|IMPACT homepage||Introduction to IMPACT||How IMPACT works||Using IMPACT|
The IMPACT models are designed to be used by the non-specialist in air pollution modelling, and have a simplified range of inputs compared with other air pollution models. They are intended to provide an estimate of indoor air pollution for the maindamaging gases that come from outdoors (sulphur dioxide, nitrogen dioxide and ozone), and to help the user understand how air pollutants interact with buildings. Models have been written for buildings that have natural ventilation or mechanical ventilation, with or without a filtration system.
The user will need to gather together some data on the zone or building that they wish to model, as follows:
Surface area of materials. The main surface materials present, up to 6 materials, should be listed with their approximate geometric area (m2). As well as wall, floor and ceiling surfaces this may include significant area due to furnishings, or even art objects, etc. The more accurate this input the more accurate the model output will be. The user will enter the material types by selecting their materials, or similar from the program's drop down list, and then entering the area associated with that material. The program contains a database of the deposition properties for each material selected.
Volume of the zone or building. This should be calculated in m3.
Air exchange rate of the zone or building. This may be know from measurement, or if not the model has a simple method for estimating air exchange, in which case the user will need to know the average, or typical, indoor and outdoor temperatures and the windspeed against their building.
Outdoor pollutant concentration (optional). If this is known the model will output the indoor pollutant concentration, otherwise the output is given as an indoor/outdoor % ratio.
Temperature and relative humidity. Pollutant deposition generally increases with higher temperature and relative humidities. However, over the range of values normally found in cultural heritage buildings this will only make a minor difference to the output.
Additional inputs are needed to run the mechanical ventilation model. These should be know by the building services engineer.
Air intake rate (m3/s). The rate at which the system draws in air.
Proportion of fresh air. The % of fresh air in the intake. For reasons of heat economy, most systems will recycle perhaps 80% of the air and introduce only 20% or less fresh air. At times when there are no people in buildings they may operate on 100% recycled air.
Filter efficiency. The efficiency of any carbon, or other filtration system installed to remove air pollutants. A carbon filtration system in good condition may be 80% efficient, falling to perhaps half this level as it approaches the end of its service life. If no filtration system is installed, enter 0% here.
The IMPACT models are written as Java Applets to run in a web browser on any computer platform. They have been optimised for Internet Explorer and Netscape. Older versions of these browsers should be able to run the applets automatically, but due to the politics of the computing world, the latest versions of these browsers may require you to install a free downloadable add-in before you can run applets. This is available from: http://www.java.com/en/download/manual.jsp
Saving your work
As you make inputs to the model the outputs change in real time. If you want to capture the model with these inputs and outputs at any time you should press the 'Cntrl' and 'Prnt Scrn' keys simultaneously in order to capture the screen image which can then be posted into other programs such as Word or Powerpoint. It is not possible to save the Applet directly.
UCL Centre for Sustainable Heritage - the Bartlett (Torrington Place Site) - Gower Street - London - WC1E 6BT. Tel + 44 (0)207 679 1665.