development of a design and performance...

T. Katsura *1 K. Nagano*1 S. Takeda *1 T. Ibamoto *1

S. Narita *1 Y.Nakamura *2 N. Homma *3

*1 Hokkaido University*2 Nippon Steel Corporation*3 Hokkaido Electric Power Co., Inc

1/33

DEVELOPMENT OF A DESIGN AND PERFORMANCE PREDICTION TOOL FOR

THE GROUND SOURCE HEAT PUMP SYSTEM

Background 2/33

The Kyoto protocol became effective at 16th February 2005CO2 emissions reduction target of Japan 6%

The number of the GSHP systems installed in Japan is increasing rapidly

05

1 01 52 02 53 03 54 0

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

Uni

ts

Markets of the GSHP in Japan

The GSHP system has been remarked as a system with large potential for reduction of CO2 emission.

2004

T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 2

Background 3/33

When the GSHP system is installed, a design tool is required.The tool is used for…

no design tool in Japan

Determination of length of the ground heat exchanger

?

Demonstration of installing effect of the GSHP system

Oilboiler

GSHP system

?CO

2em

issi

ons

We developed a design tool for the GSHP system


Advantages of the developed tool

1. User friendly data input procedure and graphical output

5. Including database of CO2 emissions, costs, and lifetimes for LCA

2. Short time calculation according to hourly heating and cooling loads(Calculation time is approx. 1 minute for calculation of two years’ operation)

6. High speed calculation algorithm for heat extraction or injection of the multiple ground heat exchangers buried in random layout

3. Calculation of internal thermal resistance in a borehole for tube geometric arrangement by the boundary element method (BEM)

4. Calculation of the heat carrier fluid in the ground heat exchanger with large diameter


4/33

Examples of the input and output screens and windows(1) Input windows

(2) Output windows

Calculations are carried out. Then right window is displayed

Output window examples


5/33

Calculation of ground temperature

Nomenclature a: Thermal diffusivity [m2/s], Jx: xth-order Bessel function of first kind, q’ : Heat flux [W/m2], r: Radius [m], T: Temperature [oC], t: Time [h], u: Characteristic value, Yx: xth-order Bessel function of second kindSubscripts b: Borehole surface, s: Soil Greek letters λ: Thermal conductivity [W/m/K]

Ts0

Ts

Ts0

Ts

rprp

Ground temperature calculation applying the cylindrical heat source theory

Infinite solid

hollow cylinder

Infinite solid

hollow cylinder

qboqbo

Theoretical solution of the ground temperature variation Ts according to radius rand uncertain time t

The developed tool uses an approximate expression of this response for making superposition Fast calculation

duruYruJu

ruJurYruYurJeq

TTbobo

bobotusa

s

boss ∫

+−

−−=∞

−

021

21

2

101020 )]()([

)()()()()1(2πλ

X

Theoretical solution of the ground temperature variation Ts according to radius rand uncertain time t

The developed tool uses an approximate expression of this response for making superposition Fast calculation

duruYruJu

ruJurYruYurJeq

TTbobo

bobotusa

s

boss ∫

+−

−−=∞

−

021

21

2

101020 )]()([

)()()()()1(2πλ

X

Vertical ground heat excahgner

6/33

Calculation of the GSHP system operation

Heat capacity change: ΔQb

T1out

T1in

Tb

Heat extraction from ground heat exchanger: Q1

Compressor power: E

Ts

T2out

Heat extraction from ground: Qbo

Flow rate: mb

Heat load: Q2

T2in

rrTbo

s =

Overall heat transfer coefficient : Kbo-out

Heat capacity change: ΔQb

T1out

T1in

Tb

Heat extraction from ground heat exchanger: Q1

Compressor power: E

Ts

T2out

Heat extraction from ground: Qbo

Flow rate: mb

Heat load: Q2

T2in

rrTbo

s =

Overall heat transfer coefficient : Kbo-out

Calculation diagram of a typical GSHP system

1

1 Radiator

1

1 Radiator

2

2 Heat pump unit

2

2 Heat pump unit

3 3 Ground heat exchanger

3 3 Ground heat exchanger

Nomenclature T: Temperature [oC]Subscripts bo: Borehole surface, b: Heat carrier fluid (antifreeze solution or water), in: Inlet of heat pump unit, out: Outlet of heat pump unit, 1: Primary side, 2: Secondary side


7/33

Example of temperature distribution calculated by BEMSingle U-tube(λbo=1.8W/m/K)

Double U-tube(λbo=1.8W/m/K)

1.0

0.0

0.2

0.4

0.6

0.832 52

120

32 72

120

32 52

120

32 72

120

Nomenclature Rb: Borehole thermal resistance [m2/K/W]

Rbo=2.23×10-2 m2/W/K Rbo=1.35×10-2 m2/W/K

Rbo=1.52×10-2 m2/W/K Rbo=7.58×10-3 m2/W/K

Case 1 Case 2

Case 1 Case 2


8/33

Calculation of the heat carrier fluid in the ground heat exchanger with large diameterComparison calculated temperature with measured temperature

Calculated Tf-out with 1.5 of λs

Tf-in as the input condition of calculation

0 100 200 300 400Time [h]

5

4

3

2

1

0

Tem

pera

ture

[ºC

]

Measured Tf-out



0 100 200 300 400Time [h]

5

4

3

2

1

0

Tem

pera

ture

[ºC

]

Measured Tf-out

0

1

2

3

4

5

0 50 100 150 200Time [h]

Tem

pera

ture

[ºC

]



Measured Tf-out

0

1

2

3

4

5

0 50 100 150 200Time [h]

Tem

pera

ture

[ºC

]



Measured Tf-out

Direct type steel pilewith diameter of φ165mm

Indirect type steel pilewith diameter of φ400mm


9/33

Life cycle analysis of the GSHP system

Life cycle analysis•Life cycle assessment•Estimation of life cycle cost

These are estimated by

Total initial + Total running

Lifetime

Electric power consumption

(Calculated by the GSHP system operation )

This tool can also compare the GSHP system with conventional systems (ex.Oil boiler system, ASHP)

Energy consumptionCO2 emission

A database of CO2 emissions, costs, andlifetimes for LCA is included in the tool


10/33

Calculation for multiple ground heat exchangers

Input window of pipe arrangement of multiple ground heat exchangers

HP

2m

Steel foundation pile used as ground heat exchanger

Header

2m2m

2m 2m 2m 2m 2m

Piping route of CASE1 Piping route of CASE2

Input


11/33

Examples of the calculation results

Difference of temperature distributions according to pipe arrangement

Elapsed time of 3000 h (Mar.7th) Elapsed time of 5000 h (May. 30th)

Piping route

CASE1 CASE1 CASE1

CASE2 CASE2 CASE2

Elapsed time of 7000 h (Aug. 21st)

1

15.015.0

10.010.0

10.010.0

15.015.0

15.015.0

10.010.0

10.010.0

15.015.0 15.015.0

15.015.015.015.0

15.015.0 15.015.0

15.015.0

20.020.0

20.020.0

23

4

5

1

23

4

5

5 10 15 20Temperature [oC]


12/33

Advantages of the developed tool

1. User friendly data input procedure and graphical output

5. Including database of CO2 emissions, costs, and lifetimes for LCA

2. Short time calculation according to hourly heating and cooling loads(Calculation time is approx. 1 minute for calculation of two years’ operation)

6. High speed calculation algorithm for heat extraction or injection of the multiple ground heat exchangers buried in random layout

3. Calculation of internal thermal resistance in a borehole for tube geometric arrangement by the boundary element method (BEM)

4. Calculation of the heat carrier fluid in the ground heat exchanger with large diameter


13/33

Especially effective to evaluate the performance of the GSHP system, which is From these advantages, this tool is…

the large systems and the energy pile systems

Today’s topics 14/33

1. Calculation of temperatures of the ground and the heat carrier fluid in the GSHP system for the multiple ground heat exchangers

• High speed calculation algorithm of the ground temperature for heat extraction or heat injection of multiple ground heat exchangers• Calculation method of temperature of the heat carrier fluid in the GSHP system for pipe arrangement of the ground heat exchangers

2. Comparison of performance of the GSHP system

• Piping route

• Numbers of the parallel and serial circuits

• Number of the ground heat exchangers (But the total lengths are the same)

• Method of calculation (Detailed method and simplified method)

The calculated conditions are changed for the comparison items


Calculation of the ground temperature for heat extraction or injection of multiple ground heat exchangers

15/33

Applying the superposition principle1 2 j

Certain ground heat exchanger i

rd,ijrd,i2rd,i1 ･･･

rp

1 2 j

Certain ground heat exchanger i

rd,ijrd,i2rd,i1 ･･･

rp

The thermal response of a certain ground heat exchanger i is calculated by summing up the all thermal responses

Equation of the thermal response is, ( ) ∑ ∆+∆=∆

=−−

n

jijdLspCspis trTtrTtrT

1,, ),(),(,

( ) ( ) ( )∑

∂∂

−−≅∆=

−

t

sCs

rItqtrT0

,'2,τ τ

ττπλ ( ) ( ) ( )

∑∂

∂−≅∆

=−

ts

sLs

arEtqtrT

0

21 4

''4

1,τ τ

ττ

πλ

Thermal response for heat extraction of a certain ground heat exchanger i

Thermal response for heat extraction of a surrounding ground heat exchanger j


Non-dimensional thermal response for heat extraction of a certain ground heat exchanger i

Non-dimensional thermal response for heat extraction of a surrounding ground heat exchanger j

Applying superposition of the approximated thermal response for the cylindrical heat source

Approximating the superposed thermal response for the line heat source

( ) ( ) ( )∑

∂∂

−=∆=

−−

*

0* *

********* ,

,t

CsCs

rTtqtrT

τ ττ

τ ( ) ( ) ( )∑

∂∂

−=∆=

−−

*

0* *

********* ,,

tLs

Ls

rTtqtrTτ τ

ττ

Approximate equation (t* ≥ 1.0 )( ) ( ) ( )

( )∑∂

∂−+∑∆≅∆

=

−

=−−

*

1* 2**

2******

1

**** ,1,t

Csn

iLisLs r

rTtqTtrTτ τ

ττ

The ground temperature can be calculated with acceptable precision and speed to be used as a tool for designing of the GSHP system

Calculation of the ground temperature for heat extraction or injection of multiple ground heat exchangers

16/33

Ts* : Non-dimensional temperature (= 2πλsΔTs / rp / q’’) [-], t* : Fourier number (= at / rp

2) [-], q* : Non-dimensional heat flux (= q / q0) [-], q0 : Unit heat flux (=1) [W/m2],

Calculation of temperatures for pipe arrangement 17/33

Detailed method - Parallel circuit-Tpin,1 Tpin,2 Tpin,k-1 Tpin,m Tpout,m

1 2 k m

Ts(rp,1,t) Ts(rp,2,t) Ts(rp,k,t) Ts(rp,m,t)

Tf,1 Tf,2 Tf,k Tf,m

Tpout,1 Tpout,2 Tpout,k

T1inT1out

( ) ),()( ,,,,,,,111

,,11 kfkoutpskoutpkoutpkpinkpoutkfff

kfkfff TtrTAKTTGc

dtdTVc −+−−= −−−ρρ

Heat balance equation of the heat carrier fluid in the ground heat exchanger

Tpoutn+1 is obtained

TT outkpin 1, =

f

m

kkpoutkf

in G

TGT

1

1,,1

1

∑==

Heat balance equation of the heat carrier fluid in the primary side


cfρf : Heat capacity of heat carrier fluid [kJ/m3], Vf : Volume of heat carrier fluid [m3]G1f : Flow rate of heat carrier fluid in primary side [m3 /s], K : Overall heat transfer coefficient


Detailed method - Serial circuit-Tpin ,1 = T1out Tpin,3 = Tpout,2Tpin,2 = Tpout,1 Tpin,l = Tpout,l-1 Tpin,n = Tpout,n-1 T1in = Tpin,n

1 2 l n

Ts(rp,1,t) Ts(rp,2,t) Ts(rp,l,t) Ts(rp,n,t)

Tf,1 Tf,2 Tf,l Tf,n

Q2 Q1

E T1out

T1inT2out

T2in

Heat pump unit

fff mcEQTT

nn

nin

nout

111

211

11

11

ρ

++

++ −−=

Equation to calculate T1outn+1

( ) ),()( ,,,,,,111

,,11 lflpsloutploutplpinlpoutfff

lflfff TtrTAKTTGc

dtdTVc −+−−= −−ρρ

Tpoutn+1 is obtained

Heat balance equation of the heat carrier fluid in the ground heat exchanger



Simplified method

Heat pump

1

Supply and return header

2 3 … n - 1 n1

2

…

m - 1

m

Heat pump

1

Supply and return header

2 3 … n - 1 n1

2

…

m - 1

m

A. Serial circuit The ground heat exchangers are

regarded as a ground heat exchanger whose length is equal to the total length of the ground heat exchangers

B. Parallel circuit The flow rate is divided into according number of the parallel circuit

From A and B, the following equation is obtained as respects all circuits

( ) ),()( 111

1111 fpsoutpoutpoutinf

ff

ffff TtrTnAKTT

mG

cdt

dTnVc −+−−= −−ρρ


Comparison of performance of the GSHP system 20/33

Heat loss coefficient：2.33W/m2/K

Floor area: 130m2

Initial ground temperature: 16.5 oC Soil heat capacity: 3000 kJ/m3

Soil thermal conductivity: 1.0 W/m/K

Location : Tokyo, Japan

Cooling period: Apr.23rd - Nov.2ndHeating period: Nov.3rd - Apr.22nd

Heating load: 28.2 GJ(Maximum load: 6.6 kW) Cooling load: 10.0 GJ(Maximum load: 6.3 kW)

Room conditionHeating periodTemperature: 20oCCooling period Temperature: 26oCHumidity: 50%

Calculated subject


Comparison of performance of the GSHP system 21/33

Hourly variation of heat load

Nov. 3rd Feb. 3rd May. 3rd Aug. 3rd Nov. 2ndNov. 3rd Feb. 3rd May. 3rd Aug. 3rd Nov. 2nd

-8

-6

-4

-2

0

2

4

6

8

Hea

t loa

d [k

W]

Heating period Cooling period

Heating load

Cooling load

Heating load: 28.2 GJ(Maximum load: 6.6 kW) Cooling load: 10.0 GJ(Maximum load: 6.3 kW)


Calculated conditions 22/33

Pipe arrangement(Parallel × Serial)

Method forcalculation

CASE1 4 × 5 Detailed methodCASE2 4 × 5 Detailed methodCASE3 20 × 1 Detailed methodCASE4 1×1 (Borehole) Detailed methodCASE5 4 × 5 Simplified method


23/33Comparison items

HP

2m

Header

2m2m

2m 2m 2m 2m 2m

CASE 1

Piping route: CASE1 vs. CASE2

CASE 2

Steel foundation pile used as ground heat exchanger

HP

2m

Header

2m2m

2m 2m 2m 2m 2m

1

2 3 4

5 5

4 3 2

1


Comparison item 24/33

CASE 1: Numbers of the parallel × serial circuits are 4 × 5

Numbers of the parallel and serial circuits : CASE1 vs. CASE3

CASE 1: Multiple ground heat exchangers of 8 m × 20 (= 160 m)

Number of the ground heat exchangers : CASE1 vs. CASE4

CASE 3: All ground heat exchangers are connected in parallel

CASE 1: Calculated by the detailed method

Method of calculation : CASE1 vs. CASE5

CASE 4: A single ground heat exchanger with length of 160 m

CASE 5: Calculated by the simplified method


25/33An example of calculation results

Operating condition (temperature variations*) of the third year

-10

0

10

20

30

40

50

Tem

pera

ture

[o C]

Nov.3rd Feb.3rd May.3rd Aug.3rd Nov. 2ndNov.3rd Feb.3rd May.3rd Aug.3rd Nov. 2nd

T2out

T1out

Tp-outave

Heating Period Cooling Period

T1out

T2outTp-outave

*Temperatures of each part

T1in

T1out

T2out

Tp-out

T1in

T1out

T2out

Tp-out

Minimum temperature：-0.4oC Temperatures are recovered

The GSHP system can operate for a long term


Comparison between CASE1 and CASE2 26/33

Changes of temperature distribution in the ground surrounding piles

Elapsed time of 3000 h (Mar.7th) Elapsed time of 5000 h (May. 30th)

Piping route

CASE1 CASE1 CASE1

CASE2 CASE2 CASE2

Elapsed time of 7000 h (Aug. 21st)

1

15.015.0

10.010.0

10.010.0

15.015.0

15.015.0

10.010.0

10.010.0

15.015.0 15.015.0

15.015.015.015.0

15.015.0 15.015.0

15.015.0

20.020.0

20.020.0

23

4

5

5

43

2

1

5 10 15 20Temperature [oC]

1

2 3 4

5 1

2 3 4

5

5

43

2

1 5

43 2

1

Temperature decrement: Almost even

Temperature decrement: Pile1 is the largest

Temperature increment: Pile1 is the largest

Temperature increment: Pile1 is the largest

Ground temperature is decreased

Effect of heat extraction is still leftT. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 2


Integrating amounts of heat extraction and injection of each pile

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Am

ount

of h

eat e

xtra

ctio

n [G

J]

Pile2, Pile1, Pile 3, Pile 4, Pile5 from top to bottom

Total amount of heat extraction：5.65GJTotal amount of heat injection ：2.87GJ



Nov.3rd Feb.3rd May.3rd Aug.3rd Nov.2ndNov.3rd Feb.3rd May.3rd Aug.3rd Nov.2nd-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Am

ount

of h

eat e

xtra

ctio

n [G

J] Total amount of heat extraction：5.65GJTotal amount of heat injection ：2.87GJ

Nov.3rd Feb.3rd May.3rd Aug.3rd Nov.2ndNov.3rd Feb.3rd May.3rd Aug.3rd Nov.2nd




Difference: Large Difference: Small

Difference: LargeDifference: Small

1. Seasonal thermal storage effect appearsThese results indicate…

2. Total amounts of heat extraction are the same although the ones of individual piles differ depending on the piping route



Performance of the GSHP system

AverageCOP

AverageSCOP

AverageCOP

AverageSCOP

CASE1 5.0 4.0 5.6 3.6CASE2 5.0 4.0 5.6 3.6CASE3 4.9 3.9 5.5 3.5CASE4 5.4 4.2 5.3 3.4CASE5 5.0 4.0 5.6 3.6


These results indicate…

In this calculated condition, difference of the performance of the GSHP system for the piping route is hardly occurred




These results indicate…Laminar flow of the heat carrier fluid yields reduction of heat extractionor injection and performance decrement of the GSHP system

AverageCOP

AverageSCOP

AverageCOP

AverageSCOP



It’s desirable to arrange the piping route to keep the turbulent flowT. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 2



These results indicate…The GSHP with multiple ground heat exchangers can operate with highefficiency as well as the system with a single ground heat exchanger

AverageCOP

AverageSCOP

AverageCOP

AverageSCOP



The GSHP system has potential to be popular in warm region in Japan




These results indicate…

The simplified method provides high advantage from the viewpoint ofprecision and computational speed for evaluation of the GSHP system

AverageCOP

AverageSCOP

AverageCOP

AverageSCOP




Summary 32/33

1. Calculation algorithm of temperatures for pipe arrangement of the multiple ground heat exchangers is shown• High speed calculation algorithm of the ground temperature for heat extraction or heat injection of multiple ground heat exchangers• Calculation method of the heat carrier fluid in the GSHP system for pipe arrangement of the ground heat exchangers


Summary 33/33

2. Performances of the GSHP system were compared by changing calculated conditions

These results indicate…1) In this calculated condition, difference of the performance of

the GSHP system for the piping route is hardly occurred although the ones of individual piles differ

2) It’s desirable to arrange the piping route to keep the turbulent flow for reason of reduction of heat extraction or injection due to laminar flow of the heat carrier fluid

3) The simplified method provides high advantage from the viewpoint of precision and computational speed

4) The GSHP system has possibility to be popular in warm region in Japan


Thank you for your attention !!

Comparison between temperatures of the calculation and measurement in field experiments

Work Shop of Annex29, 2005-05-30, Las Vegas, USAK. Nagano, T. Katsura, S. Takeda et al.

35/25

In experiment room

To outside To outside

Heat pump Fan-coil

Experiment room

Flow sensor Electromagnetic flow meterF T Pｔ-100

Steel pile

Water

Brine (Acid organic type 40 %)

U-tube (PE100)

External diameter: 140 mm

8m

Internal diameter: 130 mm

External diameter: 32 mm

Internal diameter: 25 mm

Schematic diagram of the field experiments



36/25

Field experiments

Experiment room

Steel pile



37/25

Temperature measurement points

Line4

Line1

Line2

Line3

Line5

1.8 m

Measurement room

7 6 5

4 3

2

1

8

: At GL-1, 2, 4, 6 and 8 m

: At GL-0.5, 2, 4, 6, 8 and 10 m

1.8 m7.2 m

: At GL-1, 4 and 8 m

: At GL-6 m

: Steel pile

Measuring points of water temperature in a pile

Measuring points of ground temperature (1 to 9)

9

10 m

Pile A Pile B Pile C Pile D Pile E



38/25

Result

DateMar.19th 　Mar.29th Apr.8th Apr.18th Apr.28th May.8th

-5

0

5

10

15

Tem

pera

ture

[o C]

MeasuredCalculated T1in

Point9

Point4

Point2

Point1

development of a design and performance...

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