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General Forestry => Firewood and Wood Heating => Topic started by: Fether Hardwoods on June 05, 2015, 10:51:21 PM

Title: On demand domestic hot water using water to water heat exchanger?
Post by: Fether Hardwoods on June 05, 2015, 10:51:21 PM
 I would like to use a plate heater to make the hot water for my home, my question is how big of an exchanger would I need to get my domestic water from about 50 degrees to 130 degrees assuming a flow of 2 gallons a minute?
Thanks
Title: Re: On demand domestic hot water using water to water heat exchanger?
Post by: azmtnman on June 06, 2015, 11:07:11 AM
A btu is the amount of heat it takes to raise 1 lb of water 1 degree Fahrenheit.
Water weight=8.35 lbs./gallon
You need to raise your temp 80 degrees
80x 16.7 (2 gallons) =1336 a minute or 80160 btu/hr  (the terms we typically use).
A gallon of liquid propane (LP) is roughly 96,000 btu per gallon.
Your heat exchanger will need to be sized for your water flow and the temperature of your "supply heat"--in this case, your plate heater (I'm not sure what exactly that is)--may be available flow rate/btu/hr.
 I am a redirected commercial HVAC mechanic with 20 years experience.
Title: Re: On demand domestic hot water using water to water heat exchanger?
Post by: Fether Hardwoods on June 07, 2015, 07:49:19 AM
It's a water to water heat exchanger, using the stove to heat my domestic hot water. I can get a 125000 btu unit or 225000 btu unit, I am thinking of getting the 225 to be safe.
Thanks for your help
Title: Re: On demand domestic hot water using water to water heat exchanger?
Post by: azmtnman on June 07, 2015, 09:55:04 AM
The mfg should have all the information you need. I know plenty of people who have heated their hot water with their wood boilers.
One thing about choosing a size--if you get way too big, the unit will not run "full throttle" enough to burn clean and it will soot up a lot.
 
Title: Re: On demand domestic hot water using water to water heat exchanger?
Post by: jfaulring on June 08, 2015, 07:29:08 AM
I have one of these on my setup:  http://www.supplyhouse.com/FlatPlate-FG5X12-8-8-plate-3-4-Thread-20-GPM-Heat-Exchanger-5-x-12

Mine's sitting as a "side arm" on the electric hot-water tank that we use in the off season when the OWB is't being fired. It's sitting as the first item on the loop from the boiler being fed by by a Taco 009 pump. I purposely oversized it a bit to compensate from the inevitable mineral build-up on the potable side of the exchanger from our well water. I usually end up needing to de-scale the exchanger once a season to get things back to maximum flow again; I built in some isolation valved and tap points where I can re-circulate some white vinegar with an external pump through the exchanger without needing to pull it all apart. This setup keeps the domestic tank up at about 180 degrees (which prevents any bacteria growth in the domestic hot water tank) and there's a mixer valve at it's exit to bring the temp back down to 130ish to feed the house.
Title: Re: On demand domestic hot water using water to water heat exchanger?
Post by: red oaks lumber on June 13, 2015, 06:44:32 PM
i have a 11 plate exchanger for my domestic water
Title: Re: On demand domestic hot water using water to water heat exchanger?
Post by: upsnake on July 21, 2015, 11:03:06 AM
I have a ten plate hx.
It works good. It will take the well water ~50 degrees up to about 130.
I have my setup going from the plate to the water heater, and use the water heater as a storage buffering tank.

I can run a shower and washing machine or two showers etc and keep the temps up over 120.

This is where I got mine from.
http://www.ebay.com/itm/Stainless-Steel-Copper-Brazed-Heat-Exchanger-Mounting-Studs-Water-Boiler-Radiant-/351148034715?pt=LH_DefaultDomain_0&var=&hash=item906f6f376f


Jfaulring - do you have any pictures of your setup. I am going to need to clean mine at some point it has been in service for 4 years.
I put unions on the copper so I can take it out, but something to just run vinegar through would be nice.
Title: Re: On demand domestic hot water using water to water heat exchanger?
Post by: r.man on July 26, 2015, 09:50:11 PM
Two gallons a minute sounds low, where did that number come from?  I have never heard of anyone doing on demand with a water to water exchanger.