Thursday, November 15, 2012

Fresh Air At Night

I admitted that I keep a bedroom window open nearly year-round. In Summer, it is with a noticeable breeze, full open, and indeterminate direction, windows open everywhere. Even in coldest weather, I want some fresh air, opened just a crack. Just the bedroom window. It's easy and secure with my new insulated windows, not struggling with a storm window that, else, must be closed. With security stops, a burglar could not tug out a screen and crawl in. This year-round ease of fresh air is the best justification of the window replacement. I'm not saving any money.

I must not feel guilty of energy waste in infiltration. The contribution to rest and to health is substantial. Really, what does this cost? Having developed Insulation Math for my house and region, I can readily answer.

The opened-a-crack area in November is perhaps 1/4" by 30". Call it 8 sq in.

Annual Heating Cost = $.555 * (Path Area, sq in), $4. But, that is diminished by about two thirds, where the window is open only while I sleep. Actual "waste" of heat is about $1.50 per year.

If instead of the cost, I worry about flow rate numbers, that is as:

CFM50 = 7.5 * (Path Area, sq in), probably more, with the rectangular and fairly smooth shape. CFM50 = 56. And, wow, that is a big number to foolish house tighteners. Let us please just think in tiny dollars and therms. The tiny dollars are in part the result of tiny heat capacity in air. It takes little energy to be heated, and gives up little energy in cooling. All that running of a furnace in Winter is not to heat the air. It is to heat the walls and window panes, else they quickly cool the air and we feel cold. Unless you are oblivious to ridiculous holes, heating fresh air costs peanuts.

Divide 56 by twenty, for CFMnat = 3. 
3 CFM: Doesn't that sound right? It's not a noticeable breeze. Just sweet, cool fresh air and maybe sounds of nature we should be accustomed to.

The picture is little dependent on where one lives, in zones where there is a Winter. My heating degree days, HDD, are 4400. If I lived in Minneapolis, they would be about 6000. The $1.50 per year to breath easier at night, with hopefully just some increase in sounds of nature, ramps up to $2. That's the cost for the whole year

Friends at The Energy Conservatory: Please confirm or deny. Let's get to an end of this madness that "scientifically" cranking down on fresh air will save the Earth. We just need to make sure we have all the insulation that fits. Not less. With no "pits" of convected outside air. Yes, immeasurable pits, not measurable bypasses, are the main bane in weatherization of an already-insulated home. One should never fail to do sealing, or to be credited for such work, where it has no impact on a blower door. One must not be excused from sealing, ever. 

Blower door consequences, even hundreds of CFM50, have little dollar value. Stopping convection by insulation in exterior walls or capping off pits of interior walls is what matters. Convection at windows without solar gain is accepted yet, as necessary sacrifice. In a silence from The Energy Conservatory, I read full confirmation of my understanding. With this, I read surrender, that their blower doors are not guide or measure of weatherization. TEC has benefited unfairly from frenzy with blower doors through foolish HPwES. That must end. When the misled and F-rated person who bought my blower door, can no longer steal profit with it, I want it back. They are kind of cute, and somewhat useful.

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