There remains one area of continued uncertainty in system modeling--the determination of the usage pattern of any system.

Issue: 7/01

In previous columns, I have described the advances that we have been able to make in the modeling of the water and entrained air flows in building drainage and vent systems. These advances are reliant on a better understanding of the mechanisms of drainage flow and the availability of fast and accessible computing. However, any model predictions are only as good as the data that defines both the system and its operational regime. Defining the system is generally not a problem. Pipe sizes and appliance data are either readily available or measurable. Problems may arise in confirming installed pipe gradients against those defined by the system designer; however, these difficulties may be overcome by the system analyst, or the sensitivity of any prediction to these parameters may be determined.

There remains one area of continued uncertainty--the determination of the usage pattern of any system. Recently, we assisted the U.K. Dept. of the Environment's Building Regulations Advisory Committee in the determination of the best dwelling-to-sewer-drain diameter to deal with likely domestic household drainage flows. The final code recommendations were based on our modeling capability and a series of assumptions as to the likely appliance usage pattern over a 24-hour period. We assumed that the peak in a housing estate would fall between 0630 and 0800, as the inhabitants prepared for work and the school run. However, this exercise highlighted the lack of reliable system usage data and led directly to the content of this column, where the reader will be invited to assist in confirming or disproving the long-held assumptions on usage.

This area has been addressed in the past by specialist surveys, such as the Stevens Institute survey of low flush w.c. operation in the early 1990s. Historically in the U.K., this has been accomplished by surveys of w.c. and urinal usage at Brunel University and the generation of weekly appliance usage data by a group of university staff at Imperial College, London. All of these studies have been limited. The object of the following questionnaire is to try and expand on that data by drawing on an informed constituency.

The questionnaire that follows seeks to determine the appliance usage in a domestic situation over two days--one mid-week and one at the weekend. Data should be provided for Wednesday, July 18th or 25th, and Sunday, July 22nd or 29th, 2001. The initial questions in Section A seek to determine the range of appliances and the type of dwelling occupied by the respondent. Section A also seeks to establish the confidence level of the respondent and his/her views as to the importance of water conservation and reuse.

Section B, repeated for the two monitored days, seeks to determine the water usage by both appliance type and time of day. Eight 3-hour segments are considered, including, for example, midnight to 3 a.m. for insomniacs, 6 a.m. to 9 a.m. to cover the morning "rush hour traffic," and 9 p.m. to midnight to the cover late evening. This data will yield frequency of use curves for each appliance type, as well as estimates of water usage.

The data collected will give an invaluable insight into the water discharge pattern in a particular sector of the drainage network, and will allow a more informed use of the flow simulation models developed and identification of the most suitable drain diameters and gradients. It is also hoped that the returns will indicate the acceptance of water conservation measures, albeit within a well-informed sector of the population. The data collected will be presented later in the year.

Thank you for providing the following information. You can send your responses by fax to Kelly Johnson at (847) 297-8371, or fill out the questionnaire online at by clicking on the link for this column. Commentary on the questionnaire returns will be presented in PM Engineer later in the year, and the application of the data to improved network modeling will be demonstrated in future editions of "Thoughts from Abroad."

Click on the link below to go to the survey page.