Sorry if some of this sounds like dejavu.
My L. Mich. frontage lot sits about 110′ above the beach. Setbacks keep me 50′ from the slope, 12′ from the side lines and 15′ from the road. The building site is about 150′ deep to the edge of the slope. 93′ wide. Not any room for trenching for a loop.
The lot came with the 8″ test well for the development. It’s Formation Description is:
Fine sand 6′ thick
Sandy clay 54′ thick
Sand, medium 35′ thick
Sandy clay 15′ thick
Medium sand 35′ thick
Fine sand 81′ thick
Total depth bored is 226′ Report says “rotary.”
Water test results indicate an adequate water quality and quantity at 145′ – measured at 20 gpm for 4 hours. (The topo lines give me the impression that well top sits about 120′ above the lake level.)
The snobdivision comes with both sanitary and storm sewers. The sanitary is a group septic system with expected holding tanks and pumps thruout. The storm system collects from the curbed asphalt street and dumps down a 12″ directionally bored pipe going down to the lake where it is released into a large holding tank with a screened open top and large rubble about the base. Designed to resist erosion.
My question is which type of “source” I should consider for the GSHP. Open “pump & dump” into the storm sewer or vertical loops.
Frankly, I prefer the loops as my past experience with “pumping and dumping” results in high well bills (replaced pumps, wells being drawn dry {not likely in this case} and builtup on the inside of the heat exchanger coils. But I have no experience with the loops. And this storm system would make “dumping” a piece of cake.
The size and heat load has yet to be determined, but the enclosed space probbly will be about 4-5K sq ft. Sips, superinsulated.
Which would you go? Or what else do I need to make a decision?
Replies
I think you will find the close loop system to be the most beneficial in the long run. As we get more environmental, there maybe fallout from your local authorities about having an open system. I know in some areas, they have started monitoring amounts of water coming from an open system.
Edited 6/6/2008 1:38 pm ET by unionlabel
I would use deep bores, closed loop. With medium and fine sand into the water table, you will see very good heat transfer at the levels below 145 ft. I would be surprised if open loops are not outlawed in the very near future. You can do it right now, or do it right later.
What type of heat extraction values could I expect from this application of vertical loop, per bore?
Or rather, how else is this "value" transferred into heat load calculations?
On a ground source heat pump design, I, as a design engineer, establish the load for my system and provide that to the field designer. Typically in all but the coldest environs, cooling still dominates the equipment and bore field selections.
The bore field designer will take that information, and what they know about the specific geology, installation details, etc., unless they have a test bore with specifc data to utilize, and plug it into an analysis program and determine the bore field details(depth and spacing of the bores). In a residential application, we're not talking a bore "field" but rather how deep the one or two bores need to be. They also provide the design conditions for the loop for the equipment provider to properly size/select their equipment to meet the stated building cooling and/or heating load
I have not done the bore field design engineer's job. I have done the system/building design engineer's job and presently I am the manufacturer's technical specialist for equipment selections and applications. I still rely on the input of others to "use" the information about the heat transfer capabilities of a bore.
Better heat transfer ina bore means less bore(s) to drill and less tubing buy, less pump to buy and operate and/or better loop temperatures that will affect the overall performance of the system. If, say for instance my summer max supply loop temp is 70 vs a typical 90, my WSHP's in the building will have to work 10-20% less to provide the same cooling.
Unfortunayely, "How will insulation affect my heating and cooling costs?" is a much less complex question to answer than "What type of heat extraction values could I expect from this application of vertical loop, per bore?"
Actually, what I pulled from that, is that I'll need three bores. Two to handle the heating and cooling and one as a backup and/or seperate for any MIL apt.
Any variable would be the depth of the loop.
Is that right?
Typical flow rates for pump and dump are 6 GPM, which for your pumping depth would increase the GSHP electrical usage by about 4-5%, based on just pumping costs.
No idea what your pump hardware/maintenance costs would be, negligible over a few years if DIY, high if not, you need to add those costs in to the trades.
Simple down and up loop would have pumping electrical costs << 1% if you keep air out of the system, and the pump would be easy to service if needed. However, with a single well and about 160 ft of loop, there would probably be an additional 10 degrees F temperature differential which would reduce your COP from (guessing for a typical system) say 3.8 to 3.4. This increases your power bill by 11% over a pump and dump, for a net higher power cost of a loop of about 6-7% over pump and dump. Go with the loop if you think your maintenance costs would exceed 6% of your GSHP power bill.
The legal and regulatory questions are a separate issue for you to consider as others have stated.
I'm building a GSHP this summer to take over for my present air-air system when the outside air temp drops below about 52F. I will be using a pump and dump, as I only need to pump a 10-15 ft head during the winter and dont need AC. Your trade would be different.
BTW: DO NOT bury old extension cord to power the pump <G>
I prefer closed loop. Can you do a closed loop by sinking coils in the lake? We can do it around here but I'm not sure if that is an option in MI. From my research, vertical loops are expensive and requires roughly 1 well per ton. All of our geothermals have been horizontal closed loops.John
J.R. Lazaro Builders, Inc.
Indianapolis, In.
Have you considered a loop dropped in the lake? Not that uncommon. Can be easy/inexpensive.
Someone else mentioned the lake loop.
So let's put that thought to bed...
We're 120' above the lake. The beach has about 300 feet of depth (from the water line to the base of the slope. All together, maybe over 500' away.
Plus this is the east shore of Lake Michigan. Not a pond. It would be similar to using the ocean as a GSHP source.
Lots of information at http://www.geoexchange.org/
A ways away ... but the ocean is a GREAT GSHP source of dissapating heat!!
Can you trench to waters edge? the trench can be part of the system ... if deep enough ... guessing 5-6 ft. 500++ ft gives you a lot of heat exchange in itself.
If water is too far ... wells ... dry or wet, either way ... but drilling tends to be pricy.
In order to go to the waters edge, I'd have to hire a directional boring crew. About 500' total length. Considering the complexities of the slope and shore access, I'm guessing such boring would be equal to or in excess of the per foot cost of drilling a vertical well for a loop.
And then once I get to the water's edge, my property line stops. The Great Lakes have different ownership and access rules than inland lakes. To drop a loop in that lake (to avoid ice and storm damage) would require it to be towed out maybe 1,000 to 2,000 feet. And then it would likely go thru stages of being buried and unburied as the sands shift.
I'm thinking the vertical bores are cheeper. Let alone the DNR's possible hassles.
probably right. It ain't always easy ... 'cept the concepts ... they are so sweet and simple!
Well options are dry and wet. I've seen a lot of dry w/ closed loops dropped down. I think standards/averages (is there such a thing?). is roughly 400-500 ft per ton. Guessing ground temps up there to be what 55-60 degF? That beats by a long shot those cold winters in Frostbite Falls, eh?
There was a JLC article on GSHP a while back that you might like to read. I will try to find the year and month.
It is the February 2005 Journal of Light Construction. Article is on direct exchange geothermal. 400% efficiencies.
Your test well stata results seem ideal if the soil tests low for corrsive acids and alkalis.
Actually a bit of a misnomer ... it is 400% EFFECTIVENESS ... not quite the same as efficiency. It will transfer 4 times more energy from one location to another than the compressor uses to do it. Sorry ... I geeked out on you a bit and I'm not even a geek ... well sort of .... geek wannabe, I guess.
The good news is that at least you are not building on sand.
I refuse to accept that there are limitations to what we can accomplish. Pete Draganic