[AC_Hacker]

Regarding any consideration of heating, especially alternative energy heating, your efforts are best directed toward prevention of heat loss, infiltration being the first priority, insulation being the second priority, and window replacement being third.

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From a straight-forward point of view of cost, scenarios for doing a ground source heat pump implementation would be, in ascending cost & effort:

• Exploit lake water or abundant naturally running water
• Exploit an existing well and do a "pump & dump"
• Drilled well(s) and do a "pump & dump"
• Dig trenches and do a buried loop field, the deeper, the better
• Vertical bore hole loop field

With this in mind, local climatic, geological, hydrological, and land availability conditions can change the desirability of one option over another.

Originally Posted by phreich

...reading your thread on doing a DIY cheap GSHP installation on Portland... I am a handyman by trade, and a jack-of-all-trades by predilection.

Sounds like you have the required gumption... now we just have to determine if you are sufficiently possessed by demons to proceed...

Originally Posted by phreich

I have been noodling with the idea of a GSHP since I discovered that People's Food Coop in Portland put one in I recall about 10 years ago.

Yes, their success has been an inspiration to many people. I have minor quibbles about how they implemented the radiant floor part, but that is for another thread.

Originally Posted by phreich

The thing that's been most daunting to me is the trench or bore-hole requirement. I need to put in somewhere between 2 ton and 2.5 ton unit. That means 400-500 combined feet of bore holes...

My initial idea of simply combining hole depth to get the desired heat out put has proven to be naive... not wrong but naive. The boreholes I dug are pretty shallow, and the temperature variation is greater at a shallow depth, and the temperature variations become less pronounced as you go deeper. The following diagram illustrated this idea:

As you can see, the temperature swings are greater at shallow depth, and less so as you go deeper. My bore holes are only 17 ft deep, and are greatly affected. But the variations become less as you go deeper.

This next image is also important as it explains more of the story:

Here you can see the time-delay of the temperature swings. So the 'thermal pulse' as I like to describe it, which is the solar heat working its way down through the ground, is somewhat lost in a shallow bore hole, as it is best, if possible to have heat demand coincide with the 'heat pulse' availability.

So what I'm getting at is that a simple addition of bore hole depths is not a good model, especially at shallow depth. In your case, if you went to 60 ft depths, simple addition would be insufficient, but your error would be less than mine. The moral of the story is that you are going to need more combined depth than you are now estimating.

By the way, these diagrams are from research carried out by the Oklahoma State University, and every attempt was been made by them to develop a universal understanding of ground source heating and cooling, even though local conditions may be somewhat different.

SO, there is a very interesting local exception... I have learned by observation that the frequent rain falls in Portland (annual rainfall = about 34") are in fact Heat Events, and the heat from rainfall is not inconsequential. I saw, and attempted to log (with limited success) these thermal excursions. Every time there was a rainfall (pretty frequent in Portland) there was a measurable thermal pulse that worked its way down through the ground and my loop field. I would see an 'up-tick' about two days after a heavy rain. At the time, I was running my tiny heat pump 24/7, with no thermostat, and the basement temperature would rise with the peaking of the thermal pulse, and fall as it passed... definitely something was going on.

I don't know anyone else who is thinking along these lines, but since we have this phenomenon going on in Portland, we should think about taking advantage of it.

Originally Posted by phreich

(I live on an acre, but am unwilling to deal with that much yard excavation to put in a slinky system). I also don't think that the slinky system really is all that great since it is only 4 feet underground and so is effected by temperature changes in a negative way (when you need heat the ground at 4 feet is colder, and when you want cooling the ground at 4 feet is warmer).

I think that 4' depth is a bit shallow. I know of an installation here in Portland that successfully used Slinky PEX, in a 6' X 80' trench, per Ton. As I recall, there was 700 feet of PEX in the trench. It had been successfully running, for 10 years when I saw it.

There are fluid friction issues that need to be taken into account, but they are solvable.

Originally Posted by phreich

Soooo, I have been trying to figure out a way to drill my own 50 foot bore holes. This would put me above the water table (about 67 feet at my location). I have been looking at some web-sites on drilling your own wells -- mostly by folks in the southern US states -- and they seem to think that 30 feet is about the limit to using a water-cutting method.

Southern soils are often very sandy, and water-cutting methods can work well. However, here in Portland we live on top of the aftermath of roughly a 3000 year series of cataclysms that happened between about 10,000 years ago, and about 15,000 years ago. That even came at the end of an ice age, when a gigantic inland lake (the Great Salt Lake is the tiny remnant) was no longer being held back and ice dams broke over time and a series of floods of unimaginable magnitude allowed the vast inland lake to drain into the Pacific Ocean, and the route it took was approximately that of the present day Columbia river, and the series of floods carved the geological feature that we now call the Columbia Gorge. The Indians have myths about such an event, and their mythology coincides quite well with modern gemological theory.

The upshot is that we live on the debris field of all that activity. Beneath our fertile topsoil, there is sand, clay, gravel, rocks up to the size of oranges, cobbles in sizes from an orange to a football, and boulders from the size of a football to the size of a car.

So, southern methods are unlikely to be successful.

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