Heat recovery ventilation linked to smoke alarms

[sparkol]

Hi! I'm installing some interlinked smoke/heat alarms. The customer wants it so that when the alarms are activated it cuts off the power supply to his heat recovery ventilation system (so it doesn't keep trying to replace the smoke with clean air, which would effectively be fanning the fire!).

Anyone done this before? If so, how? I'm not particularly bothered which brand of alarms I fit, but the HRV system is a Regavent, if that helps.

Thanks in advance.

 

[Marvo]

This isn't the kind of thing I would do to a customers specification, only to the HVACR engineers spec. For every action there's a reaction and shutting off the heat recovery unit may cause an unwanted pressure change elsewhere that may cause the fire to spread in an unwanted direction. HVAC systems are designed to contain fires in certain areas by pressurising surrounding areas and by doing so escape routes are maintained and smoke free zones are created. There's many considerations before undertaking jobs like this.

 

[Gazthesparky]

It can be done with a relay and contactors but as stated there's more to heating and ventilation so there's lots to consider before doing it

 

[sparkol]

Thank you for the replies, which are very helpful.

Here's a bit more info:

The 'customer' is my mum and dad. They are doing a self-build and my dad is designing the MHRV system himself, under the watchful (or perhaps not so watchful) eye of building control. It is a 3-bed cottage consisting of ground floor plus one bedroom in the loft space. There will just be one MHRV unit, and ducting to each room. My dad (the 'designer') tells me that the MHRV system should cut off when the smokes are activated. He may be right or he may be wrong but my understanding is that, overall, it is generally better if the system does cut out.

Follow up questions:

1. Would you wire it so the supply does cut out? If so, how?
2. Would I be better asking this question on an HVAC forum?
3. Should I be insisting my folks get an HVAC engineer in - please bear in mind this is my mum and dad, so in this case it's not about covering my backside, it's about reaching the pragmatic and correct solution.

Thanks!

 

[Marvo]

I don't know how the building control thing works in the UK, maybe they have an engineer you can consult with regarding compliance with the appropriate fire regs. If not I'd certainly consider getting an engineers opinion on you installation design.

*Edit* Maybe the suppliers of the heat recovery unit would be able to point you in the right direction, many large suppliers have a designer or sales engineer who's qualified to advise on best practice design and installation proceedures.

 

[a1colly]

Hi get your dad to contact a company in South Wales called neuair. They manufacture Ventalation and heat recover units but more importantly have an amazing tech team who are always willing to help anyone with design concepts. Personally as a domestic Ventalation engineer for six years now, you don't normally wire the MVHR units to shut down in the event of a fire, the same as electricians we don't fit fire switches in a domestic installation as its over kill.

As a few pointers for him on design, design it in rigid round PVC not flex and of at least 6" dropping to 5" at worst case. Keep bends to a minimum where possible and avoid flat ducting as will creat whistles through the terminals. If you have to use flexi ducting pull as taught as possible to maintain air flow rates. Remember import an export ducts to atmosphere will require wrapping in insulation to avoid condensation and any dusting through cold zones will also require wrapping.
Also, think of air volumes as required by part L of the regs and get him to check with the building inspector to see what commissioning he will require as the testing gear is several hundreds pounds and either has to be signed of by the inspector or by a governing body such as Napit by an approved installer.

If he has any questions drop me a pm always happy to help out where I can

 

[Engineer54]

I'm sure if you contact the system manufacturer ( Regavent) then i'm sure they can give you all the guidance you need...

The practice of shutting down AHU's and exhaust fans via fire alarm panels and/or BMS systems is pretty much standard in the much larger commercial/industrial systems that i am used too. Your fathers idea makes perfect sense, but as others have stated, check the Part L domestic requirements and any manufacturers instructions recommendations etc....

 

[tazz]

Good advice so far from all......commercially there is always an option to control ventilation manually or automatically from the fire alarm via a firemans overide switch....the idea with this is the fire alarm will shut it down, and once the fire is out, the fire crew manually turn it back on to vent the building of smoke.
So to your question of domestic shutdown, yes most mains linked smokes have relay modules you can use, Aico, or Firedex can supply these through most electrical counters, and could be adapted with manufactures advice. Although domestic, maybe good idea to adopt the overide issue with a labeled switch near the front entrance.