Hacker News Reader

Comment by baldfat | Hacker News Reader

We already have geothermal cooling in the northeast. The very rich in New England drill holes into the ground and send the house warm air into the ground at one hole and then return air for another hole. Works unbelievably well. I can't tell you why but it feels like cool mountain air and not just A/C.

I really hope this works. It could be a huge answer to LARGE areas that require heat.

View on HN

An open-loop geothermal is based on a standard drilled well where it pumps water up from the bottom of the well and passed through a water-to-air heat exchanger (heat-pump) and uses it to heat in the winter/cool in the summer. Water is returned to the top of the column ... about 10% is bled off to bring in fresh water.

Wells are typically your standard artesian well drilled down to 400' to 600', the geothermal needs about 12 GPM or more to be effective. If there's not enough water flow, a closed loop system can be used where a "coil" is placed in the well and the well is filled with a bentonite grout. Those are interesting because they can use glycol to run to temps below freezing.

In New England these things are very effective. The issue is the cost. The wells typically cost about $10-15K to drill, I think you get about 1-ton of cooling/heating per 100' on average.

Also, there is a large (and unnecessary) premium on these ... there's just no reason why they should cost more than a regular forced air system (aside from the well drilling, but many people in rural areas in NE have artesian wells anyway). The heat-pump units are comparable in cost to a high efficiency gas boiler ($5-8K).

EDIT: Add info on "bleeding" the well.

Most geothermal systems have the air go thru a heat exchanger of some kind and energy transfer with the Earth happens via a much more conductive medium, like anti-freeze liquid. This isn't limited to the very rich either, its as common as installing solar panels.

This is a description of such a geothermal system, but a little more specific: http://www.renbrook.org/page.cfm?p=573

Anti-freeze (glycol) is only used on a closed loop system. An open loop system pumps ground water from a drilled artesian well.

If you hook a heat pump up to that you can extract enough energy during the winter to offset some of your heating costs too.

The most recent "This Old House" series used a geothermal system. http://www.pbs.org/video/2365733023/

That really underplays ground source heat pumps which typically have a CoP between 3 and 6.

Assuming a suitable sized system correctly installed you'll save in the order of 75%.

I actually built the Django app that powers the system "This Old House" installed (http://groundenergysupport.com/) and one of the interesting things that came out of the app is what a dangerous assumption "a suitable sized system" is. I think the client has had trouble getting traction in the industry because some of the installers don't want to see their claims put to the test. Which isn't to say I think these are bad idea or ineffective, just that the sizing seems to be based more on what the installer can sell some times.

Interesting. I'm not surprised to learn that about installers, there's a lot of factors in getting sizing right and pretty difficult for most customers to have confidence until it shows up as lowered efficiency.

The app looks really useful, so I hope you succeed getting adoption.

>I can't tell you why but it feels like cool mountain air and not just A/C.

Could it be because A/C incidentally dehumidifies the air, while this method doesn't?

My sister has a http://www.waterfurnace.com with a about 1500 feet of plastic tubing buried in her yard. Works really well.

I did the savings calculator on that site and it said it will cost me more than my current system? I thought there would be cost savings from this? Does it assume I have an AC unit already?

I would save $1700 in PA. half is from A/C and half from heat.

This will be my first winter with my ground source system, a Climatemaster instead of Waterfurnace. My ground loop is 6' deep, there are 4 trenches 300' long and each one has a pipe down to the end and back for a total of 2,400 feet of pipe.

It is only starting to cool down, but so far so good. I'm very interested to see how it does when the highs are in the 30's and the lows are below freezing.

At what dept?

Shouldn't have to be far, just a few meters below ground is at the year round mean temperature iirc.

The total length that exchanges the heat at the depth is important. If you got a big yard just got 8 feet deep and a hundred feet long and loop it. If not they go deep. In the Northeast the land of $$$ for an acre and rocks everywhere they usually get a well driller and drill a few hundred feet deep.

Interesting. Is that because of the rate of heat transfer through the rocks to get to the pipe or because you need a longer pipe to exchange heat with the ground?

If you don't have a big enough field the ground surrounding the pipe changes temperature too much.

Apparently the wavelength of the "heat wave" caused by summer/winter heat changes is about 12 feet. So you should bury your pipes 6 feet under, where it will be hottest in winter and coolest in summer.

Reply on news.ycombinator.com