Why aren't Geothermal heat pumps more common?

Question

Air conditioning and heating are major energy consumers in American buildings - commercial, residential, and industrial. I have been curious for a while as to why it isn't more common to use the practically constant 50-60*F temperature of the earth just a meter below the surface to bootstrap our heating and cooling needs.

More information on Geothermal heat pumps

As I understand it, the "ground loop" is expensive to dig but lasts for decades. And once the system is in place it's 40-70% more efficient than traditional HVAC on a single household basis.

What I'm really wondering is: why don't municipalities provide geothermal ground loops like they do sewage and water pipes? They could and should be laid together. Tapping into the loop would have some monthly service fee but only for maintenance, not for consumption (unlike water usage).

Answer 1

The technology is relatively young, and not as well known to consumers as traditional heating and cooling methods. The upfront costs of a geothermal system are also higher, and there are fewer companies around with the knowledge and tools to install the systems.

In the US most homes are not built by the home owners, they are built by development companies who buy large plots of land and build as many homes as cheaply as they can on them. When they build these homes most of the products they use are "Contractor grade" (meaning cheap), so that the companies can make the maximum profit. Because of this, the builders typically will not choose a geothermal system over a more common HVAC system if the cost of the geothermal system is higher.

As for municipalities controlling a geothermal system, again this comes down to dollars and cents. If you were building a new city from the ground up this might make sense, but to retrofit a system like this would cost billions of dollars.

Hopefully as the "Green" movement marches on, geothermal and other "alternative" power sources will become more popular. And as they become more popular they will become cheaper, and the cheaper they get the more attractive they will look to average home owners and home builders.

Answer 2

For the second part of the answer, I believe the general problem is the nature of a 'loop' -- the further it goes, the more likihood of shifting, or some sort of a problem, and when it happens, it'll take out multiple homes, and require extensive work to figure out where the problem / leak / whatever is.

The other issue is a simple question of what the responsibilities of municipalities are. Now, I can say this as I'm a town commissioner, and so an elected municipal official -- I think this is completely outside the scope of our municipal charter. The closest thing I can think of is that there was a development where they wanted to put in a dry pond for water storage to deal with possible flooding issues, and our town (before I was elected in) agreed to foot part of the cost of their connection to the storm sewer system (which is run by a larger entity, on the scale of the county, not the town). The reason was, we didn't want the nuisance of an improperly maintained dry pond.

In that case, the local water company woud be dealing with the long-term maintanance, not the municipality ... and I have no idea what would be all of the issues of maintaining a ground loop long term. but I know it's not something I'd be willing to get our town involved with anytime soon. (personally, yes, I'd be willing to do it to my own house, even with the comment about a house blowing up; but I don't think it's in the best interest for the town to get involved with ... if a new development wanted to do something, and have it managed by a homeowner's association, that's fine)

update : Fine, fine ... you don't care about the political reasons ... so here's my thoughts from an engineering persepective :

Electricity, sewage and water benefit from a central processing location, rather than smaller individually sized solution, assuming there's sufficient density of the places being transmitted to (using recent technology; it's possible it might change in the future for electrical production). In some cases (septic), it limits building density if you have to provide for it on-site, so there's benefit it moving it off-site entirely. In the case of geothermal heat pumps, you actually need the ground contact for the heat exchange, and unless you're transporting the water at sufficient depth, you'll have signficant transmission losses.

If a town/county/state whatever were to get involved, they'd be better off not trying to build a large ground loop and trying to maintain it, but instead either contracting for drilling for their residents and businesses, or including such expertise and equipment necessary in their budget, and doing it in-house. (but then we get into issues with should the government being doing it, or competitively bidding, but this one isn't supposed to be the political answer)

Answer 3

Apart from the developers cost-cutting, in a densely populated area (city), there may not be enough ground to extract heat from without freezing it unless you go far downwards, ie. put the loop into a borehole.

Or alternatively, if it gets hot enough in the Summer, dumping heat in the ground for the winter by running it in cooling mode inside could help.

The late professor David MacKay did some calculations on this on page 301-305 in his free book.

EDIT: While this doesn't answer your question directly, I would also add that for smaller temperature lifts (0C-20C external temperature), air to air heat pumps (reverse AC) can be made more efficient for space heating than anything else I know of with (Seasonal) Coefficients Of Performances (COPs) of 5-6 and SCOPs over 4.

Answer 4

These are admittedly guesses...

The reason it's not more popular is that it's very new compared to the average age of most houses. Most houses have existing heating/cooling systems in place and it's easier to maintain/upgrade those than switch over to geothermal.

As for new development, at least in the US, the trend has been to maximize square footage and scrimp on everything else. Not a good trend.

There's also likely a geology aspect...if you're on rather shallow bedrock, you can only spread out horizontally which isn't viable in urban areas.

As for the municipality aspect, my guess is it's an issue of distance. The heating/cooling fluid would have to be transported across large distances losing a lot of its efficiency.

Answer 5

Good answers all; and the central theme seems to boil down to economics...with a smattering of technical issues like property considerations and rights...perhaps to which we might even add risks such as striking pipelines (flammable and otherwise), conduits and such, or violating easements.

At the most fundamental level it would seem that earth imbedded exchange offers little if any cost-benefit advantage over free-air exchange systems already used in great numbers. Those, too, have the advantage of long lives--in the sense that systems wear out and are replaced or rehabilitated (without need or or concern about excavation; or interface obsolescence).

It is that disposability aspect also that works to the advantage of conventional applications of heat pumping. The time perspective of most all household HVAC systems is one lifetime (in which, usually, one or two to a few system upgrades will happen. Ground imbed systems, however, take on more the character of use in a situation of multigenerational occupancy. Because (especially residential) occupancy that spans over, say, an hundred years invariably goes beyond the purview of land use planning: AC systems are most likely to be designed only to meet shorter, more realistic planning time horizons Accordingly HVAC systems for single unit housing are not designed for "future" generations' utilization.