Fan Pressurisation Systems
- Single fan in single door used for small buildings
- Multiple fans used in single door for small – medium buildings
- Multiple fans used in double door for larger buildings
- Trailer or lorry mounted fans for medium to large buildings
Building Envelope Calculations
Unconditional areas e.g. plant rooms, escape stairs, bin stores & external stores should not be included in the calculations of the total surface of the building (building envelope) Lift shaft vents on external walls remain open and the internal surface of the shaft is not included in the envelope calculations Riser Openings to external walls should not be included in calculations.
Fan System Selection
Adequate Fan Capacity must be available to perform the test. The fan flow supplied should be no less than 100% of the required flow @ 50 pascals to achieve the worst acceptable building specification.
Determine fan flow required
3600 Multiply by the required air permeability = flow m/s
Location of the installation of the fan equipment should be decided on prior to site meeting;
- Access for fan equipment to be delivered and installed
- Air flow restrictions around the fan location to be free
- Acceptable route for the air to flow unrestricted around the building
Testing larger & complex non domestic buildings
This section deals with various designs and sizes of buildings. In some cases it is not feasible to perform an air tightness test.
Multi Occupying Buildings
Apartments over retail units
In such cases there is a defined boundary between the apartments and the retail unit in the form of a concrete floor slab. The retail unit is tested separately and a representative sample of the residential accommodation should be tested in accordance with the current Building Regulation Requirement
High Rise & Multi Storey Buildings
In order to achieve equal pressure throughout the different stories, it may be necessary to employ multi fans at different locations to achieve this. For buildings above 15 stories by opening the lift shafts door, this will allow the air flow circulate equally around the tested area. Health and Safety restrictions are implemented during this procedure. Ideally it is advised to perform this method when the building is empty.
For buildings above 15 storeys it may be appropriate, under some circumstances to test the building by floor level. A potential testing scenario is as follows:
Test the ground floor and pressurise the first floor simultaneously to produce the same test pressures on both of those floors. The flow rates to the ground floor should be recorded and analysed in the usual way but taking the envelope area as that of the ground floor slab and external wall area of the ground floor only. If the first floor plan area is less than the ground floor, then any ground floor roof areas may be included in to the envelope area. Test a selected intermediate floor at the same time as pressuring the floors above and below the test floor at the same test pressures. The data should be analysed in the usual way but the envelope area will be the area of the external walls of the test floor only.
Test the top floor and pressurise the floor below it and take the envelope area as that of the external walls of the top and the roof area. Sufficient open area between the test floor and adjacent floors should be provided along with a route to feed the outside differential pressure tube. This aspect applies to all tests. The number of intermediate floors tested should be taken as 10%, unless there are substantially different methods of construction between floor levels. If all of the above measured are leakage rates are less than required specification then the building would have passed the air permeability criteria. If any of the building elements fail the required criteria then the Q50 for the ground floor plus the Q50 for the top floor should be summed with the highest Q50 for an intermediate floor multiplied by the number of intermediate floors. This total air flow rate should then be divided by the envelope area of the building to produce a final value.
Most triple fan blower door systems will deliver a total of >6m3/s. An intermediate floor area of 4,000m2 and a height between floors of 4 metres would require a flow rate of around 2.8m3/s per floor at an air permeability of 7m3/(h.m2). The top floor would potentially require two triple fan blowers with one double fan blower door on the floor below. Ground floors very often have a footprint greater than the main high rise portion of the building, but then normal large portable fans can be used at this level. Most high rise buildings could therefore be tested with this methodology, assuming that an adequate air seal is provided by riser shafts within the test zone. If the cross sectional area changes dramatically after the second floor level and above, extreme care and diligence should be applied to the testing methodology and air flow testing requirements. More floor levels may need to be tested under these circumstances.
Large and Complex Buildings
Large buildings like hospitals or airport terminals (80,000m2 and greater) with different air permeability requirements can be a test part tested during construction.
Recommendations in such phased hand over a significant duration
- Method designed to achieve the required air permeability during design stage
- Hire professional contractor to install the air tight system
- Liaise with project manager on progress
- A thoroughly quality management procedure is required. Nominated contractor should oversee the project with regard to air tightness issues, inspect detailed air sealing drawings, inspect the building at intervals during construction, require robust QA site auditing procedures from main and package contractors, recommend full scale mock ups of sections of the building be tested and/or recommend air tightness testing of components
- Monthly inspections carried out and tool box talks organised to inform all contractors on the site the importance of the air tightness layer
- Nominated sections of the building tested during construction and results recorded. Where the required target is not achieved, remedial works are carried out and retested until required air permeability is achieved. A log of the results and the sections of the building tested to become part of the Hand Over File.
- Constant monitoring of the air tightness system
- On completion the entire building is tested
Phased handover or occupancy of a building may preclude the testing of a whole building in practical terms. If such situations exist, a test to a representative sample may be deemed reasonable. This should represent at least 20% of the building envelope area and the areas tested must be representative of the external envelope construction for the building as a whole. Where samples are used to prove compliance of larger areas of the building, it is necessary to achieve a test result 10% below the target specification, thereby giving some comfort that workmanship and detail issues elsewhere may not compromise the envelope air leakage performance when considered for the whole.
When testing of sample areas is to be carried out it is important to consider internal walls or temporary screens isolating test zones that will also be tested. Leakage through these elements will impact upon the result for the sample in question, although ultimately they may not form part of the building envelope.
Building Extension Testing
Where the extension can be tested as a separate entity from the existing building, this will be relatively straightforward. However in some cases, it will not be practicable to test the extension separately, for example an extension to the sales floor of a large retail outlet. Under these circumstances one approach would be for the existing building, or part thereof, to be air tightness tested before extension works commence in order to characterise the performance of the existing building or section of the building will require to be air tightness tested again. The air quantity required to pressurise the existing part of the building including the new extension minus the air quantity required to pressurise the existing part of the building, divided by the envelope area of the extension will provide the air permeability of the extension. An air tightness test on the original building should be carried out.