As noted in last month’s column, accessibility to mechanical, electrical, and control system components is critical for sustainable systems operation. However, the design and construction industry is sorely lacking when it comes to agreeing on what appropriate accessibility means. In order to make a meaningful difference in how systems are delivered to owners/operators, it is critical to define measurable accessibility acceptance criteria early in the design phase and allow the commissioning professional to shepherd that criteria through the design, construction, and acceptance phases.


What are some possible quantitative and enforceable criteria? This column will outline a few ideas and, hopefully, generate some reader feedback with other options.

Most project specifications generically require that all equipment be installed per the manufacturer’s installation instructions. In some cases, this might be enough to define accessibility requirements in terms of clearances around the equipment. Finding such clearances is typical in the installation manuals for boilers, chillers, furnaces, switchgear, generators, etc. I’d like to see similar minimum clearance requirements (above, below, to the sides, etc.) for VAV terminal units, fancoil units, control sensors, and devices. Manufacturers should be most knowledgeable regarding required maintenance and repair activities and the space requirements to perform them.

This could be challenging for the manufacturer if the equipment has the option of coming with factory-installed controls. If the controls are manufacturer provided and factory-mounted, the manufacturer’s installation manual should be able to define the accessibility requirements. However, it is very common, especially with VAV terminal units, to have the manufacturer’s factory install a different vendor’s control devices. In that case, which vendor would be responsible for defining the clearance requirements to access the control panel and/or devices?

Does the responsibility fall on the design team to define specific clearance requirements for all equipment and controls, just in case the manufacturers fail to provide that information in their manuals? Perhaps, to be safe, it does. How does the design team know what is required, if they do not typically operate, maintain, or repair equipment? Clearly, the owner/operator should be consulted with respect to their expectations for accessibility.

Are there any universal criteria that might cover all equipment and devices? Is there a minimum “clear zone” required for a person to get to and manipulate a device regardless of size, type, and location? Would it be 24 in. above and/or below and 24 in. on one or more sides? Generically, 24 in. clear in all directions around any piece of equipment or device seems reasonable for human access, but it is probably unrealistic from an architectural space efficiency perspective.

Therefore, it seems necessary to qualify the requirements to be something like, “24 in. above and to one side of a device needing service from above,” or “24 in. below and to one side of a device needing service from below.”

It is important to remember that if a device needs to be serviced from above or below, the side clearance is critical in order to allow a maintenance person to actually get to the “above” or “below” clear area. Similarly, if a device only needs service from the side, a vertical clear path needs to be maintained for personnel to access the side of the device.

Another quantitative requirement to consider is distance from the floor. Something mounted too close to the floor may be hard to access for proper service, and we all know how something too high above the floor can make maintenance activities too dangerous, too disruptive, and/or too expensive to perform safely. I have seen installations where VAV boxes were mounted 14 ft above the floor on the underside of the floor above, with lots of clear area around them. The problem was the lay-in ceiling at 9 ft above the finished floor, through which a ladder could not safely be erected to reach the VAV boxes. Perhaps the most generic requirement for installation height would be in terms of the ability of a 5-ft-tall person to stand safely on an x-foot ladder with his head at the same elevation as the device needing service.

A more subjective criterion would be a requirement that the general contractor demonstrate safe access to all equipment requiring future maintenance and repair. Whenever there is a dispute about accessibility during construction and/or the turnover process, the onus would be on the contractor to show the owner/operator how the future work would need to be performed. The requirement would be for reasonable, safe, and affordable access. This is less enforceable than measurable criteria, but it is a universal requirement that could be easily added to the general conditions section(s) of any project specification.

I look forward to collecting additional accessibility criteria ideas from readers; hopefully, there will be enough to fill another column in the near future. ES