What is the best method and location to determine evaporator coil temperature?
evaporator coil temperature
walker447
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It's coldest where the liquid refrigerant enters the coil from the metering device and warmest where the superheated vapor leaves the coil. Usually a 15-30° difference between in & out so all the way through the coil it keeps getting warmer.
I want to know that my coil is about 45 degrees so that I get very good dehumidification. What is the best way to determine if coil is indeed cold enough to dehumidify and not so cold as to freeze?
I have a Lennox 4 ton CBX32MV air handler with Harmony III zone control. The Harmony III has an air discharge sensor that turns off the compressor if the AIR temperature is below 45 degrees.
Many thanks.
I have a Lennox 4 ton CBX32MV air handler with Harmony III zone control. The Harmony III has an air discharge sensor that turns off the compressor if the AIR temperature is below 45 degrees.
Many thanks.
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Again, the coil temp increases as the refrigerant goes through the coil. If you measure it right off the TXV, you'll find the coldest point. With a TXV, the refrigerant leaving the coil on the insulated line is usually about 15° warmer. Usually when a tech is checking the system, the leaving temp is what he's looking at. The temp of the coil will also depend on the load on the coil. Warm & muggy inside, the coil will be warmer. I keep my house ice cold with discharge air often 46-48° so my coil is very cold.
What "leaving temperature" on the evaperator would you be looking for when setting up a system for best dehumidification? Or should I just adjust airflow to get discharge air temperature just above 45 degrees to prevent the discharge air sensor on the Harmony III from shutting off the compressor?
System is checked and serviced each year on a hot and humid day by a qualified and conscientious professional. Humidity in old house is around 45% RH even though I have short run times of less than twenty minutes per hour due to over sized system on hot/humid days. (about thirteen minutes at night) My wife likes to keep the temperature around 76-77.
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Sounds like you should not change anything. I prefer using the suction pressure to determine the coil temperature. Go for a 45^F coil by converting the suction pressure to the boiling point of the specific refrigerant. The air temp off the coil will be 5-7^F warmer than the coil.
Hope this helps.
Regards Teddy Bear
Hope this helps.
Regards Teddy Bear
Thanks for reply and I have enjoyed your many comments concerning humidity on this forum.
I have no way to measure the suction pressure so I will assume the air temp off the coil, as you mention, will be 5-7^F warmer than the coil. This information is very useful.
Currently the compressor activates stage 2 (hi) when the discharge air temperature is above 57 degrees and then switches to stage 1 (lo of 70% capacity) when discharge air is below 57 degrees.
Above, I think, shortens cycle time. Would I be better off as far as humidity if I prevent stage 2 (hi) from activating for a longer period of time? Would this save electricity or be about the same? Colder coil and shorter cycle time or slightly warmer coil and longer cycle time?
Running longer with a cooler coil should remove more humidity. It is really critical that the coil temperature is at or below return air dew point so that the water is squeezed off as it circulates. Locking it in S1 until stat setpoint is exceeded might help.
Running lower amps longer vs higher amps shorter might be a wash but can save if comfort is maintained.
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