Another passive house with crazy tight .1 ACH50

[Daox]

Its just a quick write up, but an interesting one I think. They have R42 walls, R100 attic. For air sealing, they used a layer of water and ice around the entire house. His ACH50 is .1! Crazy tight house. They use a 6 foot 240v baseboard heater for heat. The house is in Massachusetts.

Extreme Efficiency | Home Power Magazine

I decided to forgo purchasing a fossil-fuel-burning heating system. I estimated that I saved more than $20,000 by making this choice. Saving this money allowed me to spend more on insulation—and afford a solar-electric system. I chose dense-packed cellulose to insulate the walls (to R-42) and the roof to an average of R-100. There is just over 16,000 pounds of cellulose in the house.

...

I control the humidity and ensure adequate fresh air in this extremely tight house with a Venmar heat recovery ventilator, which creates nice cross-flow in the house. The home has a 0.1 ACH50—compared to Passive House’s 0.6 ACH50 requirement. ACH50 measures air changes per hour at 50 pascals of pressure—the lower the number, the more airtight a house is.

[Higgy]

They used Grace Ice and Water Shield around the entire house you mean. When I first read what you said I had to go and check it out because...a layer of ice and water around the entire house...what? Yeah, that stuff is a wrap normally used just for roofing, but they wrapped it around the entire house.

The inside looks nice, but IMO they could have made it look nicer on the outside. I mean, if you're trying to make your house look as dull as possible that's fine, but it just looks way too plain for my taste. I like some character in my house.

[AC_Hacker]

Originally Posted by Higgy

I mean, if you're trying to make your house look as dull as possible that's fine, but it just looks way too plain for my taste. I like some character in my house.

I used to live in Massachusetts, and this house actually adheres pretty closely to the old, original Cape Cod House configuration. The more modern Cape Cod houses have evolved many patterns of variation, but the old ones are very spare, very Puritan.

I'd say that the builder has, in a very apparent way, gone back to spirit of the early tradition and applied Puritan's core value of simplicity to modern thinking of highly efficient house design.

The article also stated that the builder was trying to achieve Net Zero at minimum cost, which would lead to lower-efficiency fenestration, and less window area.

If this same Cape Cod House design were to be implemented with German technology, with even lower U-values of the walls & roof & floor, and if Ultra-High performing windows & doors were included in the design, I am positive that a more liberal and architecturally-satisfying use of windows would have been the result, but the price would have been a good bit higher.

Best,

-AC

[pinballlooking]

I thought it was interesting that they had plans to change out the heating and AC already.
“, I am planning to install a ductless minisplit air-source heat pump, which will use even less electricity to do the same job.”

[Daox]

I was also surprised by the lack of windows. Probably mostly due to the cost.

[Higgy]

YES, thank you. I was trying to remember where I've seen houses like that before. Yeah I'm just not a fan. It's not even the lack of windows so much as just the plane jane siding and front door. I know it's all just for looks, but I like a house that appeals to the eye.

[AC_Hacker]

Originally Posted by Daox

I was also surprised by the lack of windows. Probably mostly due to the cost.

From the description of the builder's chain of decisions, I think that it is a very good bet that he is using the Passive House Planning Package.

With PHPP, you can instantly see the thermal consequences of your decisions.

If I'm not mistaken, there may be a version of PHPP that will also allow you to do cost estimations at the same time.

But there is no "prettiness" calculator built in.

Regarding the resistance heater, I think he went for that because it is cheap and reliable, but inefficient. At $80 cost, not a bad decision... too bad he doesn't report resistance heating cost info.

But a very small mini-split would be much more efficient, and would be within the output rate of his PVs by a larger margin.

I just did a hasty break-even analysis, based on the scarce information available. "X-axis" is years to break-even. "Y-axis" is annual electric cost (as if it came from a power company).

If his power requirement for heating is very, very low (as it should be), the time to break even would be discouragingly long. So, my guess is that his decision was not motivated by cost and pay-back considerations, but rather he opted for the mini-split so that he could enjoy additional electrical loads and still be within his Net Zero goal.

-AC

[ChetT]

I would think that the real motivation for the mini-split is to add cooling. Massachusetts has some ugly, hot and muggy summer days.

[AC_Hacker]

Originally Posted by ChetT

I would think that the real motivation for the mini-split is to add cooling. Massachusetts has some ugly, hot and muggy summer days.

Although refrigeration cooling and de-humidification go together, my bet is on de-humidification, with his amazing insulation, his place probably doesn't get so very warm.

If I remember correctly, he also has a Heat Recovery Ventilator, which also recovers coolness, and does it's own passive job to lower humidity.

-AC

[stevehull]

HRVs and ERVs do nothing to remove humidity in a location like a New England summer. The only way to get the humidity out is to use a low capacity heat pump (AC).

The problem with many highly insulated houses is that a typical AC unit is only made down to perhaps 2 tons.

Highly insulated homes cool down too fast with normal size AC and the unit will not run long enough to get rid of latent moisture.

The new variable speed scroll is now available in geothermal heat pumps (WaterFurnace and ClimateMaster) but are only in the 24,000 BTU and up size. But running at a 10% speed on the compressor would be a BIG help!

I grew up there and the summers with a dewpoint of 75-78F, even with an air temp of 80F are simply miserable.

Steve









Steve