Hybrid geothermal systems: less is more Lessons learned, impacts and tools IGSHPA Conference 2014 Scott Hackel Energy Center of Wisconsin www.ecw.org/hybrid
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
Ground source heat pump system Cooling load Heat rejected
Ground source heat pump system Heating load Temperature ( F) 100 60 20 0 5 10 15 20 Time (yr) Heat absorbed
Ground source heat pump system Cooling load Heat rejected
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
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)
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)
Monitoring Cashman and East CTA: Tobacco Lofts:
Validation GHX Model Within measurement uncertainty System Model Within typical design goals (2oF) 95 90 Temperature (F) 85 80 75 70 65 Measured Modeled 60 55 7/12 8/31 10/20 12/9 1/28 Time (hrs) 3/19 5/8 6/27
The bottom line Annual Costs ($/ft 2 ) 1.6 1.4 ) / ft2 1.2 ($ s t o C1.0 r a te W0.8 d n a y 0.6 e rg n E 0.4 0.2 0.0 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
Effective hybrid design/operation
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.
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
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
Focus on part-load pumping Size for it Control for it Consider multiple pumps 1.0 0.9 0.8 0.7 Tobacco CashmanLofts East CTA Cashman East CTA Part Load Ratio 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2000 4000 6000 8000 Hours
Control the tower Choose variable speed equipment Ramp equipment down quickly Tweak setpoints after occupancy Don t pull energy out of the ground!
To precool or not to precool? Precooling 0-5000 Start Precooling Start Time 23 1 2 3 4 5 Operate tower at night Not all night Electricity Electricity Usage Usage (kwh) (kw) (Δ, (Precooling - No Precooling) -10000-15000 -20000-25000 -30000-35000 -40000 Load 10% -45000 Load 50% -50000 In ideal case, can save 10%+ of energy cost for pumps/towers Careful: can also cause energy penalty.
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
Should we avoid heating hybrids? Heating dominated: Multifamily in Wisconsin Some complexity with boiler hybrid; could consider direct heat Preheat Baseboard Vestibules Basement UHs
More bottom line
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
The bottom line Energy and Water Cost ($/ft2) 3.0 2.5 2.0 1.5 1.0 0.5 Cost of Energy/Water Conventional HVAC GSHP System Hybrid GSHP System 0.0 East CTA Cashman Tobacco Lofts
The bottom line 2 ) / ft ($ rs y e a 0 2 - g s in 8.0 7.0 6.0 5.0 GSHP instead 3.0 of hybrid 5% 4% 1% S a v y c le C L ife 2.0 1.0 0.0-1.0-2.0 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
The bottom line: loads dependent A high-level study with one building: office building HyGSHP w/boiler GSHP HyGSHP w/tower Boiler/Tower
The other bottom line 9 Carbon Savings (lbs/ft 2 /yr) 8 7 6 5 4 3 2 46% 47% 19% 20% GSHP System Hybrid GSHP System 14% 11% Courtesy: NREL 1 0 East CTA Cashman Tobacco Lofts
Resources
HyGCHP
Additional resources Models HyGCHP Simulation: Energy Plus, TRNSYS, equest Sizing tools: GHLEPro, GLD2010 Limited guidance on supplemental device
Additional resources References Kavanaugh design basics OSU controls information Spitler Xu Others More info on this study: www.ecw.org/hybrid Full report Fact sheet
For more information www.ecw.org/hybrid Contact us to: Obtain a copy of the software. Obtain a copy of the full report. Ask a question. Scott Hackel shackel@ecw.org