On these projects, the fans are used for normal exhaust only. They are to shut down on fire (sprinkler or alarm manual call point.) We have found a document which highlights the concerns, which we agree are valid concerns to have: • Disturb the smoke layer • Spread smoke • Affect sprinkler operation • Fan the fire • Activate wrong sprinkler heads • Spread fire to adjacent cars • CO generated during the fire will cause jet fans to increase flow output (where applicable)
But are they just perceived or are they real? Is the extent of the impact actually significant and much worse than a traditional HVAC ducted system? For those of you who like numbers: One building carpark, 37 x 23m (120 x 75 ft), has 1 supply/make-up air fan 2050 L/s and 2 Jet fans at low speed - 12N thrust. 2.6 air changes per hour. - HVAC Modelling shows velocity at chest height (for purposes of breathable air quality) as typically being less than 1.5m/s (5 ft/sec). it does not appear to exceed 3 m/s. 4 other building carparks (typical), 35 x 18m (115 x 60 ft) have natural ventilation with one inlet grille and one exit grille, plus one low speed Jet fan. No air changes calculated with natural ventilation. - HVAC Modelling shows velocity at chest height (for purposes of breathable air quality) as typically being less than 1 m/s (3.3 ft/sec). it does not appear to exceed 2 m/s. I have asked if it is possible to produce velocity information at sprinkler height... Spending NZ$15-$20,000 on aspirating detection for each building seems excessive if the effects of the jet fans are not significant. Is an on-board/duct detector adequate? Or is it prone to false alarm and shut down when it should be operating to keep air quality safe? Nicky Marshall Southern Regional Manager PROTECH DESIGN LIMITED Specialist Fire Protection Consultants Phone: +64 (0)3 579 5577 extn 2 Mobile: +64 (0)21 433 488 Email: [email protected] Skype: nicky-marshall Web :www.protechdesign.co.nz Address:105A Alabama Rd, Redwoodtown, Blenheim 7201, NZ Postal: PO Box 4022, Redwood Village, Blenheim 7242, NZ “I always wondered why somebody doesn't do something about that. Then I realised I was somebody” Lily Tomlin -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Tuesday, 15 August 2017 12:32 PM To: [email protected] Subject: Re: Jet/impulse fans I will check your links tomorrow Nicky- they look interesting. I've worked on several systems in Qatar. Qatar Civil Defense has very detailed requirements for fire modeling these systems, and negative impact on sprinkler activation is not mentioned. These small impulse fans direct the car exhaust toward the huge exhaust shafts as part of normal operation--- they have two speeds-- normal and emergency. The 10m/s is the emergency speed. If a signal from a flow switch is used kick them to emergency speed, the sprinklers already activated. Brad Quoting Nicky Marshall <[email protected]>: > Are Jet/impulse fans installed in basement carparks a serious concern > to the successful operation of sprinklers? > > Example of the fans: > http://www.fantech.com.au/FanRange.aspx?AppID=P2&RangeID=2021 which > also discusses some installation recommendations with regards to > sprinklers. > > We are starting to see more of these installed in basement carparks as > a cheaper option to ducted systems. > The velocity is around 10 m/s (32 ft/sec) at the fan discharge point. > But 1-2 m/s at chest height over car park areas. > Obviously this impacts air and heat movement and sprinkler operation. > But if they are installed in drive lanes only (where there is no fire > load) and shut down as soon as one sprinkler operates, is the risk > largely mitigated? > FM Global data sheets only discuss air velocities for storage > sprinklers. It appears to be silent for non-storage sprinklers. > I cannot find anything in NFPA 13. > New South Wales Australia, the Fire Service are asking for additional > smoke detection to shut the fans down (unless fire modelling shows it > is acceptable). Is this really necessary? > https://www.fire.nsw.gov.au/gallery/files/pdf/guidelines/impulse_fans_ > in_carparks.pdf There was also a case study done based on fire > modelling. > http://www.sciencedirect.com/science/article/pii/S2214398X13000034 , > but every building and system is different... > > We agree that it needs to be considered, but are unsure that an > additional detection system is necessary. > Your thoughts and input appreciated. > > Nicky Marshall > Southern Regional Manager > PROTECH DESIGN LIMITED > Specialist Fire Protection Consultants > Phone: +64 (0)3 579 5577 extn 2 Mobile: +64 (0)21 433 488 Email: > [email protected] Skype: nicky-marshall Web > :www.protechdesign.co.nz Address:105A Alabama Rd, Redwoodtown, > Blenheim 7201, NZ Postal: PO Box 4022, Redwood Village, Blenheim 7242, > NZ > > "I always wondered why somebody doesn't do something about that. > Then I realised I was somebody" Lily Tomlin > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkl > er.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
