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View Diary: Green Diary Rescue & Open Thread: Green Stimulus Edition (164 comments)

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  •  Theirs Is 12 Years (0+ / 0-)

    According to their detailed stats, they paid $21,340, averaged to $508.40 per window. They estimate saving 700 $2.38 oil gallons for the year, or $1,666. That's a 12 year payback time on their investment.

    Which is a lot quicker than 100 years. Plus their costs were higher owing to how long they waited to upgrade (every 12 years is breakeven, not the 100 theirs waited). And they don't get benefit from cooling months, which would shorten even more (perhaps more than 2x faster) the payback. And if (when) energy prices rise, even faster than overall inflation, their 2008 dollar investment makes the savings even higher, so payback faster.

    Plus, Americans spending money on efficient windows (and their installation) probably returns money back through our economy faster than spending it on oil, gas or electricity.

    What I really want to see now is an actual dollar comparison of your storm window (or other seasonal insulation, like heatshrunk plastic film) to the permanent double-pane upgrade costs. And, if I could get it, further comparison to seasonal insulation over double-pane.

    "When the going gets weird, the weird turn pro." - HST

    by DocGonzo on Thu Feb 26, 2009 at 10:52:42 AM PST

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    •  meaningless results (0+ / 0-)

      Sorry, but you can't say how many any particular change saved based on one house of results -- especially for an oil fueled home.  How full waas the tank when they started the year?  How much oil was in the tank at the start and end of the prior year?  How many degree days were in a each period?  How was the house used in each year?  Did occupancy patterns change? thermostat settings?  Did they make any other home improvements?  Did they add any electric end uses?  Do they have a wood stove or other supplemental heating source?  There are too many variables.

      There is no way that you can expect savings of 700 gallons of oil per year from replacing 42 windows.  That's 16.7 gallons of oil per window.  Basic heat loss calculations make that figure unbelievable -- even if they had just very leaky single pane windows without storm windows (and if that were the case,  why didn't they have storm windows?)

      •  Ask Them (0+ / 0-)

        No, that report is indeed meaningful in measuring their efficiency change in real terms, if indeed there were no other costs to increasing their decreased energy costs. The amount of extra oil in their tank is irrelevant to the savings of oil they measured, because there's no reason to think any of that extra oil was consumed and mistaken for "savings".

        In reading their report, there's no sign of any other costs contributing to their decreased consumption, except for their new $700 refrigerator. Which they say saves $18:mo, which changes ($21340 / $1666) = 12.8 years to ($22040 / $1460) = 15.2 years. Yes, that's 19% longer, but hardly 100 years.

        But since they were so quick and detailed in their response, why don't you ask them if there are other costs, or other factors pumping up their energy savings. If that somehow means they're overestimating by 6x their benefit, I'd like to see some actual evidence showing that.

        "When the going gets weird, the weird turn pro." - HST

        by DocGonzo on Thu Feb 26, 2009 at 12:10:10 PM PST

        [ Parent ]

        •  sorry, but you are wrong (0+ / 0-)

          A homeowner doesn't usually install a special metering device on their oil furnace.  What they know is how much oil they had to buy in a given time period.   Let's say I bought 1000 gallons from October through January this winter and I bought 1500 gallons last winter over the same period.  Did I save 500 gallons?  Hmmm.  What if this winter I started out with 200 gallons in the tank and had 20 gallons at the end of January?  That would mean I used 1180 gallons.  What if last winter I started out with 10 gallons and ended with 220 gallons -- that would mena I used 1290 gallons.  So now my savings are actually 110 gallons -- not 500 gallons.  What if this winter had 10% fewer heating degree days -- well then that means I really saved nothing from efficiency changes

          As you can see, oil purchases alone (especially for part of a season) doesn't tell you that much.  

          Second, even without this uncertainty, we still don't know anything about cause and effect for the "savings".  You can't answer my other questions about the building or its operation.  Even the people actually living in a house often can't answer them well.  That's why we don't base science on observational studies with no experimental control and a sample size of 1.   A single anecdote is not a scientific finding.  

          BTW, I do energy efficiency program evaluation and research for a living.  Most efficiency programs exclude window replacement because they are not cost-effective, but I've done some analysis of whole house Energy Star window replacements in a heating climate and found average savings of about 6% of heating usage and an average payback of more than 100 years.  It's only based on about 20 houses -- but I'd believe that a fairly scientific analysis of 20 homes is more reliable then a single partial year oil heated home's experience.  

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