Water Catchment and Purification/Rain Harvesting System
The water usage sub-system for The Home Depot Smart Home has a two-fold purpose: the primary goal is to minimize dependency on the municipal water system with a secondary goal of recovering thermal energy and thereby reduce electrical costs.
Several goals of The Home Depot Smart Home water system were delineated as follows: meeting most of the water needs of the house by catching rainwater and reusing the gray water in the house; purifying water to make it suitable for all household uses; reducing water consumption by implementing household devices aimed at conserving water; reducing amount of sewage generated by the house; meeting LEED standards pertaining to water usage.
The rainwater harvesting system explores an alternative and commonly overlooked method of water usage in an effort to propel water conservation and efficiency. By opting to use rainwater as an active source of household water, city water usage can be reused, and unlike ground or surface waters, is naturally soft and contains no dissolved chemicals or minerals.
The basic rainwater harvesting system consists of five components: catchment, conveyance, storage, and delivery with filtering and treatment interspersed. This system encompasses efficiently collecting, filtering, transferring, storing, and distributing rainwater.
The gutter design was chosen to be a semi-circular PVC trough with a “Cinch Gutter Guard” Because this allows the gutter to have the highest area, aperture, and stiffness ratio, higher resistance to corrosion when compared to aluminum and galvanized steel, and a blocking mechanism against leaves and pine needles.
The tank was chosen to be an underground cylindrical ferrocement tank, which is relatively easy to construct and allow for an even distribution of stresses around the tank. Pipes were chosen to be of a 2” radius to minimize pressure loss and a floater and rod system was chosen as the first flush mechanism. Appropriate filters, pumps, and pressure tanks were purchased and a prototype was constructed to test the feasibility of student designs.
For water purification of rainwater, a filtration system consisting of 3 carbon filters (20, 5, and 1 micron) and a UV filter will be implemented for drinking water. The presence of a roof-top garden will also be an effective filter.
For gray water recycling, a sand filter will be used to filter out some solids present in the water, which will then be pumped through the constructed wetland and then through a UV filter to ensure proper removal of pathogens. This water will then be pumped into a water storage tank connected to the house pump.
For water conservation, water efficient appliances, low-flow toilets or compost toilets, and low flow shower heads prove a viable start. Moreover, a water efficient landscape can limit or eliminate the use of potable water for landscape irrigation.
This system will minimize dependency on the municipal water system with reduce electrical costs by recovering thermal energy.
From testing, some further considerations were noted: a cylindrical tank is important to reduce bending stresses at the corners; to minimize stress concentrations around the drainage holes, these areas should be reinforced; a rubber seal around the flap is necessary to reduce water loss into the first flush tank; all parts must be verified to be resistant to corrosion. Furthermore, a system that requires no user input would be ideal.