In my early years of designing HVAC systems, I had come to learn key budget values to check my engineering data and continuously benchmark these rules of thumb. If I saw an out-of-line budget value, such as an improper cfm, I could go back and review the calculations to double-check how the total cfm for a floor was calculated. An example of this would be to have a computer program complete the heat gain for a single-story building with the results showing 3 cfm per square foot. Knowing my rule-of-thumb budget value to be 1.5 cfm per square foot, this check indicated there were errors in the computerized heat gain calculation. I then would go back to find where the error occurred to bring the simulation down to a value closer to 1.5 cfm.

A side note to this check and balance of my 1.5-cfm rule of thumb was a pre-energy-crisis value. Once the oil embargo of the 1970s hit, and energy conservation took control of design engineering, my rule of thumb check figure dropped to 1-1.25 cfm per square foot. Those buildings that had less than 1 cfm per square foot were designed to be incredibly energy efficient. This often resulted in “sick building syndrome.” The computerized heat gain calculation told the designer what to engineer the cooling capacity at, but the program didn’t have a default minimum ventilation rate. Over time, we hear less about sick building syndrome from lessons learned as designs take into account the space required for adequate ventilation when the area is occupied.

Another useful benchmark I would use to check my engineering design was square feet per ton (sft) of air conditioning. This value varied significantly depending on the application. An office building could have a rule of thumb of 425 sft, while a computer room space could have a value of 60 sft. Hospital areas will have a variety of values depending on the space application, e.g., patient room versus operating room.

Benchmarking one’s HVAC design is a useful way to review the HVAC equipment, and I presume most engineers have their own rules of thumb to spot-check their projects. But, what are and/or will these benchmarks be when it comes to achieving the environmental goals set for today and tomorrow?

There is, and has been, a correlation between the energy input within a facility and the global warming impacts that followed. Now, HVAC engineers are being challenged to provide decarbonized designs that need to be benchmarked. One sometimes can feel this type of building design requires a degree in environmental science in addition to mechanical engineering. Consulting engineering companies may soon be looking to fill positions within their firms similar to having in-house department heads, e.g., with the new position being titled environmental compliance reviewer. This professional will have benchmark values at his or her disposal to assure compliance with decarbonization, net-zero, carbon neutral, etc., so as to certify these goals/benchmarks on the cover sheet of each contract document being issued for construction.

Without some form measuring certification compliance, the builder, as well as the building owners, may tout the new or renovated facility is Leadership in Energy and Environmental Design (LEED), Building Research Establishment Environmental Assessment Method (BREEAM), etc. But, what benchmarks can be applied that allow building owners to monitor and measure annual results?

Reiterating the above, “If I saw a budget value out of line, such as cfm, I could go back and review the calculations to double-check the total cfm for a floor.” Today, I don’t have environmental benchmarks that would tell me the project is complying or not. So, as it was said in the movie “Ghostbusters,” who are you going to call?