primary loop circ sizing

kev

Small system with high temp fan coil loops and very low radiant loops. I am thinking of using a 1 1/2" primary loop in boiler rm. to help give the system some volume? If I use the system sizing software all of the pumps give me twice the flow I need through primary loop. What should be used to properly slow the flow and how will I know when I have the correct flow? 10 gpm and 20' of 1 1/2" loop.

John Siegenthaler

Kev,

What's the boiler capacity supplying the primary loop? Let me know and I will run a quick scenario on the Hydronics Design Studio software and give you some feedback

Siggy

kev

105,000 is the output. I have your software and there are are no pumps listed where the gpm is around 10. Am I thinking right by oversizing the primary loop?

John Siegenthaler

Using 1.5 inch pipe for the primary adds a small amount of thermal mass to the system which may slightly lengthen operating cycles. But the amount of extra mass is minimal.

I ran the scenario of 20 ft of 1.5 copper with 10 elbows assumed in the Hydornics Circuit Simulator. A Taco 007 will yield 21.9 gpm. a Taco 005 will yield 18.2 gpm. These will yield temperature drops of 9.6 and 11.5 F respectively for the 105,000 Btuh boiler rating.

I also ran the same scenario using 1" copper for the primary loop. a Taco 007 yields 16.6 gpm, and the 005 yields 14.9 gpm. This provides plenty of flow for the rate of heat input. It also lets the circulators run a bit farther up their curve which improves efficiency.

Siggy

kev

Thanks for your input. I had the same numbers, so at least I know I am using the software correctly!