Simple question

Steve Fontas

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?

Mark Eatherton

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

Kevin_in_Denver_2

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.

Steve Fontas

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!

rt_2

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

Kevin_in_Denver_2

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.

hot_rod

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.



hr

Kevin_in_Denver_2

ECO switch Opens at 180F

And it must be manually reset.