Geothermal Heat Pump Systems: From Basics to Hybrids

Transcription

1 Geothermal Heat Pump Systems: From Basics to Hybrids January 17, 2013 Scott Hackel Energy Center of Wisconsin

2 Today s discussion The basics of geothermal The hybrid approach, our recent study Design and operational lessons learned Economic / environmental impacts of the geothermal and hybrid approaches Resources for you

3 What we do Energy analysis Geothermal project assistance Daylighting studies Campus energy planning Economic analysis Field research and evaluation Education and training Offices in Madison, Chicago, Minneapolis

4 Geothermal: The Basics Earth absorbs solar energy Heat is stored in the earth Constant temp below the frost line Exchange/storage medium for heat transfer Closed loop system

5 Field Types Vertical bores: 300 deep common, >600 possible Smallest footprint Horizontal bores: 6-10 deep Can be stacked layers Typically the largest footprint Lake coupled Medium footprint High cost: need other reason to justify the lake

6 System/ground interaction

7 System/ground interaction

8 Loop Design

9 Distributed Geothermal Heat Pumps

10 Central Geothermal Any size available Some modular, ton units

11 Plumbing and geothermal Domestic hot water often just preheat Desuperheater (smaller units) Water-to-water heat pumps Heat recovery chillers (central geo)

12 Costs Cost Percentile 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Wisconsin study, 2009 Cost Difference ($/ft 2 )

13 Hybrid Geothermal

14 Ground source heat pump system Cooling load Heat rejected

15 Temperature ( F) Ground source heat pump system Heating load Heat absorbed Time (yr)

16 Ground source heat pump system Cooling load Heat rejected

17 Hybrid ground source heat pump A typical system Cooling dominated Coupled hydronic loops Series supplemental device Dedicated supplemental pump

18 The buildings (cooling dominant) Cashman Equipment 300k ft 2 equipment dealer in Henderson, NV Distributed heat pumps Dedicated outdoor air GHX: 144,000 ft Towers: 500 tons (var. spd. fluid coolers) Courtesy: SH Architecture

19 The buildings (cooling dominant) East Career and Technical Academy 250k ft 2 vocational high school in Las Vegas, NV Courtesy: SH Architecture Distributed heat pumps GHX 168,000 ft Towers: 333 tons (two spd. fluid coolers)

20 The buildings (heating dominant) Tobacco Lofts 74k ft 2 multifamily building in Madison, WI Distributed heat pumps Dedicated outdoor air GHX: 11,300 ft Boiler: 199 MBH (condensing)

21 Temperature (F) Data Collection and Validation Modeled Measured Feb 2-Apr 22-May 11-Jul 30-Aug 19-Oct 8-Dec 27-Jan

22 Annual Costs ($/ft 2 ) Energy and Water Cost ($/ft2) The bottom line Conventional HVAC GSHP System $12,000,000 Hybrid GSHP System $11,000,000 $12,000,000 $10,000,000 $11,000,000.for East CTA Cooling Tower Cost GHX Cost Other Costs $10,000,000 $9,000,000 $8,000,000 $9,000,000 $8,000,000 GSHP Hybrid Conventional GSHP Hybrid Conventional 0.0 First Costs East CTA Cashman Tobacco Lofts

23 Effective hybrid design/operation

24 Lessons learned Cashman/East CTA No antifreeze, low DP Towers ramped together Tower downstream Simple, circuited loops, decoupled To Separate Borefields Flow Meas. Temp. Meas.

25 Lessons learned Tobacco Lofts Flow rate measurement Temperature measurement 100% / 60% pumping Boiler downstream Pump T2 T3 T4 GHX Bypass Blr. T1 T5 Buildings Allow bypass to switch direction Condensing boiler

26 Extra care needed in sizing Ground Heat Exchanger actual optimized Supplemental Device actual optimized Cashman 144,000 ft 86,000 ft 500 tons 430 tons East CTA 168,000 ft 92,000 ft 333 tons 400 tons Tobacco Lofts 10,900 ft 7,400 ft 199 MBH 300 MBH Primarily the GHX is oversized Systems oversized in general

27 Pumping is significant Pumping energy: (% of HVAC) Cashman: 7% East CTA: 12% T. Lofts: 21%

28 Focus on part-load pumping Part Load Ratio Size for it Control for it Consider multiple pumps Tobacco Lofts Cashman East CTA Cashman East CTA Hours

29 Control the tower Choose variable speed equipment Ramp equipment down quickly Tweak setpoints after occupancy Don t pull energy out of the ground!

30 To precool or not to precool? Electricity Usage (kwh) (D, Precooling - No Precooling) Electricity Usage (kw) (Precooling - No Precooling) Precooling Operate tower at night Not all night Start Precooling Start Time Load 10% Load 50% In ideal case, can save 10%+ of energy cost for pumps/towers Careful: can also cause energy penalty.

31 Other control learnings Boiler On setpoint should be ~5 10 o F below the GHX 40 o F optimum at Tobacco Lofts Facility staff should maintain this setting

32 More bottom line

33 The bottom line Energy and Water Cost ($/ft2) Cost of Energy/Water Conventional HVAC GSHP System Hybrid GSHP System East CTA Cashman Tobacco Lofts

34 The bottom line Life Cycle Savings - 20 years ($/ft 2 ) Life Cycle Savings, over conventional GSHP System Hybrid GSHP System Cashman East CTA Tobacco Lofts 4.0 Hybrid instead of Conventional 10% 12% 9% GSHP instead of hybrid 5% 4% 1% East CTA Cashman Tobacco Lofts East CTA, institutional economics

35 The bottom line: loads dependent Hybrid GSHP instead of Conventional GSHP instead of Conventional Cashman Building Life Cycle Savings, 20 years ($/ft 2 ) Balanced buildings benefit less

36 The bottom line: loads dependent A high-level study with one building: office building HyGSHP w/boiler GSHP HyGSHP w/tower Boiler/Tower

37 Carbon Savings (lbs/ft 2 /yr) The other bottom line % 47% 19% 20% GSHP System Hybrid GSHP System 6 Courtesy: NREL % 14% 1 0 East CTA Cashman Tobacco Lofts

38 Resources

39 HyGCHP

40 Additional resources Models HyGCHP Simulation: Energy Plus, TRNSYS, (equest?) Sizing tools: GHLEPro, GLD2010 Limited guidance on supplemental device

41 Additional resources References Kavanaugh design basics OSU controls information Spitler Xu Others More info on this study: Full report Fact sheet

42 For more information Contact us to: Obtain a copy of the software. Obtain a copy of the full report. Ask a question. Scott Hackel [email protected]