Boiler primary pump question
Boiler primary pump question
(OP)
Hi all,
how common and/or advisable is it to run a boiler without a primary pump? I have come across a set-up where the 500kw boiler (700L internal water capacity) runs with zone circulators off a common header. is this a good idea? pros/cons?
cheers
how common and/or advisable is it to run a boiler without a primary pump? I have come across a set-up where the 500kw boiler (700L internal water capacity) runs with zone circulators off a common header. is this a good idea? pros/cons?
cheers





RE: Boiler primary pump question
Ask the same question of the boiler mfg. as different boiler materials will cause different problems.
RE: Boiler primary pump question
RE: Boiler primary pump question
RE: Boiler primary pump question
RE: Boiler primary pump question
RE: Boiler primary pump question
An energy "upgrade" lately removed 40 HP primary chiller pumps at a stadium, replaced the pumps with valves, so the secondary 150 HP pumps could serve the dual purpose of primary pump plus remote DP gratifier. The larger pumps work at a much higher rate for the same duty, negating the primary pump removal savings. Ludicrous. Some compressors on the chillers fried because of imperfect controls (is that a reach?); no sympathy from the manufacturer, who said that if you remove the primary pumps you're on your own.
Whoever is selling the "secondary pump can do it all" philosophy, is selling it very well, but they need to just go away.
The primary-secondary decoupled loop is a good invention and should be stuck with until something better comes along. Removing primary pumping to replace with control valves is not that solution.
RE: Boiler primary pump question
:off topic:
ESD is great for engineers to play around with technology just for the hell of it, maybe a thousand monkeys playing can come up with something useful. I get the feeling though that it is getting out of control. We are being requested to install economy cycles in small cool climate schools! I think it is the word economy that does it!
RE: Boiler primary pump question
RE: Boiler primary pump question
There's no easy answer to this, and the best answer is: it depends.
- What are these zone circulators serving? Do they all serve similar loads with similar schedules? Are the zone circulators of a similar size, or do they vary?
- What is the control strategy on the boiler? On-off? Hi-lo? Modulating? Is there thermal protection on the return side of the boiler? What is the pressure loss through the boiler?
I am rather new to the HVAC game, but I've had it drilled into my skull to never starve a boiler/chiller of flow. Allowing a boiler to fire w/ only 15% of design flow through it rings many alarm bells in my head.
RE: Boiler primary pump question
RE: Boiler primary pump question
RE: Boiler primary pump question
No worries, I saw your post more as presenting the facts, much better for this forum than the one-way opinion I posted. We seem to be on the same page. With the system that you describe (that seems you reluctantly "signed on" to) — I hope you note all the trials and tribulations you go through with this system, dig up this old thread, and let us know how it worked out.
RE: Boiler primary pump question
RE: Boiler primary pump question
RE: Boiler primary pump question
From your brief description I would keep the boiler pump, install a buffer tank. My two-cents.
RE: Boiler primary pump question
Just to chime in, I use primary/variable speed secondary piping loops for just about every boiler/chiller loop I do.
Robust, simple and cost and energy effective.
RE: Boiler primary pump question
RE: Boiler primary pump question
RE: Boiler primary pump question
I'm pretty sure I just said robust, simple, cost and energy effective.
Robust: good flow through the chiller or boiler. Easy to setup and a long history of stable operation.
Simple: differential pressure sensors on secondary loops are pretty standard, control sequences for variable primarly loops are not standard.
Cost effective: A small primary pump has little impact to project budget.
Energy effective: I've read articles stating that variable speed primary only pumps have the potential to save some energy over primary/variable secondary systems. I've also read articles describing numerous problems in application.