https://youtu.be/xhnz7WNR3aQ

I think the proper term for this entry is "Brute *BLEEP!* Force".

These people built their home in a manner that they rated a HERS of 41.
Not the best I've seen, but not bad.  They're dealing with thermal bridging in a standard foundation, and they've left the ICF walls at a baseline of R24.

Then they go and throw a 25 KILOWATT SOLAR PV system at the thing...







This apparently took 55 POINTS (nearly as much as the entirety of their improved construction and and mechanical plant did) off their HERS score, leaving them with a final value of -14...

Looks like they just took a WAG on the power consumption, and sized the PV array to fill the available roof area on their shop building (which is something of a Net Zero "cheat" in my book: WTF it doesn't even fit on the house!?!), but it's not surprising that it turned out to be overkill. The 4 tons of geothermal heat pump is probably a similar (or even higher) level of bludgeoning it to death.

I'm curious as to how much (if any) of the CT taxpayer/ratepayer subsidy money went into the overkill, if any? Seems likely they could have made Net Zero with 3.5-4 tons of air source heat pump and 15-20kw of PV, at a substantial overall cash savings.

A 1-page description of the house lives here:

https://www.ctzeroenergychallenge.com/participant_overview.php?ID=Moser

(I can't quite believe they got sucked into the "R16" Prodex Total Under Concrete Insulation under the slab!)

The R24 high density fiberglass in 2x6 framing isn't much better than code-min performance, a spendy marginal performance improvement, not even an R1 whole-wall-R improvement over a code-min R20 cavity fill. A 3/4" foam-over using high-permeance polyiso such as IKO Ener-Air, or better yet high permeance, R4 fiberboard sheathing such as SONOclimat ECO4 (about the same price point as standard ZIP) with cheap ~R20 damp sprayed cellulose cavity fill might have come in at about the same price point, but measurably higher performance.

The ~U0.25-ish windows seem like the most upgraded component over IRC 2015 code min.

So, it looks like a slightly-better-than-code-min house that's probably a bit tighter than most, hammered into lower energy use with super-expensive mechanical systems then clobbered over the head with an oversized PV system. Even if they end up with couple of plug in electric cars they'll probably still have a bit of PV capacity left over.

The whole claim about the foundation being insulated, if you look at the pictures they provided, is bollocks. They're standard, poured-in-place footers with no insulation around them.
So I think their contractor was cutting some corners...

As for the array being a "cheat", I'm inclined to agree.  Partially.  Stuffing overkill physical plant in is a cheat.

Not having it directly on the house?  No so much.  I've seen ground-rack mounted arrays on places.  I've also seen tracker-mounted arrays.  So I'm inclined to be lenient on use of available roof space.

The foundation walls are insulated, but not the slab. Local deep subsoil temps are in the mid-50sF, so yes, there is some performance hit from the thermal bridge to the footings, but that's small relative to the uninsulated slab.

If using other real estate other than the house for the PV it's arguable that ANY house with a big enough yard can be Net Zero Energy- just add more racks of PV. But that makes it a function of the available real estate, not the performance of the house. I'm sure my crummy 2x4 framed 1920s antique with clear glass windows has enough yard space to hit Net Zero with ground mounted PV.

A 4 ton ground source heat pump for a ~2000' rancher on a ~2000' conditioned walk-out basement is ridiculous. Even at raw code-min that house could be heated with 2.5-3 tons of mini-split in that central CT location. The spec sheet page ( https://www.ctzeroenergychallenge.com/participant_specs.php?ID=Moser ) claims that a code-min house that shape & size would use 42.6 MMBTU/year for space heating, in that ~6500 HDD (base 65F ) climate, which is a credible number. That's works out to (42.6 MMBTU/6500 HDD =) 6555 BTU- degree day, or (/24=) 273 BTU per degree-hour. Outside design temps are in the low single digits F, but for yuks let's assume a 70 heating degrees, for an implied load of 70 x 273= ~19,000 BTU/hr.

Now some of that is undoubtedly being covered by passive solar gains, and it doesn't reflect the peak infiltration potential, but the true 99% heat load on that place would be under 30,000BTU/hr, even as a code min house. Most IRC 2015 code min-houses with code-min windows would come in ~25,000 BTU/hr @ 0F in an aggressive Manual-J, maybe 30,000 BTU/hr if most of the walk-out basement wall area was above grade.

And their house is slightly higher performance, with a 99% design load in the low 20s, maybe even under 20,000 BTU/hr (maybe). That takes 4 tons of GSHP? Try 2 tons.

Their stated 13 MMBTU/year as-built heating energy use is simply NOT credible without factoring in the average COP of the GSHP system (which they probably are). If they're talking about input-energy only, their GSHP system is something of a dog, with an average COP about 3 (maybe less) when all pumping & control power is added in.

To be sure they're not much better than code-min. The biggest envelope upgrade above code min was again the U0.25 windows. The rest is rather "in the noise". Yes the R21 foundation walls beats the IRC's R15 code-min, but the net effect on the total energy use of that upgrade is pretty small. The R21 ICF walls on the above grade portion of the walk-out basement is also a step above code. My WAG would be that the building envelope is at best ~15% more efficient than an absolute code-min house of the same shape. Their 1.72ACH/50 air tightness is isn't anything to write home about- it's still over half the code-max limit, and 1 ACH/50 just isn't that tough in a house with that simple of a shape.

Yeah. I was actually more impressed with one of their fellow winners. The "Best HERS score before renewables"

A place where they actually opened up a window during the blower door test and STILL pulled a score under 3 ACH50.

Does the program have a Razzy Award prize for "The least well thought out design that actually made it"?? :-)

Seriously, you can take pretty much any 40-50 year old 2x4 framed raised-ranch that size, do a tiny bit of spot air sealing & insulation fixes, retrofit it with 4 tons of GSHP & 25kw of PV and magically hit Net Zero Energy, and skip the expense of building a new house.

The "Best HERS score before renewables" is indeed a FAR better house, with a 12" dense-packed double-studwall approach to the walls, and 0.45ACH/50 air leakage, the kind of house that's applause-worthy, even if they DID use more HFC blown foam than I'd personally like to see, between the 2" XPS under the slab, and the 2" closed cell foam under the roof deck & on the interior of the foundation, much of which could have been done with reclaimed rigid foam at lower or comparable cost.

https://www.ctzeroenergychallenge.com/participant_overview.php?ID=Alexander

I expect that everyone has a different definition of "better house".