Primary/secondary questions

Dan_8

Dan's P/S book seems to cover this in decent detail doesn't it? I'm pretty sure that he's got several examples where he talks about the primary flow required to satisfy various secondary circuits and even different arrangements of those circuits.

Siegenthaler briefly outlines the process in MHH but he's got an article here that chats about it in a good bit more detail:

http://www.pmengineer.com/pme/cda/articleinformation/features/bnp__features__item/0,2732,93794,00.html

And, as Noel says, if you can't characterize your secondary circuits pretty accurately then it's all just hand waving.

mpd61s

Primary/secondary questions

How do you size the circulator for the primary loop? If the secondary loops use 3/4" piping, should the primary loop use a larger diameter pipe? And finally if I use a condensing boiler, how do I keep the return temp to the boiler loop below 127 degrees to allow for condensation?

Mike F

dan's book does a great job of explaining everything you need to know and then some.

mpd61s

I agree, Dan's book does touch on this issue, but in general terms. On the design I'm looking at there are three secondary zones and the boiler loop off from the primary. My question is, how do I size the primary circulator in regards to GPM? I may have missed it, but I did not see this in Dan's book nor in Modern Hydronic Heating.

Caselli

On the piping....

I'll take a shot.

Determine the Btu's to deliver to the system.
Each gpm is about 500 Btu's per hour per degree of temp difference..
( about 8 lbs per gallon x 60 min. per hr. x 1 Btu per pound = about 500 Btu per hour ) Take into account the temperature difference to allow.

Select the pipe sizing to place it into the correct velocity range... Less than about 5 - 7 feet per second, or so.

Unknown

You need to know

You need to know the ACTUAL return temp, under full load, and the number of BTUH you want to deliver. If you have a 20° F. delta T., you need 1 GPM per 10,000 BTUs. If your actual Delta T. is 40° F., you need 1 GPM per 20,000 BTU.

You size the primary pipe to the GPM that you come up with. The more Delta T., the smaller the components can be.

Noel

DanHolohan

It's in Pri/Sec Made Easy

You first have to figure what your secondaries are going to do, then you size your primary loop flow based on those conditions. It's in the book, step by step.

mpd61s

Thanks

Thanks all. I did find the information