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Project Info COMPLETE Project Title Central Valley Research Homes: Mayfair House 2018 Cooling Season and 2018-19 Heating Season Crawlspace Vapor Barriers & Variable Capacity Heat Pump Sizing Project Number ET18SCE1706-3 Investor Owned Utilities SCE End-use HVAC Sector Residential Project Year(s) 2018 - 2019
The Pacific Gas and Electric Central Valley Research Homes (CVRH) project is the product of multiple years of effort by leading energy efficiency researchers and represents a significant investment of funding from the California Energy Commission, California Investor Owned Utilities (IOUs), and industry.  The Energy Commission’s PIER program supported the first three years of testing in the four unoccupied homes (Mayfair, Grange, Caleb, and Fidelia) in Stockton, CA. Prime contractor Frontier Energy is leading the air-to-water heat pump (AWHP) research at one site and Bruce Wilcox and his subcontractor team is managing the three other test sites.


There were three objectives for the testing done at the Mayfair house in the summer of 2018 and winter of 2018-19.
  • Evaluate the need for a moisture barrier in a mechanically ventilated crawlspace. 
  • Compare the energy impact of two schemes for continuous ventilation of the house: a crawlspace exhaust fan and a bathroom exhaust fan.
  • Compare how variable capacity heat pump (VCHP) sizing affects energy use and electricity demand by testing 1, 1.5, and 2 ton VCHPs from the same manufacturer.
Project Results


Crawlspace monitoring found that even in the dry summer climate of Stockton with continuous active ventilation, a crawlspace vapor barrier is needed to control humidity. Industry standard practice recommends maintaining relative humidity below 60% to prevent mold formation.


Annual energy use projections show that the house at best used the same amount of heating energy when the crawlspace fan operated as when the bathroom fan operated, and at worst more energy when the crawlspace fan operated. The crawlspace exhaust fan warmed the crawlspace air by a degree or two, but did not reduce crawlspace humidity levels. We theorize that the crawlspace fan use did not translate to lower heating energy use because the air exhausted by the bathroom fan followed a path that kept it cooler than the air exhausted by the crawlspace fan.


VCHP system sizing is a complex issue with multiple interacting factors, including the range over which the system is capable of modulating capacity, and differences in onboard control programming that may or may not cause the system to operate efficiently at part load conditions. In general, the results of the sizing experiment suggest that sizing the VCHP to the smallest system with the capacity to meet Manual J loads for both cooling and heating should remain the recommended approach at this time.



Keyword Search:
Heat pump, HVAC, VCHP, all-electric, electrification

Project Report Document
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