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Thread: Variable Speed AHU Questions
03-04-2009, 09:48 AM #1Regular Guest
- Join Date
- Mar 2008
Variable Speed AHU Questions
Late last summer I had a contractor install a new American Standard (Trane) variable speed air handler and A/C unit along with a new Trinity condensing boiler and a heat coil in the AHU. I thought the system would be "smarter" than it is. I haven’t used the A/C much since it was the end of the season so my experience and questions so far are mainly about the heat side. The boiler has an outdoor temp sensor and resets the boiler output temp according to changes outdoors. The AHU fan runs at a low speed (compared to the A/C) all the time. The (not so variable) fan speed is what disappoints me. One problem is that when the heat is satisfied and the boiler is off, the same air volume circulates and it’s uncomfortable. At the other end of the scale when the heat comes on in the morning after being set low overnight it takes forever to bring the house up the temp at the low fan speed. It seems to me the AHU fan should drop to very low CFM with heat satisfied and then ramp up to high volume when the room is more than a degree or two below set point. The t-stat is programmable and is capable of sending virtually any signal to the AHU but the installer told me there’s no way to wire the AHU to vary the fan speed the way I hoped and expected. Is he correct? I suspect the answer is no. Please advise what I can really expect of the system and what specifically to tell the contractor I want.