Environmental Measuring

Oxley Conservation have a long term partnership with Peter Warm Environment Conscious Building Services to provide environmental testing of traditional buildings. Together the two firms are at the forefront of developing solutions to enable the energy consumption of traditional buildings to be lowered without compromising the performance of those buildings.

Air Infiltration Tests

Air infiltration, or 'fan', tests are a direct way of measuring the permeability to air of a building. From this permeability it is possible to imply how draughty a building is likely to be. Air permeability also affects the overall thermal efficiency of a building

Blocking up chimneys in advance of the test

The test involves blocking up man-made ventilation openings such as ventilators and extractor fans, and closing chimney dampers where fitted. A calibrated fan is then installed in a door opening. The fan depressurises (or pressurises) the building to approximately 50 Pascals (Pa), equivalent to 5mm of water gauge pressure. This pressure is used as it is larger than normal wind pressures, allowing testing to be carried out on all but the windiest days. Pressurisation and depressurisation should produce the same results in the quantitative tests. Qualitatively, however, it is far easier to feel the draughts in a building which is depressurised than pressurised, and this ability to feel where the air is entering the building provides important information about the best ways to improve the building's performance. For example if a particularly large leak is discovered it may be appropriate to temporarily seal it and then re-test the building to determine the proportion of the airflow through the building attributable to that single defect.

When the fan is running the pressure just inside the fan and just outside is measured. Since the fan is calibrated the pressure differential can be accurately converted into the airflow through the fan. The fan is run at several speeds to produce a range of airflows corresponding to pressure differentials between 10 and 60 Pa. The data produced by these various tests can be analysed and the airflow at exactly 50Pa deduced. Combined with volume and surface area information obtained from a physical measurement of the building, airflow data allows the calculation of the background air leakage of the building in air changes per hour (achr), and the average permeability of the structure in m/h, both at a standard @ 50 Pa pressure difference.

Of course a building will never be subjected to a steady pressure of 50Pa from a 360° spread of directions. Hence the theoretical result is then translated into an actual result by taking into account the likely real wind pressure exposure. This will be approximately 4Pa rather than 50Pa, but will depend upon the exposure of the site. Further adjustments can be made to take account of the blocking up of openings in the test if those are normally open.

Two fans were needed to depressurise this large Tudor house

This well documented procedure forms the basis of ventilation heat loss calculation in modern UK housing stock and is used in both SAP calculation and the British Research Establishment (BRE) Domestic Energy Model (BREDEM), which provides a framework for the calculation of energy use in dwellings.

Temperature and Humidity Logging

A second very important source of data on the thermal performance of buildings is direct, long term measurement of temperature and humidity data inside and outside buildings. When combined with information about fuel usage (from conventional meters) this data can show exactly how a building is performing under a full range of climatic conditions.

A typical week's output from a series of data loggers in several rooms

In order to produce a good record of temperature and humidity over time discreet loggers, about the size of a matchbox, are installed in various rooms around a house. A further logger is installed just outside the house to collect data on external temperature and humidity. The data from the loggers is downloaded into a portable PC, or into a handheld 'palm' device, on a monthly basis for analysis. Utility meters are read monthly or weekly.

As well as providing information about fuel usage and thermal performance, the loggers are also useful diagnostic tools for the early detection of damp.

Practical Application

To date air infiltration testing has rarely been attempted on traditional buildings. Logging of temperature and humidity data has only been attempted in very sensitive environments where the protection of contents is important.

The poor thermal performance of many older buildings has typically been ignored. It would be nice to believe that this was because it is widely understood the need for traditional buildings to breathe, but it could also be this is because the costs of adapting traditional buildings to meet modern standards are too high, or that traditional buildings are simply seen as beyond help. That is about to change as society as a whole becomes more concerned about the burning of fossil fuels. Pressure is increasingly being brought on traditional buildings to increase thermal efficiency.

Pressure testing a domestic scale traditional building

Oxley Conservation support moves to encourage the environmental upgrade of traditional buildings, but oppose the meeting of thermal standards by the application of modern techniques, such as double glazing and fibreglass insulation, to traditional buildings. Mixing incompatible technologies in this way will provide only short term solutions and will endanger the historic fabric. Instead Oxley Conservation works with clients to thoroughly analyse the performance of their particular buildings, and devise individual solutions to improve the thermal properties of the building without compromising the traditional performance of its materials. As such Oxley Conservation & Peter Warm Environment Conscious Building Services are at the forefront of developing a means of improving thermal performance without jeopardising the traditional performance, the condition of the building or the health of the occupants.