I screwed up and need guidance. 

I have a two story very nearly fully ICF home near Des Moines, Iowa with a finished walkout basement on 25 acres that is nearing completion.  The attic is spray foamed under the rafters.  The few linear feet of wall that is not ICF is spray foamed as well.

I have two Unico high velocity air to air heat pumps installed already.  The basement unit is a two-ton and installed in the center of a finished basement.   The other unit is a 1.5 ton and installed in the attic.  I hate these units and really, really wish I would not have had them installed - the ducts themselves are noisy (I can turn the fan speed down, but at the cost of efficiency I'm told) and the outside units are heard throughout one end of the house as my contractor hung them off of brackets attached to the chimney and their noise transfers into the house directly.  I plan to relocate them to a cement pad.

The original thought two years ago when this DIY project started was to use a Knight propane boiler for radiant heat in the dead of Iowa winters and use the heat pumps the rest of the time for heating and cooling from April to November.  Propane is at $2.25/gallon now though. I do have 1/2" pex (though very, very foolishly not the Oxygen barrier variety) installed in all of the floors, either in the concrete or encased in Maxxon's Thermafloor product (a whole lot like gypcrete), depending on whether we are talking the garage floor, basement floor, or general living floors. 

Since coming up with this 'fabulous' idea to not use geothermal from the get-go, I've learned that my house was wired in on 'all-electric rates' meaning that usage above 1000kwh in a given month is only $0.031/kwh.  Usage below 1000kwh is at somewhere around $0.075/kwh.  My family's electric energy use for my old home, heated with propane, was 877kwh/mo on average.  If I migrate to a propane boiler, my electricity rates will jump to $0.08/kwh pretty well all the time. 

So...given the price of propane, I am better off dollar-wise to heat my home with my backup strip heat in the Unico units (they have two 10kw heat strips each) in the dead of winter rather than hook up a boiler to drive the radiant!  I remain concerned whether these are of sufficient capacity though since they were never, ever intended to be the primary heat source for the home.

Here come the questions:

1.  Can I convert my systems at this quite late hour to geothermal (not sure how I'd get piping to either air handler, though could, I suppose rip up some sheetrock to get it done...sigh).  I'd have to get water coils installed in each (they are available), I know.  How would/could this work with two separate airhandlers?  Going this route would allow geothermal cooling, an option for geothermal heating, and leave me with two paperweights (the current condensing units) outside.

2.  I ran 3/4" pex from the various zone manifolds back to a mechanical room that has an outside wall in it in the basement.  Can I install/is it economically feasible to install geothermal for JUST the radiant heat floors (and maybe try out cooling this way as well, albeit only through the floor)?  If so, I could have the stubs from my loops enter this area of the home pretty readily and without chopping into sheetrock. 

3.  Does anyone know of a stainless steel heat exchanger electric boiler that operates on 220V?  I have two 200 amp panels coming into my house so could support the electrical load of such an animal (though I may have do something else for water heating since that is burning a 125AMP breaker in the one panel, see next question).  Manual J calcs aren't handy at present, but the size of the Unico units (3.5 tons total) is telling.

4.  Any reason why I couldn't use my 27kw instantaneous hot water heater for all but the coldest days to heat the fluid that I'd put in my radiant tubing (I have the model 2700 at www.AmericanTanklessElite.com)?  I noted that this unit's heat exchanger is made from copper and brass soldered with silver...I would think that this would be okay with the non-oxygen barrier pex I foolishly chose but am not sure.  I am also not sure about the compatibility of using a tankless unit with radiant.

Any advice you could provide would be most appreciated - I'm in a pretty good quandry here...

ICFam,

If I were in your situation I would move to a water to water geothermal unit, and use a ground loop with the amount of property you have. Forget trying to cool with the radiant floor, all it will give you is nice cold sweaty floors. However, you could use your air handlers with water coils in place of the refrigerant coils. In fact, if you have sometime before changing things up, I'm working on a project for a friend of mine. I'm attempting to convert a standard refrigerant A coil to a water coil. I should be completing the conversion by the end of next week or sooner depending on how my spare time goes. So far I have the high pressure side lines removed from the coil and have the new manifold built to allow a ¾ inch inlet and the existing low pressure side just needs a fitting as it is already ¾ inch. This ¾ inch inlet feeds a total of 6, 3/8 inch lines. Calculations shows it should flow up to 10 gallons per minute. I believe it will work fine, but we will run testing to find the actual capacity. I would expect all the testing and conversion to be done in no more the 3-4 weeks.

Regards,

ICFam,

You could solve the problems with EarthLinked DX geothermal. To do this, I'd probably have an EarthLinked system installed large enough to heat the entire house with the radiant floor. Next, change the coils in the unico systems to water coils.

Now, the EarthLinked unit will heat or chill water in a storage tank. The Unico systems can draw from that water tank either heated or chilled water, depending on the heating/cooling mode at the time. In the coldest times, from Nov. to Mar., the radiant floor draws from the heated tank, and the EarthLinked system keeps the house comfortable.

On the idea of cooling with your radiant floor, DON'T! We experimented on my dad's ICF house. We installed a radiant floor and a radiant ceiling. While he can keep the house cool with the ceiling most of the time, he sometimes has to chill the floor. This is completely UNCOMFORTABLE!!!! Also, you need a way to remove moisture from the home. Chilled radiant will not do that. Anyway, maybe that's a discussion for a whole different time...

With your "all electric" rates compared to the outrageous price of propane, you'd be crazy not to do geothermal. EarthLinked would be a very viable solution. If you need more design help, let me know.

Oh, with the non-oxygen barrier pex, that's not a problem. Just use non-ferrous pumps (use brass or bronze), and make the floor loops to be open loops. We've done this many times. It works wonderfully.

If I move to a geo setup, would I be able to get just one geo unit that would serve both Unico units or would I need two to maintain the zoning presently enjoyed? If two, would I have to do two separate sets of outside loops?

If you use the EarthLinked product, and still want to have the unico refrigerant coils used, then yes, you need 2 geo systems. That's why I suggested using one larger EarthLinked DX system to heat or chill water, and replace the unico coils with water coils.

If they are 2 separate geo systems for DX, they need their own loops. This wouldn't be much more loop cost than just doing a larger system with the heated/chilled water. In fact, it'd be close to the same on the loop cost.

Clark,

Unfortunatley In the state of Iowa DX geothermal is not approved by the states EPA depeartment. I am a Earthlinked dealer in Illinois right on the mississipi river and imagine my suprise when I started inquiring about drilling permits and liscencing for iowa and was told of this. The reason given for this is that no one has proven to them that the refrigerant in the DX system is safe for the ground water supply.  I intend to start going to work on the people making these descisions and trying to get this resolved. I am currently amasing all my information on this and preparing to present it to the necicary people.

Wow, Iowa really needs to join the current century. That's really unfortunate. Hopefully they'll work with you and get it approved. In Wisconsin, they're working on the same thing. We're working with Wyoming's consumer dept. for approval, too. It's all but approved now, though.

Good luck

You may want to contact A-One geothermal, or possibly Ed McNair. They are local contractors in the area and have done many installation in the Iowa area. These are both reputable companies and do excellent work. These contractors started installing geothermal loop fields horizontally utilizing horizontal boring machines and it sounds like you have the space to utilize that technology and as noted above, using a water to water heat pump system, I can't think of a better way to heat and cool your home.

A-One's website is http://www.a-onegeothermal.com/index.html

Hope this helps.

One question I'd ask them in Iowa is about the water source systems. A water source loop has some sort of anti-freeze in it. Typically, because of cost, it gets methanol. Glycol is the more expensive option.

Ask them if methanol is safe for the ground water. It's toxic to ground water. Refrigerant, no matter what kind, will boil (turn into a gas) if leaked into the ground. It will then vent to the atmosphere. It CANNOT contaminate ground water, because it's a gas. It doesn't mix with it.

Methanol is not allowed per Iowa codes for geothermal systems for vertical systems. Food grade propylene glycol is the antifreeze of choice. At least this was the case a couple of years ago.