That is my concern too. It also depends on how much tonnage your system is. We cannot go down 500' so that is my limit. But I think 1 475' would give better performance than 2 250' holes. less surface loss. I have a creek near my house and also a large river that is tidal. I am less than 100' above the river. So there should be lots of water. My water well is maybe 100'. It has a surface pump.

Are you in the Northeast?

We spoke once of trenches, is drilling a must or can you install horizontal loops?
j

My lot is too cut up for horizontal. I even considered doing a huge retaining wall and bringing in fill and grading existing land.

Posted By Volleyball on 01 Jul 2010 09:57 AM
That is my concern too. It also depends on how much tonnage your system is. We cannot go down 500' so that is my limit. But I think 1 475' would give better performance than 2 250' holes. less surface loss. I have a creek near my house and also a large river that is tidal. I am less than 100' above the river. So there should be lots of water. My water well is maybe 100'. It has a surface pump.

Are you in the Northeast?

I'm on the Eastern PA/NJ border, near the Delaware. If you can get into the aquifer and go down a few hundred feet, you might consider a standing column well. I probably would take that approach if I were to do it again because I have a 900' "backup" well on my property. Or a simple closed loop system, like you suggest. The good thing about a standard water/antifreeze system is that you can simply monitor entering/leaving water temperatures over the first year of operation, along with basic operational parameters like system run-time, and you can very accurately quantify the efficacy of the ground loops. If you get too much seasonal fluctuation and you determine inadequate performance, you bite the bullet and add another ground loop. If you're a tinkerer, you can also run your own tests prior to backfilling that will tell you how much heat the ground is capable of absorbing. Roughly put, you pump a known amount of hot water through the loops for a period and you monitor the return water temperature and its change over time.

> run your own tests prior to backfilling that will tell you how much heat the ground is capable of absorbing

Now if we could just get all installers to do such testing, we wouldn't see so many underlooped stories.

In fairness, large, commercial installations usually do test bores with thermal testing like this but it costs thousands to do it. Not bad for a million dollar install but for a residential install, it usually isn't economical.

If ethical residential installers routinely added the cost of
on-site thermal testing to their bids, we'd probably see even
more underlooped systems -- because it would push more
work to the fly-by-night lowball corner-cutters.

...you pay for what you get,

Looby

I agree that it is cost prohibitive. Would cost less to just dig more than you need, sort of the way they use to oversize equipment. When fuel was cheap, why not be sure and if they added on, it would still be enough. I did talk to one guy that has two bores and he usually uses just one and then switches to the other. Don't know if I understand the logic of exhausting one while letting the other recover.
I am thinking of insisting on lots of guages so I can monitor and record the different parameters. That way if something is off, I have some data to help expedite resolution.
Wonder if there are any electronic data recorders out there. I could build my own I guess

You're not alone. There's a group of people out there using the Wel system
http://www.ourcoolhouse.com/
http://www.welserver.com/

This allows for very cost effective monitoring of a great number of sensors.

Thermal testing at low depths (ie, for trenches, not for boreholes) is easier than people think. It's just a probe that outputs a fixed amount of heat and monitors the temperature rise/drop. With hundreds of dollars of loop at stake on every install, payback should be very fast for someone in the business.

have you seen or used such a device?

Yeah, how about a link and some prices.

Here is some information.
http://en.wikipedia.org/wiki/Soil_thermal_properties

I don't know the price - probably high since so few are sold. But simpler ones could be built (for example, using a voltmeter and then a programmable calculator to calculate the number). http://www.innopave.com/en/download/FTN01.pdf

.

Looks like an ideal solution for geothermal wells up to 5 feet deep.

.

Is there any reason something like this can't provide useful soil information on a horizontal loop?

I would think once you disturbed the ground the values would not be very useful. From what I've been told, even though the frostline is 42", the ground temp does drop significantly. Could be because the snow does not remain to insulate. So 8' deep horizontal loops perform poorly in winter. And how would you insert in in frozen ground? leave in since fall? If you drilled down, you would not get good contact .

Back to the original question. I had an energy audit done today. Don't have the calculations done but the guy was here 4 hours. He was pretty impressed for the age of the house. No surprises other than the house is tighter than I thought. Said I was almost ready for a HRV.


So I am still questioning system size. Some say 3T is enough. Some say 4T. One said 3.5T with their manual J and with the 2 stage ECM blower pump, that the 4T would be cheaper to operate since it has more heating capacity and the backup heat or my existing baseboards would not be needed as often. Most agree the 3T would give me upper 90% demand on its own.

If 3T meets 90% of calculated heating load, that is almost certainly the right way to go. 100% of load occurs only 1-2.5% of the time. Meeting 10% of your load with aux strips on only the few coldest nights is a trivial cost compared with the much higher installed cost and likely lower overall efficiency of an oversized system

Make sure system meets 100% of cooling load - there ain't no such thing as auxiliary strip coolers...

I'm skeptical of the hypothesis that 8' horizontal trenches don't perform well in winter. 8' would be an excellent depth for trenching but is uncommon owing to the expense and safety issues (shoring against cave-in). Hence most horizontals are shallower.

Posted By Volleyball on 02 Jul 2010 03:26 PM
  So 8' deep horizontal loops perform poorly in winter.

A properly designed and installed horizontal ground loop buried 5' deep works very well in winter.  We have installed many of these.

You are right about a  poorly designed and installed horizontal ground loop buried 8' deep   as it  will perform poorly.