/33 DEVELOPMENT OF A DESIGN AND PERFORMANCE PREDICTION TOOL FOR THE GROUND SOURCE HEAT PUMP SYSTEM T. Katsura * K. Nagano * S. Takeda * T. Ibamoto * S. Narita * Y.Nakamura *2 N. Homma *3 * Hokkaido University *2 Nippon Steel Corporation *3 Hokkaido Electric Power Co., Inc
Background 2/33 The Kyoto protocol became effective at 6 th February 2005 CO 2 emissions reduction target of Japan 6% The GSHP system has been remarked as a system with large potential for reduction of CO 2 emission. The number of the GSHP systems installed in Japan is increasing rapidly Units 40 35 30 25 20 5 0 5 0 98 Markets of the GSHP in Japan 983 985 987 989 99 993 995 997 999 200 2003 2004
Background 3/33 When the GSHP system is installed, a design tool is required. The tool is used for Determination of length of the ground heat exchanger Demonstration of installing effect of the GSHP system? CO 2 emissions no design tool in Japan Oil boiler? GSHP system We developed a design tool for the GSHP system
Advantages of the developed tool 4/33. User friendly data input procedure and graphical output 2. Short time calculation according to hourly heating and cooling loads (Calculation time is approx. minute for calculation of two years operation) 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 5. Including database of CO 2 emissions, costs, and lifetimes for LCA 6. High speed calculation algorithm for heat extraction or injection of the multiple ground heat exchangers buried in random layout
Examples of the input and output screens and windows 5/33 () Input windows Calculations are carried out. Then right window is displayed (2) Output windows Output window examples
Calculation of ground temperature 6/33 Ground temperature calculation applying the cylindrical heat source theory Vertical ground heat excahgner Infinite solid r p T s0 q bo T s hollow cylinder Theoretical solution of the ground temperature variation T s according to radius r and uncertain time t T s = T s 0 2 q bo πλ s ( e 0 as u 2 t J ) ( ur ) Y ( u r bo ) Y 0 ( ur ) J ( u r 2 2 2 u [ J ( u r bo ) + Y ( u r bo )] The developed tool uses an approximate expression of this response for making superposition Fast calculation 0 bo ) du X Nomenclature a: Thermal diffusivity [m 2 /s], J x : xth-order Bessel function of first kind, q : Heat flux [W/m 2 ], r: Radius [m], T: Temperature [ o C], t: Time [h], u: Characteristic value, Y x : xth-order Bessel function of second kind Subscripts b: Borehole surface, s: Soil Greek letters λ: Thermal conductivity [W/m/K]
Calculation of the GSHP system operation 7/33 Calculation diagram of a typical GSHP system Radiator 2 Heat pump unit Heat extraction from ground heat exchanger: Q T 2out T in Flow rate: m b 2 T 2in Heat load: Q 2 T out Compressor power: E Overall heat transfer coefficient : K bo-out Heat capacity T b T s change: ΔQ b Heat extraction from ground: Q bo 3 3 Ground heat exchanger T s r r = bo Nomenclature T: Temperature [ o C] Subscripts bo: Borehole surface, b: Heat carrier fluid (antifreeze solution or water), in: Inlet of heat pump unit, out: Outlet of heat pump unit, : Primary side, 2: Secondary side
Example of temperature distribution calculated by BEM 8/33 Single U-tube (λ bo =.8W/m/K) Case Case 2 20 20 0.0 0.2 32 52 32 72 0.4 0.6 R bo =2.23 0-2 m 2 /W/K R bo =.35 0-2 m 2 /W/K 0.8.0 Double U-tube (λ bo =.8W/m/K) Case Case 2 20 20 32 52 32 72 R bo =.52 0-2 m 2 /W/K R bo =7.58 0-3 m 2 /W/K Nomenclature R b : Borehole thermal resistance [m 2 /K/W]
Calculation of the heat carrier fluid in the ground heat exchanger with large diameter 9/33 Comparison calculated temperature with measured temperature Direct type steel pile with diameter of φ65mm Temperature [ºC] 5 4 3 2 Measured T f-out Calculated T f-out with.5 of λ s T f-in as the input condition of calculation Indirect type steel pile with diameter of φ400mm Temperature [ºC] 0 0 00 200 300 400 Time [h] 5 Measured T f-out 4 3 Calculated T f-out with.5 of λ s 2 T f-in as the input condition of calculation 0 0 50 00 50 200 Time [h]
Life cycle analysis of the GSHP system 0/33 Life cycle analysis Life cycle assessment Estimation of life cycle cost These are estimated by Total initial + Total running Lifetime Energy consumption CO 2 emission 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) A database of CO 2 emissions, costs, and lifetimes for LCA is included in the tool
Calculation for multiple ground heat exchangers /33 Input window of pipe arrangement of multiple ground heat exchangers 2m 2m 2m 2m 2m 2m 2m Header HP Input 2m Piping route of CASE Piping route of CASE2 Steel foundation pile used as ground heat exchanger
Examples of the calculation results 2/33 Difference of temperature distributions according to pipe arrangement 5.0 0.0 CASE 5.0 CASE 5.0 CASE 3 2 4 0.0 5 5.0 5.0 20.0 5.0 5.0 5.0 CASE2 5.0 CASE2 CASE2 3 2 4 20.0 0.0 0.0 5 5.0 5.0 Elapsed time of 3000 h (Mar.7 th ) Elapsed time of 5000 h (May. 30 th ) Piping route Elapsed time of 7000 h (Aug. 2 st ) 5 0 5 20 Temperature [ o C]
Advantages of the developed tool 3/33. User friendly data input procedure and graphical output 2. Short time calculation according to hourly heating and cooling loads (Calculation time is approx. minute for calculation of two years operation) 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 5. Including database of CO 2 emissions, costs, and lifetimes for LCA 6. High speed calculation algorithm for heat extraction or injection of the multiple ground heat exchangers buried in random layout From these advantages, this tool is Especially effective to evaluate the performance of the GSHP system, which is the large systems and the energy pile systems
Today s topics 4/33. 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 The calculated conditions are changed for the comparison items 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)
5/33 Calculation of the ground temperature for heat extraction or injection of multiple ground heat exchangers Applying the superposition principle 2 j r d,i r d,i2 r d,ij The thermal response of a certain ground heat exchanger i is calculated by summing up the all thermal responses r p Certain ground heat exchanger i Equation of the thermal response is, T n ( p, t) = s C ( p, t) + s, i r T r T s L ( rd, ij, t) j= T s C 2 πλ t ( r, t) q' ( t τ ) s τ = 0 I ( r, τ ) τ Thermal response for heat extraction of a certain ground heat exchanger i T s L 4πλ τ = 0 t ( r, t) q'' ( t τ ) s E 2 ( r a τ) 4 τ Thermal response for heat extraction of a surrounding ground heat exchanger j s
6/33 Calculation of the ground temperature for heat extraction or injection of multiple ground heat exchangers T s C * * * * t * * * * * T ( ) ( ) ( r τ ) s C t * * * * * * r, t = q t τ * T ( r, t ) = q ( t τ ) *, τ * = 0 τ Non-dimensional thermal response for heat extraction of a certain ground heat exchanger i T * * ( r τ ) * * s L, s L τ * = 0 * τ 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 T Approximate equation (t *.0 ) Ts n * * t * * * * * *, C s L ( r, t ) T + q ( t τ ) s Li i= τ * = * * *2 ( τ r ) * *2 ( τ r ) The ground temperature can be calculated with acceptable precision and speed to be used as a tool for designing of the GSHP system T s* : Non-dimensional temperature (= 2πλ s ΔT s / r p / q ) [-], t * : Fourier number (= at / r p2 ) [-], q * : Non-dimensional heat flux (= q / q 0 ) [-], q 0 : Unit heat flux (=) [W/m 2 ],
Calculation of temperatures for pipe arrangement 7/33 Detailed method - Parallel circuit- T out T in T pin, T pout, T pin,2 T pout,2 T pin,k- T pout,k T pin,m T pout,m T f, T f,2 T f,k T f,m T s (r p,,t) T s (r p,2,t) T s (r p,k,t) T s (r p,m,t) Heat balance equation of the heat carrier fluid in the primary side T T T = pin, k out in = m k = G f, k G f T pout, k 2 k m Heat balance equation of the heat carrier fluid in the ground heat exchanger dtf, k c ρ Vf, k = c ρ G ( Tpout, k Tpin, k) + K A ( Ts, f f f f f, k p out, k p out, k p out, k dt T n+ pout is obtained ( r, t) Tf k) c f ρ f : Heat capacity of heat carrier fluid [kj/m 3 ], V f : Volume of heat carrier fluid [m 3 ] G f : Flow rate of heat carrier fluid in primary side [m 3 /s], K : Overall heat transfer coefficient
Calculation of temperatures for pipe arrangement 8/33 Detailed method - Serial circuit- Heat pump unit T pin, = T out T pin,2 = T pout, T pin,3 = T pout,2 T pin,l = T pout,l- T pin,n = T pout,n- T in = T pin,n T 2out T in Q 2 Q T 2in E T out T f, T f,2 T f,l T f,n Equation to calculate T out n+ T = T Q c n+ n+ n+ 2 out in f E ρ m f n+ f T s (r p,,t) T s (r p,2,t) T s (r p,l,t) T s (r p,n,t) 2 l n Heat balance equation of the heat carrier fluid in the ground heat exchanger dt f, l c, (,, ) ( (, ) f ρ fvf l = c f ρ f G f Tpout l Tpin l + K p out, l Ap out, l Ts rp, l t Tf, l) dt T n+ pout is obtained
Calculation of temperatures for pipe arrangement 9/33 Simplified method Heat pump Supply and return header 2 3 n - n 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 2 m - m 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 c f ρ Vfn f dt dt f ρ G f = c ( T in T out) + K A f f p out p out m n( T s ( r, t) Tf ) p
Comparison of performance of the GSHP system 20/33 Calculated subject Location : Tokyo, Japan Cooling period: Apr.23rd - Nov.2nd Heating period: Nov.3rd - Apr.22nd Floor area: 30m 2 Heating load: 28.2 GJ (Maximum load: 6.6 kw) Cooling load: 0.0 GJ (Maximum load: 6.3 kw) Room condition Heating period Temperature: 20 o C Cooling period Temperature: 26 o C Humidity: 50% Heat loss coefficient: 2.33W/m 2 /K Initial ground temperature: 6.5 o C Soil heat capacity: 3000 kj/m 3 Soil thermal conductivity:.0 W/m/K
Comparison of performance of the GSHP system 2/33 Hourly variation of heat load 8 6 Heating period Cooling period Heat load [kw] 4 2 0-2 -4-6 -8 Cooling load Heating load: 28.2 GJ (Maximum load: 6.6 kw) Cooling load: 0.0 GJ (Maximum load: 6.3 kw) Heating load Nov. 3 rd Feb. 3 rd May. 3 rd Aug. 3 rd Nov. 2 nd
Calculated conditions 22/33 Pipe arrangement (Parallel Serial) Method for calculation CASE 4 5 Detailed method CASE2 4 5 Detailed method CASE3 20 Detailed method CASE4 (Borehole) Detailed method CASE5 4 5 Simplified method
Comparison items 23/33 Piping route: CASE vs. CASE2 CASE CASE 2 2m 2m 2m 2m 2m 2m 2m 2m 2m 2m 2m 2m 2 3 4 5 5 HP 2m 2m 4 3 2 HP Header Header 2m 2m Steel foundation pile used as ground heat exchanger
Comparison item 24/33 Numbers of the parallel and serial circuits : CASE vs. CASE3 CASE : Numbers of the parallel serial circuits are 4 5 CASE 3: All ground heat exchangers are connected in parallel Number of the ground heat exchangers : CASE vs. CASE4 CASE : Multiple ground heat exchangers of 8 m 20 (= 60 m) CASE 4: A single ground heat exchanger with length of 60 m Method of calculation : CASE vs. CASE5 CASE : Calculated by the detailed method CASE 5: Calculated by the simplified method
An example of calculation results 25/33 Operating condition (temperature variations*) of the third year 50 40 Heating Period Cooling Period T 2out *Temperatures of each part Temperature [ o C] 30 20 0 T p-outave T out T 2out T in T out 0 T 2out T p-outave T p-out -0 T out Minimum temperature:-0.4 o C Nov.3 rd Feb.3 rd May.3 rd Aug.3 rd Nov. 2 nd Temperatures are recovered The GSHP system can operate for a long term
Comparison between CASE and CASE2 26/33 Changes of temperature distribution in the ground surrounding piles 5.0 2 3 4 0.0 CASE 5.0 CASE 5.0 CASE 3 2 4 2 3 4 5 0.0 5 5.0 20.0 5.0 5 Temperature decrement: Almost even 5.0 4 3 2 5.0 5.0 Temperature increment: Pile is the largest CASE2 5.0 CASE2 CASE2 3 3 2 4 2 4 20.0 5 0.0 5 0.0 5 5.0 5.0 Temperature decrement: Pile is the largest Elapsed time of 3000 h (Mar.7 th ) Elapsed time of 5000 h (May. 30 th ) Piping route Ground temperature is decreased Effect of heat extraction is still left Temperature increment: Pile is the largest Elapsed time of 7000 h (Aug. 2 st ) 5 0 5 20 Temperature [ o C]
Comparison between CASE and CASE2 27/33 Integrating amounts of heat extraction and injection of each pile.5 Heating Period Cooling Period.5 Heating Period Cooling Period Amount of heat extraction [GJ].0 0.5 0.0-0.5 -.0 -.5 Pile2, Pile, Pile 3, Pile 4, Pile5 from top to bottom Total amount of heat extraction:5.65gj Total amount of heat injection :2.87GJ Difference: Large Difference: Small Pile2, Pile3, Pile 4, Pile, Pile5 from top to bottom -0.5 -.0 Nov.3 rd Feb.3 rd May.3 rd Aug.3 rd Nov.2 nd -.5 These results indicate Amount of heat extraction [GJ].0 0.5 0.0 Pile5, Pile, Pile 4, Pile 3, Pile2 from top to bottom Pile4, Pile5, Pile 3, Pile 2, Pile from top to bottom Total amount of heat extraction:5.65gj Total amount of heat injection :2.87GJ Difference: Small Difference: Large Nov.3 rd Feb.3 rd May.3 rd Aug.3 rd Nov.2 nd. Seasonal thermal storage effect appears 2. Total amounts of heat extraction are the same although the ones of individual piles differ depending on the piping route
Comparison between CASE and CASE2 28/33 Performance of the GSHP system Heating Period Average COP Average SCOP Cooling Period Average COP Average SCOP CASE 5.0 4.0 5.6 3.6 CASE2 5.0 4.0 5.6 3.6 CASE3 4.9 3.9 5.5 3.5 CASE4 5.4 4.2 5.3 3.4 CASE5 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
Comparison between CASE and CASE3 29/33 Performance of the GSHP system Heating Period Average COP Average SCOP Cooling Period Average COP Average SCOP CASE 5.0 4.0 5.6 3.6 CASE2 5.0 4.0 5.6 3.6 CASE3 4.9 3.9 5.5 3.5 CASE4 5.4 4.2 5.3 3.4 CASE5 5.0 4.0 5.6 3.6 These results indicate Laminar flow of the heat carrier fluid yields reduction of heat extraction or injection and performance decrement of the GSHP system It s desirable to arrange the piping route to keep the turbulent flow
Comparison between CASE and CASE4 30/33 Performance of the GSHP system Heating Period Average COP Average SCOP Cooling Period Average COP Average SCOP CASE 5.0 4.0 5.6 3.6 CASE2 5.0 4.0 5.6 3.6 CASE3 4.9 3.9 5.5 3.5 CASE4 5.4 4.2 5.3 3.4 CASE5 5.0 4.0 5.6 3.6 These results indicate The GSHP with multiple ground heat exchangers can operate with high efficiency as well as the system with a single ground heat exchanger The GSHP system has potential to be popular in warm region in Japan
Comparison between CASE and CASE5 3/33 Performance of the GSHP system Heating Period Average COP Average SCOP Cooling Period Average COP Average SCOP CASE 5.0 4.0 5.6 3.6 CASE2 5.0 4.0 5.6 3.6 CASE3 4.9 3.9 5.5 3.5 CASE4 5.4 4.2 5.3 3.4 CASE5 5.0 4.0 5.6 3.6 These results indicate The simplified method provides high advantage from the viewpoint of precision and computational speed for evaluation of the GSHP system
Summary 32/33. 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 ) 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 35/25 Schematic diagram of the field experiments Experiment room In experiment room Heat pump Fan-coil Steel pile External diameter: 40 mm Internal diameter: 30 mm To outside To outside Water Brine (Acid organic type 40 %) 8m U-tube (PE00) External diameter: 32 mm Internal diameter: 25 mm F Flow sensor Electromagnetic flow meter T Pt-00 Work Shop of Annex29, 2005-05-30, Las Vegas, USA K. Nagano, T. Katsura, S. Takeda et al.
Comparison between temperatures of the calculation and measurement in field experiments 36/25 Field experiments Experiment room Steel pile Work Shop of Annex29, 2005-05-30, Las Vegas, USA K. Nagano, T. Katsura, S. Takeda et al.
Comparison between temperatures of the calculation and measurement in field experiments 37/25 Temperature measurement points Measurement room.8 m 7.2 m Line.8 m Line2 Line3 Pile A Pile B Pile C Pile D Pile E 9 7 6 5 4 3 0 m 8 Line4 2 Line5 : Steel pile Measuring points of water temperature in a pile : At GL-, 2, 4, 6 and 8 m Measuring points of ground temperature ( to 9) : At GL-0.5, 2, 4, 6, 8 and 0 m : At GL-, 4 and 8 m : At GL-6 m Work Shop of Annex29, 2005-05-30, Las Vegas, USA K. Nagano, T. Katsura, S. Takeda et al.
Comparison between temperatures of the calculation and measurement in field experiments 38/25 Result 5 Point Temperature [ o C] 0 5 0 Point2 Point4 Point9 Calculated -5 Mar.9 th Mar.29 th Apr.8 th Apr.8 th Apr.28 th May.8 th Date Work Shop of Annex29, 2005-05-30, Las Vegas, USA K. Nagano, T. Katsura, S. Takeda et al. Measured T in