Primary / Secondary Pump size's

kpc_73

what was the boiler, output, pipe size add zone load and pipe size....were you using for circs.

David Lambright

Primary / Secondary Pump size's

We had an application where the secondary pump was larger then the primary (boiler) pump. The Lochinvar Rep said we needed to install a pump that was 10% larger then the primary pump in the secondary loop. I don't feel this is correct. My understanding is that the pumps are sized independent of eachother. Could you please clarify this or direct me to where I can get the information. Thanks.

don_205

Could it be

That he wants to used the tee connection as some what of a mixing valve?

Thats what going to happen you know when the secondary circ is bigger then the primary.May even have to increase the temps on the primary loop.

Pyro

Primary pumps should be only sized for the needs of the boiler PERIOD! OFC you need to keep in mind that to do the job right, you need to size it vs. GPM needed at the boiler, Delta T intended (condensation or not), and pipe size.


Pyro

Andrew Hagen_2

Flow Rate vs Pump Size

For a condensing boiler, there is no reason to have a boiler flow rate higher than the system flow rate. That would unnecessarily warm the return water and raise the average temperature of the boiler.

You are correct that it is the flow rates, not the pump sizes, that are important.

DanHolohan

I think you would enjoy

my book, Primary-Secondary Pumping Made Easy

It's all about the whys and hows of pipe sizing for these systems.

Unknown

just to back up Dan, that's a great book and it should definitely be purchased and read.

David Lambright

Add it to my order

Dan, can you add that book to my order I made earlier for the IBR training manual? You should have all the info.

In regard to the pump question, I have to get with my technicians to find out more details. The part that had orginally got me was the comment from the Lochinvar rep that the primary pump needed pump 10% more then the secondary loop pump. When I get further information I will post it. Thank all of you for such a prompt reply. I'll have to spend some time reading past threads.
David Lambright.

Unknown

you have two choices. As others have said, it's really about flow, not about pump size.

if boiler flow is greater than secondary flow, then secondary gets boiler temp supply water... and return water is a blend of boiler supply and secondary return, which is warmer than it could be.

If boiler flow is less than secondary flow, then secondary gets a mixture of boiler supply and secondary return, so it's cooler than it could be otherwise, but the return to the boiler is coldest possible.

This means you might need to turn up your boiler temp to get the same temp out to the zones... but your return should be cooler, which is better for your boiler efficiency.

that's my take at least.

DanHolohan

Done.

Thanks!