Photovoltaic power with Solar energy storage, augmenting Heat Pump to achieve Carbon Zero CIBSE Liverpool Oct 2013 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 zero-carbon, for heating and hot water combined Hybrid retrofit; could be applied to existing houses Project from Aug 2009- present day
Threats to our survival on this planet •• Climate change •• End of Oil •• Water-Food •• Population • •• No easy solutions: as architects and engineers, we do the best we can
Carbon reducing tricks without special technology Simplify lifestyle - ‘power down’ 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, urbanized society Insulate and design better? Yes! But what about existing housing stock? Do as many of these as we can - then follow with Technology to reduce carbon emission
Amount of Solar Energy falling on the planet billions of GWhr/annum. It is Free! Catch it! • All our energy comes from Sun - if not now, then from fossil fuels millions of years ago • In Urban areas, direct solar heat cannot reach ground, too much shading • Buildings can reach up and claw that energy down into storage Buildings and urban landscape shade the earth
Magma energy PS, We are not talking about Geothermal Energy from the Magma!
• As found in Iceland, near Etna, etc. • Very localised availability - great if you have it! • To get it, must drill very deeply - 3 km • Risks of Seismic kickback • Magma energy rising to surface is 1000th of the Solar falling
If you live near volcanoes, use them! But not in London
If you have hot springs, use them too, e.g. in Bath, Lourdes
on to it - about 1 watt/sqm. Not harvestable unless it is naturally near surface. Hasn’t stopped the ice in Antarctica being several kilometres deep
Interesting use of Thermal Mass, as passive design idea
Solar capture in buildings THREE main methods available to us for using Sun: Passive design •Form of building, orientation, sunspace design, materials, stack effect etc Active design •Solar Thermal: Panels or tubes or devices to capture thermal energy
•Solar PV: Panels or devices to capture electricity
‘Passive House’ ‘Passivhaus’ ‘Active House’ BRE distinguishes : •Passive House as at Hockerton, or Integer house (BRE). Sunspace, thermal mass etc •Passivhaus - as defined by Passivhaus Institute Also: •Active House - defined by Active House Alliance. New build or Retrofit, the Key thing is to return more Energy than you use • IMHO, all Newbuild should be bioclimatic and close to Passivhaus, then use Technology
Above, Passivhaus. Below, Active
Storing Energy, or Heat?
Energy is different from Heat Energy can be converted • Direct transfer suffers losses (entropy) • Heat pump enables conversion of energy - Solar energy enables plants to grow into trees, or to feed us - Food enables us to run a Marathon - Countless examples of energy conversion Example: The Earth under my house doesn’t get Hot when it is thermally charged, but the Energy level increases (widening sphere of thermal influence)
Ice houses proof that Man made use of thermal storage for thousands of years
Red hot ball bearing dropped into a cup of cold tea cools immediately. Tea has vastly more energy than the ball.
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
Peveril Solar house Large field to the south, it’s a hill! Causes solar shading in winter - sunrise 1 hour late
( : e p o l S
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
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
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 2,600-3,600, averaging 3,200 kWh/ year over three years Delivery by Underfloor Heating No woodburning stove
Borehole, vertical Storage 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 Nowhere for energy to escape to 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
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
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 • Sunny spells 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 AKA Controller 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 / restorative Heat pump busy much of the day - causes strong
Delta-T Even in Winter, the sunbox is warm enough to restore energy level rapidly when Delta-T is good after a GSHP heating cycle
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
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,
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
Second Design: 700mm deep solarium 2.8 cu metre volume Sloping front panel, matt Top reflectors only Multi-wall thin
polycarbonate Insulated detailing
Surya Sunboxes Wall mounted Sunbox
refronted with ETFE
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
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 Chat to passers by....
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 could 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 3,300 kWh Solar House
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 is 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’
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)
Thermal Energy model Energy simulation based on 4 years of meter readings Input data is GSHP meter, Solar thermal energy 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
Thermal Energy model How done? • Project started in 2009 • based on logical hunch - knowing there is a benefit, not knowing the
numbers or system design • Real world - Peveril installation is testing Sunboxes (and Tubes) in one inhabited building : Learning by Doing! • Each monitored several times a week • Combination is too complex for existing spreadsheets to forecast or model. • Transient model is required! Inputs and Outputs on a Timeline: • to understand energy flows of existing, on a day-by-day basis • can this be used to predict future system? • For this to progress to replicability, it needs credible track record of both modelled and installed examples • Human & Architectural and Technical factors also need to be researched. • July 2012, author set out to write Thermal Model using Geometric Description Language (GDL), a programming system within ArchiCAD.
Thermal Modelling: Re-define Borehole • Real borehole is twinset - 48m deep, 5m apart,
overlapping - ideal for solar charging. • For Modelling purposes, regard the Energy Level as a Virtual Volume: a single deep cylinder, approx 85-100m deep. • As volume increases, can only expand outwards, not downwards. • Therefore: Volume is proportional to square of Radius. • Imagine energy volume expanding and contracting as inputs and outputs occur. • When energy level is low, earth energy sucked in from infinite surrounding mass. • Surface area to volume ratio changes with expansion/ contraction, proportional to square.
• Assume a consistent
thermal conductivity of the earth. • Borehole cluster better for solar charging
Above: Real boreholes Left: virtual borehole
Thermal Modelling: Data collect Daily monitoring of all electric and thermal energy meters in a large multi-tabbed spreadsheet See it at: http://tinyurl.com/peveril-metering/
Another tabbed page reads relevant columns from the first page, places in new columns with separating commas
Thermal Modelling: Data convert Readings are copied and pasted into field of a GDL data-file as numeric text with comma separation. PUT statement tells it to read the data into memory
GDL script reads file and places all data into ‘Arrays’ in memory, with significant names like ‘daynum’, ‘gshpconsume’, ‘sbinput’ etc.
Thermal Modelling: Parameters GDL allows one to build a ‘parameter table’, to display to the user some of the constants required.
•Peak summer energy volume: the
maximum charged level beyond which energy will leak away.
•Starting date and energy volume - in
this case 8400 kWh in Aug 2009.
•SPF of heat pump: average COP.
Reading in the electric consumption, the algorithm determines how much energy needs to come from the earth.
•System loss: all systems have losses
in pipework, and in top part of borehole, and liquid left in pipe after pump stops.
•System upgrade: What happens if the
solar panel area is increased?
•Borehole depth: a constant that
allows the Radius to be a variable.
Thermal Modelling: Algorithm Recharge Adjust Factor • The most useful discovery of the model - a technique to quantify natural recharge which occurs all the time, not only in summer. • Think of as: “index of elasticity of thermal conductivity of soil as energy is brought in from the surrounding mass”. • Large numbers are involved, so the RAF. for this model is in the region of 35x10-6. • Method: View the graph without charging; get the peaks and troughs to level nicely in accordance with weather records; the RAF is then correct. • If RAF. is wrong, curve will shrink to nothing, or expand infinitely after a few years.
• The main Algorithm is this short loop. • Running through the timeline (daily intervals
over 4 yrs), algorithm incrementally adjusts Energy Volume based on inputs and outputs, and then calculates the elastic Recharge from the surroundings. • Algorithm fills two arrays with values for RADIUS, one that allows solar charging and one that assumes zero charging.
Thermal Modelling: Form curve
â€˘ The array contains daily figures for theoretical Radius of the Energy Volume.
These are converted into 2D polygons
Above: Final Curve, Vertical black lines show significant moments on the timeline. Dates are printed along the baseline. Right: Subroutines to draw out diagram. Far Right: Most of the drawing routine.
Thermal Modelling: Results
•Dual Energy Curve Shape is the end result of the process •Compare with the Ground Temperature curve Updated Above: Final chart, Blue is Uncharged, and Red is the cumulative effect of charging relative to Weather. Weather: 2009 there was no charging, 2010 was cold, 2011 was very warm, 2012 rainy, 2013 Spring cold, summer long
•Graph can show the energy level
without charging, with charging, or in this case with both options displayed. • Tweak parameters if necessary.
COP is assumed to improve by 3% / degree C. The deep ground
temp 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 SPF improvement is greater - more than 40% annually Heating +DHW requirement of 14,600 kWh is met by 3,200 kWh of electricity - suggests a SPF 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
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 ‡ Plumbing as, at Oct 2013
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. â€˘ First lifts were in shops and warehouses. It took until 1883 before the first Tall Building emerged Some inventions take time to be accepted!
Conclusion1: 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 Renewable Heat Incentive could be amended to reward those who Solar Charge 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 : [Leicester house] Only possible if ground conditions permit Solar Boreholes should be shallow and clustered, not deep and singular
Conclusion2 1. Solar capture: Sunbox is more effective! • Low-temp, large-volume collector (Sunbox, 3000kwh/ yr) proved more effective, versatile and simple than hightemp collector (Tubes, 350kwh/yr). • If starting again and had a South Roof, would do it with PVT (Photovoltaic-thermal) 2. Accelerative Effect: take note of this: TIME factor contributes more than bland annual input / output figures. Immediate restoration of energy level takes place after a heating cycle. 3. Modelling: Useful exercise, but where next? • Understanding natural recharge rate has helped. • Could use typical Degree Day and PV data • Re-write the algorithm to read typical year data and forecast solar panel area based on different house-size, GSHP capacity and borehole size. • Adapt it to clustered boreholes. •Proof that ‘Learning-by-Doing’ sometimes works
Scaling up the technology Hearst Tower in New York & Manitoba Hydro in
Winnipeg 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 ‡ The principle can be applied
to larger buildings ď ‡ Authorâ€™s postgraduate students applying it to very tall buildings for sites in New York, Rotterdam 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 Learning-by-Doing experiment has worked!