Fallout from “value engineering” spurs an idea about security and performance.
I recently ran into a project situation that got me thinking about a new criterion that owners may want to incorporate into their Owner’s Project Requirements (OPR) prior to starting design. The project was a four-story apartment building with a central ERV and exhaust system. Pre-conditioned 100% outside air was ducted into each of the apartments, while toilet exhaust was ducted out. Interbuilding pressure relationships were to be maintained by balancing each apartment to have constant airflows in and out. The main supply and exhaust ducts ran above the corridor ceilings with takeoffs into each apartment and with both airstreams passing through a rooftop energy recovery unit.
Energy conservation was a well-documented and well-understood top priority for the owner, thus the relatively pricey ventilation system. At the same time, the owner had a strict budget with which to construct the building. By the time the design was reconciled with the budget (can you say “value engineering?”), neither the exhaust nor supply air system contained balancing dampers in the takeoffs to individual apartments.
Without going into all of the painful details of that decision, the justification for not needing volume dampers in the ducts was the fact that airflow at the individual units could be balanced via the opposed blade dampers at each supply and exhaust register. I was not privy to this decision when it was made and am not sure if the issue of potential noise was mentioned to the owner. Even if it was discussed, I would bet there was no quantitative information about how “noisy” some registers might be.
As should be expected, balancing the system was quite challenging and resulted in register dampers being fully closed at the end of the corridor closest to the duct risers and fully open at the other end. The leakage alone through the closed dampers was enough to meet (or exceed) the design airflows in those apartments. As you can imagine, the noise was objectionable to the residents and they began (1) complaining and/or (2) manually adjusting their own opposed blade dampers to reduce the noise.
Neither of these two resident reactions was acceptable to the owner, nor were they surprising. In the first case, the owner/landlord concurred that the noise was not acceptable for someone’s home. In the second case, some tenants were manipulating the system to the detriment of other tenants, i.e., those at the far end of the corridor whose ventilation and/or exhaust air was taking the route of least resistance through other people’s apartments. Also, with the tenant-adjustable dampers, the internal building pressure relationships between apartments and common areas were thrown out of whack, resulting in undesirable shared odors.
This is what got me thinking about the OPR. Based on this experience, I recommend that owners consider documenting a design criterion that requires all systems to be reasonably tamper-resistant by untrained building occupants or users. Clearly, this does not apply to system features intended to be adjusted by occupants (e.g., thermostats, fan speeds, etc.). However, it would apply to all elements of a system put into place in order to achieve other criteria defined in the OPR.
For example, in the case of this project, the vulnerability of the opposed blade dampers in the apartments put the intrabuilding pressure relationships at risk while it also put the minimum ventilation criteria at risk in some apartments. To a certain extent, it also resulted in the air balancing and commissioning testing having a very short-lived benefit. Why bother paying for those services if the residents can so easily mess up system performance?
In summary, this is really about maintainable performance. The best word would be “sustainable,” but that conjures way more baggage than intended here. In many cases, it does involve maintaining original energy conservation or waste reduction performance, but it also involves maintaining all other owner performance requirements including IAQ, temperature and humidity control, and system reliability throughout the life of the systems. ES