So How is the House Working?

The goal of building a passive house was to decrease my carbon footprint, and it's time to look at the data. Historically, January is one of the coldest and therefore most energy demanding months of the year. Historically, the average temperature is 41F and the house has been held at 68F day and night. I experimented with decreasing the temperature at night, but the thermal inertia of the house is large, and the heating power is small. That combination is not well suited to dropping the temperature at night. An 2.5 kW electrical heater in the duct leaving the energy recovery ventilator was installed to provide heat. However, to get that much heat out, the ERV has to be run at fully capacity, namely 200 cfm, which is 3 times what is needed to provide healthy indoor air. At that volume, the ERV would need ~ 270 W for the blower - a waste of energy. For that reason, I've been heating the ~1500 sq ft  house with a 1500 W electrical radiator.



It provides enough power as long as the outside temperature is above ~32F. When it gets colder at night, which it did a number of times in January,  I used a second electric radiator operated at 600W to give me a boost. Because the radiator is on intermittently, I need a power meter to tell me how much electricity is being used on average. I like the Belkin Conserve, pictured above. The thermostat on the radiator isn't very good, so I used a Lux plug-in thermostat to regulate the temperature.

For the month of January, I needed 590 kW hr for heating, which translates into a average continuous power of 820 W and a cost of ~$59/month. Given that $300 monthly heating bills are not uncommon in Port Townsend, this is a good result! At this rate, my heating cost for the entire year should be less than $400. [A Seattle friend emailed me on reading this part that his bill for natural gas heating a poorly insulated older house is only $600 because natural gas in Seattle is much cheaper than electricity in Port Townsend.  He uses five times as much energy in a cold month and pays only 50% more than I do. The important number to note in evaluating the performance of the house is the kW hr for heating, not the $ cost. It may be that the only way to encourage energy conservation is to increase energy prices through taxes that are used to bring renewable energy to market.  There is a reason why hybrid cars weren't developed a decade or two earlier. Staring climate change in the face, we have begun to pay a high price for our access to cheap energy.]

So is the ERV performing? It has 2 functions: to bring fresh air into an otherwise airtight house and to extract heat from the outgoing air. I measured the efficiency of my ERV, which is defined as (Texit-Tcold)/(Tin - Tcold). Tcold is the temperature of the air entering the house from outside. Tin is the temperature of the inside air that is flowing into the ERV to have its heat extracted, and Texit is the temperature of the incoming cold air after extracted heat has been added. On a cold day, I got 0.985, and on a warmer day, 0.927. For the higher efficiency, 98.5% of the heat in the exhaust air was extracted, and the corresponding number for the warmer day was 92.7%. These numbers are higher than I expected, which I attribute to latent heat transfer. I think that the exhausted air is cooled sufficiently to condense some water and that the enthalpy of vaporization that is liberated is transferred to the incoming air.

Another function of the ERV is to get rid of moisture. Only the dryer is vented directly to the outside; there are no kitchen and bath exhaust fans. Instead, air from these rooms is sucked out by the ERV and moisture is vented to the outside in parallel with heat extraction. Although the bathrooms and kitchen have a booster switch  to bump up the ERV to its full capacity of 200 cfm to remove water vapor, we have never used this capability. Just the normal air circulation is sufficient to dry out the shower, remove water from boiling in the kitchen, etc. The Ultimate Air Recouperator is great!

My total electrical energy use for January is 1062 kW hr.The only other energy source is ~ 5 gallons/month of propane for cooking and baking. I used 472 kW hr in January for hot water, lighting, refrigeration, computers, other plug loads and my panini press. I'll track down these uses in the next blog.

Siding, Paint, and Solar Panels

 

My initial plan was to put cedar shingles on the whole house. That plan ran into several snags: 1) Shingles are made from old growth cedar and plastering old growth wood over my house didn't seem like the right thing to do. 2) I wanted to see the wood grain through the finish which means that I woud have to use a transparent or semi-transparent finish. The people at Miller Shingles in Granite Falls told me that going that route, I'd have to refinish the south side every 3 years and would eventually need to put on a solid stain to hide the blemishes. That sounds like too much work. So I went with Hardie boards and planks. They are made from cement and fibers, take paint well and last forever. Glo and I played with color samples and patterns for a while with Jesse's help and finally decided to break up the wall area by using a board and batten pattern on the ground floor level coupled with 7" sidings above. We also decided to use a single color for both areas with a separate lighter trim color. Here are the results on the south and west sides.

The south view also shows the 3.1 kW photovoltaic array on the dormer. I hadn't planned to do this, but the incentives from the electrical utility and the IRS are quite attractive: there is a tax credit for 30% of the purchase price (which was $30k) and I get $0.54 for every kilowatt hour produced because the panels and inverter are manufactured in state - even if I use the electricity generated rather than dumping it in the grid. With those incentives, I should be able to pay off the purchase cost in 10 years. The control panel on thenorth side of the house is pretty ugly, but we'll cover it up with artwork further down the line.

For my sister Carolina, pictures of the kitchen granite counter.

What a relief to have the outside (almost) done just in time for the rainy season. I still have to put cedar shingles on the north side porch. I've stained them all and will get started on this project next week. In the meantime, there have been lovely meals outside, enjoying the view to the south.

First pictures of the interior

Two postings in one day! Gotta catch up. I moved into the house on May 1, which was 8.5 months after excavation started. The last phase went slowly because Charles was no longer working on the house, (because I needed to save money) and I divided my time between building and writing on the new edition of my physical chemistry textbook.

The ground floor has the kitchen - dining - living room on the south side, going from east to west. A workroom/studio, a bathroom, and the media room/guest bedroom are on the north side. If needed, there could be 2 bedrooms on the ground floor. The pictures below show the kitchen-dining-living areas. No handles on the cabinets, and no art on the walls yet. More pictures of the other rooms in a later posting.

 

Here is the stairs going up to the second floor

The bedroom, two office areas, the laundry area, and a second bathroom are on the second floor. The picture below is of the bedroom and the door goes out to a small west facing balcony. Pictures of the other spaces in a later posting.

The energy recovery ventilator

 I've been really busy working on the house, so no postings in a long while, but now I'm back!

A passive house is practically airtight, so a whole house ventilation system is needed to assure the indoor air quality. Quoting Wikipedia, "indoor air quality can be affected by microbial  contaminants (mold, bacteria), gases (including carbon monoxide, radon, volatile organic compounds from rugs, furniture, paint, etc. ), particulates,  or any mass or energy stressor that can induce adverse health conditions. Indoor air is becoming an increasingly more concerning health hazard than outdoor air. Using ventilation  to dilute contaminants, filtration, and source control are the primary methods for improving indoor air quality in most buildings." Generally the outdoor air is healthier than the air in your house. For residential use, 60% of the air in the house should be exchanged with fresh air every hour. However, if the exhaust air is at 68 F and the incoming air is at 40 F as is typical for the winter in Port Townsend, ventilation results in an appreciable energy loss. The remedy is to use an energy recovery ventilator.

 

The heart of an ERV is an enthalpy wheel shown above. It is a wheel of about 20" diameter and is divided into pie segments. Each segment is both an air filter and a heat storage medium. In the picture, the warm exhaust air goes through a pie segment and transfers heat to it so that its temperature increases. The wheel turns, and the warm segment is now in the path of the cold incoming air. In passing through the segment, the air is warmed up and the pie segment is cooled. Pretty simple heat exchanger: the air exiting the house gets cooled before it leaves, and the incoming air gets warmed before it is distributed in the house.

I used a Recouperator made by Ultimate Air, which claims an efficiency of 90% - that is, 90% of the energy in the exhaust air gets transferred to the incoming air.  The picture below shows the unit (second picture).

The aluminum foil covered box to the right bottom brings in the incoming air. It is well insulated to keep from cooling down the mechanical space. The vertical black pipe on the right goes to the exhaust vent on the outside of the house. The black flexible ducts on the left of the unit bring exhaust air into the unit and send air out into the house. 8" ducts necking down to 6" ducts pull air out of the kitchen, 2 bathrooms, and the laundry area. Corresponding ducts send air into bedrooms and the living room.

The top picture shows the "furnace" and is the only heating unit in the house. It is a galvanized box roughly 20" x 10" x 10" which contains a 2.5 kW heating element. The tan box in front f it contains control electronics. By comparison, a typical oil filled radiator is rated at 1.5 kW.  The good news is that this is a pretty small furnace. The bad news is that this is a pretty small furnace. It takes about an hour of operation to heat the house one degree Fahrenheit. That is OK if the heating is under thermostatic control, and my thermostat can be controlled remotely over the internet. So, on the way back from vacation, I can bump up the heating the day before I get home. In the normal ventilation mode, the ventilator blows ~ 60 cubic feet per minute (cfm) of air through the house. In the heating mode, the blowers are bumped up to 200 cfm. In the ventilation mode, you can hardly hear the unit. In the heating mode, it is audible, but not loud.

Making the house airtight

To be certified as a passive house, the leakage rate at a pressure difference between the inside and outside of the house of 50 Pascals has to be less that 0.6 of the house volume per hour. That turns out to be 160 cubic feet per minute (CFM) for this house. How much of a pressure difference is 50 Pascals? It's equivalent to sucking on a straw and pulling up your drink by 0.2 inches. Getting the house leak-tight took a lot of time. All the sips seams were taped on the outside and inside using Grace Vycor, a butyl rubber tape. We later switched to Fortiflash, which stuck better on OSB. However, we got good adhesion only after going over the taped areas with a heat gun. Very time consuming. The top two pictures show areas that have been taped.

The biggest problems was making the house tight around the windows. The gap between the window frame and the opening in the sips panel was too small to be able to inject foam. Based on our experience, the gap should be around 0.5 inches on each side. We wanted to make an airtight bridge between the inside wall and the window frame, but the plane of the window frame was ~9'' from the inside wall. We pushed a thick plastic sheeting past the inside window frame, and sealed it against the window frame using silicone rubber gasket material. That was only moderately successful because the gaps varied between 1/32" and 3/8". Because the typical opening in the sips panel was not perfectly rectangular, the gap also varied along each side of the window. To give one more layer of protection, we sealed the plastic against the frame using Fortiflash tape. The end result is shown below.

We were confident that the windows were not going to leak. The Vycor did not stick to the concrete slab, so we had to come up with something else to seal the perimeter at the floor. We used the mastic that Premier supplied to glue the sips panels together and put it between the OSB wall and the vapor barrier under the plywood subflooring as shown in the picture above. This caulk will remain flexible and the drywall will provide additional insurance.

OK, we were ready for a blower door test, and it turned out to be difficult to find someone qualified to do it. After about 20 phone calls, I located Bill Foley from Sequim, about an hours drive from Port Townsend. The day he was scheduled to come, we had a blizzard! He made it anyway, after driving for 3 hours. He set up his equipment and pronounced it the tightest house he had ever seen. Unfortunately, he measured 330 CFM, twice what the Passive House Institute requires for certification. he was in a big hurry to get on the road, but just testing with our hands, we indentified about 10 leaks, nearly all of which were around electrical boxes. We had also forgotten to foam around the gas pipe for the kitchen range, Bill had a leak around his fan, and we suspect that the intake and exhaust vents for the energy recovery ventilator were also leaking.


Ideally, we would have sealed the leaks and had him come again. However, he was leaving town, so we pulled out all the boxes, foamed inside the sips panel, and reinserted the boxes with the foam still soft. We're quite confident that we are below the 160 CFM target, but won't know for sure until the house is tested again upon completion. How good is 330 CFM? The blower door manual states that 64 new houses in Minnesota (1984) averaged 1390 CFM, and 6711 older houses in Ohio tested in a weatherization program averaged 4511 CFM.

Now that the house is sealed up, we started heating it using a 1500W oil filled radiator. We have to bring the electricity in through a window, and can only seal up the gap using duct tape, which isn't great insulation. However, on cloudy days at 20F with wind gusts, we could get the temperature up to near 60F. On a sunny 20F day, we had to turn off the heating and crack a window to be comfortable. We have 5 Thermatru exterior doors, 4 of which have full glazing, which I estimate to be 70% of the door area. It is not a good glazing and we plan to switch it out with a higher quality double glazing in the summer. The glass in the doors is the major source of heat loss. We can see that by  the appreciable water condensation on the door glass, and there is none on the Serious windows.

OK, one more picture of my other construction project this summer. This one is finished! Drywall begins tomorrow!

The windows go in

Finding appropriate windows has not been easy. The usual sources (Andersen, Pella, Milgard...) do not make sufficiently well insulating windows to allow Passive House certification. We considered Serious Materials and one Canadian source which was more expensive. German windows are available and top of the class, but not in my budget. We finally went with the fiberglass frame Serious windows. The hard part to swallow was the cost which was about $50/sf based on rough opening - $19k for 16 windows. By comparison, you can buy vinyl frame windows at Lowes for about $15/sf and double pane low e fiberglass frame windows for about $30/sf.

So why have windows? Well, it's useful to be able to get light into the house, and to look out of the house, particularly if you can look at trees and the sky as opposed to your neighbor's walls. Can you have too many windows? Yes, because windows are not as well insulated as walls, the floor, and the roof.  Heat leaks out of the house in a number of ways, and a major pathway is windows -especially after the sun goes down. However, there is a big positive potential to windows, namely, in the daytime, they can harvest light from the sun and convert it to heat. So the goal is to maximize light harvesting and to minimize the losses from the windows that don't collect much light and from all windows at night.

In the heating season, the sun is low in the sky, and although it seems hard to believe, if your house were in the form of a cube with the area of all sides being equal, more light would hit the south face than the roof. So the obvious rule ought to be to carefully orient your house to the south, and maximize the window area in that direction. Take a walk around your neighborhood and see how many houses have been designed that way. You won't see many.

Maximize the window area to the south, minimize the area to the north, where you will not harvest sunlight and have intermediate values on the east and west sides where you have some light harvesting, but significantly less than to the south. On my house, there are 363 sf of windows including the glass doors. 167 sf are on the south side, 81 on the west side, 71 on the east side, and 45 on the north side. The images at the top of this posting show (from top to bottom) the east, south, west, and north sides.  Each window must give values for 3 numbers. The U value where U = 1/R is a measure of the insulating strength. The solar heat gain coefficient (SHGC) measures what fraction of the sunlight is harvested, and the transparency measures what fraction of the light incident on the window enters the house. There should be a fourth number that is a measure of air infiltration, but disclosing that number is voluntary, so it’s not done.

Ideally, you want U to be as high as possible on all windows. It varies between 0.14 and 0.20 for my windows. The lower numbers are for Serious 925 series windows, which have 2 glass layers and two polymer film heat mirrors, which is equivalent to quadruple glazing. These windows are expensive, and we have them on the east and west sides of the house. We used the 725 series which have 2 glass layers and one polymer films on the north and south. Both series have krypton gas as a filler The SHGC should be large for the south windows (it is 0.50), smaller on the north windows (it is 0.21) with intermediate values for the east and west windows(~0.40). Ideally, you want the transparency of the windows to be high, but that is incompatible with large U values. How can one harvest sunlight? Sunlight enters the house as visible light, but leaves as infra red light. Efficient windows are coated with materials that have a high transmission for visible light, and a low transmission for infrared light. You harvest sunlight by allowing the visible light to enter, but making it hard for infrared light to leave. The coating reduces the transparency, which varies between 38% for the north windows, and 65% for the south windows.

Given all these variables, how should one choose window area, U values, etc? That was Jesse Thomas’ responsibility, and he relied heavily on a software program from the Passive House Institute that allowed him to vary window area, U values, etc and calculate the energy usage by the house. The inputs to the program included detailed average local weather information throughout the year, and a lot of the details on how the house was constructed. He did a cost-benefit analysis of using 725 vs 925 windows and came up with the final window design. The performance numbers are interesting. 41% of the heat loss from the house goes out through the windows, even though the windows are only 8% of the surface area of the house including the slab and roof. However, 47% of the energy needed to operate the house comes from harvesting sunlight .

So the windows are doing their job, allowing in natural light and passive heat gain. Importantly, we have more gain than loss from the windows. To say this differently, if we had left out all but one of the doors and all windows and lived in the highly insulated space, we would need more energy than having the somewhat energy leaky windows and doors. However, without the expensive windows, the energy loss would be significantly greater than the gain.

The roof goes on

Before the roof panels go in place, we need a ridge beam, which is supported on two 21' high fir logs.The top picture shows us hauling the logs onto a trailer using a come-along. We got five, of which 2 will support the roof over the front porch. That was a good morning's work.I peeled them at the site as shown in the second picture, and two posts were hoisted in place using the crane. In the lowest image, the ridge pole is placed on the log posts.

On day 30, the roof panels arrive.  They are unloaded in an hour or so, and the first panels on either side of the dormer the go up the same day. The fourth image below shows the dormer roof, which was put together from smaller panels on the ground. The come-alongs seen in the left of the image allow the tilt to be set so that the panel comes down with the same clearance everywhere. In the fifth image, it is being set in place. The sixth image shows a short log post being slipped in before the roof is shut.  All roof panels are in place on day 34. The last image shows the added on eaves. The 12" roof would be too thick to extend out as eaves, so we had to add on eaves built with 2 x 8s.

in the

So how are we doing with the cost and how does it compare with a more conventional house? The  wall and roof panels cost $33k, including the crane rental, sales tax and delivery. It took 3 men 8.5 days to put them up plus 2 days for the eave construction. Counting workers comp, social security, etc and the 8.4% sales tax, the labor costs for putting up the walls and roof were $6.2k. Total cost of the fully insulated shell is ~$40k. One of the contractors I interviewed priced out conventional framing and sips for this house. The labor would have cost ~$5k more, and the insulation would have cost $12k. The total cost was identical to within ~$2k.