Low flow circulating pump vs high flow circulating pump

RichardStropoli_2

I have two 150 HP Scotch Marine hydraulic boilers with a recirculating line off the header manifold and returning back to the return manifold (for circulation through the boiler) (1725 RPM, 1/2 HP, 120 V). Then I have a water to water heat exchanger for domestic hot water with a circulator (1725 RPM, 3/4 HP, 208 V) circulating the hydraulic water through the exchanger. I also have a 1600 gal domestic hot water storage tank with a circulator pulling cold water off the bottom going through the exchanger returning to the bottom of the storage tank (the hot water return has a reverse dip tube going haft way up into the tank).

My question is the circulator (1725 RPM, 3/4 HP, 208 V) circulating the hydraulic water through the exchanger should this be a low flow or high flow pump?

Jamie Hall

It's all in the delta T's across the heat exchanger, and how the heat exchanger is piped. If the heat exchanger is counterflow, you can run a much higher delta T across it (if you want to) than if it is parallel flow.

That said, your circulator within the restriction above -- will govern the delta T. High flow, low delta T. Low flow, high delta T. Adjust the flow to get the output temperature you want...