out door reset for fuel economy

Bob_36

I've read alot on this site of outdoor reset to conserve fuel. If you apply this feature to a ci boiler, and install a safety boiler bypass to protect against too low return water, where does the fuel savings come from? I know if a condensing boiler is used, then the return water can be much lower. I could see then how savings could be realised. Can someone explain where I'm missing the boat? Thanks

Alan_6

> I've read alot on this site of outdoor reset

> to conserve fuel. If you apply this feature to a

> ci boiler, and install a safety boiler bypass to

> protect against too low return water, where does

> the fuel savings come from? I know if a

> condensing boiler is used, then the return water

> can be much lower. I could see then how savings

> could be realised. Can someone explain where I'm

> missing the boat? Thanks



With primary-secondary piping, and only lowering the secondary water temperature with controls as the outdoor temp goes up, would save money. But is costly project.

Constantin

Do a search...

... we've been throught his before. Yes, your boiler will only "modulate" from 140-180°F due to its CI construction and condensation protection. However, even such a narrow range of water temperature swings will provide some benefit, such as reducing temperature swings and hence over- and under-shots.

Besides, a lot of it has to do with how the boiler/pumps are set up. Witness the Vitola series that is "shockproof" by design and that can handle very low water temps from radiant systems despite being CI construction. The same approach can be achieved, IIRC, with more conventional boilers by handling low water temps with bypass controls (where a lot of water goes past the boiler instead of through it). Bingo, low water temps despite CI construction.

See the literature from Burnham's Opus and other fine CI boilers for more info on this topic. At least that's where I think I saw it this way.

Rick T

fuel savings from reset

Some savings results from lower distribution system losses and some from lower off-cycle losses.
Distribution system loss decreases as the temperature difference between the pipe and surrounding air decreases. If you decrease the water temp from 180 to say 140, your distribution loss (pipe heat loss) will decrease.

If the reset control decreases the water temp, the boiler will lose less up the chimney due to less temperature difference across the heat exchanger.

Hotter objects always lose heat at a faster rate. Dropping the temperatures in the pipes and boiler reduces losses.

Geno_15

exactly

When it's cold out you need your boiler to be able to run to 200*. To run that high year round is wasting money and whenever you can lower your water temp all heat loss, standby, jacket, flue loss is cut substantially. When it's warm out you don't need the water temp to be that high. Actually the higher your temp with ci the more shock the boiler receives if the return isn't tempered. I've seen several commercial boilers crack sections because of the amount of water returning

For example until it gets below 50* outside my boiler may run to 160 hi, and then only when I'm calling for heat or hot water, my low temp will be 140. To be efficient your system needs to be as close to "on demand" as possible, for it to sit and run to 200 all day while you're at work is a waste.

Some new systems like Amtrols Boilermate will monitor the temp rate of rise and will shut the burner down before it reaches hi limit because the computer can sense that you will overrun it. A few years from now the new technology is going to leave some service people and homeowners in the dust.