• The Client:Montreal Data Centre
  • The Asks:120 gpm at 70psi and minimal maintenance

The Problem:

The large roof area will be exposed to significant atmospheric deposition of dust and fine sediment. In addition, vehicular traffic and other industrial activities around the area will also contribute to sediment loading on the roof. The sediment particles will eventually be carried by rainwater into the cistern and treatment filters of the rainwater harvesting system. This could result in increased maintenance of these and other system components.

The client wanted a system with minimal maintenance. Since the particles from the roof are typically very fine, the challenge was to select a pre-treatment filter that would filter out the majority of the silt sized particles prior to entering the cistern.

Due to the large size of the site, another challenge was ensuring the right pump system was selected to move the water from the cistern to the mechanical room where the Net Zero Water rainwater distribution pump, treatment and control system was located. The cistern was to be located outside, below grade, in the opposite corner of the building from the mechanical room. Roof drainage from the building has a 15” pipe diameter that had to be intercepted at about 6 feet below grade. Adding to the complexity of the project, the severe Canadian climate and frost line must be considered with most pre-treatment devices restricted by shallow burial unless installed in a concrete manhole.

The Answer:

For pre-filtration treatment prior to the cistern, Net Zero Water incorporated an Ultra Filter featuring 20 micron pleated filters with large surface areas. The filter was buried 6ft below grade and intercepted the large 15” diameter drainage pipe from the roof. Since the Ultra Filter has an overflow, it eliminated the need for an overflow pipe in the cistern as well as the requirement for a backflow valve. There are no mechanical moving parts on the filter which removes another potential element for maintenance. The filter cartridges can be removed through a filter platform which eliminates the need for confined space entry. Maintenance of the re-usable filter cartridges is easy. Simply wash the sediment off with a garden hose and place them back in position.

An effluent pump was installed in the cistern to transfer water into a day tank where it is chlorinated before distribution into the non-potable system. A booster pump using an energy efficient Variable Speed Drive takes water from the day tank and supplies water for toilet flushing and irrigation as required.

Net Zero Water designed a rainwater harvesting package that is simple, automated and highly functional. The system is easy to monitor and control via an HMI touch screen allowing the operator to see the status of all components and equipment. A host of additional information such as the level of water in the cistern and day tank or the total amount of potable and non-potable water consumed is also available using the HMI screen.

A bypass to city water was also built into the system controlled by a failsafe solenoid valve and protected by a reduced pressure backflow preventer. Should system maintenance be required or should the cistern become empty, city water tops up the day tank so that water is continuously available.

The Design:

The Net Zero Water rainwater harvesting system was commissioned in June 2016 and is operational during spring, summer and fall months. To view a sample design of this application, download the spec below.

The Features:

  • Net Zero Water Pre-assembled Treatment, Booster and Control Package
  • Complete with Stainless Steel Piping, isolation valves and gauges
  • Day Tank
  • Color HMI Touch Screen
  • PLC Programmed to Run with Minimal Supervision
  • Potable and Non-potable Water Consumption Tracking
  • Make-up Water Top Up to Day Tank
  • Simplex Booster System
  • O&M Manual
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