What's Up With The Commercial Load Calculation Proposal?

June 1, 2005
Sometimes I just don't understand certain issues. When it comes to load calculations, I'm no engineer heck there are many who know that my math skills

Sometimes I just don't understand certain issues. When it comes to load calculations, I'm no engineer — heck there are many who know that my math skills are somewhere on the 9th grade level. However, the logic or intent behind some technical standards just elude me.

Here's the deal: on May 6, 2005, the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) released a proposed ANSI standard for 45-day public review. The proposal is entitled, ANSI Standard 183P, "Procedures for Performing Peak Heating and Cooling Calculations in Buildings Except Low-Rise Residential Buildings."

This is a fancy title for new rules on how to perform commercial load calculations. Now here's the rub — the way the proposal is worded, the rules apply to both large commercial buildings as well as smaller, light commercial buildings. This is where I get confused. It seems to me, there are significant design differences between a 10-story office building and a convenience store.

Let me elaborate: the proposal states, "The calculation of cooling (and heating) loads . . . shall use a series of consecutive time steps to account for the time-dependent relationship between cooling load and heat gain, and the maximum interval between steps shall be one hour.

"Cooling load calculations shall be performed for at least one day per month . . . . The cooling load calculation shall address all appropriate hours of the day and months of the year . . ."

Did I read that right? If contractors are required to do this for light commercial applications, doesn't that mean they can no longer do calculations by hand? And what about all the load calculation procedures and software that are currently used by HVAC design professionals throughout the U.S.? These procedures and software programs have been the standards used by this industry for years.

The Air Conditioning Contractors of America (ACCA) has come out strongly against this proposal. Greg Leisgang, chairman of the ACCA board of directors said in a recent press release, "Adoption of this proposal as a standard . . . would place (HVAC) contractors, engineers, and other design professionals in real jeapordy as the procedure is simply not realistic for light commercial applications."

That's how I see it as well. The bulk of light commercial work includes retail centers, churches, banks, automotive repair centers. Doing load calculations that address every hour of the day and every month of the year could increase contractor liability, put you at risk financially, and increase the costs of construction.

This is the first time that I can remember when ACCA opposed an ASHRAE standard proposal. I believe the technical committee worked hard on this. Maybe they just moved too quickly.

Perhaps Leisgang's call for a seperate standard for light commercial projects is the answer — something that distills 180P to, as Leisgang says, " useful, simplified representative approximations that can be used by design professionals in a quick, costeffective manner."

Now that makes sense to me. The 45-day comment period is now over. We'll just have to see if it made sense to the rest of the industry.

Do you agree or disagree?
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