This is my first post, but I have been following this forum for several months now trying to learn everything I can about geothermal.  I am building a new house in Indiana and the time has come to finally start getting serious about the HVAC.

I think I am going to require a 3 ton unit.  According to my calculations, heat loss is 28300 btu and gain is 34400 btu.  The house is 884 sft first floor on a full finished basement, and has a 609 sft finished 2nd floor with a gambrel roof.

As with so many posters on this site, several contractors I have met with use a rule of thumb to size the equipment.  Unlike many that I have read about, they all seem to agree that I need a 3 ton unit.  Some have said that I could go with a 3.5 ton or even a 4 ton and still be OK, but 3 ton seems to be the consensus.

My first is concerning horizontal loops.  I was under the impression that a 3 ton unit would require three separate loops spaced a minimum of 10 ft apart at a lenght of somewhere around 300 ft (600 ft of pipe).  One of the more experienced contractors I have talked to claims that a single trench 600 ft long with 3 pipes in the trench will suffice.  The trench would leave the house head out about 300 ft and arc back to the house in a teardrop shape.  The lines would header inside the basement.  The trench would be 6 ft deep and 2 ft wide.  There would be two runs on the bottom at opposing sides of the trench (2 ft of separation).  He would then backfill 2 ft and run the third loop at this level (4 ft below grade). 

My concern is that there is not enough separation between the loops, and my EWT may become to low in the winter or too high in the summer.

The system he is proposing is a climatemaster and I have played around some with their GeoDesigner software.  It seems that what he is proposing is similar to several of the configurations on this software, althought they do not have the 3 pipe trench (only 2, 4, and 6).

Is this common practice?  Have I explained this well enough for anyone to understand?  Thanks in advance for any insight.

ID

Posted By ideburger on 15 Feb 2010 07:08 PM

I think I am going to require a 3 ton unit.  According to my calculations, heat loss is 28300 btu and gain is 34400 btu.  The house is 884 sft first floor on a full finished basement, and has a 609 sft finished 2nd floor with a gambrel roof.

I think you need to recheck you figures, you heat gain is greater than your heat loss, which is possible for places Naples, Florida and hotter, but very unlikely for Indiana. You figures indicate you only require cooling, not heating, perhaps you built your house on an active volcano

Posted By ideburger on 16 Feb 2010 01:53 PM
I found a major mistake in my calculations. I now come up with something more reasonable I think. Heat loss is still 28300, but heat gain is more like 25400. Does this sound more reasonable?

Here's an example of how to calculate heat/loss for a 1300 sq ft house.

http://www.diydata.com/planning/ch_design/example1_imperial.php

They come up with around 25k heat loss per hour.

Posted By TechGromit on 16 Feb 2010 07:47 PM

Posted By ideburger on 16 Feb 2010 01:53 PM
I found a major mistake in my calculations. I now come up with something more reasonable I think. Heat loss is still 28300, but heat gain is more like 25400. Does this sound more reasonable?

Still sounds way off to me, lets flip the number around for a minute and say that Heat gain is 28300 and Heat loss is 25400 in the summer, that would make the difference 2900 btu, so your tell me you can cool your 1500 sq ft house with a 3000 btu window air conditioner? I don't even think them make 3000 btu A/C's, smallest they make is 5,000 btu.

Here's an example of how to calculate heat/loss for a 1300 sq ft house.

http://www.diydata.com/planning/ch_design/example1_imperial.php

They come up with around 25k heat loss per hour.

So no, it doesn't sound reasonable to me. I might buy 10 or 15k, but not 3k.