The Impact of Air Leakage on Energy Efficiency
Uncontrolled air leakage in buildings can account for a high proportion of the total heat loss (up to 30% in some cases) due to warm air being replaced by cold air. This not only causes uncomfortable draughts but also significantly impacts running costs and the efficiency and effectiveness of heating and ventilation systems. Uncontrolled leakage also significantly affects indoor air quality, impacting occupants’ health and productivity.
The control of air leakage in buildings is well recognised as a key factor in achieving energy efficiency and is referred to in the UK Building Regulations that concern the construction of new homes and non-domestic buildings.
Originally part funded by InnovateUK, PULSE has been developed by a consortium of leading specialists and academics in the energy efficiency industry with the vision of a more efficient, accurate, assessor and occupant-friendly means of air tightness testing all buildings.
The Low Pressure Pulse Test
Using a quick low pressure burst of air, the low pressure pulse test makes the prospect of routine testing a reality, even in occupied buildings. The new technique measures envelope infiltration more accurately than the traditional blower door method and is also a far more cost effective and both user and occupant friendly. Our research shows that this new method will dramatically improve the accuracy of baseline performance assessments as well as the applicability of impact modelling and upgrade recommendations
Our test is designed to deliver the following benefits:
- low cost of equipment
- Speed of test
- Clean and quiet operation
- Ease of calibration
Key applications for the technology:
- Establishing air tightness in existing dwelling which may lead to ability issues
- A demonstration of improvement that can be achieved with the installation of measures that improve air tightness
- Pre compliance checks on new build commercial and domestic properties.
The background ...
Early work on the University of Nottingham technique began with a study by Carey and Etheridge (2001), where a simple gravity-driven piston device was used to generate an unsteady pulse. Following this, Cooper and Etheridge, funded by an EPSRC Industrial Case Award with Airflow Developments Ltd, worked on the development of a more practical version in which the piston was driven by a supply of compressed air. This had the distinct advantage that the incoming air was supplied from a compressor tank, and there was no need to penetrate the envelope. Some early results are described by Cooper and Etheridge (2004). At this stage, two versions of the technique were under investigation. In the first version the whole of the pulse pressure signal was analysed to determine the leakage. In the second version only the final part of the pressure signal, which was found to be quasi-steady, was used. The first version was subsequently abandoned due to uncertainties arising from the inertia of the openings and possible flexing of the building envelope. However, the second version, the so called ‘quasi-steady pulse technique’, was developed further (Cooper & Etheridge, 2007b). It was demonstrated that direct measurement of Q4 could give a much more accurate measure of the infiltration potential of an envelope than the current high-pressure technique, by a factor of three or more (Cooper & Etheridge, 2007a).
During the latter stages of this work the possibility of replacing the bulky piston unit with a simple nozzle was first investigated. Having obtained further funding from the EPSRC (EP/H023240/1), Cooper and Zu (2011) describe the development of the so called ‘Nozzle Technique’. This latest version of the pulse technique obtains the mass flow rate from the nozzle by measuring the transient pressure in the air receiver. To determine the leakage of a building, the pulse volume flow rate and internal pressure change must be obtained. The latter can be measured directly, but the former requires the use of a theoretical model. Consequently, CFD simulation has been used to numerically validate the model. The technique has been proven to work well for a variety of building sizes, ages, construction types and airtightness levels in both calm and adverse wind conditions. Furthermore, its sensitivity to changes in leakage, the use of multiple units in synchronisation and other factors has been investigated with successful results.
The problem with current methods of air tightness testing
Having completed extensive research into the high pressure testing method of air tightness testing and published various papers, Pulse concludes that the current approach:
- Brings unnecessary inconvenience to occupants
- Is overly time consuming, requiring extensive site preparation and onsite presence
- Leads to inaccuracies due to wind or user error.
The low pressure air pulse method
As a solution to these issues, Pulse has developed a revolutionary approach to the air tightness test. This centres around the use of a low pressure air pulse which is passed through a dwelling to provide a more accurate measurement of the way in which pressure drops and the actual air infiltration. Not only is the approach more accurate but by using low pressure, it offers the following benefits:
- The test can be carried out using a relatively small, light weight composite pressure vessel which is standalone and portable, capable of being fit into a small boot.
- There is less disruption and intrusion for occupants as the test is quiet and will not disturb household objects?
- Provides a more accurate measurement of fabric infiltration
- Reduces the time taken to complete a test
- The less intrusive method reduces the need for site preparation – further reducing the overall time taken to test.
- The pressure vessel is simple to operate so there is less scope for user error
- The test is designed to enable a low unit price.
When will the low pressure pulse be available?
We have already developed a number of prototype units and have undertaken thorough validation and safety testing. These units will be available for demonstration and trial from November 2015 whilst a full production model will be available in early 2016.
Preview the low pressure pulse unit
We are currently taking bookings for a preview of the new low pressure pulse unit as soon as it is available. Be one of the first to see the new benefits of the technology and book your preview by using the contact us page of this website.