Two compressors are better than one. That's the message from HydroDelta, the latest manufacturer to announce a dual-compressor, ground-source heat pump. Most of the time the smaller of the two compressors can meet the house's heating or cooling load. Running the smaller unit closer to its capacity uses less energy. When the smaller compressor can't keep up, the larger one takes over.

And there is another efficiency booster. The evaporator and condenser coils are sized to match the larger compressor, so they are oversized for the smaller one. The dual compressors help HydroDelta's Meg-Tek heat pump reach very high efficiency with COPs up to 4.1 and EERs as high as 20.7.

Mega-Tek uses a permanent magnet, brushless DC motor. It can match the air flow to the capacity of the operating compressor. Most other ground source heat pumps offer water heating that operates only during space heating or cooling operation. As an option, HydroDelta offers dedicated water heating that uses a separate heating coil to heat water whenever it's needed.

Controlling operations is the job of the specially designed microprocessor control. The control receives seven temperature inputs: source water entering, source water leaving, domestic water entering, domestic water leaving and refrigerant in three locations.