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An alternative to a deep energy retrofit

IgorP | Posted in General Questions on
I am cautiously looking at going with geo (heating/cooling) and pv (electrical).  
I have a 2000 sqft, two story, attached garage home in Edmonton, Alberta, Canada.  The house was built in 2004 – it’s not too old but probably not very efficient either.  My plan is a follows:
 
– Start with a home energy audit, including a blower test.  I hope I could make some quick gains looking at the Attic, Basement and air sealing/insulating it.
– I am assuming I could reduce my heating/cooling requirements cost-effectively by about 25% – and a lot of it could by DIY (~$5,000);
– I am also assuming that air sealing and insulating the Center of the house to get to a low ACH/high insulation value (walls, windows) would be cost prohibitive, work intensive and (in some areas) way beyond my DIY skills (~$25-$100K);
– Got a rough estimate to put in geo to replace my heating/cooling needs (no AC right now) for about $35K.  I hope that by addressing some air tightness and heat losses, I might be able to lower this cost even further (4 ton system instead of 5 ton)?  My furnace is 14 years old and may need replacement within the next 10 years at a cost of $3,000-$5,000 so part of investment into geo offsets that;
– Got a rough estimate on PV installation to offset my electricity consumption at about $15K.  I need to replace the roof first which could potentially decrease PV installation costs if I were to move some vents around to better position the panels and install a compatible racking system at the same time.
 
So being the optimist that I am, here is the cost structure:
– Attic/Basement air-sealing/insulation – $5K
– Geo – $30K (lower than the estimated $35K due to better air-tightness of the attic and basement)
– Roof – $5K (a lot of DIY)
– PV – $10K (including DIY (panel racking) when working on the roof)
 
So for a total of $50K I would be off natural gas and producing my own electricity (net zero on an annual basis).  So, the payback period for PVs @$10K is about 7 years with a projected warrantied life of 25.  Payback period for geo @ $30K  is about 20 years with a projected life of well over 50 years.  I am not counting changes in utility costs and maintenance.  Given the federally (Canada) promised $40K zero percent, 10 year home efficiency improvement loan, I could be net-zero CO2 in 10 years (Yes there is still a gap of $10K between total cost of $50K and the federal loan of $40K).  Also, my loan payments would be about 38% higher than my current utility bills for the next 10 years.
 
Above setup insulates me from anything that the government would like to do to utility prices unless they change the micro-generation bill which guarantees that my solar electricity will be bought at the same price as me purchasing it from the grid.  Furthermore, all these improvements should somehow increase my real estate value (still researching how in the Canadian/Alberta/Edmonton market).  Am I missing something or is this a sound way to proceed with becoming net zero in the most economical considering an existing house?

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    >" hope that by addressing some air tightness and heat losses, I might be able to lower this cost even further (4 ton system instead of 5 ton)? "

    How certain are you that it needs a 5 ton even with the house in it's current where-is-as-is condition? A reasonably tight 2000 square foot 2x6/R20 type house with low-E double-pane should come in at or under THREE tons at Edmonton's -27C/-16F 99% outside design temp. (For design temps see: https://higherlogicdownload.s3.amazonaws.com/ACCA/c6b38bda-2e04-4f93-bd51-7a80525ad936/UploadedImages/Outdoor-Design-Conditions-1.pdf )

    Installing 4 tons to cover the remainder of the load when it's colder than that usually results in lower system efficiency than adding some resistant heat to cover the shortfall for those few 10s of hours per year. Sometimes it's more economic to cover only the 97th percentile heat load with the heat pump, using strip heat for the rest. Whatever you do take pains to NOT oversize the system!

    Short of a Manual-J or better load calculation, start with inferring the heat load from wintertime fuel use logged against heating degree-days:

    https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/out-old-new

    1. IgorP | | #2

      Thanks Dana. I am not a professional but a very curious homeowner and the 5 tons was a number suggested by the geo contractor who (as the article you referenced) probably used one of those "rules of thumb". Thanks for the references on how to better estimate/measure actual heating loads - I will definitely do the math and if it further lowers my geo estimates then I am laughing all the way to the bank! Keep poking holes in my theory - I can only come out more educated from it! Thanks again.

      1. Expert Member
        Dana Dorsett | | #3

        >"Keep poking holes in my theory - I can only come out more educated from it!"

        OK.

        >" I am assuming I could reduce my heating/cooling requirements cost-effectively by about 25% – and a lot of it could by DIY (~$5,000)"

        You probably don't have to spend anywhere near five grand to do the air sealing and insulation. A large window fan to depressurize the room (or whole house) and a $200 FLIR can find most of less obvious yet easy to DIY fix air leaks, and any glaring gaps in the insulation. Figure MAYBE a grand as a DIY, unless some really huge deficiencies show up.

        Attics are usually dead-easy to insulate to a higher R, but air sealing it comes first. Pressurizing the house with a window fan and scanning from the attic side with the IR camera is sometimes easier to spot some attic floor leaks.

        >"I am also assuming that air sealing and insulating the Center of the house to get to a low ACH/high insulation value (walls, windows) would be cost prohibitive, work intensive and (in some areas) way beyond my DIY skills (~$25-$100K);"

        I can't imagine it costing more than $25K to do the insulation & air sealing work, even if it's all performed by a pro unless the approach taken is 100% closed cell foam everywhere. It wouldn't be anywhere near cost effective against saving from the smaller system size and lifecycle operating cost at $100K.

        >" Geo – $30K (lower than the estimated $35K due to better air-tightness of the attic and basement)"

        In my area geo runs about USD$9-10K (=CDN$12.5K- $14K ) per ton, but the savings of going from 5 tons to 3 tons isn't proportional. I'd be surprised if you could get a 3-4 ton geo system installed turnkey for CDN $30K unless you own the drilling rig and DIY your own wells. Typical 3-ton Dandelion Energy (a Google spin-out, but only serving parts of NY) systems are a bit north of USD$20K, (about CDN$28K). They have very low capitalization costs and lower production cost for their heat pumps (being a vertically integrated company), using cookie-cutter system designs to streamline design & installation cost, as well as proprietary cheaper than average drilling techniques, all of which adds up to beating all competition on cost. I can't imagine coming in anywhere near that with a one-off custom system design.

        Keep the gas-burner until you've finished as much of the building envelope stuff that seems reasonable, and use it to measure the 99% design load. Only then would it make sense to solicit bids for the heat pump system, sized based on your fuel use, not a rule of thumb or a contractor's Manual-J (where the contractors' thumbs are too often on the scale with way too conservative assumptions on air leakage and R values, even when you have measurements.)

  2. IgorP | | #4

    Dana, thanks again.

    Air-sealing basement and attic estimate assumes about $1K to air seal attic and add insulation. Thinking all DIY. Basement is more tricky. It's already insulated (stud walls + fiberglass batts) but probably could be improved. Not sure if $4k will be enough. Hence my $5k.
    As far as the envelope is concerned (I have 3-pane windows but walls aren't very tight most likely) and assuming your estimate of 3 tons is right, and assuming $35k estimate for Geo remains, spending $25k on air-sealing and insulating the envelope will not save me $25k on Geo. So my whole point is that with Geo and pv I am already green and comfortable in my house then why should I strive for efficiency at this point by spending an extra $25k?

  3. Doug McEvers | | #5

    Harold Orr described a method of retrofit for homes in your part of the world. They would wrap the exterior of the house in 6 mil poly and then add Larsen trusses to the exterior for an airtight and superinsulated wall. This would carry all the way down to the footing as I recall. I think they just extended the rafter tails as needed to create an overhang.

    With this you can cut the cost and size of the heating system drastically, put the first money into the building envelope.

  4. IgorP | | #6

    Dana, I did my calculations as per the above-referenced article and I think I do need 5 tons. See attached picture.

    Doug, I have looked at the pyramid of what one should do when with regards to DER and going geo and pv would be at the top but I am asking why? Even if I was building a new house and knew that I was going geo + pv then why would I not build to bare bare minimum (up to current code) + pv + geo if it would be cheaper than going highly efficient house + pv + geo, assuming same comfort level? My objective is zero emissions with minimal capital investment and my house is currently comfortable as it is.

    1. Expert Member
      Dana Dorsett | | #7

      >"Dana, I did my calculations as per the above-referenced article and I think I do need 5 tons. See attached picture."

      NO!! You absolutely DON'T need 5 tons of geo- you need 3 tons plus some heat strip.

      ASHRAE's 1.4x oversize factor makes sense for a gas-burner, or for the geo + heat strip as a whole, but it would be sheer lunacy (and use more kwh) to size the GEO at 1.4x.

      As stated previously, it's often more efficient (and nearly always more cost-efficient on a lifecycle basis) to even downsize the heat pump to the load at the 97th percentile temperature bin rather than the 99th, and use resistance heat strip to cover the deeper cold snap loads. The last thing you'd want to do is size the geo to 140% of the 99% load, since 99% of the time it doesn't need any more than 38-39,000 BTU/hr, and 99.997 % of the time (as in "pretty much never") it won't need the full output if sized at 1.4x. It only takes 5 kw of heat strip to fully cover the rest of the load when it's cooler than the 99% outside design temp.

      Note, even during ultra-cold periods when the heat strip is being used to cover the shortfall, the lion's share of the heat is coming from the heat pump. If sized for the load at the 97% temperature bin only 3% of the time would the heat strip be used AT ALL, and then only at the duty cycle needed to cover the shortfall. If sized to the 99% load only 1% of the time would the heat strip be seeing a non-zero duty cycle.

  5. Jan Juran | | #8

    Hi Igor: Gary Reysa at BuildItSolar.com has a summary re how to make a good, usable DIY blower door device for $30-$50 or so: https://www.builditsolar.com/Projects/Conservation/BlowerDoor/BlowerDoor.htm
    You should be able to air seal the various sections of your house one step at a time with this DIY blower door. As you are probably aware, various studies have estimated that air sealing can save 25%-35% of the heating load of an average type home in a cold climate. Very cost effective and worthwhile to do prior to sizing new HVAC mechanicals.

  6. IgorP | | #9

    Dana, fair enough. I get your reasoning. How do I get the 97% percentile design temperature? I can see that 1 kWh is equivalent to about 3,412 BTUs which could bring me down to below 3 tons even with 1.4 adjustment as long as my 97% load requirement can be satisfied with geo only. Furthermore, I don't know the kW requirements of the geo setup but would have to weigh that against the 5 kW power-strip but I see your point.

    Jan, I 100% agree. These are theoretical discussions and a blower door test will be definitely my number 1 task. Following that, I would have to see what makes sense from a financial perspective - 0% to 100% air-sealing vs. appropriately sized geo + pv. I also need to be able to figure out air-sealing impact (lowering the ACH50) on my heating requirements. I may end up modeling the whole thing and as long as I don't piss off any of the people who are providing their input (thanks you and thank you again), its a great learning experience for me, while contributing to an very informed and (hopefully) critically reviewed, solution.

  7. Expert Member
    Dana Dorsett | | #10

    >"How do I get the 97% percentile design temperature?"

    According to first page of the attached document, the 97.5th percentile temperature bin for Edmonton is -13F (-25C), but if you look at page 6 of the document that was based on: "Period of Record = 1967 to 1996".

    That may be a degree or two colder than the most recent 25 year average, given that they also put the 99th percentile at -20F/-29C, which is colder than the -16F ACCA datasets were were showing for a 99% design temp as of 2014.

    Using -10F as WAG for the 97.5th percentile bin wouldn't be insane, and the step sizing of compressor sizes are large enough that a heat pump that covers the load at -10F will nearly always cover the heat load at -13F (or maybe even -20F.)

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