Heating DHW

[larryjbjr]

Ok, I've done some reading and such but I still am not clear on this at all.

My home is around 2000 sf with 2 baths. We have 4 children. I'm wanting to heat my DHW with my OWB. I've read about using sidearm and flat plate heat exchangers. From what I can tell I would be better off with a Flat plate.

But, for my situation, how big of an exchanger do I need? 10? 20? 30? I'll be running 1" pex from the OWB, but I'd like to use that to heat the 1000 sf basement as well. Though I will need a separate heat exchanger for that I know.

And, doing it that way, how do you hook it up so that the circulator pump kicks on when you need hot water? Or do you just hook the pump up to constantly circulate?

And, last but not least, if the water from the OWB is about 170 deg, and the water from the well is 50 deg, how hot will the water be coming out of the heat exchanger going into the water heater tank? Will it heat 50 deg water up to 130 deg in one pass? That would be an 80 deg Delta Temp, so my water going back to the OWB would be 90 deg? Or am I missing something here?

[Bull]

I would go with the larger water to water exchanger because it has less restriction. It will heat the water fine and you won't lose that much temperature in the owb water.
I run 1 inch line about 115 feet to the house, then another 35 feet to my water to water plate ex. then 10 feet to the water to air ex. in my heat pump, then I go about 50 feet into another water to water ex.(my sons mobile home) 20 feet to another water to air in another heat pump then back to my basement where I have another pump to help circulate through my radiant floor and then back to the owb. My house is well insulated so my heat pump doesn't come on and if I turn the pump to the floor on it gets to hot and my wife opens the windows LOL

[RSI]

With plate heat exchangers you mostly need to size for minimal restriction on the boiler side. If you used a 10 plate it would probably be as restricting as the entire rest of the system.
20 plates usually work fine but it you are getting close to the limits of the pump then a 30 plate can sometimes avoid having to go with a larger pump.

You calculations would be correct if you had equal flow on the domestic side as the boiler side but that is not very likely. I have seen 150-170 degree water coming out of the plate when a faucet it running. It is usually closer to 140 when using a shower or something with higher flow rate. Also, the hotter the water in the tank gets the slower it will be passing through the plate because you will be mixing in more cold to adjust faucet temp.

[larryjbjr]

With plate heat exchangers you mostly need to size for minimal restriction on the boiler side. If you used a 10 plate it would probably be as restricting as the entire rest of the system.
20 plates usually work fine but it you are getting close to the limits of the pump then a 30 plate can sometimes avoid having to go with a larger pump.

You calculations would be correct if you had equal flow on the domestic side as the boiler side but that is not very likely. I have seen 150-170 degree water coming out of the plate when a faucet it running. It is usually closer to 140 when using a shower or something with higher flow rate. Also, the hotter the water in the tank gets the slower it will be passing through the plate because you will be mixing in more cold to adjust faucet temp.

OK, that makes sense.

So I guess one final question, how do you hook it up as far as the pump goes? I'm assuming you would not want the pump circulating water from OWB to the heat exchanger all the time would you? But how would the pump know when to kick on when It needs heat? That's the main part I cannot figure out.



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[larryjbjr]

And, for the record, my current water heater is propane.


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[RSI]

You want the water always circulating through the plate. Otherwise it will be too slow to react when turning on a faucet and you will be putting cold water into the tank.

If you go long periods without using any hot water at all, you could set it up different to not always circulate but would be much more complicated.

[larryjbjr]

I see


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[Crow]

I have a 20 plate and pump runs continuously. I put a bypass and valves on the domestic side so I don't run well water through it during the off season, and unions so I can take it off and clean it if need be.