condensing dhw

smp74

On a mod-con boiler with indirect dhw is there any worthwile efficiency to be gained by setting the temps to condense on dhw production?

Zman

Sure, there are a few percentages possible. You need a fairly large heat exchanger on the indirect in order to make it work.

smp74

I have a Smart 40 indirect. Would the hx on that be large enough?

hot_rod

Lower temperature to the tank will allow condensing, but increase recovery time. So if you do not need rapid recovery, give it a try. Some boiler brands have adjustable settings like ramp delay that may help fine tune that approach.

smp74

Well, I guess it can't hurt to try it out. This is on a TT Prestige Trimax Solo 60 so it's very easy to change the settings. It does have the DHW sensor installed in the Smart40 as well.

This gets me to thinking......if it's recovering slower and at a lower temp, then is the DHW priority providing any benefit? I'm assuming that the boiler would not be running at 100% on a DHW call with the lower temp settings.

Zman

It can't hurt to play with the settings. A condensing boiler is most efficient at low fire and with low return temps. As long as the DHW priority time is not so long that it hinders heating the house, turn it down and see what happens. You can always activate the anti legionella feature to occasionally crank it up.

smp74

I set things and gave it a run today. DHW setpoint 120, storage adder 20, anti-legionella enabled.

Looks like condensate is flowing during the whole run now. Ran the shower for 30+ minutes and temp held steady so recovery seems reasonable. Boiler supply 140, boiler return 110 - 130. Modulation starts off at around 80% and ramps down slowly to low fire to finish off the last few minutes of the cycle.