Aug 9, 2012 HVAC
TROUBLESHOOTING HEAT PUMP SYSTEMS…R-22 VS R-410A
Unless you’ve been living under a rock for the past several years, you know R-22 is on the way out and R-410A appears to be the manufacturer’s weapon of choice for heat pump and comfort cooling equipment. If you’ve already encountered a 410A system and had a less than pleasant experience, possibly attempting to correct or understand what appeared to be abnormally high system pressures, your confusion may be with a misunderstanding of mechanical refrigeration, rather than the refrigerant.
Mechanical refrigeration is all about heat transfer and temperatures, especially boiling and condensing point temperatures. The whole point of a refrigeration system is that of creating a heat sink or low heat energy level, causing heat to transfer from a higher energy level. For comfort cooling applications, the indoor coil operates at a temperature lower than that of the indoor air temperature, and I’ll say in the 40ish degree range. When the system is in operation, the indoor air is pulled through the coil, where some of it’s heat is transferred to the coil. That heat is then carried to the outdoor coil, where it is transferred to the outdoor air. When heat pumps are operating in the heat cycle, the outdoor coil has a temperature less than the outdoor air temperature. Then the heat in the outdoor air transfers to the refrigerant in the outdoor coil, is carried to the indoor coil, where it is transferred to the indoor air. So, the dynamics of a mechanical refrigeration system simply control the refrigerant temperatures within the indoor and outdoor coils, maintaining a continuous process of heat transfer, in whatever direction is needed.
I don’t claim or even pretend to know, the engineering details necessary for the design of refrigeration systems. But I have a reasonably good idea of how they’re supposed to operate, relative to system pressures, subcooling and superheat, and particularly with comfort cooling and heat pump applications. And so long as I know what refrigerant the system uses, and have a way to convert pressures to saturated temperatures, I’m comfortable with the system. We’re all probably guilty of becoming familiar with system pressure measurements, and forgetting what we’re actually measuring, which is the saturated refrigerant temperatures in the evaporator and condenser coils. Once we see what those numbers are, we then measure the suction line and liquid line temperatures so superheat and subcooling values can be calculated. With the system pressures / saturated temperatures, superheat and subcooling values, we can make an intelligent decision about the operation of the system.
An R-22 system operating in the cool cycle on a hot summer day will usually run a suction, or low side pressure, of 75 psi or so. And the superheat could range from 5 to 15 degrees depending on the type metering device, equipment brand and outdoor temperature. An R-410A system would be running around 120 psi low side, but would have a similar superheat range, again depending on the metering device, brand and outdoor temperature. The difference in pressures is due simply to the difference in saturated temperature / pressure characteristics of the two refrigerants. So long as your gauges have a “temperature conversion scale” for the type refrigerant you’re working with, and you know what the evaporator temperature is supposed to be, you can analyze the system for proper charge and operation, whether or not the pressures are “familiar”.
Author: Wayne Shirley HVAC Tips
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