Inconsistencies

One of the interesting aspects of compiling the information for my Facility Decisions energy standards talk were the apparent inconsistencies in requirements and recommendations across the standards, guidelines and rating systems I reviewed (14 publications in all). For example, in LEED individual lighting controls are to be provided for 90% of building occupants; the exception is 50% in LEED for existing buildings -- though there's likely a good reason for that exception.

When it comes to turning off exterior lighting during the day, though, ASHRAE 90.1 says to use a combination of photosensor and time switch, or astronomical time switch. GBI 01-2010 says to use a time switch, photosensor or astronomical time switch. ASHRAE 189.1 doesn't care how you do it, just turn off the lights within 30 minutes after sunrise.

For CO₂ sensors and demand-controlled ventilation (DCV), ASHRAE 90.1 says to use DCV for large, densely-occupied spaces. GBI 01 specifies regularly-occupied spaces (it defines "regularly-occupied") with occupancy variation >= 30%. LEED specifies it for densely-occupied spaces. And ASHRAE's Advanced Energy Design Guide for Small Offices says to use DCV in varying AND high-occupancy areas.

The list of inconsistencies goes on, including on alarms for ventilation system performance variation, the dampers to be used in air economizers, what water uses are to be metered or submetered, and so on.

Perhaps this isn't surprising. Some requirements are based on experience while some are speculative. Some of the differences are probably the result of independent publication development or disagreements with other requirements.

But nearly all of these documents are relatively new, having just been published within the last three years. I expect that with time and experience they will converge towards very similar recommendations or requirements.