Can an ‘AFAD’ system work as well as UFAD?
In last November’s Back2Basics, I created a test for the readers based on the idea that the patient room design was similar to a pharmaceutical cleanroom, with an air lock for people to enter and leave the room. The number one reason for this design is to protect the patient from hospital-acquired infections (HAI).
Now, many authorities will say you can’t do that for numerous reasons. To them I say, “Why not?” Just go out and hire an open-minded, creative architect, engineer, and builder! The pharmaceutical industry does it all the time. So, with this caveat approach to HVAC design and infection control, let’s look at the problems with conventional commercial office building renovations and ask, “Why not?”
Commercial office building retrofits are cost-driven, and the results can be a sick-building environment or simply an uncomfortable space environment for its occupants. These HVAC retrofits often entail very little alterations to the existing duct distribution. More often than not, the installing contractor will simply move ceiling diffusers around, maybe add a diffuser if necessary, use a return air plenum ceiling, and keep the same number of thermostatic control zones. The HVAC zones are probably VAV terminals, VAV terminals with heating coils, and/or fan-powered terminals with a heating coil. This concept is what we call “down and dirty” and will most likely not satisfy many of the occupants’ space comfort.
A popular but very expensive office space renovation alternative is to engineer an underfloor air distribution (UFAD) that is very costly and complicated to install, but the benefit of this HVAC system brings the supply air directly to the occupant’s workstation. So why not think outside the box: take the UFAD design and place the concept into the ceiling plenum with my “above-floor air distribution” (AFAD) concept, and furnish and install individual ducts with flexible hose connections hanging down from the ceiling in the vicinity of the occupant? Many a retrofitted warehouse-to-office space has used the “exposed electrical system look” with light fixtures hanging down from above. Why not AFAD?
The occupant will have all the HVAC benefits of the UFAD approach, and the building owner doesn’t have to invest in a raised floor with its associated architectural, mechanical, and cost issues. The added benefit for the design team is to be able make an architectural statement using supply air hoses hanging down from the ceiling. When it comes to a floor space renovation these supply air hoses can simply be moved to an adjacent workstation location.
ASHRAE Standard 55 states that only 80% of a building’s occupants need to be comfortable to qualify as a comfortable building to work in. I’m not all that familiar with property managers sending out a survey requesting the occupants check off comfortable or not comfortable in their work environment, but maybe some commercial offices do this. Based on my experience, most property managers do not want to ask the question of space comfort in their building because of the number of complaints they will receive. Assuming the office building is 100,000 sq ft with 400 occupants, a comfortable building with 80 complaints (20%) would make this building in compliance with Standard 55. Eighty complaints seems to me to be a lot, and I’d question whether the majority of office buildings are OK with 20% complaints or maybe they just prefer not to know.
And what does this do to worker attendance and worker performance? There is a lot that goes into satisfying occupant comfort, so organizations like BOMA have come up with a three-class building definition with Class C “….competing for tenants requiring functional space at rents below the average for the area.”
Seems to me that my AFAD concept would do a lot of good in the Class C building, as well as for Class B buildings at no increase in the construction cost.
So I’m throwing down the gauntlet to those design teams who concentrate on the office building market, challenging them to create a better environment at no increase in construction cost. ES