<!--[if gte mso 9]> Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 <!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:1; mso-generic-font-family:roman; mso-font-format:other; mso-font-pitch:variable; mso-font-signature:0 0 0 0 0 0;} @font-face {font-family:Calibri; panose-1:2 15 5 2 2 2 4 3 2 4; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:-1610611985 1073750139 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin-top:0in; margin-right:0in; margin-bottom:10.0pt; margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:Calibri; mso-fareast-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:Calibri; mso-fareast-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} .MsoPapDefault {mso-style-type:export-only; margin-bottom:10.0pt; line-height:115%;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.0in 1.0in 1.0in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> <!--[if gte mso 10]> I’d like to hear thoughts on how I should modify my existing water-source heat pump.  Because of reasons that will be apparent from reading below I want to convert my existing open-loop system to a closed-loop system.  I consider this for several reasons including: possible well contamination by HVAC system, wear on our well pump, energy used by well pump, building codes, etc.  

Here's some basic info on our current configuration:
- 3 Ton Florida heat pump, about 20 years old, seems adequate for our heating needs. 
- Heat exchanger in HP fed by domestic drinking water well

-  3 HP well pump set at 300 ft, 500 ft. total well depth, water lies at 200 ft. below surface.
- Well capacity when dug was about 10 GPM
- Water from well pump is stored in a pressure tank in basement
- Water from pressure tank serves domestic and HP uses. 
- After water passes through a copper coaxial heat exchanger in the HP unit it returns to the water supply well (dropping 200 ft.) to the water surface (lots of potential energy lost there!)
- We're located in SW Virginia, 5 acres, hilly, mostly wooded.
- Water is hard and we have a lot of bedrock in the yard.  Trenches would be difficult but not impossible.
- I've inspected the inside of the heat exchangers but don't see significant scaling.
- We have no surface water sources. 
- Water temp entering the from the DW well HP is about 49 F

What I’m considering doing:
- installing a closed loop in my existing drinking water well while continuing to use the well for drinking water (may be a code issue there)
- If additional heat sink/source is needed , look into installing some trenches with poly loops
- Can the HP heat exchangers that were designed for open-loop water operation be used in a closed-loop mode with a glycol mix?

- Other issues/options?

Apologies in advance if this topic has been covered elsewhere.  I'd appreciate links to previous discussions or search keyword suggestions.  I know well what it’s like to see recurring issues come up in a discussion board.

Thanks in advance.

You currently have a standing column well. Why not just extend the discharge pipe to bring the head loss to the same level as a closed loop? And perhaps use a smaller pump for the geothermal flow.

I considered that but you can only gain back 30 ft. of head or about 15 PSI doing that before you experience cavitation in the discharge pipe.  The idea of using a smaller pump is hopefully where I"m headed though.  Thanks.

Good Luck,
Joe

It appears that your existing system is a Standing Column Well. The GSHP Leaving Water is returned to the same well. If your lowest heating season supply temp is 49F it has served you well. Code acceptance of this type system varies by municipality.

"What I’m considering doing:
- installing a closed loop in my existing drinking water well while continuing to use the well for drinking water (may be a code issue there)"

Not recommended because-
-You risk freezing the water in your well. The closed loop heat exchange process introduces a time delay in heat transfer (depending on the surface area of your loop). I doubt you could stuff enough pipe in the there to overcome this.

If you decide to go closed loop keep it out and away from your Domestic well.

-or-

Consider retaining open loop with a second discharge well if your well GPM capacity allows to reduce any fear of immediate domestic water contamination. A possibility of contamination is often feared (understandably) but seldom documented.

-or- retain your working system that has proven itself over 20 years.

If you decide to go open loop in any case your discharge should not free fall down the well. It should flow down a dip tube to below to lowest recorded level of water in the well. I can not substantiate but have been told this-
-Prevents aerobic action on water supply (something about stuff coming out of suspension)
-Down force will pull water thru the system reducing pumping cost

If trenching may be difficult, is closed vertical loops an option?

Makes me wonder if a hybrid system is possible. If you were to use the closed loop for part of the heating season and the open loop for the rest of the season, you could have the best of both worlds.  It really doesn't matter when you tap your close loop, but when you do, you EWT will be well above what your well water EWT is. Once the Closed loop drops below the EWT from the open loop, you could switch back. And do the same thing during the summer months. While normally this wouldn't be cost effective, since you planning on doing it anyway, it could be an option.

 

I think I'd prefer open loop, personally.

Thanks for the responses so far. I'm going to do some measurements tonight to see just how much power I"m using to supply the HP with water. That should help me answer some questions about whether it makes sense to switch to a closed loop system.

Quickly, since I'm at work: vertical loops are an option but one I'd like to avoid due to expense. Our area is riddled with caves also so drilling is somewhat risky.

I was originally considering some sort of hybrid of vertical and horizontal loops but had not considered a closed/open hybrid system.

Joe, you say a loop in my well might freeze the well. I expected only about a 10 degree F temp drop from inlet to outlet temp. I can't see how that could freeze.

You guys that like open loop; you wouldn't worry about contamination of the drinking water well with compressor oil if a heat exchanger goes bad?

Back to work. Thanks again.

Not a major concern, I think the odds of contamination are extermely low, if not nil. The water doesn't actually pass thru the heat pump, the water is pumped thru an exchanger where the freon lines from the heat Pump and the water lines are interwoven together to exchange the heat between them. 
 
For my system, it's a straight pump and dump, I don't have a return well, the return just dump into the woods in the back yard. I had initially feared the ground wouldn't absorb the water during the coldest of the winter months, (figuring on frozen ground) and it would develop into a nice skating ring in the back yard.  But when I checked the system during the coldest of the winter nights, I couldn't feel any wetness on the ground only a few feet downhill from the return.  The ground absorbs the water that well.
 
For other returns, the return well isn't as deep at the supply well, so I think some filtering in the ground occurs before it returns to the source, but I wouldn't go dumping any oil in it. 

 

A pump sized for the lower pressure needed for geothermal and then a booster pump for domestic water pressure has been discussed elsewhere. Good point about cavitation limiting your discharge depth - closed loop would allow that energy to be retained.

I did some measurements on my well pump tonight and found that the pump draws 7.5 amps at 220 volts and runs about 75% of the time when my GSHP is running.  This comes up to 1.3 kW or about 4400 btu/hr if I've done my calculations right.

I guess I now need now to compare that energy usage to how much it would take to run the circulating pump in a closed loop system to see what sort of energy gains I might gain by going closed loop. 

A 2nd thought I had is to discharge the water exiting the GSHP heat exhanger to a location other than back to the well.  I was wondering if this might possibly raise the the EWT increasing the efficiency of the system.   Since I'm not gaining any energy by dumping the water back into the well and as long as I don't overdraw the well this might be worth trying.

Can anyone tell me what size pump is normally used for closed loop circulation?

Thanks all.

I'd take the savings in pumping cost and then account for:

1) the energy used in the pump is added back to the water (ie, not lost)
2) closed loop would be less efficient

If your yard is full of bedrock, and the driling process may encounter caverns. You allready "have" the most cost effective exchanger for your specific locality. If it has lasted 20 years with no complaints, why the complaint now?
If you are concerned with the consumption of electric to run the well pump the industry now has a wide variety of variable speed products that could reduce usage. If I were in your position I would leave the geo alone and spend budget on generating electric via solar or wind and reduce consumption in the rest of the building. Your lust for reducing electric consumption will just not muster past the KISS principal.
Eric

Thanks for the response but I don't understand it.

These are good points.  While energy consumption is one concern, well pump failure may even be a bigger one.  I may not have made that clear.

When I bought the house 10 years ago there were 2 old pumps/motors in the scrap pile as well as many joints of galvanized pipe.  I was told that they replaced the metal pipe with plastic to minimize start-up "shock" at the pump. 

I do almost all my own repairs/modifications including HVAC but pulling and replacing a well pump may not be something I want to take on.  Replacing a loop circulating pump would be easy comparatively.

Another issue that I've not brought up is that I have to do some trenching for other projects and thought why not set some poly pipe while in there and maybe make use of it later as a ground loop?

Also, we try to heat with a wood stove as much as possible but as we get older that will get more challenging and we'll likely need to rely upon our heat pump more but won't be able to afford the higher electric bills.

So, I'm just trying to get all the facts straight like:

• Can I install a closed loop inside my existing water well and combine that with some trenches and get adequate heat transfer capacity and still use the well for drinking water?  Is it worth it?
• Now that someone educated me on what my system is actually called, a "standing water column", after further research on the web I may try bleeding off some return water to increase groundwater flow towards the well.  What improvements might this result in. 
• If I later install solar water panels on our house would those integrate better with a closed-loop HP?  I suspect they would.  
  
• If I sell my house would the current SWC HP system be an issue because of local code issues or just perceived fear?

Helpful responses like yours and others will hopefully better educate me about the issues involved so I can make an informed decision.   

Thanks to all.

If your system was to code at the time of the installation there are no code issues.
Re freezing your well, while the difference between E and L water is modest, your closed loop in the well idea would continue to drop water temp in the well if no one was using water (say a winter vacation).......
Re contamination it could make the water bad for a few gallons just like bleaching a well. If ref oil got in the well you might want to run the garden hose for awhile, but that would be the end of it. Closed loop systems could also impact water briefly if breeched.
J

If your well is getting much colder than the ground temperature and you have a place to dump some water, I'd use some bleed (say 10%, as needed).

You ask the right questions, but full modeling of the situation requires lots of math and lots more data than you are going to be able to collect.

Okay, the freezing the well issue makes more sense to me now.

The contamination issues still concerns me since no amount of flushing would like remove a floating contaminant.  I may be able to drop a sorbent sock or something else down the well on a rope to soak up the oil on top though.  

Thanks for the response.

I think I can try the 10% bleed relatively easily and have ready place to dump the water (a sinkhole). 

I could probably handle the modeling and would find it fun but you're right, It would take a lot of work and money to get all the data I'd need to get a decent result. 

Thanks.