Smoke detection and poisitive input ventilation

[a1colly]

PIV (positive input ventilation) unit sited in attic space and ducted through ceiling in hallway. Smoke alarm sited within ceiling area. I am aware of manufactures instructions for distances for the unit being installed with their standard grill, however if you were to install such a unit with a standard diffuser such as supplied for a MVHR what would you consider to be an acceptable distance between the two. Also what about cubic volume for the area for smoke detection, with an input of 20 to 30litres per minute?

 

[Anthony S]

PIV (positive input ventilation) unit sited in attic space and ducted through ceiling in hallway. Smoke alarm sited within ceiling area. I am aware of manufactures instructions for distances for the unit being installed with their standard grill, however if you were to install such a unit with a standard diffuser such as supplied for a MVHR what would you consider to be an acceptable distance between the two. Also what about cubic volume for the area for smoke detection, with an input of 20 to 30litres per minute?

Iv'e fitted a piece of foam that comes with the PIV kit to close off the air in the direction of the smoke alarm. In my house by the way.

450mm edge to edge - Note: This is not a guide for the op to use, its part of my set up.

 

[tazz]

Then there are 2 things which you need to consider here, positioning detectors away from the grill and more important full shutdown of the PIV. Problem with extracting or input air under pressure, is that smoke can not naturally rise to the detector....it will be either be extracted passed the detector or forced into a side wave, past the detector, as it finds lower pressure. So conclusion without PIV shutdown, the detector will fail to operate in a fire condition.

 

[tazz]

Iv'e fitted a piece of foam that comes with the PIV kit to close off the air in the direction of the smoke alarm. In my house by the way.

450mm edge to edge

Suggest you conduct a simple test....buy a 20gram smoke test pellet, set off in an old tin. You will be able to see the smoke path, and more importantly test weather the detector is not bypassed.

 

[test electrical]

It should say on the installation instructions, but they can be misleading.These fans blow air in to the building from the roof space at a slow rate.Smoke will get up to the upstairs ceiling with out much help,the problem is that your smoke detector should go were the fan grid is. And if you go to close to a wall your in dead air space and if you go with in a meter of the fan your in a positive pressure zone. Keeping with in manufacturing and the regs the only cure I found was to put two detectors in ideally the fan grid should go over the stairs in the middle of the landing but its cheaper than putting scaffolding up.Hope this helps!

 

[a1colly]

Cheers both, yes the standard diffuser comes with foam to eliminate this issue but due to the small area the standard grill isint suitable.

tazz as always sound advise, my concern is that without detection the unit won't shut down as the detection is only in the areas wher the ventilation wil take place. Time to go back to the housing association and quote for additional detection within the prooerties

 

[tazz]

With all respect Test.....I hope you have proved it works with 2 detectors

 

[tazz]

Can I ask...Are we talking about a domestic dwelling, How many floors, where grill is situated,

 

[Anthony S]

The PIV is well positioned and working a treat with a very slow rate of air. Smoke Alarm is well positioned is relation to air flow and walls etc.

The landing is not massive and I can always fit smokes in bedrooms if I felt I needed to. Non smokers, rewired, re-plumbed, Gas checked, Boiler serviced, house completely re-furbished from top to bottom, all new appliances.

Tazz and I will take on board your advice with regards the smoke pellet to see what direction the smoke takes and I have the option foam insert adjustments and speed control.

Thanks

 

[tazz]

Hope this has helped....As this can be very misleading when dealing with extract or pressure, and alot of installers miss this problem, which can result in serious problems. I have seen extractor ducts suck up smoke quickly in fire conditions without touching the smoke detectors, and duct fans push an fuel fires again away from the detection. It needs some careful thought and planning with manufactures, BC and and simple proof tests.

 

[Engineer54]

Hope this has helped....As this can be very misleading when dealing with extract or pressure, and alot of installers miss this problem, which can result in serious problems. I have seen extractor ducts suck up smoke quickly in fire conditions without touching the smoke detectors, and duct fans push an fuel fires again away from the detection. It needs some careful thought and planning with manufactures, BC and and simple proof tests.

Better off installing duct smoke detectors in the extract duct then, which i would have thought was standard practice where HVAC or forced air ventilations systems have been installed....

 

[tazz]

E54 this is positive air input, if extraction would agree.

 

[Engineer54]

E54 this is positive air input, if extraction would agree.

Before my second morning coffee mate, so crossed thoughts on my part i'm afraid!! That or reading too much into your reply that was quoted....

 

[marc8]

Hi all
bit of topic here last year was installing MVHR unit for customer they supplied new house, I know you can get fire collars but I had moment when I considered what should happen should there be a fire, should the MVHR unit shutdown or remain in operation after all with all the combustable material in a house timber frame & the heat recovery brining in fresh air in other words fuel to the fire.
Spoke with manufacturer of the system about this they said down to system installer & they would not commit either way,
we had put heat detector in loft next to unit & relay base installed & stopped the system at least I won't feed the fire. We set this up to restart when alarm silenced. Going forward I thought more about this & would put a reset button in so that client would have to reset.
What are your thoughts on this ?

 

[a1colly]

I do what you have done, don't bother with a manual reset as they won't remember after two weeks of moving in