Return Air Temperature Industry Standards
Return Air Temperature Industry Standards
(OP)
I have Lennox roof top HVAC units. Most are 10 to 20 years old. They range from 5 ton to 10 ton with economizer inlets.
Are there set standards for the return air temperature coming back into the unit? I have approx 58 to 63 degree's F leaving the different units entering the building.
For some strange reason some of the units freeze up and need to be manually defrosted for about two hours. The refrigerant pressures are in the ball park and the evaporator coils and filters and condenser's are clean.
Any help would be great.
Thanks toolbag
Are there set standards for the return air temperature coming back into the unit? I have approx 58 to 63 degree's F leaving the different units entering the building.
For some strange reason some of the units freeze up and need to be manually defrosted for about two hours. The refrigerant pressures are in the ball park and the evaporator coils and filters and condenser's are clean.
Any help would be great.
Thanks toolbag





RE: Return Air Temperature Industry Standards
Older controls and equipment do not cope well with high latent loads and freeze up. You could do a hot gas bypass on the evaporator.
RE: Return Air Temperature Industry Standards
Maybe there's been a change in the usage profile as well. A/C salesmen are notorious for selling overcapacity. If the user decides to cut back on usage because of cooling costs, the system might wind up grossly oversized.
TTFN
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RE: Return Air Temperature Industry Standards
Can you drill a hole, or find an existing check hole, and get a pitot /static tube in there, to measure the velocity at the face of the coil? That would confirm or eliminate low velocity as a source of the problem. although it is more likely that you have a leak in a duct.
B.E.
RE: Return Air Temperature Industry Standards
Are your OSA Dampers working correctly
Is The CFM correct for tonnage and application (static pressure)(velocity pressure)
What are the entering & leaving WB and DB temp.
Is the compressor amperage in the ball park and if you have similer units (tonnage) are amps about the same
When have the evaporators been cleaned? You may have to cut access holes to get a good look; or take a series of static pressure drops across the coil and find out from mfg. what it was originally
It all comes down to a process of elimanation.
RE: Return Air Temperature Industry Standards
RE: Return Air Temperature Industry Standards
Question: Is there a rule of thumb for RA temperature and actual temperature coming out of the trunk line.
Question: What is the temperature difference in the winter months?
Thanks toolbag
RE: Return Air Temperature Industry Standards
Your return air should be coming back to the unit at a higher temperature than 64 degrees. Are you sure that is not an exit temp off the coil?
What is the average room temperature in the buildings the units are serving?
B.E.
RE: Return Air Temperature Industry Standards