Running geothermal system killing hot water heater temperature
Last Post 03 Nov 2014 11:08 AM by newbostonconst. 51 Replies.
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ascorbateUser is Offline
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27 Jun 2013 12:45 PM
Almost 2 years ago, I had a geothermal system installed in my home. It consisted of the Envision NDV038 (3 ton) dual capacity system with hot water assist (de-super heater) and approx 600 vertical bore (two 300 feet well bores) with 1,200 feet of 1-1/4” geo-pipe plus a 85 gal Rheem Marathon electric hot water heater. During the first winter season, I noticed that the more my geothermal system ran (to heat my home)... that the temperature of the hot bath water exiting the Rheem electric hot water dropped from approx ~125 degrees F down to ~110 degrees F (a very noticeable drop). So I initially found myself increasing the thermostat temperature on both the upper and lower heating elements in my electric hot water heater to compensate and make the bath water hotter. When Spring arrived and the geothermal system was running much less, I found my hot bath water was scalding hot. I brought this to the attention of the original installer and he sent out his plumber to investigate... and he subsequently replaced: 1) the upper thermostat, 2) the lower thermostat, and 2) one of the heating elements. We then took a wait-n-see approach until the following winter season when once again I found a noticeable drop in the temperature of the hot bath water exiting the Rheem electric hot water heater the more my geothermal system ran. This time, the installer sent out another tech who slowed the velocity of the water circulating thru the 1,200 feet of 1-1/4” geo-pipe. Measurements taken at that time were as follows (before the tech touched anything): EWP - Entering Water Pressure (bottom line): 50 psi. LWP - Leaving Water Pressure (top line) 42.5 psi. Difference: 7.5 psi. EWT - Entering Water Temperature (bottom line): 45.5 degrees F. LWT - Leaving Water Temperature (top line): 40.8 degreees F. Difference: 4.7 degrees F. After determining that the pressure difference between the entering and leaving water pressure was too high, the tech adjusted the entering water pressure (coming from my closed ground loop) by reducing the incoming flow so that the pressure difference was somewhere between 2.5 and 3.0 psi instead. This action resulted in the following revised readings the tech measured before he left: EWP - Entering Water Pressure (bottom line): 52 psi. LWP - Leaving Water Pressure (top line) 49 psi. Difference: 3.0 psi. EWT - Entering Water Temperature (bottom line): 45.5 degrees F. LWT - Leaving Water Temperature (top line): 37.9 degreees F. Difference: 7.6 degrees F. This brings me to the present with the onset of Spring this past year. Once again, I found my hot bath water was scalding hot with the geothermal system running much less. The installer (with over 200 installations) seems at a loss to explain these results noting I am the only one who has reported findings like this. Anybody have a clue about what might be going on here?
ChrisJUser is Offline
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27 Jun 2013 01:11 PM
Single tank set up, that's the problem.

You really should have a seperate tank (could be just an un-powered elec tank) for the DSH to circulate water in. Then your marathon would be the finishing tank, to bring the water up to 125* or so.

ChrisJUser is Offline
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27 Jun 2013 01:21 PM
Here is a picture of the two tank setup.



ascorbateUser is Offline
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27 Jun 2013 01:26 PM
So my installer has 200 plus installations (supposedly just like mine) minus the Rheem Marathon electric hot water heater as they are using conventional (not Rheem Marathon) electric hot waters instead. Wouldn't some of these customer(s) also be seeing what I'm seeing? BTW: The installer has never made mention (before, during or after) that I might need two hot water heaters!
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27 Jun 2013 01:32 PM
Posted By ChrisJ on 27 Jun 2013 01:21 PM
Here is a picture of the two tank setup.





If my existing hot water heater is 85 gallons... does a second buffer tank also need to be 85 gallons... or could it be smaller?
geomeUser is Offline
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27 Jun 2013 02:12 PM
Maybe Doc can provide some data, but it's my understanding that Envision units are not supposed to run the DSH unless conditions are favorable to making the water hotter (not colder.) Does the WF setup work under all conditions?

What was the original lower (and upper) thermostat settings? WF recommends a very low (can't recall) setting for the lower thermostat in a single tank setup.
Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon.
ChrisJUser is Offline
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27 Jun 2013 02:42 PM
I am pretty sure Geome uses a single tank setup with a timer so that the elements in the tank are off except for certain time frames before times of hot water use.

50 gal. I think is a typical DSH tank size.
Palace GeothermalUser is Offline
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27 Jun 2013 07:31 PM
Posted By ascorbate on 27 Jun 2013 01:26 PM
So my installer has 200 plus installations (supposedly just like mine) minus the Rheem Marathon electric hot water heater as they are using conventional (not Rheem Marathon) electric hot waters instead. Wouldn't some of these customer(s) also be seeing what I'm seeing? BTW: The installer has never made mention (before, during or after) that I might need two hot water heaters!

So he has been doing wrong for 200 times.   Still does not make it right.

It will still be wrong if he does it 200 more times.
Dewayne Dean

<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system
ascorbateUser is Offline
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27 Jun 2013 09:14 PM
Posted By ascorbate on 27 Jun 2013 12:45 PM
Almost 2 years ago, I had a geothermal system installed in my home. It consisted of the Envision NDV038 (3 ton) dual capacity system with hot water assist (de-super heater) and approx 600 vertical bore (two 300 feet well bores) with 1,200 feet of 1-1/4” geo-pipe plus a 85 gal Rheem Marathon electric hot water heater. During the first winter season, I noticed that the more my geothermal system ran (to heat my home)... that the temperature of the hot bath water exiting the Rheem electric hot water dropped from approx ~125 degrees F down to ~110 degrees F (a very noticeable drop). So I initially found myself increasing the thermostat temperature on both the upper and lower heating elements in my electric hot water heater to compensate and make the bath water hotter. When Spring arrived and the geothermal system was running much less, I found my hot bath water was scalding hot. I brought this to the attention of the original installer and he sent out his plumber to investigate... and he subsequently replaced: 1) the upper thermostat, 2) the lower thermostat, and 2) one of the heating elements. We then took a wait-n-see approach until the following winter season when once again I found a noticeable drop in the temperature of the hot bath water exiting the Rheem electric hot water heater the more my geothermal system ran. This time, the installer sent out another tech who slowed the velocity of the water circulating thru the 1,200 feet of 1-1/4” geo-pipe. Measurements taken at that time were as follows (before the tech touched anything): EWP - Entering Water Pressure (bottom line): 50 psi. LWP - Leaving Water Pressure (top line) 42.5 psi. Difference: 7.5 psi. EWT - Entering Water Temperature (bottom line): 45.5 degrees F. LWT - Leaving Water Temperature (top line): 40.8 degreees F. Difference: 4.7 degrees F. After determining that the pressure difference between the entering and leaving water pressure was too high, the tech adjusted the entering water pressure (coming from my closed ground loop) by reducing the incoming flow so that the pressure difference was somewhere between 2.5 and 3.0 psi instead. This action resulted in the following revised readings the tech measured before he left: EWP - Entering Water Pressure (bottom line): 52 psi. LWP - Leaving Water Pressure (top line) 49 psi. Difference: 3.0 psi. EWT - Entering Water Temperature (bottom line): 45.5 degrees F. LWT - Leaving Water Temperature (top line): 37.9 degreees F. Difference: 7.6 degrees F. This brings me to the present with the onset of Spring this past year. Once again, I found my hot bath water was scalding hot with the geothermal system running much less. The installer (with over 200 installations) seems at a loss to explain these results noting I am the only one who has reported findings like this. Anybody have a clue about what might be going on here?


FYI: So it was recommended to me by my installer to turn off the DHW switch (eg. the de-super heater) on my Envision Water Furnace. Right before I did, I measured the hot water temperature at 107.4 degrees F. Here I am approx 6 hours later and I just finished running bath water for the evening... and the hot water clocked in at 124.2 degrees F.
geomeUser is Offline
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28 Jun 2013 08:31 AM
ChrisJ is correct regarding my setup.

Some people in this forum (including me) have noted better DSH performance using fewer cycles per hour (CPH) settings on their thermostat (usually found in the installer setup section). This leads to longer run times, but larger temperature swings in the house. I suggest going with as few CPH as you can consistent with comfort. It would be interesting to see temperature readings with (much) lower CPH settings.

Fewer unit cycles may also help with unit longevity. I find all the on/off cycles with the typical 3 CPH for first stage and 3 CPH for second stage annoying.
Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon.
joe.amiUser is Offline
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28 Jun 2013 08:46 AM
If your installer dates back to R22 installations, we had far less problems with one tank set-ups in those days. We have documented proof that single tank set-ups offer little to no to negative benefits. I look forward to manufacturers taking it out of their installation manuals.
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
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28 Jun 2013 11:38 AM
Posted By geome on 27 Jun 2013 02:12 PM
Maybe Doc can provide some data, but it's my understanding that Envision units are not supposed to run the DSH unless conditions are favorable to making the water hotter (not colder.) Does the WF setup work under all conditions?

What was the original lower (and upper) thermostat settings? WF recommends a very low (can't recall) setting for the lower thermostat in a single tank setup.


All major manufacturers have a logic in their control board now to prevent the tank loosing heat to the ground loop during conditions when the loopfield is too cold in cooling mode. The DSH does not get up to temperature , the tank is hotter than the DSH discharge, heat it transported from the tank to the DSH into the refrigerant gas to the heatexchanger and out to the loopfield.
Usually they turn the DSH pump off when source EWT is below 50F in cooling mode, or when the DSH EWT is less than 25F above the refrigerant temperature.
However, all those scenarios would not occur when a buffer tank is installed.
While the manufacturers, for unknown reasons, still endorse single tank DSH installs, one has to understand that it neglects the purpose and function of the DSH when the tank is already heated by electric elements.
It does not matter if your installer has 200 installs, if he does not measure or check his outcome, he will never understand or seek to improve his installs. Be assured that his other 199 customers are having the same issue, they just don't know, nor does your installer.
www.buffalogeothermalheating.com
ascorbateUser is Offline
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01 Jul 2013 09:52 PM
Posted By docjenser on 28 Jun 2013 11:38 AM
The DSH does not get up to temperature , the tank is hotter than the DSH discharge, heat it transported from the tank to the DSH into the refrigerant gas to the heatexchanger and out to the loopfield.
So I showed this thread to my installer... and a light seemed to go off in his head. My installer then asked me how often my geothermal system ran on low... and then high. I responded that the geothermal system ran on low speed practically all the time except for really cold days/nights when it then kicks up to a higher speed. We then also reviewed that I have the equivalent of a 4 ton vertical loop (in the ground) with a 3 ton water furnace... the net effect is that I have a very efficient system (probably getting something close to 30 EER with the geothermal system running on low speed). With my system spending sooo much time running on low... is it conceivable that the refrigerant gas is just not getting hot enough to overcome the 125 degreee F set point of my Marathon hot water heater? Might this explain how my running geothermal system (on low speed 99% of the time) could be killing the temperature of the hot water in my hot water heater?
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02 Jul 2013 12:14 AM
The issue is in COOLING mode, not heating mode. A larger loopfield is usually beneficial, but it can result in the loopfield warming up slower, so you don't have enough desuperheat.
www.buffalogeothermalheating.com
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09 Jul 2013 10:02 AM
Posted By docjenser on 02 Jul 2013 12:14 AM
The issue is in COOLING mode, not heating mode.


Confused... I'm losing heat from my hot water heater during BOTH the Cooling (summer use) and the Heating (winter use) mode!
engineerUser is Offline
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10 Jul 2013 08:12 AM
For $15 each, get a couple digital meat thermometers and use foil tape to attach their probes to various points of interest. Mine would be:

1) Hot gas leabing compressor

2) DSH heat exchanger water inlet

3) DSH heat exchanger water outlet

Disclaimer: Go carefully into system cabinet - lethal voltages and high pressures lurk therein.

If my DSH system was plumbed to a fired water heater tank set for 125*F, it might well transfer heat "backward" My unfired buffer ranges in temperature from 100-115. It is a 3 ton system with approx 72 EWT, 84 LWT summer 60 LWT winter, low stage 99+% of the time.

A review of the vapor compression refrigeration cycle in play will show that condensing temperatures, even in heating mode, are well below useful domestic water heating temperature. A desuperheater really only accesses the extra shot of superheat added by the compressor in the course of cooling its innards. While the hot gas at the compressor discharge pipe ranges from "pretty warm" to "what was I thinking touching THAT tube"; that gas has very low specific heat, so the heat needs to be gathered intelligently (unfired tank) and line losses mount quickly, especially during off cycles - water lines to and from DSH fall to near ambient perhaps 30 minutes after compressor stops, resulting in the volume contained in the round trip water lines returned to the water tank near room temperature upon next restart.

Performance of single tank systems, as has been oft-written here, well, think of a four letter word meaning "produces vacuum"...
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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10 Jul 2013 09:44 AM
Perhaps more people should be using combination (water and air) heat pumps or zones to get 100% of DHW.
After determining that the pressure difference between the entering and leaving water pressure was too high, the tech adjusted the entering water pressure (coming from my closed ground loop) by reducing the incoming flow
Was this done by replacing the pump or just throttling the flow?
ascorbateUser is Offline
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11 Jul 2013 09:31 AM
Posted By jonr on 10 Jul 2013 09:44 AM
Perhaps more people should be using combination (water and air) heat pumps or zones to get 100% of DHW.
After determining that the pressure difference between the entering and leaving water pressure was too high, the tech adjusted the entering water pressure (coming from my closed ground loop) by reducing the incoming flow
Was this done by replacing the pump or just throttling the flow?


Via an installed valve... which was closed by about one-third.
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13 Jul 2013 01:28 AM
That's a waste of pumping power.
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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13 Jul 2013 12:38 PM
I agree, although it's a little less than most people think because centrifugal pumps draw less power when throttled.
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