The development of the VSGSHP is motivated by several needs that cannot be completely fulfilled by constant-speed GSHPs. In cold-climate residential installations, the design heating requirement (DHR) often exceeds the design cooling requirement (DCR). If a single-speed unit is selected to meet the DHR, it will be oversized in cooling. This will cause excessive cycling, which may result in poor efficiency and latent cooling capability. If the unit is sized to meet the DCR, a large amount of auxiliary heating will be required to meet the DHR. This will result in high winter demands and larger required electrical service capacities. Variable-speed equipment has the potential for dealing with these problems. This type of equipment can also improve comfort levels and be integrated to effectively heat water with waste heat (cooling mode) or with excess capacity (heating mode) or on demand when air heating or cooling is not needed.

The design of the VSGSHP attempts to:

• improve the heating capacity in order to eliminate the need for auxiliary heating;

• reduce energy consumption compared to constant-speed ground-source heat pumps and variable-speed air heat pumps;

• eliminate the high cooling demand characteristic of variable-speed air heat pumps;

• provide near-continuous operation with a limited number of on-off cycles and abrupt speed changes;

• improve water-heating capability and efficiency compared to existing integrated appliances;

• maintain high heating-mode air delivery temperatures (even at start-up);

• enhance latent cooling effectiveness, especially during mild loading periods; and

• simplify control schemes compared to existing variable-speed heat pumps.