REFRIGERATION AND AIR CONDITIONING Thermostatic Expansion Valves - What is a BTU

Thermostatic Expansion Valves -  What is a BTU

Thermostatic Expansion Valves

 -  Thermostatic Expansion Valves :

These are also referred to as TEV’s.  There are really only two kinds of TEV’s:

1.    Internally Equalized
2.    Externally Equalized

Internally Equalized TEV’s has only two ports: the inlet and the outlet.  It is used with evaporators that also have one inlet and the refrigerant flows back and forth until it reaches the one and only outlet to the evaporator.

Externally Equalized TEV’s has an Inlet and Outlet and a ¼” Equalizer Port on the side of the valve where a ¼” line runs from the end of the Evaporator to the TEV.  This Valve is used on the Evaporator with multiple feeder tubes at the start of the Evaporator.  When the refrigerant leaves the Outlet of the Valve, it enters a Distributor that distributes the refrigerant into several smaller tubes that go to the beginning of the Evaporator.  This Evaporator has a circuit for each Feeder tube the refrigerant now has a shorter distance to travel as it  exits the Evaporator where each circuit to reach a common header pipe that now becomes the suction line.  This         shorter distance is where the equalization comes end to allow for a faster Responding Valve.    It has been my experience that Freezers work best with a Maximum Operating Valve (MOP) and should never be used with a suction line press valve at the compressor. This has a maximum set pressure of usually 30 lbs to help keep the load of the compressor after defrost.


-    What is a BTU?

A BTU is to cooling what horsepower is to a car engine.  It is the way we measure the load of an air conditioning or refrigeration system.  BTU is an abbreviation for British Thermal Unit.  A BTU is the measure of the amount of heat that is required to raise one pound of water 1degF in temperature.  These measurements are usually in increments called Tons. Therefore, 12,000BTU’s = 1 Ton.
This is a detailed as we need to get as others have done all of the heavy lifting. There are charts available for each brand of compressor or unit chosen.  Other resources are load calculation books and software programs that can assist us in sizing any building, house, cooler and freezer.

A couple of things you do need to know other than the size is if there are any glass doors in the freezer and coolers.  Glass doors really eat up BTU’s. The second is always matching the BTU to a temperature of at least 10 – 15 deg F below the desired room or box.  This will allow you to know that there are enough BTU’s to allow the Evaporator to be colder than needed.  If it is not, the box will stall and never get to the desired temperature.

                                      abo bahaa eddine


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