commercial boiler - burner on all day for this very cold day - is this healthy?

elfie

commercial hot water boiler (cast iron 16 section) firing all day on this very cold day



no problem keeping place warm



burner fire rate is set at 35% of full potential



should burner setting setting be raised? so it shuts off once in a while??

jumper

don't think so

I figure it's temperature changes that stresses metal so constant fire sounds good.

icesailor

Running Efficiency:

The only time a burner is efficient is when it is running. When it is off, all is lost.

You say that the boiler (?) is firing at 35% of full potential? Does the burner modulate? That's what modulating burners are supposed to do. Vary their firing rate to match the heat loss load of the structure.

Burners are designed to run 24/7/365. Its normal.

elfie

burner on continuously

this commercial boiler is oversized and despite being 5 degrees outside it can satisfy heating needs at a continuous fire rate of 35% of capacity



i know that burners are most efficient when cranked alot higher but in this case burner would short cycle quite alot if set higher when temps are in the 30's etc.



burner does have modulation but its pointless when so oversized.

ttekushan_3

modulation

I disagree. I don't think modulation is ever pointless. It's only pointless if the system is so undersized so as to require full fire under all conditions. The larger the boiler's headroom, the more useful it is.



Don't forget that both fuel and air are modulated, giving good flame to water temperature differentials and residency times before exiting through the stack. Combustion efficiency shouldn't suffer. Taken to its logical conclusion, this is why modulating condensing boilers work out. The boiler's output is matched to the heat demanded by and dissipated into the living space. The physical size and water content are mere intermediaries between the flame and the conditioned space. Is a grossly oversized boiler a bad idea? Yes, but mostly when the system shuts off and you have a large vessel of stationary heated water losing its energy into a boiler room or chimney. Under conditions of continuous operation? Not that big a deal, IMO. Boilers operated continuously tend to last forever.

elfie

oversized boiler - modulation benefit

an oversized boiler (ie. 15-20 of capacity used most of the time) being set at the lowest manuf recommended range on boiler would seem to be the best for purposes of lengthening burn cycle.



its tough evaluating benefits of scrapping a 12 yr old non-condensing cast iron boiler (15 section) when NG cost are 15-20k per yr. and investing in a better configuration.



seems keeping a larger tank of water heated for 5 months is not all that expensive (boiler water is kept heated all winter long)



also, we may be expanding use of the hot water boiler to handle more heating needs in the future (although, it still would be very oversized despite this).



is this all a good rationale or should serious efforts occur to evaluate a need for a new boiler setup?

SWEI

Burners vary

but boilers generally have higher thermal efficiencies when fired at lower rates.



If your burner is a modulating one, it should run for days or even months before shutting down.  Don't be alarmed -- the system, the burner, and the boiler actually prefer things this way.



If you are meeting demand at or below design temps with 35% modulation, you should seriously consider the eval and re-commissioning I suggested in the other thread.  Assuming the existing boiler is not shot, the existing burner may be able to be tuned for a rate closer to your actual requirements.   If the boiler won't take that low an input, you might be able to remove some sections and then fire at half the current maximum.

Mark Eatherton

Fixed low burner issues….

By now, certainly you are aware of the need to maintain a return temperature above 140 degrees F. If not, then let me be the first to warn you that the fluids you are seeing coming from the bottom of the boiler may not necessarily be a system leak, but in fact may be condensation, which is BAD.



You stated that the building is comfortable, but you didn't tell us what your supply and return temps were. Keeping a non condensing boiler running at its minimum can cause the production of condensation, which as I said, is BAD.



A modulating burner, if properly controlled and set up is an EXCELLENT thing. Set up and controlled improperly, it will create a whole lot more problems than it avoids…





Proceed with extreme caution.



ME

elfie

supply return temps

return temps are above 140,  further there is a circulating pump running across the top of boiler, which is of further benefit. the boiler water temp is set at 170.



there is a mixing valve between the boiler loop and the facility loop, which helps protect the boiler



dont think its condensation



awhile back boiler was treated poorly (ie. supply temps reduced to 110 when bldg was too hot because actuators were not working properly); and thermal shock could have occasionally occurred due to poor maintenance practices; and there has been no chemical treatment for 12 yrs (recent began treatment) and makeup water quality is poor (and replaced several times due to plumbing work)