Primary/Secondary Piping

Keith_29

Will P/S piping help a low volume boiler heat a multi zone system more efficently? Boiler only holds 5.5 gallons of water and has a Net rating of 107000 BTUH. Problem is when a zone calls the boiler cools down extremly fast, even with a bypass. Then takes a long time to heat up even at a low GPM flow rate(burns alot of oil).
Will appreciate any input. Thanks

John Faust

Primary /Secondary Piping

Most of the mod con boilers I have looked at show primary/secondary piping for all applications. Is this required for a one zone - one temperature system and if so why?

ALH_4

P/S

Whether P/S piping is required is more dependent on the flow rate required for the system and whether that flow rate can reasonably be circulated through the boiler heat exchanger. The number of zones is somewhat irrelevant, though it is easier to do with a single zone system.

Mark_46

John,

Homeowner here but I can share with you what I learned in my research of mod/con piping.

P/S is not required if the one zone you describe is a one temperature system (eg no DHW) and the minimum amount of GPM flow through the boiler, relative to the BTU input, is met. I think the likelihood of that is typically slim to none.

I know Heat Transfer specifies 1 GPM per 10,000 BTU.

Hope this helps.

Chris S

Most of the manufacturers have their installation instructions available online. In there you can find the flow required through the boiler & equations to relate it to your piping situation. If all of that's not too daunting for you, you'll find you answer. Keep the flow up, but don't erode your piping.
good Luck

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Uni R_2

No its not...

P/S is totally wasteful for what you describe. Even an indirect shouldn't mean that you need P/S. My guess is that the manufacturers don't have the confidence that the boiler will have an ideal flow, so spec'ing P/S along with a circ size or even including makes it less of a risk. After all, if the boiler's flow is way off one way or the other, there is a major risk of a warranty claim through no fault of the manufacturer, so they make it simple for installers that can't or won't do the proper math. It's us homeowners that end up with higher electrical bills, higher install costs and lower efficiencies from this.

ALH_4

Size

For smaller boilers, that's absolutely true. For larger boilers, P/S can be a more attractive alternative to one large single-speed circ and large delta-P valve. However, the new VS circs might work fine as a single circ on larger systems.

Phil_17

P-S

piping adds one circulator to the system that he described. Other than the juice to run that circ, what inefficiency is there that would make a difference? You are going for that 'efficiency' and giving up the ability to easily control delta T etc. Without P-S the boiler pump has to be the SH pump!

Uni R_2

JohnG...

But John, why make it more complex if it doesn't need to be? If either pump fails the heat is down. With double the circs there is double the risk of a circ issue. Plus, the circs are the vast majority of electrical load on a modcon. On mine, the computer uses 14 watts and the blower's about 10. The rest is used circulating water. An extra 007 sized circ takes 75 watts and when running 210 days a season, 16 hours a day at 15 cents a kWh that's $40 a year or more - forever. And in Canada, that darned near a case of beer! ;-)

Pr/Sec can't help but mix the return temps from the heating circuit with the boiler supply temps. This increases the return temps to the boiler. Modcons increase in efficiency as the return temps drop. Why add a P/S connection just for the sake of doing that when it hurts efficiency? As Andrew pointed out, if it needs P/S that's one thing, but if it doesn't, why do it?

Anyway, for those houses where you could do it either way, why have more piping costs, an extra circ and isolating flanges, extra lifetime electrical costs, twice the risk of a pump failure, return temps mixed upwards reducing the ΔT / efficiency of the boiler? I'm not seeing and clear advantages for P/S here.

I'm pretty sure that ECR, T-T and Viessmann support direct piping if the application allows it.

Phil_17

Knight

requires P-S in their new boiler piping. Surely they are not just trying to sell pumps or increase HO costs?

ALH_4

Head Loss

There is a lot of head loss in those Giannoni heat exchangers. Take a TT Prestige, and P/S could easily be unnecessary, particularly with a Solo 110.

hvacfreak

I always thought...

that any " low water content " boiler would be better off piped as primary-secondary ( if not for higher boiler temperature than at least a more consistant boiler temperature throughout a given heating cycle ).

edit : Sorry...didnt see the latest post on this...lagging on my end for some reason...oh well - what he said

" Oh by the way , which ones " Pink "? " -M

Keith_29

which ones

Not sure what you ment at the end there. But if I'm right its a Peerless Pro-05 Boiler

hvacfreak

just an old song...

to quote myself...

[quote] if not for higher boiler temperature than at least a more consistant boiler temperature throughout a given heating cycle [/quote].

I'm not an expert on these at all , but I would imagine the above statement would apply to the original question...if I missed something in between please disregard...I am now lagging for a couple of " known " reasons

[Deleted User]

btw, this one's pink

http://www.pinkspage.com/

and i always have a cigar

hvacfreak

I'm thinking...

Bevis and BHead facial expressions as " shocked ".-M

[Deleted User]

huh-huh, huh-huh

he said, facial