (5,000 kWh) No further need for â€˜panicâ€™ mode Saves 1,200 kWh / year
The components have performed well in the first year of testing. Before the project, the heat pump used 5,000 kWh/year. Since the sunboxes have been storing solar heat, the consumption has fallen to 3,330 kWh/year - equal to the power generation of the PV roof.
temperature is key performance indicator Efficiency of GSHP related to warmth of source GT not fallen below 10.0º even after cold December’10
Graph of ground temps over two years 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 low figures. Since the Sunboxes were installed, recovery was quick, and the curve is smoothed. The worst Winter temperature at 1st Jan 2011 was 10.0ºC, 5 degrees above the temperature in the previous year. The ground has not gone above 14ºC. In practical terms, we are defrosting the ground, not heating it.
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)
Another key performance indicator is the electrical consumption of the heat pump, relative to the local heating requirements, expressed as degree days. In the extremely cold British winter of 2010, the heat pump worked with less power consumption than the previous winter.
COP improvement? Heat pump electrical consumption saving is 33%
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 If COP is improved by 15%, the author surmises that the
remaining 18% is saved by the heat pump never having to use its emergency ‘panic’ mode, switching to 6 kW direct heating.
The electrical consumption of the heat pump has improved by 33%. Such an improvement in COP is unlikely, but the author surmises that more than half of the improvement is based on the heat pump never needing ‘panic’ mode, which saves 1,200 kWh/ year over previous years.
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 by David during the winter of 2009-2010, and modified in 2011. The system was 3D modelled on a computer, but many final decisions were made as the construction proceeded.
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 two completed years of recorded data, it is possible to re-calculate annual performance, every week this is how we know that the house is Carbon Zero.
Solar thermal charging: will it happen? â€˘ The catalytic converter was invented in the 1950s, but took until the late 1990s to become a requirement. â€˘ 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! The catalytic converter for petrol engines was invented in the 1950s, but took until the 1990s to become a mandatory. Elisha Otis demonstrated the safety elevator in 1853 and died in 1861, but it took until 1883 for the first Tall Building to emerge, in Chicago.
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
Note well: Can be done with standard panels, not
sunboxes 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. All new buildings under construction on Nottingham University campus are using heat pumps with summer charging to boreholes, to boost their heat pumps. These are using incidental heat gains in the buildings, but not using solar panels. If ground source heat pumps are specified and if the ground conditions are good, the author proposes that they should also include solar earth charging. Architects of the future should ensure buildings have space for solar panels, and work from the wonderful source of free clean energy right above our heads!
Surya One: March 2010- July 2011
Surya Three: August 2011--> ? NYC Green Canyons by Modi, Modi and Qiu
As a technology combination, this could be applied to existing houses and buildings, and used in new designs. Davidâ€™s design students have even applied it to designs for a 65 storey skyscraper in New York, winning an international prize. Thankyou!