As a building service professional one of the most important aspects of your job is to design, specify and oversee/install air handling systems that are fit for purpose and that, over the whole life of the building, offer building owners and occupants the certainty of adequate amounts of controlled fresh air that is heated or cooled as required.
If the detail that you put into all aspects of the installation are asked to function outside an optimum operating environment then much of the hard work that has been done is for nought. Even worse, an acknowledged top-quality system that has to work against its environment could significantly have its lifespan and energy efficiency reduced.
The benefits therefore of the air handling system will either be significantly reduced or simply will not work, regardless of what remediation is attempted. This can lead to much strife between the designer, the installer and the client who, despite going to “professionals”, feels cheated that the system does not work. More often than not the client has to resort to legal proceedings to get the system fixed and/or to seek recompense.
In order for the system that you are responsible for designing/installing to work properly, the building has to be either reasonably or very airtight. The continuous airtight layer has to be formed during construction by either a combination of bespoke materials (tapes, membranes, cuffs etc) or an expertly-installed plastered layer. How the layer is formed varies from project to project, construction materials, building types and intended usage, but any building can be constructed to be airtight (ie, to have controlled ventilation).
Achieving significantly-improved levels of airtightness is much less difficult than commonly expected and, from experience, most construction companies will rise to the task very quickly once they realise that something as simple as greater attention to detail will make big improvements.
The best and most practical way to ensure an adequate level of airtightness is achieved is to have it specified as part of the build process. Ideally, a couple of air leakage tests should be done by an independent testing professional – both during the construction and on final completion – to verify that the airtight layer as per specified in the design has been achieved. The purpose of testing it during the build is to identify any weak points which can be quickly, and much less expensively, addressed than when the building is finished.
Air leakage testing provides an empirical outcome about how well the building’s envelope has been constructed and, put simply, if the envelope is not achieving the required specification then it is leaking! The good news is that leaks can be easily located by an experienced professional using specialised equipment, and the cracks and/or gaps fixed to eliminate the problem.
The procedures and reporting outcomes are standardised and qualified, experienced professionals – who have all the necessary equipment and testers – are now available locally throughout the country. Established best practice parameters have been formulated over a number of years using data collected from literally thousands of air leakage tests on all types of construction.
Further detail and guidance can be found by referring to the following:
– IS EN13829;
– 2008 Irish Building Regulations
Conservation of Fuel & Energy – Buildings other than Dwellings Section18.104.22.168;
– CIBSE TM23:2000;
– ATTMA TS1;
Another very useful reference document is a publication titled: Department of Education & Skills August 2011 – Information on air-tightness & Building Thermographic Surveys in schools for use only on 2011- 2012 Rapid Developing Areas Schools Programme.
It is vitally important that the various professionals involved in the airtightness and related sectors of building services access this information, refer to it, and strive to achieve what is regarded as best practice.
Is it n50 or q50? — Air leakage is typically described in Ireland using two terms – n50 and q50. The n50 is how the air permeability rate is expressed in air changes per hour (ac/h). It is the relationship between the total volumes of air in m3 and how often leaks in the building envelope allow the air to exchange at 50 Pascals air pressure. This is often the reference value used by ventilation manufacturers/ installers.
The q50 is an expression of the amount of air leaked from the building envelope in relation to the total exposed area (ie, the sum of the area of the floor, roof and all external wall areas) per building and is expressed as m3 h m2. The air permeability rate (q50) is the reference value used in Irish Building Regulations.
Uncontrolled air movement — All penetrations through the external envelope of the building have to be addressed to prevent uncontrolled air movement or air leakage as this can result in:
(1) Heat/cooling loss through holes in the building fabric;
(2) Increased CO₂ emissions due to unnecessary fossil fuel heating being used to compensate for heat loss or excessive cooling;
(3) Discomfort to users of the building because of draughts;
(4) Potential damage to the building fabric where cold and warm air meet in an uncontrolled fashion. Over time this can lead to a build up of moisture which causes rotting of timbers/ construction materials and mould growth with unhealthy spores being released.
Buildings in excess of 1 million m3 have been tested using a number of testing fans linked to one master control unit and, in a recent test, a warehouse of this size tested to almost Passive House standard of 0.6 ac/h. The consequential comfort levels generated, and the reduction in wasted energy costs by having a controlled environment, far outweigh the initial investment in making the building airtight.
Airtightness of any building, either new or existing, is a very achievable goal but is a multi-disciplinary task that requires design, installation and testing.