Restaurant hood heat detector

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mopowr steve

mopowr steve

Senior Member
Location
NW Ohio
Occupation
Electrical contractor
Does anyone know what I should do about a heat detector with N.O. Contacts, the blueprints say to interlock with appliances but the problem I have is that the appliances are standing pilot only with the gas valve being only cable style actuated via the ansul system.
Im hoping that by just connecting it to the horn/strobe and shunt trip breakers should suffice even though none of the appliances will be utilizing the receptacles under the hood. Or is there something I'm missing I don't have a NEC 96 book
 
mopowr steve said:
Does anyone know what I should do about a heat detector with N.O. Contacts, the blueprints say to interlock with appliances but the problem I have is that the appliances are standing pilot only with the gas valve being only cable style actuated via the ansul system.
Im hoping that by just connecting it to the horn/strobe and shunt trip breakers should suffice even though none of the appliances will be utilizing the receptacles under the hood. Or is there something I'm missing I don't have a NEC 96 book
Click to expand...

You are still on the 1996 NEC?:blink:

When the heat detector hits it's limit the contacts close and do the job you want done, so in this case you want to cut power to the appliances.
 
LEO2854 said:
You are still on the 1996 NEC?:blink:

When the heat detector hits it's limit the contacts close and do the job you want done, so in this case you want to cut power to the appliances.
Click to expand...

Shunt trip breaker(s) is easy way to do this.

If it is not acceptable to leave the standing pilot burning you may need an electrically operated gas valve ahead of the pilot that gets shut down as well when everything else shuts down.
 
mopowr steve said:
Does anyone know what I should do about a heat detector with N.O. Contacts, the blueprints say to interlock with appliances but the problem I have is that the appliances are standing pilot only with the gas valve being only cable style actuated via the ansul system.
Im hoping that by just connecting it to the horn/strobe and shunt trip breakers should suffice even though none of the appliances will be utilizing the receptacles under the hood. Or is there something I'm missing I don't have a NEC 96 book
Click to expand...

Sounds like they will be adding an electric valve beside the manual one.
 
kwired said:
Shunt trip breaker(s) is easy way to do this.

If it is not acceptable to leave the standing pilot burning you may need an electrically operated gas valve ahead of the pilot that gets shut down as well when everything else shuts down.
Click to expand...
I think the bigger problem than the standing pilot is the fact that there is apparently no electrical component in the main burner control.
If it is purely a mechanical valve and thermostat, the only way to cut off the flame would be to introduce an electrically operated NO gas valve.
If the main burner has a thermocouple safety for the pilot flame it might be possible to find a relay which can work reliably to interrupt that voltage. But some thermocouple have totally enclosed (metal tube) wires, making that difficult if not illegal.
 
GoldDigger said:
I think the bigger problem than the standing pilot is the fact that there is apparently no electrical component in the main burner control.
If it is purely a mechanical valve and thermostat, the only way to cut off the flame would be to introduce an electrically operated NO gas valve.
If the main burner has a thermocouple safety for the pilot flame it might be possible to find a relay which can work reliably to interrupt that voltage. But some thermocouple have totally enclosed (metal tube) wires, making that difficult if not illegal.
Click to expand...

I was thinking more on the order of a main electrically operated gas valve, that is powered all the time, but on a shunt trip breaker so if called on to shut down you just energize shunt coil and loss of power closes (shuts off) gas valve.

Maybe there even is some kind of gas valve that can close when powered but needs manually reset to open again, but I don't like that idea from a fail safe approach, seems more likely that it may fail when it sits there for years and when finally called upon doesn't operate when energized. One that is energized constantly is likely to lose power once in a while and will remind you it is working when pilot needs re-lighting because the power was lost.
 
I have always activated the gas solenoid with the Ansul panel output relay. Why isn't the heat detector connected to the panel? All the ones I see are furnished with the hood. Ansul heads are just a nozzle - not like sprinkler heads. They need a heat detector to set off the panel and the panel should 1) open a discharge valve 2) close a gas solenoid valve and 3) activate the building alarm system. (It should also have a trouble supervisory output to the building system.)
 
JoeStillman said:
I have always activated the gas solenoid with the Ansul panel output relay. Why isn't the heat detector connected to the panel? All the ones I see are furnished with the hood. Ansul heads are just a nozzle - not like sprinkler heads. They need a heat detector to set off the panel and the panel should 1) open a discharge valve 2) close a gas solenoid valve and 3) activate the building alarm system. (It should also have a trouble supervisory output to the building system.)
Click to expand...

Its funny how different things are done around the country. The company I work for does literally dozens of commercial kitchen hoods each year and I have never seen any system like the one you describe.


What we have will be a hood with an ansul fire suppression system that is triggered without the use of electricity at all. There is a steel cable run under tension through the hoods that has melt out elements along it. If there is a fire the cable is released and that triggers the fire suppression system which also manually closes the gas valve supplying the under hood equipment

The Ansul cabinet will have a number of micro-switches connected to it. Generally the switches are used for the following.

1) Trip the fire alarm system into alarm

2) Signal the hood fan contrail panel that the fire suppression has been activated.

3) Open contractors or trip shunt trip breakers for power shutdown of under hood equipment.


Beyond that we also now install multi-gas sensors that stop the gas supply to the area if the sensors detect the wrong PPM of certain gases. These have to be wired to be manual reseting. They are not allowed to self reset when the gas sensors go back to normal.

In many cases there are air flow switches in the exhaust duct that also tie into the gas valve and contactors. No air flow (hood fan not turned on etc) than the cooking appliances cannot be used.

Its getting more complicated all the time and it provides many service calls for us.
 
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iwire said:
Its funny how different things are done around the country. The company I work for does literally dozens of commercial kitchen hoods each year and I have never seen any system like the one you describe.


What we have will be a hood with an ansul fire suppression system that is triggered without the use of electricity at all. There is a steel cable run under tension through the hoods that has melt out elements along it. If there is a fire the cable is released and that triggers the fire suppression system which also manually closes the gas valve supplying the under hood equipment

The Ansul cabinet will have a number of micro-switches connected to it. Generally the switches are used for the following.

1) Trip the fire alarm system into alarm

2) Signal the hood fan contrail panel that the fire suppression has been activated.

3) Open contractors or trip shunt trip breakers for power shutdown of under hood equipment.


Beyond that we also now install multi-gas sensors that stop the gas supply to the area if the sensors detect the wrong PPM of certain gases. These have to be wired to be manual reseting. They are not allowed to self reset when the gas sensors go back to normal.

In many cases there are air flow switches in the exhaust duct that also tie into the gas valve and contactors. No air flow (hood fan not turned on etc) than the cooking appliances cannot be used.

Its getting more complicated all the time and it provides many service calls for us.
Click to expand...

I agree, never seen that set up, only the one iWire refers to.

ME's are also specing FA intergration with low voltage CO sensors now. They want to dump a whole building, and kill the gas solenoid valve. A standard line powered CO that removes power from a 'gas valve control panel' that requires manual restart is enough.

No need to evacuate, it's crazy. The solenoid is fail safe, manual restart is required. Once the valve is closed, the problem has resolved its self. Owners/tenants are demanding a supervisory alarm only for a kitchen CO sensor when tied to the FA.
 
Folks, this detector has nothing to do with shut downs. It is there to provide a parallel means to turn on the exhaust fan if the kitchen staff forgets at start up. When the temp gets above the set point, the detector closes contacts to turn on the exhaust fan. The set up should lock in so that the exhaust fan doesn't "hunt" with the change in temperature in the duct or plenum where the detector is located.
 
iwire said:
I did not get that impression from the OP at all. :huh::?
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Me neither.

Most of time when I have had restaurant customer with exhaust fan problems, they are well aware they have fan problems, so forgetting to turn it on will give those same performance issues and they will be turning it on long before any heat detector in the hood would turn it on.
 
iwire said:
I did not get that impression from the OP at all. :huh::?
Click to expand...

I think if the OP goes back to his drawings, he'll understand the intent a little better with the aid of the following:

International Building Code, 2009 edition
507.2.1.1 Operation. Type I hood systems shall be
designed and installed to automatically activate the
exhaust fan whenever cooking operations occur. The
activation of the exhaust fan shall occur through an inter-
lock with the cooking appliances, by means of heat sen-
sors [bolded by me] or by means of other approved methods.​

Typically the only practical method to get this done is with a sensor (frequently Detect-A-Fire by Fenwal) in the plenum or duct that detects elevated temperatures and acts in parallel with the exhaust fan switch. You set it for some temperature below the melting point of the fusible links (most often 360F minimum). We've used 145F detectors.
 
gadfly56 said:
I think if the OP goes back to his drawings, he'll understand the intent a little better with the aid of the following:

International Building Code, 2009 edition
507.2.1.1 Operation. Type I hood systems shall be
designed and installed to automatically activate the
exhaust fan whenever cooking operations occur. The
activation of the exhaust fan shall occur through an inter-
lock with the cooking appliances, by means of heat sen-
sors [bolded by me] or by means of other approved methods.​

Typically the only practical method to get this done is with a sensor (frequently Detect-A-Fire by Fenwal) in the plenum or duct that detects elevated temperatures and acts in parallel with the exhaust fan switch. You set it for some temperature below the melting point of the fusible links (most often 360F minimum). We've used 145F detectors.
Click to expand...

I guess what is throwing me is that the OP said he had to interlock the heat dectector with the appliances not the hood.
 
gadfly56 said:
I think if the OP goes back to his drawings, he'll understand the intent a little better with the aid of the following:

International Building Code, 2009 edition
507.2.1.1 Operation. Type I hood systems shall be
designed and installed to automatically activate the
exhaust fan whenever cooking operations occur. The
activation of the exhaust fan shall occur through an inter-
lock with the cooking appliances, by means of heat sen-
sors [bolded by me] or by means of other approved methods.​

Typically the only practical method to get this done is with a sensor (frequently Detect-A-Fire by Fenwal) in the plenum or duct that detects elevated temperatures and acts in parallel with the exhaust fan switch. You set it for some temperature below the melting point of the fusible links (most often 360F minimum). We've used 145F detectors.
Click to expand...


You might be on to something,
I'll have to check the plans again I do recall the temp sensor shown on the plans next to the lines to exhaust fan. The diagram was more like a flow chart than a schematic of how things should be connected. Kinda confusing when they have lines going thru devices in series, joggles the mindset of looking at regular electrical drawings.
I hope you're right. They are showing heat detector set at 100*F. Seemed low for setting off horn/ strobe and shutting off appliances! Seems like your explanation makes sense. Don't know why the plans would say interlocked with appliances unless there referring to the appliances also having some kind of "in use" set of contacts to also turn on exhaust.
 
mopowr steve said:
You might be on to something,
I'll have to check the plans again I do recall the temp sensor shown on the plans next to the lines to exhaust fan. The diagram was more like a flow chart than a schematic of how things should be connected. Kinda confusing when they have lines going thru devices in series, joggles the mindset of looking at regular electrical drawings.
I hope you're right. They are showing heat detector set at 100*F. Seemed low for setting off horn/ strobe and shutting off appliances! Seems like your explanation makes sense. Don't know why the plans would say interlocked with appliances unless there referring to the appliances also having some kind of "in use" set of contacts to also turn on exhaust.
Click to expand...

Yes, that's the intent of the code section. Appliances on, exhaust on. With gas-fired appliances, it's very difficult to achieve the interlock directly. You could, I suppose, install a flow meter on the gas line, but rangeability is always a problem. That's why they allow the "heat sensor" option.
 
One more question,
Should it also turn on make up air as well as the exhaust?, (So not to create a negative pressure in building. The make up air is directed thru duct to the rear of appliances.) and would be energized during normal operation of a wall switch to turn on/off hood ventilation.

The ansul system will shut down make up air, trip shunt breakers, activate horn/strobe and close (cable actuated) gas valve. Sound good?
 
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