ASHRAE Headquarters Building: GSHP vs. VRF systems

Transcription

1 Jeffrey D. Spitler Oklahoma State University ASHRAE Headquarters Building: GSHP vs. VRF systems Session C: Technical

2 Learning Objectives Understand how a GSHP system and VRF system compare when applied in the same building with very similar loads. Understand some of the real-world influences on system performance. 2

3 Acknowledgements Laura Southard Oklahoma State U. Xiaobing Liu Oak Ridge Nat. Lab. Financial Support GEO Southern Company US/China Clean Energy Research Center ASHRAE / Mike Vaughn 3

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7 A Living Laboratory Over 1000 measurement points 2-story office building, built in 1965 Renovated and enlarged in Open plan office design allows for more daylighting Three systems: Variable refrigerant flow system serving 1 st floor Ground source heat pump system serving 2 nd floor Dedicated outdoor air system serving both floors

8 First Floor / VRF System 17,213 ft 2 (1599 m 2 ) served by VRF system Not served by metered VRF system: Computer server room Rear staircase Entry foyer Served: Office space Mailroom Learning Center Two outdoor heat-recovery units (28 tons nominal capacity) 22 indoor FCU

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10 VRF Controls Single setpoint. Users can reset thermostats ±3 F System attempts to maintain setpoint, within ±1 F Individual units do not switch back and forth between heating and cooling, though. Adjacent units in open floor plan office do run in opposite modes.

11 Second Floor / GSHP System GSHP serves entire 2 nd floor + rear stairwell. Total floor area 15,558 ft 2. (1445 m 2 ) Office space and two conference rooms.

12 GSHP System 12 boreholes, 400 ft. deep 14 water-to-air heat pumps, 31.5 tons nominal capacity Heat pumps: Two-stage ECM fan motors, variable speed Staged controls: Separate heating/cooling setpoints 68 F/74 F typical Temperature deviates > 1.5 F: low-stage Temperature deviates > 2.5 F: high-stage Users can reset thermostats ±3 F

13 DOAS Provides partly conditioned ODA to both floors. Generally, always lower than room temperature. Sometimes overcools. Increases heating loads, decreases cooling loads.

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15 Qualitative Comparison of Loads 1 st floor and 2 nd floor: same lighting and plug load densities. Occupancy: 1 st floor (normal): 400 ft 2 /person 2 nd floor (normal): 259 ft 2 /person 1 st floor, learning center: used ~26 hours/month DOAS average flow rate: 1 st floor: 2560 CFM 2 nd floor: 1480 CFM

16 Qualitative Comparison of Loads Rooms on 2 nd floor have heat gains from roof. 1 st floor has more glass façade, but part of this is conditioned by nonmetered VRF systems. As a result: 1 st floor has higher heating loads. 2 nd floor has higher cooling loads. Cooling loads are much higher than heating loads.

17 Results Energy consumption Heating and Cooling Loads System COP and EER Why?

18 Total Monthly Energy Use Monthly Energy Use, kwh 20,000 18,000 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 GSHP VRF DOAS

19 Monthly Energy Use per ft GSHP VRF 0.30 Monthly Energy Use, kwh/ft

20 Avg. Power vs. Outdoor Temperature 2.0 GSHP VRF DOAS Average Power Use, W/ft Ambient Dry Bulb Temperature, F

21 July June 2013 Temperatures Number of hours Temperature ( F)

22 VRF Heating and Cooling 2.0 VRF Heating Cooling 1.8 Average VRF Power Use, W/ft Ambient Dry Bulb Temperature, F

23 GSHP Heating and Cooling Average GSHP Power Use, W/ft GSHP Heating Cooling Unallocated Ambient Dry Bulb Temperature, F

24 Avg. Power Cooling Only Average Power Use, W/ft GSHP VRF Ambient Dry Bulb Temperature, F

25 Avg. Power Heating Only Average Power Use, W/ft GSHP VRF Ambient Dry Bulb Temperature, F

26 A moderate day April 3, 2013 Morning low: 43 F Afternoon high: 63 F

27 Power Use VRF GSHP 0.8 W/ft :00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00

28 GSHP Zone Temperatures Zone Temperature, F Zone 207 Zone 204 Zone 209 Zone 224C Zone 224D Zone 206 Zone 215A Zone 215B Zone 215C Zone 224B 69 7:00 10:00 13:00 16:00 19:00

29 VRF Zone Temperatures (Cooling) Zone Temperature, F Zone 116 Zone 117 Zone 119 Zone 120 Zone 134B Zone 134C Zone 134D Adjacent zone was heating 69 7:00 10:00 13:00 16:00 19:00

30 VRF Zone Temperatures (Heating) Zone Temperature, F Zone 103 Zone 104 Zone Zone 109 Zone 110 Zone 111 Zone 112 Zone 134A Zone Zone 140A Zone 140B Zone 140C 69 Zone 145 Zone 147 7:00 10:00 13:00 16:00 19:00

31 Why is GSHP So Much Better? Source temperatures. Equipment efficiency at actual source temperatures. Apparent control issue most VRF units run most of the time under moderate load conditions. Unnecessary (?) simultaneous heating and cooling. Loads are different. (Yes, but how much?)

32 Source Temperatures Ambient air Ground Loop Water Supply Temperature, F /1/11 12/31/11 7/1/12 12/31/12 7/2/13

33 Heating and Cooling Provided How much heating and cooling are provided by each system? Heat pumps and 14 VRF FCUs: Need air flow rate + temperatures and (for cooling) humidities.

34 Actual Available Measurements Airflow from flow hood measurements (VRF system changed control boards and flows in April 2012) Discharge air temperature Zone air temperature Zone air humidity

35 Estimated Quantities Entering and discharge air humidities GSHP system, from measurements in one zone Entering air humidity ratio without DOAS with DOAS 1:1 line Zone humidity ratio Discharge Air Humidity Ratio Zone 215B data 78% relative humidity Discharge Air Temperature, F VRF system, from mfr. data, SHF=f(EAT, ODAT); spot-checked by us

36 Uncertainty Analysis Details in 2nd ASHRAE Journal paper. Accounts for: Sensor errors Approximations like using the zone humidity to estimate entering air humidity Aggregation (reduces uncertainty) Final uncertainties for entire systems. GSHP VRF Cooling +14/-11% ±5% Heating ±7% ±4%

37 Monthly Heating Provided Heating Provided, kwh/ft GSHP VRF 0.0

38 Monthly Cooling Provided Cooling Provided, kwh/ft GSHP VRF

39 Heating and Cooling Provided For July 2011 March 2012: GSHP provides 62% less heating than VRF GSHP provides 6% more cooling than VRF GSHP System Cooling Provided (MBTU/sq. ft.) Heating Provided (MBTU/sq. ft.) VRF System

40 Monthly System Heating COP 6 5 GSHP VRF Heating System COP

41 Monthly System Cooling EER Cooling System EER GSHP VRF

42 Cooling Performance GSHP VRF System Cooling EER OA Temp, F

43 Heating Performance GSHP VRF System Heating COP OA Temp, F

44 Counterintuitive Trends GSHP system heating COP goes up from 1 st winter to 2 nd winter. For both systems, system cooling EER increases with increasing ODA temperature (to a point) For GSHP system, performance increases with higher loads. (next slide)

45 Why is GSHP EER Better in Hot Months? 18 Monthly GSHP System Cooling EER ,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 Monthly Cooling Provided by GSHP System, kwh

46 Why Does GSHP Heating COP Improve From 1st Year to 2nd Year? Pump 6 control: differential setpoint on loop reduced from 20 psig to 8 psig GSHP VRF Heating System COP Measured Power, kw psi loop dp 15 psi loop dp Loop Flow, GPM

47 Why Does GSHP Heating COP Improve From 1st Year to 2nd Year? Pump control: differential setpoint on loop reduced from 20 psig to 8 psig Measured Power, kw psi loop dp 15 psi loop dp Loop Flow, GPM

48 Why Are Trends Counterintuitive? For GSHP: Entering fluid temperature does not correspond directly to outdoorair temperature. Higher run time fractions correspond to less pumping energy and parasitic losses (per unit cooling or heating provided) For VRF (we speculate): Simultaneous heating and cooling may not be as efficient as imagined.

49 Conclusions GSHP system significantly outperforms VRF system. For July 2011-March 2012: GSHP VRF Heating System COP 3.3 ± ±0.1 Cooling System EER 14.5 ± ±0.4

50 Conclusions (Why?) GSHP has more favorable source temperatures. Heat pump unit efficiency is higher than VRF efficiency over actual range of operation. VRF controls lead to unnecessary (?) heating and cooling.

51 Bibliography Southard, L.E., X. Liu, J.D. Spitler Performance of HVAC Systems at ASHRAE HQ Part 1. ASHRAE Journal. September 2014, 56(9): Southard, L.E., X. Liu, J.D. Spitler Performance of HVAC Systems at ASHRAE HQ Part 2. ASHRAE Journal. December 2014, 56(12): Spitler, J.D., L.E. Southard, X. Liu Final Report - Performance of the HVAC Systems at the ASHRAE Headquarters Building. Available online at: 51

52 Questions? Jeff Spitler 52