Loop for cheap-and-cheerful system: step 1, how to test?

Discussion in 'Vertical and Horizontal Loops' started by norwood, Jan 27, 2021.

  1. norwood

    norwood New Member

    Ready for something really different?

    We're a farm, and are hoping to put in a 16x25 greenhouse this coming spring. We had the use of an excavator because we had to rent it for another project, so we made a long (150ft) trench, 5' deep, and put in 500 feet of 1" PE-RT (because that's what was available while we had the machine, and because it seems closer to HDPE than PEX is).

    Went smoothly apart from one kink that I immediately straightened, at the end of the first evening when I was installing it. I was kicking myself, investigating different ways to cut that area out and fix it, but the next morning when I went to look at it, it had recovered to a point where I literally couldn't figure out exactly where that area was. Cool. Put the rest of the pipe in, routed it, great.

    We have compressed air. What do folks here use to seal the ends of the 1" pipe, in order to pressure test with the air? I'm sure I could rig something up, but no need to reinvent the wheel if there's a standard way of doing it already.

    Thanks in advance!
     
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome. If you had used hdpe you could have used a fusion fitting to transition from poly to IPS. I would recomend a barbed poly adapter with clamps to transition from poly to IPS, then put a gauge on 1 side, air chuck on the other. Normal test pressure is 1.5 times normal anticipated working pressure.
    Hope this helps.
    Eric
     
  3. norwood

    norwood New Member

    When you say clamped to a barbed adapter, is this the sort of thing you have in mind?

    pxlf7409-01.jpg pxlf7409-04.jpg

    If that's it, I think I get the idea. I do also want to make sure it's not gotten kinked or crushed. Is there any half-decent way to do that with air? Set it up so that I can drain off the pressure from either end, and put gauges on each end, and see if it's possible to get the system to have pressure on one end but not on the other? Or is that something that's just going to happen anyway, with 500 feet of tubing, even if it's working properly?

    Thanks again for your time, this is really helpful.
     
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Picture above is xactly what I intended. Typically when testing we loop the ends together to test the whole loop field or each individual circuit. Prior to backfilling we pressure test the loop or circuits as they are going to be put into operation. Think, no joints burried that were not tested prior to backfill.

    You are very welcome! That is why we are all here, to help others.
    Eric
     
  5. norwood

    norwood New Member

    I actually don't have any joints in it - it's a single 500 foot loop. I realize that would generally be too little for a house, but it's for 400 square feet of space.

    From what you're saying, it sounds like leaks are a more common problem than kinks or crushing by soil and rocks. Do you think it's overkill for me to be testing to make sure that none of that happened? My concern is that if I connect the two ends together and pressurize, then if there's a kinked or crushed area, it would pass the test as long as there isn't a hole anywhere. But maybe I'm being too concerned here. This pipe is supposed to be OK for geothermal, so I assume it shouldn't crush at 5 feet of depth, and if I couldn't see the kink the next morning, it must be pretty resistant to kinking.

    We did try to make a reasonably even 'bed' for it, and to fill in over it by hand with soft dirt before using the machine to bury it (we'd dug up a fair bit of rock in some areas, usually at about 2-4 feet deep).
     
  6. ChrisJ

    ChrisJ Active Member Forum Leader

    What are you planning to connect to this loop? It would work for a pre-heat for an HRV or ERV, to temper the incoming air.

    Chris
     
  7. norwood

    norwood New Member

    Ah yes, that!

    So the original plan was to do something rather primitive, since this is a greenhouse and not living space, and therefore doesn't need to have the kind of temperatures you'd want in a house. I'd like to keep it from freezing in the winter, and get some cooling in the summer, but we're not aiming for 72 degrees year-round. Thus what I originally had in mind was just to circulate glycol through the loop with a pump, then pass it through a car radiator with a fan attached to it.

    (Also, as far as how much heat I was originally planning to need, I'd originally envisioned this to be a passive solar greenhouse. It has great southwest exposure and I have a somewhat unlimited supply of large tempered double-pane window glass from a friendly window shop owner who gives me sliding door panels he replaces.)

    With that said, I then bumped into someone selling used Bosch 2 ton units for $1000 each. I could run sufficient 220 to the greenhouse to drive it, but would it be able to do any good with such a short pipe loop? What would happen if I tried to hook it up that way?
     
  8. gsmith22

    gsmith22 Active Member Forum Leader

    500ft is a pretty decent amount of pipe for a 400 sq ft building so I don't think that is your issue. Your primary issues are a greenhouse with double pane windows essentially doesn't have insulation - maybe an R6 at best. So no heating or cooling, and you will probably get wide temperature swings day to night given the windows. Not sure where you are located as that will determine a lot about the effectiveness of your plan and whether or not a heat pump (and what size) should be attached to the piping. Could always treat this like a house and do manual J, size heat pump, and then size ground loop to verity what you have. the only issue is manual J doesn't take into account solar heat gain during winter (which helps heating during day but no effect at night). It does take it into account for summer cooling which is typically the issue for houses (since they aren't usually all glass).
     
  9. norwood

    norwood New Member

    Well said about the insulation -- although for what it's worth, the NW and NE wall probably will not be windows, so I can insulate there. I could also dig down a few feet (or to bedrock) around the perimeter and put insulation vertically to limit heat loss into the surrounding soil, as I've seen suggested.

    We're north of Pittsburgh, zone 6b.

    I tried registering for a free account at "CoolCalc," which lets me get a somewhat preliminary report. I don't think it had a very precise idea of what I had in mind -- the closest I could get was to describe a 400 square foot house with a "high" number of windows on the SW and SE walls, and 10 (highest number I could specify) skylights. With that it suggested 20000 btu of heating, perhaps 17000 btu of cooling (which, again, is a secondary priority since I can also just open windows).

    I'm trying to rig up USDA's "Virtual Grower" software to see if that's going to give me anything more edifying.

    Reason for my interest in the used Bosch 2 tonner is that it's cheap, so I guess my question boils down to whether using that size heat pump with 500 feet of 1 inch pipe makes any sense mechanically. It doesn't have to get to a point where I can work in a T-shirt in January, but if I can gain (say) 20 degrees over what I get from sunlight and heat storage (i.e., barrels of water to absorb sunlight during the day and give off heat after sundown), that would be really helpful. I'd love to be able to heat it to 50 degrees, and more would be gravy.

    It's the difference between keeping barely-frost-tolerant things alive in there in the winter, and being able to grow peppers and tomatoes...
     
  10. gsmith22

    gsmith22 Active Member Forum Leader

    I wouldn't go nuts trying to get something more accurate than the 20k BTU/hr. What interior temp did you consider to come up with the 20k BTU/hr (asusming you entered a location nearby to get outside design temps)? if you figured interior at 70, then you are probably fine with a 2ton unit (ie you might not get there but you don't care). If you used 50F for interior temp, then this might not work. if you know the model number of the Bosch unit, you can look up its parameters online/probably find the manual. Use LoopLinkRLC (online program) to verify the loop design using that equipment and your 500ft of pipe in the ground. 5' isn't really deep and you are in a climate with cold winter time temps but your spacing heating isn't huge either and if you are just trying to maintain 50 it might all work out.
     
  11. norwood

    norwood New Member

    LoopLinkRLC actually comes up with a much smaller estimate of needed BTU, about 8K BTU/hr, and that assuming a heating set point of 70 and a cooling set point of 75 -- on the other hand the lowest insulation values I could enter were 4 inch exterior walls, defined by its help page as

    4-inch Exterior Walls: This selection assumes the home was built using Southern construction methods (assumed use of R-11 wall insulation and R-21 ceiling insulation).​

    and "loose" tightness, which it defines as

    Loose: This selection assumes above average infiltration levels (built pre-1970's, leaky windows, poor insulation, etc.).​

    Clearly I'm nowhere close to R-11, much less R-21, on the glass walls. (On the other hand, I can insulate the living daylights out of the 2 other walls.)

    It also won't let me specify dirt floor, just "slab on grade" - which presumably adds at least a slight amount of insulation.

    Any idea how to adjust my calculations for all of this?

    Also, LoopLinkRLC thinks that the pipe run should be somewhere between 400 and 600 feet, although I am not confident I'm choosing the correct options there. My loop run goes out, back, out once more, and back once more. I had wanted to do something "slinky" style but it was almost impossible to bend the PE-RT that tightly without kinking it, so I chose the layout that minimized the number of bends. Is that considered "2 pipe laying," "racetrack," or none of the above?
     
  12. gsmith22

    gsmith22 Active Member Forum Leader

    i've only ever used looplink to do the loop calcs - I wasn't aware of their ability to calculate a heating/cooling load.

    the heat loss stuff is all linear and because of your simple building, is probably easier to do by hand. heat loss per surface area is the temperature difference across the insulating medium divided by the R value. so if you have a 10ft*10ft wall (surface area) with an R value of 6 (ft*ft*deg F*hr/BTU), 70 degees inside and 40 degees outside temperatures, the heat loss of that wall is (70-40)*10*10/6 = 500 BTU/hr you could extend this example to your whole greenhouse taking into account heat loss on all walls and roof planes substituting actual interior/exterior design temps, actual wall/roof areas, and estimated overall R values for those walls/roofs. add all of the heat loss at each surface up and that is your design heat loss. google R value and look at the wikipedia page

    I used looplink for vertical wells so I'm not familiar with their nomenclature for horizontal piping but if I had to guess, "2 pipe layering" is a trench with out and back loops laid on top of each other (so 1 loop say 4' deep and the other is 8' deep in same trench). I think what you have is probably more akin to "racetrack" which is an out and back type loop in one plane. Your two out and back loops are in the same trench/same elevation next to each other, correct? I don't know what options it has but if it doesn't have an option like your layout, I would probably do racetrack out and back with dimensions corrected to match your total pipe in ground knowing it won't quite perform as good since all your pipes are next to each other heating/cooling the adjacent ground and each other.
     
  13. norwood

    norwood New Member

    Yikes, I just looked it up and R value for double pane glass is more like 2.0. Ouch. OTOH looplink's original assumptions were so conservative that if I allow for (being really pessimistic here) another 8000 BTU/hr of heat loss, I'm basically to what it considers 118% sizing for the heat pump in question (Bosch SM024) and it still says I'd be on geo 99.9% of the time. So it actually sounds like this 2 ton unit might be pretty much appropriately sized, and the loop more or less the right size to support that.

    Also, looplink's default heating set point is 70 degrees, and that's not necessary if it's asking too much of the GSHP. Warm temps would certainly help crops inside it to grow, so if I can actually reach that kind of temp on renewables (geo + PV) then fantastic, but if I find that I can only hit (say) 55 or 60 degrees in January, that would still be very much worth the effort and expense. Cooling, I'm even more flexible with that since the point is just to keep the greenhouse from overheating in the summer. Original plan was to take care of that with vents, and I think that's still the main route for it. Even more efficient than geo...

    You have a good point about the loop performance. I'm sure our loop performance will be a little lower since it's arranged the way it is, although I did try to keep the loops from being right on top of each other. Without massive changes like a much wider trench, multiple trenches, or switching to a slinky material, I think it's the best we would have been able to do.
     

Share This Page