I’ve read the discussions regarding the pro’s and con’s of using the temperature split (supply -vs- return temps) on freon based a/c systems. Earlier this week I inspected a fairly expensive hi-rise condo unit that used a chiller for the a/c system. The building purchased btu’s from the city, ran city chilled water thru a heat exchanger for the entire building and then circulated the resulting secondary chilled water thru-out the building for each unit’s individual a/c. For lack of a better method I used the temp split as an indicator of the proper performance of that system. My question is, can I use the 14° to 21° split that I normally use for a freon based split system as a guide for a chiller system? If not, then what split temp or other method should I have used to judge the performance of the system?

Depending on how well the CHW lines are insulated, and how far the unit is away from the chiller, usually one would get about 40/45F into the coil, and 55/60F out. These would be the readings with the apt. at 70-75*F.
The only problems likely are dirty air filters, coil, or defective water modulating valve.
Discounting problems with the primary water chiller, of course…

Thanks Thomas. This was a 5 year old upscale condo ($440,000 for 820 sf), the unit was on the 9th floor of the 12-14 story building. I was getting a 12° temp differential and the building maintenace supervisor told me even before I checked the differential to expect 10° to 12°. Sounds like you agree with those numbers. I did not call anything out as in need of repair or service.


You may also want to make sure they are not using any reheat devices, (electric coils) to raise the discharge air if they are doing dehumidification.

Interesting…I hadn’t considered that possibility. I may call the building super and ask him if they do dehumidify the air. Thanks!

There may be 2 stats or a single, dual element device in the room for sensing both T&H. Real easy to do if they have an Energy Management System, (EMS). If no EMS, they may not be doing it.