Delta T too high?
Can delta T be too high? If so, what does it indicate, and how high does it need to be before you call for help?
I told a friend about checking delta T as suggested here and it should be 20F or so. His is 28.
Thanks for the good info on this site. It helps the home owner and increases business for the hvac pros.
low air flow....dirty filter....low latent load.
20F is a myth.....it can be 10 or much higher.....all depends on the condition of the air entering the system and it's velocity.
Have him change his air filter and then check the delta T again.
20^F is not carved in stone. Depending on how humid it is in the house, the delta T can vary between 16 - 22^F.
On the other hand. Since we don't know what system it is. It could be the right delta, it might be a HV system. And 28°F delta would be about text book perfect.
I have seen 30 degree TD on mini-splits. I have seen 30 degree TD on VS indoor units with a TXV in the first minute of run time when set to enhanced dehumidification mode.
Remember, Air Conditioning begins with AIR.
A 28 delta T is a bit out of bounds for these higher SEER systems.
Originally Posted by jax1
Back in the 6 EER & lower systems the larger compressor capacities to coil size resulted in low suction/temp conditions even with moderate load conditions.
The actual RA & Return Entering air delta-T could go as high as 35-F on systems less than 7-EER, an 8 EER was around 32-F delta-T. Therefore, one can see why when sized right, they were terrific for latent load dehumidification.
If there were almost no latent load & low airflow, it could be achievable with the unit you checked. With a 28-dT, I would up the wet coil CFM to 450-cfm per/ton of cooling.
Last edited by udarrell; 06-23-2008 at 02:08 PM.
Reason: Stating actual delta T data vs EER
More fine examples of why a properly operating system could have a high delta.
Originally Posted by Kevin O'Neill
calling for service
I checked with the homeowner and the system is a variable speed. He doesn't know about hv, txv, or enhanced dehumidification, so he's calling the techs. Thanks for the input. At least now he knows what they should be looking for.
Never hurts to have it checked.
Since it is a VS blower he may have checked it while it was in a lower speed for dehumidification.