question about P/S piping

DanHolohan

has to do that, but at the proper system delta T, which is rarely 20-degrees.

Gravity systems have different needs.

Have you had a chance to read <a href="http://www.heatinghelp.com/shopcart/product.cfm?category=2-44">Primary-Secondary Pumping Made Easy!</a>

R. Kalia_3

slowly learning

Am I correct that the primary pump must move as much gpm as might be needed by all the zones put together, since all zones might come on at the same time? Iif this is not done, the flow in each zone will drop if the other zone pumps are running, right?

Now if this is true, isn't it a problem if you have a converted gravity zone needing much higher flow than deltaT=20 would indicate, as specified in

http://www.heatinghelp.com/newsletter.cfm?Id=125

and at the same time a small boiler such as a Munchkin that produces high head pressure at high flow? Now the primary pump needs to be not just high volume or high head, but high volume at high head, so you need a big pump that draws a lot of electricity 24 hrs a day, and this is in addition to the zone pumps also drawing current.

Am I misunderstanding something?

dconnors

P/S

Primary pump shouldnt have to be high head. If your boiler requires that much pump, maybe you should pick a different boiler. Most boilers and near piping require high flow at low head in a typical P/S system.

Wally Hoffmann_4

Munchkin does

Munchkin requires high head (see picture from installation manual) and I assume other small boliers do too.

dconnors

you have a choice

keep searching for a boiler with a low pressure drop through the vessel or pick a circ that will produce the flow you need at the head you have.

jerry scharf_2

Now I'm confused

Standard plumbing for the munchkin is to put the expansion tank on the load side and it's pump would be sized for head and flow of the converted gravity system (low head...) The secondary is the pump that pushes water through the Munchkin, and it needs the head and flow that is needed to get the BTUs out of the boiler. If the boiler is running more GPM than the load side, you will get mixing of boiler supply water and load return water to the boiler return, but thats fine. The whole idea of P/S was to separate these and give each pump it's own job.

Am I missing something really dumb?

jerry

Plumbob

I don't know

I thought the primary loop was the one that goes through the boiler. But I am basically an amateur.

It seems to me that if you have 4 zones, which of these is "primary"? They can't all be top dog. So the boiler loop must be primary.

Unknown

It can be either

A pure system would have the boiler(s) as secondary loop(s) off a primary loop. The zone(s) (load) would also be secondary loop(s).

The primary loop would be a pipe and low head pump matched to the pipe, sized to carry the WHOLE load at the Delta T that you actually see, pumping in a circle with closely spaced tees feeding secondary loops.

Variations are using a single boiler piped within the primary loop, and the zones are secondaries.

Or a big gravity system as a primary loop with a boiler as a secondary loop.

They all use the closely spaced tees to decouple the pumps from each other.

Everybody's right, this time.