Efficiency and Adding more storage

This is a pretty unusual approach, the reason for storage is usually that wood boilers just do not turn down well and really only hit maximum efficiency at full load. Therefore the storage is set up to allow the wood boiler to run at maximum efficiency. I thought a pellet boiler could adjust its output by adjusting the feed rate of pellets, therefore I am unsure how much overall efficiency you will gain adding storage although I expect there would be a boost in efficiency.

Unless I have it wrong I think you are just plain using more heat then normal years. I have used a lot more wood this year then in past years. I would expect if you look at degree day data they are much higher than average.

I see one question there and IMO the answer is no.

If you would like some feedback about differing fuel consumptions and/or efficiencies, more info would be needed on complete before & after setups....

I always thought a ton of pellet BTU was a bit greater than a cord of good wood BTU. Crappy pellets?

Pellet boiler needs a few tweaks? Is the stack temp too high blowing BTU's up the flue?

I would think an on/off pellet boiler would benefit from storage, where as a modulating unit may not see much of a difference. The big benefit of storage is longer burns & fewer short cycles, right?

I have 500 gallons of pressurized storage and I'm heating about 3900 sq/ft plus DHW. On average I burn about 115 pounds a day in the winter. Last year I was also doing a 20 degree delta. This year I'm doing a 45 degree delta with the boiler set to come on when the tank temp drops to 120. So far it's kept up with heating everything down to 10F. I'm sure when I get below 0F I'll have to increase the lower limit.

It's recommended that pellet boilers also have storage. Otherwise the boiler could fire several times an hour based on calls for heat and this just isn't efficient. You generally want to have a minimum burn time of one hour for good efficiency. My Pellergy takes a little over 2 hours to heat my tank 45 degrees.

Last year with a 20 degree delta ( 160F to 180F) my boiler would fire about 8 times a day for a little over an hour each time. This year with a 45 degree delta so far it's been firing 3 times a day for an average of 1 hour and 40 minutes. My boiler will only fire for a maximum of 2 hours before shutting down and doing a cleaning of the burn pot.

Right now my minimum water temperature in the storage tank is 120 and max is 165 and my average daily pellet usage is 98 which is down 17 pounds per day over last year. Last year I was averaging 2.8 pounds of pellets burned per degree day. So far I'm burning 2.1 pounds per degree day this year.

I hope this trend continues.

AndrewChurchill said:

It's recommended that pellet boilers also have storage. Otherwise the boiler could fire several times an hour based on calls for heat and this just isn't efficient. You generally want to have a minimum burn time of one hour for good efficiency. My Pellergy takes about 2 hours to heat my tank 45 degrees.

Last year with a 20 degree delta ( 160F to 180F) my boiler would fire about 8 times a day for a little over an hour each time. This year with a 45 degree delta so far it's been firing 3 times a day for about 1 hour and 40 minutes.

Right now my minimum water temperature is 120 and max is 165 and my average daily pellet usage is 98 which is down 17 pounds per day over last year. Last year I was averaging 2.8 pounds of pellets burned per degree day. So far I'm burning 2.1 pounds per degree day this year.

I hope this trend continues.

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I am thinking since the OP already has some storage, he would likely be able to improve his situation more by simply changing settings & the way it is operating. Such as you seem to have this year by changing yours. We don't have much info though on how his is running - aside from 'chasing' a 20 dT. Which by itself would seem like there is some room for improvement.

My first statement was in response to Peak Bagger thinking storage was an unusual approach for a pellet boiler. I agree we need more information about the OPs current set up.

maple1 said:

I am thinking since the OP already has some storage, he would likely be able to improve his situation more by simply changing settings & the way it is operating. Such as you seem to have this year by changing yours. We don't have much info though on how his is running - aside from 'chasing' a 20 dT. Which by itself would seem like there is some room for improvement.

Click to expand...

@ejhills Just posted a response in your other thread. The answer was given under the assumption you were burning a cord wood boiler. It is relevant to pellet boilers too if they have a storage vessel.

Two things you can do to improve the performance of your system. 1) Replumb the boiler loop to draw from the bottom of storage and feed to the top of storage. 2) Implement outdoor reset into your system on the house side.

220 gallons of storage can hold approximately 100,000 usable btus depending on your emitters. Meaning, if your demand take 20,000 btus per hour, there should be approximately 5 hours of idle at the boiler. If your pellets hold 8,000 btu per pound and your boiler efficiency is 85%, it should use 15 pounds of pellets to recharge the storage. By the way, I have zero experience in pellet stoves and boilers.

35kw (19,000 btu/hr) is not small. How many starts are you having per day. The fewer starts the better, because that means the boiler is following the load and should be more efficient. It still has to be capable of heating the place on the cold days though, unless you also have another source of heat, ie, wood stove.

Heating big storage with a modulating pellet boiler doesn't seem like a win to me. Unless you have to because the boiler is way oversized and you're getting way too many starts/day. Remember though, it's gonna get colder, and there will be less starts/day.

That said, I've been burning oil with my unmodulating cast iron boiler and heat my 200 gallon tank. It burns for a long time, but on cleaning, it seemed to stay cleaner, less sooty. But that's oil, with lots of start/stops without the tank.