GSHP DHW zone?

Bob Eh?_2

I don't think so..... That's why I have the booster downstream. If I thought I was going to have zero hot water usage for a while I would be concerned about the water in the indirect that may be a bit too cool for safety....

Since that never happens around here I haven't done anything about it. If I had to I might consider running a pump that circulates the booster though the indirect once daily until the booster tank cuts out at the 140* or better.

This whole legionaires (et al) thing scares the hell out of me because there just doesn't seem to be a pat answer on what constitutes safe conditions. We treat all water coming in (from a river BTW) with UV as a grand finale so I am not sure where the virii/bacteria would ever come from but I figured the booster setup would give me a second line of defense!

Bob

BC

Geo DHW question

I am checking out various geothermal options, and one thing I would really like to do is get a large portion of my DHW from it. I don't really like the desuperheater option since I wouldn't be running the system in the summer, so I'd only get useful heat from it in the coldest winter months.

I was thinking of running an indirect water heater as a seperate zone with priority. Given that the output of the heat pump is limited to 120F or so, and there would be some loss in the heat exchanger, I would probably need a booster of some sort to heat the water up the last 10-15 degrees. I'm wondering if there's any reason not to use a desuperheater to do this. In other words, when the tank called for hot water, the DHW zone would come on and circulate through the indirect. At the same time the desuperheater would be circulating water through its loop, boosting the temperature at the same time.

Bob Eh?_2

This does work but there are several things you need to think about. In heating mode the desuperheater does somewhat derate the main heat output. If you are piped correctly there is no good reason not to use the heat pump to heat the water in the summer time. This means you need to be able to run the indirect loop without the main system circulator so all the output goes to the tank.

The only "problem" is that you really need an auxiliary boost of some sort on the tank to get that last bit of temperature lift. It is really not a good plan to run the heat pump just to get the that last few degrees of boost from the desuperheater. This situation will occur due to standby losses etc. I have a small, 40g, regular electric tank downstream of the 120g indirect for that reason. Given it never needs to provide more than about 20* of lift the power consumption is very low and you can stand in a HOT 5gpm shower for at least 45 minutes with no problem! I set the indirect thermostat at 120*, I also let the desuperheater run at all times, and the electric at
140* with a 5* differential on both.

Hope this helps.....

BC

Thanks!

Thanks for the info - this seems to be a good way to set it up. My only concern is the temperature of the indirect HW tank - is 120F high enough to keep bacteria growth from being a problem?