Transient identification of the location of defective water seal traps within building drainage and vent systems.

Lead Research Organisation: Heriot-Watt University
Department Name: Sch of the Built Environment


The prevention of the ingress of contaminated air into habitable space has been a central concern in the design of building drainage and vent systems since the 1850s. Failure to provide the necessary protection, primarily through appliance water trap seals, was a major contributor in the SARS epidemic in Hong Kong in 2003 and in particular to the fatalities in the Amoy Gardens housing complex where the WHO(1) identified dry trap seals as a primary cause. Prevention depends upon both good design and good maintenance, however a maintenance regime within a large complex building network requires a degree of prior knowledge of possible defective appliance trap seal locations. This application proposes a novel and timely use of air pressure transient simulation and transient response measurement to identify, during periods of system non-use, the location of depleted trap seals.Low amplitude air pressure transients propagated within building drainage systems obey the mechanisms of transient propagation and system response. The propagation may be simulated by the proven method of characteristics solution of the St Venant equations so that the changed response of a network with a dry trap to a low amplitude applied pressure pulse - effectively a new open termination with an identifiably different reflection coefficient / may be predicted. In practical terms it is possible to predict the arrival time of a new termination reflection at any monitoring location within the network. Predictions at two monitoring locations within the network would clearly identify the location of the dry trap. In practice it would be necessary to subject the building drainage and vent system to a low amplitude pulse / probably by activation of a fan / during a quiescent period, practically a nighttime short duration automated pulse would be sufficient. Activation at periods of non-flow within the network will enhance the probability of a successful identification of the dry trap seal and will remove many of the operational difficulties encountered in similar methodology directed towards water supply network leakage identification.In view of the proven consequences of poor maintenance and trap seal depletion in complex building drainage networks this application is seen as both novel and timely. Its application will have implications for Facilities Management in complex buildings and the research will involve FM academics at HWU and appropriate support organizations that will make available suitably complex buildings for site trials. Identification of persistent trap seal depletion allows local installation of active control devices to prevent further failures by the addition of either Air Admittance Valves to limit trap seal loss due to negative transients or variable volume containment devices to limit trap seal loss due to positive pressure transients.This application will develop the necessary system simulations as well as undertaking laboratory and site validation of the proposed technique. The laboratory tests will draw on the group's experience and test facilities and will support and validate simulation development.Site trials will be undertaken in suitably complex building drainage networks with the full cooperation of the FM group of the Royal Bank of Scotland, with buildings in both Edinburgh and London being made available. These trials will allow an evaluation of the proposed methodology under operational conditions and will generate 'good practice ' guidelines for further implementation across the FM sector. The objective will be to deliver a proven defect identification methodology that will be of direct application with the Facilities Management of large complex buildings.Dissemination will be a primary objective and it is intended that close contact will be maintained with the both the organisations formerly supporting the application and the larger support group with whom the researchers are in constant contact.


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Kelly D (2008) Pressure transient identification of depleted appliance trap seals: a pressure pulse technique in Building Services Engineering Research and Technology