Energy Efficiency

Eco Cars

2011-11-11T15:28:00.000-08:00

Canadians will soon be able to buy all-electric vehicles. I decided to compare one to the hybrid and an inexpensive car with good fuel economy. I'll calculate the cost of 20,000km of highway driving with gasoline costing $1.25/L. Vehicle prices are SRP.

The Mitsubishi i-MIEV will sell for $33K, at a claimed 1c/km for electricity. Total driving cost: $200.

The Prius is $28K and has a fuel economy of 4.0L/100km. Total driving cost: $1000.

The Kia Rio 5 is $14K and has a fuel economy of 4.9L/100km. Total driving cost: $1225.

Dividing the cost of the vehicle over 10 years (excluding financing & maintenance costs) puts the Rio5 on top:
Prius: $3800/yr
i-MIEV: $3500/yr
Rio5: $2660/yr

I often drive a motorcycle in good weather, so for fun I calculated the annual cost for a Honda Shadow 750: $1975. A smaller CBR125R: $1050.

Saving with timers

2011-04-24T18:06:00.000-07:00

Many states and provinces now meter electricity based on time of day, with weekend and night rates near half of the daytime rates. Besides timers for hot tubs, many other high-use appliances can be timed to run when electricity rates are lower.

Dishwashers with electronic controls typically have timers, and especially if you use added heat or heated dry the timer is worth using. Some washers and dryers also have timers, and although most people know an electric dryer uses a lot of power, washers also use a significant amount. Using a clamp-on ammeter, I measured the power of a 240V electric dryer on medium heat setting to be 5600W. Using Nova Scotia's power rates, running the dryer for an hour would cost 73c, but only 39c during off-peak rates. The washer uses 750W, so using the washer for an hour during off-peak rates would save about 5c.

Hot water heating is the second largest household energy user in Canada after space heating. When I first switched to TOD rates I installed an Intermatic EH40 timer on the hot water heater. One year later it failed. For a replacement I installed an Aube TI040. I paid less than $100 at Harris & Roome, which is less than I paid for the EH40. It also has a 3-year warranty vs. 1-year on the Intermatic. When installing a water heater timer, it's a good time to check your water heater element; many 40-gallon hot water heaters come with two 3000W elements installed, but can accept up to 4500W elements. A 4500W element will heat 50% more water in a given amount of time than will a 3000W element.

Cost savings will depend on household hot water use. A 2008 study by NRCAN, "Hot Water Use Field Test Results" indicates a four-person household uses about 190L of 50C hot water per day. Assuming a cold water supply temperature of 10C, heating 190L of water uses 8.8kWh of electricity. At normal rates that is $1.15 vs. 62c at off-peak rates. With savings of 53c/day, the timer will pay for itself in less than 7 months.

Air infiltration

2010-12-11T14:17:00.000-08:00

I think air infiltration doesn't get the attention it should. Air sealing gives the best heating savings for your dollar when compared to almost every other building envelope improvement; insulating exposed concrete basement walls is the only other thing I can think of that comes close.

I'm pleased to see marketing funds being spent on this issue, like this commercial featuring David Suzuki.

Using Hot2000 to model a house located in Halifax, NS with R26 walls, R40 ceiling insulation, and energy efficient windows, about 27% of the heat loss in January comes from air infiltration. Hot2000 doesn't count the heat loss due to the moisture in the inside air (latent heat), and recent research indicates it underestimates the total air infiltration rate. Considering Hot2000 errors, a more accurate estimate would be 40% of the heat loss coming from air infiltration.

Although I think the best way to find air infiltration points in a house is with a blower door test (typically $50-$100), there is a cheaper way. I read on builditsolar.com the idea to turn on a clothes dryer, then go around your house checking for leakage. If you have a kitchen range hood exhaust fan and bathroom exhaust fans, turn these on too. In addition to checking the usual places like around windows and electrical boxes, check for air infiltration along the floor on outside walls. If you have tile or hardwood floors, a bead of translucent or clear caulking between the baseboard and floor can cut down air infiltration.

windows

2010-10-17T10:45:00.000-07:00

Choosing energy-efficient windows is probably the most complex aspect of building. In this article I'll offer some advice to simplify the seemingly innumerable choices. The focus is on northern climates, where heating energy costs significantly exceed cooling energy costs.

Most windows now include a specifications label. All these labels include a U-factor which indicates how much heat is lost out the window, and a solar gain (SHGC) which indicates how much heat from the sun is gained through the windows. A good window should have a U-factor less than 0.3 and SHGC more than 0.5. It should use an Inex spacer or Super Spacer at least 5/8" wide. A window with a cheap aluminum spacer will lead to much more condensation on the window in winter.

Use fixed(picture) windows where possible instead of operating (slider/casement). Not only are fixed windows cheaper, they have smaller frames than operating windows which allows for more glass area and a higher SHGC rating.

According to LBNL Resfen, a window rated U 0.29 and SHGC 0.56 facing south in Portland, ME will have a net gain 76,430 BTU of energy per square foot of area. This is the amount of heat energy from 22 kWh of electricity or about 2/3 of a gallon of heating oil. The same window facing north will have a net loss of 17,500 BTU of energy per square foot of area, so minimizing north-facing windows in a new build reduces heating energy use.

Hot Tub (Spa) Power

2010-04-14T17:22:00.000-07:00

We recently purchased a 120V hot tub. We installed it in our indoor pool area, which was unheated this winter as the insulation is not completed. The unit is insulated with what appears to be low-density spray foam and has a ~2" insulated cover. The bottom of the tub (below the footwell) doesn't seem to have any insulation.

I recorded the power use in January using a P4400 when the air temperature averaged 32F/0C and the temperature set to 103F/39C. The tub was using 14kWh/day which works out to $50/mth @11.8c/kWh. When we switched to TOD rates I put a timer on it so it only comes on during off-peak rates, cutting electrical costs down to around $20/mth. It will drop from 103F at 7am when the power shuts off to the low 90's by the evening so we turn on the power manually in advance when we plan to use it during the week.

A tub 8' * 3' high has a surface area of 126sf, so with a 100F delta-T and R10 insulation the heat loss would be 1260BTU/hr or 370W. Therefore a well-insulated outdoor tub should cost around $30/mth to operate in Jan/Feb at standard power rates or half that for off-peak.

Computer power use

2009-12-22T18:52:00.000-08:00

A typical desktop computer (including a monitor) will consume about 150W. If the computer is used 5h/day, it will use $33/yr of electricity @12c/kWh. With a few changes it is possible to cut power use significantly.

The first power saving adjustment is monitor display brightness. Setting brightness to the minimum will cut monitor power use by about half. For professional photographers this may cause color rendering issues, but for most people there is no negative effect.

The second adjustment is CPU power saving modes. With a 1.4Ghz Sempron I was able to reduce idle power usage from 78W to 49W with this technique.

The last adjustment is using system standby power mode. Whenever you go away from your computer for more than a few minutes, put it into standby power mode. Also set your system standby timers (I think 30 minutes is good) so your computer will go into standby mode automatically.

Cellulose Insulation

2009-12-01T17:54:00.000-08:00

I used dense-pack cellulose insulation in my walls, but I won't use it in walls any more (I'll still use it for attic insulation). After reading Paul Fisette's article and others, I decided to go with dense-pack cellulose due to improved air tightness, sound attenuation, and ability to penetrate tight spaces. There was only one insulation contractor doing damp-spray in the province two years ago, and even he said he still did a lot of dense-pack work. During the winter for new construction he would not do damp spray as the water lines will freeze up.

Cellulose insulation is a bit more expensive than fiberglass. The best contractor pricing I've found for cellulose is $9.05/bag at Kent. Using the minimum 3lbs/cf density works out to 50c/sf to insulate a 2x6 wall. I've found R20 batts at Acadia Drywall for 38c/sf, so for materials cellulose is 30% more expensive.

Cellulose insulation provides more resistance to airflow than fiberglass, but the CMHC has shown that it's still a lousy air barrier. They have also shown that plywood or OSB glued & nailed at the edges to studs and/or blocking makes a great air barrier. In a climate where temperatures are below freezing for most of the winter, it's more important to make an airtight assembly than to add insulation beyond standard R20 levels. A reasonable target is 0.5ACH@50Pa (R2000 only requires 1.5ACH). When the temperature is -10C and a 20kph wind is blowing a two-story R2000 home (R25 walls, R50 attic, 1.5ACH@50Pa) will loose more heat from air infiltration than from conductive heat loss.

If you are set on cellulose for it's lower embodied energy vs fiberglass, I'd strongly recommend using damp-spray, and still build a good exterior air barrier. Although manufacturer specs say cellulose doesn't settle when blown to 3lbs/cf, I've found at least 4lbs/sf is required to avoid settling. I blew cellulose into 2 22.5x48" 2x6 wall cavities behind 6-mil poly. After 2 years I
had more than 2" of settling at the top. I removed the insulation from one of the cavities and weighed it; 14.8lbs which equates to a density of 4.3lbs/cf. Some of that could be moisture absorbed, but the specs state a maximum of 20% water absorption which would still leave 3.6lbs/cf. Testing by the Nordic Innovation Centre shows cellulose at 3.1lbs/cf settles to 4.2lbs/cf when exposed to humidity cycling between 50% and 80% and pressure less than the weight of 3ft of cellulose above it (300Pa is equivalent to the weight of 2' of celluose at 3.1lbs/cf). I suspect adding in temperature changes from 30C to -30C would further increase settling.

Testing has also shown that settled density is a function of blown density, so to ensure no settling after humidity cycling cellulose would likely need to be blown to densities higher than 4.2lbs/cf.

Photo of cellulose test behind 6-mil poly

Solar Hot Water in Eastern Canada

2008-09-30T06:39:00.000-07:00

Most domestic hot water systems I have seen in Canada are designed for year-round use. I don't think the added cost over seasonal systems is worth it.

I'm assuming a 5:12 pitch roof-mounted install of a Thermo-Dynamics G32 collector in Ottawa. An inlet water temperature half way between the cold(10C) and hot (50C) will be used. Converting the data in CBD-39 to metric, at summer solstice 1087 watts/m^2 will fall on the collector vs. 538 watts at equinox. According to Environment Canada, the June & December average temperatures are 18.4 and -6.6C. For insolation, 253 hours of bright sunshine are normal for June vs. 82 hours for January.

Summer solstice efficiency works out to 68% vs. 38% for the winter equinox. Factoring in the number of hours of bright sunshine, the panel will collect over five times as much energy in June than in December. To save more on a seasonal system, an unglazed absorber such as the AG32-P could be used instead of a glazed panel.

I've written a guide to installing an inexpensive solar hot water system to help people do it themselves.