.... geo novice here seeking advice. Help me to understand, why geo is not for everyone, but for many others?

Read this thread?

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/79140/afv/topic/Default.aspx

-Rosalinda

That's an awfully open ended question. I'll try.
Geo:
Is more expensive to install.
Consumes large amounts of electricity (so if you have cheap natural gas and high electric rates....)
Is not while supported in all areas by competant techs
Does not offer as high a savings in more moderate climates
Is even more expensive to install in some regions or some sites

My customers enjoy it because:
Tax credit (especially on new homes where few other heat technologies qualify)
We have cheap electricity and many around here are on expensive fuel oil or propane
Comfort; most of my customers experience more even temperatures in their homes and often select higher temps than they did with other fuels
Competant installers: mid MI may not be the Mecca, but it is been a hot bed of geo (for 60 years) as it is a heating dominated climate with cheap electric, soils are well suited for horizontal (cheaper) geo loops and well water is easy to come by for open loops. There are many good and experienced installer/service techs in the area.

If the house is not huge and is built to 2012 technology (ie: very well insulated & very tight) you will be able to heat it with less initial and long term cost. Geo is not efficient with less than three ton load & it's pretty easy to get to that level.

Posted By Bob I on 29 Jan 2012 11:45 AM
If the house is not huge and is built to 2012 technology (ie: very well insulated & very tight) you will be able to heat it with less initial and long term cost. Geo is not efficient with less than three ton load & it's pretty easy to get to that level.

I would argue that. Lets say you get down to a heatloss of 30KBTU/H with 70/0 degrees inside/outside design temp. In Western NY. that is a 2 ton forced air system. Operational costs with oil or propane get close to $1800-$2000 per year, whereas geo does it for less than $600. A horizontal system in my neck of the woods runs about 19K incl. hot water, plus 3K for ductwork. Deduct 30% fed tax credit. Out of pocket is around $15K. Then a conventional system runs about $12K. Premium for geo is 3K. Payback 2.5 years. So economically it is very thesible, but less if compared to natural gas. May be you could elaborate what you mean that geo is not efficient below 3 tons? The efficiency does not change with smaller systems.

I think we all have conceded from time to time geo is not a good fit in some applications. The best way to determine if it's for you is to get different estimates that employ different technologies.

Posted By Bob I on 29 Jan 2012 11:45 AM
If the house is not huge and is built to 2012 technology (ie: very well insulated & very tight) you will be able to heat it with less initial and long term cost. Geo is not efficient with less than three ton load & it's pretty easy to get to that level.

I don't know if I agree with the 3 ton 'hard line drawn in the sand' threshold, but otherwise, I agree in general.  Today there are smaller (2 ton and less) air-to-air heat pump technologies available that run via variable speed compressors, such that EER and COP performance rivals what is available with water-to-air heat pumps.  The up front capital cost savings includes a big one, that is no borehole field (for geo) is needed.  And operating expense is the the same or similar.

Take any size structure whose thermal characteristics are such that it only needs upwards of about a couple of tons or so, and now you're looking at mini-splits as a lower cost of installation option with same or similar operating costs and Heat Rejection/Extraction performance.  Plus, there's no mess or fuss with a water loop of any kind.

Best regards,

Bill

Yes,

this is a good example. For you in texas, and air sourced heat pump is a very good, if not better alternative. But for people in my neck of the woods, with 98% design temps around 0 F, the geo performance still beats the air sourced ones. But the gap is closing....

Posted By docjenser on 30 Jan 2012 05:14 PM
Yes,

this is a good example. For you in texas, and air sourced heat pump is a very good, if not better alternative. But for people in my neck of the woods, with 98% design temps around 0 F, the geo performance still beats the air sourced ones. But the gap is closing....

I believe the gap is closed for the small capacity units (1.5 - 2 tons or so), regardless of climate.

Best regards,

Bill

I'd beware of hard and fast rules. Cost premium for waterside is a huge factor, varying widely by area and individual circumstances.

Cost of alternative fuels is a huge factor as well - availability of cheap natural gas reduces geo's advantage in heating dominated areas.

Geo's efficiency is markedly higher in temperate climates. The sweet spot is in areas with deep ground temperatures around 60. Geo enjoys an advantage in climates with wider air temperature swings. Consider Austin, TX vs Jax, FL. Both have 71*F deep ground temps, yet Austin outdoor design temperatures are both 4*F higher in summer AND 4*F lower in winter. Those wider extremes mean there are many more hours in both summer and winter where ASHP efficiency falls off...advantage - GEO.

Posted By a0128958 on 30 Jan 2012 10:05 PM

Posted By docjenser on 30 Jan 2012 05:14 PM
Yes,

this is a good example. For you in texas, and air sourced heat pump is a very good, if not better alternative. But for people in my neck of the woods, with 98% design temps around 0 F, the geo performance still beats the air sourced ones. But the gap is closing....

I believe the gap is closed for the small capacity units (1.5 - 2 tons or so), regardless of climate.

Best regards,

Bill

What am I missing?

I was thinking much the same way as Doc about air source COP in the -30C cold snaps we've been experiencing this month. Then I remembered all the hype about those Acadia ASHP's that were supposed to be good for cold climates, and I googled to see what's new with that technology. Wow! That turned from good to bad fast!

http://www.coastalcontractor.net/article/463.html

I see that Mitsubishi is now marketing something called a Zuba ASHP which is supposed to be good down to -30C. Hope that winds up better for them than the Acadia.

To the OP.....as engineer suggests, the availability of natural gas seems to be a major deciding factor in cold climates. Geo makes a lot more economic sense when the only alternatives are propane, oil, or electric. The long-term forecasts for natural gas and electricty rates that seem to have swapped places in the past few years sure make me a bit nervous.

Posted By jml on 31 Jan 2012 06:24 PM
http://www.coastalcontractor.net/article/463.html

jml, thanks for the link.

Purchase price of equipment, operating cost, performance and durability of the equipment all matter.
In our area, as I dissect op costs I usually find pay back period for geo and ASHP to be the same due in large part to the tax credits. I think ASHPs will benefit when geo tax credits are no longer available.

That is why I am not a 1 solution company.

OP doesn't indicate where he is from so I'll just throw this in. The more heat dominated the requirement, the less effective GSHP's are. If there is very little need for air conditioning than the ground temps will drop over time because you don't put any heat back in. I suspect if all gshp locations were plotted on a map, you could tell by the density of them where it makes sense. Yes I recognize that some areas may not have much support and therefore not many installs but that would be the exception.
Bob
Calgary AB. ground temps at about 42º F

Bob,
I would argue the opposite is true.....the more heating dominated the more you can save with geo. The energy "banked" during cooling season only has brief impacts on COP.
A horizontal field in MI at 6' deep is as much passive solar as geo. Sunshine in Jan has way more impact than August cooling loads. In bumper seasons if heating or cooling is not required, "banked" energy would be migrating away from loops anyway.
There are studies that show a drop in ground temps on large commercial verticals over the years but that's modest and a whole 'nother ball of wax.

Interesting pape,r along these lines, of geo in Alaska for space heating.

http://www.uaf.edu/files/acep/Ground-Source-Heat-Pumps-in-Cold-Climates.pdf

Posted By FBBP on 01 Feb 2012 12:34 PM
OP doesn't indicate where he is from so I'll just throw this in. The more heat dominated the requirement, the less effective GSHP's are. If there is very little need for air conditioning than the ground temps will drop over time because you don't put any heat back in. I suspect if all gshp locations were plotted on a map, you could tell by the density of them where it makes sense. Yes I recognize that some areas may not have much support and therefore not many installs but that would be the exception.
Bob
Calgary AB. ground temps at about 42º F

The opposite is true. The higher the seasonal swing, the better GSHPs work. There is certainly is limit, since they have a certain operating range where for example Alaska was not a big stronghold with permafost, but even there they become more thesible. Pretty much anywhere in the continental US, ground temps are within the operating range of a geothermal heatpump.
Here is a graph of a system which is heating and domestic hot water only (radiant, no AC) and the last graph on the bottom is the EWT over the last 12 months. As you can see, it is the same as it was 12 month ago, right on target at 32 F.
What you are describing is an observation with larger commercial loopfields, where the boreholes in the center of the loopfield do not recover as much as the ones on the outside. However, that can be incorporated into the design, and you can compensate for it.
http://welserver.com/WEL0383/

Joe - I agree completely that the source is passive solar. I don't understand how January sunshine hitting two feet of snow on a minus 25ºf day will effect the 18 to 36" of frozen soil laying over top the 6' deep slinky.


sesmith - very interesting read! No conclusions though other than in southern Alaska (maritime climate) gshp can compete with high priced fuel oil IF the hydro electric costs remain low. All conclusions indicate that the jury is still out with regard to long term heat loss of source.


doc - heat dominated climates are somewhat subjective ;-) I was born and raise in southern Ontario and have spent 30 plus years in Alberta. I no long consider Ontario to be heat dominated. Maybe balanced?? Five or six years ago a number of gshps went in in this region. One of which I saw the calc's for. My comments to the mech. eng. were "if you look at the proposed cost of the electricity to run the pumps, compressors and backup, it would be cheaper to heat with resistance and then you would not need to install the five miles of 3 phase power line." Yes it was a big custom home. Just because you can afford to doesn't mean you should.Three other systems failed completely within five years. Not saying they were designed properly 'cause I don't know that. But they were at best break even operating cost compared to n.g. At that time gas was running at 6.50 to 7.50 on the open market. Electricity was around five cent give or take a penny. This year power went up to .14 cents and gas is what, just under three bucks? I totally agree with you and Joe and others when you keep repeating that each site needs to do its own due diligence but the amount of times I have had people quote comments like above and talk about how much they are going to save in the Calgary switching to geo just makes me sick. I don't know of a single install over five years old that the owners are still happy with. Odds are that there will be some in the area that are and if anyone in the Calgary area is reading this I would be most interested to hear about your install.

We are in Buffalo, NY, which I consider heat dominated. I private residences we see 90% of the operating costs going into heating, and 10% into cooling. Yes, you benefit from heating up the loops to about 65F in the summer, but that effect is gone by x-mas time.

We design our systems in a way that the loop drops down to 30F min at the peak of the heating season. You could have an open system if you have enough water and enjoy a 42F EWT all year long. Or at 42F ground temp, it is just a matter of designing the loopfield correctly, to give the heatpump the same 30F minimum temp as it would enjoy in the eastern United States.

Sure, natural gas at todays prices make geo systems have a longer payback period, sometimes too long that they do not become economical thesible. However. systems in locations where propane or oil is the only other alternative, geosystems shine like never before.

Systems failing at 42F ground temp is a matter of poor design, and not a matter of the ground being too cold. I would understand the argument if we are talking permafrost ground, but not at 42 F. I cite Sweden all the time, which the highest GSHP density in the world, and pretty much all the systems are heating only. Ground temp in Stockholm, Sweden: 43F!!!

So I am sorry here, but the statements you made above are not true.