Head-Reducing Valves

Designing of systems of air conditioning and refrigeration systems using air cooling, condensing units includes two key issues that must be addressed if the system will work reliably and economically. These problems are the high environmental and low ambient operation. If the condensing unit correctly size, it will normally operate under extreme ambient temperatures. However, most modules will be required to work at ambient temperatures below their design dry bulb temperature during most of the year. Thus, the solution to low ambient operation more complicated.

Without a good head-pressure control under low ambient operation, the system may have running, cycle and off-cycle issues. Two runningcycle issues of primary interest:

Pressure (134a pressure diagram differential thermostatic expansion valve port affects the rate of refrigerant flow. Thus, low pressure, as a rule, leads to the insufficient refrigerant is fed into the evaporator.
Any system using hot gas defrost or compressor capacity control must be normal pressure to work properly. In any case, the refusal of sufficient pressure will result in low suction pressure and/or iced dimensions of the evaporator.

The main off-cycle problem is the possible inability to obtain a system of on-the-line, if the refrigerant was moved to the condenser. The evaporator pressure can build up to the cut-in point of the low-pressure control. The compressor does not start, even though the cooling required. Even if the evaporator pressure builds up to cut in setting, insufficient flow through TEV will cause low suction pressure, which results in the compressor.

There are unregulated and regulated methods of head control of pressure on the head. Each method uses two valves designed specifically for this type of application. Low-ambient conditions occur during the autumn-winter-spring operations, air cooling system, with a resultant drop the pressure of condensation. Then, valveР‚s to contain enough of condensed liquid refrigerant to make part of the surface of the condenser inactive. This reduction is active condensation surface raises the condensing pressure and plenty of fluids-line pressure for normal system operation.

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