Major geekage

A short note on wiring and instrumentation...

Submitted by Ted on October 4, 2012

Peter has been asking us about doing the final installation of the monitoring system for our house, so that he can get some data out of it (finally!). In order to make that happen, we needed to finish the electrical work, and that's been a bit of an obstacle because of various lighting needs and also because our electrical subcontractor, Andy Harkness, has been in high demand recently. But we managed to lure him and one of his electricians, Karl, up to the house over the past two days to finish up the electrical work.

Imagine my excitement when Andy called me down to say "Ted, can we combine any of these circuits? The panel's full!" It turns out that we are able to keep all the circuits separate, at the cost of having _zero_ free space in the panel. If we need to add even one more circuit, we'll have to add a secondary panel.

Why so many circuits? Peter wants to be able to measure the power consumption patterns of individual devices and rooms. Along with the per-room temperature sensing and an outside weather station, this will give him (and us!) a really good idea of how the house is actually performing.

The snarl of wires coming out of the wall here are the wires to individual temperature sensors in each room, all of which terminate in the utility closet. There's also network wiring, of course—that's the other, smaller snarl of wires.

This is the control/status monitoring panel for the solar hot water. We may collect some data off of this as well.

This is a flow meter that will detect the flow rate of the hot water. We also want a flow meter for the glycol, but had some trouble sourcing one that would be reliable—Peter originally sent us a flow meter that's mostly made of plastic, and Gary, our solar subcontractor, took one look at it and refused to install it. When I called Peter about it, he told me that there had actually been some problems with the device in the field (nothing serious—one leaked a tiny bit, and another failed after a year). So we aren't installing this particular device—Peter's researching other options.

Oh, the reason for the weird bend in the pipe that comes into and out of the hot water flow meter is that we need a certain length of pipe after a bend or a valve before the flow meter, or the turbulence caused by the water flowing around the bend or through the valve will affect the measurements.

This is the flow meter for the well. We're not actually measuring this—it's just used by the sewer department for billing. But it's a meter, so I included it... :)

A gratuitous picture of fall foliage..

The spiral stairs, from above...

Stepping back (temporarily) from LEDs

Submitted by Andrea on May 8, 2012

Ted and I were all set to install LED strip lights, as described in my recent post about choosing LED lights. But then we spoke with my father's friend John—a major techie at a major technical manufacturing company—and he suggested we wait a bit longer.

He said that for the next two years or so, the best LED products will be Edison-style replacement bulbs that use remote-phosphor technology. LEDs do not produce a wide spectrum of light on their own, but when LED light strikes a phosphor, the phosphor emits a wider range of colors. You can see this in the Philips LED replacement lamps: the unlit bulbs look yellow, but the light that comes off them is a nice warm white.

Those kind of replacement lamps are the best short-term approach, but the longer-term approach will be multi-string ("but not RGB"). He said, "They will be phosphor-shifted blue LEDs picking up green-yellow (called BSY), with some combination of red/orange/amber LEDs at the longer wavelengths."

He added, "CRI is only a start at analyzing the problem. It's very outmoded, made a lot more sense in 1950 than today. Doesn't measure reds well (which are very important to human perception), and the spectral absorption are too broad-band." This confirmed our experience of CRI — the lights we were going to buy had a good CRI (85) but was noticeably weak in the red part of the spectrum. Ted looked OK under our test lights, since he has fairly rosy cheeks to begin with, but they made me look a bit more wan than usual.

Our informant likes two lighting models right now:

  • CREE LR6 (BSY/orange two string) — "This dims well, but the color changes a lot"
  • Philips remote phosphor A19 bulbs (the ones that look yellow when off), remote phosphor with Europium-doped YAG (gets good red rendition)

One thing he likes about these models is that neither has 120Hz ripple, admitting that not everyone is sensitive to this, but that it drives him nuts. He also notes that efficacy is approaching 100 lumens per watt, "which is a good benchmark for a warm white bulb."

He suggested we wait at least a year before installing LED strip lights for the following reasons (direct quotes):

  • The models that you're looking at don't actually use DC, but rectified high frequency AC that tracks the input line (120Hz modulated 25kHz). This means a lot of flicker.
  • They are also are "local phosphor single string", which means bad color.
  • The efficacy with transformer is probably about 50 lumens/W, not awful, but not good either.

Our new plan is therefore to postpone installing the strip lighting, but to leave all the rough wiring in place. We'll make do with floor and table lamps for a year or so and then install strip lights once they've improved the color rendering and efficacy.

I told him that most of the light fixtures we're buying take regular A19 lamps (Edison standard), but a few will take B10 lamps (Edison candelabra bulbs). He warned that it's harder to make good replacement lamps for smaller bulbs because there's not enough mechanical volume to make a good LED ballast. I asked whether CFLs at that size are any good, and he said, "Most of the fluorescent at that size are CCFLs, which have good life, but won't dim well, and have lower efficacy than larger CFLs. There's a effect called cathode drop which fundamentally decreases the efficacy of these small lamps."

He concluded, "Maybe this gives you something to think about. A lot is going to change in the next few years."

So you want to use LED lights...

Submitted by Andrea on March 23, 2012
Addendum: We got more advice and decided to wait on installing LED strip lights. Read more in "Stepping back temporarily from LEDs" (May 9, 2012).

I could not have designed and built this house without our good friend Google. I created all of the 3-D drawings in the free version of SketchUp, and I researched literally every component of this house using Google's indispensable search engine.

Unfortunately Google is nearly useless for researching items that are aggressively marketed online, particularly LED lights. The problem is that discount LED vendors use every trick in the book to rank among the top Google search results, so it's nearly impossible to find helpful online advice about how to buy LED strip lights.

Until recently I had only a dim (ha!) idea of what components we'd need for LED strip lighting. But now that we've figured it all out and completed our lighting schedule, I'd like to share what I've learned about illuminating a room primarily with LEDs.

Not all LED lights are created equal

I do not usually use all-caps (the Internet equivalent of screaming), but this is hugely important. It is tempting to order LEDs online from discount vendors, and you might know people who like the lights they purchased that way. Ted and I have some friends in Austin who purchased a lot of accent lighting from Eco Light LED, and the lights look really cool. Installed inside bookcases and behind valances, they have RGB controllers and can be adjusted to display a huge range of fun colors. Ted and I assumed we'd light our house with something similar, only on a larger scale.

We subsequently learned, however, that you can only get away with cheap LEDs if you aren't using them as a primary lighting source. When you look at a person, you're seeing the light that's bouncing off of them; the surface of their clothing, skin, etc., absorbs certain parts of the spectrum and reflects the rest back out. So if your light source is missing crucial colors, that person will look downright creepy.

Any decent LED manufacturer will publish the product's Color Rendering Index (CRI). This is an adequate (though incomplete) measure of the light's color fidelity. CRI is measured on a scale from 1-100, with ordinary incandescent lights at 100 and everything else somewhere below that. For your primary indoor lighting source, you shouldn't go below a CRI of 80.

Color temperature is also important, and it is easily misunderstood. "Warm" light actually has a lower temperature — incandescent bulbs are 2,700K and those blue-white LED xmas lights are around 6,000K (compact fluorescent bulbs usually range from 2,700 to 3,500K). All of our LED lights will have a color temperature around 3,000K and a CRI in the mid-80s.

Once you know a little about CRI and color temperature, the discount LED vendors no longer look so good. Eco Light sells Warm White LED Strip Lights for about one-quarter the price of the strip lights we're buying, but a closer look at their downloadable spec sheet reveals that the color temp is a not-so-warm 3,500K, and they don't mention CRI at all. I found CRI info on a few other discount sites, but the numbers were unacceptably low (70-75).

Most of our LED strips will be installed behind a valance, with the light shining upwards across the ceiling (the sole exception is the under-cabinet lights in the kitchen). The LEDs we selected have a good overall CRI (85) but are a little weak in the red part of the spectrum, which means we need to choose ceiling paint with a hint of red pigment so it won't absorb all the red coming from the LEDs. Our lighting consultant told us a cautionary tale about how indirect non-incandescent light bouncing off cream-colored walls can turn everything yellow, and we don't want that to happen to us. In fact, we had planned on using pigmented plaster for our walls, rather than the usual paint over drywall, but the lack of fine-grained color control pushed us back to the standard approach.

LED strip lighting basics

The first thing to know about LED strip lights is that they run at a much lower voltage than most other electric devices in your house. In North America, we use 120 volts AC (alternating current), and most LED strip lights run at either 12 or 24 volts DC (direct current). You will therefore need a transformer to convert from line voltage (120V) to the voltage of your LED system.

In case you're rusty on how electricity works, I should point out that the voltage has nothing to do with how much energy the lights draw. Voltage is analogous to water pressure (not the total amount of energy used), so the important number is how many watts a fixture requires.

Each circuit of strip lighting will require its own transformer (by "circuit" I mean a strip that's controlled by its own switch), and the total wattage of the strip lights cannot exceed the maximum output of the transformer. Our strip lighting draws 3W per foot and our longest stretch on a single circuit is 14'-4" (the upstairs hallway), which means our heaviest circuit will only draw 43W. The smaller WAC Lighting transformer is rated up to 60W, so we'll be well within the limit.

In case you're curious, here's what you'd need to run 14'-4" of strip lighting:

  • Two 2-inch LED strip lights
  • Four 1-foot LED strip lights
  • Two 5-foot LED strip lights
  • One 12-foot lead wire (connects the light strips to the remote transformer)
  • One end cap
  • One remote transformer (driver). Converts from 120V (line voltage) to the 24V required by the lights.
  • One dimmer switch for an electronic low-voltage fixture

Each segment of strip lights connects to the next, and the end cap terminates the string.

Incidentally, the reason we're fiddling with the 2-inch segments instead of just trimming a 1-foot segment (the lights are trimmable every three inches) is that it's marginally less expensive. This will give us the exact length we need.

Why bother with LEDs?

I confess that writing this post has made me wonder why we're installing LED strips when CFLs use roughly the same amount of power. People criticize fluorescent bulbs (compact and otherwise) for containing mercury, but it's just a tiny amount and can be recovered if the bulb is properly recycled. LEDs don't contain mercury, but various toxic chemicals are used during production, and their heat sinks are made from valuable metals like aluminum.

So why are we using LEDs? I suppose it's partly the eco-bling factor. But we're installing plenty of conventional fixtures too, and in the short run we'll probably fit most of them with CFLs. LED replacement bulbs tend to shine in a single direction; this makes them a good choice for recessed downlights, but not so good for wall sconces and multidirectional fixtures.

We considered using a series of T5 fluorescent tubes for all the indirect lighting, but then we'd run into "socket gap" — dark spots where two bulbs meet. We would also have to build a larger valance to hide the bulbs, and there are a few places where we need to keep the valance quite small.

We therefore succumbed to the blingy lure of LEDs, and I sincerely hope they'll earn their keep during their projected 50,000-hour lifespan. That's 17 years, assuming we run them eight hours a day, which I doubt we'll do. Again, this is why it's important to choose the manufacturer carefully, since we're likely to be stuck with these things for a long long time.

I keep thinking I can cover lighting in a single post, but each time I try I wind up having too much to say. In a future post I'll share diagrams and photos of our indirect lighting setups. I'd also like to talk a little about switches (whee!), and now that my eyes have been opened to the subtle art of lighting design you can expect a rant or two about bad lighting.

Added on May 9, 2012: We changed our minds. See "Stepping back temporarily from LEDs" for the details.

To PHPP and beyond

Submitted by Andrea on July 17, 2011

Our building site was relatively quiet last week. Concrete is curing, and our electrician set up the main panel and meter in anticipation of CVPS turning on the electricity this week. Ted and I also spoke with several solar installers to see about getting some PV panels at the roof ridge and also a solar hot water system. More on that as it unfolds.

The biggest news is that we recently partnered with Efficiency Vermont to pursue Passivhaus certification [follow the link to read their "About Us" page]. The cool part is that our house will be part of a research project to evaluate the suitability of Passivhaus construction for Vermont. They'll install monitoring equipment in our house and closely study its performance.

Peter Schneider, Efficiency Vermont's Passivhaus consultant, was particularly interested in studying our house because it has several unusual features: a pier foundation and partial shading. Vermont's abundance of sloping, ledgy lots makes pier foundation a tempting solution, and of course trees are rampant hereabouts. So hopefully we'll provide useful data for would-be Passivhausers in North America.

Peter was on vacation last week, so he hasn't gotten farther than the first few rounds of PHPP tweaking, but Marc helped pick up the slack. This will all probably change this week, and I'm probably jinxing things just by typing this, but so far it looks like we can pull off Passivhaus performance with the following general specs:

  • 11-7/8″ I-joist floor deck (16 oc), stuffed with dense-pack cellulose and with 4″ of polyiso underneath.
  • 9.5″ I-joist wall framing (24 oc) filled with dense-pack cellulose and with 4″ of exterior polyiso.
  • 24" roof joists, filled with dense-pack cellulose.
  • Schuco SI-82+ windows, which we ordered this week from European Architectural Supply in Lincoln, MA. The windows are PH-certified and made from uPVC. Yes yes, PVC is evil, but this is unplasticized PVC which is apparently a bit less evil. It's made without phthalates and can be recycled, at least in Europe. But hopefully the windows won't need recycling for a long long time.
  • Climatop Max and Climatop Ultra-N glass. The glass offered by Schuco is pretty darn impressive. For the south windows we upgraded to Climatop Max, which has a SHGC of 0.6, but for the rest of the house we went with the Climatop Ultra-N, which has an SHGC of 0.5. All the glass has a Ug of 0.105 (which PHPP callously rounds up to 0.11).
  • We haven't decided for sure on the HRV yet, but we'll probably either do the Zehnder ComfoAir 350 or the Paul by Zehnder Novus 300. The latter adds about $1,400 to the already formidable cost, but the efficiency is 93% as opposed to the ComfoAir's 84%, which would win us quite a bit within PHPP. Another knob to turn would be to add more polyiso under the floor or use larger I-joists — we'll hopefully do the cost-benefit analysis this week and reach a verdict.

It seems like the biggest advantage in our design is the ludicrously simple house shape. We're basically building a shoebox with a shed roof, which means there aren't many corners or thermal bridges undermining our envelope. Marc, Ben, and Eli already minimized thermal bridging before we decided to go for Passivhaus certification, so we're picking up a lot of PHPP points without having to change our plans.

We're waiting on a few more details, though, including some THERM data Peter is confirming with PHIUS. Hopefully that won't kick us back out of the ballpark, but as I said we still have some knobs left to turn.

Coordinating the roof

Submitted by Ted on June 8, 2011

I was on the phone with Marc the other day and he pointed out something that hadn't really occurred to me until he mentioned it: when we hired Ben and Eli, we took on a new job. One of the key things that you will hear from anybody who has any experience building a passive house is that your team has to be on the same page about what you're trying to do, or important things will fall through the cracks, and compromises will be made that make a lot of sense from the viewpoint of one participant in the project, but create a huge problem from the perspective of another participant.

We've made a ton of changes to our house since we first started brainstorming about it with Marc a year and a half ago. A lot of them hit quite recently, when Ben talked us out of our Shogun foundation, and when Eli talked us into flipping the roof. We had to give up some things we'd been looking forward to, but we tried to keep a razor focus on the air barrier and insulation, because together those give us what we really want in this house: a consistently comfortable indoor environment.

But one point that Eli really pushed us hard on was the roof. In order to understand what the controversy was, I need to explain the original roof design that Marc came up with. On the way, let me point out that because Andrea and I are so interested in the details of this process, we never have a conversation with our honored teachers in which we just listen to what they tell us and do it. Consequently, nearly every aspect of the house has our fingerprints on it in some way, and we don't always remember which things we decided to do were "nice to have" and which were crucial. The roof design wound up being one of those things.

The problem with an almost-passive-house roof is that it has to perform consistently in two senses: first, the insulation has to be consistent. We can't have it settling down from the top, bunching up on the bottom. Way back when, when we got our first estimate from Keith at Thermal House on insulating the roof, we were absolutely floored: it was going to cost about twenty thousand dollars. Why so expensive? Because we'd chosen to do a cathedral ceiling, not a sensible flat ceiling.

Flat ceilings are easy to insulate--you can just dump the insulation on top of the ceiling joists and spread it out, or if you want to get fancy, use dense-pack cellulose. Because the ceiling is flat, there is nowhere for the insulation to go. You wind up with an irregularly-sized air gap above the ceiling, since your roof certainly isn't flat, but in most situations it should be pretty easy to get a nice thick blanket up there.

With a cathedral ceiling, you don't have the luxury of flat. Keith solved that problem by using a really expensive foam product that he was confident wasn't going to move. But we can't afford to spend $20k insulating our roof. So Keith and Marc and Andrea and I did quite a bit of negotiating. At the time, we'd been planning to use open-web trusses to support the roof. We were confident we could get trusses that would span the distance from the north to the south wall, and would support the dramatic 7' overhang we wanted on the north. But insulating open-web trusses is really hard, as Andrea explained in her recent post.

What we came up with was that instead of using trusses, we'd use I-joists. Andrea did some research on the Internet, and found a supplier for a 24" deep I-joist that would span the distance we wanted, and additionally would support the cantilevered overhang. Marc and Keith both liked these better, because Keith was confident that he could do a dense-pack cellulose installation without any voids using the I-joists. Marc liked the I-joists because they cause very little thermal bridging: the webbing between the flanges on the I-joist is only 7/16" thick, so even though its R-value is substantially less than that of the roof, there isn't enough of it to create a problem.

At this point I need to talk about roof venting. There are two kinds of roofs: warm and cold. A warm roof is a roof with no air vent. They are popular in applications like ours, because building roof vents is fussy when you can't just vent the eaves into the attic. Typically a warm roof consists of a ceiling, rafters of some sort with insulation packed between, a layer of waterproof sheathing, a layer of insulating board (typically polyisocyanurate), a waterproof layer, and then the roofing material. So it's not a particularly simple roof.

So we got this brainstorm to do a vented roof, even though we're doing a cathedral ceiling. Marc had a clever design. He proposed that we cut a piece of insulation board to the spacing between the webbing of each I-joist. We could then cram this up against the top flanges of two I-joists. This would create an air space between the insulation board and the sheathing that's nailed to the top of the I-joist. Now we have a clear vent running the entire rise of the roof. It's pretty easy to construct, and it'll keep the roof cold.

So that's the roof design we'd been planning on for nearly a year. But then Eli comes along, and he has a number of problems with it. And they are real, serious problems. First, the top flange of the I-joist is going to be really cold on a cold winter's night. The bottom flange is going to be really warm. So the bottom flange is going to expand, and the top flange is going to contract. The roof is supported on both ends, so it might bow in the middle, or the I-joists might warp a bit, but the bottom line is that there's going to be some unwanted movement. Eli felt that this was potentially a big deal; Marc wasn't sure it was, but he didn't claim it definitely wasn't, either. I have no informed opinion on the matter—I have to trust Eli and Marc.

The bottom line is that this got Eli to thinking about some other advantages of trusses over I-joists. One of the big problems we'd left somewhat unsolved with the I-joists was how to construct the overhangs. Remember that there are four overhangs. We'd been planning to stick the I-joists out over the north and south overhangs, and didn't really have a solution for the east and west overhangs. Eli didn't like the idea of sticking the I-joists out like that, because it was going to potentially expose the webbing in the I-joists to moisture on the ends, and possibly wick moisture into the roof. He wasn't entirely clear on how big a problem this was, but it was definitely a concern.

Also, whereas the I-joists are only strong if the webbing and the flanges are preserved, trusses can be engineered so that what sticks out past the envelope is thinner, and yet still provides enough support. We'd been trying to figure out how to avoid having the overhangs be two feet thick, and were talking about cutting off the bottom flange and attaching something to the webbing higher up. Eli didn't like that idea from an engineering perspective.

A final advantage of trusses is that they are open, which means you can stick things into them. This gave us a way to do the rake overhangs—the overhangs on the east and west sides of the house. With the I-joists, we had no answer for the rake overhang other than nailing a box to the side of the roof. This could probably have been made to work, but making it structurally sound would have been quite involved.

I heard about Eli's counter-proposal on roof structure while we were up at the site seeing what had been done, I think on Monday. We'd been talking about using trusses for a while, but on Monday we came to the conclusion that we really couldn't use the I-joist roof as originally designed, and we were starting to go down the path of figuring out how to insulate the trusses. We also started thinking about going back to a warm roof, because the cold roof was starting to look like it would be pretty difficult to build with trusses.

I should mention that in the background we'd been hearing about another scheme that Ben, the structural engineer, was thinking about, that involved a two-layer roof. I didn't really like the sound of that, because it sounded like a lot more work, so I hadn't made the effort at this point to find out precisely what he was talking about. I had visions of having to insulate two sets of cavities. Not a happy thought.

On Tuesday, Marc called Andrea to weigh in on the rash of changes we were suddenly making. I was sitting in my chair minding my own business, working on something or other, and suddenly Andrea thrust the phone at me and said, "You talk to Marc." So I wound up explaining the whole truss thing to Marc, and Marc of course was asking his usual intelligent questions and making comments, and I was starting to feel pretty sheepish about where we'd gotten with Eli.

I mentioned some harebrained schemes for mitigating the problems with trusses, and Marc was pretty patient with me, but he reminded me of what we'd been trying to accomplish with the trusses, and the complexity of getting a good air barrier with trusses, and so forth, and by the end of the conversation I was back to believing that I-joists were the right thing, and that we just had to figure out how to make them work. Marc also explained why warm roofs have insulation on top. In a warm roof, you have warm, moist air below, a piece of wood, and then a moisture/vapor barrier. This means moisture can condense on the wood, and has nowhere to go. Venting the roof provides a place for the moisture to go. Without it, the wood could rot.

Andrea reported the outcome of this conversation to Eli via email. A while later Eli called me and set up a Skype session so that he could draw stuff in his CAD package while I watched. What he drew was a roof that used I-joists for structure, but then had a venting system on top of it. The venting system is essentially a second roof, with ribbing that mostly runs parallel to the I-joists.

The eaves are cantilevered on the ribbing, but the ribbing is also used to form ventilation channels. The corner overhangs are done by installing a rib at each corner at a 45-degree angle to the I-joists. The rake overhangs are done by installing ribs at 90 degrees to the I-joists. Throughout the rake and corner overhangs, ribbing is also installed parallel to the I-joists to form vent channels, and vent holes are drilled in all the ribbing that is not parallel to the I-joists, so that even the corner and rake overhangs are still vented.

Of course, this roof has a problem as well. Because it's so nicely vented, if you get a wind across the roof, it can form a relative vacuum at one of the vents. This vacuum can then suck rain or snow into the vented part of the roof, which falls into that roof. If the roof isn't waterproof, the wood gets wet. So Eli is proposing to put down some kind of waterproofing.

One thing that just occurred to me while I was typing this, though, is that now we essentially have a warm roof with wind channels above it, because the bottom layer of sheathing has a moisture barrier on it. So I need to try to understand whether that aspect of this roof really makes sense. But at least from the perspective of supporting the eaves, this roof is the best design we've seen so far, and I'm feeling pretty good about being able to iron out the details.

But now perhaps you can see what an interesting job the prospective owner-builder faces when trying to get a passive house built with the help of a lot of really talented and experienced people. I feel very lucky, but Marc is right in saying that this is a significant job.