Desuperheater and Geyser

[sloeffle]

All of the threads on becoming more energy conscious have gotten me thinking about my own electric usage. My house is all electric and we generally use around 1,000KWH - 1500KWH a month depending on the time of year. We tend to use less energy in the summer because our GSHP makes "free hot water" via the desuperheater.The COP of the GSHP on the setup that we have is 4.6 in first stage and 4.0 in second stage. The furnace generally runs in the first stage.

I usually turn off the desuperheater going into the winter so I can keep my loop temperatures higher. We heat our hot water with a Rheem Marathon hot water heater. The tanks shows an annual usage of around 4700KWH a year. Based off of that ((4700KWH / 12) * .16), it is costing me roughly 63$ a month to make hot water. My wife lovers her hot and long showers so it could be costing me more $$$. So this leads me to the idea of buying a Geyser to help with my hot water needs.

During the coldest months of winter we heat the house with a PSG Caddy wood burning furnace that is in the basement. The basement is roughly 800 sq ft and is insulated on the outside via R-10 close cell foam so it stays in the 60's during the winter if we are running the GSHP. With the wood furnace running the basement stays in the 70's. We do have to run a dehumidier when we are not heating or cooling.

Does it make sense to have both a desuperheater and a Geyser ? The Geyser would probably run 6 - 8 months of the year. I would not run it during the summer months. Would I be better off just leaving the desuperheater turned on all of the time and let the GSHP supplement my hot water needs.

 

[Circus]

Would I be better off just leaving the desuperheater turned on all of the time and let the GSHP supplement my hot water needs.

I would. Unless you plan using the wood burner to heat the basement being cooled by the Geyser, the GSHP is supplying the hot water anyway. Why power another pump?

 

[sloeffle]

The furnace is not always running, so it is not always supplementing the hot water heater. But we are always ( dishes, laundry, showers ) using hot water while we are home. I like the idea of the Geyser. But like you said, the idea of running another pump that is going to break down the road is not desirable also.

 

[woodgeek]

I thought the desuperheater only worked when the geo was in AC...? Would it be running the AC while the furnace was going? What does the furnace run on?

 

[Highbeam]

If your GSPH can make hot water with a COP of anything better than 1 then of course you should use it to heat water instead of the COP 1 of the marathon. Worst that could happen is you need to run the GSHP harder to heat your home but that won't cost any more energy than what you saved by cutting the hot water resistance heat off.

Those HPWHs are noisy.

 

[maple1]

I think I would turn the GSHP off all together in the winter, and heat with the Caddy - except for when you are away from home for overnight. And combine that with a HPWH - the HPWH will do your dehumidifying for you too.

That seems like a lot for heating DHW - our new 'ordinary' 80 gallon heater uses about $30/month in the summer. That's a family of 5. My wife isn't in the shower for that long - but 2 of my kids make up for that.

 

[sloeffle]

I thought the desuperheater only worked when the geo was in AC...? Would it be running the AC while the furnace was going? What does the furnace run on?

On the GSHP that I have, you can manually turn the desuperheater off and on. It will run in both AC and heat pump mode.

Waterfurnace does have a unit that now that can sense the loop temperatures are getting low and automatically turn it off.

 

[sloeffle]

I think I would turn the GSHP off all together in the winter, and heat with the Caddy - except for when you are away from home for overnight. And combine that with a HPWH - the HPWH will do your dehumidifying for you too.

That seems like a lot for heating DHW - our new 'ordinary' 80 gallon heater uses about $30/month in the summer. That's a family of 5. My wife isn't in the shower for that long - but 2 of my kids make up for that.

I really should buy an energy monitoring tool to verify the electric usage on the hot water heater. I am just going off of what is on the generic energy usage label itself. Our electric rates are pretty high so that does help with the cost per month either.