Geothermal questions

[LD1]

Been doing tons of reading on geothermal as I will likely be installing one this spring. Have a few questions and want to see what some of you have done.

Main thing is DWH and the best way to get the most out of the system. Are you guys running a single tank, two tanks, something else?

Currently have a single 50gal tank. My understanding is that with a single tank, and in heating or cooling season the geo unit will do most of the "maintaining". But when everyone is taking a shower in the evening, and especially if the geo isnt calling for heating/cooling, the electric is going to be doing most of the heating of the cold incoming water. And even if the geo is running, electric is still going to run because the geo wont recover quick enough.

So, I like the theory behind the twin tanks. To keep a pre-heat tank nice and warm, and pull from the electric tank. The pre-heat tank supplies the electric tank so the elements likely wont come on, then whenever heating/cooling is needed for the house, the buffer tank works on heating back up. But with this, the roles are basically reversed. Geo heats incoming cold water, but rely on the electric to "maintain". So its not like one can "shut off" the electric. or the electric tank will go cold while the geo keeps the buffer tank warm.

Is there a way to make the desuperheater "maintain" both tanks? And if not, since I would have to buy another water heater anyway, I was kicking around the idea of a 13kw or 18kw on demand heater and using my existing tank for the desuperheater and unhooking the electric to it. My main concern doing this, is not having enough water heating capacity in spring and fall months when I am neither using heating or cooling. The storage tank, allthough insulated, should still somewhat serve as a pre-heat tank and take the ~40 degree tap water up to maybe 50-60 degrees. But I would still need a ~60 degree temp rise, and a 13kw is good for 1.5gpm, and the 18kw would be ~2gpm. Is that enough for a standard shower? What about 2 showers? (I know I should probably test the GPM of my shower heads) Cannot really go bigger than 18kw as house only has 200a service. So any of you guys running a tankless + buffer tank as opposed to twin tanks? and how big is your tankless heater, and how does it preform.

Next topic. I will likely be doing the install myself. Those that also did their own, who did you get your stuff from? good online sources? Got some quotes and did some chatting with these guys last year and Im kinda leaning towards them Geothermal Heating & Cooling Systems Dayton & Cincinatti, OH

Finally.....pressurized or non pressurized loops? I have read for hours about the pros and cons of both. Still undecided. Any usefull info you can add would be appreciated.

 

[jk96]

We started with one tank and switched to two. Used the old tank for a buffer tank and a 50 gal Marathon as our heated tank. Here's my reasoning for two tanks.

Single Tank Setup
With a single tank setup as soon as you draw down your hot water from your tank it refills with cold water (45 degrees +-) and your heating elements kick in to reheat the water. The tank recovers fairly quickly, maybe one to two hours depending on how much it was drawn down. During this time even if your desuperheater is running the entire time (which it may or may not depending on call for heat/air), you only get the benefit of an hour or two of help until the water heater is satisfied and the elements turn off. After the water heater has recovered the desuperheater is now worthless other than maintaining standby temp which uses very little electricity. The desuperheater takes much longer to heat your water than a hot water tank itself. Even if the unit and desuper is running for the full two hours that the water heater is re-heating the benefits of the desuper are minimal.

Two tank setup
Now consider a two tank setup. Most peak demand, especially Monday through Friday is in the morning and evening for most households. Most of our showers, laundry, etc are done between 7pm and 10pm and hot water usage does not pick back up again until 6-7am. This gives us 8-9 hours for our desuperheater to warm our buffer tank. We have the powered tank set to 115. Our desuper set to 125. On a cold night our buffer tank is reaching our setpoint of 125 by morning. Now in the morning when we draw hot water, our 115 degree powered tank is being refilled by our 125 degree buffer tank. The heating element never comes on unless we use more than our 50 gallons of preheat water. It only turns on to maintain temp in standby. Everyone leaves for school and work and the cycle repeats during the day. We have all day for the buffer tank to reheat again until evening when hot water demand returns. Even on warmer days when the unit is not running as much, we are typically feeding 85-95 degree water to the powered tank. Recovery is much faster.

Jeremy

 

[buickanddeere]

We just use the buffer tank as a warmed feed water into a standard electric hot water tank.

 

[jk96]

Is there a way to make the desuperheater "maintain" both tanks?

The desuper is a very slow process for heating the tank. 8-10 hours to bring a cold tank up to temp. I don't see a benefit to running both two tanks off the desuper. Just use the unpowered tank as a buffer and heat it with the desuper.

On a side note. If you have an extra breaker available for the buffer tank, you can go ahead and wire but leave the breaker off. This gives you an extra tank you can heat up if you have guests staying over, grand kids, etc and anticipate needing extra hot water for the day.

 

[LD1]

The desuper is a very slow process for heating the tank. 8-10 hours to bring a cold tank up to temp. I don't see a benefit to running both two tanks off the desuper. Just use the unpowered tank as a buffer and heat it with the desuper.

On a side note. If you have an extra breaker available for the buffer tank, you can go ahead and wire but leave the breaker off. This gives you an extra tank you can heat up if you have guests staying over, grand kids, etc and anticipate needing extra hot water for the day.

Most of our hot water comes in the evening. No one normally showers, does laundry, dishes, etc in the morning. So would have 20 hours to recover.

If it were to only take 8 hours to recover the buffer tank, the other 12 hrs of potential is lost.

even though minimal, the thought was to get away from the electric having to "maintain" for that 20 hr period. thus the though of either maintaining both with the desuperheater, or only having the buffer tank combined with a tankeless.

 

[jk96]

Maybe someone can chime in that has some numbers but I would think maintaining temp on a high efficiency tank such as a marathon would use very minimal electric. Most use is going to come from heating. I've never seen or heard of circulating two tanks through the desuper. I would think the recover would be extremely long and may cause your elements to kick in on the heated tank. In fact most recommend a 50 gal over 80 gal buffer. One buffer one heated seems to be tried and true in geo. Not sure about the tankless combo. Sounds good in theory.

 

[LD1]

Maybe someone can chime in that has some numbers but I would think maintaining temp on a high efficiency tank such as a marathon would use very minimal electric.

Dont have a marathon. Just a standard run-of-the-mil 50 gallon.

And while I understand that "maintaining" the heat is not a huge user of electricity, it is still a user. And if there is a way to minimize it or eliminate it (tankless) I want to explore those options

 

[jk96]

Dont have a marathon. Just a standard run-of-the-mil 50 gallon.

And while I understand that "maintaining" the heat is not a huge user of electricity, it is still a user. And if there is a way to minimize it or eliminate it (tankless) I want to explore those options

Your standard tank would be fine as the buffer tank. I'm not sure how usage would compare to maintaining temps with a standard tank or firing a tankless when demand calls? I'm interested to see what you find out? Will be following.

 

[wngsprd]

We have the two tank system and have been pleased. The desuper tank feeds the primary water heater used for laundry/kitchen/2 bathrooms, but the desuper also feeds a bathroom located just above it in the back of the house. Not sure if this is the most efficient but works well.

 

[fishheadbob]

We have 2 50 gallon tanks, one is the buffer, and are pleased. My electricity usage is minimal.
I had mine done by pros, the cost was substantial, as are the savings. The professionals from both companies I was shopping with said go with the buffer tank so I did.
My old back was giving out under 22 cords of wood per year, while still burning some oil and propane.

 

[davesl708]

I have the dual tank with DHW. Very happy with the setup. My brand is Water Furnace.
The buffer tank w/o the DHW on maintains 95 degrees in the winter when the heating is operating. This feed the hot water heater. Lot cheaper heating 95 deg. to 130 deg. than 55 deg. to 130.

When family is here I turn on the DHW. Never a shortage of hot water with 100 gals. available and the DHW going.

My house is total electric. My high bill in summer is $65 and high in winter is $165. I have a six person hot tub that runs year round.
With the 30% energy tax credit my system with the vertical wells cost about the same as a high end gas/electric HVAC and no noise outside unit.
My energy cost were cut in half by getting rid of gas and not running an outside unit.

The system runs on 30amp 220v and can run the system on a generator if needed. Have never had a power failure yet.

 

[buckeyefarmer]

Buffer tank, as the others have said.

 

[s219]

We have a single Rheem Marathon hooked up to the geo system (ClimateMaster 22). The geo unit pulls water off the bottom of the tank (from what would normally be the drain port), runs it through the de-superheater heat exchanger, then delivers the water back into the tank through the top "cold" input. I can't give pros or cons of single versus dual tanks based on real experience since I don't have any -- we only went single because that's what the geo installer recommended for our setup. I believe dual gives you more options however.

 

[LD1]

Thanks everyone. I have pretty much decided on the buffer tank for efficiency. Maybe I wasnt that clear in my post this morning.

The question is really about the second tank hooked to the electric, and weather or not a tank type is better than a tankless. and weather a 13kw or 18kw tankless is a better option. And weather those will actually keep up with reasonable demand in the months that the geo is not needed?

 

[davesl708]

Thanks everyone. I have pretty much decided on the buffer tank for efficiency. Maybe I wasnt that clear in my post this morning.

The question is really about the second tank hooked to the electric, and weather or not a tank type is better than a tankless. and weather a 13kw or 18kw tankless is a better option. And weather those will actually keep up with reasonable demand in the months that the geo is not needed?

My geo operates year round. The hot water is 50 gal. electric with 50 gal. buffer tank feeding 85 to 95 degree water. With 5 people in the house hot water has not been an issue. My geo people used my old gas water heater as the buffer tank.

 

[techman]

The biggest disadvantage of a single tank system is temperature. The desuperheater takes the heat from hot freon at the compressor outlet. When compressor head pressures are low (a good percentage of cooling and some during heating) there is not a very high temperature extracted. If the WH is near or above the desuperheater temp (mass of freon times the temp) there will be no heat added to the HW heater. In other words if the desup generates 80 or 90 deg, it will do nothing to add to the HW heater which is at 120-130 deg. Many new design geo units have a temp switch that will not run the desup pump when the temp is not high enough.

With a second tank you are generally working with a lower water temp so heat is easier to add to the water. Any temp added to the preheat tank are BTUs that directly benefit the main tank by having warmer water coming in and therefore does not need to be heated as much. Just thermodynamics at work.

paul

 

[jk96]

You might also consider the expense of service for the on-demand water heater. Maybe they're more reliable now. When we built a few years ago our plumber talked us out of one. He didn't have one and said he wouldn't install one in his home due to the high number of service calls he has for them.

 

[LD1]

Techman, I understand how a twin tank works. I am not even considering a single electric tank tied to the desuperheater.

And as far as BTUs go, a second uninsulated tank, even if you don't have geo, would also help. Allow your 45 degree ground water to warm up to house temp of 70 prior to going into the main tank. Same theory, just not as much benefit as the desuperheater.

My focus now is on either:
1. Dual tanks
2. Single buffer tank + on demand heater in lieu of second electric tank

 

[buckeyefarmer]

For the loops, I'm happy with my non pressurized.

Find a local supply house that deals with geo. There is one online, up in sugar creek ohio.