Iconic Milwaukee greenhouse implements rainwater harvesting & reuse
Since 1899, Mitchell Park Conservatory and Mitchell Park have been Milwaukee icons and destinations for locals and visitors alike. It was not until 1959, however, when the three large spherical greenhouses were constructed, that the beautiful park site situated along the Menomonee Valley was named the “Milwaukee Domes.”
Housing three different climates (Desert, Tropical and Floral Show), the Milwaukee Domes showcase thousands of plant species for visitors. Separate greenhouses are managed by the Milwaukee Park System to provide plantings for city and county events, as well as a staging area for plants that eventually will be placed in the Milwaukee Domes. Recently, a major highway construction project in Milwaukee required the relocation of the existing greenhouses, and gave the city the opportunity to build a new state-of-the-art greenhouse on the same property as the Milwaukee Domes.
Milwaukee engineering company the Matrix Group received the plumbing design for the project, which included a rainwater harvesting system that would capture water from the new greenhouse’s 60,000-sq-ft rooftop and use it to irrigate the plantings inside. Milwaukee is a mecca for water technology companies—so many, in fact, that an entire organization, the Water Council, was created to promote the area’s water expertise. The region boasts more than 150 companies in the water industry. When the Matrix Group sought a vendor for the rainwater harvesting system at this iconic site, it went local and selected Milwaukee-area company Watertronics.
Plumbing & Installation
The project implemented SkyHarvester, a product line specifically designed to integrate all of the required elements needed to provide non-potable water to an irrigation system.
The first step in the process was to balance how much water could be collected with the greenhouse’s anticipated usage. The system will capture approximately 38,000 gal of water for every 1 in. of rainfall. Although usage inside the greenhouse varies, 38,000 gal provides water for approximately two weeks of irrigation.
Because Milwaukee winters provide more snow than rain, and in light of the county’s growing needs, 80,000 gal of storage were specified. Locating a single tank for this amount of storage on the jobsite presented a challenge, so the final design incorporates four 20,000-gal storage tanks interconnected to form a single 80,000-gal vessel. The tanks are installed in pairs—two of them on each side of a breezeway—with balance piping running underneath the structure.
Cornerstone Plumbing of Milwaukee provided installation for the entire system. Oftentimes, portions of a rainwater harvesting and reuse system are split into multiple disciplines during installation, with different companies responsible for installing each portion. Making Cornerstone responsible for the entire system, from rain gutters to distribution inside the building, led to a smooth installation.
Treatment & Controls
To get the water to its desired quality, the treatment process begins with two stainless steel screen filters that filter the water to 700 µ before it enters the storage tank. The filters are located in the gravity piping between the roof and the storage tank, and contain self-cleaning spray heads powered and controlled by the SkyHarvester pump station located in the mechanical room. The filters run a nightly two-minute flush cycle at 2 a.m. This removes any debris that may have collected on the screen surface. If the screen is clean, most of the water drains back into the storage tank.
A wet well located adjacent to the storage tanks houses the submersible pump, which provides pressurized water to the SkyHarvester control and filtration skid located in the mechanical room. Once inside, the water passes through a 5-µ automatic screen filter, and then through an ultraviolet unit for disinfection.
Because the water from the irrigation system is the only water plants inside the greenhouse will receive, a backup city water supply is incorporated on the discharge of the control and filtration skid. The control panel is engineered to automatically provide city water in the event of a problem with the rainwater system, or if the system does not have rainwater available for use. This assures the Milwaukee Domes staff that they will never miss an irrigation cycle.
The entire system is operated through a color touch-screen operator interface that provides information on tank level, pump status, flow, pressure, filtration set points and alarms. The system starts on a pressure drop sensed in the irrigation mainline, and regulates a constant pressure at a variable flow rate with variable-frequency drive technology, which operates the pump at the required speed to satisfy the water demand. This ensures that the Milwaukee Domes only consume the minimum amount of energy required to provide water for irrigation, no matter the flow rate required by the irrigation system. The system is capable of providing 95 gal per minute at 60 psi directly to the irrigation mainline, and keeps track of the total amounts of rainwater and city water used.