Below is the information from ORNL on the frostless heat pump.
Who know more about it? I can't send email to the researcher.
Any one can give comment on it? thx.
http://www.ornl.gov/sci/btc/apps/frostlesspump.htm
Frostless Heat Pump
During a substantial portion of the heating season in temperate climate regions, where most heat pumps are installed, frost will build up on a conventional heat pump ’s outdoor heat exchanger coil (when the ambient temperature is below about 40°F). Shortly after this frost accumulation begins, the temperature of the indoor heat exchanger coil – and of the air supplied by it to heat the indoor space – starts to decrease. When temperature, time, or demand controls mandate defrosting of the coil, a four-way valve temporarily reverses the heat pump cycle. During the reverse-cycle defrost period, heat is taken from inside the house (from air blown across the indoor coil) and is pumped outside to raise the temperature of the outdoor coil sufficiently to melt the accumulated frost. In an attempt to compensate for this heat loss and to temper the resulting decrease in the temperature of the air supplied to the indoor space, conventional systems must energize supplemental resistance- heating elements. However, even with substantial power flowing through the heating elements, the indoor air temperature is temporarily lowered – resulting in what is commonly called "cold blow," a major concern of heat pump manufacturers and consumers. The term "cold blow" in heat pumps means the indoor supply air temperature by the heat pump is usually lower than our skin temperature which gives us a "cold blow" feeling.
The characteristics of the defrosting cycle just described (a) reduces occupant thermal comfort because of the cold blow effect and (b) decreases system reliability because of the periodic cycle-reversing stresses imposed on components such as the four-way valve, the compressor, and the resistance- heating elements.
The Frostless Heat Pump addresses, in a cost-effective manner, all the concerns outlined above by drastically reducing the frequency of defrost cycling (by a factor of 5 in the Knoxville, Tennessee area) and by eliminating cold blow. The key innovation is the addition of heat to the accumulator, which increases the temperature of the refrigerant entering the outdoor coil. The innovation is based on the principle that adding heat internally into a Rankine cycle can shift the heat absorption and rejection temperatures upwards. Tests have shown that the addition of moderate amounts of heat dramatically retards frost formation over a substantial range of outdoor ambient conditions where frost is likely to form. Most of the heat added to the accumulator is delivered to the indoor coil, providing increased heating capacity and improved thermal comfort in the form of higher air temperatures entering the indoor space.
Because of its increased heating capacity, the Frostless Heat Pump is likely to meet the heating demand of a house sooner and therefore cycle off sooner, before the outdoor coil requires defrosting. If the outdoor ambient temperature is lower than about 30°F, adding a moderate amount of heat to the accumulator may not retard frost formation sufficiently to avoid cycle reversing. However, when the Frostless Heat Pump does require cycle reversing, the indoor fan is shut off, thus avoiding "cold blow" draft and heat removal from the conditioned space. Heat to defrost the outdoor coil is taken from the heat provided to the accumulator.
In summary, in comparison with conventional heat pumps , the Frostless Heat Pump increases occupant thermal comfort, increases system reliability, and reduces power surges.
