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Old 06-04-14, 03:16 PM   #291
NiHaoMike
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You can attach a temperature sensor to the cold water inlet (a few inches from the exchanger) and start the pumps when there's a drop in temperature. Try to arrange it so that the exchanger is right above the 40 gallon tank. Then it would tend to stay warm by convection instead of short cycling the pumps.

The ideal is to put some copper tubing in the tank but that doesn't seem to be practical for your case.

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Old 06-04-14, 07:59 PM   #292
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The Taco Delta-T pump on the tank side of HX would work.

This should work well for recirculation to get almost instant hot water at fixtures.
There will be a small 10W El-Sid 24vdc pump at each of the 3 bathrooms & at kitchen island sink with temp. controlled pumping back to HX via a 3rd return line. The hot water out to fixtures & return line will be well insulated.

The well water input into the HX load side has been preheated in solar storage tank.

http://www.taco-hvac.com/uploads/Fil...ry/102-143.pdf

Pump requires a Run signal OR I could jumper this so it's always on at lowest power (8W).

Pump dip sw controls: #5=off, #4=on, #3=on, #2=off, #1=on

Sensors:
S2 (source) would be on pipe between top of tank & HX.
S1 (load) would be on pipe between bottom of tank & HX.

5*F is the minimum switch selected Delta-T.

Pump slows to it's minimum speed (8W) if S1 is hotter than S2 - Delta-T)

When load (shower etc.) is drawing hot water S1 will drop in temp. relative to S2 & pump will speed up trying to maintain 5*F Delta-T.

This setup will cause a constant circulation in tank, which has good and bad effects.

Good = tank is almost completely up to the temp. set by aquastat, on a long draw the 40 gal. tank will provide as much hot water as say a 60 gal. stratified tank.

Bad = heating tank with DSH & HP will not draw cool water from bottom, which decreases Eff. & thus will take longer run times, I think.

Last edited by buffalobillpatrick; 06-06-14 at 11:31 AM..
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Old 06-11-14, 07:10 PM   #293
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Found more info:

Heating Help


"Domestic water is heated instantaneously as it passes through the external
stainless steel heat exchanger. A flow switch turns on the small circulator
supplying this heat exchanger whenever there’s a demand for domestic hot water.
Hot water from the top of the tank flows through the primary side of the heat
exchanger and instantly transfers heat to the other side. This heat exchanger
is easily replaceable (and recyclable) if ever necessary due to scale or other
issues. The minimal quantity of domestic water residing in this heat exchanger
(probably less than one pint) reduces the possibility of legionella
growth."


A comment from Fortunat:

Regarding heating DHW in a single pass flat plate HEX, I
can't seem to find it right now, but I read a good paper (maybe by ZfS
- Rationelle Energietechnik GmbH in germany) about the control
challenges of this arrangement in large SHW systems. I suppose if you
just bang the pump to full speed anytime the flowswitch on the potable
side registers any flow it would work ok, but you'd be mixing the tank
up unnecessarily. The germans tried variable speed pump based on
heat exchanger exit temperature and (not surprisingly) found the
control to be quite challenging because of the odd and spikey nature of
DHW demands. Have you actually tried it?
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Old 06-25-14, 04:29 PM   #294
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I started a thread over in Solar Heating

http://ecorenovator.org/forum/solar-...-insulate.html

a couple of websites are linked, that combine Solar, HP, underground heat storage battery (large uninsulated tank (Austria 6600 gal.))

The website from Austria has a DHW tank with internal HX kept @ 42-49C, which can be heated at a fairly high COP by Heat Pump, without fear of Legionella.


Last edited by buffalobillpatrick; 06-25-14 at 06:22 PM..
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