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Residential Variable Capacity Heat Pump Field and Lab Testing: Final Results. 20 November 2013 Ecotope. History.
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Residential Variable Capacity Heat Pump Field and Lab Testing: Final Results 20 November 2013 Ecotope
History • Inverter-driven compressor tech making increasing inroads (ductless systems now at 20,000 plus installs in NW); BPA has incented central ducted systems via PTCS on provisional basis • Advisory committee formed to guide research plan • Range of experience on committee • Interest in zoned systems, delivery temperatures • Timeline/budget limited research scope • Study summary • Heating season only • ‘Detailed’ (full capacity/COP) vs non-detailed sites • Combination of field/lab info (EPRI) • ASHRAE 152 duct model exercised plus SEEM for full season estimates
Major Findings – Expectations/Reality • VCHP performs 25-30% better than a single speed 7.9 HSPF heat pump on an annual basis (note nominal average HSPF for this product ~12). • Duct losses increased ~5% over a single speed heat pump • Overall system offers improved performance over single speed base cases • Heat pump sizing still matters • Auxiliary heat lockout control still matters
Field Deployment • Planning/refinement occurred through late 2012 • Field deployment set for late February, 2013 (six sites); central OR chosen for likelihood of remaining cold weather (about 24 potential sites) • Critical points measured • 5 minute metering for electricity usage (including air handler circuit power- CFM mapping) • One-time measurements of house heat loss (including blower door test (system sizing, heating season simulation)), duct area/R-values, duct leakage, system CFM (at least 3 points so CFM could be correlated with power), heat pump control settings
Airflow & Fan Power • Site 91009
Capacity and COP Calculations • Capacity determined by multiplying fitted airflow by coil temperature split • True RMS power is measured at the panel for both indoor and outdoor units and converted to Btu/hr • COP is ratio of capacity to input power at a given outdoor temperature • Following 2 graphics do not include duct losses
Compressor Response to Changing Heating Load • Low compressor speed: input power < 1.25 x observed minimum input • Medium compressor speed: anything in between low and high • High compressor speed: input power > 0.87 x observed maximum input
Air Handler Response to Changing Heating Load • Low fan speed: airflow < 1.25 x listed minimum airflow (comfort mode) • Medium fan speed: anything in between low and high • High fan speed: airflow > 0.87 x listed maximum airflow (comfort mode)
Operating Mode Summary • Fan and compressor speeds track one another • Given a compressor speed, there is a preferred fan speed • High compressor outputs almost never pair with low and medium fan • Low compressor speeds pair with both low and medium fan • Runtime Fractions:
Duct System Inputs • Duct leakage, normalized to fraction of air handler flow (which changes at different flows) • Duct R-value • Duct area • Buffer space temperature (measured only for supply buffer space) • ASHRAE 152 used to calculate distribution efficiency
Average Duct Performance and Calculated Duct Distribution Efficiency (DE) (common five week period)
Modeling VHCPs – Annual Performance • Annual performance estimated with SEEM • Simulation largely unchanged from September 2012 RTF presentation • Performance curve from catalogue data found to work well enough for systems modeled • Field study found that the operating modes pair fan and compressor speed (previous default assumption in simulation – remains unchanged)
Modeled VCHP and Duct System Efficiency (using SEEM for entire heating season)
Lab (EPRI) vs Field Results • Agreement on capacity and COP measurements generally good; more divergence for some cases • Lab tests done in EFFICIENCY mode • All sites in Oregon set up in COMFORT mode • Lab showed higher COPs as expected because of EFFICIENCY vs COMFORT mode • Possibility of variability for individual pieces of equipment, as well
Lab vs Field Comparison(2 ton system) Lab results Field results
Overall Findings • VCHP performs 25-30% better than a single speed 7.9 HSPF heat pump on an annual basis • Duct losses increased ~5% over a single speed heat pump • Overall system offers improved performance over single speed base cases • Heat pump sizing still matters • Auxiliary heat lockout control still matters
Next Possible Steps • Cost analysis. Collect data on installed costs and compare to annual estimates of savings. • More complete set of SEEM runs- additional comparisons to base cases (HP and/or EFAF) • Possible UES process (depends on cost analysis) • Further discussion of how system could be commissioned (PTCS)