Seasonal Performance Evaluation Procedures for Domestic Electric Driven Heat Pump's and Air Conditioner's.
Seasonal Performance Evaluation Procedures for Domestic
Electric Driven Heat Pump's and Air Conditioner's.
Didion, D. A.
Japanese Association of Refirgeration, 1988 Annual
Meeting. March 1988, Tokyo, Japan, 1988.
heat pumps; air conditioning; performance evaluation;
vapor compression; refrigerants; equations; temperature;
Virtually all of the residential and commercial heat
pumps available in today's market operateDT on the same
fundamental principles as do, that of the vapor
compression cycle. Also, virtually all of these systems
use fluorocarbon compounds as a working fluid and have a
constant speed positive displacement compressor with
leaf spring valves. This concept has been continuously
developed throughout this century and has served society
well; however, it contains a couple of inherent
limitations which cause any particular design to perform
somewhat less than ideally. The first and most
significant of these limitations is due to the fact that
a refrigerant's density is proportional to its pressure.
Therefore, when the evaporator temperature is required
to be decreased, the saturation pressure must also be
decreased with a corresponding reduction in the
circulating refrigerant suction density, causing a loss
in system capacity. This capacity loss is accented by
the use of constant speed piston compressors whose
valves operate on a differential pressure between the
interior cylinder conditions and either the suction or
discharge line pressures. If either the condenser or
evaporator temperature conditions increase or decrease,
respectively, less valve open time will exist per stroke
and thus less refrigerant will be pumped; leading to an
additional loss in capacity. This capacity reduction is
particularly significant in the heat pump heating
application for residences since it occurs
simultaneously with an increase in building transmission
(and thus heat pump) load. Of course, this overall
decrease in refrigerant aass flow rate which causes the
decrease in capacity also causes a decrease in
compressor work. However, since the pressure difference
or lift has increased the worle per unit mass of
refrigerant has increased and thus the compressor work
never decreases as such as the capacity, resulting in a
net decrease in heat pump efficiency or coefficient of
perforuance (COP). This study state part loael phenomena
has the most significant influence on the aaasonal
performance of today's heat pumps and thua must be
determined most carefully in any evaluation procedure.