Residential HVAC
A Titon Purge ventilation unit
Titon UK sales director Lee Caulfield
A Purge ventilation schematic
(using a fan, for example). Utilising purge ventilation throughout a residential building aids the removal of indoor pollutants and water vapour, caused by activities such as painting and decorating, as well as cooking. Part F states extraction should see four air changes per hour (ACH) from each habitable room (living/bedroom) directly to outside.
The traditional route
When using windows or doors for ventilation, there are regulations covering the angle(s) at which they open, as well as the opening area, in order to achieve purge. For instance, hinged or pivot windows with an opening angle greater than 30° require an opening area 1/20th the size of room floor area; alternatively, an angle between 15° and 30° requires 1/10th of a room’s floor area. When using sliding sash windows, these are required to open 1/20th of a room’s floor area. However, if a window opens less than 15°, it is not suitable for providing purge ventilation. Plus, not every room will have access to openable windows – in either case, other arrangements need to be made.
Mechanical alternatives
So, if windows or doors aren’t suitable, what is the next step to consider? In some cases, mechanical ventilation systems can be used, but there are some issues and restrictions. For instance, large (oversized) MVHR units and increased ductwork/terminals for reduced resistance can both lead to additional costs, as well as struggle to achieve four ACH. Plus, there can be extra pressure put on the bypass of the MVHR, which can lead to heat being transferred from the ducting system, which is not effective for cooling when purged. Also, when using MVHR to purge, contaminated (supply) air from habitable rooms will be pushed into wet rooms – potentially moving contaminated air around a house, rather than directly outside, which can have health implications. As a result, an application needs to be thoroughly researched before MVHR is added in to any design. In fact, the recent BRE independent report on purge highlighted the fact that MVHR systems will generally not achieve purge ventilation rates, due to the necessity to oversize components in order to meet Building Regulation requirements.
Perfect purge
A more effective way to achieve purge is via inline ventilation. This involves fitting an inline fan within a room, alongside an extract valve and an airbrick for exhaust.
26 July 2018
Purge ventilation P
Due to the increasing complexity of the Building Regulations, ventilation strategies must be considered at the earliest stages of a domestic building project. Part F outlines three types of ventilation: whole building, local extract and purge. Lee Caulfield, UK sales director at Titon, discusses purge ventilation
urge is the controlled ventilation of rooms or spaces at a relatively high rate to rapidly dilute pollutants and/or water vapour. This can be achieved by either natural means (such as opening a window) or mechanically
These fans can be fitted inline or in ceiling extract ducting, as well as split into two or more zones, depending in the ducting design requirements. Purging between multiple rooms (e.g. bedrooms) is also possible by adding a cross-talk attenuator to the ventilation system. There is also a security benefit to having a purge system fitted; after all, some
ground floor properties and apartment blocks with adjoining access balconies cannot afford to leave windows open, due to the risk of burglary and intrusion.
A winning combination
The good news is an inline purge fan can be used with MVHR. Indeed, the two can work together, although they have to be viewed as two different types of system – and both have to satisfy the requirements of the Building Control Body (BCB). When these two types of system are used in tandem, the MVHR should be used for daily ventilation (based upon floor area, occupancy, wet rooms etc), with purge used intermittently to achieve higher rates only when required. Using MVHR alone for daily ventilation achieves approximately 0.5 ACH, so purge is necessary to raise this rate accordingly.
Legislative requirements
Whatever system is designed into a property, it should be capable of achieving the high levels of air change rate required for purge ventilation without impacting the residents, i.e. it must be acoustically attenuated and sized appropriately. Purge ventilation units/fans need to be designed to satisfy Part F of the Building Regulations 2010 requirement for purging, as outlined in Appendix B. Such units allow for the rapid removal of stale, odorous and poor-quality air, creating a healthier, more comfortable indoor environment. They should also comply with all relevant standards, including the EU RoHS
Directive and the EC council directives relating to electromagnetic compatibility and electrical safety. In addition to removing indoor pollutants, purge ventilation also prevents a dwelling from getting too hot and uncomfortable during warm summer periods. Plus, there is the further benefit of removing any condensation within a home caused by trapped heat, as well as creating a healthier indoor environment by removing the volatile organic compounds (VOC) that can cause disease. So, when designing a building’s ventilation system, it is important to consider all the options available. When windows and doors cannot do the job alone, purge ventilation is available to help eliminate unwanted heat, moisture and pollutants, either on its own or as part of an MVHR system. This option still complies with Part F of the Building Regulations, while also providing a comfortable and healthy indoor environment for occupants.
www.heatingandventilating.net
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