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In this short podcast, Bryan explains what the heat of compression is and why we should care about it as HVAC/R professionals.

More heat is rejected in the condenser than absorbed in the evaporator coil, and that\u2019s because the compressor adds heat. That added heat is called \u201cheat of compression.\u201d That heat does NOT contribute to the net refrigeration effect (NRE), as it doesn\u2019t contribute to cooling.

When we compress something, we increase the system entropy during that process. Entropy is the waste and disorder associated with work. There is some inefficiency, which we see in the form of additional heat. So, the HVAC system needs to reject that additional heat of compression, and we can plot and track reversible changes by following lines of constant entropy.

As the temperature increases, the molecules begin moving more quickly. However, the refrigerant doesn\u2019t absorb many more BTUs in the compressor (in a properly operating system). The temperature spikes, but the compressor doesn\u2019t typically add a significant number of BTUs to the refrigerant.

Heat also enters the system via the suction line, which also doesn\u2019t contribute to the NRE. Long, uninsulated suction lines can absorb a lot of heat without cooling the space at all. That heat also has to be rejected in the condenser. So, short, well-insulated suction lines tend to absorb less heat.

When plotting the heat of compression, we\u2019re looking at BTUs added into the system in the compressor, discharge line, and suction line. BTUs that don\u2019t contribute to the NRE may fall under the \u201cheat of compression\u201d label, though the actual definition may vary by organization.

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Check out Eugene Silberstein\u2019s book, Pressure Enthalpy Without Tears, at https://escogroup.org/shop/itemdetail.aspx?ID=1445.\xa0

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