Hello, In 1990, with my trencher, I installed a ground loop for my house, using 2,000 feet of blue polybutyl ene plastic line, 6 feet deep. I am here in eastern Nebraska, clay loam hills. I then installed a 4 Ton, Command-Air heat pump, with a scroll compressor. That unit didn’t wear out, but I decided it would die when I least expected, so in November of 2021, I replaced it with a Bosch 2-stage Scroll Compressor 4-Ton unit. I also replaced the Grunfus circulator pumps. My problem is that my ground loop is marginal. My old Command-Air unit would kick-out on low water temp (set at 21F) sometimes in January. My Bosch unit kicks-out more often, requiring a breaker reset – very aggravating. My local well driller wants 3K per hole, 200’ deep, for 4 wells, or 12K. That would do the job, abandoning my ground loop. But what would you think of my adding just 1 well, tied on to the end of my existing ground loop? Would you think it best to add it to the water exit or the entrance? Thank you.
Added pipe should help with heat exchange with the ground, but there are flow rate and pressure drop (pumping power) considerations that depend on the pipe geometry. I saw your reddit post saying you're using a 50/50 mix of propylene glycol. Using that much antifreeze reduces the ability of the fluid to transfer heat, which is bad. I would expect that to contribute somewhat to your low EWT, since the ground loop can't exchange heat as well with the soil. It's like using a shorter ground loop. It will also greatly reduce the system's heat output and increase the pumping power required, reducing efficiency. According the the WF docs, antifreeze concentrations above 35% aren't recommended due to "extreme performance penalty." For 50% PG, the heating capacity would be reduced to 77% and the pressure drop through the HX would be increased by 81%, as compared to water. I'd recommend using methanol if you can. If not permissible, I'd use the minimum glycol concentration needed to provide freeze protection, which I believe is typically 20% to 25%.
WOW SShaw -- that is very good info -- maybe that will fix my problem without having to add more loop. BUT -- how can I now get the percentage of propylene glycol down? Just using the circulation pumps, I suppose I could run the pumps manually, and break the return line, disposing of that, while letting the pumps put pure water into the loop. Then calculating, I could then close the loop at some point and let it circulate for a while. Then take a sample to see what? The freezing point? Wow -- what a process! I can't imagine the fluid mixing very fast. By the way, it appears that my Bosch100 thermostat is faulty. What brand do you recommend?
I'm beginning to see the light. So my loop volume is 81 gallons. For 30%, that means I want to add 24.3 gal of poly. That means I would leave 48.6 gallons (24.3 x 2) of my present 50/50 mixture. 81 - 48.6= 32.7 gal of my present mixture taken out, and add pure water. So first I need to test the density of my existing mixture to see if is 50/50, or something else. I have a friend who can check the density.
Hi SShaw -- I have been reading your posts on other subjects. You would be probably suggest I dump all my glycol and use methanol or ethanol. I remember the old alcohol antifreeze used in cars -- the alcohol would find its way out of the smallest cracks in the system. Is that a problem with the ground loop piping? It looks like a 20% by volume mixture would work, but I want to be safe. How would I proceed? If I left some glycol in the system, I assume that would be OK. Is the alcohol mix better for heat transfer?
I don't have a specific thermostat recommendation. I think any conventional two-stage heat pump thermostat would work. I would prefer a professional model from a company that specializes in HVAC, like Honeywell. I would avoid Nest. I have heard Ecobee is decent though. Regarding the loop antifreeze, at 20%, methanol is similar to PG. See chart. One issue with glycol is it can become slushy as it approaches freezing, increasing pumping power. The loop and the entire system is supposed to be watertight, so alcohol is no issue there. Mixing antifreeze is probably not a good idea, or necessary. Adjusting the water is probably best done with a flush cart and a tool to measure the antifreeze concentration. You would circulate the water through an open tank, drain some, and replace it with plain water until the desired concentration was reached. You need to avoid introducing air. Probably best to hire a pro with the equipment to do that. I'm not an installer, so I've never done it. The standard for ground loops is to use heat-fused HDPE pipe, which has been shown to last 100 years. You wrote that you used blue polybutylene (PB.) I don't whether this applies to you, but this type of pipe was popular circa 1990 for household water. It's no longer made, and had an expected lifetime of less than 30 years. Many PB pipes failed and resulted in a class action lawsuit. I have a house that was built in 1989 using PB pipe, and the prior owner replaced all the interior piping. The failures were thought to be related to water chemistry, so I'd want to know how PB stands up to glycol or ethanol.
SShaw -- you scare me -- my blue polybutylene pipe is passed the end of its life (It's been in the ground for 35 years)! But I was told to cover it with fine sand, which I did, to keep it from losing contact with the earth when it squirmes around when the temperature changes. I take it, that theory has changed. When I built my house in 1988, I buried black plastic water line. Mine hasn't failed yet, bit I witnessed my neighbors failing -- it just went to pieces. I am 85, so I expect to see my water line failing soon as well as my geo loop, as well as me! I'm thinking the wise thing would be to leave my loop alone until it fails, then put down 4 wells, 200' deep. Over the years, I noticed that when I get a good cover of snow in the winter, my loop is better.
Yes. Who knows, your loop might last another 15 years or more. If it were my loop, I think I'd reduce the PG concentration and see how much that helped with the EWT. Should be a quick process for a technician that does GSHP installs to do that. You could ask a local installer's opinion on the longevity of PB pipe, and the impact of PG concentration.
SShaw -- I certainly appreciate all the hep, and for the info on PG concentration. Wells obviously have a higher EWT year around, avoidi
SShaw --( I got iterrupted) I certainly appreciate all the help, and for the info on PG concentration. Wells obviously have a higher EWT year around, avoiding the 15F or so kick-out on the loop. Has the energy savings been studied on that?
The industry standard design practice has been to size the loop such that the min/max EWTs are 30/90 degrees F in winter/summer. So, closed loop well systems do not necessarily have a higher EWT in winter. It all depends on the loop sizing.
