I am retrofitting a poorly designed multiple-zone hydronics/forced air system at my house in Oakland, CA. In its original conception, the air handler fans are always on. That is, there is a manual switch for every fan. And the handlers are not that quiet either. I am adding relays to control fan on/off. I bought a few 30A mechanical contactors (the fan motors range from 1/3 HP to 3/4 HP) for about $10 each and installed one, and it works fine, but it is wicked noisy! THUNK!
This one isn't close to a bedroom so it doesn't matter too much, but I have to do better for the bedrooms. I am considering these three choices.
1. Small 10A relays. They click too, but they are much quieter. However, I don't know if the contacts can stand the inrush current. I bought 3-pole relays and connected the poles in parallel, so that gives me 30A in theory. Is this a good idea?
2. Mercury relays. These can handle high currents and cost about $25, but are they quieter than the small relays? Does anybody know?
3. Solid-state relays. I am looking at the Carlo Gavazzi models, which seem very nice. They have models with 24VAC input, and a 50A relay costs about $30. The voltage drop across the relay is 1.6V, and at steady state the currents I am dealing with are low enough that I won't need to install heat sinks.
Thanks for any help! Luigi Semenzato