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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

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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

Solar Energy

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 view.php?id=398820&section=1

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?

Try this

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 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

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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

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 • 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

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,


 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

Dec 2012

 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  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 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 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’

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)

Instal Sunbox

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:

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&#x20AC;˘ 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

Oct 2013

•Graph can show the energy level

without charging, with charging, or in this case with both options displayed. • Tweak parameters if necessary.

COP improvement?

 COP is assumed to improve by 3% / degree C. The deep ground

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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 &#x2021; Plumbing as, at Oct 2013

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!

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 &#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, Rotterdam and London: intermediate stores on mechanical floors

Website  Research process and construction  

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process is recorded on a blog / website: Daily, weekly + monthly meter readings are stored on a web based spreadsheet: The project is continuing and evolving into the long term Data collected shows that the Learning-by-Doing experiment has worked!


Peveril Sunboxes lecture oct 2013