3977 -- An Experimental Comparison of Two-Speed and Single-Speed Geothermal Heat Pumps PDF

Ground-coupled or geothermal heat pumps have become more accepted as an energy-efficient way to heat and cool houses. Multiple-speed heat pumps offer even greater efficiencies than conventional single-speed systems that must cycle when the load is less than maximum capacity. To better understand multiple-speed geothermal heat pump operation, a two-speed water-to-water heat pump was installed in parallel with an existing single-speed unit in a residence located in Moscow, Idaho. Both heat pumps were tested in heating mode using a sub-slab ground coil as the source. Both short-term transient tests and 16-day operational tests were performed with each heat pump during the winter of 1993-1994. Results show an average 14% increase in coefficient of performance (COP) for the low-speed operation compared to high-speed results for the two-speed unit. Also, it was found that shorter cycle times tend to improve performance, especially for larger capacity heat pumps.

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