Hot Water Pre-Heat Coil Question

[ryanmcd77]

Hi All, I'm new here and have two questions. My first question is how do you size a freeze pump for hot water pre-heat application? Second question is how do you control it?

 

[imok2]

You have to determine how many GPM is required through the coil. You can use this: GPM = 2.16(cfm/1000)(air temp. rise*F/water temp. drop *F)Then you can use an eletric controller with a remote bulb. The formula is derived from ASHRAE guide for ACHVR.
Roger

 

[ryanmcd77]

Thanks Roger, I have done the calc for the coil GPM, but is the pump typically sized for the full coil flow rate. Teh second question was more of a sequence question. Some say run it all the time, others say run it based on Outdoor Temp.

 

[ChasBean1]

I've seen this start and run at and below 40°F OA temp.

 

[imok2]

I like to run it based on OSA temp I see no need to run it all the time if OSA gets above 40*f and yes its sized for full flow.