Pump Control Based on OA

Matt_49

I have a hot water heating system with two constant speed pumps set up in a lead lag control fashion. No DDC, all stand-alone controls. During very cold days, when all the control valves open, I get a very large supply and return water delta T and not enough heating capacity. I would like to use a controller that will bring on the second pump to run in parallel based on outdoor air temp.

Does anyone know of a controller that will work?

Uni R_4

Johnson A419

What about a simple setpoint controller like the A419?

Brad White

That or a Ranco ETC

Anything simple as these will work. I prefer external thermistor sensors. The Ranco ETC also has a two-stage model so you can set it up in a variety of ways.