Superheat & Subcooling

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CEO1
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Superheat & Subcooling

Postby CEO1 » Wed Mar 05, 2014 11:44 am

Superheat and subcooling are the terms used to describe two of a cooling system’s operating parameters. We generally rely on these numbers to evaluate system performance, as well as diagnose system problems. The values essentially provide us with information about what’s going on inside the evaporator and condenser coils. And depending on the metering device used in the system, one or the other number is the value used to determine optimum system charge.

If you wanted to define the words non-mathematically, superheat is the increase in temperature of the refrigerant vapor in the evaporator before it exits the coil, and subcooling is the decrease in temperature of the refrigerant liquid in the condenser before it exits the coil. The diagram below offers a visual illustration.

SuperheatSubcoolingPic.png


The two numbers are actually calculated temperature values, using simple arithmetic with saturated temperatures and tubing temperatures.

Normal operation always results in some percentage of the evaporator coil filled 100% with vapor and some percentage of the condenser coil filled 100% with liquid. Since the vapor starts out at the same saturated suction temperature, the vapor will take in heat or warm up, before it exits the evaporator coil. Likewise, the liquid starts out at the same saturated condensing temperature, so it will give up heat or cool down before exiting the condenser coil.

To calculate subcooling, subtract the liquid line temperature from the saturated condensing temperature: 110˚ – 100˚ = 10˚ F subcooling.

To calculate the superheat, subtract the saturated suction temperature from the suction line temperature. Which in the diagram is 50˚ – 40˚ = 10˚ F superheat.

Now, in the "real world", we don't generally measure superheat at the indoor coil. Most times, we're measuring the suction line temperature at the condensing unit, purely as a matter of convenience. And most mfg's service literature will provide target superheat values for suction line temperatures taken at, or near, the service valves.




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MechAcc
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Re: Superheat & Subcooling

Postby MechAcc » Tue Jun 02, 2015 4:38 pm

Oh please don't use turquoise colored font on a grey background. Cannot read it unless I highlight it. Thanks :shock:

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CEO1
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Re: Superheat & Subcooling

Postby CEO1 » Tue Jun 02, 2015 6:01 pm

MechAcc wrote:Oh please don't use turquoise colored font on a grey background. Cannot read it unless I highlight it. Thanks :shock:


We had the black background, had to revert to the lighter shade, and I missed some of those that needed editing...if you find another, let me know. :)

How you doing, Mech? Long time, no see... :)
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