Sep 142014

One small issue with LEDs is they have a different quality of light. We have measurements that worked well with Incandescent, HIDs, and Fluorescent lamps. CRI (Color Rendering Index) which gave us a relative measure of quality and CCT which gave us a lamp’s color temperature. But these measurements were based on factors that are no longer in play in the world of solid state lighting.

In the July-August 2014 issue of Architectural Lighting, Alice Liao writes about the issues facing the consumer of quality lighting and the issues facing the professional user of lighting.

“Both CRI and CCT are derived through rote mathematic simulation rather than through empirical measurement. CRI testing is calculated on a computing device using a source’s spectral power distribution (SPD), a diagram that depicts the radiant energy a source emits at different wavelengths of visible light—wavelengths of 380 to 780 nanometers—and the spectral reflectance of each color chip. CCT is also computed from the source’s SPD.”

After Lias discusses the short comings of these measurements, we’re introduced to the Color Quality Scale (CQS). Developed by the National Institute of Standards and Technology. The CQS tests with a broader range of colors, higher chromas and deeper saturation.

“CQS also factors in extreme color temperature, which impairs a source’s ability to render color, and takes a root-mean-square of the color shifts of all 15 test colors rather than an average. This ensures that poor performance on a few samples is given proper weight.”

I am hopeful the IES Color Metrics Task Group will come up with a simple scale for consumers who are already confused about LEDs. They should also develop a set of ratings for Professionals, whose requirements for light require more data not less. For those interested in this important topic, I highly recommend this article.

The CIE chormaticity diagrams map perceived color.

The CIE chormaticity diagrams map perceived color. Lightness, the third dimension of the color space, is not shown in these two-dimensional graphs. The CIE created the 1960 Uniform Chromaticity Scale (UCS) to reduce the limitations of the 1931 system; it has since been updated by the 1976 UCS. The Planckian, or black body, locus—shown by the curved lines within the filled areas—indicates the color that a black body radiator emits within each chromaticity diagram as it is heated up.
Credit: U.S. Department of Energy

Nov 222011

Recently I fielded a call from an equipment engineer in Minneapolis regarding a HVAC modeling project. He asked about my experience working with ‘Typical Meteorological Year” (TMY) data sets. I’ve modeled a number of Heating, Cooling and Ventilation jobs were I needed the fine detail that TMY data sets provide. I told him the problem I had was using a spreadsheet. I found 8760 lines made for some unwieldy spreadsheets. Instead I put the TMY data in a database and worked my models using a hybrid of database calculations and spreadsheet calculations. He asked where to get the data. It can be found from a number of different sources online. I have been using TMY2 and now TMY3 data sets* from the National Renewable Energy Laboratory (NREL), other sources include…

  • TRY – ASHRAE’s Test Reference Year
  • WYEC – Weather Year for Energy Calculations
  • IWEC – International Weather for Energy Calculations
  • NCDC – National Climatic Data Center
  • TMY – Typical Meteorological Year

According to D.B. Crawley’s paper, “Which weather data should you use for energy simulations of commercial buildings?“, either WYEC nor TMY will work fine. These data sets are pretty good, however you need to keep in mind- they fail at the temperature extremes. The data sets are designed to weed out extreme tempertures in order to create smoother data sets. This can be problematic if you’re also using the simulation to size your equipment. Having said that, these TMY based models will be far more accurately modelling energy usage than using bin hours. They are also better when running what-if scenarios. In order to truly model a building for energy use, particularly where humidity control comes into play it is essential to model the energy use for each hour in a typical year- all 8760 data points.

Detailed hour-by-hour modeling using hourly weather data sets has become commonplace in the evaluation of design alternatives and the design of HVAC systems for larger buildings. For residential and small commercial buildings, calculating design loads based on high and low design temperature is still common practice. The economic issue is when the added cost of the more involved hour-by-hour modeling exercise can be expected to be justified by helping to guide the selection of equipment that provides significantly better part-load performance, resulting in tangible benefits of lower total annual energy cost and better comfort control in the building.-December 2010 ASHRAE Journal.

Other uses of TMY data sets are to adjust set-points based on outdoor temperature to control early morning pre-cooling. Both to take advantage of Lower temperatures and reduced peak demand rates. Building mass can also be used for energy storage. Off-peak heating and night cooling can be based on TMY modeling; shifting HVAC demands to off-peak hours and lower energy rates.

Some of this predictive control is finding its way down to the residential market with smart thermostats. I predict we’ll be seeing more of these smart thermostats… “A trial in 2000 households by Oncor Utilities in Texas resulted in heating and air-conditioning power cuts of 20% to 30% and annual savings up to $400. It also achieved complete AC turnoff at peak hours due to pre-cooling. These examples indicate that approximately 10% of energy to condition buildings can be potentially be saved by the use of control algorithms using forecaster weather conditions.”

*Note: The TMY3s are data sets of hourly values of solar radiation and meteorological elements for a 1-year period. Their intended use is for computer simulations of solar energy conversion systems and building systems to facilitate performance comparisons of different system types, configurations, and locations in the United States and its territories. Because they represent typical rather than extreme conditions, they are not suited for designing systems to meet the worst-case conditions occurring at a location. -NREL

Jun 192009

ASHRAE and its partnering organizations have made the Advanced Energy Design Guides available as free PDFs. The guides encourage energy efficient design in a range of building types: K-12 schools, small office and retail buildings, small warehouses and self-storage buildings and highway lodging.
They are available at
The guides help to educate the marketplace on how to build energy efficient buildings that use significantly less energy than those built to the minimum code requirements.

Continue reading »

Mar 122009

I’ve notice many of my favorite articles in the ASHRAE Journal are written by Mr Lstiburek Ph.D., P.Eng. I like his sarcastic writing style. I find it fun to read. His topics revolve around proper building construction and how it relates to HVAC. This makes sense as he’s a principle of the Building Science Corporation.

Some might think he’s a curmudgeon but it sounds like common sense to me. The ASHRAE Journal gets pretty dry at times so Joe gets my thanks. One of his many articles is “Some Old Lessons Distilled” about Bourbon Distillers in Kentucky. He tours an old distillery and shows how new distilleries are recreating the temperature swings and humidity control using newer and cheaper building materials. 

This is one of the few articles that seems to be available for free on the website. You can also buy a reprint of this September 2008 article.

Continue reading »

Dec 302008

Measuring Light Levels, Selecting the Right Ballast & Lamp Combination, and Graphing the Results.

Before this grocery store was retrofitted with energy efficient T8 lamps and Electronic Ballasts, we went in and took light level readings. (In Lumens)

Then we graphed the results using an overlay of the store walls, aisles and check out tellers.

By doing this we were able to match the correct ballast and lamp combination to the fixture.
In areas were there was inadequate light we used a high output combination.
Where there was adequate light we used standard combinations.
Where there was more light than required we de-lamped the fixture.

Lumens Before Retrofit

Lumens After Retrofit

Jan 052008

This post isn’t about dating. I’m the last one to give advice on that topic. Instead this about what to do if you have a bunch of digital photos with the wrong date. This can be caused by forgetting to reset the clock when changing the batteries, or vacationing in a different time zone, or even scanning film photos.

Continue reading »

 Posted by at 2:58 pm