BPA Math Check
The work product of Bonneville Power Administration, Regional Technical Forum, in support of weatherization policies, is an unprintable and hard-to view Excel spreadsheet, posted here from Google Docs:
Content includes cost and benefit numbers for insulation measures that I routinely analyze with my Insulation Math, in preparation of bids and a variety of reports to customers and rebate managers. This math has been posted to the web for review and comment, for more than two years. So far, no one has felt competent to publicly confirm or criticize the presentation. Effort to promote feedback includes a topic at Saturn Online, Saturn Resource Management, Inc, http://rl.srmi.biz/Forum/showthread.php?68-Insulation-Math. I am advised that the appropriate technical expert at Energy Trust of Oregon, has done sufficient study, to report absence of error.
Several decisions permit use of firm numbers, in simple hand-calculations.
1. Numbers are for heating costs only, at 4400 HDD currently applicable in Portland, Oregon. Correction to any other HDD is by simple ratio.
2. Absent any insulation, a value of three is used as base R-value, allowing for convection at interior and exterior of boundaries. The number of three has fuzzy real basis, for example as itemized at Build It Solar. In some cases, three is a slightly large "zero", with resulting under-estimate of savings.
3. Ground moderation of temperature in a weakly-ventilated crawl space is credited as reducing HDD by 25%.
4. Fuel cost is taken to be $2 per therm, recognizing majority heating with natural gas, and allowing for some of the societal costs of fuel, beyond utility fees.
One key thing gives me confidence I am in tune with consensus math: I show that adding attic insulation from R19 to R38 is borderline justified, with payback in about fifteen years. I understand that the goal in a one-shot upgrade is to choose maximum insulation that has payback at lowest consumer-desired interest earnings, about 7%. There is more-rapid payback if lesser insulation levels are chosen.
I compare RTF numbers with my calculations, in the following database extract: RTF MathCheck
Commentary is supported by posted calculations for each spreadsheet line.
I wonder if very low energy savings by RTF for improvement from no insulation, are a lifestyle matter. People coping by being cold and perhaps inactive. That would not give fair comparison.
I note that RTF assigns no value for air conditioning cost, cooling degree days, CDD, vs. measures. We may allow ourselves to be unproductively cold or hot, with grave economic loss. The passive means of staying comfortable in Summer, with weatherization, have great economic value.
This page has been brought to the attention of Bonneville Power Administration and RTF, and they do not deign to respond. This is unsupportable arrogance. Attempts to communicate include this message posted on the BPA public comment page.
At 1/7/2012, add Line 8a, suggesting a better insulation requirement for Attic Walls, than for exterior walls, where space is not limited. This addresses disregard in the Pacific Northwest BPA service area, of value in maximizing insulation isolating a home from attic temperature from summertime heat. Existing incentives in Portland, Oregon, apply only where found insulation is under R4, and call for a target of only R15 insulation (R11 wall). This would not be in the current RTF math, or whatever it is that now justifies rebate programs.
Links to the calculations are:
Line 8: Insulate Walls R0 to R11
Line 8a: Insulate Attic Walls R0 to R22
Line 9: Insulate Walls R0 to R19, 2x4 Reconstruction
Line 9: Insulate Walls R0 to R19, 2x6 New Construction
Line 10: Insulate CS Joists R0 to R30
Line 11: Insulate CS Joists R19 to R30
Line 12: Insulate Attic Floor R0 to R19
Line 13: Insulate Attic Floor R0 to R38
Line 14: Insulate Attic Floor R0 to R49
Line 15: Insulate Attic Floor R30 to R38
Line 16: Insulate Attic Floor R30 to R49
Line 17: Insulate Attic Floor R38 to R49
Line 18: Insulate Attic Floor R19 to R30