Building pressure testing
The primary task of facility managers is to achieve the optimal performance of the building under management. Achieving this requires the effective control of a web of components and systems such as HVAC. The starting point for achieving the optimal level of control doesn’t lay in the components themselves but in understanding the environment to be optimized. Building pressure is one aspect of this.
Building pressure, also known as air pressure, should be tested by facility managers as a foundational step when optimizing a building. This testing provides the metrics by which to judge your success and alert you to issues that need to be addressed.
Pressure testing determines what’s known as the “tightness” of the building, meaning its air permeability or air leakage rate. All buildings suffer from normal leakage to some extent as air inevitably escapes through the gaps, holes, cracks, or other faults that are unavoidably present in the fabric of the building itself. When these become excessive, the building’s energy efficiency has the potential to become severely impacted with predictably negative consequences - not the least of which is that the facility becomes more expensive to run. That’s the last thing facilities managers want.
Why testing is a prerequisite
All this being the case, it’s easy to see why air pressure testing must be a prerequisite, which is underlined by the reality that failing to maintain air tightness can result in as much as 40% heat loss. Given that facilities invest increasing sums in pursuit of energy efficiency, imagine investing in commonly seen steps such as installing a new boiler or adding extra insulation, then failing to accrue the benefits of these investments due to air leakages. Be clear: if the building isn’t tight, that’s what will happen.
So, what’s involved in building pressure testing? For a start, it’s important to understand that all buildings have some level of pressure, either positive or negative. The ideal is a positive pressure of about 0.02-in/w.c. and assuring this generally involves introducing fresh or outside air into the facility.
Outcomes in numbers
Let’s see how pressure works by numbers. For example, operating a 1,200 cubic feet per minute (CFM) fan that returns 200 CFM through an outside air duct will only pull 1,000 CFM from the building itself, even though the fan’s supply side delivers the total 1,200 CFM. In other words, there’s a discrepancy between return and output which, in this case, causes a 200 CFM positive pressure within the facility. This being the case, the imbalance would be described as the building being under positive pressure.
Of course, as we suggested earlier, it’s the job of the facilities manager to optimize the building’s performance and eliminate this issue. Still, they can’t do that (because they won’t be aware of the problem) without first testing. Think of testing as mandatory because it’s not possible to guess with any degree of accuracy what sort of results testing will yield as so many facets define building pressure; the tightness or leakiness of the building itself is just one; what pressure generating forces exist within it such as wind, appliances, fans, exhaust systems, and more all which are both invisible and variable.
An interesting wrinkle
There’s another interesting wrinkle, too. Testing can reveal not only the pressure within the building but also differences from room to room. This is important because it determines the impact of an HVAC system on the building’s overall performance, and HVAC is another element of the building that can be optimized according to the results of pressure testing.
Although pressure differences between rooms present a slightly different issue to overall building pressure itself, they’re nevertheless related. Room pressure is essential because it significantly contributes to whether the environment in any particular location is comfortable and whether air quality is of the standard required. In commercial properties where the productivity of the occupants is required, this matters a great deal.
If testing reveals a room with negative pressure, likely the cause will be too much outside air being drawn in through structural leaks. If the readings are opposite and indicate high positive pressure, conditioned air is likely leaking from the building, creating discomfort for the occupants. In either case, the facilities manager will only be able to take remedial actions once aware of testing results.
Health and safety considerations too
There’s also another reason why pressure testing is necessary: health and safety. For example, rooms with negative pressure yet which house combustion appliances could lead to injury or even death due to carbon monoxide poisoning. Conversely, in some commercial facilities, rooms containing cleaning fluids or chemicals (for instance, a hospital or a manufacturing plant) must be kept under negative pressure to avoid fumes polluting other areas of the facility.
Pressure testing and HVAC
As we noted earlier, for facility managers an optimally performing HVAC is a key contributor to energy efficiency due to the scale of investment in the HVAC system. Pressure testing enables optimization. Once you’ve measured the supply and return registers in a room or facility and compared them to each other, you’ve discovered the effect of the HVAC system. If the supply CFM exceeds the return, the pressure from the system fan is positive - or vice versa if the reverse is the case. In either eventuality, steps to optimize performance can be taken based on the results yielded by the pressure test.
The NexRev advantage
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