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School&of&Civil&EngineeringFACULTY&OF&ENGINEERING
School&of&Civil&EngineeringFACULTY&OF&ENGINEERING
Ground=source&Heat&Pump&Applications
CIBSE&YorkshireMarch&16th 2016
Simon&Rees
Outline
• Heat*pump*principles
• Historical*developments
• Domestic*field*trials
• Non6domestic*Systems*6
• Ground*heat*exchange
• System*Integration
• Measured*Performance
• GSHP*Research
Rees,%S.%and%R.%Curtis%(2014)%National%Deployment%of%Domestic%Geothermal%Heat%Pump%
Technology:%Observations%on%the%UK%Experience%1995–2013.%Energies.%7(8):% 5460T5499Free%online%at:%http://www.mdpi.com/1996T1073/7/9/6224
Heat&Pump&Principles
• Based&on&a&vapour=compression&refrigeration&cycle
• Heat&is&‘pumped’ by&a&compressor:&more&heat&out&than&electrical&power&in.
• Coefficient&of&Performance&defines&thermodynamic&efficiency
• The&smaller&the&temperature&difference&Inside=to=outside,&the&greater&the&efficiency.
Compressor
Heat Rejected ( to the heat sink at high
temperature ( )TH
QH)
Compressor Electrical Power ( )P
Heat extracted ( the heat source at low
temperature (T )
QC) from
C
Heat&Pump&Characteristics
Staffell,%I%(2009).%A)review)of)domestic)heat)pump)coefficient)of)performance,%2009.%
Heat&Sources:&Air&or&Ground?
The&ground’s&high&thermal&mass&means&it&has&a&temperature&that&is&more&favourable&for&heat&exchange&than&the&air.
!10
!5
0
5
10
15
20
25
Tempe
rature)(°C))
Time)()mm)yy))
Daily+Mean+Ground+Loop+Average+Fluid+Temperature Daily+Mean+Air+Temperature Initial+Ground+Temperature+ (+12.3+°C+)
Ground&Temperatures
CIBSE&TM51&
(Busby&et&al.&2009)
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Approaches&to&Ground=coupling
The&coupling&with&the&ground&can&be&through&
closed=loop&systems&with:
• Vertical&borehole&heat&exchangers&(100=150m&typical&in&UK)
• Single&U=tube
• Double&U=tube
• Co=axial
• Horizontal&loops&with&straight&pipe
• ’Slinky’&horizontal&loops
Water&sources&can&be&used&through:
• Extraction&from&wells,&rivers,&lakes&(open&loop)
• Closed&loops&submerged&in&lakes
Seasonal&storage&can&be&achieved&using&large&groups&of&boreholes&(BTES)&or&pairs&of&wells&in&aquifers&(ATES).
SingleU-tube
DoubleU-tube
Co-axial
E
C
Horizontal&Slinky&Heat&Exchangers
Source:&GeoScience&Ltd
Source:&Carbon&Trust
Heat&Exchanger&Technology
Vertical&Boreholes:&Drill,&Insert,&Grout.
Energy&Piles&and&Walls
REHAU Soga*and*Rui (2016)*Energy*Geostructures
Seasonal&Performance
• Coefficient*of*Performance*(COP)*is*a*steady6state*parameter*at*particular*operating*conditions*(catalogue*values).
• Seasonal*Performance*Factor*(SPF)*is*based*on*seasonal*energy* inputs*and*outputs.*This*is*of*more*interest* in*evaluating*real*performance
• SPF*is*the*ratio*of*total*useful*thermal*energy*to*system*electrical*energy*consumed.
• In*reality*systems*are*complex*and*SPF*can*be*calculated*different*ways*depending*on*what*electrical*demands*are*included.
• Heating*and*cooling*can*be*separated:*SPFH,*SPFC
SPF&Defined
• SPF1 is*heat*pump*product*alone
• SPF2 includes*the*ground*loop*pump
• SPF3 includes*supplementary* heater
• SPF4 includes*the*heating*circulating*pump
SPF&Target&Values
• Acceptable*values*vary*depending*on*the*comparison*being*made:*site*energy,*primary*energy,*carbon*saving,*running*cost,*renewable*contribution…
• A*modern*domestic*gas*boiler*system*has*SPF4 about*0.85.
• For*carbon*benefits*in*the*UK,*HP*SPF4 needs*to*be*>*2.21
• For*cost*savings*(DECC*2014*values)*SPF4 needs*to*be:
• >*2.49*relative* to*gas
• >*1.9*relative* to*LPG
• >*1.65*relative* to*oil
• For*the*purposes*of*the*RES*Directive*SPF2 >=*2.5*to*be*classed*as*renewable*(saving*primary*energy).
Historical&Developments
Early&Heat&Pump&Pioneers
• Originally&proposed&by&Lord&Thompson&Kelvin&“On&the&Economy&of&the&Heating&or&Cooling&of&
Buildings&by&Means&of&Currents&of&Air.”&Proceedings+of+the+Physical+Society+of+Glasgow 3:&269–72.
• Further&comments&in&a&book&‘The&Steam&Engine&
and&other&Heat&Engines’&(1910)&by&James&Alfred&Ewing:&“Burning+fuel+to+warm+a+room+by+a+few+degrees+is+a+wasteful+way+to+utilise+heat”.
• First&GSHP&patent&by&Swiss&engineer,&Heinrich&
Zoelly in&1912.
Early&Heat&Pump&Pioneers
Haldane,&T.G.N.&1930.&“The&Heat&Pump===an&Economical&Method&of&Producing&
Low=Grade&Heat&from&Electricity.”&Journal+of+the+Institution+of+Electrical+Engineers68&(402):&666–75.
Results&from&his&Glasgow&home:&
1926=1928&season
Haldane’s&proposal&for&a&River=source&
heat&pump&and&radiant&panel&system
Early&work&in&the&USA
Crandall,&A.C.&1946.&“House&Heating&with&Earth&Heat&Pump.”&Electrical+World 19&(November&9):&94–95.
‘Earth&coils’&were&metal&pipes&to&directly&evaporate&
the&refrigerant&(DX)
The&origins&of&GSHP:&USA
Coogan,%C.%H.%1948.%The)residential)heat)pump)in)New)England.%Waterbury,%CT,%USA:%Connecticut%Light%and%Power%Co.
A&Divergence&of&Opinions…
The%heat%pump%holds%promise%of%permitting%the%industry%to%supply%domesticT
heating%service%in%an%economical%manner.%Up%until%now%the%electric%utility%
industry%has%supplied%very%little%of%this%market%and%we%think%that%without%the%
heat%pump%we%are%not%likely%ever%to%supply%very%much%of%it.
Andrews,%S.%W.%1948.%The%Heat%Pump%From%the%Utility’s%Point%of%View.%Transactions)of)the)American)Institute)of)Electrical)Engineers,%67(1),%562–564.%
undesirable%electrical%features%such%as%highTstarting%current,%lowTpower%
factor,%and%high%demand,%which,%otherwise,%would%have%adverse%economic%
effects%upon%the%electric%supply%system%and%thus%result%in%economic%
handicaps%in%the%utilization%of%the%electrical%service%by%this%device.%
Bary,%C.%1948.%The%Heat%pump%– Its%Significance%As%a%Potential%Residential%Load.%Electrical)Engineering,%p.%340T344.%
The&origins&of&GSHP:&UK
Proceedings)of)the)IEE)Part)A:)Power)Engineering,%1956,%104(15),%262–271.%
Origins&of&the&GSHP:&UK
Comment% from%J.%Sumner%(1957)%in%response%to%Miriam%Griffith’s%
presentation:
It%has%been%said%that%nowadays%we%cannot%afford%the%capital%
required%to%build%heat%pumps.%I%understand%that% the%National%
Coal%Board%is%proposing%to%spend%£1000%million%in%the%next%ten%
years%in%order%to%increase%the%output%of%coal%by%10%million%tons%a%
year.%I%think%it%could%be%demonstrated% that,%if%the%N.C.B.%were%to%
allocate%even%£1%million%of%this%to%building%heat%pumps,%they%
could%conserve%more%coal%than%if%it%were%spent%on%new%plant.%
After&the&1950s&…
In&the&UK:
• Miriam&Griffith&and&BEAIRA&did&no&further&work
• John&Sumner&was&a&lone&campaigner&for&HP&technology
• Natural&Gas&was&a&clear&winner
• Some&EA&Technology&work&on&ASHP&in&70/80s
• No&GSHP&interest&until&mid&1990s
In&the&rest&of&the&world:
• The&immediate&post&war&US&oil&shortage&eased&– little&further&interest&in&50/60s
• Domestic&air&conditioning&demand&in&the&USA&grew&hugely
• The&1973&oil&crisis&saw&a&big&spurt&in&GSHP&research&– National&Labs,&Universities,&Utilities&and&IGSHPA.&Similarly& in&Europe&(Sweden&and&Switzerland)&but¬&UK.
• Plastic&pipe&meant&corrosion&and&DX&could&be&avoided.&Better&compressors&by&the&80s
Current&Worldwide&Deployment
1400000
981667
476842
314502
144069
141833
122250
94288
85307
51638
45986
31038
22750
19908
13200
8875
6996
5500
4272
3201
3020
2839
2828
2597
1250
1144
106
0
200000
400000
600000
800000
1000000
1200000
1400000
1600000USA
China
Sweden
Germany
France
Switzerland
Canada
Austria
Finland
Denmark
Netherlands
Poland
UK
CzechGRep.
Italy
Estonia
Belgium
Slovenia
Bulgaria
Ireland
Portugal
Slovakia
Lithuania
Hungary
Romania
Spain
Luxembourg
Installatio
ns
Current&Worldwide&Deployment
5028
5
1755
4
1579
4
1121
4
9253
6697
4390
3915
3874
2749
2676
2207
1895
942
805
723
698
631
583
525
358
286
261
222
202
62 24
0
10000
20000
30000
40000
50000
60000Sw
eden
Switzerland
Finland
Austria
Denmark
Estonia
USA
Germany
Canada
Netherland
s
Slovenia
France
CzechGRep.
Lithuania
Poland
China
Ireland
Belgium
Bulgaria
Slovakia UK
Portugal
Hun
gary
Italy
Luxembo
urg
Romania
Spain
Installaions)per)million)captia
Large&Systems&in&the&UK
Churchill&Hospital,&Oxford
240&x&100m&borehole
8&x&500kW&heat&pumps
Domestic&Systems&in&the&UK
UK&Developments&(later&1990s)
Initial&installations:&one=off&‘low&energy’ houses&and&refurbs
Source:&GeoScience Ltd
Along&came&ECC&and&Clear&Skies&…
Source:&GeoScience Ltd
UK&Support&Programmes
Grant&programmes
• Clear&Skies&(£10m,&8.2%&for&GSHP)
• Low&carbon&building&Programme&(£139m)
• Renewable&Heat&Premium&Payments&(RHPP)
Supplier&Obligation&programmes
• Energy&Conservation&Commitments:&ECC1,&ECC2&(£500m)
• Carbon&Emissions&Reduction&Target:&CERT&(£1.2bn)
• Energy&Company&Obligation:&ECO&(£1.3bn&– now&cut)&
Current&programmes:&RHI&and&Green&Deal&.&ECO&does¬&support&renewables
UK&Support&Programme&Outcomes&to&2014
0
5000
10000
15000
20000
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
Cumlative*GS
HP*In
stallations
Year
Other0funding
RHPP
EEC1,0EEC2,0CERT
Clear0Skies0&0LCBP
National&Trials&and&Monitoring
• EST&National&Field&Trial&– Phase&1&(54&GSHP&sites)
• Monitored&‘system&efficiency’
• User&research&by&the&Open&University
• DECC&technical&investigation
• EST&National&Field&Trial&– Phase&2.&After&a&range&of&interventions
• RHPP&– more&detailed&monitoring&but&without&manufacturers.&User&data&from&online&questionnaires.&Initial&results&published&in&2014.
• Related&domestic&fields&trials:&
Stafford,%A.,%&%Lilley,%D.%(2012).%Predicting%in%situ%heat%pump%performance:%An%
investigation% into%a%single%groundTsource%heat%pump%system%in%the%context%of%10%
similar%systems.%Energy)and)Buildings,%49,%536–541.%
Field&Trial&Results&– Phase&1
Field&Trial&Results&– Phase&1&Findings
A&number&of&systems&with&Efficiencies&>&3&but&some&very&poor&performing&systems
Main&technical&findings:
1. under=sizing&of&the&heat&pumpq
2. under=sizing&of&the&ground&heat&exchangerq
3. poor&insulation&standards&(pipes&and&tanks)q
4. flow&temperature&unnecessarily&highq
5. excessive&pump&usage&(time&control&or&number&of&pumps)q
6. poor&control.
Non=technical& findings&from&user&surveys:
• 86%&satisfied&with&heating&performanceq
• only&63%&satisfied&with&level&of&supportq
• only&62%&satisfied&with&cost&savingsq
• controls¬&easy&to&understand&and&use.
Issues&for&the&industry:&changes&to&Micro=generation&Certification&Scheme&standards&(MIS),&better&training,&better&user&support&and&information.
Field&Trial&Results&– Phase&2
Field&Trial&Results&– RHPP&2013
• Mean&SPF4 is&2.92,&System&efficiency&2.74&(from&2.39)
• 84%&of&systems&would&be&classed&as&renewable
• 85%&would&show&carbon&savings&relative&to&gas&heating
• 64%&would&show&cost&savings&relative&to&gas.&Nearly&all&RHPP&participants&
saved&money&as&initial&fuel&was¬&gas
Further&Technical&Challenges
• Performance&levels&are&improving&but&still¬&as&high&as&other&EU&trial&results
• Some&systems&are&still&‘failures’
• User&survey&highlights&some&control&issues
• UK&Specific&issues:&small&houses,&high&thermal&mass,&high&heating&temperatures?
Non=Domestic&Systems:&Ground&heat&exchange
Ground&heat&exchange
The*design*question:*for*a*given*set*of*heating*and*cooling*demands,*how*many*and*how*deep*do*the*boreholes*need*to*be?
Key*design*points:
1. System*efficiency*depends*on*fluid*temperatures* and*so*we*want*these* to*be*close*to*the*‘undisturbed’*or*background*ground*temperature.
2. The*relationship*between* fluid*temperatures* and*the*ground*temperature*depends,* in*general,*on
• Ground* thermal*conductivity
• Borehole*thermal*resistance.
3. Long*term*(seasonal)* temperatures* depend*on*long*term*energy*exchange:*
• design*is*based*on*annual*energy*demands*– not*just*peak*loads.
• consider*several*years*of*operation* to*find*the*min/max*fluid* temperature*range.
4. In*design*methods*(software)*we*define*the*temperature* limits*we*want*to*work*with*(targets).*These*can*be*based*on:*
• Heat*pump*min/max*operating* temperatures
• Values*that*are*going* to*give*the*SPF*we*are*looking* for
Borehole*resistance*and*ground*conductivity
• First,*think*about*rejecting*a*given*amount*of*heat*per*meter*of*borehole.
• Local*temperature*gradient*depends*on*the*thermal*resistance*of*the*components*in*the*borehole*and*the*thermal*conductivity*of*the*ground
• High*thermal*resistance*means*fluid*temperatures* have*to*be*higher*to*reject*a*given*amount*of*heat.
Borehole*resistance*and*ground*conductivity
• Borehole* resistance*depends*on
• Configuration*– single,*double*or*co6ax
• Pipe*size*and*spacing
• Grout*properties*– thermally*enhanced*grouts*are*often*used
• Borehole*diameter*– typically*1206150mm.
• Fluid*resistance*– flow*rate*and*fluid*properties*(Reynolds*number).
!"∗ =%& − %"("
0.000.020.040.060.080.100.120.140.16
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
R g[(m
$K)/W]
λg [W/(m$K)]
Zeroth0order2Multipole
10th0order2Multipole
Bauer2et2al.2(2011)
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
R a[(m
$K)/W]
λg [W/(m$K)]
Zeroth.order0Multipole
1st.order0Multipole
10th.order0Multipole
Javed and%Spitler (2016)
System&hydraulic&design
• Propylene&or&Ethylene&glycol&based&mixtures&are&the&common&heat&transfer&fluids&for&geothermal&systems
• Viscosity&is¬iceably&higher&than&water&and&varies&with&temperature&
significantly
• Reynolds&numbers&can&be&low&and&heat&transfer&drop=off&without&care.
• Some&optimization&is&required:
• High&flow&rate&gives&better&heat&
transfer
• Higher&flow&rate&gives&higher&pressure&drop&and&pump&energy&demand
• Pump&demand&no&more&than&3%&of&
heat&delivered&is&required&for&compliant&domestic&systems
Long6term*borehole*field*response
• Long*term*temperature* trends*are*important*and*depend*on*annual*heating*and*cooling*energy*balances
• Whether*the*long*term*trend*is*rising*or*falling*temperatures* depends*on*whether*heating*or*cooling*is*dominant
• Borehole*depth*is*selected*on*the*basis*of*the*long6term*trend
• Balanced*demands*lead*to*the*most*economical*solutions*– shortest*boreholes.
• Max*and*min*temperatures* depend*on*a*combination*of*demands*and*peak*loads
• Simulation*results*are*needed* to*estimate*the*costs*accurately
15
17
19
21
23
25
27
29
31
33
35
37
0 1460 2920 4380 5840 7300
Temperature3[°C]
Simulation3Days3
163bh 323bh 1203bh
!70!55!40!25!1052035506580
0 730 1460 2190 2920 3650 4380 5110 5840 6570 7300 8030 8760
Time0(hours)
Building0Loads0(kW)
Borehole&field&configuration
• After&a&few&seasons,&boreholes&interact&– temperature&changes&at&one&influence&those&at&neighboring&boreholes.
• This&effect&is&well&understood&and&can&be&modelled.
0
2
4
6
8
10
12
14
16
18
0 5 10 15 20
ΔT)(°C
)
Distance)(m)
DT DT)1 DT)2
Borehole&field&configuration
• Different&configurations&(rows&and&columns&of&boreholes)&respond&differently&e.g.&2&x&6&
is¬&the&same&as&3&x&4&etc.&
• Response&characteristic&also&depends&on&spacing/depth&
ratio.
• Response&can&be&characterized&by&‘g=function’&
data.&This&relates&temperature&change&to&heat&input. 0
24681012141618202224262830323436384042
(5 (4.5 (4 (3.5 (3 (2.5 (2 (1.5 (1 (0.5 0 0.5 1 1.5 2 2.5 3 3.5
ln(t/ts)
g(t/ts,rb/H=0.0005)
Borehole&Array&Design
Simulationof+GHE
Adjust+size
User+input:GSHP+Loads+&+(optionally)GHE+Loads
User+inputs:+Ground+properties
BH+info.HP+characteristics
HP+Simulation
Spitler and%Bernier%(2016).%Vertical%Borehole%Heat%Exchanger%Design%Methods
Ground&heat&exchanger&design&software&helps&with&the&iterative&process&needed&to&find&the&design&heat&exchanger&size
Essential&Design&Data
To&summarize:&the&design&data&needed&is:
1. Local&undisturbed&ground&temperature
2. Ground&thermal&conductivity&and&diffusivity
3. Building&heating/cooling&rejection&demands&(monthly)
4. Monthly&peak&heating&and&cooling&loads
5. Borehole&resistance&– pipe&size,&spacing,&grout&properties,&
borehole&diameter
6. Target&temperature&range&for&the&system&– avoiding&
freezing&and&high&pressure&limit,&or&targets&for&SPF.
Ground&Thermal&Response&Testing
Ground&thermal&conductivity&is&a&key¶meter&– how&do&we&estimate&it?
• Reference&book&valuesq
• British&Geological&Survey&desktop&study
• In=situ&Thermal&Response&Testing&(TRT)&f
In&Situ&Thermal&Response&Testing
1. A&single&test&borehole&is&completed
2. A&closed&circuit&is&formed&and&electrical&heaters&used&to&
apply&a&pulse&of&heat&over&48+&hours.
3. Flow,&power&and&temperature&data&are&collected&and&
analyzed.
Typical&TRT&Responses
The&key&data&needed&for&
analysis&is&the&average&fluid&
temperature&and&power&input
Data& source:& IGSPHA
Data& source:& Groenholland
Research&Equipment
Photos:&J.D.&Spitler
Electric&heaters&
(3&x&3kW)
Flow&
meterFlow/return&temp.&
sensors
Pumps&and&purge&valves
Compact&Site&Equipment
A.&ChaissonGroenholland Geo&Energy&Systems
TRT&Analysis
1. Plot&temperature&vs natural&log&of&time2. Find&the&slope&– ignoring&some&early&data
3. Use&the&slope&to&derive&the&effective&conductivity
! = #4%&'!
Where&s is&the&slope&of&the&temperature&vs natural&log&time&plot
Non=Domestic&Systems:&System&Integration
System&Integration
Operating&temperatures
• Chilled&water&temperatures&can&be&in&the&usual&range&– hence&able&to&serve&AHUs,&Fan&Coils&etc.
• Heating&temperatures&can&be&up&to&55&but&better&at&40/45.&Hence&well&suited&to&underfloor&heating/&oversized&radiators,&fan&coils.
Central&Plant&Integration&– 3&basic&approaches
1. Reversible&heat&pumps&with&sliding&headers.
2. Reversible&heat&pumps&with&Independent&header&connections.
3. Reversing&on&the&water=side&and&heat&exchange&between&buffer&tanks.
Sliding&header&configuration
CIBSE&TM51
• Header&is&split&between&heating&and&cooling&depending&on&valve&position&
and&demand
• Heat&pumps&are&controlled&in&sequence&according&to&
heating/cooling&demand&by&BMS.
• Heat&pumps&can’t&be&
independently&switched&between&heating&and&cooling.
Independent&Header&Connections
Naicker and&Rees&(2011)
Plantroom installation
Header&pipes&and&valves
Water=side&reversing&and&buffer&tanks
Groenholland Geo&Energy&Systems
Plantroom Installation&(Skids)
Groenholland Geo&
Energy&Systems
Non=Domestic&Systems:&Measured&Peformance
• A*multi6use*building*(15,607*m2)
• Monitored*since*opening*in*Jan.*2010
• GSHP*system*provides*all*AHU*and*FCU*cooling*(360*kW*peak)*and*all*underfloor heating*(330*kW*peak*capacity)***
• Has**Four*Water*Furnace*26stage*reversible*heat*pumps
• 56*x*100m*deep*borehole*heat*exchangers,*125mm*diameter.*30*l/s*peak*flow
Monitoring*at*De*Montfort*University*Hugh*Aston*Building
Naiker,%S.S.%(2016)%Performance%Analysis%of%a%LargeTscale%Ground%Source%
Heat%Pump%System.%PhD%Thesis:%De%Montfort%University.
Hugh&Aston&Building&Ground&Heat&Exchangers
19&+&37&arrays,&100m&deep
Heat&Pump&Installation
Header&pumps
Ground&loop&pumps
Header&pipes&and&valves
Monthly&Heat&Balances
0
2
4
6
8
10
12
14
16
18
20
'0.6
'0.4
'0.2
0
0.2
0.4
0.6
0.8
1
Tempe
rature)(°C))
Heat)Ex
chan
ge)(M
Wh)
Time)(mmm)8 yy)
Monthly0daily0Mean0Heat0Extraction(MWh) Monthly0daily0Mean0Heat0Rejection(MWh) Monthly0daily0Mean0Net0Heat0Exchange0(0MWh)
Monthly0daily0Mean0Ground0Loop0Temp.0(°C0) Monthly0daily0Mean0Air0Temp.0(°C0)
System&Efficiencies
2.89
3.99
3.31
2.69
2.22
3.55
3.87
3.67
3.16
2.61
3.19
4.06
3.54
2.97
2.49
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
SPF//H1 SPF/C1 SPF/1 SPF/2 SPF/4
SPF
May/52010/to/April/52011 May/52011/to/April/52012 Feb/52010/to/July/52012
Year%(%Season) SPF%%H1 SPF%C1 SPF%1 SPF%2 SPF%4May%52010%to%April%52011 2.89 3.99 3.31 2.69 2.22May%52011%to%April%52012 3.55 3.87 3.67 3.16 2.61Feb%52010%to%July%52012 3.19 4.06 3.54 2.97 2.49
Seasonal&performance&Factors:
• SPF1&is&heat&pump&alone
• SPF2&includes&the&ground&loop&pump&demand
• SPF&4&includes&the&heating/cooling&header&pumps
RES&Directive&requires&SPFH2&>&2.5
Dynamic&Operation
Only&one&compressor&stage&is&needed&for&much&of&the&time.&On/off&control&leads&to&short&cycle×.
0
5
10
15
20
25
30
35
%"of""Occurrence
Hourly"kWh
Heating Cooling
0
5
10
15
20
25
30
%"of"O
ccurrence
Daily"kWhrHeating Cooling
0
1
2
3
4
5
6
7
10
11
12
13
14
15
16
17
18
Flow%(l/s)
Temp
eratur
e%(°C)
Time%(Date%Hour)
Source0side0outlet0Temperature0(°C) Source0side0intlet0Temperature0(°C) Source0side0Flow0rate0(l/s)
Dynamic&Operation
0
1
2
3
4
5
6
7
8
0 200 400 600 800 1000 1200
Daily&&SPF
H1
Daily&Heating&Demand&(kWh)
0
1
2
3
4
5
6
7
8
9
0 200 400 600 800 1000 1200
Daily&&SPF
C1
Daily&Cooling&Demand&(kWh)
0
10
20
30
40
50
60
0(1 1(2 2(3 3(4 4(5 5(6 6(7 >7
%""of"O
ccurrence
Hourly"SPFH1
Cycle0Time0(0(100min/cycle) Cycle0Time0(11(200min/cycle) Cycle0Time0(21(300min/cycle)Cycle0Time0(31(400min/cycle) Cycle0Time0(41(500min/cycle) Cycle0Time0(51(600min/cycle)
0
5
10
15
20
25
30
35
40
45
0'1 1'2 2'3 3'4 4'5 5'6 6'7 >7
%"of"O
ccurrence
Hourly"SPFC1Cycle0Time0(0'100min/cycle) Cycle0Time0(11'200min/cycle) Cycle0Time0(21'300min/cycle)Cycle0Time0(31'400min/cycle) Cycle0Time0(41'500min/cycle) Cycle0Time0(51'600min/cycle)
Circulating&Pump&Operation
Pump&sizes&are&large&relative&to&compressor&sizes
Pumps&also&operate&unnecessarily&– valve,&flow&switch&
and&control&faults
0
10
20
30
40
50
60
70
80
90
100
Ope
ratio
nal+Hou
rs++/%
Time+(+mmm/yy)
Compressor2Operational2Hours2;%22(Both2Cooling2and2Heating2)2 Useful2Heating2and2Cooling2Energy2Delivered2Across2Manifold2; Hours2%
Heating2or2Cooling2Loop2Circulating2Pump2Operational2Hours22; % Ground2Loop2Circulating2Pump2Operational2Hours2; %
Circulating&Pump&Energy&Demands
Pump&demands&have&a&big&effect&on&SPF2 and&SPF4
Monthly&Pump&to&Compressor&Power&Ratio&Vs Monthly&SPF2,&SPF4
0
0.5
1
1.5
2
2.5
3
3.5
0 0.2 0.4 0.6 0.8Mon
thly(SP
F 4
Power(Ratio(((Wp(SPF4)(/Wc)
0
0.5
1
1.5
2
2.5
3
3.5
4
0 0.1 0.2 0.3 0.4
Mon
thly(SP
F 2
Power(Ratio(((Wp(SPF2)(/Wc)
Improving&Performance
Overall,&performance&is&satisfactory.&
Cycle×&would&be&improved&by
• Smaller&lead&machine
• Variable&compressor&speed
• Buffer&tanks
Lift&could&be&reduced&by&heating&temperature&
tuning/reduction
Pump&energy&demands&could&be&reduced&by:
• Better&hydraulic&design
• More&robust&control&(fault&detection/correction)
• Reduced&start=up/shut=down&running
• Ground&loop&demand&control
Geothermal&Heat&Pump&System&Research
The&EU&Horizon&2020&Programme
Aim:&reduced&complexity,&improved&robustness&and&efficiency
Key&Technologies:
• Innovative&drilling&technology
• High&efficiency&heat&exchanger
• Dual=source&heat&pump
• Robust&control&systems&and&
monitoring
• Foundation&heat&exchange&systems
Geothermal&Technology&for&Economic&Cooling&and&Heating
� Innostock�2012� ���The�12th�International�Conference�on�Energy�Storage�
�
� 1
INNO-U-32
The GEOTHEX geothermal heat exchanger, characterisation of a novel high efficiency heat exchanger design
Henk Witte
Groenholland Geo-Energysystems, Valschermkade 26, 1059CD Amsterdam, Netherlands,
Phone: 31-20-6159050, e-mail: [email protected]
1. Introduction
The Geothex heat exchanger (http://www.geothex.nl/en/), figure 1, has been developed to provide a highly efficient ground source heat exchanger for use with geothermal heat pumps. The goal has been to develop a high-quality heat exchanger with a very low thermal resistance, even at laminar flow conditions and, at the same time, achieve this with a low pressure loss.
Geothermal heat pumps are widely recognized as very efficient systems for heating and cooling applications that combine a high potential for saving on primary energy and greenhouse gas emissions with a very long life span and low maintenance. Different ways to interface the heat pump with the ground are in use, but by far the largest number of systems use a closed loop heat exchanger placed vertically to depths varying between perhaps 30 and 400 meters. In these so-called "Borehole Heat Exchangers" (BHE) heat is exchanged between the primary side (the fluid flowing through the loop and heat pump) and secondary side (the ground volume) due to a temperature difference.
Figure 1. Impression of the Geothex heat exchanger showing the insulated inner pipe and helical vanes (source: Geothex BV). Shown is the functioning in heat extraction mode with flow through the inner tube or flow through the
annulus.
As with any heat exchanger, there is a relation between the amount of heat transferred (q), the thermal resistance of the heat exchanger (R) and the temperature difference ('T) between the primary and secondary side:
q = 'T/R
This implies that, for a given constant heat flux rate, the higher the thermal resistance of the heat exchanger, the larger the required temperature difference between the fluid and the ground. Now, the efficiency of the heat pump depends mainly on the difference between the source (cold) and sink (hot) temperatures. In fact, it can be shown that for every degree of temperature
The&EU&Horizon&2020&Programme
The&EU&Horizon&2020&Programme
• A&hybrid&dual=source&approach:&air&and&ground&heat&exchanger&for&optimal&choice&of&source/sink&temperature
• Variable&speed,&DC&permanent&magnet&motor,&scroll&compressor,&refrigerant&R32.
• Hybrid&design&and&smart&controls&make&the&implementation&robust
• Reduced&complexity&to&improve&uptake&(consumers,&developers&and&SMEs).
New&Heat&Pump&Development&in&the&GEOTeCH project&=
Sources&of&information
http://geotrainet.eu
http://www.gshp.org.uk
http://www.igshpa.okstate.edu
http://www.egec.org
CIBSE&TM45,&TM51&and&CP2&– via&knowledge&portal
Useful&web&sites:
UK
EU
US
