The University of Washington Botany Greenhouse is a prime candidate for rainwater reclamation. Capturing rainwater that flows through the existing gutter system and re-routing it to storage tanks located within the confines of the greenhouse would save from purchasing city water, increase the quality of water used for irrigation, save energy currently used to warm irrigation water, and dramatically increase the thermal mass of the enclosed greenhouse space which would save on space heating energy demands. We are requesting $78,944 to fund this project.
The greenhouse demands approximately 350 gallons of water per day (corresponding to 128,000 gallons of water annually). In order to adequately meet this demand there must be a balance between the quantity of rain falling on the roof and the physical storing capacity of the greenhouse. It turns out that the limiting factor is the storing capacity of the greenhouse. To date there is available space underneath six of the tables to store six, 3ft diameter by 32ft long water tanks, allowing for a maximum storing capacity of 7050 gallons at any given time. These tanks would not impose a spatial burden on the greenhouse and could be connected to existing plumbing systems with relative ease. A volume calculation that took into consideration the average monthly rainfall rates in Seattle (in ft) and the available roof area that projects onto the floor of the greenhouse (in ft^2) gave the volume of rainwater supplied equal to 92,800 gallons/year. This accounts for 73% of the total water demanded, or in other words, 265 days of irrigation (assuming the tanks continuously remain filled to supply the greenhouse with at least a days demand of water) . As stated above, physical restrictions within the greenhouse are limiting the number of tanks to six. However, a year or two from now if it is decided that the rainwater reclamation system is effective enough to warrant an increase in storage capacity, it would be very possible to relocate materials currently located underneath the tables to a new location, freeing space for additional tanks. This proposal focuses on six tanks because it utilizes the space that is currently available, and also because inherent in any rainwater collection system is uncertainty in rainfall rates and overall system functionality. At this point in time 73% is a happy medium between available space, adequate irrigation supply, and reducing overflow potential on a high volume rain day. The Department of Biology, more specifically the UW Botany Greenhouse (managed by Doug Ewing), will be involved with this project.