Posted By Paul Lepkowski on 25 Jul 2011 04:07 AM
1) It doesn't really matter if a larger loop field costs more to install, and requires more energy to circulate the working fluid. The point is that too small a field won't exchange enough heat, and,
2) due to the variability of soil moisture, it is impossible to calculate exactly what field size is really needed during any given year,
3) therefore it is mandatory that all geo installers should only install fields that are somewhat oversized.
4) Most system failures that I have had personal experience with have been due to insufficient heat exchange capacity in the loop field.
Paul Lepkowski
1) True an undersized field won't work, so? What's wrong with a right sized field?
2) Are you suggesting that soil changes from year to year? So- what, I have dampsand and gravel now but it might be dry clay later? Huh. Most geo pros are familiar with the type of soil in their kneck of the woods and it's year to year and seasonal performance. It is not only possible to predict a required field size but it is done every day.
3) Mandatory? By definition wouldn't "somewhat oversized" mean more than enough? What's wrong with right sized? Wasn't your previous suggestion that folks should install as much loop as the lot will hold? Is your suggested field shrinking?
4) Had alot of system failures have you? By and large undersized loops make for underperforming equipment but seldom does a catastrophic failure occur, usually just higher auxilliary contribution.
I dare say most of the underlooped geos I've heard of have been here, on the web not in my AO. Knowing that most of the folks around here were trained by the same guys and use the same loop designs, I dare say most are using less loop than design software with predictably satisfactory results.
Now without trying to bust your stones, I want you to understand something as a new poster here.
With your PHD and articulate presentation folks will take everything you say at face value and demand as much loop as their lot will hold because paul said so. The loop installer will then ask for 30K or so for the 5 miles that will fill the lot and knock people out of their socks.
Then folks will wanna know why it cost so much more when paul said it was cheap and their potential installer will tell them to have "paul" install it and write the customer off as a crack-pot.
Nobody here suggests that undersizing loop is a good idea, but there is nothing wrong with "right sized". Furthermore, because soil conditions are different, someone with dry soil and 3 times the loop of someone with wet soil, might actually have a field that performs worse. Therefore to give the impression that the most feet wins is folly as well.
"If you add loop, you can reduce flow and pumping costs at the same thermal performance. This forum has seen quite a few cases of underperforming loops, so some amount of loop oversizing is cheap insurance. One may not expect it to be cost effective, but it's so much cheaper to do it upfront vs fixing it later."
jon,
How many cases is "quite a few"? I don't recall a dozen in the last 3 years. 2 were DX (manufacturer decides loop length), and this site has had international contributions.
It is not so common a problem as the direction of this thread would indicate. The biggest defense people can employ is references and competitive bids and use their heads. Micromanaging design is more likely to land someone an inexperienced installer.
j