Boiler Return temperature mixing valve

[barkeatr]

my question is...if I hook a mixing valve in to protect my boiler, will it further reduce or otherwise restrict flow in a probably already too small pipe? My profab 200 boiler manual says absoulty nothing about return temperaturs less than 140 are verbottten, but I find out on hearth.com that its required. Im using one inch thermpex insulated unerground pipe...most likely very undersized as part of decisions made before hearth.com visits. Yes, i know i need a heat loss done...I will get working on that for sure. Im looking at solutions either electrical switch or mixing valve. I would prefer mixing valve as I think its variability will help keep some hot water flowing in my conc slab radiant system...



thanks in advance!

TIm

 

[ewdudley]

my question is...if I hook a mixing valve in to protect my boiler, will it further reduce or otherwise restrict flow in a probably already too small pipe? My profab 200 boiler manual says absoulty nothing about return temperaturs less than 140 are verbottten, but I find out on hearth.com that its required. Im using one inch thermpex insulated unerground pipe...most likely very undersized as part of decisions made before hearth.com visits. Yes, i know i need a heat loss done...I will get working on that for sure. Im looking at solutions either electrical switch or mixing valve. I would prefer mixing valve as I think its variability will help keep some hot water flowing in my conc slab radiant system...

You would probably want to add a loop at the boiler to maintain return temperature and have your load pump draw from that.

Here's one way of doing it with a mixing valve. It's for a Seton type boiler where supply is on one side and return is on the other, but schematically a supply top / return bottom setup would work the same. Load draws from the closely spaced tees.

You could also do it with a boiler recirc loop but without the mixing valve with a higher-mass boiler like the Profab 200 by cycling the load pump according to return temperature. Boiler recirc pumps runs whenever there is demand for heat and then load pump is enabled when return temperature above 155 degF and is disabled when return temp drops below 145 degF, something like that.

 

[barkeatr]

thanks so much for the comments and picture, this helps. I belive i already have the recirculation loop you mention in the form of my primary continous running loop from outdoor boiler to house, but Im wary of that circulator/pump shutting of as the water goes through my underground lines. Im going to look closer at the picture and go the mixing valve route. i think i will just have to eat any line loss due to the mixing valve.

thanks

 

[in hot water]

the valve will not change the pressure drop through the underground tubing, but it may add more "load" to the pump. The cv of the valve will tell you how much pressure drop it presents. So if that mix valve has a cv of 8, 8 gpm will flow thru with a 1 psi pressure drop.

Look fof a valve with a high Cv, some thermostatic valves do have a big pressure drop.

hr