Mass balance calculations are often performed by engineers to estimate the total usage in a zone or system. This is often used by hydraulic modelers to develop diurnal curves of water usage.

Usage can be directly calculated for a given time interval as the sum of inflow volume minus the sum of outflow volume, minus the change in storage in that zone or system.

Here we apply a negative sign on the change in storage volume, because losses in tank volume represent water used in the zone, while increasing tank levels represent flow returning from the zone to the tank.

These calculations use a backwards difference approach, since in real-time data we only know what happened in the past and not the future. Specifically, the hourly usage value output at 3:00 represents the water that was used in the zone from 2:00 to 3:00.

Inflow/Outflows are converted to volume approximately by simply taking the average flow rate throughout the time interval and multiplying it by the time step.

Changes in storage volume are simply the difference in volume between the current time step from the previous time step.

In the case of a cylindrical tank, you can take the change in tank level multiplied by the area of the tank.

Manually validating in a Chart or BizBlock

You can actually reproduce the same results manually in Info360 using the Volume function. The following could be used in a BizBlock for a zone with two inflows, one outflow, and one tank as a simple example:

*Note that you will need to be careful with units here and convert as necessary. If flowrates are in gallons per minute, then Volume() will return gallons, while a tank with units of feet will get Volume() outputs in cubic feet.

Example Calculation

Lets say we have the following 15 minute data for a zone with two inflows, one outflow, and a cylindrical tank with surface area of 500 square feet.

We will calculate the water that is used between 0:00 and 1:00, which is the value Info360 will report for hourly results at 1:00.

The inflows and outflows can be converted to volumes in and out of the zone by taking the average and multiplying by 60 to get total gallons used in the hour. We must be careful though that the values at 0:00 are not included in our 1:00 calculations.

The change in storage volume will be simply (19.4 - 21)*500 to get -825 cubic feet, or -6171.4 gallons (multiply by 7.48 gal/ft3).

The volume associated with each data feed as well as the resulting usage are calculated as:

Non-Revenue water is simply the water that is used minus what is billed. Further description of NRW is given in the following section.

   
For many, billing data is only available on a monthly basis and comes in a format that is difficult to bring in to Info360. If this is the case, billing data could be manually brought in to an updatable sensor on a monthly basis. Calculating non-revenue water in each zone for even a monthly interval can reveal a lot about a system.

With the growing adoption of smart meters and Advanced Metering Infrastructure (AMI), non-revenue water can be calculated in near-realtime with excellent temporal resolution.

When implementing AMI or Smart Meters, it is best to cover one full zone at a time, rather than scattered throughout the network. This will enable the data to be utilized as it comes in for each zone.

Wherever pump energy usage is available, Info360 can report on the energy costs for a given zone.

Info360 needs pump energy data to come in either feeds of power (Watts) or both current and voltage (Amps x Volts = Watts). Power is then integrated over time to track the KWH (Kilowatt Hours) which is the total energy used. The manually set Power Cost ($/KWH) for each zone is then used to output the cost of operating all pumps in that zone. Finally, KWH can also be converted to estimated carbon footprint as lbs of CO₂.