We are building and new home and are looking at an open loop system supplied by a well.  We're in central MN where hard water and high iron content is common.  The well in not drilled yet.  We have a location to "dump" the water where the additional flow would be an advantage.  The option for an open loop system can impact other heating decisions we need to make, so we'd like to know options sooner, rather than later.

As I understand, the big issue in our area (in addition to water volume) is the Ferric Iron content of the water.   I'm told that high Ferric Iron content will wear out equipment and/or require frequent maintenance. 

But I'm having trouble finding any good info on allowable levels of Ferric Iron.  If I knew, I might be able to have my neighbor's water tested (1 on each side, each about 350 feet away) to at least get a ballpark idea.

Any sense of what that allowable level might be? Are there reasonable measures to deal with high Ferric Iron?  Thanks.

Try contacting the engineering dept of a couple of water source heat pump mfrs such as Water Furnace or McQuay. They can give you the best info.

All I know is I've been told the water should be drinking quality level. Also, the guy I plan to buy my direct exchange heat pump (ECR Technology) from said he installed one open loop water source heat pump system. He would never do another. Closed loop only, specifically because of the corrosion problem. I believe he's doing DX heat pumps almost exclusively now.

I am considering replacing my current oil furnace with an open loop system and using the my existing well. I also have the question of whether or not the water would be a problem. The well water does not exibit typical hard water characteristics (I drink it, with no conditioning) but it does have significant dissolved iron (the toilet bowl and tank are stained red), possibly from the well itself or from the old galvanized pressure tank (no bladder). Most of what I have read regarding water quality and open loop systems is vague. Here are some of the different opinions I have read regarding open loop and water quality:

1. If water is hard, an open loop system should not be used
2. If water is hard, a cupronickel heat exchanger should be used (to resist scaling and corrosion)
3. A cupronickel heat exchanger will do no good, it is a waste of the extra cost
4. The heat exchanger and piping must be periodically cleaned
5. Use a second heat exchanger to isolate the water from the main heat exchanger
6. In the case of dissolved minerals, scaling will only occur if the water is aerated or there is a severe temperature change in the water (which should not occur). Aeration is prevented by maintaining the water at high pressure, using a bladder tank (so no air in contact with the water), and adding an automatic valve at the water discharge (so air cannot come in through the discharge and pressure is maintained)

No. 6 above makes sense to me and agrees with what I see in my current water system.

Anyone have any info to share?

I've heard #4 several times from various HVAC people.

Severe temperature change may be a problem. You're going to be dropping the water temp by 10 to 20° so I'm not sure you can say it won't be severe. If you don't drop it that much then you are doing so by pumping a lot more water than you need to be.

If you have high iron you have the potential for iron bacteria problems. Yeah, there is such a thing. My brother's water system suffers from it.

Thanks for the reply.

I forgot about the iron bacteria, thanks. And I'm pretty sure I have it in my water. Most info on this is vague, but I have some that indicates most of the slime iron bacteria deposits occur in the return well, and this can be minimized with a valve (keep air out, keep it pressurized). In my case, I can dump the water into a creek. I suppose cleaning will be necessary but it's very difficult to determine how often this will be necessary. I wonder also if there is a way to address this without using chlorine (I hate having chlorine in my drinking water, and would hate to dump chlorine into the creek).

Also, I think actually the scaling problem with temperature change applies to a temp. rise during cooling mode. Most info I've read indicates the temp. will typically rise 10-12 deg. in this case. For me no problem, I rarely have need for cooling anyway.

It's been our experience that open loop systems with iron content are a maintenance headache. Periodically, the solenoid valves will corrode and won't work. The heat exchangers do get plugged.

It is less expensive on the installed price than a closed loop system, but the maintenance headache (you being without heat when you need/want it) is not worth it. You should look into a DX system. Their loop is maintenance free.

Unfortunately a closed loop system is not possible, just don't have any area for excavation (surrounded by trees and steep slopes).

Any experience with other types of valves or seals that are resistant to iron/iron bacteria deposits?

I don't have any corrosion problems now, including the hot water tank, just a red stained toilet. I'm hoping that the concentration and type (dissolved) of iron may be ok. Are you aware of the type and concentration of iron in the water for the installations that had problems? Was an analysis of the water done first?

Is your well drilled already? If not there is hope. I read somewhere that by sterilizing the drilling equipment and keeping everything sterile during the drilling and pump installation process you can avoid introducing the bacteria into the well. It's a tall order but apparently can be done.

You say you have no room for excavation. How about wells? A direct exchange system can be installed with wells in a fairly small footprint. It also needs only about 1/2 to 2/3 the well length of closed water loop system. Until I changed plans I was going to put in a 4 ton DX system with 4 100' wells in a 10' x 10' space. You sure don't have that available?

He's right. A DX system should be able to be installed in a very small footprint.

I do have a water well already. I have a 20'x40' pad area (outside this is steep slopes and trees), already with a septic on one end of the 40' and the well at the other. I would like a DX system for its efficiency but I figured the excavation would be too difficult and of course there is the cost issue. Is vertical loop drilling similar to what is done for water wells?

Since a DX system circulates the refrigerant, doesn't this make it a simpler system that should then cost less than the water closed loop system?

Krisps,

Where will you be building.  What is the lowest winter and highest summer temperatures.  E-mail me.  I have some ideas to share.

alton at auburn dot edu

Seems awfully close together. That was OK'd by the local health officials?

Check with your code officials about spacing from the water well to DX wells, which really aren't wells in the normal sense. You drill a hole, drop in the tube, and fill the well back in with grout. If separation isn't a problem for them you should be OK, I think. Better to stay closer to the well than to the septic tank and field. You don't want to risk cooling the septic system as that can adversely impact the bacterial action there.

Yeah, the well and septic are pretty close, but this house is 30+ years old and the septic actually drains down ~20 foot to the leech field.

Thanks for the comments.