Geo-Thermal heat-pump?

[Dargo]

Although I'm a few years from retiring the Geothermal we have will make it much easier to live on the fixed income that comes with retirement. Payback on an investment is an important consideration. Making this investment and having paid for it while I am still working is a very important part of my retirement plan.

Important point. Having rock not far down seems to not be such a good thing for me to go geothermal. I'd still love to if I could, but it doesn't look very cost effective. The deep part of my lake is almost 20' deep. I wonder if I could coil lines down there?

Oh well, too many going to college this year and momma says that I've made enough real estate investments and I'm cut off.

 

[bxn]

I would love to get rid of my propane.

Looked at geo quotes, sounds like a great idea but the system aside from the well cost its not making a lot of sense right now for me. That include future estimates of fuel cost. At least until they start taxing my CO2 and soot output. (Please don't vote for that junk.) I also think the popularity is going to bring these systems(above ground part) down in price through competition. Right now in geo its a sellers market.

I don't believe an ounce that these geo systems (the above ground part ) are going to last 40years or that they should. Efficiency improvements in future systems are likely to mean you'll want to replace it sooner if it could last that long. Payback over 7 years was a no go for me. Like wise the resale boost in doing this is a limited time benefit.

If you have a massive home you might get it back sooner. Get your quotes for systems on both sides and see how many times you can replace it with a conventional system and use some average estimate for the future cost of fuel. If it adds up then your on your way. Mine didn't.

bxn

 

[corndodger]

I've read quite a few of the geo thermal posts and thought I'd write about my experiences of getting one of them installed in our new house. Being a retired (if not retarded) engineer, it seemed like a good idea. However, if you want to know how much it'll cost before installation vrs. how much you really need to buy, well, that's another issue entirely. Let me explain.

First of all, the financials are all there if you stay in the house for a while. There is an up front cost that makes a geo system cost at least 30% more (and possibly a lot more) than a regular system. But because our federal government can print and pass out free money, these systems can be discounted substantially through tax credits.

Payback for geo varies with where you live and cost of heating and electricity, of course. Estimated annual geo costs for us is under $900/year, just about the same as heating with wood. But it includes AC year round, so for right now, for us, the estimate is break even, with the side benefit of AC, something we've never personally had before.

The real cost driver is the connection between the geo pump and the earth. Several variations exist for establishing the connection, but comes down to making a field of buried pipe or a well system. We found you can either bury an indeterminate amount of pipe below the frost line (600-900 feet/ton of capacity) or drill a well for about the same price, about $10k.

There seems no science in setting up a geo system, and nearly every financial decision must be based on rules of thumbs because nobody measures soil thermal conductivity or has thermal estimating systems that can actually be driven by individual house designs.

Again in our area, most geo "installers" turn out to be simple contractors who sub out nearly all the work. We found they are charging about $12k over subcontractor and material quotes that we've received for a complete system. Without exception all installers claimed to "know how to properly install geo systems" but say that more than half of their business is cleaning up the botched installations of others. WITHOUT EXCEPTION!

It is a very discouraging situation because the potential energy savings and operating costs in geo systems really are exceptional, but with such buffoonery going on, installing such an expensive system shouldn't be trusted too far from home. In most cases a geo installation is therefor a project that only masochists or the insane will enjoy.

We are building a new home and found that an ordinary natural gas installation for the house was about $13k for the ductwork, and something around $2k for a quality conventional furnace. Geo installation quotes included ductwork and came in at about $22k. These do not include the ground loop/well portion of the system which is where most of the "risk" actually is.

If you don't have enough ground radiation, you'll run out of heating or cooling capacity no matter how hard the geo pump works. With closed ground loops the only "safe" thing is to bury lots and lots of pipe. In well systems, the "rule of thumb" is that you need 140 feet of well for every ton of capacity. In our case the other rules of thumb indicate that we should have a 4-ton geo pump, thus we "need" an almost 600' well. There's no mention, of course, about how much water should be in the well, only how deep it should be!

So for us, the whole project seems to be one of buying heating/cooling capacity without knowing or being about to figure out just what the real need is. The solution sold by contractors seems simply one of installing, probably, way too much capacity. If you have too much capacity the system efficiency drops (thus raising the operating cost), but you'll never know it because the system "works." Too little capacity will show up when you can't heat or cool the house to the temperature you like, and then it's too late to fix it!

We are about a month from firing up our geo system for the first time. I wish this project was more fun than it has turned out to be because of all the uncertainties and the added cost of covering for them.

But the bottom line is that when the geo system is actually running, without exception, the costs of operation will be lower than with conventional heating. For us the payback is something around 8 years, if all goes well.

 

[buckeyefarmer]

Corndodger, welcome to TBN.

Following is in response to multiple posts.

Actually geothermal loops should be engineered based on soil conductivity. The entire system should be engineered based on a Manual J calculation for the house. For horizontal loops, thermal conductivity is most often done by identifying the soil type. For vertical wells, this is done based on thermal conductivity of rock. For commerical installs, a test well is normally drilled and the thermal conductivity is actually measured, which then determines exactly how long the loops must be. This testing is normally not done on residential, but you can request it, at a cost, if it will make you feel better. An installer that says they are using a "rule of thumb" needs to be avoided. The software to design a geo system is not cheap, so I'm sure there are installers our there not doing it right. Same for manual J software.
The connection from the indoor unit to the outdoor field is the same, regardless of if it's a well system or horizontal system. The only difference might be that most installers will manifold outside, bringing only one large loop inside, while a few installers prefer to bring all the loops inside and manifold inside. The connections are actually identical, it's just a matter of where you put the manifold.

There are lots of reason for cost difference from an Air to Air heatpump. Technically, they work the same, it's just geothermal has a much better temperature to work with for heat transfer. The largest cost of geo is labor to install the ground loops. Also, the heat pumps cost more. All equipment costs more as it's efficiency increases, doesn't matter if it's air to air or water to air. Another potential cost increase for geo is the duct sizing in the house. geo units have higher air velocity, requiring larger ductwork. As in any system, retrofitting costs a lot more than a new install.

If I was only paying .04 per KWH, I wouldn't think of using anything but electric.

someone mentioned 30 SEER for geothermal. Geothermal systems are rated in EER for cooling, not SEER, see my earlier post about derating SEER to achieve the EER rating.

If anyone is seriously considering a geo system, take an IGSHPA course. It will cost you over $1K, but you will then know the BS from the truth.

I do agree that most geothermal quotes are really high, but I can say the same thing about air to air system quotes I have received.

 

[Wacky]

All great info I am trying to prepare myself for the Great Rate hike for electric. What may be the ideal thing for me is to put an outdoor wood furnace and go with an outside central air unit. I know my outside unit is a '92 model year, it has needed alot of work in the past, and is very noisey. Just getting all my ducks in a row, you all have been very informative, Thanks:thumbsup:

 

[whistlepig]

There is a lot of very good technical information here. I am not the one to advise on the technical side. Our geothermal came with the house we live in that was built in 1999. I knew nothing about geothermal until we moved in here 3 years ago. Ours is a Waterfurnace horizontal ground loop system. From 105 degree heat to 25 degree below wind chill it has worked flawlessly. The energy savings over the fuel oil and standard central air that we had in our previous home is just short of amazing. We do have the Desuperheater that helps with the hot water heater heating cost. Our Waterfurnace is also equipped with auxiliary heat. Auxiliary heat is an electric furnace assist addition to the geothermal furnace for bitter cold temperatures. I have only seen the auxiliary heat kick on four times in three years. And that was only for less than an hour each time. Although this technical data is very informative people shouldn't be scared off by it.

 

[handirifle]

I am not an engineer, but have mt degree in heating and refrigeration, plus 5 years of field work (moved to a different field of work) and am suprised no one uses a more efficient system than any mentioned. I have yet to see anyone use it, for that matter, but here goes.

AC units and Heat Pumps work by simply removing heat from one source and moving it to another. Where I used to live was the high desert of CA. There, I have built systems for cooling that used water circulated from a swimming pool, through a heat exchanger that cooled the hot refrigerant gas of the AC condensor. The added plus is free heat for the pool. Water removes heat from the condensor something like 20 times more efficiently than air does, thus a small pump suffices, unlike the 1/3 or higher HP rated condensor fan.

For your system, is it possible to bury a tank below the frost line, as in do you have the yard space? The tank would NOT require deep drilling (a typical geo well will be hundreds of feet deep) but jat hole big enough for a tank. For example, I have a 5400 gallon water tank for my well. Its about 7' tall at the highest, and about 12' in dia. Now if you have a frost line of, say 6 feet, then the hole would have to be 13' feet min and 12 or 13 feet dia. I think a poly tank that size can be had for about $2500 or less.

I'm talking a tank of sufficient size to handle enough BTU transfer to heat the house? The calcs will tell you how much is needed. I'd supect, depending on the house size, something in the range of 2-3000 gallons. Unlike the geothermal well, you'd have a far greater surface to absorb and transfer heat with the buried tank.

Just a thought. I think we limit ourselves to to many pre determined ways to heat and cool the home. Oh yea, can you imagine how much better a tank full of 55 deg water will cool the condensor than a fan blowing 90 degree air over coils would?

The Heat Pump unit would be the same, it would care less if the water came from 400 feet down or 14.

Oh yes, one other thing, a water cooled unit is WAY quieter than air cooled, and smaller outside unit as well.

 

[handirifle]

One quick correction, we did used to install a heat pump unit that used a tank of house water, that was in the garage, and served as a pre-heater for the home water heater, you could even save that way as well.

 

[patrick_g]

I have two air to air heat pumps with propane backup for when it gets below 40 degrees F. I also have a geothermal unit (Waterfurnace) to handle my hydronics. These are all about 6 years old now and all work fine. At the time we were doing the design I had envisioned going all geo but the newest high SEER air to air units were just too good to ignore. The break even analysis showed the geo to be a dead heat with the air to air units with breakeven coming at 20 years (life expectancy of the geo unit.)

So it didn't actually matter cost wise which way we went. The geo cost more to install but ran cheaper and our best calculations show that after 20 years it is a draw. Why go geo in my case? Hydronics. I needed hot water from electricity and a geo unit does that very well. If forced air were the only concern then it was a tossup.

Another consideration is backup heat for air to air units where the outside temps get down to and below 40 degrees F. The efficiency of air to air heat pumps crashes pretty spectacularly when the temps get down toward freezing. We have 2 each 1000 gal propane tanks and can go 2-3 years per fill. Geo needs no backup and works great irrespective of the outdoor temps.

Pat