Communally Ducted Ventilation Systems: Smart Smoke Protection and Automatic Mechanical Balancing

Communal ducting servicing numerous dwellings are widespread across the country, and although have their benefits, can also lead to issues. The main issues being faced are; smoke spreading through the ducting, with the possibility of smoke migrating into other dwellings; and the balancing of the system, especially when updating the mechanical parts.

Smart Smoke Protection

The systems built in the 60’s and 70’s often include downward facing shunt ducts, based on a theory that smoke and hot flames cannot travel against their natural upward path, therefore would not enter into any dwelling by the branch. It was also possible for many shunt ducts to be fitted with either fusible links triggered dampers or intumescent grilles or collars, which would be activated by a high temperature caused by a fire. These ideas do have some warrant, however, due to recent events, it is clear that while a fire may cause more damage to the dwelling, it is the smoke which can lead to the loss of life.

Whilst the ideas mentioned above do have merit, they are based on the assumption that are no longer relevant. Some of these are:

1. The ducting would be kept in pristine condition, with periodic cleaning by the landlord. The cleaning of the duct is a time consuming and intrusive process for residents. In practice this is not possible. Cleaning of the ducting is an expense and demand that is readily overlooked. This leads to a build up of dust, grease and detritus, this in turn produces a fire risk, allowing flames to spread through the ducting shafts.

2. The fan motors would be regularly serviced and maintained through the life of the property, with the motors being changed on a regular basis. In most scenarios, the fans may be serviced for the first few years after installation, as part of a maintenance plan, however after that they would not be looked at until another service plan. This would mean for long periods, the motors would be seized up and rusted, or possible vandalised, this would lead to little or no extraction within the riser, leading to dampness related repairs and expenditure by the landlord.

3. Residents would be educated to how the system works, provides protection and allows for a better air quality within their dwelling. Major factors that are often misunderstood or not told to the residents include; how the centralised fan system is powered by the landlord supply and how the ventilation reduces the risk of condensation related issues. The common action by the residents is to block up the ducts, under the concept that it is costing them to run the fan.

It is a known fact that fire dampers within domestic properties with communal ducting are lacking fire protection within the vertical shafts, which are commonly found within commercial properties, where the maintenance is more readily funded. Where there are fire dampers installed, they are in the horizontal branch ducting. While this is a plausible way of dealing with a FIRE, it is not adequate for dealing with the major killer, SMOKE, as was tragically discovered with the fire at Lakanal House, where ambient temperature smoke and combustible products are the main cause of fatalities. The smoke is not at a sufficient temperature to trigger a fused linked fire damper or intumescent, allowing smoke to migrate through the system into other dwellings, which when other factors, such as the ‘Stay Put Policy’, can lead to fatalities. Furthermore, the dampers are near impossible to be able to service, maintain or test after the building has been closed up.

LFEPA “Stay Put” Fire Policy

The London Fire Brigades advised “Stay Put” Policy, giving guidelines to have tenants to stay within the dwellings if not affected by fire until ordered to leave by the relevant authorities, although great in theory, is designed to be implemented when all fire protection system work perfectly. The idea of all dwellings being ‘compartmentalised’ (segregated from neighbouring dwellings with adequate fire retardant materials which would inhibit the spread of fire and smoke beyond the affected dwelling), is all well and good, however, there is currently no smoke control protection device to control smoke spreading, especially within the retro fitting.
In existing building, ensuring the that building works are completed without compromising these measures can prove be difficult, requiring extensive invasive inspections.

How the PyroSafe Vent Can Assist

The PyroSafe Vent is designed to be retro-fitted onto existing communal duct systems, fitted on to each port. The principle of the unit is to continually be sensing the air quality, to detect any smoke present, using Ionisation smoke detection, within the property. With the unit located on a constant negative pressure (extraction) port, air from the whole dwelling will be able to be sensed, allowing the unit to act earlier that a standard smoke detector, which is passive. On detection of smoke, the valve will be activated, sealing the valve, using the smoke seal to ensure no smoke is admitted into the ducting, this whole process takes 20 seconds, and isolates the property from the rest of the riser, at this time a sounder will be audible, alerting the tenants. The unit also has a Rate of Rise detector, for instances where smoke may not be present, such as a larger negative pressure drawing the smoke than the duct provides. If the fire was to reach the valve, the smoke valve will hold until temperatures reach in excess of 140°c, at which time the graphite intumescent disc within the valve will activate, which has the potential to expand to 40 times its original volume, filling the ducting, ensuring no smoke is permitted to the riser and adjacent properties through the ducting.

In the event of a fire in the riser itself or unprotected dwelling, the smoke detector is located in such a position that any smoke traveling down the brand duct can be detected (this would only be in instances where the main extract fan is non-functional).

The residents would have the ability to stop the sounder, however, in the instance smoke is present the valve will stay closed until such time as the smoke is cleared.

The whole unit is served by a 12v supply via the supplied remote transformer, and is backed up by a Lithium Ion Battery, which is rated for a 10 year life span, and will keep the unit active for a minimum of 100 hours, with the last action of the unit to shut the valve when the battery is discharged, ensuring the dwelling is isolated.

As the main areas that communal ducting system extract from is bathroom and W/C, the device uses our AutoStat Humidity Controller to keep track of the humidity levels, desensitising the smoke detector during times of high humidity, reducing the chances of false alarms due to smoke and water vapour particles being of similar sizes.

As previously mentioned, the main historical reason for failing ventilation systems has been the lack of maintenance. Moving from a standard, passive approach to fire survivability to a smart, digital solution clearly attracts the need to test the systems periodically, as would happen with any smoke and fire protection devices. With many landlords there are already existing periodic testing, and replacement of devices such as smoke, fire and carbon monoxide detectors and systems. This is usually hampered by the need for access, which in recent years is becoming negated with the advance in technology and wireless connection, which has been taken into account. The PyroSafe vent has been developed with Bluetooth connectivity, allowing for remote testing and information gathering. Due to the range of Bluetooth, most units will be able to be tested from communal areas and will not need access to the property.

The PyroSafe vent has a built in data logger, which will log data such as; humidity levels; battery status; smoke activation; testing of unit; and if the unit is powered down. This data is easily able to be emailed to the relevant person to file. All data is time and date stamped, helping with analysis and can prove compliance to regulations on behalf of the landlord.

Automatic Balancing Valves

The work involved in balancing communal ducting systems can be time consuming and is something that can be easily overlooked. With the link between ventilation and both damp/condensation issues and health issues becoming more prevalent , after investigation and research by both the World Health Organisation and the Building Research Establishment. With the investigations noting that there is a direct correlation between inadequate ventilation rates within dwelling and the start plus exacerbation of such things as respiratory diseases including asthma and skin disorders.

In relation to the health issues mentioned above, the inadequate ventilation can lead to damp related issues, which can lead to damp related repair bills. Significant repair bills can be pressed on landlords, with this accounting to many local authorities counting this as a large proportion of disrepair claims. The extraction provided by the communal ducting system, when balanced correctly, is able to reduce the moisture levels down by drawing fresher, drier air into the property, controlling the air quality and reducing the risk of condensation issue and mould growth.

The common issues seen in communal ducting in regards to extractions rates, is that the ports immediately in line from the fan will draw more extraction, with the ports furthest drawing considerably less. This issues is due to air and pressure seeking the easiest route to equalise itself.

The current attenuators and valves require continual access to properties to allow contractors to adjust each individual port, measure all the ports and continue to adjust the units. This has many downfalls, with the most significant being access to each dwelling over sustained periods. Other downfalls include; multiple ‘tuning’ session to balance the system and potential minor changes throughout the system that undo the works carried out to balance the system.

How the AutoFlow Valve can assist

The AutoFlow Valve is designed to be a self balancing, mechanical valve, which requires no interference by the installer once installed, as long as installed correctly. The unit uses gravity as a spring, with a weighted pendulum and constant free area to control the air flow.

On installation, the installer will set the required airflow rate by ‘snapping’ off the marked section of the free area, to increase the free area as required as per the clients specification. Once installed, the unit will continually balance itself with the fluctuations in pressure, by the pendulum opening and closing to increase and decrease the free area available.

The AutoFlow Valve works by regulating the airflow, making the system apply more pressure further down the riser, and by knock on, after all ports have the valve in, the system spreads the same pressure and extraction rate equally to each property. This device does not require any modification once installed, meaning the access that causes issues for balancing is negated.

Once the system is balanced and each property is receiving the correct ventilation rates, the landlord is complying to building regulations, reducing the chances of condensation and mould issues, and any health related issues as mentioned above.

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