Trying to determine the econimics of a horizontal loop (or verticle if necessary) for a home in Southern California.  This is an existing home that we would be installing a ClimateMaster 5 or 6 ton unit in.  Have costs for new duct work, (with 4 zones).  We have equipment for horizontal loop installation, but do not own any well drilling equipment so were hoping to do horizontal loop.  Have read data Bill submitted on his system in Dallas.  Our weather is similar to his, coolling in the summer will be the most critical situation for the system, heating will not be to difficult. Our mean earth temperture appears to be about 73 degrees.  The current soil temperature at 6 feet deep is around 80 degrees.  Soil is dry and sandy.  Water table is 64 feet down.  Soil temp at 4 feet dep about 3 degrees higher (83 degrees).  Can I install enought pipe at 6 feet deep to keep the ClimateMaster cooling?  According to charts temp at 12 feet deep should be about 5 degrees cooler.  I could install at 12' depth if necessary.  We have 2 acres with minimal landscaping, so trenching for individual pipes or slinkies is possible.  Do not have any of the nice programs that help determine pipe lengths.  Thoughts from this group are appreciated.

Craig M
Riverside CA

For loop design, we need reference city, type of soil, manual j load, desired set point etc.
Good luck,
joe

Soil is dry sandy material. Soil temperature low 80's in summer (measured). Loop to supply 5 or 6 ton ClimateMaster Tranquility 27 unit. Manual J load calculates higher than 6 tons but home can be divided to make one unit work. Location Riverside California. Winter soil temps 70 or so (guess 73 minus a little). Summer air temps in low 100's, home set in mid 70's.

Dry sandy soil in a cooling-dominated climate is a tough row to hoe. Horizontal loop at 12 feet may not be as easy as it seems owing to cave-in safety concerns with such deep trenches. OHA rules apply deeper than six feet. Vertical may be a better fit.

Steps to reduce load (windows, exterior shading, awnings, insulation improvements) may have much faster payback than brute force application of a geo system sized to meet current calculated load.

Most critical decision is identifying competent local contractor(s) with good references installing similar systems

You have identified one of my problems. There do not appear to be any local contractors installing stytems in the area, or for that matter in the state. Called the one listed installer I could find (in Bakersfield, 150 miles from me) and he has been out of the Geotheramal buisness for a couple of years. I understand that dry sand has the worst Thermal Conductivity of most backfill materials. If other hot climates (Texas, Florida, Utah et al) can make the systems work, I would think that California could also. Installing longer loops would appear to be an additional factor for the area (combination of hot soil and sandy material). Vertical slinkies as another member has done might be one method to help. With no installers in our area am considering doing the install ourselves, with an HVAC outfit helping with final balancing. Our Company does shoring and excavations deeper than 30 feet so the issues associated with deep excavations are a know quantity. We work with large diameter HDPE pipe so the 3/4 or 1" pipe is a snap. I am unsure if the fact that is is not prevalent in the area is because it does not really work well in heavy cooling areas or it just has not been promoted and pushed in the area. We are not affraid of being a test subject, just want to have a system that performs adaquitely. Hopefully we could show that it can work in Southern California. I have looked at some of the 1 to 3 day design/install classes offered. Need feedback from attendees before I go to one of them. Am not affraid to spend the monies, just do not want to go to a 3 days sales pitch and get very little real information.

Craig M
Riversdie CA

I would try certified designers at http://www.igshpa.okstate.edu/directory/directory.asp.

LA deep earth temp should be around 64F.

I looked at two Mean Annual Earth Temperature maps, and both have the 72 degree line very close to our area. A temperature probe in 26 feet of groundwater (77 feet deep) read 73 degrees, so it appears to jive with the two maps.

I checked two sources for the LA figure. Phoenix is 73F. San Diego is 64F. Las Vegas is 69F.  But I agree, nothing beats a thermometer at the exact location.

General rules of thumb mention 800' per ton (on the high range) or about 4000' for a 5 ton unit.  This enought for this relatively warm soil?

The only rule of thumb I know of for horizontals in north and central Florida (deep earth temp 70+) is 1000' per ton.

if your climate is like mine (Dallas, TX), if your structure and associated size (3400 sf) is like mine, and you set the tstat like we do (77°, 4° setbacks), you'll  need to be able to handle upwards of three-quarters of a million of BTUs per day  being removed from the structure and being put into the ground.  See first image below.

My system is a vertical loop, with a 'down deep' undisturbed temp of 68°.

At this time of year, there's a good 8 - 18° difference from down deep undisturbed temp of 68°, daily.  If you're going horizontal, you'll need the ability to get rid of a lot of heat.  Do not underestimate how slow the ground is to abosrb rejected heat.

Hope this helps.

Best regards,

Bill

Dry, sandy soil with 73F ground temp and 6 tons, WF says 2800ft of slinky trench at 12' depth. 4400' at 6 ft depth. Add a soaker hose to get damp sand and the former drops to 1400'.

With sand and your reasonable water table, you might consider open loop.

4 dozen or so installers on IGSHPA web site including one in San Jacinto....951-654-7724

Bill;

    Yes our loads are somewhat similar.  My soil is a bit hotter than yours.  73 degrees deep soil temp.  81 degrees current temperature at 6 feet deep with no gethermal pumping all that heat into the ground.  I am guessing that EWT will be above that 81 degree mark.  That is hotter than your current EWT from your graph.  You have deep vertical bores going to the cold soil, so are getting rid of the heat better than my horizontal layout would.  Again less heat  loss from a horizontal system in warmish soil.  Am thinking about putting a temp gauge down at 12 feet deep to check that temperature.  See if it really is 5 degress cooler at that depth.  5 degrees might help with this design.  I was hoping to be able to use horizontal because we have equipment to do that (ie cheaper for me).  I know a few drillers around here, we do big and small Cast and Drill Hole (CIDH) pile in our business, so maybe I could get a little price break on verticle bores.  Not sure how deep bedrock is in our area.  Am really trying to get horizontal to work, but if not ?

     Soaker hose.  I have read the charts that show wet sand has better Thermal Conductivity than dry sand  (0.44 vs 1.44 in one chart).  Obviously when I backfill the trench I can get it good an wet.  But this "wet sand" would appear to be a short term help to the system.  The heat generated from the system and normal moisture settlement would tend to dry out this sand.  If this sand is an average of 8 feet deep, water from the top would not seem to be very effective in keeping the soil moist at 8' deep.  Would the increased water bill would offset the system savings?  I see where clays work well also.  If I imported some heavy clay and backfilled around the pipe with "clay", wet it up good and backfilled, would this be a help to the system?  The clay would probably not loose the moisture as quickly as the sand, but with the hight BTU load even it might get dried out  relatively quickly. Is a dried out clay surrounded by dry sand that much better than all sand?

     Will give the guy in San Yacinto a call.  Have not had much luck getting residental Geo in the area.  

Mack, if you think the amount of heat you need to 'shove' into the ground during the cooling season is similar to me, then, using a sophisticated estimated technique called 'rectal analysis,' I think you'll need about 2 miles of 1" HDPE pipe buried in some type of slinky horizontal manner.

I arrived at my number by doubling the amount of 1" pipe I have in a vertical orientation.  My guess is the horizontal style in your sand will be half as efficient as my clay soil vertical bore field.

But,

although I'm starting to get pretty good at understanding thermal dynamics in eath heating/cooling situations, I'm not even close to being qualified to suggest numbers that use any technique other than the one noted above. 

I recommend you find someone who is certified to do loop designs, that has the sophisticated s/w that when heat load, geographical location, soil type, etc. is input out comes how much pipe you need, what size pipe is required, and how deep it's got to be dug.  I would think paying someone to do this would be a small amount compared to cost of the project.  And even smaller when compared to what your cost will be if your DIY effort doesn't end up working well.

I think for someone who has business/industry experience 'digging in the dirt,' putting in a GSHP loop is a reasonable DIY project (assuming HDPE pipe fusion skills are also at hand), if, you've got a good loop/pipe design to start with (which means you're going to also need as a pre-req a good Man J analysis).

I don't think you're going to be able to successfully design your loop from contributions here.

Best regards,

Bill

Hi Bill;

     I do not expect to get a complete "design" from this forum.  Am at the beginning steps of the project. I am not committed to anyone idea or system.  I really like the idea of GSHP and hope I can make it "calc".  If not I can always go to a conventional air conditioner and heater, or try out the Coolerado modernized swampcooler.  Have done the Manual J with an HVAC profesional.  Think a 4 zone system will work in our situation;  3700 sf leaky old plaster home home with soon only 2 people in it.  A single 5 ton system is way undersized per his calculations, but by heating and cooling only 2 of the 4 zones the 5 ton system could work out ok.  Your charts on temp and KWH for your system are great.  I like to work with real world data not charts and guesses.  The fact that no else appears to be doing GSHPs in this area is not a good sign.  Local Vendors and manufacturers are all are clueless when I call to talk about this stuff.  We just finished a project where we instaled a few thousand feet of 36" and 48" HDPE so I have some experienced guys to help with the 1"HDPE.

I am not a fan of soaker hoses to shorten a field. You are essentially, improperly sizing your loops and offering a band aid repair at the same time. I think cost of tube one time vs cost of water in perpetuity is the better buy. Bringing in a modest amount of clay to surround pipes will bring heat to the pipe more quickly once the dry sand brings it to the clay. In other words, you will still be limited to the conductivity of dry sand.
It may be that horizontals are not very practical in your area. This is where local experience matters.
Not a fan of your zoned system either by the way. Geo's are refrigeration systems where airflow is king. To set out with a design that impedes air flow on purpose goes against my grain.
Incidentally, San Jacinto guy is a driller, but hopefully he knows some local geo pros. If you check out the igshpa site you will find many other pros in CA.
Good luck,
Joe

Adding a thermally conductive material (concrete, soil kept wet, etc) around a loop (aka grouting) is, thermally speaking, just as effective for horizontal loops as it is for vertical loops. It conducts heat to/from the loops to a larger area of surrounding soil - helping heat flow considerably.

Had an idea for a homemade soaker.  Drill 1/16" diameter or so hole in 1/2" PVC pipe.  Install the PVC about 8" above the top of the HDPE pipe.  Attach water to this PVC soaker at some best guess frequency.  Maybe install some kind of moisture meter to determine frequency of turning on the soaker.  Basic idea is to keep the HDPE pipe zone material wet but not water the whole 4 or 5 feet above the HDPE. Clay backfill around the pipe would minimize the frequency of watering.