The Water Supply Redundancy Runtime Calculator calculates how many days a water supply redundancy can support its critical loads during a water outage. This information is an input for characterizing redundant systems in the TRN Lite risk assessment methodology. The calculator can account for three types of
- Onsite storage tank(s) connected only to the primary water supply,
- Onsite or offsite secondary water source that supplies onsite storage tank(s), and
- Onsite or offsite secondary water source that directly supplies critical load(s)
After providing answers to the questions below, you will obtain an output estimating the number of days current supply redundancies will be able to meet critical loads. This analysis provides a high-level estimate. For users who have done or are planning to do more refined assessments of the runtime capabilities for their supply redundancies, those estimates may be more appropriate to use as inputs for the TRN Lite analysis. Note that if your system is more complex than one of the system types listed above, it may require a more involved analysis to estimate system runtime. Review the system definitions to check to see if your system meets the criteria of analysis for this tool.
To see the calculations behind the results, click the “Show Calculations” checkbox. Click “Example” to see an example analysis including entered data and results.
Enter the data below to characterize your
An onsite storage tank could be connected to only a primary water supply (e.g., municipal or utility) or connected to a secondary, onsite or offsite water source. Whether or not it is additionally connected to the primary supply, if the tank is connected to a secondary supply it falls into the category, “Onsite or offsite secondary water source that supplies onsite storage tank(s)”. Rainwater storage tanks are often considered secondary water sources, but for the purpose of this tool, rainwater does not qualify as a secondary source as it is not reliable enough to model as a consistent secondary source. The storage tank itself still counts as a supply redundancy as the water that is available in the tank can be used during an outage, so the user should select Onsite storage tank(s) connected only to the primary water supply for rainwater systems with no additional secondary source.
Useable volume: The storage capacity of the tank(s) that can be used during an outage to supply the critical load(s) assuming the tank were full. It is equal to the total storage volume minus the dead volume and reserved volume.
Dead volume: The volume of water at the bottom of the tank that, when the water level reaches this level, there is not enough head to supply the system. This level depends on the elevation of the tank(s) and the system pressure requirement. This volume may be nominal, but it is important not to include it in the usable tank volume to receive an accurate runtime estimate.
Reserved volume: Tank volume that must be reserved for emergency fire suppression requirements or similar uses and therefore is not included in the useable tank volume.
Enter the data below to characterize the water available from
Onsite: When fully operational, the source is not expected to be exhausted within a reasonable timeframe (e.g., months) and it must be able to continuously provide the design flow rate over the entire duration of the outage. An onsite secondary water source, such as a well, aquifer, or lake, should have enough capacity such that it can be considered infinite for the purpose of this tool.
The results below show the calculated runtime for the supply redundancy described by the inputs to this calculator. The runtime is shown in days and in hours. Use the runtime in hours as an input to characterize your water supply redundancy in the TRN Lite Detailed Information – Supply Redundancies subsection.