Friday, October 17, 2014

Slabs vs. Crawlspaces

As mentioned previously, slabs get the nod as the greenest foundation strategy.

"The tipping point in favor of slab-on-grade over crawlspace is that the slab can be the finished floor. Stained concrete is still trendy, bulletproof, and saves at least $3/sq.ft. on your floor system.

My concrete floor is six years old, had zero maintenance*, and looks just like the day we moved in.

The thermal mass and the way it buffers the temperature is just a bonus."

This floor has an oil-based polyurethane finish, which should work for you if the slab is truly decoupled from the soil.

Tuesday, October 14, 2014

Grid Defection Will Make More Sense if Net Metering is Compromised

Going Off-Grid in the City
1. Net zero homes are usually all-electric, and already are off the natural gas grid.
2. Misguided utilities and PUCs may ruin net metering. This makes it desirable to go off grid if your climate is sunny enough.
3. Batteries can provide daily backup.
4. A propane generator is currently the most logical off-grid backup electric source for long sunless periods.
5. If your climate isn't sunny enough, or if propane prices increase too much, then you may want to get back ON the natural gas grid.  You'd do this to minimize your backup electricity costs during cloudy winter months by using an automatic natural gas powered generator.
A comment about home design:
An off-grid house needs a much steeper tilt angle for the PV panels, to produce more in the winter and not over-produce in summer. This has another benefit of shedding snow better.

Wednesday, October 1, 2014

Denver's "War on Cars" is Real and Cars Will Lose

Here's a good summary of the controversy from Streetsblog USA:

Denver Urbanists vs. Traffic Calming Conspiracy Theorists

With a fast-growing transit network, Denver is grappling with how to build walkable places around its new rail lines, and the Denver Business Journal is running a package of stories about the potential for transit-oriented development. Overall it looks like a solid introduction to the notion that Denver needs to reduce car dependence, but the series did take an unfortunate detour into “war-on-cars” fantasy-land today with a he-said/she-said piece titled ”Are transit-oriented developments a campaign against cars?”
Transit oriented development isn't a conspiracy against driving, it's an attempt to level the playing field for other modes. Photo: City of Denver
Guys, this is not a conspiracy against the middle class. Photo: City of Denver
Still, it’s helpful to get a reminder of what urbanists are up against in cities like Denver. In this case, the “debate” started with a Denver Post column by City Council President Mary Beth Susman published in June. In a fairly moderate plea for better transit options, Susman noted that in addition to providing incentives — “carrots” — to entice folks to try walking, biking or transit, the city is planning to use some disincentives — “sticks” — to discourage driving. The two “sticks” she mentioned were reducing parking requirements — we’re talking about loosening government regulations that compel  – and refraining from widening roads in some areas of the city.
In response, the conservative Colorado Peak Politics called Susman’s editorial an “astonishing” admission that the city’s policy was trying to “actually make driving inconvenient.” The outraged, anonymous blogger asserted that nobody with kids to drop off, or a “client-facing position,” or groceries to pick up will ride a bike in Denver, and that policies that try to make biking safer and more practical are a “dangerous” attack on the middle class.
But the real hidden gem of this whole episode comes from Kathleen Calongne of the sprawl-loving American Dream Coalition. While it’s regrettable that Business Journal reporter Caitlin Hendee treated Calongne as a credible source, she’s at least good for some laughs.
“Research reveals that traffic calming projects are often motivated by individuals in our federal and local governments willing to sacrifice safety in an effort to discourage travel by car,” Calongne claims. Exactly what is motivating national and local government leaders to mislead the public in their quest to make driving worse, she doesn’t say. She does, however, go on to argue that traffic calming and transit-oriented development are bad for people with disabilities and the elderly.
Calongne doesn’t specify what research backs up her claims, but her credentials appear to consist mainly ofthis ancient article hosted by the National Motorists Association, purporting to show evidence that traffic calming harms people. Even back in the early aughts, when that article appears to have been published, there was ample evidence that traffic calming saves lives: A 1997 study [PDF] published in the Institute of Transportation Engineers reviewed 85 studies of traffic calming cases in Europe, North America, and Australia and found a decrease in collisions ranging from 8 to 95 percent.

A Simpler, Foam Free "Perfect Wall"?

I’m still researching wall and roof/ceiling assemblies because I haven’t been totally happy with anything I’ve tried yet.

in some areas of the country, especially in the Northeast, insulation contractors have been dense-packing unvented rafter bays with cellulose for years.”

Then I discovered a project by David Posluszny in Shirley, MA, that used a simple, very easy to build double wall section.  From inside to outside:   Drywall, netting, 12” of cellulose, plywood sheathing, (Henry Blueskin), furring, wood siding.

Since intra-wall condensation was a concern, he did some moisture testing after an extreme cold spell: “With the help of Bill and Jim from National Fiber, we tested my wall assembly. We took moisture readings in North, South, West and East walls, checked the moisture gradients, lofts, and crawlspace. We are pleased to find all the moisture levels came back well within comfort zone. This wall assembly works.”

David actually used Grace Ice and Water Shield as the air and weather barrier, but as he mentions in the video, Blueskin would accomplish the same tasks, is cheaper, and is vapor open.

This is an extremely tight house.  It’s possible that this wall section could develop moisture problems in leakier house.  However, David and the insulation suppliers emphasize that dense packed cellulose mitigates moisture problems in two ways:  It retards air movement and redistributes moisture because it is hygroscopic. So this could be a very robust assembly that can tolerate sloppier air sealing than what David has done.   (0.1 ACH 50 might be some sort of record)?  

This assembly also solves the tricky problem of how to air seal at the eaves where trusses meet walls.   The trusses don’t include the eaves, which are built after air sealing.  By laying 2x4s flat on top of the first layer of roof sheathing and covering  them with another layer of plywood, he ensures that shingle nails will never penetrate the air barrier and the cold roof has generous venting:

Some more features of this wall:

1.  Since all the air sealing is done at the exterior weather barrier, no air sealing is required for the electrical work.
2.  The air and weather sealing is done in one layer, which simplifies everything and reduces cost.
3.  The self adhesive air barrier has no penetrations due to staples.

The Problem

The theories behind vapor diffusion in walls would show that this is a risky assembly.  In practice, however, the wall seems to work.  Apparently cellulose can pull moisture from the inside of the exterior sheathing and release it back into the house as fast as the condensation occurs.

The next step would be to prove this in the lab and in the field.  This would be worthwhile because I don’t think there is an easier or cheaper way to build an R42 wall.

In the meantime, the IECC codes do NOT allow this assembly, and require foam on the outside of walls:

Friday, September 12, 2014

Dual Hose Portable Heat Pumps Don't Work Well in Practice

For years I've wondered if a dual-hose portable heat pump/air conditioner would work as a poor man's ductless minisplit heat pump. The advantage, as my logic went, was that I didn't have to drill any holes or charge any refrigerant.
I bought a 14kbtu portable heat pump (Edgestar AP14001HS Portable Air Conditioner)
I did some primitive temperature and airflow measurements.
I was impressed by the overall quality and the 11.2 EER, but what I found was very disturbing.
There is so much internal leakage, that the heat pump blows almost twice as much air out of the house that it pulls in. That difference in air volume gets sucked from outside into the house. The net effect of that is to reduce the COP in heating mode from the advertised 3.3 to roughly 1.4.
For heating, that makes it hardly worth the extra money over a resistance heater. I might as well have purchased an electric resistance heater with a COP of 1.0. In the air conditioning mode, this problem makes the unit worthless except for spot cooling. A window unit would work three times better at a lower first cost.
Has anyone seen a dual hose unit that actually works well?

Monday, September 8, 2014

Pretty Good Duplex HERS Scores

We just finished and sold both units of a spec duplex in SW Denver.  The HERS scores were "pretty good" at 59 and 62.

One of the more important components of the HERS score is the infiltration measurement.  Building Joe Lstiburek identifies 3.0 ACH50 as a pretty good goal.  We scored a 3ACH50 without trying very hard.  The main reason for the good score was the "flash and fill" insulation strategy.  About 3 inches of polyurethane spray foam was sprayed on the inside of the sheathing, and the rest of the cavity was filled with cellulose.

Did the HERS score even come up during the sales or marketing process? Not at all.   Was it good experience for our building professionals in anticipation of the IECC 2012 requirement of 3.0 ACH50?  Absolutely.

Heat Pump Dryer Update

Apparently production of the LG heat pump dryer for the US has been stalled.  A call to customer service yielded no knowledge of it.

But now there is a report that Whirlpool will have one available Q4: