A comparison of the energy use for different heat transfer fluids in geothermal systems

Transcription

1 IGSHPA Technicl/Reserch Conference nd Expo Denver Mrch 14-16, 2017 A comprison of the energy use for different het trnsfer fluids in geotherml systems Lurent Ggné-Boisvert Michel Bernier ABSTRACT Geotherml systems tht operte under 0 C must use ntifreeze mixtures insted of wter to void opertionl problems. This pper exmines the energy consumption of the circulting pump nd het pump for vrious het trnsfer fluids used in residentil geotherml system. Propylene glycol, ethnol nd methnol solutions t different concentrtions re compred. Effects of fluid temperture nd viscosity on hed losses, borehole therml resistnce nd het pump opertion re reviewed. Efficiency curves for currently vilble circultors re proposed. Annul energy simultions re then performed on residentil GCHP system. Energy consumption (pump nd het pump) is evluted subhourly bsed on fluid temperture nd properties previling during ech time step. Results show, s expected, tht higher mixture concentrtions nd higher flow rtes led to higher energy consumption. Methnol with concentrtion of 15% nd 1.5 gpm/ton flow rte provides the best energy performnces while ethnol t 30% with 3 gpm/ton is the worst choice, requiring 16% more energy nd 525% more pumping power thn for the methnol cse. Lminr flow in boreholes ppers to be fvorble when compred to turbulent flow which leds to reltively high pumping energy consumption. Shorter boreholes piped in prllel decrese energy consumption s well. INTRODUCTION A typicl residentil ground-coupled het pump (GCHP) system is presented in Figure 1. When such system opertes under 0 C, n ntifreeze mixture must be used to void opertionl problems. Typiclly, designers select solution with freezing point pproximtely 3 C (5 F) lower thn the lowest nticipted temperture (Dow, 2001). Antifreeze solutions ffect the performnce of the system in mny wys. The greter viscosity of these fluids my led to lminr flow in boreholes with corresponding increse of the borehole therml resistnce. Pressure drops in the vrious prts of the system ( ppipe, pbore, php nd pvlve in Figure 1) s well s pumping power (WPump) re incresed when fluid other thn wter is used. Moreover, ntifreeze mixtures ffect het trnsfer in the source-side het exchnger of the het pump, which decreses het pump cpcity (QCp) nd het pump input power (WHP) but to lesser extent. The objective of this pper is to study the totl energy consumption (pump nd het pump) for vrious het trnsfer fluids typiclly used in GCHP systems. WPump WHP QCp pvlve Pump Het pump ppipe Borehole Het Exchnger php pbore A A A-A Figure 1 Representtion of residentil GCHP system. Figure 2 Overll efficiency of vilble circultors. Lurent Ggné-Boisvert is M.A.Sc. student in the Deprtment of Mechnicl Engineering, Polytechnique Montrel, Montrel, Quebec, Cnd. Michel Bernier (michel.bernier@polymtl.c) is professor in the Deprtment of Mechnicl Engineering, Polytechnique Montrel, Montrel, Quebec, Cnd.

2 LITERATURE REVIEW Solutions of methnol, ethnol nd propylene glycol re often used in GCHP systems. An ASHRAE sponsored study (Heinonen, 1997) concluded tht propylene glycol ws the best compromise minly becuse of its low environmentl risk despite the fct tht systems with propylene glycol use more energy s noted by Bernier et l. (2005). The toxicity of the inhibitors dded to propylene glycol solutions must however be considered. Pumping energy, which increses with the use of ntifreeze, is sometimes considered negligible when compred to the overll energy consumption of geotherml system. In relity, it cn represent up to 45% of the totl energy consumption, even in recent geotherml systems (Liu et l., 2015). Pumping energy is lso influenced by the pumping strtegy (Kvnugh nd McInerny, 2001). Kvnugh nd Kvnugh (2012) suggested mximum ground loop pump power of 10 hp/100 tons (2.1 kwelec/100 kwtherml). A decrement fctor (DF) evluting het pump convective het trnsfer vritions due to the use of ntifreeze mixtures ws developed by Spitler nd Jin (2003). The DF corrects the fluid-side het trnsfer coefficient initilly clculted for wter. In follow-up study, Khn nd Spitler (2004) stted tht propylene glycol increses system energy consumption by 6 to 7% compred to ethnol or methnol. In residentil cse study, with reltively blnced heting nd cooling lods nd low ntifreeze concentrtions, they concluded tht typicl ntifreeze mixtures hve similr lifecycle costs while wter presents higher life-cycle cost becuse longer borehole is required. Spitler nd Ghelin (2015) chllenged the stndrd industry recommendtions to hve turbulent flow in the borehole t ll times nd to mintin hed losses in the rnge of 1 to 3 ft/100 ft of pipe (10 to 29 kp/100 m). Their work confirmed Kvnugh s wrning (2011) tht high fluid velocities my result in high pumping power with little therml benefit nd even less economic dvntge over occsionl lminr flow. They lso confirmed Mescher s guideline expressed in n ASHRAE Webcst (ASHRAE, 2011) stting tht properly designed bore field should hve hed loss ( pbore) of less thn 25 ft (75 kp) with mximum totl system pressure drop of 50 ft (150 kp). CIRCULATOR EFFICIENCY Circultors re low power pumps typiclly used to circulte fluid in residentil, one-pipe nd decentrlized GCHP systems. Until recently, circultors hd typicl efficiency round 20 to 25% (Kvnugh nd Rfferty, 2015). However, the efficiency of circultors hs nerly doubled in recent yers (Bidstrup, 2012). Following the methodology used by the COSTIC (2003), n in-house nlysis performed for the present study exmined the efficiency of 86 commercilly vilble circultors from two mnufcturers (Grundfos, 2016 nd Slmson, 2016). In ech cse, the best efficiency point (BEP) ws used to extrct the nominl overll efficiency t given nominl hydrulic power. The results of this nlysis re shown in Figure 2, which shows the circultor wire-to-wter efficiency s function of the hydrulic power in the 0 to 300 W rnge. Circultors re ctegorized into three clsses (Low, High nd Best Efficiency) ech with its own regression eqution. In this work, circultors with the High efficiency re used. HEAT TRANSFER AND REQUIRED HYDRAULIC POWER The thermophysicl properties used in this work re obtined from the EES softwre (Klein et l., 2015). For concentrtion of 30% by weight (m/m), this tool gives the following freezing points: -13 ºC for propylene glycol, -20 ºC for ethnol, nd -27 ºC for methnol. The viscosity of ntifreeze mixtures is the property hving the most notble effect on the energy consumption of geotherml systems. High fluid viscosities led to low Reynolds numbers nd lminr flows in the borehole which tend to decrese the het trnsfer coefficients inside borehole pipes. Figure 3 (left) shows the stedy-stte convective therml resistnce, Rconv, nd stedy-stte therml resistnce, Rb, of typicl borehole using propylene glycol (30% m/m) nd different flow rtes (chrcteristics re given in Tble 1). Rb is the effective borehole therml resistnce between the fluid nd the ground nd is the sum of the grout, pipe nd convective resistnces (Eq. 1). The well-known reltions from Hnsen nd Gnielinski/Petukhov re used to evlute the convective het trnsfer coefficient in borehole pipes for lminr nd turbulent flows.

3 R R + R + R b = (1) grout pipe As shown in Figure 3, Rconv increses significntly when the flow becomes lminr t flow rte smller thn 0.32 L/s (for propylene glycol 30% m/m t 0 C). In turn, this increses the borehole therml resistnce, Rb, from 0.12 mk/w to 0.20 mk/w. Thus, for given ground lod, the fluid temperture for the lminr cse must be lower thn for the turbulent cse in order to increse the temperture difference between the fluid nd the ground. However, s shown by the Phydr curve on Figure 3, the required hydrulic power for lminr flow is significntly less thn for turbulent flow. The trnsition to lminr flow lso depends on the fluid temperture nd pipe dimeter. This is shown in Figure 3b where the dip in ech curve represents the trnsition to lminr flow. The liner hed loss is bout three to four times higher for 9 gpm flow rte in 1.25 pipe thn for 4.5 gpm in 1.25 pipe. conv Figure 3 nd b Borehole therml resistnces nd required hydrulic power (left) nd hed loss s function of temperture (right). Tble 1. Min Chrcteristics of the Borehole used in this Study Prmeter S.I. Vlue S.I. Unit I.P. Vlue I.P. Unit Depth 150 m 492 ft Borehole dimeter 0.15 m 6 in Inside pipe rdius m 0.51 in Outside pipe rdius m 0.63 in Grout conductivity 1.5 W/m.K 0.87 BTU/hr.ft. F Grout therml cpcity 3000 kj/m 3.K 44.7 BTU/ft 3. F Ground therml conductivity 2.2 W/m.K 1.27 BTU/hr.ft. F Ground therml diffusivity m 2 /dy 0.94 ft 2 /dy Pipe conductivity 0.42 W/m.K 0.24 BTU/hr.ft. F Flow rte 0.28/0.57 L/s 4.5/9 gpm Borehole resistnce Rb t 0 C (PG30%) 0.202/0.123 m.k/w 0.350/0.213 hr.ft. F/BTU High fluid viscosities lso increse pumping power due to incresed pipe friction. Hed losses ( ppipe, pbore, php nd pvlve) increse s viscosity ffects the friction coefficient. With higher hed losses, pumping power WPump is incresed nd lrger pump must be used. Incresing flow rte to mintin turbulent flow lso increses pumping power. In this work, the Drcy-Weisbch eqution is used for pipe hed losses nd the Churchill eqution is used for the friction fctor (Eq. 2) s it is suitble for lminr, trnsient nd turbulent flows. A Power Prmeter, PP, is lso proposed to combine flow rte nd pipe dimeter (Eq. 3) to llow simple pumping power predictions. f = 8 8 Re ln + 7 Re / ε (2) D Re

4 3 Flow PP = (with Flow in gpm nd D pipe in inches) (3) 5 D pipe Figure 4 shows the required liner hydrulic power for PG30% t 0 C s function of PP. Dots represent detiled clcultions while the stright line represents liner regression through the dt. The sme exercice is performed for different ntifreeze solutions with flow rtes vrying from 2 to 12 gpm nd pipe dimeters vrying from 0.75 to 1.5. Liner regressions re then obtined for ech fluid (Figure 4b). Ech regression presents n bsolute RMSE under W/m nd llows n dequte first estimte of pumping power. The well-known criteri of 3 ft/100 ft of pipe (29 kp/100 m) for hed loss is lso overlyed for 4.5 nd 9 gpm flow rtes (Kvnugh nd Rfferty, 2015). Figure 4b lso shows tht for specific flow rte nd pipe dimeter, pumping power is higher s fluid viscosity increses. Pumping PG30% t 0 C requires pproximtely 45% more power thn for wter. The use of Figure 4b is best illustrted with n exmple. A flow of 9 gpm of ethnol (30% m/m) t 0 C through 1 meter pipe with dimeter of m (1.25 ) leds to vlue of PP = 239 gpm 3 /in 5 with corresponding vlue of 0.18 W of hydrulic power (0.19 W/m is obtined with detiled clcultion). If the system consists of 100 m borehole with 10 m of connecting pipes to the het pump (thus totl pipe length of 220 m) then 39.6 W of hydrulic power is required. Pumping this fluid with 50% efficient circultor would then require 79 W of electricl power, WPump. Figure 4 nd b Required hydrulic power t 0 C clculted for PG30% (left) nd predicted for different fluids (right). Hed losses through the source het exchnger of the het pump s well s in connecting hoses nd vlves re lso importnt. Het pump het exchnger hed loss is typiclly given by mnufcturers nd is function of flow rte nd inlet fluid temperture. Eqution 4, where php is in kp, Flow in L/s nd TinHP in C, is regression bsed on het pump performnce mp presenting hed loss for severl flow nd temperture combintions (ClimteMster, 2012). It is vlid for flow rnging from to L/s (4.5 to 9 gpm) nd for inlet tempertures rnging from -1.1 to 48.9 C (30 to 120 F). Vlve nd hose hed losses, combined in one term, pvlve, re clculted using flow coefficients used by Kvnugh nd Rfferty (2015): Cv equls 25 for the vlve nd 8 for hoses (bsed on flows in gpm nd 1 psi (6.9 kp) pressure drop). For 4.5 nd 9 gpm flow rtes, pressure drops then vry from 0.2 to 0.9 kp (0.07 to 0.3 ft) for the vlve nd from 2.2 to 8.7 kp (0.7 to 2.9 ft) for connecting hoses. p = 88.0 Flow T 13.3 (4) HP An ntifreeze correction fctor for these hed losses, fwpd, is proposed (Eq. 6). This fctor, bsed on Blsius eqution (Eq. 5), corrects mnufcturers pressure drops, which re bsed on wter. Blsius eqution is vlid for low turbulent Reynolds number (White, 2009), which is the cse in typicl smll dimeter hoses nd het exchngers. The vlue of fwpd (Eq. 6) is then the rtio of the pressure drop for the ntifreeze solution over the one for wter. This fctor inhp

5 evluted for different ntifreezes nd concentrtions t 0 C ws verified ginst mnufcturer s dt (ClimteMster, 2012). As shown in Tble 2, the method proposed here (Eq. 5 nd 6) is within 2% of the mnufcturer s dt for PG. Similr results were obtined for other fluids. php nd pvlve (vlve nd hoses), clculted for wter, re then multiplied by this fctor to obtin the ctul ntifreeze pressure drop, p / 4 ρ D (5) p = 0.158L µ V f WPD p = p w ρ = ρw 0.75 µ µ w 0.25 (6) Tble 2. WPD, cpcity nd power correction fctors for PG fwpd fcp,het fpower,het Prop. Glycol (% m/m) Eq. 6 Mnufcturer Eq. 9 Mnufcturer Eq. 9 Mnufcturer 5% % % HEAT PUMP CAPACITY AND POWER The use of ntifreeze mixtures lso ffects het trnsfer in the source-side het exchnger of the het pump, which hs detrimentl effect on het pump performnce. Het pump heting cpcity QCp decreses becuse of reduced convection in the het exchnger pipes. Viscosity, density, therml cpcity nd conductivity vritions reduce cpcity, by up to 10% for 30% ethnol solution (ClimteMster, 2012). Power consumption WHP is lso ffected nd it cn decrese by up to 3% s cpcity decreses. However, het pump energy consumption increses with the use of ntifreeze s it must operte for longer periods to meet the lod s cpcity is reduced. Cpcity nd power consumption cn be djusted by correction fctors to ccount for those effects. A cpcity correction fctor derived from Nguyen s work is used here (2010). This fctor, fcpcity, (Eq. 9) predicts het pump cpcity vrition bsed on het pump constnts (C1 nd C2) nd Spitler nd Jin s (2003) Decrement Fctor (Eq. 7). As shown by Eq. 8, the two constnts re used to evlute the totl het pump source-side therml resistnce Rt. C1 stnds for the fluid convective resistnce initilly clculted for wter. It is divided by DF to correct the fluid-side convective het trnsfer coefficient. C2 combines the pipe conductive, the refrigernt convective nd the fouling therml resistnces, which re not ffected by the choice of the ntifreeze solution. C1 nd C2 re bck clculted using pir of cpcity correction fctors from mnufcturer (ClimteMster, 2012) with DF clculted for ech fluid nd ech concentrtion. This leds to two equtions/two unknowns system tht cn be solved esily. C1 nd C2 equl 1.0 nd 16.35, respectively, when clculted using propylene glycol. C1 nd C2 differ slightly when clculted for ethnol nd methnol. Fluid specific vlues of C1 nd C2 re used to predict fcpcity for the simultions performed in this pper. DF = h h w µ = µ w 0.47 ρ ρ w 0.8 C C p, p, w 0.33 k k w 0.67 (7) C1 Rt = Rconv, fluid + Rcond, pipe + Rconv, refrigernt + R fouling = Rconv, fluid + ΣR = + C2 (8) DF f R C + C t, w 1 2 cpcity = = (9) R C t, 1 + C2 DF

6 It lso ppers tht the use of this cpcity correction fctor proves to be ccurte to correct the het pump power consumption (fcpcity is replced by fpower in Eq. 9). The sme DF is used but C1 nd C2 re bsed on the mnufcturer s power correction fctors. They equl 1.0 nd 75.68, respectively, when clculted using propylene glycol. As shown in Tble 2, the predicted cpcity nd power correction fctors re in good greement with mnufcturer s dt. Finlly, there re opertionl benefits resulting from the use of ntifreeze mixtures. Indeed, llowing colder fluid tempertures to the het pumps (-3 C insted of 0 C for exmple) leds to shorter boreholes s the temperture difference between the borehole fluid nd the ground is lrger. However, this effect might be counterblnced by incresed pumping energy nd reduced borehole nd het pump performnces. It is thus importnt to evlute the overll effects of using specific ntifreeze solution. This is done using nnul simultions s shown in the next section. ANNUAL SIMULATIONS Annul simultions using TRNSYS v17 (Klein et l., 2010) re performed to compre the energy consumption of GCHP system using different ntifreeze mixtures (PG, EA nd MA) nd two flow rtes (4.5 nd 9 gpm or 1.5 nd 3 gpm/ton). A 1-minute time step is used, which is smll enough to cpture borehole trnsient effects. The system under study is the one presented in Figure 1. It consists of 3-ton (10.5 kw) wter-to-ir ground-coupled het pump linked to 150 m borehole. The GCHP system provides spce heting for single-fmily house with enough cpcity to void the need for n uxiliry heter. The building is simulted in heting dominted climte (Montrel, Cnd) with n nnul heting requirement of bout kwh. Typicl models found in TRNSYS for the building, thermostt, het pump nd pump re used. Het pump performnce is modeled bsed on mnufcturer s stedy-stte performnce dt (ClimteMster, 2012). The TRCM borehole model from Godefroy nd Bernier (2014) is used to model the single U-tube borehole. This experimentlly vlidted model (Godefroy et l., 2016) ccounts for fluid nd grout therml cpcity, which indirectly ffects het pump performnce (Ggné-Boisvert nd Bernier, 2016). The min chrcteristics of the borehole re given in Tble 1. The pump is high efficiency wet rotor circultor. When operting, it is ssumed tht it provides constnt volumetric flow rte yer-round. Pump efficiency is evluted bsed on the High regression curve presented in Figure 2. Thermophysicl properties, correction fctors, hed losses, nd borehole therml resistnce re clculted t ech time step. Comprison results Tbles 3 nd 4 present one-yer simultion results while Figure 5 shows the pump power nd het pump inlet temperture evolution over the yer. In these tbles, pump frction is the rtio of the pumping energy over the totl energy consumption; sesonl performnce fctor (SPF) is the rtio of the nnul heting requirement over the totl energy consumption (Nordmn nd Zottl, 2011); Hedmx is the highest totl hed loss over the yer while pump power is the highest required pump power. As illustrted in Figure 5, pumping power decreses by bout 10-15% with higher fluid temperture occurring in summer. Rb lso vries over the yer s fluid temperture fluctutes, s shown by minimum nd mximum vlues in Tbles 3 nd 4. These tbles show the importnce of considering the ntifreeze properties nd how they influence system opertion. Figure 5 nd b Pump power nd het pump inlet temperture for PG30% t 4.5 (left) nd 9 gpm (right) over one yer.

7 Tble 3. Simultion results for 4.5 gpm flow rte Fluid Totl Pump Pump Frction SPF Hedmx Pump power Rb, min/mx TinHP, min (% m/m) (kwh) (kwh) (%) (-) (kp/ft) (W) (W/mK) ( C/ F) Prop. Glycol 15% % / / /33 Prop. Glycol 30% % / / /29 Prop. Glycol 40% % / / /29 Ethnol 15% % / / /33 Ethnol 30% % / / /30 Methnol 15% % / / /33 Methnol 30% % / / /33 Wter % / / /33 Tble 4. Simultion results for 9 gpm flow rte Fluid Totl Pump Pump Frction SPF Hedmx Pump power Rb, min/mx TinHP, min (% m/m) (kwh) (kwh) (%) (-) (kp/ft) (W) (W/mK) ( C/ F) Prop. Glycol 15% % / / /32 Prop. Glycol 30% % / / /32 Ethnol 15% % / / /32 Ethnol 30% % / / /33 Methnol 15% % / / /32 Methnol 30% % / / /33 Wter % / / /32 PG 30% Prllel % / / /34 MA 15% Prllel % / / /36 Wter Prllel % / / /36 Results show tht higher concentrtions nd higher flow rtes increse totl energy consumption of the GCHP system. Using methnol with concentrtion of 15% nd 4.5 gpm gives the best energy performnces with n energy consumption of 6014 kwh, SPF of 3.36 nd mximum pump power of 53.4 W. It is worth mentioning tht propylene glycol t 15% with 4.5 gpm is not recommended for tht ppliction considering its -5 C freezing point. Ethnol 30% with 9 gpm requires 6966 kwh (+16%) nd 334 W of pump power (+525%) with SPF of 2.91 (-13%). This cse gives the worst energy performnce nd bigger nd more expensive pump would be required. For pumping, flow rtes of 4.5 nd 9 gpm led to pump frctions of bout 2% nd 10%, respectively. Bsed on n verge 8 kw pek heting lod, pumping grde of A on the Kvnugh nd Rfferty (2015) scle is chieved for ll 4.5 gpm cses. A grde of F is obtined for 9 gpm cses. Higher flow rtes nd concentrtions re responsible for bigger hed losses, leding to higher pumping power nd energy consumption. It ppers tht systems with hed losses under 100 kp (4.5 gpm) led to better overll energy performnces thn ~300 kp (9 gpm) cses, which is in line with Mescher s sttement presented erlier. Interestingly, for propylene glycol 30% nd ethnol 30% with 4.5 gpm, pumping energy is lower thn for cses with 15% concentrtion, which is counterintuitive s these solutions re more viscous. This is becuse those two cses re in lminr flow round 90% of the opertion time, which leds to lower hed losses (Figure 3b). The PG40% t 4.5 gpm cse lwys opertes in lminr flow nd presents higher hed losses thn the PG30% cse. Its minimum het pump inlet temperture is lso slightly higher becuse more energy comes from the het pump compressor nd less from the ground. It is importnt to note tht these three 4.5 gpm lminr cses, with typicl lminr Rb vlues nd lower loop tempertures, yield lower energy consumption (-10%) thn the sme cses with the fully turbulent 9 gpm flow rte. This is minly due to the higher pumping requirements. Bsed on tht, common GCHP system using propylene glycol t 30% would require less energy if working with 4.5 gpm versus 9 gpm, even if the borehole flow is lmost lwys lminr. This confirms Kvnugh s recommendtion. Thus, designers must be wre tht the het trnsfer dvntge of turbulent flows is smll compred to the incresed pumping energy consumption in GCHP systems. Figures 6 nd 6b present brekdown of pek hed losses to help understnd flow rte effects on results. Cses with 4.5 nd 9 gpm using propylene glycol 30% re presented. As expected, the vrious hed losses re bout four times higher when the flow

8 rte is doubled. Figure 6, b nd c Brekdown of pek hed losses for PG30% t 4.5 gpm (left), 9 gpm (center) nd in prllel (right). The sme simultions re performed without the correction fctors (fcpcity, fpower nd fwpd) to ssess their importnce. In ll cses, neglecting correction fctors underestimtes energy consumption. The extent of the underestimtion is higher for higher ntifreeze concentrtions. Neglecting the cpcity nd power correction fctors underestimtes het pump energy consumption by 2 to 6%, pump consumption by 3 to 9% nd overll energy consumption by 2 to 7%. Neglecting the hed loss correction fctor (het pump, hoses nd vlve) underestimtes pump energy consumption by 3 to 8% nd overll energy consumption by 0.1 to 0.7% s pumping represents 2 to 10% of the totl. Neglecting both fctors underestimtes pump energy consumption by 6 to 15% nd overll energy consumption by 2 to 7%. Tble 5 presents these differences for propylene glycol 15 nd 30% t 9 gpm. Tble 5. Effects of correction fctors on energy consumption (Propylene Glycol 9 gpm) Pump Without Totl Without Fluid % m/m (-) fcp+fpower fwpd fcp+fpower+fwpd (-) fcp+fpower fwpd fcp+fpower+fwpd PG15% (kwh) Difference (%) -2.8% -3.2% -5.9% -2.0% -0.3% -2.3% PG30% (kwh) Difference (%) -7.2% -5.9% -12.7% -5.2% -0.7% -5.8% As finl test, two 75 m boreholes re piped in prllel with totl flow rte of 9 gpm. Hed losses re consequently modified (Figure 6c). As shown in Tble 4, this leds to the lowest overll energy consumptions nd highest SPF. Using MA15% requires 5865 kwh with corresponding SPF of Using shorter boreholes in prllel must then be considered s n effective design in terms of energy performnce, even if lminr flow occurs in boreholes. Shorter prllel boreholes lso led to higher vlues of TinHP, min which my decrese the required ntifreeze concentrtion or boreholes length. CONCLUSION The min objective of this pper is to compre the energy consumption of GCHP system using vrious ntifreeze solutions. It reviews the effects of ntifreeze on hed losses, borehole therml resistnce nd het pump opertion. It lso proposes efficiency curves for currently vilble circultors; grph estimting required hydrulic power for different flows nd pipe dimeters; nd ntifreeze correction fctors to correct het pump cpcity, power nd hed loss. Annul energy simultions re then performed on residentil GCHP system. Results show, s expected, tht higher concentrtions nd higher flow rtes increse totl energy consumption. Methnol with 15% concentrtion nd flow rte of 1.5 gpm/ton gives the lowest nnul energy consumption. Ethnol t 30% nd 3 gpm/ton is the worst choice, requiring 16% more energy nd 525% more pumping power compred to the methnol cse. Lminr flow in boreholes ppers to be fvorble when compred to turbulent flow, which led to reltively high pumping energy consumption. Finlly, plcing shorter boreholes in prllel ppers to decrese energy consumption nd increse the sesonl performnce fctors.

9 ACKNOWLEDGMENTS The uthors would like to express their sincere grtitude to ASHRAE, Hydro-Quebec nd the Nturl Sciences nd Engineering Reserch Council of Cnd (NSERC) who provided scholrships to the first uthor. This work ws lso performed with funds provided by NSERC s Smrt Net-Zero Energy Buildings Strtegic Reserch Network. NOMENCLATURE C = Antifreeze concentrtion (%) C 1, C 2 = Het pump constnts C v = Flow coefficient (gpm) Cp = Therml cpcity (kj/kg.k) D = Pipe dimeter (m) ε = Pipe rugosity (m) f = Friction fctor (-) h = Convection coefficient (W/m 2.K) k = Therml conductivity (W/m.K) p = Pressure drop/hed (kp) REFERENCES PP = Power Prmeter (gpm 3 /in 5 ) = Density (kg/m 3 ) Q = Cpcity power (W) Re = Reynolds number µ = Dynmic viscosity (kg/m.s) SPF = Sesonl performnce fctor (-) V = Fluid speed (m/s) W = Power (W) Subscripts = Antifreeze mixture cp = Cpcity conv = Convection HP = Het pump min = Minimum t = Totl w = Wter WPD = Wter pressure drop % m/m = Mss Conc. ASHRAE Ground Source Het Pump Systems: Putting the Erth to Work for You (K. Mescher). ASHRAE Webcst Dvd. Bernier, M., Ldng, O., Hulot, J., Effet du choix du fluide cloporteur sur l énergie de pompge des systèmes de pompes à chleur géothermiques, VIIème Colloque Interuniversitire Frnco-Québécois sur l Thermique des Systèmes mi 2005, Sint- Mlo. Bidstrup, N EU Pump Regultions. ASHRAE Journl 54(5): ClimteMster Trnquility 27 (TT) Series Performnce Mp. USA: ClimteMster. COSTIC Circultors efficiency bsed on mnufcturers ctlogs (Study ). Angers, Frnce: ADEME. Dow Engineering nd Operting Guide: DOWFROST Inhibited Propylene Glycol-bsed Het Trnsfer Fluids. USA: Dow Chemicl Compny. Ggné-Boisvert, L., nd M. Bernier Accounting for Borehole Therml Cpcity when Designing Verticl Geotherml Het Exchngers. Presented t the 2016 ASHRAE Annul Conference, St-Louis, MO, June Gehlin, S.E.A., nd J.D. Spitler. (2015). Effects of Ground Het Exchnger Design Flow Velocities on System Performnce of Ground Source Het Pump Systems in Cold Climtes. ASHRAE Meeting. Godefroy, V., nd M. Bernier A simple model to ccount for therml cpcity in boreholes. Proceedings of the 11th IEA Het Pump Conference, Montrel, Qc, Cnd. Pper #P.4.8. Godefroy, V., Lecomte, C., Bernier, M., Dougls, M., nd M. Armstrong Experimentl Vlidtion of Therml Resistnce nd Cpcity Model for Geotherml Boreholes. ASHRAE Winter Meeting, Orlndo, Fl. OR-16-C047. Grundfos Cnd Product Center. Access on Mrch th Heinonen, E.W., M.W. Wildin, A.N. Bell, R.E. Tpscott. (1997). Assessment of ntifreeze solutions for ground-source het pump systems. ASHRAE Trnsctions, 103(2): Jin, H., nd J.D. Spitler Prmeter estimtions bsed model of wter-to-wter het pumps with scroll compressors nd wter/glycol solutions. Building Serv. Eng. Res. Technol. 24(3): Kvnugh, S.P., nd S.A. McInerny Energy Use of Pumping Options for Ground-Source Het Pumps. ASHRAE Trnsctions. 107(1): Kvnugh, S.P Less Pumping Mens Cooler Ground Loops. ASHRAE Journl 53(7): Kvnugh, S.P., nd J. Kvnugh. 2012, Long-Term Commercil GSHP Performnce Prt 2: Ground Loops, Pumps, Ventiltion Air nd Controls. ASHRAE Journl 54(7): Kvnugh, S.P., nd K. Rfferty Ground-Source Het Pumps: Design of geotherml systems for commercil nd institutionl buildings. Atlnt, GA: ASHRAE. Khn, M.H., nd J.D. Spitler Performnce Anlysis of Residentil Ground Source Het Pump System with Antifreeze Solution. Proceedings of SimBuild 2004, Boulder, Colordo August 4-6.

10 Klein, S. A. et l TRNSYS, trnsient simultion progrm. Solr Energy Lbortory, University of Wisconsin-Mdison, USA. Klein, S. A. et l EES: Engineering Eqution Solver. Mdison, WI: F-Chrt Softwre. Liu, X., M. Mlhotr, P. Im, B. Hbibzdeh Cse studies for GSHP demonstrtion projects in the US. IEA Het Pump Center, Newsletter, Vol. 33, No. 3. Nguyen, A Personnl communiction bout ntifreeze correction fctors. Nordmn, R., nd A. Zottl SEPEMO-Build - Europen project on sesonl performnce fctor nd monitoring for het pump systems in the building sector. REHVA Journl 48(4): Slmson Product Center. Access on Mrch th White, F.M Fluid Mechnics. 7th edition. McGrw-Hill. p.366.