Sub-Cooling & Super-Heat in Refrigeration

sub-­‐cooling is a temperature below saturated pressure-­‐temperature. Sub-­‐cooling is a measurement of how much liquid is in the condenser. In air condi0oning, it is important to measure sub-­‐cooling because the longer the liquid stays in the condenser, the greater the sensible (visible) heat loss.

Low sub-­‐cooling means that a condenser is empty. High sub-­‐cooling means that a condenser is full. Over filling a system, increases pressure due to the liquid filling of a condenser that shows up as high sub-­‐cooling.

Sub-Cooling

To move the refrigerant from condenser to the liquid line, it must be pushed down the liquid line to a metering device. If a pressure drop occurs in the liquid line and the refrigerant has no sub-­‐cooling, the refrigerant will start to re-­‐vaporize (change state from a liquid to a vapor) before reaching the metering devise.

How to Measure Sub-­‐cooling

Get the refrigerant satura0on pressure-­‐temperature. Take a pressure reading of the liquid line leaving the condenser. Refrigerant satura0on temperature is the pressure-­‐temperature, when the refrigerant is turning from a high-­‐pressure vapor into a high-­‐pressure liquid (giving up heat). At satura0on pressure-­‐temperature, both liquid and vapor are at the same temperature.

  • Convert pressure to temperature with a P/T chart.
  • Take a temperature reading at the leaving liquid line of the condenser.

Compare both, the saturated temperature and leaving liquid line temperature. Subtrac0ng one from the other, the difference is the amount the refrigerant has cooled past saturated temperature.

How to Measure Evaporator Superheat

Get a pressure reading of the suc0on line leaving the evaporator to get refrigerant satura0on pressure-­‐temperature. Refrigerant satura0on temperature is the pressure-­‐temperature, when the refrigerant is turning from a low-­‐pressure liquid to a low-­‐pressure vapor (absorbing heat). At satura0on pressure-­‐temperature, both liquid and vapor are at the same temperature.

Convert pressure to temperature with a P/T chart. If reading is obtained at the compressor, not at the evaporator line leaving, you may have to add a few pounds of pressure due to pressure drop in the suc0on line.

Take a temperature reading at the leaving suc0on line of the evaporator. Compare both, the saturated temperature and the leaving suc0on line temperature. Subtrac0ng one from the other, the difference is the amount the refrigerant gas has heated past saturated temperature.

Read also, Refrigeration P/T Chart Tutorial

About GSM

Hassan is a HVAC & Refrigeration and Technician. He specializes on Electrical Engeneering and Green Energy solutions

View all posts by GSM →

One Comment on “Sub-Cooling & Super-Heat in Refrigeration”

Comments are closed.