Automatic Fire/Smoke Dampers 2

[TomFitz]

In the Unified Facilities Guide Specifications, Paragraph 2.12.4 states:
"Pressure drop in the damper open position shall not exceed 25 Pa 0.1 inch w.g. with average duct velocities of 13 meters per second 2500 fpm".

Are there manufacturer's who actually comply with the .1 inch w.g. requirement at 2500 fpm? The manufacturer's that I have checked, "Ruskin" and "Safeair", only comply at 2000 fpm.
Thanks for any assistance..

TomFitz

 

[ChasBean1]

Here's another example of specifiers outstepping their bounds. If we make it big enough, maybe we won't approach these limits(?) That said, UFGS does military specs, and size becomes an issue when you cram stuff into a sub...

Anyway, looks like this one might fit the bill:

http://www.ncamfg.com/CATALOG-PDF's/D-Fire-SmokeDamper-PDF's/A--FSD-AF-S-211.pdf

 

[TomFitz]

Thank You!
I appreciate your reply..
I'll check it out

 

[friartuck]

Sorry I came late in on this one. Are we talking fire.smoke or volume control.

If you are talking about smoke/fire dameprs, we use Actionair Ltd dasmpers. These are rated for 4 hours and are completely out of the airstream so the PD is zero (apart from a bit of turbulence at the connections)

If you are talking about volume control, then the spec appears a bit severe and I wish you luck. (Actionair also do aerofoil VCD's but I would be surprised if the PD was as low as 25Pa at 13m/sec

Friar Tuck of Sherwood

 

[lilliput1]

That pressure drop does not seem reasonable. SMACNA estimates pressure drop on fully open parallel or opposed blade damper to be 0.52 x the velocity pressure.
Thus foryour case PD = .52 x (2500/4005)^2 = 0.203 in. w.g.

 

[boonng]

May I know how does a combination fire/smoke damper works? As I know, combination fire/smoke damper is coupled with a fusible link and an actuator. If there is fire, the fusible link will fuse off and the damper blade will be closed by means of tensioned spring. But, can the actuator open up the damper blade again if if receives a signal from smoke detector? The actuator has to overcome the spring force to open up the blade, is it possible? If not, how do the fusible link and actuator work together?
Thank you.

 

[friartuck]

Generally the damper will need a manual reset so an access door has to be fitted adjacent to the damper to allow you to reset it.

Friar Tuck of Sherwood

 

[quark]

Why should the damper open up if it receives signal from smoke detector? In both cases, either smoke or fire dampers, the damper should be closed. It should be opened only after you rectify the source of smoke. Note that a fire damper also senses smoke and the link fuses depending upon the temperature of the smoke.

The main difference between a smoke and a fire damper is the amount of leakage permitted.

There are automatic motorised fire/smoke dampers available which open and close taking signal from smoke detectors.

Regards,

 

[boonng]

I received an email regarding combination fire/smoke damper. But I doubted the explanation. Could anyone give me some ideas about the following explanation? Is it correct?

The concept of fire/smoke damper is derived because it was realised that alot of time people died because of smoke rather than the fire. Therefore there is a need to decide whether to open or close a fire damper when there is a fire. In the old day or in design where you only have fire damper, the dampers will be closed when the fusible link break, and that is it, no more movement, and the fire dampers support to remain closed and blocked the air, which is sometime wrong. A fire/smoke damper allowed the control station to decide if certain area need to discharge the smoke, and thus fire damper need to be open again. Therefore the actuator of the fire/smoke damper selected need to be able to have a torque that can override the spring force to open the damper again.

But I doubted the above explanation. Could anyone give me some ideas about the above explanation? Is it correct? Thank you.

 

[jsummerfield]

I too don't like the description but I am not an HVAC expert.

With an automated damper the control system can determine whether or not to close the damper based upon other room fires. Perhaps you shutdown fans and close the damper to minimize smoke from other room fire. Perhaps you leave most dampers open, close recirculation and open additional inlet and open exhaust dampers to remove smoke.

I think that the fusible link will cut the air-supply from an actuated damper, thus closing the damper if the room exceeds that temperature, such as 70 degree C.

I too would like to see comments from others about the explanation; and comments regarding my impression as well.

John

 

[friartuck]

Fire dampers generally operate with a fusible link and only when the temp has risen sufficient ly to operate it. In a real fire, smoke can be quite cool and consequently will not operate the thermal link...hence you die.

Smoke dampers are smoke tight (unlike fire dampers which are not certified smoke tight).

as an example, If you are using a fan to extract smoke from a fire, it would be crazy to size the fan to evacuate the whole building when the fire is only on the first floor. Hence the smoke dampers safely close off the areas that are not affected and the damper serving the smoke laden are is operated to exhaust the smoke.



Friar Tuck of Sherwood