Manitoba Loop Design and Geo DIY possibilities

Discussion in 'Quotes and Proposals' started by Jolt, Dec 7, 2018 at 1:08 PM.

  1. Jolt

    Jolt New Member

    I live in Canada, and in our area we have limited heating source possibilities. Right now we are on electric resistance heat, and it has been reasonable cost, but the utility is proposing doubling the rate over the coming number of years. So Geothermal Ground Source sounds promising. 6000 heating degree days per year in my area.
    BUT, can it be done? We have an electric forced air furnace, and the ductwork is all behind finished panels. Our yard space is generous (1/2 acre), but still a suburban, not rural, setting. I have a clear 5000 sq foot yard area to heat a 1500 sq foot house, so it might work. And I can take out some trees/bush to expand that a little, if need be.
    The soil is pure clay, from 6" down to as far as I can dig (some holes to 10'). The one sample I tested (from 5' down) is at just over 25% moisture. Undisturbed soil temperature at 6 1/2' gets down to 36F by April. And only rises to 50F by Sept. Frost can push many feet into the ground, all depends on snow cover and cold snaps.
    Most 3-ton water-to-air heat pumps are rated to flow 1200 CFM of air, which is what my present furnace with a cooling coil (AC) actually flows. So if I want to retain my existing ductwork, I guess it will need to be a 3-ton unit. And plan to use resistance heat to make up any shortfall, if/when required in a 'hybrid' system. A larger system, with associated ductwork changes, drives the price up far too high.
    With 36F soil temps in April, if I assume a 15 degree drop, my EWT will be no more than 21F by late in the heating season, and leaving temps running 15F or even less. So I need freeze protection to 10F or so.
    My present heating load on the 'coldest day of the year' seems to be very close to 150kWhrs (maybe a bit less, at 50 heating degree days), so a 3-ton unit delivering 23,000 BTU (with the low EWT) would be running pretty much 100% of the time under those conditions - but should just keep up, if my calculations and conversions are correct.
    If I use standard loop sizing for the 3-ton, my soil temps would be dropping quite a bit with the 100 duty cycle, so I expect to use a bit more loop. At least 4 loops of 800' of 3/4" pipe in a slinky arrangement dropped vertically, one each in a 100' trench about 7-8' deep. With a 100' header trench feeding the 4 trenches, also 100' long That trench would be a bit wider. So a total of 500' of trench, 400 with a single slinky loop in each, 100 with 8 single 3/4 pipe, all at the bottom.
    With the 28% propylene glycol antifreeze I will need, in the above system, it looks like my Reynolds number will be around 1900.
    I expect to need to use some resistance heat to supplement the geo (and maybe some solar thermal in March/April, but that's another story).
    Some my main questions are:
    1) How much of my present 61 million BTU heating needs per year can the geo supply (heating load for the season is about 18,000 kWhr) vs need for electric resistance heat?
    2) how big a problem will the lack of turbulent flow present to achieve the heat flow required for 23,000 btu?
    3) how much of an impact will the high duty cycle have on the life of the heat pump?
    Any help would be greatly appreciated!
     
  2. Jolt

    Jolt New Member

    Well, the Metric/US measure differences tripped me up after all. I had converted everything to US measure (I thought) then noticed I was still used Celsius Heating Degree Days.
    So the proper US measure Heating Degree Days per year are 10,800F instead of 6000C, and 90F Heating Degree days on the coldest day of the year instead of 50C.
    Might make more sense that way. An update to the soil moisture is that the clay is close to 40% moisture.
     
  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    1) yes, geo can do all your 61 million annual heating needs.
    2) Don't know. Get methanol instead and have a much higher Reynolds number. helps with pumping power too.
    3) None. What high duty cycle do you talk about?

    Make your loopfield larger. You can compensate for almost everything. Get more loop in the ground and put it deeper. Design for 30F EWT.

    61 million BTUSs is nothing, nor are 6000 heating degree days. geo is easily scalable.

    where are you located?
     
  4. Jolt

    Jolt New Member

    Thanks for looking at this proposal! It means a lot to me; there is nobody I can ask around here.
    I live in the small town of Pinawa, about 60 miles east of Winnipeg, Manitoba. On the edge of Whiteshell Provincial Park. We have a Lund Mania fishing tournament here every July; the first in Canada.
    If I put the slinky loops in vertically, to make for a narrow trench, then how deep should the bottom of the trench be? And how many feet of trench do I need, total? I suppose the same 800' length of pipe could be used, but spacing the loops more to fit a longer trench? Or would 1000' of pipe in each trench and loop be better, keeping the loops close together?
    I expect to be renting a medium-sized mini-excavator, to get a narrow trench and limit the soil excavation required.
    My undisturbed soil temperature right now (at 6' down) is 44F. The present temperature is by measurement (I brought up a soil sample a few days ago and used a digital thermometer on it) and that confirms a report written by a Government department some years back. That is where I get the 36 degrees from; the report says in Sept it gets up to 50. So I can use a 30 EWT if I maximize the loop? A Climatemaster spec sheet lists full data for 20 EWT, so I thought that should be OK for March. Still plenty cold here some days in March, but I suppose Buffalo has some cold days then as well.
    If I can, I would like to use methanol, but I will need to check on the regulations. Still need to figure out who to ask about that. What type of company supplies the stuff? I understand ethanol can be sourced as racing fuel; or is that actually methanol?
    Can you recommend a Climatemaster 22 2-stage from Ingrams? For me, the simpler the better. Only Geo-Cool brand GSHPs to be had (for a DIY) around here, and they look a little sketchy. The suppliers are no better.
     
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Where do you have all those numbers from?

    150 kwh/day resistance heat are 6.25 kW/hour, but that assumes linearity over the day. The peak is likely higher during early morning temps are likely much colder than daily average.

    Where do you get the 61 Million BTUs from? You r electric bills?
     
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You shall not design for 20F EWT, heat pump can operate down to that limit, but it is not advisable to have your design that low.

    You are better off with a larger unit, you can slow down the blower to avoid any needs for ductwork modifications.

    What are your annual KWH total?

    How many people in the household?
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    What are the dimensions of your 5000 sqf area?
     
  8. Jolt

    Jolt New Member

    I looked at my annual bills, but am also tracking my daily consumption over the last month (I put a KWH meter on my Forced Air Electric furnace) and am calculating the ratio of consumption vs daily degree heating days. So I get 2.8 to 3.1 KWH per heating degree day (Celsius) average and various sources tell me I am in a 6000 heating degree day per year area (C), with a daily max of 50 C heating degree days (90 F). It all agrees fairly well, so I am confident in it (yearly variances will occur, of course). The 61 million BTUs are calculated from the 6000 heating degree days (C) x 2.95 KWH/heating degree day (C) converted to BTU.
    My peak load calculation will be way off, so it's not really usable. My wife and I really sleep well at about 15C, or 59F using our set-back thermostat. I am sure she would not even agree to the GSHP installation if she losses that. The recovery from the nighttime setback will be almost impossible for the Geothermal alone (since it falls in the coldest part of the day), I get that, so the plan all along has been to use (force if needed) the Aux heat for an hour or so each morning to warm things up at a good rate. That would also ease the load and run time on the GSHP (and field). Getting that to work might be tricky, but I would not rule out 2 thermostats. Another subject, but that load would not be expected to be on the GSHP.
    I agree with the larger unit; I was looking at a 3 ton single stage at first, but a 3.5 ton 2-stage seems a better fit (with a '4-ton' field kit or even 5 loops if I can fit them, but they would be close) with the variable-speed fan, as you say.
    Annual household consumption is about 24,200 KWH; average over 3 years (3 people). Only about 2000 of that for domestic water heating. A 1500 sq foot 2-story house built in the 60's; 750 per level.
    The area I had identified is 50' by 100'. There are smaller trees/bush bounding one side and end (field area could be extended a bit; this is still my property) with a shed on a concrete pad close to one long side (frost will go down under it, so I'm staying at least 12' away) and more trees along the 4th side. The whole area is about 50' from the house (corner to corner), so that would be trenched with 8 individual pipes in it running to the house; I had planned to locate the manifolds inside the house. I had thought a wider header trench 100' from house to the far corner of the field (50' to field, plus 50' field dimension), with 4 narrow slinky loop trenches (upright slinkys) 100' long each branching to the side from that. Could stretch them to 125' each by taking out more trees.
    Is getting a lot of pipe in each trench important? That is, would using 600' of 3/4" pipe be very different from 800' (simply using closer loops in the slinky) in the same trench length and depth?
     
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    I get over 10,000 heating degree days for Winnipeg. Buffalo has 6,900, thus you are way above that.

    Not a problem. Forget your heating degree days, they just confuse that's, what you have is a pretty good idea of your annual energy usage, which should also include your internal gains, but also include your solar gains, both of those which should not change. Your current setback strategy is now masking your peak capacity requirements a bit, that seem like your only unknown variable. We could certainly model this, but it is not worth is, we fall for the illusion of precision.

    Lets say we take the 24,200 KWH, subtract the 2,000 KWH, we have 22,200 kwh of heat going into your house annually, which equals about 75 million BTUs. Add about 10 heating degrees per night for 8 hours, so you are talking about 80 million BTUs. Ballpark. Roughly 60 million is coming from the ground.

    99% Design heat load would be 26,400 btus/h at -8F. Now you would be trying to cover a -33F peak night, would would take 34,500 BTUs/h. Thus the 4 ton as a minimum.

    Thus I would be putting in a 4 ton dual stage and slow down the ECM blower, and lock out the aux heat for the recovery, either via separate breaker or via a really smart thermostat, and slow the blower down.

    I would also put in 6 x800 ft of slinky, 3feet diameter, 18" offset, 8 feet down, flat in the ground, about 9 ft OC apart, and use 20% methanol. Your deep ground annual average should be around 44F, that loop design should keep your loops above 30F and avoid many other issues. Reynolds is around 2000, but that would be fine.

    Hope this helps thus far.
     
  10. Jolt

    Jolt New Member

    We agree on the annual heating degree days; I was quoting Celsius, so the Fahrenheit heating degree days number is 1.8 times as high or 6000 x 1.8 = 10,800.
    I would have thought Buffalo was closer to our temps; but I guess your lake effect snow makes up for some of the difference in 'feel'. Our lakes freeze over early...then we drive on them to go ice fishing.
    My wife and I drove through Buffalo on our honeymoon...38 years ago. Bought a pair of CB antennas there...it was another time.

    Wow. That's a LOT of digging. But I understand that would be the only way to get the EWT up, that would also allow the extraction of all of the heating load BTUs.

    The talk from our local utility is to go for a 'hybrid' system, where the GSHP supplies most of the base-load BTUs, but resistance heat takes care of the peaks. The system is smaller, in my case fits the ducting, and the cost is less. The size of the ground loop called for in that situation would be out of sync with the size of the GSHP, though. Cookie-cutter designs of ground loop, anyway. Which was my basic concern. The EWT would be low, and create some of the issues you (and I) are concerned about.

    I'll have to go over the numbers, but the size of that dig seems to put it outside the scope of DIY. For the equipment I can rent here, anyway. And if I hire it out, that means it may never pay for itself; it may well be lower cost to just pay the increasing cost of electricity. Maybe just add a wood stove. At first glance, I'll need 20 years or more for simple payback, and if you include any interest...by then I may need a 6' hole myself.
    It seems the only benefit would be the 'going green'.

    A modest ground loop size and amount of dirt excavation makes it possible to DIY, at less cost. At first glance it seems to be the only way the system can be justified; a recently retired mechanic taking on a large DIY project. I might be able to do 5 trenches 9' deep and 9" wide with a locally sourced rental excavator, but never 6 trenches 9ft OC at 8' deep by 3' wide. I don't believe I have the room to pile all the dirt at once, all other concerns aside.
    THAT could be a real shuffle; dig one trench, add some sand, put in the slinky, add more sand, fill in with dirt moved over while digging the next trench, repeat. Minimum 4-man crew; using a large excavator and skid-steer loader, I figure. Plus the dump truck driver to deliver the sand. It would be fast, though!

    Thanks for the analysis; it is Very appreciated! I'll have to look at everything real close. Any further thoughts you might have will be considered.

    Have a Merry Christmas! Wishing you and yours the very best of the season!
     
  11. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You dig one trench, put in the pipe, 5 min backfill, on to the next trench. You make the slinky in advance and roll it up in donuts, so it is just you. Should be 1 excavator for 1 day, if it is an experienced excavator. Vertical slinkies tend to kink from the weight of the clay soil.

    No sand.

    What is your electricity price for 24,000 KWH of electricity? How much will it get up?
     
  12. Jolt

    Jolt New Member

    I can certainly see the vertical slinky kinking with clay placed on it. I had expected to use sand to backfill to the top of the loops, and water the sand to compact somewhat before backfilling with clay. Would the horizontal loops not suffer from lumps of clay being dropped, or should the excavator use the bucket to 'place' the first layer? With a pressure test while you work?

    Right now we are paying about 0.095 per KWH (Cdn $), so about $1,800 US for the year with a 0.75 Cdn dollar. I expect it to rise between 4 and 8 percent per year for a while, so if the heating load is all moved onto the GSHP with a COP of 3, in 20 years I should see savings of between $25,500 and $36,000. That would be a heating load of 6300 KWH instead of 18,000 KWH. In the first 10 years the savings would just about cover the cost of materials only - if purchased from Ingrams. Of course, there would be some maintenance casts for the GSHP that I never see with a forced air electric (which is heating elements and a fan in a box), plus interest. I think my maintenance costs for the FAE furnace have been about $20 per year averaged over the 20 years we have been in this house (one fan motor and a few relays).
     
    Last edited: Dec 11, 2018 at 12:46 PM

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