Geo-Thermal Heat Pumps

[Guest]

I'm hoping in the next few years to build a house that is as energy efficient and self-reliant as possible..probably a combination of passive solar, geo thermal, and a good old fashioned wood stove.

Anyone have any experience with these heat pumps? They sound great..about twice as expensive to start with, but if the savings are up to 40% per year, that should be recovered  quickly enough. But in the spirit of TANSTAAFL, I'm wondering about the down sides to them.

One of my biggest questions is how effective they'd be in a cold Mid-western winter.

[Guest]

I'm also interested in other forms of energy, like passive solar and wind power if anyone uses those. I know I'm not likely to get completely away from the power company but I'd to be as self-sufficient and environmentally friendly as possible.

[280plus]

Hi Barbara,

I happen to be a heating contractor in CT

First off, I can't say for sure that a geo thermal heatpump will actually deliver 40% savings. Each installation is different so it's very hard to make and prove that claim. It sounds more like an advertising claim. I do know that they are touted as the most efficient way to heat. Another thing I know is that many people dislike heat pumps because the air coming out of the registers is only around 105* F and while it is more than enough to heat the place it feels cool / cold when it blows on you. People want to feel nice warm air coming out of their heating system. It's what they are used to.

As long as your "heat sink" in the ground is adequately sized (it's good to go 1/3 bigger than the figures tell you to) and deep enough it should be able to keep up in your climate. But only someone familiar with your area can say that for sure. I do not know if a GHP will have "supplemental heat" to make up for when the heat pump CANNOT keep up. In most cases this would be electric heat. Very bad (the worst of all) efficiency. You need to investigate that.


Building a passive solar house with a geothermal supplemental system is probably the best route. So that when the solar has enough sun to work you get a "free ride" but on cloudy or very cold days you'll have the heat pump to back you up.  Be aware none of this stuff will be cheap.
FYI What I'm concentrating on right now is putting in high efficiency oil fired boilers combined with radiant "floor warming" under tile floors and forced hot air heated by the hot water from the boiler for the rest of the house. Very comfortable, very efficient. Excluding heat pumps, a high efficiency oil fired boiler will give you the most heat for your fuel dollar. If you wanted to couple the system to a solar array it would probably save you money during the milder days. I have kicked this idea around with a few people but again, it ain't cheap. You would have to put antifreeze in it which opens up a bg can of worms which means $. Plus you have to find a company that's willing AND CAPABLE of doing the job the way you want. Most guys I know are stuck in ther ways and as soon as you start venturing away from what they are comfortable with they get antsy. They do make GHPs that will heat water instead of air which opens up more possibilities.

I need to get going but we can continue the discussion any tme. Feel free to pick my brain.

Maybe some other HVAC people will chime in, I'd love to hear what others have to say on the subject!

I also have a passive solar design in my head to heat your domestic hot water for you. Again, it would only be feasible as a supplement to a conventional hot water heater but would save you fuel $ when the weather is right. Unfortunately, still not cheap because, in effect, you are installing TWO hot water making systems vs the usual one. Then there's the antifreeze thing as well.



Water Furnace is a GHP brand that I know is popular around here. Google them and they should come up.

[thumbody]

My Dad had one installed about 7-8 yrs ago he loves it. His electricity provider is a coop  and the unit is on a seperate meter that he is charged 1/2 rate.
The heat is kept constant so it runs more often but you don't get the 5 -8 degree temperature fluctuations. The air conditioning is through the same compressor so you dont need a seperate unit. He had fuel oil before and his heating cost dropped dramatically .

[K Frame]

The biggest problems with geo-thermal (either ground or water loop) are that they're expensive to install, they're expensive to repair if something goes wrong, and it can be hard to find someone to repair them.

The advantages are that they're probably the most economical form of heating and cooling your home over the long run, they don't burn anything, and they're not affected by changes in air temperature like air source heat pumps.

[Guest]

Are there any advantages of the closed loop systems over the open loop/water ones?

[K Frame]

Open loop systems depend on wells or large bodies of water to supply enough water to allow for heat recovery (heating season) or exhaust (cooling). I'm not 100% certain, but I THINK that every ton of cooling requires something like 1.5 acre feet of water if drafting out of a pond or lake. That's a pretty substantial lake if you have a large home. I don't know what the water requirements are for heating, but I suspect they're similar.

Of course, your water supply depends on mother nature not throwing drought your way, too.

[280plus]

Unless you have a substantial pond  or lake closed loop is the way to go.

[Dave Markowitz]

Barbara,

Send a PM to Vern Humphrey over on THR.  I believe he has some kind of geothermal HVAC system.

[K Frame]

For a closed loop system you need to have the land available, and that's also directly proportional to the side of the heating/cooling load.

[Gewehr98]

One of my long-term goals, solar heating and everything else:

http://www.geocities.com/s_wheaton/

And for folks in the snowbelt, take a look at this residence in Colorado (which was for sale, last I looked, I may make a bid on it next year):

http://www.wagonmaker.com/

How about a wood-fired hot tub?

[280plus]

Nice! Isn't the wood soggy and hard to light though?

Barbara, are you planning to have a basement or build on a slab? I don't know how they do it in your area. Either way, heating either the basement floor or the slab with hot water tubes embedded is the most comfortable and efficient way to heat there is. There are GTHPs that produce hot/cold water instead of air. You could, once again, couple it to a solar system as well. The machine will also make domestic hot water (DHW) IIRC. I believe I once talked to a Water Furnace rep on the phone about it. But, I can't recall exactly. I've talked to a few reps around here about it all. Once again, I can't stress it enough, none of this stuff is cheap. I get a lot of people that talk about all the latest technology they found on the net and, don't get me wrong I'd LOVE to sell it to them, but when I show them what it costs they usually choke. I get frustrated because I KNOW they should be willing to make the investment, it's WORTH IT! ESPECIALLY IF YOU PLAN ON STAYING THERE A WHILE!! They'll spend $40K 0n a car every 3 years but balk at the same price for the heating system that will last them for a lifetime, that they can figure into their mortgage. It just doesn't make sense to a logical thinker but in this world, the bottom line rules.

And the old adage applies, "You get what you pay for."

If someone could give me a quick rundown on posting pix I can show you some of my latest project and explain a few things if you'd like. It is NOT a GTHP system though. I get the feeling I need to post them to a website and then reference them from here?

One more thing on open loop. It can/will suck up all kinds of junk from the pond or stream and requires more maintenance than a closed loop which requires viurtually none and it can fail at the most inoportune time because of a clog.

One thing I do NOT like about GTHP is if the power fails, no heat. And it requires a good sized generator if you were to go that way. I could run my fossil fuel heat systems on just a midsized portable generator and have juice leftover for the fridge.

Another advantage of heating the concrete, it gives you ~ 3 days worth of leftover heat if it does fail.

[Guest]

It would be a basement, instead of a slab. Or better yet, something earth-bermed.

It looks like I need to do some more digging on this. For instance, can the GTH be backed up with solar panels, instead of relying completely on outside power? We'd had ice storms here that knock out power for a couple weeks in a time, so I want something that can be used even if that happens.

It will be a couple of years before I can do this..but when I do, I want to have something that is going to last and be as fuel efficient and self-reliant as possible over the next 30-40 years. If that means spending more immediately on energy efficiency, and less on interior froo-froo stuff, I'm good with that. Carpet gets replaced, trim can be upgraded, etc. What I want is a good basic structure and energy systems in place.

[K Frame]

"Either way, heating either the basement floor or the slab with hot water tubes embedded is the most comfortable and efficient way to heat there is."

In-floor radiant heat is amazing, but I'm not so sure that there are any systems that integrate a geothermal heat pump with in-floor radiant. That's usually a fossile fuel option.

The one drawback to IFR is that if you want air conditioning, you still need ductwork, which adds quite a bit of price to an already pretty expensive system.

As for drafting from a pond, that's generally not how it's done because of the problems you mention. The pond option is almost always a closed loop system with the coils suspended in the pond.

Open loop residential systems are virtually always done with wells, and then only where codes permit.

Here's a good link for information on these systems: http://www.geoexchange.org/about/how.htm

[280plus]

In-floor radiant heat is amazing, but I'm not so sure that there are any systems that integrate a geothermal heat pump with in-floor radiant. That's usually a fossile fuel option.

Mike, I'm pretty sure water furnace offers a water based system as oppsed to forced air. Someone does, I talked to somebody about it. GTHP is the PERFECT system to couple with IFR due to the low temp of the water produced by the GTHP being in the same neighborhood as the temps needed for IFR. There are no issues with terying to keep the return water temp up as GHTP does not have any flue gas exhaust that could condense water in the chimney and cause premature erosion of the mortar and a boiler's cast iron.

Yes a closed loop system is the best option for a pond but I HAVE seen systems that draw and use directly from ponds and streams. A GTHP is really nothing more than a water source heat pump (WSHP) (as opposed to air source) so any way you get water to it works as long as the temperature of the water is within design specs. There is nothing new about WSHPs the newer part is the method of using the earth as a heat sink.

Yes, if you do IFR you indeed must install ductwork anyways in order to cool the home and all along I have been saying "not cheap" This is where the hybrid design of only "warming" certain floors but then using a hot water coil in the A/C ductwork shines. The overall cost is reduced as you are not tubing the whole place. Just the concrete basement floor and bathrooms, kithcen and any other tile floor. Still I am doing a house this way right now and the price of the system is in the range of $38,000. If we were to tube the whole place and do A/C the price could easily get to $50,000.

The thing about any hot water heating system is versatility. With the same hot water system you can heat your DHW, your home, your pool, you can have towel warmers in the bathrooms, anti bathroom mirror fogging, melt the snow on the steps sidewalk and driveway. Again NOT CHEAP! But available. You can always add these niceties later too, as long as you have a big enough source of hot water.

Barbara, you are smart. Most people design and even begin to build a house before they give serious consideration to heating and cooling it. The correct way is to decide how you want to condition the home and then design around that. As far as solar panels, the compressor in a GTHP will draw a good bit of power but as long as your solar electrical system is adequate, it is not a problem.

[Guest]

Ok, bear with me, but couldn't water also be used to cool as well? The goal would be to keep the house one temperature, rather than necessarily heat it in the winter and cool it in the summer?

I'm new to all this, and definitely need to do some more reading and work on the options.

I'm really leaning towards some sort of earth-bermed or earth sheltered kind of thing if I can find some options that are affordable, moisture resistant and don't leave me living in a basement.

This looks like the same general idea I'm headed for, if not exactly.
http://www.ourcoolhouse.com/

[K Frame]

I'm not exactly sure what you're asking, Barbara.

Water can be used to heat and cool, but depending on the season, its temperature has to be modified somehow, either through the burning of fossile fuels (hot water heating systems) or chilling it (mostly used in commercial buildings, though).

If you're drawing ground water from a well, the water temperature, depending on depth of the well, will remain fairly constant, say at 58 deg. F year round. That's much colder than you want to keep your home in winter, but even 58 F water has a HUGE amount of latent heat in it -- that's what these systems capture, the latent heat.

In summer, you don't capture latent heat from the well water, you exhaust heat removed from the home into it. Again, at 58 deg. F, the water has the ability to absorb a great amount of heat.

You can't, however, cool your home with infloor radiant tubing. Remember, chilled surfaces collect condensation, and a floor that's wet all the time isn't a good thing.

[cfabe]

To expand on what mike said, when you're cooling air, water condenses on the surface that is doing the cooling. In a 'normal' a/c setup this is the coil in the furnace plenum. There is a drain pan to catch the water and it's piped into the drain or outside. In an heat pump setup with forced air inside, this works exactly the same, just the source of the cooling has changed. However, if you are looking into doing radiant floor heating, instead of the heat exchanger in the furnace/ductwork, the heat exchanger is the floor itself. So if you were to try to cool the home with the floor during the summer, the moisture would just condense on the floor, and you'd be left with a mess.

So, if you want to cool with your heat pump as well, you'll need the ductwork and air handler anyway. A nice hybrid system could probably be designed that would heat both the air through the air handler in the winter as well as heat the floors, and then in the summer, just cool through the air handler system. That'd probably be a pretty expensive system though.

This is a great thread, I'm always amazed at the variety of knowledge we have on these forums. I'm not going to be building my house for a few years at least, but this is great information to have.

[280plus]

Yup, all that has been said is very true. In a place like Germany they actually DO cool the floors and walls for that matter but they also have a dehumidification system to eliminate the condensation of water on the floor. Now you're REALLY starting to put a dent in the wallet though. I would simply take the chilled water (as it is known) and put it through a finned coil (similar to the radiator in your car) in the airstream. The temp of that water will need to be around 40*. So yes, unless you want to get REALLY exotic you will need ductwork if you want A/C due to the reasons described above. I have also seen people try to cool areas using the water from a nearby stream which IS around 58* F but it was not very successful, the water wasn't cold enough.

I agree on the depth of knowledge around here and it's nice to have a forum to discuss non gun related items without getting all in trouble too!

[K Frame]

I can't imagine that cooling the walls and floors would be an effective, or espeically cost effective, means of cooling people.

Cold doesn't radiate like heat does, it's much more effective when actually circulated via a fan.

I also can't imagine why you would expend the energy to dehumidify the air (which requires chilled surfaces) and not combine it with a cooling aspect, as well.

[Guest]

Yep, that was a silly question.

What do you think about combining the use of a GTHP with either an earth-bermed or earth-sheltered design and some amount of solar energy usage?

Any thoughts on materials?

The construction costs on this would be pretty high with all this. But like I said, I'm willing to go cheap on some cosmetic things to start with if I can get the structure right.

[280plus]

I can't imagine that cooling the walls and floors would be an effective, or espeically cost effective, means of cooling people. I also can't imagine why you would expend the energy to dehumidify the air (which requires chilled surfaces) and not combine it with a cooling aspect, as well.

You'd have to talk to the Germans, apparently it works. Are you familiar with the term "Cold 70"? The Germans have square pipe too, figure that one out The real story is humidity. If you can dry the air out you will feel cool even at 80* room temp. Vice versa when you heat, 65* will feel warmer at 50% humidity than 30% humidity.

I am familiar with two solar heated houses in my area. One is is free standing the other buried into the side of a hill. The buried one is a lot like being in a cave and can feel a bit uhhhhh dank(?) claustrophobic too. Only the front of the house had windows. You do feel like your in a basement. The free standing one had the better design circulating air through panels on the roof and down under the slab where they had put very coarse rock that would allow the air to pass through, thereby heating the rocks and the slab during the day which would hold overnight. They had both a wood stove and a gas funace as backup. Every solar house needs backup heat.

The cave had a wood stove. It was designed with a huge overhang so that in the summer the sun was high and did not get into the house but when it was winter the sun was lower and it would shine on the concrete floor and warm it during the day again holding overnight. So the cave was passive and the free standing was active. It used a fan to circulate the air.

Now that I think about it, the reason I came in contact with the cave is because the new owner did not feel warm enough and had me install a furnace!

[Guest]

http://www.ourcoolhouse.com/images/construction/external.htm
http://www.ourcoolhouse.com/images/construction/internal.htm

These don't look bad. I'd want to look at different exterior materials, and style, but they've done some neat stuff with the house..including the etched concrete floors inside..the house is bermed on two sides, but doesn't look dungeonish at all, from the photos. As long as the bedrooms had two means of egress, it should be workable.

http://www.ourcoolhouse.com/images/construction/equipment.htm

This is a picture of their heat pump setup. This is where I get in over my head, for sure. I need to do some serious reading in the next year or so.

[280plus]

This is a picture of their heat pump setup.

That's pretty much all the bells and whistles there! Major dollars!! I have a little issue with the way they use the DHW heater for the slab. Most towns around here won't let you do that because in the summer that water stagnates in the slab abd then can contaminate your fresh hot water (or DHW) tank and make you ill. All you see there is very similar to what I'm doing right now except I'm using an oil fired boiler.

Do they mention cost anywhere?

[280plus]

Here are some pix. if they work. They probably will dissappear at some time in the near future