Simple question
Would there be any adverse effect to the unit itself if using a conventional gas hot water heater as a backup to a single coil solar storage tank?
-S.
Just make certain..
that there is an anti scald mixing valve between the solar PH tank and the gas fired aux. tank and you should be OK. There will be times during the summer, that the preheated hot water could be hot enough to cause the ECO (Energy Cut Out) switch to fail, hence the need to mix down betwixt the two.
Other than that, can't think of anything that would cause adverse affects.
ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
Auxiliary Tank Standby Losses
Over the years, I've had customer complaints about the fact that he standby losses of the gas-fired tank aren't being supplied by solar.
One solution is a tiny pump and another differential controller to add solar heat to the auxiliary tank whenever solar is hotter than the auxiliary setpoint.
A house with a timed or demand recirculation loop has this problem partially solved if it's piped right.
It's a problem worth investigating because most gas water heaters have a typical energy factor of 0.6. That means that 40% of the gas it uses is wasted. Most of the waste heat goes right up the flue.
Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
Interesting point Kevin
The house I am working on has no recirc pump. If I move forward with this project I shall investigate and report back!
-S.
by-pass
Seeing that pretty much all my hot water is now being heated by solar, what I did was install a by-pass so the hot water doesn't go thru the gas heater. If we get 3 or 4 days of cloudy weather, I merely have to swap a couple of ball valves putting the heater back in line. Any idea what kind of temperature this ECO switch will take before it possibly fails?
RT
Summer bypass
rt,
That's a pretty good solution. Save even more money by shutting off the aux. heater pilot light once the sun takes over. When a gas-fired tank like this can be isolated from city pressure, an expansion tank will keep pressure spikes to a minimum and extend its life.
$35 at Home Depot.
If you provide a bypass like this for a customer, watch out because many homeowners aren't used to changing valves around a couple times a year. Clearly labeling the valves may help.
Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
ECO switch Opens at 180F
And it must be manually reset.
Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
mix valve on the second tank
would allow the standby tank temperature to be elevated for legionella protection, seeing as some water heaters are limited to 120F.
The warmer you maintain the tank(s) the more draw down you will have and you want to pull the solar tank down as cold as possible for the next harvest. Wouldn't installing the mixer on the solar tank, before the back up tank would limit how cold that tank is pulled down.
To prevent heating the standby tank to a temperature where the ECO could trip out you can limit the solar tank temperature on most controllers.
Also some installers use a dual control solar control and a motorized three way valve to shuttle between tank.
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