Building Envelope

Building Envelope Questions

  1. What are useful benchmarks for office energy efficiency? Where can I find average annual kwh draws for comparable buildings?
  2. Where is the best place to get data on performance of window film?
  3. Has anyone found any sort of model or way to calculate the KWH or $$ saved by things like solar shades, window tinting, reflective roofs? I can find (wide) ranges of % savings in Electric bills, but want something more concrete.

Building Envelope Answers

1. Q: What are useful benchmarks for office energy efficiency? Where can I find average annual kwh draws for comparable buildings?

A: Benchmarking is important because it gives one a sense of whether an intensive energy audit would be a good option for a given building.

Useful metrics for benchmarking the efficiency of a building are electricity intensity (annual kWh consumption per square foot) and natural gas intensity (annual therms or BTUs used per square foot). Chapter 5 in the handbook details how to calculate these metrics, and lists the US average values for a range of office building sizes. We got those values from the Energy Information Administration's Commercial Buildings Energy Consumption Survey (CBECS).

The CBECS data is available from EIA, and is presented in many different formats: by building type, size, climate zone, etc. The data divided by climate zone information is probably the most useful for estimating regional benchmarks; see tables C20 and C30 on their 2003 detailed tables webpage. One thing about the climate zone tables is that they don't also parse by building size; so you have to chose between looking at national data divided by climate type or by building size (in tables C21 and C31)). This is probably ok if your building is medium sized (10,000-100,000 square feet), but if it's very small or very large you might want more specific data.

I've found the folks at EIA who maintain this data to be very useful, if you contact them up they can provide additional specific data or can answer questions. Note, the tables linked above are for 2003 data. New 2007 data is due in "mid-2009" so may be up soon.

A map that shows which climate zone you fall into is accessible here: [http://www.eia.doe.gov/emeu/recs/recs97/zonemap.pdf]

Another good tool for benchmarking efficiency is the EPA Portfolio Manager. Portfolio Manager has benchmarking information built in, and will also be able to tell you whether your building may be eligible for Energy Star certification.

One last point which I've just had clarified for me: these efficiency benchmarks for office buildings encompass the server rooms found in offices (those that are serving the data processing needs of those inside the office building). So for the purposes of benchmarking efficiency, there's no need to try to separate out the server room energy and benchmark it separately. So, unless it's a data center serving a non-office purpose (e.g. supporting your company's software platform for clients) that just happens to be housed under the same roof as offices, you can include it in your overall office space benchmarking calculations.

2. Q: Where is the best place to get data on performance of window film?

A: First off, for a general overview about window film, visit the following article at facilitiesnet.com: Window Film: A Window Of Opportunity.

Most vendors have information on their products’ performance and many do free site assessments, including ROI. 3M offers a "proof of technology" test where they will install film on one window and track the temperature over a certain period of time. Below are a few companies that Climate Corps fellows have been in touch with:

In addition, it may help to speak with a glass company representative from glass companies such as Viracon and Pilkington. They have a lot of information on their glass regarding U-value, solar heat gain coefficient (SHGC), etcetera. Since the SHGC is likely most important in reducing cooling load in hot climates, maybe they have some experience or a rule of thumb for your climate about any correlation between SHGC and cooling loads. If they do, then once you get the delta SHGC for adding your film, you can make a similar calculation.

3. Q: Has anyone found any sort of model or way to calculate the KWH or $$ saved by things like solar shades, window tinting, reflective roofs? I can find (wide) ranges of % savings in Electric bills, but want something more concrete.

A: The Department of Energy has a website that lists the available building energy software tools for building envelope systems. This webpage shows the Envelope Systems list of tools.

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