I have a new geothermal heat pump system.  It uses 6 - 200' deep wells.   We used it over the winter to provide hot water for the radiant heating system and the temperature of the fluid returning from the well field was 45-50 degrees.  The delta between the supply and return lines to/from the well field was only about 5 degrees (F). 

Now we are shifting it over to the cooling mode - producing chilled water for air handlers.  I am suspcious that something is wrong with the well field because of the fluid temps to/from the well field.  Now, the returning fluid temp is about 68 degrees and the delta between the supply and return to/from the field is only 3-4 degress (F).

There is no way that the ground temperature in the well field has changed that much.  I think that the water should be returning from the field at around 50 degrees - just like it was when we were in heating mode.  With over 1200' of well to absorb the heat from the circulating fluid, the heat transfer should allow the circulating fluid to lower its temperature close to that of the surrounding ground.

Can anyone give me any feedback as to whether these fluid temperatures seem "normal".  I am located near Sacramento, CA so the summers are toasty and I was hoping that this heat pump would not have to work very hard to "sink" the heat into the well field.  So far, that has not been the case.

Thanks,

Dave

sounds good to me

for your return temps to be around 50 , ground temps would need to be around 32

Ummm, water temps vary by region, but yours seem great. Tell us EWT and LWT in July and let's see if we still like'em.
J

For the past 8 weeks my GSHP water-to-air system, with a closed loop vertical bore hole field, my system has gone back and forth a few times between heating and cooling.  My Dallas climate (hot in summer, mild in winter) may approximate yours.

My EWT swings at about 5° whenever there's a change from heating/cooling.  You can see this by looking at this chart: http://welserver.com/cgi-bin/plot/WEL0043/EnteringWaterTemperatureDailyAvg.gif .  The 4 EWT peaks in the past 8 weeks correspond to shifting from heating to cooling and back.

My bore hole field is 8 wells, each 300' deep.  My daily average heat transfer to/from the earth this month is so far a +16 KBTU/day (heat rejection to the earth).  My 'down deep' undisturbed earth temp is 68°.

My EWT numbers are rolling continuous 24 hour averages, so I'm averaging out EWT noise.

Your 18 - 23° EWT 'jump' going from heating to cooling seems high.  But, maybe if measured over a 24 hour period and averaged, it wouldn't be as big of a jump.

My instantaneous EWT values move around quite a bit, at any given moment.  Here's an example for the past few hours: http://welserver.com/cgi-bin/plot/WEL0043/InstantaneousEnteringWaterTempsEWT.gif .  Here you can see that 2 hours ago my 3 ton unit's EWT instanteously rose 5°, waiting for the bore field to catch up.

Best regards,

Bill

Thanks for the responses.   Bill, I wish I had the monitoring system that you do - all I have are some analog temperature and pressure probes on the plumbing to/from the wells.  I'd be interested in learning about the type of monitoring system you have which records the information for you.

I'm still going to school on this system.  I thought I knew quite a bit about it but some of my assumptions were apparently not correct.  My installer, who I do trust, tells me that it can take several hours for the water to completely circulate throught the well field (it takes less time when the second stage of the heat pump is operating).  If the water is moving that slowly through the field then it seems to me that the following could happen in the cooling mode...

1. Water enters the wells and starts to sink its heat into the ground.
2. Water exits the wells at a lower temperature.
3. In my system, it then has to travel about 30' from the well field to the house.  This is in relatively shallow trenches (12" deep).  The water would warm up again since the ground in this shallow trench is warmer than the ground in the wells.
   
4. It then enters the crawlspace of the house where is travels another 30' exposed to the ambient temperatures in the crawlspace.
5. It then reaches the heat pump in my basement.

Since the water in the loop is traveling so slowly (again, my installer said it would take up to 4 hours to do the full loop) then it has plenty of time to warm back up in the shallow trench and in my crawlspace.   This is causing the to/from water temp delta to shrink.

I apologize in advance if any of this exposes my ignorance of this system but I'd appreciate any additional responses. 

Thanks,

Dave

1. I can't believe it takes 4 hours to circulate through the well field! It takes mine 20 minutes, others are 10 minutes.
2. Do you have an internal switch that sets the flow at higher flow rate when the second stage compressor is on?

Thanks,
Howard

Dave, I started out the same as you - temperature and pressure guages inserted into P/T ports installed at EWT and LWT GSHP locations.

It became obvious pretty quickly that the information from the guages is 'noisy' - i.e., there's a lot going on such that the values move around quite a bit.  And thus while there's a lot to learn from the instanteous values, there's equally plenty to learn from historical and statistically sampled values.

I suspect a significant contributor to your situation is simply inability to get the data you need to draw conclusion on your bore hole field performance, assuming you have a well performing GSHP unit and bore hole field.

A key item to keep in mind is that even as EWT may vary quite a bit on an instantaneous basis, due to the response lag of the bore hole field to sink/source the heat, the delta-T across the GSHP water-to-refrigerant heat exchanger stays much more steady.  For example, for the period of cooling centered at about 15 hours ago, even though EWT is moving around quite a bit due to bore hole field heat sink lag ( http://welserver.com/cgi-bin/plot/WEL0043/InstantaneousEnteringWaterTempsEWT.gif - blue line), delta-T is much more steady, at between 4.5 and 5.5 °F, as seen here: http://welserver.com/cgi-bin/plot/WEL0043/LoopWaterDeltaT-CoaxHeatExchangers.gif (blue line again).  And my delta-T would be even less variable if it weren't for the influence of another GSHP unit connected in parallel to the same water loop (black line).

What's really instructive is look at the performance of the water-to-refrigerant's BTU output (Heat of Extraction - HE and Heat of Rejection (HR)).  This eliminates getting too caught up in the very noisy EWT values, and the somewhat noisy delta-T numbers.  Here, for my units, HE and HR is very steady: http://welserver.com/cgi-bin/plot/WEL0043/SampledLoopKBTUperHr.gif .  My two units are removing heat from the structure (rejecting to the earth) at rates of about 50 and 30 KBTU/hr for my 5 and 3 ton units respectively (both running at 67% in first stage only).

Given that I can see HE and HR, the more noisy EWT and delta-T values are not as valuable as predictors or indicators of problems.

All of my charts are visible, real-time, at http://welserver.com/WEL0043/ .  There are others on this forum, much smarter than me, who also have monitoring capability, using the same system, such as geodean, at http://welserver.com/WEL0114/ .  And here's a map of a number of very creative implementations of the same monitoring system: http://welserver.com/ww/ .

And here's info on what I'm using, overall, at http://www.ourcoolhouse.com/index.htm , and specifically at http://www.welserver.com/ .

Hope all of this helps.

Best regards,

Bill