Radiant Barrier savings calcs

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  #1  
Old 07-16-08, 01:39 PM
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Radiant Barrier savings calcs

Sorry if you've seen this question posted on another board. I'm trying to find someone with specific experience with these calcs. My apologies..

Anyone use the radiant barrier and increasing insulation savings wotksheet at the DOE ORNL site, here http://www.ornl.gov/sci/roofs+walls/radiant/rb_05.html ?

I'm not getting the calcs to predict great savings for my home that I expected. Anyone else look at those calcs? Did it persuade your decision on an RB or not?
 
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Old 07-20-08, 05:16 AM
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My experience with similar projections concerning Radiant Barriers had to do with Low Income retrofits. In this particular case it was a statewide program and everything was on the table. As long as each retrofit met certain requirements. For example, if I could prove, mathematically, that a new door for this house met certain energy conservation requirements, I could install a new door in that house. The same was true for wall/attic/floor insulation, replacement windows, water heaters, heating systems, plumbing fixtures, roof repair/replacement, plaster repair to removal of plaster and sheet rocking, etc.

That one year that I worked in this program, I was asked repeatedly to come up with new and innovative applications for the program. Radiant barriers was one of the applications I was repeatedly asked to look into. Under this program Radiant barriers just did not meet the energy conservation requirements.
 
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Old 07-21-08, 01:39 PM
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Thanks for the reply! Can you give general examples (or specifics) of how/why radiant barriers didn't meet the energy conservation requirements? What was the criteria?
 
  #4  
Old 07-21-08, 04:05 PM
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Some one in Washington decided some time ago (more than 30 years) that for any application or measure under a government energy conservation program to be cost effective, the payback period had to be 10 years or less. While this may sound straight forward, in most cases it is quite complicated.

In cases where the government wishes to promote such applications that would otherwise never meet these requirements they provide rebates. Example, Solar Panels could never meet the 10 year payback. So the States give large rebates like California which has a 50% rebate. In New Jersey where the Solar is less effective than California, a few years ago the rebate for Solar Panels was 70%. In either case the rebates were offered to meet the 10 year payback requirement. FYI, I questioned New Jersey's calculations and I didn't make too friends that day.

In the case with radiant barriers to determine the payback period you take the cost of the installation and divide that by the amount it saves a year. For example, if it costs $500. to install and it saves $50. a year. (500/50=10 years) the payback period is 10 years. These tables you see on sites like the one you provided are used to make these calculations on a particular application like radiant barriers. They usually show a percentage of savings per square foot. So if I have a 400 square foot attic and I know the saving per square foot for the radiant barrier, I can calculate the savings in percentage. In my case the savings ranged from 2 to 10%. Without getting into too much detail, I was literally told to use the 10%.

The question one should ask is 10% of what? The average energy bill for this segment was $1,000. a year in 1999. So 10% of a $1,000. is $100. But this program used what is known as the "Whole House as a System" approach. Which meant that the "Law of Diminishing Returns" applied.

For example, if the house had wall and attic insulation it usually saved 50%, the annual heating bill dropped to $500. and 10% of that is $50. If a new heating system saved 20% of $500. the heating bill dropped to $400. and 10% of that is $40. If new windows and doors were installed and it saved 10% the heating bill dropped to $360. and 10% of that would be $36.

I could have manipulated these numbers by calculating the 10% savings from the annual heating bill of $1,000. However, in more than 60% of the homes involved in the program it would of meant that either the wall. attic insulation, windows, doors, heating system, thermostat, repairs would have been eliminated. Now you tell me, is a radiant barrier as important and/or could ever save as much on an energy bill as any one of the things mentioned.

So I was pressured to go the other route. That is to reduce the costs of installation. This was futile exercise because the costs of the product was fixed, on average it took 8 man hours to install, so using 4 people it took 2 hours to install. And there is such a thing called "Minimum Wage".

I can assure you I am leaving out a lot here.
 
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Old 07-22-08, 07:17 AM
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I was able to follow what you're saying. I'm just trying to see if anyone that installed the RB did these specific calcs and how did they compare with actual results. Of the 8 or 10 RB applications I've read about on an HVAC message board, only 1 or 2 said they saw no significant/measurable improvement on the bill (in terms of KWH per degree day), but most agreed it made the attics cooler. The other 6-9 said they saw very good reductions in HVAC energy usage.

I've got an old brick 1 story ranch house, somwehre between R-11 and R-19 in the attic, little to no insulation in the walls, ductwork in the crawl space, and SEER 16 cooling / COP 3 heating mode heat pump with multi-stage compressor and variable speed blower so it's not predicting that the RB will pay for itself in the pay back period (it looks like the Oak Ridge site's calcs justifiable payback period works out to 11-12 years.

I appreciate your replies. They're really helpful!
 
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