Hybrid geothermal systems: less is more

Transcription

1 Hybrid geothermal systems: less is more Lessons learned, impacts and tools IGSHPA Conference 2014 Scott Hackel Energy Center of Wisconsin

2 Today s discussion The basics of the hybrid approach Buildings we studied, and how we studied them Design and operational lessons learned Economic / environmental impacts of the hybrid approach Resources for you

3 Ground source heat pump system Cooling load Heat rejected

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

5 Ground source heat pump system Cooling load Heat rejected

6 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

7 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)

8 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)

9 Monitoring Cashman and East CTA: Tobacco Lofts:

10 Validation GHX Model Within measurement uncertainty System Model Within typical design goals (2oF) Temperature (F) Measured Modeled /12 8/31 10/20 12/9 1/28 Time (hrs) 3/19 5/8 6/27

11 The bottom line Annual Costs ($/ft 2 ) ) / ft2 1.2 ($ s t o C1.0 r a te W0.8 d n a y 0.6 e rg n E Conventional HVAC GSHP System $12,000,000 Hybrid GSHP System $11,000,000 $12,000,000.for East CTA $10,000,000 $11,000,000 $10,000,000 $9,000,000 $8,000,000 $9,000,000 GSHP Hybrid Conventional $8,000,000 GSHP Hybrid Conventional First Costs East CTA Cashman Tobacco Lofts Cooling Tower Cost GHX Cost Other Costs

12 Effective hybrid design/operation

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

14 Parallel approach (not monitored) Simple on-off or VS tower based on downstream temp See Xu (2007) for more on control Need this approach if: ground loop << building load

15 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

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

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

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

19 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

20 Should we avoid heating hybrids? Heating dominated: Multifamily in Wisconsin Some complexity with boiler hybrid; could consider direct heat Preheat Baseboard Vestibules Basement UHs

21 More bottom line

22 The bottom line 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Energy Energy End Uses Tobacco Lofts Cashman East CTA Heat Pumps Pumping Supplemental Courtesy: Lundy, Ann

23 The bottom line Energy and Water Cost ($/ft2) Cost of Energy/Water Conventional HVAC GSHP System Hybrid GSHP System 0.0 East CTA Cashman Tobacco Lofts

24 The bottom line 2 ) / ft ($ rs y e a g s in GSHP instead 3.0 of hybrid 5% 4% 1% S a v y c le C L ife Life Cycle Savings, over conventional GSHP System Hybrid GSHP System Cashman East CTA Tobacco Lo0s 4.0 Hybrid instead of Conven9onal 10% 12% 9% East CTA Cashman Tobacco Lofts East CTA, institutional economics

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

26 The other bottom line 9 Carbon Savings (lbs/ft 2 /yr) % 47% 19% 20% GSHP System Hybrid GSHP System 14% 11% Courtesy: NREL 1 0 East CTA Cashman Tobacco Lofts

27 Resources

28 HyGCHP

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

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

31 For more information Contact us to: Obtain a copy of the software. Obtain a copy of the full report. Ask a question. Scott Hackel shackel@ecw.org