Geothermal Heat Pumps use the same mechanical principals as air to air. Except geothermal heat pumps use water and earth to transfer heat. The ground temperature remains relatively constant all year round providing the desired heating and cooling temperature. We find that the best way to go is water base fluid circulated through plastic tubing into wells (a closed loop geothermal system). 95% of geothermal heat pumps in the US are water based systems. Geothermal heat pumps can reduce energy consumption by over 40% compared to air to air heat pumps, and over 70% compared to electric heat strips. They are 48% more efficient then the best gas furnace on a source fuel base. They are 75% more efficient then fuel oil furnaces. So you would think that it would be a no brainer in this industry to use geothermal heat pumps. Change is slow and new technology is a hard sell.
Mitsubishi Electric new technology on air to air heat pumps uses advanced hyper heating inverter (H2I) technology. These heat pumps can operate efficienly in outdoor temperatures well below 0. How it works is Mitsubishi Heat Pumps use FE Compressers that use a rare earth magnet rotor to reduce compresser energy consumption while producing more heat . Way to go Mitsubishi Electric! Hope this helps.
Heat Pumps
There are two types of heat pumps, air to air and geothermal. Air to air is the most used; its source of cooling and heating is the outside air. It uses a reversing valve and two expansion devices. The reversing valve changes the refrigerant flow. The therory on this principal is that heat transfer will move from higher temperatures to lower temperatures allowing the heat transfer coil to be kept at a lower temperature. The surrounding air will pick up heat making the evaporator coil and the condenser coil the heat transfer devices. The problem with air to air heat pumps is deminished capacity. When the temperature outside drops so does the output. These heat pumps are best suited for southern climates. The problem that we have found is the sizing of the auxillary heat (heat strips). The heat strips should be sized for the heat load for heating. For example: if the loss is 60,000btu, and 1kw is equal to 3,413btus,then the heat strip should be 20kw, equal to 68,260btus of heating. A 15kw heater is equal to 51,195btus of heating, some customers would be happy with that. So the ideal heater would be 68,260btus of heating. When using air to air heat pumps the heat strip sizing is everything.