Thread: WonderFridge
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Old 08-21-16, 09:15 AM   #6
jeff5may
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r600a is a little lower pressure than r-134a on the pt curve. When the freezer is freezing, there is actually less than atmospheric pressure in the evaporator and suction side of the circuit. As box temperature falls, so does evaporator pressure. At design minimum freezer box temperature, the evaporator may be operating with half a bar of vacuum.

The condenser side of the circuit follows room temperature. At normal room temperatures, the high-side pressure is usually in the 2 to 3 bar range during operation. This relatively low pressure is the reason most refrigerators last many decades before they develop a refrigerant leak. Even a badly fatigued or corroded run of tubing will hold this amount of pressure until it literally crumbles apart.

The condenser has one main purpose: move heat to ambient air. As long as it is warmer than room temperature and airflow is not obstructed, it is doing its best. Even if airflow is somewhat blocked, it still does a good job, as manufacturers routinely oversize this hx.

Trying to improve condenser performance is challenging with refrigerators. Due to the low compression ratio the compressor works against (2 to 3 bar), lowering condensation temperature doesn't have much energy saving effect. On large, commercial walk-in freezers, the most common upgrade is a txv, which matches up evaporator temperature and flow rate of the compressor to save energy. On residential iceboxes, the txv is considered an unnecessary extra moving part that can fail.
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