Temp flow and return - what am I shooting for?

[MrEd]

OK, got my IR Thermometer, and have put masking tape at all the appropriate places...what is the goal?

I now can measure temp going out, and temp coming back - but in an effort to improve performance, what is the goal? Is the goal the biggest drop? smallest drop? a predetermine amount of drop?...trying to understand what I am shooting for (besides a warm house)

 

[WoodNotOil]

I think a delta T of 10-20* is usually the range you are shooting for. Make sure you measure return temp before the termovar mixes hot water in on return side. I think more than that it fine as well. Not really sure on this one, but those are the ranges I have heard about a lot.

 

[MrEd]

So if I am shooting for a 10-20 degree differential, is a bigger delta always better? today for a while I had a 50 degree delta - water out at 205 and coming back at 155. Early in the burn it was going out at 170 and coming back on 132.

My house heats *much* better when I am at at least 185 or so on the way out.

Just trying to figure out out the various things in play here...for example, if I wanted to get a smaller differential, I would assume a bigger pump might help, if I wanted a bigger delta, I assume I could clock down on or both of my 3 speed pumps...just trying to fine-tune the "sweet spot" on my burns.

BTW: All the baseboards on the first and second floor are cast-iron ones. Basement has the cheap stuff.

 

[WoodNotOil]

As I said before I don't know a lot about this so hopefully someone else will chime in. However, I think those sound like really good numbers. Your zones with not have to run long to deliver heat with such a large delta T and the return temp still seems high enough that hot water does not have to mix with returning water to protect the boiler return. I would leave the pumps on the high setting. Just my guess.

 

[Nofossil]

Probably a lot of different approaches to this. I think most systems are typically designed for about a 20 degree drop and an output temp of 180. You don't want sustained inlet temps of less than 140 in order to avoid corrosion from condensation inside the boiler. Other than that, the lower the temps you can run at, the less heat you lose up the chimney. Some systems change the temperature of the circulated water based on outside temps to match the output of baseboards/radiant/radiators to the building's heat loss.

When they tested the EKO 80 in Europe, they ran it at a very high flow rate and a very low outlet temp - about 35gpm at an outlet temp of 145 degrees. They got over 90% efficiency running it that way.