regular geothermal vs. direct geothermal

girlsmom4October 13, 2004

I'm starting to learn about the two different systems and was wondering which is better. Anyone want to weigh in?

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So called direct geo uses buried copper tubes, high performance potential with high accompanying risk. Stay with "regular" geo with heat fused plastic pipe, better chance of long-term satisfaction, excellent energy saving, and long, trouble-free operation..

    Bookmark   November 24, 2004 at 5:46PM
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I'd weigh in on the Direct Exchange method. Yes it has buried copper tubing and high performance. It also has less parts to its system, so less parts to go wrong and cause a problem.

Plus with a Direct Exchange System, if you add on the Superexchanger, you'll get free hot water when your system is in it's cooling mode.

With a non-DX System, you have heat fused plastic PVC pipe. Tell me - what would you rather have freon running though - Plastic Pipe or thick copper pipe? Oh wait second - in Non-DX, water runs through the Plastic Pipe, not freon. Water has to run through the plastic pipe, pick up heat (or release it) then transfer that heat to the Systems containing Freon pipes, then repeat.

Too many things can go wrong with a non-DX System. Just go with a state of the art Ground Loop DX Geothermal System. That's what I'm going with for my new house in Westminster Maryland.


Here is a link that might be useful: link to my new house's website

    Bookmark   February 21, 2005 at 10:38PM
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We have reg. geo and will go with direct geothermal on our next house. Direct geo takes the use of water directly out of the equation. No wells, no water to transfer the heat. Much more efficient to run- so I've been told. I love my regular geo system which was installed almost 10 years ago, but will go with the direct geo system in my new home, it just makes more sense.

    Bookmark   February 24, 2005 at 7:48AM
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Regular geothermal systems provide domestic hot water if they have a desuperheater, and do so during both the heating and cooling seasons. DX is not required for this feature. Of course, neither system will do so when the heat pump is not operating unless it is set up to give priority to heating water. Our closed loop conventional geothermal system heats water summer and winter, but not much during spring and fall, when neither the heat nor the AC come on.

Only open-loop geothermal systems require wells and water. Conventional geothermal systems that use closed ground loops do not need wells, and circulate a water/antifreeze mixture through a closed circuit in the ground and back to the heat pump.

DX systems also use ground loops, but use much shorter (and therefore less expensive to install) copper loops rather than plastic. This also has the advantage of using refrigerant in the ground loops rather than a water/antifreeze mixture, making these systems more efficient.

The concern I have about copper loops is that copper nicks and scratches easily. If not installed carefully, it may be scratched or gouged during installation, which could easily shorten its life. In areas where the soil and ground water are highly acid (like ours), I am concerned that the life of copper may be reduced. But this is not as big a concern as with a conventional closed loop system, since the shorter loops requiring a smaller drill hole can probably be replaced if they leak more economically than the deeper, wider holes of a conventional closed loop system.

    Bookmark   March 3, 2005 at 8:11PM
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Knoto..obviously you are not quite as familiar with geothermal systems as you would presume us to believe. Refrigerant is never run through plastic piping.

In a direct system refrigerant copper tubing is buried and the refrigerant passes through that.

In an indirect system a loop of plastic tubing is buried and a water/antifreeze brine solution is circulated through a heat exchanger. The refrigerant passes through the opposite side of the heat exchanger in a short loop.

Desuperheating for domestic hot water can be achieved on both types of systems, and if connected correctly it can be used in both heating and cooling modes.

I first became interested in geothermal systems while attending HVAC school in Corpus Christi, Tx in the early 80's. Since then I have custom built a number of geothermal systems in Texas, Florida, and recently on my new home in western Pennsylvania.

The system i have in my home now is an adaptation of a commercial/institutional chiller type circulating hydronic system that incorporates hydronic heat by means of infloor radiation, some baseboard radiation and forced air coils for quick recovery or peak demand. It is running three separate compressors. a two ton, and two one ton units. During worst case demand all three compressors run for a total of four tons, but as the demand drops compressors drop offline to conserve energy.

This system originally cost me $11,000 in materials plus my labor and engineering, but I have now recieved a grant from both the Ohio Edison Electric company and the Ohio State University to operate this as a "Good Sense Home" proto type system.

AC is accomplished by means of conventional AC evaporator coils for cooling and humidity, with re-heat for actual temperature control.

Although I did initially install a 40 gal natural gas water heater during the primary testing period I intentionally did not light the gas burner to see if the Geothermal could meet the demand. A year later while performing some preventative maintenance on the system I realized i still had not lit the water heater.

    Bookmark   April 15, 2005 at 3:28PM
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Does it matter what area of the country you live in as to what type of Geothermal you need to use? I just had a conversation with a heating person today and he stated because of the area we live we have to have the type which requires an extra well. The area we were discussing is southern NH. He felt it would cost too much money for any savings. I do not think this is a specialty of their heating business. I really want to have some energy saving feature included in our house plans and I think the solar would be much more expensive. I do not even know where to begin to find a reputable company in our area to talk to.
Any help you can offer will be appreciated.

    Bookmark   May 3, 2005 at 7:10PM
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The prevailing soil conditions have a great effect on the efficiency of a geothermal unit. Dirt is a rather poor insultor which is demonstrated by the "frost depth" indicator for your region. The frost depth is the average depth at which normal winter conditions will reduce the ground temperature to freezing or 32degF. In most instances the ground loop of a geothermal unit must be buried to a depth of approximately twice the frost depth to reach a layer of consistant geothermal heat energy.

In most areas once you have reached the consistant geothermal heat layer the ground temperatures will remain constant at about 50 to 55degF year around, which is ideal for both heating and cooling with geothermal equipment.

With some adjustments in the system geothermal heating systems are capable of working at much colder temperatures which is evidenced by an experiment being conducted at McMurdo Sound, Antarctica. They have installed an experimental geothermal ground loop buried directly in the ice, where the surrounding temperature remains a constant -20 deg.F year around, and the system has been working fine for over ten years.

    Bookmark   May 5, 2005 at 11:17AM
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A friend sent me an e-mail telling me about the postings on this site concerning Geothermal heating for greenhouses. The Direct Exchange system can be installed much cheaper and is much more efficient. Basically this technology uses cooper loops installed in drilled 3" holes in the ground filled with safe refrigerant (such as NU-22) that can deliver the capacity of heating and cooling of one's home. It can be used for greenhouses, commercial buildings, schools, etc.

If you are interested in information, do a search on Google for "direct exchange geothermal heating and cooling". You will find many sites that explain this better than I can in this short space. We are facing major environmental crises that will be costly to our pocket books but more important costly to our environment, which we will be passing on to our children and our childrenÂs children.


    Bookmark   April 7, 2006 at 3:38PM
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Java Man got it mostly right. I wouldnt worry much about nicks or scratches to the copper ground loops in a DX installation. The refrigeration grade copper is quite malleable and the risk of damage is low. He is right regarding the acidity of the ground. You MUST be absolutely certain of a neutral ph or else you WILL have problems. This is not less of a concern with a conventional HDPE system, its of NO concern; in fact if you think about it, many corrosive chemicals, such as liquid Drano, are shipped in plastic.

Jim DX is great for smaller systems, such as residential and smaller commercial installations. Once you get into larger commercial, institutional and industrial use, conventional liquid systems are the ONLY way to go.

DX systems would require too great an expense in refrigerant. DX units are generally not available in sizes much larger than 5 tons. Liquid systems are available up to at least 35 tons, thats closing in on a half million BTUs or more depending on ground temperature and COP. The ground loop with a large DX system would be near impossible to design and build with predictable results. No engineer would sign off on it. Mechanical rooms would be nightmares with about 7 DX units verses 1 liquid unit.

Bottom line is cost, design limitations and engineering norms just do not allow for large DX installations.


    Bookmark   April 11, 2006 at 1:28AM
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This post is very interesting and convince me to adopt DX system. Where can I found manufacturers of Geo DX heat pump ?
Thanks a million for help

    Bookmark   June 3, 2006 at 11:44AM
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I am about to start a house gut-rehab project.
As part of the project we are digging the basement 2 feet to a total depth of 5 feet undergound and pouring a new concrete slab. I am wondering if it is possible to install geathermal tubing under the basement? I also would like advice about the tubing should be PEX or cooper DX. We have a plant of 1400 square feet of basement and we are looking at an output of 250 to 300,000 BTUs.
How can I get contractor's names that design these types of systems?
Thank you for your help

    Bookmark   June 3, 2006 at 11:34PM
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Like most of you I'm also interested in reducing energy consumption for both economic and ethical reasons.

My wife and I are building a 7500 sq ft home in Wisconsin that as my username implies is on a large lake. We are breaking ground shortly and have planned the home to be built as an Energy Star certified building.

In addition to that my wife and I are very interested in using a geothermal heating system (heatpump) as well. We are building on a nearly 1 acre lot and thus should have decent space for a horizontal pipe system. As we are on the lake the water table is shallow (for well digging) and easily accessable should we need it.

From what I've read in this forum it would seem that our home will be too large for a direct exchange system? If I'm getting that correctly I would be interested in recommendations for what the best type of system might be for us. My builder has suggested (or estimated based on others he has installed) that the "payback" looks to be about 8-10 years but has yet to actually run the numbers.

I'm a little concerned with the up-front costs being so high but we are commited to being as "green" as possible for our child's sake. Also, we suspect that energy costs will only continue to go up so that 10-year payback may actually shrink.

Any suggestsions on how to get this off the ground would be much appreciated.

    Bookmark   December 31, 2006 at 7:29PM
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A couple of comments on this thread.

LazyPup wrote :

AC is accomplished by means of conventional AC evaporator coils for cooling and humidity, with re-heat for actual temperature control.

LP, this surprises me. This is the way automotive air-con used to be controlled (maybe still is). It seems like a waste of energy to me, to chill the air and then reheat it. Why can't the system be more precisely controlled to regulate cooling? Is there a practical way to resolve this limitation?

Lakeshorebuilder wrote :

My wife and I are building a 7500 sq ft home in Wisconsin ... we are commited to being as "green" as possible for our child's sake.

I don't want to sound critical, but I'm intrigued by the apparent dichotomy between these two parts of your post. Building a single-family home that large is rather difficult to reconcile with green intentions.

I admire your efforts to build "green," but such a large home has a considerable impact on the environment, regardless of how "green" it's built. It's the land it sits on; the quantity of materials consumed; the embedded energy; the large amount of energy required to heat, cool, and light the home; even the energy, materials, and chemicals required to repair, clean, and maintain the house. For example, I can hardly imagine the amount of paint required to coat (and, in 10-20 years, recoat) the interior.

In 1950, the average family had 3 members (down from almost 5 in 1919), and the average home was less than 1000 square feet. Today family size is about 2.5 members, but the average home size is approaching 2500 square feet.

You're planning a home over three times the present average size, and over seven times the average size in 1950. You mention "child" singular, so I guess your family size is about that of 1950.

Again, I don't want to sound like I'm preaching or criticizing. I also realize that I'm pushing convention here. I've met a few people who have homes in the size range you're describing, and even larger, but most of them seem to have little or no environmental concern. Thus I've been reluctant to discuss these matters with them. And I'll understand if your response is "MYOB."

On the other hand, you clearly do have a "green" side, and you seem fairly open. So I'm keen to learn how you reconcile such a large home with your concern for the earth (maybe you're fostering dozens of refugee kids?).

I'm also wondering what other strategies you're following to reduce the house's environmental impact.


    Bookmark   January 2, 2007 at 9:37PM
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Re: davidr,

Good post!

Re: lakeshorebuilder,

Your planned home is NOT too big for DX.

Can you go horizontal even if you want to; can you dig trenches 6 to 8 ft deep without hitting rock?

Since your water table is so high, in your case a conventional GSHP may be less expensive than a DX system as a result of less drilling.

Were I in your situation with a house that large, I would look into an open loop, passive cooling GSHP. This would provide THE most efficient and cheapest way to air-condition a home of that size. This would certainly shorten the payback period considerably. Lets really put this in perspective; you could air-condition your home, totally, with about the same amount of power consumed by your wifes hand held blow dryer!


    Bookmark   January 3, 2007 at 12:38AM
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LazyPup, I think you make a reasonable point and that apparent dichotomy you speak of isn't something that's escaped me entirely. It sounds as if you ask the question with genuine curiosity and not simply to call me out as a hypocrite, which perhaps to some people I am. If by explaining our (my) reasoning it helps to elicit good advice as to how to make our home as "green" as feasible then it's well worth the effort on my part.

First, to clarify things a bit the 7500 sq ft includes almost an entirely finished basement level (which has a walkout). It is probably not as large as some 7500 sq ft" homes you have seen and probably is the size of many 5000 sq ft homes (without finished basements). Yes, it's still a large home.

You are correct that my wife and I currently have only one child but we intend to have at least one more. As such there are two kids bedrooms in the upper level. Since my wife and I both work from home a significant portion of the time there are two large offices in the upper level as well. That partially offsets the energy footprint of many other Americans as they lumber down long stretches of highway to make it to their cubicles in expansive office complexes.

As you suggest the main level is quite large as we enjoy a very open style floor plan. The master suite is quite large since we have a large exercise room to help us keep fit. The lower level was designed to accommodate the large number of visitors we anticipate (since it is a lake home with all the associated fun water activities) from our extensive extended families. My wife is from another country so often visitors stay for extended periods and a guest suite helps maintain everyone's sanity during those visits. We will also have a home theater since that is a favorite pastime of ours. The home was designed to be wide to take advantage of the views of the lake and as a result some of the rooms are somewhat larger than we might otherwise have specified in the plan. To some degree we had to do that to justify the very high price we paid for the land.

It's true we could clearly have cut the size down of the home and still have been comfortable but there is one huge incentive for us to build as large a home as we possibly can manage. I'm sure you've guessed what I'm referring to... the wonderful American tax system. In our tax bracket there is really only one single way for us to keep from paying insanely high taxes - carry a huge mortgage. Our bankers, tax accountant and investment advisors have all made it clear we "need" a large mortgage (and thus a large home). That wasn't the main reason we are building a large home but it certainly didn't give us incentive to shrink it. The truth is for purely economic reasons we probably should have built a substantially larger home than what we are. That may be a cop out but then again we're not responsible for the tax code and you can hardly blame us for trying to avoid paying the maximum possible tax rate.

Of course along those same lines for the home to build strong equity it must be appropriately sized and proportioned to the property itself and to the neighborhood. Our home will not be as large as the neighbors. Yes, we could have built on a less expensive lot somewhere else but I'm more than convinced that someone else would have built a home as large or larger on our lot and just perhaps they wouldn't have bothered with any "green" technology whatsoever. So, as you suggest at least we are trying to reduce our big footprint impact as best we can whereas many others in our situation don't.

My builder is an energy star builder and only builds with the latest "green" building techniques including the use of non-petroleum based materials such as cement siding, cellulose insulation, maximum efficiency windows and doors, energy conscious heating/cooling zones, the use of energy conscious landscaping and a host of other methods and techniques. We also voluntarily paid to reconstruct the waterfront to a more environmentally friendly state than it was in when we purchased the property. Purhaps it was partially out of a sense of selfishness (as it was largely so we can watch the giant and ancient sturgeon spawn on our beach) but I think the wildlife will benefit as well. To some our sprawling 7500 sq ft behemoth might seem excessive but certainly not compared to the 13000 sq ft monster our builder has just completed in a nearby town. Interestingly he used the same "green" approach to that home as well.

We are open to other types of green technology besides the geothermal as well. According to my builder the energy our home will consume (assuming we remain energy conscious of course) following the implementation of the green building techniques and the geothermal heatpump will be quite comparable to the current average American home. That doesn't seem so bad for such a spacious home.

    Bookmark   January 3, 2007 at 1:24AM
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fsq4cw, yes, according to our builder and excavator (which I saw in action just today) we have very favorable soil for such a horizontal system. The excavator (he has apparently installed many trenches for geothermal systems) said the packed material under the organic soil is very moist and should be very good for use with a horizontal system. The front yard is very large (DNR only allows us to build hard surface on 25% of the property surface) and has plenty of room for horizontal trenches.

I believe the builder is thinking along the same lines as you (conventional GSHP) as he was discussing the use of an out-of-use well that exists on the property. From what I understand that would entail using an open system like you suggested.

Since we are building on a very large lake (at least according to what we've been told) cooling costs in the summer are significantly reduced as a result of constant cool breezes off the lake. It sounds like with the use of a GSHP system we could really make out well. Of course since we live in Wisconsin the winter is of primary concern and we will look to minimize heating energy expenditures as much as possible. I don't understand the passive systems well enough to know if they would be appropriate in our climate or not.

Thanks much for the link; I'll do some reading on that material.

    Bookmark   January 3, 2007 at 1:49AM
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I won't weigh in on the geothermal issue because I have no experience with that. What I do have some experience with is building a larger home with a large construction budget and taking pains to make the house as "green" as possible.

There's nothing wrong with questioning what kind of home you really want. But in my view, once you've decided, there's also nothing wrong with making it as efficient as possible, within the constraints of your budget.

Look at it this way, davidr. Many people building new homes nowadays want lots of space. As long as they're doing that, they should be encouraged to do what they can, without being embarassed.

Take my example. I'm building a 5000 square foot home for myself and my partner - just two of us. We took great pains in the design to do things that increased its efficiency, both those that were cost-effective and many that weren't. For example, using a strongly passive-solar design, all our ducts run in conditioned space, etc.

But we also are paying for things that don't necessarily make the most economic sense. For example, we're installing a huge photovoltaic system the payback period of which is (charitably) several decades at today's electricity prices. We're also using icynene insulation, which costs 2 1/2 times fiberglass batts - but we're convinced that the comfort from the sealing capabilities (which, frankly, a crew running around with tubes of caulk could never equal as a practical matter) will be worth it for us.

Our view is, some people spend discretionary income on luxury junk just because they want to. Why not treat "green-ness" as a luxury good that's desirable for its own sake? If technologies like solar and geothermal expand their appeal beyond the stereotypical hippie-on-a-farm or technogeek crowds, to those who can afford to install them on a bigger scale, markets will expand, costs will go down, etc. Today, the practical applications of these technologies are not ready for the average consumer, because of both cost and complexity.

lakeshorebuilder, I say, go for it!

    Bookmark   January 4, 2007 at 6:02PM
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Thanks Chazas, you make some excellent points and I agree you don't have to be a hippie-on-a-farm to benefit from building green. As you suggest we are paying a premium price for the latest green technology and by doing so we are helping to bring it to the greater market at more affordable prices.

I'm still waiting on my builder to get me the numbers from the geothermal installer but like you said we're going for it... even if it takes a decade or more to reach the payback point. I really don't think the geothermal heating system will take that long but many of the other green investments very likely will. In fact some of the hefty investments we made such as the reconstruction of our lakefront that benefit the wildlife/ecology will never provide a monetary payback.

I know we're not off the hook but at least we're doing the best we can to mitigate our transgressions. :)

    Bookmark   January 4, 2007 at 10:02PM
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Re: lakeshorebuilder

May I make a suggestion, if you are going to include a fireplace in your new home, consider a masonry heater. They are THE MOST efficient wood burning appliances not to mention stunningly gorgeous! If youve never heard of these Old World beauties you can read up on the theory at some of these sites.

Here are some links:!OpenForm&id=Gourmet&id2=TA4


    Bookmark   January 5, 2007 at 12:37AM
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Very interesting reading, it's a very appealing idea indeed. They appear (starting @ $10k) to be quite expensive, I'd be curious to know if they would cost less to run (over time) than a very high efficiency gas furnace?

From what I understand our home will be so well insulated that the furnace will actually have to pull in air from the outside or the indoor air quality will degrade. I'd be curious how the masonry furnaces would cope with this issue (or if we'd still have to simply run a fan to suck-in cold winter air). Since the masonry heater would not be capable of heating the entire home we would probably need a backup gas furnace and perhaps that's how we would deal with that issue. As I understand it very high insulation levels are required for energy star certification and thus just making the house less air-tight wouldn't necessarily be an option to address the "fresh air" issue either.

We planned on having just a single (high efficiency) wood-burning fireplace. Because we anticipate using the lake in all seasons (i.e. swimming, skating X-country skiing, etc.) it is important that we have a fireplace that can actively warm-up shivering family and friends. The fireplace we were looking at has a glass sealable door which (when open) can actively warm people but (when closed) apparently radiates heat for much longer periods. I doubt that fireplace is nearly as efficient as a masonry fireplace but I wonder if the biofire type is capable of actively warming?

Where I live (Wisconsin) firewood is actually quite available and I don't think it's expensive - I'd guess it's possible to save money on heating over time to actually reach a payback. I have no idea how long that might be but I'll look into it. If the hearths cost $10-15k (i.e. $10K more than a standard fireplace) I would think it would have to be measured in decades. Of course the radiant heat has benefits of it's own without considering heating costs.

In any case thanks for the links this is something I'll definitely look into.

    Bookmark   January 5, 2007 at 1:32AM
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Re: lakeshorebuilder

True they are more expensive than a conventional system, but so is geothermal. Many of these soapstone heaters output an average of 16K - +20Kbtu over an 8 - 12 hr. period with just a 1 1-1/2hr. burn time at an efficiency of over 92%! That puts them in the realm of a high efficiency gas furnace. 1400º - 1800ºF means that there is almost nothing coming out of the chimney (about a 230ºF exiting temp.) and all that heat is comfortably radiated into the living spaces.

Truth be told, its one of my dreams to install a masonry bake oven/ heater, but after installing the geothermal system my wife asks, just how many tens of thousands do you want to spend on heating systems? The answer is I would do it in a heart beat but I prefer to remain married!


    Bookmark   January 5, 2007 at 5:16PM
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Hi all - Would like to add to this geothermal/masonry heater discussion if I may....DH & I are building a "paltry little" 2500 sq. ft. home, one story, in the Pacific Northwest. We were all set to go with having a masonry heater installed in our home to be used in conjunction with geothermal heating, but were talked out of it - told that the two systems in use together would be overkill and that we would be roasted out of our home (not such a bad sounding idea today - 33 degrees outside)! This came from both the mason and the geothermal guy. But now, here we are on a forum discussing the possibility of using them both together. Is it a size thing?? Bigger house could handle both?? Would love a bit more info. Anybody using both together?? Thanks!

    Bookmark   January 5, 2007 at 9:49PM
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Re: honeysmomcooks

I look at it this way, first of all, once the stat has been satisfied the geothermal will not come on. Second, just as in a regular fireplace, youre not obliged to load up the combustion chamber to the max. So you can regulate the thing and your home shouldnt feel like a runaway thermo-nuclear reactor. Theres also the options of raising the stat if it gets too cool or heavens forbid, opening a window if it gets too hot and getting some fresh air.

Just a thought; common sense I guess. Its also a lifestyle choice.


    Bookmark   January 6, 2007 at 1:07AM
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In Austin, Texas to the west we have highly alkaline soil filled with limestone rock, AND we have a far greater cooling load. My architect says that due to asymmetric heating/cooling load, our ground tends to have heat build-up, resulting in hot loops. An HVAC contractor tells me it's all a matter of sizing the loops correctly.

Does anyone here have knowledge of this issue?

    Bookmark   January 16, 2007 at 2:12AM
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Re: dividdqxo,

Your HVAC contractor is right, its all a matter of proper sizing of the (closed) loops. If theres an issue regarding the ph of the soil, go with a HDPE/liquid system, that way you cant go wrong providing its properly installed!


    Bookmark   January 16, 2007 at 9:49AM
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At the risk of getting the whole heat pump crew mad a me, I think the following point should be made:

Ground Source Heat Pumps when used primarily for heating are not a "greener" solution than a modern gas furnace or gas condensing boiler. As the very straightforward calculation below shows, if you compare the green house gas generated to deliver 1 million BTUs to a house with a GSHP compared to a 95% efficient furnace, the GSHP generates 170 lbs of greenhouse gas and the gas furnace generates 125 lbs of greenhouse gas.

This assumes that the GSHP is achieving a COP (efficiency) of 3.5, and that the electricity for it was generated at a coal fired power plant (as is true for 60% (and growing) of the US). The COP of 3.5 comes from a study that carefully measured the COP actually achieved in 5 real homes with GSHPs.
The reason it works out this way is that while a GSHP is 350% efficient, the coal fired power plant is only about 35% efficient, and it is powered by a very high carbon content fuel.

If you want to be "green" (a fine idea), an alternative approach would be to take the extra money that would go into a GSHP, and spend it on excellent insulation, windows, and sealing. And, invest in very energy efficient lighting and appliances. And, if you have the site for it, on passive and active solar, solar water heating, and perhaps solar electricity. All of these things will save money on energy AND reduce greenhouse gas emissions.
I'd also suggest investing in a copy of "The Not So Large House" -- can't remember the authors name, but its in most book stores. It focuses on building homes that are truly a pleasure to live in rather than truly huge -- its a very good book, even if you decide to build a large house.


The Calculation:
The calculation that I use to compare GHG emissions for a ground source heat pump and a gas furnace is simple, and easy to understand -- it goes like this:

Figure out how much green house gas is produced to deliver 1,000,000 BTU (1 MBTU) of heat to a house using 1) a ground source heat pump, and 2) a modern natural gas furnace.

1) Ground Source Heat Pump:
Assume a COP of 3.5

Electricity used by heat pump to deliver 1 MBU to house =
(1000000 BTU)(1 KWH/3412 BTU)/(3.5 COP) = 83.7 KWH

Using the carbon calculator here:
the greenhouse gas for 83.7 KWH is 169 lbs CO2
This is assuming western coal (eastern coal is a bit worse).

The COP of 3.5 (effectively 350% efficiency) comes from a paper that measured the actual COP for 5 real homes over a full heating season.

2) Natural Gas Furnace:
Assume efficiency = 95%

Therms of natural gas used by furnace to deliver 1 MBTU to house =
(1000000 BTU)(1 therm/100000 BTU) /(0.95 efic) = 10.53 therms

Using the GHG calculator, the GHG for 10.53 therms is 125 lbs.

So, by this estimate, the ground source heat pump CO2 emissions are 35% higher than a modern natural gas furnace or a natural gas condensing boiler to deliver the same amount of heat to the house.

I'm sure one could do a more exact calculation, but I don't think the answer would change much. Heat pump people will argue that when you include cooling as well as heating, that it helps the heat pump numbers, and it does. But, I have read accounts from people who bought heat pumps for heating, and found that they now use them for cooling as well, even though they had no form of AC before the heat pump -- this does not seem like GHG progress to me.

The studies that I have seen showing ground source heat pumps reducing GHG always (it seems to me) tilt the deck toward the heat pump by including a very healthy dose of cooling or by comparing the GSHP to very inefficient heating plants or electric resistance heating. But, for most people in the US the more valid comparison is between a GSHP and an efficient gas heating plant along with upgrades to insulation, weatherization, and possibly some solar heating is a more valid comparison. The 2nd alternative would come out far ahead of the GSHP on GHG emissions -- maybe by a factor of 2 or 3.

    Bookmark   January 17, 2007 at 6:59PM
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Re solargary:

No one should become angry with you for expressing a thoughtful viewpoint.

Do your calculations include the cost in GHG emissions to produce and deliver the natural gas?

In our case, living in Quebec, our electricity is produced hydroelectrically, so there is either zero, or virtually zero GHG emissions associated with running our GSHP. The more energy efficient we become here, the more excess electrical capacity we can export to the United States.


    Bookmark   January 17, 2007 at 9:13PM
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Hi SR,

Right -- Canada has a lot of hydro in the mix, and my understand is that you are on a path to eliminate coal fired electric plants all together. In the US we seem to be on the opposite path, with applications in for 150 new 1000 megawatt class coal fired plants -- 5 in my state alone. All but a tiny handful of these are proposed to use the old technology plant design that offers no opportunity for carbon dioxide sequestration.

This is quite a good article on the subject: "How to Clean Coal"

The calc does not include GHG emissions to produce and transport the energy for either gas or electricity. Its hard to imagine the these costs would be different enough between the two to make a whole lot of difference?


    Bookmark   January 18, 2007 at 1:36PM
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Some thoughts to chew on :

Your GSHP may become greener if you re-source your electricity from a renewable or lower-impact source, such as wind, hydro, or PV. In what ways could the fuel gas for your furnace be obtained from equally renewable sources? What is the likelihood that either electricity or fuel gas from renewable sources will be more readily available to you 5 years from now? Which are you more apt to purchase?

    Bookmark   January 24, 2007 at 8:39PM
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Is there any plastic pipe that is compatible with any refrigerants?

I agree that a complete DX GSHP is going to be most efficient. But plastic pipe is durable and priced right.

    Bookmark   December 27, 2007 at 12:31PM
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The best efficiency will be to burn natural gas in some type of engine and 1) use it to drive a GSHP and 2) utilize almost all of the waste heat.

Yes, you can burn very cost effective natural gas and exceed 100% efficiency (measured btu in source fuel to usable btu produced).

    Bookmark   December 27, 2007 at 12:40PM
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What could be the best source of energy for melting snow on pathways in a gated community...

    Bookmark   February 9, 2008 at 8:53PM
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Hands down geothermal. Lowest maintenance too once installed.



    Bookmark   February 9, 2008 at 11:53PM
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"What could be the best source of energy for melting snow on pathways in a gated community..."

No matter what form of energy you use, and how efficient it is, this is going to take a lot of energy. Do you really want to send many tons of CO2 into the atmosphere each year just to avoid shoveling?


    Bookmark   February 10, 2008 at 9:54PM
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For uptodate info go to: and

With the new stimulus bill giving a 30% tax credit for installing a geothermal system, going Geo makes a lot of sense.

    Bookmark   April 13, 2009 at 1:28PM
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