supplemented hot water

J Matthers_2

I have a GSHP with a de-superheater that heats water in a storage tank. This water in-turn supplies my instant hot water heater with pre-heated water theoretically saving gas.



The result at the shower head is very hot water early in the shower needing to be mixed down and then adjustments throughout until the supply of pre-heated water runs out.



My thoughts to correct is to put in a mixing valve after both the instant and storage tank allowing the hot water temp to be constant.



Any other ideas?



Thanks

Big Ed_4

mixing valve

The geothermal hot water is used to preheat water going into a tankless water heater ? The two are in series ?



if so the mixing valve would go after the tankless on the hot water supply to maintain a more constant and tempered hot water supply temperature ...

J Matthers_2

Thanks

thanks Big Ed. currently the cold supply to the instant tankless runs into a storage tank and is preheated via de-superheater and then on to the water heater. Over night the water in the storage tank will reach set-point - 122*. So, first shower of the day you need to mix the hot way down. As the preheated depleats you need to adjust the temp in the shower. If I supply both the HWH and the storage tank with separate supplies and then put a mixing valve beyond them would the water temp be consistent? Or, if both are at the same set-point (tank and HWH) would it stop pulling from the storage tank as soon as the temp dropped?

Big Ed_4

Piped Parallel

Piping in a set of different type hot water heats in parallel will bring in new issues .. Resistance and output ...



The water would flow through the unit with the least resistance , which I assume would be the storage tank and there maybe will not enough flow to turn on the tankless ..



Then once the storage tank is depleted cold water would flow into your hot water supply ... The mixing vale will not shut down on the flow....



As you found out in series steps up the temperature .. Two like heaters you would pipe in parallel for quantity but piped reverse return to equalize the resistance of piping to help obtain equal flow between them ..



With your system keep them in series and add the mixing valve after the tankless..

hot_rod

thermostatic valves after tankless

check with the manufacturer of the valve you are considering. We advise against 3 way thermostatic valves after tankless DHW heaters. It can effect the way the heater operates.



More and more, installers are adding a small 3-6 gallon buffer tank with tankless heaters. this eliminates the "sandwich' effect, and allows for DHW recirc systems.



hr

Gary_Sacto

Need to know more about the tankless water heater

Can you tell me whether the tankless water heater is gas(natural or propane) or electric?

There are different control strategies for each type and different capabilities to handle small temperature differences.

What you want to occur is that as the temperature drops in the preheated storage tank, the tankless water heater adds heat at the flow rate and temperature rise that is needed. To do this, the burner or element needs to be able to handle as little as a 1F temperature rise. So, at 1 gpm, a 1F temperature rise requires 500 btuh. This is very small!

Also, depending on the answer, you may also want to consider a different mixing valve for the shower. So, what is the temperature control for the shower? Pressure balanced? Thermostatically balanced? Nothing?

Thanks!