Tuesday, December 22, 2009

Computer power use

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.

Tuesday, December 1, 2009

Cellulose Insulation

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