We prefer wet-pipe sprinkler systems over dry-pipe systems for a handful of reasons: lower cost, no pipe slope requirements, potentially less points of drainage, can locate inspection & testing at the riser, less maintenance, testing and inspection requirements, no power needs, less noisy, and much less potential for corrosion.
However, when dry systems are needed, there's several issues to consider for the end-user.
For owners who are not associated with the intricacies of design and maintenance of dry systems, the most frequent compliant we hear about is with the noise associated with the dry system air compressors.
Dry-pipe systems are fed with pressurized air by a compressor. The compressor run-time frequency and duration is directly attributed to the amount of leakage in the system. Some people directly attribute the leakage of the system to the quality of installation due to the final tightness of fittings.
Air injected into a leaky system develops two problems. The first is increased potential for corrosion as fresh air naturally contains water moisture and oxygen, the two ingredients for corrosion. Air that feels comfortable to us offers sufficient products to encourage corrosion, and leaky systems tend to fail with corrosive issues much earlier in their lifetime.
The second issue is noise. While it sounds trivial, noise isn't for the employee whose cubicle is next to the riser room.
If leaky systems cause issues, why don't contractors prevent or fix leaky systems?
Fixing Leaky Systems
Once a system is installed and pressure tested to meet minimum standards, finding points of leakage is very tedious and time consuming. Just finding a few leaky fittings requires inspecting every joint and adjusting connection points. Needless to say, if a system isn't installed with tight fittings it becomes a very time-intensive and costly proposition to fix.
Lessening Leakage and Noise in Design
As a designer I naturally have less impact on the quality of installation than I do of the design, and there are several ways to help lessen the impact of leakage and noise.
Leakage requirements could be mandated to be leak less than prescribed code minimums. I've found this route doesn't exactly make good friends of contractors.
Noise can be reduced in a number of ways. First is to use tank-mounted air compressors in lieu of riser-mounted air compressors. Tanks act as a pressurized reserve, where they can reduce the frequency which compressors run in order to supply the system. Mounting to the tank also vibrates the tank, and not the piping network that runs through a building. Vibration on the pipe network requires absorption by the building, which contributes to higher ambient noise. The base of the tank can be isolated with vibration isolation (often rubber pads), again helping to reduce vibration transmission to the building. The downside to tank-mounted compressors is an increased cost and needs for additional floor space.
Another important consideration is where the compressor is located. Often the allotted space for risers are determined architecturally, but upfront coordination and planning to help prevent locating dry riser rooms next to normally occupied spaces can have major benefits. If the dry riser room must be near occupied spaces, consider requesting insulation within walls or acoustic panels to help absorb sound.
Quiet-Series Air Compressors
Lastly, one of my favorite products to hit the market in the last couple years offers a major solution to the noise issue. I'll start by saying I don't have any family or friends that work for General Air Products. They have not reached out to me to offer any money (although if you're out there General Air I'd be happy to share an address for a check). That disclaimer aside I really love the Q-Series (Quiet Series) General Air Compressors for fire sprinkler systems.
The Q-Series air compressor model can be tank-mounted and is significantly quieter than standard air compressors. The noise for the Q-Series have reduced noise by 20 dBA from the previous 80 dBA of standard oil-less compressors. For drywalled, carpeted rooms the effective sound from the Q-Series compressor is only slightly higher than ambient noise levels of a typical office.
The video above (by General Air) shows the difference in compressor noise. Needless to say it would be great for applications in hospitals, schools, offices, hotels, retail, nursing homes, and other areas sensitive to noise. We've found these to be a great solution to a common and intrusive issue of noise with dry risers near occupied spaces.
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Joseph Meyer, PE, owns/operates his own Fire Protection Engineering practice in St. Louis, Missouri. See bio on About page.