Fan shutdown???

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Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
Fan shut down is a bit fuzzy to me. When a smoke duct detector says it is to be wired so as to shutdown the hvac unit/fans how is that done. I sometimes hear "status" "control" terms thrown around. Is that in reference to this. Is there some good reading on fan shutdown that would give me a good overview?

Thanks.
 

steelersman

Senior Member
Location
Lake Ridge, VA
your 2 conductor fire alarm cable should connect to a normally closed contact on the duct detector and be run through the auto side of the hand-off-auto switch if that applies or the safety or permissive point in a VFD.
 

quogueelectric

Senior Member
Location
new york
Fan shut down is a bit fuzzy to me. When a smoke duct detector says it is to be wired so as to shutdown the hvac unit/fans how is that done. I sometimes hear "status" "control" terms thrown around. Is that in reference to this. Is there some good reading on fan shutdown that would give me a good overview?

Thanks.
Fan shutdown is usually accomplished by a relay within 3 ft of the unit breaking the control ckt or to a fire point in the unit logic module. Status is just a feedback loop indicating status of fire dampers or fan ct switches fan running or fan off status. Outside air damper open or closed you dont want to run a fresh air intake fan with the dampers closed. Ask me how I know??
 

480sparky

Senior Member
Location
Iowegia
Fan shutdown is usually accomplished by a relay within 3 ft of the unit breaking the control ckt or to a fire point in the unit logic module. Status is just a feedback loop indicating status of fire dampers or fan ct switches fan running or fan off status. Outside air damper open or closed you dont want to run a fresh air intake fan with the dampers closed. Ask me how I know??


OK... "How do I know?"
 

nakulak

Senior Member
most modern hvac units have an estop or shutdown terminals for exactly this purpose. they have a factory jumper on these two terminals for the express purpose of shutting the unit down completely by use of a firestat, duct detector etc NC terminal set. This is generally better than any other alternative, since the factory shutdown is designed to shut down everything controlled by the unit - auxilliary dampers, fans, economizer inlets, multiple stages, etc.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
your 2 conductor fire alarm cable should connect to a normally closed contact on the duct detector and be run through the auto side of the hand-off-auto switch if that applies or the safety or permissive point in a VFD.


Is a fan permitted to run on "hand" even in an alarm condition?
 

iwire

Moderator
Staff member
Location
Massachusetts
Is a fan permitted to run on "hand" even in an alarm condition?

I believe yes if part of a purposely designed smoke evacuation system. I would not wire it that way unless clearly shown that way.

If the unit I am shutting down does not have terminals for shut down already I generally interrupt the ungrounded secondary of the units control transformer.

But as nakulak pointed out many times there are now terminals already assigned for shutdown, the odd thing is many of those factory installed shutdown terminals are wired IMO backward, they must be closed to shut the unit down so they are not fail safe.
 

steelersman

Senior Member
Location
Lake Ridge, VA
Is a fan permitted to run on "hand" even in an alarm condition?
well you're probably right in asking me that. I have wired stair pressurization fans that were suppossed to still run in the event of a fire alarm. This makes sense as the elevators always shutdown when there is a fire alarm. You wouldn't want the smoke entering the stairwells so those fans would still be acceptible to be running.
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
well you're probably right in asking me that. I have wired stair pressurization fans that were suppossed to still run in the event of a fire alarm. This makes sense as the elevators always shutdown when there is a fire alarm. You wouldn't want the smoke entering the stairwells so those fans would still be acceptible to be running.



I was just refreshing my memory as I haven't wired a fan shutdown in 10 years. It justs seems strange to require a fan to be shut down in an alarm condition but allow the same fan to run in an alarm condition if someone turned the HOA to hand.
 

iwire

Moderator
Staff member
Location
Massachusetts
I was just refreshing my memory as I haven't wired a fan shutdown in 10 years. It justs seems strange to require a fan to be shut down in an alarm condition but allow the same fan to run in an alarm condition if someone turned the HOA to hand.

You have never had to install a panel full of HOA switches beside the FACP for the FD to override the duct smokes?
 

steelersman

Senior Member
Location
Lake Ridge, VA
I was just refreshing my memory as I haven't wired a fan shutdown in 10 years. It justs seems strange to require a fan to be shut down in an alarm condition but allow the same fan to run in an alarm condition if someone turned the HOA to hand.
well honestly I can't remember how we wired it. I do think that most of them were set up to not run at all in an alarm condition. Most of the ones I deal with are not hand-off-auto switches. They are mostly addressible logic controllers that we have a number off analog and digital inputs and outputs wired into. And actually usually the EC does the fire alarm wiring or at least pulls it and usually lands it in our control panel, but sometiimes we land it for them. And it is simply landing on a relay and from there the controller does the rest.
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
You have never had to install a panel full of HOA switches beside the FACP for the FD to override the duct smokes?


From what I remember the last smoke purge system I was involved with used modules and relays at the fan starter to operate smoke purge fans from the FACP. A remote fan starter couldn't keep the fan running if someone left the HOA in the hand position during an alarm condition. I'm not saying that's the only way to perform the operation but based on my sketchy memory that's how we ran the fans during a purge condition.
 

iwire

Moderator
Staff member
Location
Massachusetts
From what I remember the last smoke purge system I was involved with used modules and relays at the fan starter to operate smoke purge fans from the FACP.

That is also common here, but another common way to go is a panel full of HOAs located at the FACP. They will have a keyed 'enable' switch.

I like the addressable module route much better, less wiring.:smile:
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I like the addressable module route much better, less wiring.:smile:

Yup, an addressable loop to the 10th floor machine room would be a lot less wiring than bringing the HOA conductors down and back up from the lobby. ;)
 
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