Poor indoor air quality (IAQ) in any building has a significant effect on the occupants, so it is essential to ensure that IAQ remains acceptable – which, in existing buildings, may call for improved ventilation with a view to upgrading IAQ.
In new buildings and major extensions, IAQ is addressed by Part F of the Building Regulations. However, there are many offices, schools and other types of building that were built to less demanding standards and that now suffer from poor IAQ. This has an inevitable impact on the comfort, well-being and productivity of occupants.
Where a project involves extension to an existing building, this may leave some spaces ‘landlocked’ or may increase the distance of those spaces from windows. In such cases, upgrading IAQ will also need to be considered.
In existing buildings, upgrading IAQ can be a challenge. If there already is an existing ventilation system based on a centralised air handling unit (AHU), there will be a limit to the additional load that can be imposed. Furthermore, any extension of a system based on centralised ductwork would be disruptive and expensive.
In some cases, the re-design of windows can offer an alternative solution, but not where there is noise and pollution from nearby roads. Moreover, the depth of the space may also limit the opportunity for natural ventilation solutions.
Solutions for Upgrading IAQ
For the reasons given above, the majority of refurbishment projects and building extensions will require an improvement in IAQ.
From an energy performance standpoint, it is clearly desirable that any solution for upgrading IAQ uses demand controlled ventilation, to align the operation of the system to the ventilation requirements of the space.
An increasingly popular approach to upgrading IAQ is the use of direct, zone-specific mechanical ventilation recovery units (MVHR). These are installed within the space to be ventilated and are ducted directly to the outside through an external wall or roof.
This localised ventilation approach minimises disruption and if required, can be upgraded in phases to fit within budget constraints. Similarly, where a building is extended the use of local units makes it very straightforward to install highly effective ventilation in the new space(s).
Indoor units can be mounted at high wall or floor level. In the case of high wall mounted units, the Coanda effect ensures that air moves evenly across the ceiling, making ductwork unnecessary. In doing so, the room air is entrained and draught risk is eliminated. This has positive implications for capital costs, installation time and occupants’ well-being.
SAV’s AirMaster MVHR units use separate fans for supply and extract, with a counter-flow air heat exchanger to recover energy from the extract air, having thermal efficiencies of 84% (dry air) or 92% (accepting humidity).
Energy savings are achieved by using electronic commutation (EC) fan drives, resulting in Specific Fan Power within the range 0.7 – 1.2 W/l/s.
AirMaster units also address concerns over noise levels , by restricting casing breakout noise to just 35dB(A) @ 1m at full throughput, falling to 30dB(A) at 80% flow. This has proven to be particularly important in applications such as drama and music rooms, as well as SEN facilities (Special Educational Needs).
In keeping with current best practice, AirMaster MVHR units provide demand controlled ventilation. This is achieved by linking fan speed to CO2 level in the room space. CO2 sensors can be wall mounted or built in to the master air handling unit. Using demand control in this way means that CO2 can be held to an average value of, say, 1,000 ppm, which is regarded as a marker of good air quality. With reduced occupancy, CO2 level would fall below, say, 500 ppm, when the unit can then be set to switch off or go to maximum turndown.
Where required, the control strategy can also be linked to movement sensors so that the units only start on signs of occupancy, with a limited run-on period (e.g. 30 minutes) following the last detected movement.
Centralised control is also possible, as up to 20 decentralised AirMaster MVHR units can be controlled from a single control panel. At the same time, the heat recovery units retain their ability to operate independently of each other.
Additionally, AirMaster MVHRs can be used to provide free cooling by automatic bypass around the heat exchanger, so that the bypass portion of inlet air remains unheated. By operating on full bypass at night, the system can take advantage of lower ambient night time temperatures during heat waves, to cool the room’s thermal mass. This is known as night cooling, which gives a fresh feel to a room in the morning and helps to deal with the problem of overheating.
When upgrading IAQ by introducing air from the outside, effective filtration is necessary to protect occupants from outdoor pollutants. AirMaster units use M5 class intake filters as standard, in line with the recommendations of standard EN 13779. Filtration level can be increased to F7 or F9 as necessary.
In fact, AirMaster units filter both incoming and outgoing air flows, as this prevents fouling of the heat exchanger, thereby maintaining efficiency for the expected life span of 15 years.
AirMaster direct, decentralised heat recovery units have been proven in a wide variety of refurbishment projects and extensions, encompassing many different building types. They are ideal for bolstering IAQ in spaces where the existing ventilation is under-performing, as well as for areas that are not connected to an existing centralised system.
Similarly, they provide an effective solution for windowless rooms within a natural ventilation cluster and for areas where windows cannot be opened because of proximity to roads or other external sources of pollution.