Pellet/corn boiler low gpm high temp vs. high gpm lower temp

[chadhumm]

I'm trying to find out what is the most effecient way to run my hot water boiler system. I am using a bumblebee pump which uses very little electricity. I currently run it at the lowest of the 3 set speeds. So I have low gallon per minute but a higher temperature differential through the boiler. I didn't know if it may be more effecient to use the highest set speed that results in more gpm but a lower temperature diff. through the boiler. Or does it all average out in the long run?

The exchanger on the furnace side - I have the blower on the lowest speed available for 2 reason 1) electrical usage and 2) The output of my boiler is low enough that the furnace fan shuts off an on. I have cycles of about 5 minutes on to disperse the heat and 5 minutes off to recover water temperature before it comes back on. If I were to put my furnace fan on a faster of the 4 speed option, I would get shorter cycles. Example 3 minutes on 5 minutes off. Yes, there was more air volume during those 3 minutes. Im going with what provides the least amount of cycles. 5 on 5 off results in 6 cycles per hour.

Ultimately a smaller exchanger in the furnace side would be the ideal scenario so the boiler output matches whats disspersed by the furnace fan.

Thats my setup. Back to the question whats better (more efficient) low gpm with higher temp differential or higher gpm with lower temp differential. Thank you to anyone that can shed some light on this topic.

 

[maple1]

IMO it's low flow/higher delta T.

Not much science/engineering to back that up, just based mainly on the principle that the cooler you can get your boiler return water, the more heat it will extract out of the boiler on its way up to the exit fitting. Thereby aiding heat exchange efficiency in the boiler (less heat out the stack).

Don't know what you have for a boiler though - some seem to need higher temps to burn more efficiently.

 

[chadhumm]

Thank you for that advice. Just needed the confirmation that I was running it at optimum efficiency. The other benefit of this way being I would think is a lower electrical cost of the circulator pump running on low and maybe longer pump life.

My "boiler" is basically a corn/pellet stove modification, an exchanger in it to produce hot water. It works very well. Uses a lot less fuel than a manufactured pellet boiler.