Geothermal Heat Exchanger?

[plosmundson]

I want to use my 30 gal/min flowing well for an open loop geothermal system but my township has an ordinance against open loop systems with no appeal. The well currently flows into a large tank and then overflows down to a creek. Would it be practical to build a heat exchanger that I could put in a tank and thereby have a closed loop for the township but still use my well? The heat exchanger would have 30 gallons of 53 deg. F. relatively low mineral content water flowing accross it per minute. I have no room for a pond or horizontal loop field. A local contractor sized the house for a 5 ton Waterfurnace NDV064A with an open loop system but that's not an option now.

[larobj63]

Why do you constantly pump this well?

If you have to pump the water to combat hydrostatic pressure or the like, it would make wonderful source water for a heat pump.

[plosmundson]

It is an artesian well. I don't pump it. It flows like a spring. It is crystal clear and flows at about 30 gallons per minute out of the ground at a constant 53 degrees F. It has flowed like this for 11 years. It actually flowed at almost 50 gallons per minute 11 years ago when we drilled it but it has slowed some over the years. I would like to know if it would be practical to build a heat exchanger that could be placed in a tank that allowed this well water to flow over it as it overflowed to the creek. I'm looking at using it to heat my house in Michigan. The heat load on the calculations is 74077 btu/hr and cooling load is 29844 btu/hr. The contractor is proposing a 5 ton unit. If it can be done in a practical size tank I'd like to investigate having it done. Is the design of something like this something that you'd expect from a regular geothermal contractor or would you have to have it designed by engineering people?

[geodude]

Won't work well if at all. what about an injection well or vertical bores/ closed loop?

[plosmundson]

I'm not sure but I think the township considers an injection well to still be open loop. I got a price on vertical bore and it came back at an additional $12,500. Together with unit and installation it would come to about $23,000. That is beyond my reach. The contractor told me that I had a perfect setup for an open loop system. But instead of forcing people to properly install an open loop the township decided it was easier to just outlaw the technology. I'm just trying to see if there isn't some way to make my well look like a closed loop system. Thanks for the response.

[bc3141]

With flow like that available, it's criminal not to use a GSHP! I think this could certainly be made to work, but you will need to find someone who is willing to think outside the box to make it happen. Copper coils sunk in the tank would work fine, you'd just need to figure out the surface area required and whether you could fit enough pipe. It might be a good application for a DX heat pump since it uses the copper anyway. There's a guy who posts on www.ourcoolhouse.com that has a setup just like this - a buried tank with coils of copper and I believe his system works great. I can't remember the name, but if you search or ask in a post you'll probably come across it.

I want to use my 30 gal/min flowing well for an open loop geothermal system but my township has an ordinance against open loop systems with no appeal. The well currently flows into a large tank and then overflows down to a creek. Would it be practical to build a heat exchanger that I could put in a tank and thereby have a closed loop for the township but still use my well? The heat exchanger would have 30 gallons of 53 deg. F. relatively low mineral content water flowing accross it per minute. I have no room for a pond or horizontal loop field. A local contractor sized the house for a 5 ton Waterfurnace NDV064A with an open loop system but that's not an option now.

[bc3141]

This is the guy I was thinking of here:
http://www.freewebs.com/rwooldridge/heatpump.htm

With flow like that available, it's criminal not to use a GSHP! I think this could certainly be made to work, but you will need to find someone who is willing to think outside the box to make it happen. Copper coils sunk in the tank would work fine, you'd just need to figure out the surface area required and whether you could fit enough pipe. It might be a good application for a DX heat pump since it uses the copper anyway. There's a guy who posts on www.ourcoolhouse.com that has a setup just like this - a buried tank with coils of copper and I believe his system works great. I can't remember the name, but if you search or ask in a post you'll probably come across it.

[plosmundson]

Thanks for the reply. I'm already looking at some of the sources referenced. The guys doesn't really tell how he actually sized the heat exchanger. The one that he built is larger than I hoped and has some additional underground piping that he added because it sounds like he had room to do it. I'd like to know whether it has to be that big or did he build it that big because he guessed it would be "big enough". I'll keep looking. Thanks again.

[tecman]

There are plenty of water-water heat exchangers available. Modern plate type will offer good thermal coupling in a small unit. You will need a pump on the heat pump side to pump through the exchanger (flow panel) and you may also need a small pupm to push the water from the well through the exchanger. Still all-in-all not a lot of power required in addition. Do a google search on heat exchanges should get you some sources. You will need the flow rates, BTUs to be transferred and temps, and any of the manufacturers can size one for you. Big names like American Standard can fit the bill. You might also be able to find something used or surplus to fit the bill. Being too big is no problem, actually lower delta T.

paul

[bc3141]

As far as I can tell he didn't design it but made a guess based on the area he had available and got lucky. I think a denser configuration with more pipe packaged in a smaller area would actually work better. Or a DX system as I said before. I believe the ARI test for DX actually uses a configuration like this - the dx coils are put into a water bath that is maintained at a constant temp.

I took the liberty of posting your problem over at greenbuildingtalk.com - there are some very knowlegable geo folks there including a contractor in Michigan that might be able to help you out.

Thanks for the reply. I'm already looking at some of the sources referenced. The guys doesn't really tell how he actually sized the heat exchanger. The one that he built is larger than I hoped and has some additional underground piping that he added because it sounds like he had room to do it. I'd like to know whether it has to be that big or did he build it that big because he guessed it would be "big enough". I'll keep looking. Thanks again.

[plosmundson]

Thanks again for the help. I'll go to greenbuildingtalk.com and see if anyone there has any other suggestions.

[alex_in_fl]

Sure you can do this. it should not even be hard. Simply get the standard flex pipe they used for the groundloops, coil it, and put it where your well flows over it. If you use as much pipe as you would for a groundloop you will be oversized.

You could also use copper piping (but I would recommend using coppernickel instead for corrosion reasons - but it costs more and will take more pipe).