On demand water heater concept

tim smith

I have been thinking about using an oversized brazed plate heat exchanger with a flow through design like an on demand water heater and maybe a pump to circulate a small 6 gallon storage tank. The tank hopefully could buffer the lag time for boiler to start up and for small draws. sensor in bottom of little tank. cold water flows through heat exchanger to get best transfer efficiency. What does every one think, am I crazy? I attached a simple ethch a sketch drawing also. Tim

tim smith

very likely but my main reason is here in Seattle they will only qualify a 1000 rebate if it has less than I think 15 gallons of storage. Just an idea, also with a braze plate with cold directly flowing through heat x your exchange rate is much better from lower temp boiler water. Keeping in condensing mode more also. This is just a rfi round to see what all think.

kcopp

Triangle tube used to have this....
http://www.triangletube.com/documents/20/Mini Smart LIterature.pdf

tim smith

Kevin, I think mine would be more effective due to the cold water going through heat exchanger whenever a draw, what do you think? Thanks, Tim

4Johnpipe

One issue I see would be flow rate differences between the tankless heat EX and the flat plate heat EX. HTP has this technology somewhat in their floor mount combi unit EFTC-140F.
Take a look...
http://www.htproducts.com/EFT_Combination_Floor.html

njtommy

it could be a pretty cool project. I was thinking of doing the same idea or so with my combo boiler and a domestic hot water pump. I really hate waiting for hot water and watching cold water go down the drain.

JStar

njtommy said:

it could be a pretty cool project. I was thinking of doing the same idea or so with my combo boiler and a domestic hot water pump. I really hate waiting for hot water and watching cold water go down the drain.

This gave me an idea.

Why not incorporate a recirc loop into this idea? Instead of circulating water from the tank outlet to inlet, circulate it from the furthest fixture to the tank inlet.

njtommy

JStar said:

njtommy said:

it could be a pretty cool project. I was thinking of doing the same idea or so with my combo boiler and a domestic hot water pump. I really hate waiting for hot water and watching cold water go down the drain.

This gave me an idea.

Why not incorporate a recirc loop into this idea? Instead of circulating water from the tank outlet to inlet, circulate it from the furthest fixture to the tank inlet.

Jstar your right on track.
Basically what i'm plaining on doing running my tankless unit like normal and have it feed into a electric hot water heater or indirect tank. Then out of the electric hot water heater or an indirect tank, but already have an electric hot water heater that is 4 years old and I was using before we got gas this year. It would feed all my fixtures and then add a Taco smart pump.

tim smith

I had already planned on a recirc add if recirc line available but a lot of old houses around here don't have recirc so I left it out of the drawing. Recircs can be a waste of energy although unless tied to occupancy sensors in rooms where hot water draw is regular.
Btw, this was not with a tankless water heater but a boiler. The small storage tank should cover the prepurge and ramp up time of the condensing boilers.

4Johnpipe

@njtommy Take a look at page 38 of the Rinnai manual that is exactly what they specified O have at least 3 piped this way for years now and the customer loves it!

Rich_49

http://www.slantfin.com/products/other-products/domestic-hot-water-generator.html

Snowmelt

you don't need a flat plate heat exchanger just go into an electric water heater.