Hello everyone, I am planning to install a 6 ton unit with a closed horizontal loop. I have spoken with several installers and all seem to have a different idea about the loop field that varies greatly. The smallest is 2 loop trenches 300 ft long with the loops 5 feet deep with 10 foot separation and the largest is 7 loops 250 feet long, 7 feet deep with 20 foot separation. I am in Northern Virginia and I have access to heavy equipment that will allow me to install whatever size loop field is appropriate. This is a major expense to me and I want my system to work correctly. Can anyone point in the direction of some design standards for the field before I become loopy myself? Thanks in advance for any help.
You can do a multitude of layouts for any given load - as you're noting. To get things more "apples to apples", what is your heat loss/heat gain? What is your total pipe in the ground?
Hi Chris, Thanks for the response. One installer provided a Geolink report and it shows my heating load is 46929 Btuh at 53*F delta T and cooling load of 33850 Btuh@ 20*F delta T. and proposing 555 ft. of trench. Does that answer your question?
You mention 6 tons, but your load numbers would suggest a 4 ton heat pump could cover that load. It is not clear if you mean trench length or pipe length. 555ft with how many circuits per trench? What kind of pipe configuration? Could you post the geolink report? That would make it easier to comment.
Hello Doc, I wish I could post the report, but I am not that technically savvy. The report shows 555 l.f. of trench. The installer told me 2 loops 300 ft. long. Looking at the report again it shows 4 ton, but I currently have 6 tons. It seems to me that I am better off to put in a 6 ton variable system with the correct size loop field. If the system operates at a lower load requirement then the loop field would be more efficient. Any recommendations?
6 ton unit with 4 tons of loop is a bad combination. A 4 ton unit with 6 tons of loop would probably be the more efficient and, since you are doing your own earthwork, extra loop may not be too bad an investment. You really need to understand the impact on pumping requirements though, as that can become a significant part of electrical consumption.
What size is the pipe? 3/4", 1" or 1.25"? Are we talking 2 trenches, 280' long, with one loop (now 560' long) in each trench? There is not such thing as a 6 ton variable speed heat pump on the market I am aware of. 6 ton unit runs less efficient than 4 ton unit. To Trent: I started to play cautiously with increased heat pump size on same sized loops, especially with variable speed compressors, to allow them to . The total amount of seasonal in crease of BTUs extracted is small, thus they do not need significant larger loops, and they seem to withstand short term higher loads on them. The additional costs are minimal for the larger HP, and we avoid the supplemental heat. While in the past our wisdom in terms of supplement heat was driven by the notion that it costs a minimal amount of supplement heat to cover the peaks and allows for lesser costs installation (e.g. $50 in supplement per year can save $3.000 lesser upfront install costs), this might change if we see significant geo install numbers. I do not see a midterm and longterm alternatives to electrically driven heat pumps for space conditioning to achieve the current CO2 reduction goals, thus we will have policies in place which will mandate higher efficiencies which will essentially eliminate fossil fuel for space conditioning, and electricity is the only way currently we can make renewable. If we use air sourced heat pumps, we create a huge winter peak way beyond our current peak demand summer problem, and we create the same winter peak with supplement heat. Thus the only way we can circumvent that problem is to design for the full peak load, which does not have many disadvantages with variable capacity equipment. And one can actually do that without in creasing the loops significantly. Again, while 4 tons of loop is relative, we might see a different design philosophy serving all the stakeholders needs (electrical suppliers) in the future. Not meaning to hijack the thread, but eluding that system designs might have different priorities down the road, to make sure a significant market penetration of electrical heat pumps does not create a chaos for the grid! Thus a 5 ton unit on a 4 ton loop might be desirable in the future.
