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Behavioural Water Use
Introduction
A water use node represents urban water demand and water consumption behaviour. Urban Developer offers two methods for simulating water use behaviour:
- Average daily model (the Average Water Use node)
- Behavioural model (the Behavioural Water Use node)
The behavioural model provides simulation of water use using the Behavioural End-use Stochastic Simulator (BESS) of Thyer et al. (2011). BESS stochastically simulates individual end-uses (outdoor, shower, washing machine, toilet, tap etc) at the household scale at sub-daily time steps using algorithms that probabilistically simulate an individual household’s use of common household water-using appliances. The conceptual framework for BESS is as follows:
Figure 1. BESS conceptual framework.
For indoor water uses, the water use simulations for each household are based on the type of water-using appliance and the household occupancy of that household. The difference from the average daily model is that instead of specifying an average daily volume and percentages for each end use, the user specifies the water-using appliance and household occupancy and BESS simulates the water for each individual end-use using the in-built parameters for the water use event dynamics. The types of water-using appliances for each end-use are configured in the appliance types. This enables users to simulate the effects of changes in the uptake of water efficient appliances.
The appliances and occupancy for each household can be specified in several different ways:
- Fixed appliances and occupancy – where the type of appliances and occupancy for each house are fixed by the user
- Sampled appliances and occupancy – where the users inputs probability distributions for the occupancy and water-using appliance. At the start of Urban Developer run the occupancy and appliance type is randomly sampled for each house in the Behavioural Water Use nodes.
- Average appliance demand – rather than sampling from the probability distribution of water consumption for a usage event for each appliance, the average water use is selected. This mode can be used in conjunction with Fixed or Sampled appliances and occupancy.
Further details on these configurations are given in Behavioural Model Configuration.
The statistical distributions used by BESS to generate the sub-daily indoor water use are based on the end-use study of Roberts et al. (2005). Users are encouraged to check that the predicted water use statistics provided by BESS match their expectations.
BESS uses a diurnal pattern based on Roberts et al. (2005) to vary the probability of water use events occurring throughout the day. Future versions of Urban Developer will enable users to input their own diurnal pattern.
For outdoor water use, the behavioural model uses a time series or monthly varying pattern of average daily values, which can be input by the user - similar to the average daily model. For the sub-daily outdoor water use, the daily values are evenly distributed throughout the day. Future versions of the behavioural model may incorporate the behavioural impact daily weather has on outdoor water use variability (Micevski et al., 2011).
Contents
Restrictions
There are restrictions on which node inputs and outputs you can connect together. See Urban Developer node connection rules.
The Behavioural Water Use node is available for Urban Scenarios only.
Node Dependencies
| Node Input | Notes |
|---|---|
| Mains supply | Connect to a mains supply node (if available) (Not currently implemented in the Urban Developer Plugin) |
| Tank supply | Connect to a tank node (if available) |
| Alternative supply 1 | Connect to an Alternative supply node (if available) (Not currently implemented in the Urban Developer Plugin) |
| Alternative supply 2 | Connect to an Alternative supply node (if available) (Not currently implemented in the Urban Developer Plugin) |
As well as the node connections listed in the table above, the Behavioural Water Use node requires that the following inputs are configured:
- Climate inputs
- Diurnal pattern
- Appliance types
- Sampled Appliances & Occupancy (optional, required for the behavioural model with sampled appliances and occupancy only)
The Behavioural Model Configuration describes how these inputs are utilised by the behavioural model.
Node Outputs
| Node Output | Notes |
|---|---|
| Blackwater | Connect to a blackwater stream (if necessary) (Not currently implemented in the Urban Developer Plugin) |
| Greywater | Connect to a greywater stream (if necessary) (Not currently implemented in the Urban Developer Plugin) |
| Irrigation/Other | Connect to any other end-use stream. For example, you can track your garden irrigation through this end-use, and link it back to a pervious area node in your model to capture the effects of run-off of irrigating your pervious area. (Not currently implemented in the Urban Developer Plugin) |
Node Properties
| Node Property | Notes |
|---|---|
| Number of houses | Specify the number of houses the node represents |
| The following two properties (Occupants per household and End-use appliance type) apply only when the behavioural model configuration is set to fixed appliances and occupancy. When the behavioural model configuration is set to sampled appliances and occupancy, these properties are not used. Refer to Behavioural Model Configuration for details. | |
| Occupants per household | Specify the number of occupants per household. |
| End-use appliance type | For end-use, specify the appliance type (e.g. type of shower, dishwasher, toilet, etc). See indoor water use appliance types in Behavioural model with fixed appliances and occupancy. It is currently not possible to specify an appliance type for the Outdoor end-use. |
| Outdoor average daily demand | Specify the average daily demand using a monthly pattern or a time series. |
| Supply source priorities | For each indoor/outdoor end-use, specify which supply sources are available an order of preference. For example, for the end-use Toilet (illustrated in Figure 2):
Un-checking Use for a supply source specifies that it will not supply that particular end-use. |
| Discharge breakdown | For each indoor/outdoor end-use, specify the percentage of water discharged as blackwater, greywater, or other wastewater. The values will be rescaled so that they sum to 100%. |
User Interface
The Behavioural Water Use node is configured via the node Feature Editor, illustrated below.
Figure 2. Behavioural Water Use node editor.
Behavioural Model Configuration
Sampled appliances and occupancy
The behavioural water use model with sampled appliances and occupancy allows you to specify random sampling of occupancy and appliance types, for each household, from statistical distributions.
Using the behavioural model with sampled appliances and occupancy is only recommended when you are simulating a larger number of households (> 400) and you do not want to set the appliance types /occupancy for each house.
When using the sampled appliances and occupancy model, the occupancy and appliance type node properties do not need to be configured. Other properties, such as the number of households, supply and discharge preferences do need to be configured. Refer to the Node Properties for details.
The sampled appliances and occupancy model is enabled and disabled using the Sampled Appliances & Occupancy Menu.
Details of the sampled appliances and occupancy algorithm are provided in Thyer et al. (2009) and references cited therein, a summary is provided below.
Capturing Spatial Variability in Occupancy and Appliances
The household size and the type of water using appliances varies from household to household. To capture this spatial variability the household size and appliance type for each type of water use event is randomly sampled for each household from a probability distribution based on the proportion of household sizes/appliance types. The probability distributions are specified in the Sampled Appliances & Occupancy Menu.
Capturing Temporal Variability in Indoor Water Use Events
Individual end-use events are generated in a two-stage process. The first stage determines whether a given water use starts in a particular time step, and is based on the probability of occurrence, for a particular end-use. The second stage tracks the subsequent behaviour of that water use over the following time steps, and is dependent on the end-use event volume and water usage pattern.
In general, the probability of occurrence for each event is a function of the frequency of events per person per day, the household size and a diurnal factor. The diurnal factor converts the frequency of events per day into the probability of an event occurrence in a given minute. The water use event volume and the water usage pattern is dependent on the type of water use event and the appliance type. In general, the end-use event volume is sampled from a probability distribution, and the water usage pattern is applied to this volume to produce a water use time series.
For each appliance, the frequency of events per person per day, and the probability distributions of water consumption for an event, are defined in the Appliance Types menu.
Sample size requirements
If you specify sampled appliances and occupancy, you must specify a minimum number of houses in order to provide a statistically-reliable sample of the household occupancy and appliance type.
Due to random sampling in any particular Urban Developer run, the percentage of houses actually sampled for each household occupancy and appliance type (the sampled percentage) will not be exactly the same as what you specify (the true percentage).
For example - if you specify only 10 houses, with a true probability of 0.2 for 3-Star showers and 0.8 for 1-Star showers, the chance of the sampled percentage being very different (eg: 0.5 3-Star and 0.5 2-Star) is much greater than with a large sample size.
The recommended minimum number of 400 houses ensures that for true percentages greater than 10%, the sampled percentage of houses is within 30% of the true percentage for 90% of the time.
You can specify a number of houses smaller than 400, but should be aware that the sampled percentage of household occupancy and appliances types may be different than the percentage you originally specified.
Random Seed
Random seeding provides a way to control randomisation of simulation outcomes. Random seeding applies to both sampled, and fixed, appliances configurations. The seed applies to both allocation of appliance types (eg Shower 0-Star or Shower 3-Star) to a house, and the actual water use, given the specified appliances. You can obtain repeatable results, or varied results, or repeatably-varied results with the random seed settings.
When using probabilistic simulations in models such as BESS, it can be difficult to reproduce results due to the random generation of water use.
The random seed is currently not editable in the Urban Developer Plugin, but this feature is planned for future versions to allow repeatable results with sampled appliances and occupancy.
Fixed appliances and occupancy
The behavioural water use model configuration with fixed appliances and occupancy allows you to set appliance types for each end use (showers, washing machines, and toilets), household occupancy and outdoor use for each water use node. The water consumption for individual water use events is still sampled from probability distributions, as described in Capturing Temporal Variability in Indoor Water Use Events.
Using the behavioural model with fixed appliances and occupancy is the recommended approach when you are simulating a smaller number of houses (< 400), and you want to specify exactly the type of appliances and occupancy for each house.
For this behavioural model configuration, you set the indoor end-use appliance types and occupancy for each water use node. Refer to the Node Properties for details.
The fixed appliances and occupancy model is enabled by disabling the Sampled Appliances & Occupancy Menu.
Average Appliance Demand
The average appliance demand is an option that can be used in conjunction with sampled or fixed appliances and occupancy. Rather than simulating the water consumption for individual appliance usage events by sampling from probability distributions, as described in Capturing Temporal Variability in Indoor Water Use Events, the average values for usage frequency and water consumption are used. The average values are configured in the Appliance Types menu.
The average appliance demand model is enabled using the Use Average Demand check box in the Behavioural Water Use node Feature Editor.
References
Micevski, T., Thyer, M., Kuczera, G. (2011) A Behavioural Approach for Household Outdoor Water Use Modelling. Paper submitted to Water Resources Research (April 2011).
Roberts, P. (2005) 2004 Residential End Use Measurement Study, Final Report: Yarra Valley Water, Victoria.
Thyer, M. A., Duncan, H., Coombes, P., Kuczera, G., & Micevski, T. (2009) A probabilistic behavioural approach for the dynamic modelling of indoor household water use. In H2009: 32nd Hydrology and Water Resources Symposium: Adapting to Change, 30 November - 3 December 2009, Newcastle, Australia (p. 1059).
Thyer, M., Micevski, T., Kuczera, G., and Coombes, P. (2011) A Behavioural Approach to Stochastic End Use Modelling. Paper presented at Oz Water, 9-11 May 2011, Adelaide.
Acknowledgements
This material has been adapted from:
eWater Cooperative Research Centre (2011) Urban Developer User Guide: Urban Developer v1.0.0, eWater Cooperative Research Centre, Canberra, 29 June 2011. ISBN 978-1-921543-40-1