Photovoltaic power 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
Carbon Zero Why do we want it? Climate change Long term, major risk Sea levels, migration, food
water
Energy shortage Short term, serious risks Long term, major breakdown
Only one planet to live on!
What can we do? (...as architects & engineers) Design better buildings and
systems Teach others to do it
Increasingly difficult to get energy from the ground
Carbon reducing tricks without special technology Simplify lifestyle Buy power from 100% renewable suppliers Yes, we do that! Feed in tariff Yes, financial incentive Plant trees Yes, but where? We are doing that Not being done enough, takes too long Live off Grid? No, we cannot all do it, urban society Insulate and design better? Yes! But what about existing housing stock? With all these - follow with the 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 energy) • In Urban areas, direct solar heat cannot reach ground, too much shading • Tall buildings can reach up and claw that energy down into storage Buildings and urban landscape shade the earth
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
Peveril Solar house Developer house 120m2, 2007 Brick-block, well insulated 3.6 sqm extension added 2012
Includes: • Vertical Elevator • Disabled kitchen • Light tube • PV panels • Thermal bottle-store • Partial Heat reclaim • Efficient lighting • GS heat pump • Underfloor heating • Double glazing • Vegetable garden
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
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 3,200 kWh annually Space available
Space available
3,200 kWh annually
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 3,200 kWh/ year average
Borehole, vertical ‘Warm’ medium is 2 vertical boreholes, 48 metres deep (equivalent to 16 storeys) Soil is dense ‘Marl’ (Glacial Clay-Rock mixture) Vertical boreholes are ideal to recharge with solar heat if soil is good No garden space here for horizontal ‘slinkies’ or collector These could not easily be solar charged If too small, horizontal ones can freeze or swell ground
Borehole, vertical 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 Opposite of normal advice for boreholes. Shallow hole less risk of hitting caverns
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 sunshine • Equinox sunshine • some Sun even in winter!
Charging Principle 2 Use Solar collector 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 >2.5 degs C or Real-T >15ºC
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 if there is a Delta-T Sunbox captures 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 2 kW but for shorter hours
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->
Third design Autumn 2012
Design Two
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
Solar cooker reflectors Installed 2010, de-installed 2012 Concentrate additional solar heat
into the container
Millions of these in use in rural villages,
India+Africa
Reflectors used to boost the performance on
sunny days - were effective Removed 2012 because the addition of ETFE is so significant that contribution of mirrors is reduced.
Illustrations: Mark Aalf
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
Surya Sunboxes Wall mounted Sunbox
refronted with ETFE
Design Three
Greater thermal
transparency Lightness, long life Double stretched skin Increasing winter capture
New roof mounted
Sunbox
Metal radiator collectors Polycarbonate enclosure Small bore pipes Unitised construction on
standard racking
Design Four
Sunbox build 2010 Designed and built
entirely by DNC, 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 Keep it all Plumb and Square!
System: schematic during 2011 Three possible system layouts Left, Peveril Solar house uses the simplest possible
circuit, entire loop through Sunbox Right, a idea combining HW tank or heat exchanger with high performance solar panels Third, the one we are using, see next slide
System: schematic layout 2013
Plumbing in airspace above the heat pump
Technology pentangle:Performance (annual) The Grid PV roof 3,200 kWh
Sunbox 2,700 kWh Solar House
The Earth
The Borehole 12,000 kWh
These two are in balance = Carbon Zero GSHP 3,200 kWh (5,200 kWh) No further need for ‘panic’ mode Saves 1,200 kWh / year
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 three winters since Sunbox installed Ground does not get ‘hot’ - energy level expands to a larger cylinder of ‘warmth’
Instal Sunbox
Graph of ground temps over four winters shows that the solar augmented one has a smoother curve and recovers quickly after the heating season
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
Thermal Energy model Energy simulation based on 3+ years of meter readings Input data is GSHP meter, Solar thermal meter Computes figure for amount drawn from borehole Computes a figure for the thermal elasticity of soil, i.e. the
tendency for borehole to restore its temperature from the infinite surroundings Computes a radius of a theoretical single borehole energy volume Displays radius as a curve - the orange one
COP improvement?
COP is assumed to improve by 3% / degree C The deep ground hints that there is approx 5 degrees of
benefit in the cold season compared with previous year Heat pump electrical consumption saving should be 15% but improvement has been greater - is more than 40% annually Heating requirement of 14,600 kWh is met by 3,200 kWh of electricity - suggests a virtual COP of >4. GSHP annual running time (FLEQ) is reduced to 1200-1600 hrs depending on weather The author notes that some of the saving is by the heat pump never needing to use its ‘additional Heat’ mode, saving perhaps 1000 kWh/yr
Addition of Tubes 2012 Evacuated tubes were added March
2012
Comparing the types of collector: all connected to same ground loop Tubes need a Heat Exchange or they
‘snuff out’ with cold ground loop Very intermittent operation Early indication is that Sunbox is far more effective DONT fit tubes unless facing due south and have space to fit them upright! Solar controller can manage two pumps, so a heat exchanger can be positioned between the loops.
Tubes operate in ‘swimming pool heating mode
Additional Roof unit 2012 Unitised construction Can be built off site, delivered and
set up on rails Piping with 15mm copper Metal collectors Working well during first winter
Views of the Loft ď &#x2021; Plumbing as, at May 2012
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. â&#x20AC;˘ First lifts were in shops and warehouses. It took until 1883 before the first Tall Building emerged Some inventions take time to be accepted!
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: Could be done with standard or PVT
panels, not sunbox Only possible if ground conditions permit Solar Boreholes should be shallow and clustered, not deep and singular
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
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
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!
Thankyou!