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Posted by kickaha(remove) on September 24, 2004, 7:19 pm
 

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  Hi, all-

We just had a solar domestic hot water system installed and I think it's
plumbed wrong (but what do I know?)

Here is how it is plumbed: We have two storage tanks (call them B & C)
that are plumbed in a loop with the solar panels..

There's a third tank (call it A) that is just an electric water heater
and it is supplied by tank C.

I fired everything up, but wasn't getting any hot water. The solar guy
came out and told us we have to have the electric water heater turned on
to heat the water in tank A and that as tank A is drained, hot water
from tank C will flow in to replace the water in tank A.

This just seems stupid to me. Why the heck am I electrically heating
water when I have a solar DHW system? The electric water heater is
supposed to be there just to pick up the slack. The solar guy is telling
me it won't cost much to keep the water in the electric water heater
(tank A) warm but I can't imagine it will be cheap.

Here is what my brain is telling me needs to be done: put all three
tanks (A, B & C) in the solar panel loop so the sun is heating ALL of
the water. The only thing that makes me think I may be wrong is the guy
who installed our system seems to be quite experienced and should
therefore know more than I.

What do you think?

kickaha

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<font class="post"> Hi, all-<br>
<br>
We just had a solar domestic hot water system installed and I think it's
plumbed wrong (but what do I know?)<br>
<br>
Here is how it is plumbed: We have two storage tanks (call them B &amp; C)
that are plumbed in a loop with the solar panels..<br>
<br>
There's a third tank (call it A) that is just an electric water heater and
it is supplied by tank C.<br>
<br>
I fired everything up, but wasn't getting any hot water.  The solar guy came
out and told us we have to have the electric water heater turned on to heat
the water in tank A and that as tank A is drained, hot water from tank C
will flow in to replace the water in tank A.<br>
<br>
This just seems stupid to me.  Why the heck am I electrically heating water
when I have a solar DHW system?  The electric water heater is <i>supposed</i>
to be there just to pick up the slack.  The solar guy is telling me it won't
cost much to keep the water in the electric water heater (tank A) warm but
I can't imagine it will be cheap.<br>
<br>
Here is what my brain is telling me needs to be done: put all three tanks
(A, B &amp; C) in the solar panel loop so the sun is heating ALL of the water.
 The only thing that makes me think I may be wrong is the guy who installed
our system seems to be quite experienced and should therefore know more than
I.<br>
<br>
What do you think?<br>
<br>
kickaha<br>
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Posted by Bert Menkveld on September 27, 2004, 12:34 pm
 
Most SDHW systems seem to be plumbed the same way yours is.  The idea is
that if the solar system has not heated the water all the way to the desired
temperature, the electric water heater will warm it up the rest of the way.
You still benefit from the pre-heating by the solar system.

If you're willing to live with variable hot-water temperatures, you can turn
off the electric water heater.  How practical that is depends on your local
climate.  It certainly wouldn't work well for me in Southern Ontario, Canada
(lots of cloudy days, even in summer).

The only "extra" loss you incur with this arrangement is the heat loss from
the electric hot water heater tank.  If you want to avoid this heat loss,
you could replace your electric water heater with a tank-less (on-demand)
water heater.

Regards,

Bert Menkveld



Posted by Niels Lyck on October 7, 2004, 6:58 am
 I agree with kickaha that it's a quite silly way to connect the system, but
if that's the way it's done in your neighborhood, then it might be difficult
to change. One easy thing to do would be to make a shortcut-connection
directly from tank B (or C), surpassing tank A, so that the (sufficiently
heated) solar hot water can be delivered directly out to the taps, eg. in
summer. Remember to consider eventual scalding risk here, if theres no
anti-scalding device in the system.

Niels Lyck

"Bert Menkveld" <bertATreentronicsDOTcom> skrev i en meddelelse


Posted by Bill Kreamer on October 7, 2004, 2:46 pm
 What do I know from solar hot water, but as a machine designer, my question
is, why would you _ever_ feed electric-heated water back to the solar
panels? Not a good system design. It's ok by me to have the solar feed the
house via the electric tank.

Bill Kreamer


kreamer@adelphia.net
www.sol-air.com

difficult

(on-demand)

telling


Posted by News on October 7, 2004, 3:24 pm
 

One way is to have a diverter valve in the pipework, with a controller that
senses the heat from the panels and what is in the main run tank.  When the
water from the panels is hotter than the tank then it diverts to the run
tank and cuts out the electric heater, if not then to a pre-heat tank and
the electric heater cuts in to maintain the run tank setpoint.

As been mentioned using the pre-heat tank as a feed to an instantaneous
on-demand water heater maybe more efficient. The water heater just tops up
the heat if the pre-heat delivers under temperature water.  Or better still
have a blending valve from the pre-heat to ensure the optimum temperature,
probably 60C.  The pre-heat tank could actually be 95C on hot summer days.
The on-demand heater could be throttled open to accept a high flow from the
pre-heat tank to fill a bath quickly; on-demand heaters generally have poor
flow rates.  When the pre-heat is cool a thermostat tells a flow regulator
to restrict the flow into the water heater to a lower flow rate that will
give acceptable heat and flow.


difficult

(on-demand)

telling


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