How to Design a Net-Zero Rainwater-Harvesting Home in the Desert
Arizona’sÂ DesignBuild Collaborative founder Paul Weiner, AIA, is thinking ahead about how to rely year round on only the 12 inches of monsoon rain the Sonoran desert typically gets in July.
The Rincon Mountain Residence provides a model. For only the first year, the desert home will access groundwater, while DesignBuild samples and tests rainwater for contaminants. Once these are known a filtration system tailored to the contaminants found during testing will be created and two huge rainwater harvesting cisterns forming a gigantic 50,000-gallon reservoir will supplyÂ the year round needs of the house sustainably from the July rains.
In preparation, each roof system already includes gutter collection, downspout, and Gabion walls and berms to control monsoon rains in the summer; directing it into swales, releasing that water more slowly so that it will percolate slowly into the ground.
Separate graywater systems at the main house and guest residence provide extra irrigation to the native landscaping in piping under the ground that will transport rainwater to the existing and future cisterns.
To moderate the wild swings from daytime heat to freezing night time temperatures common in desert environments, the walls are rammed earth.
This creates thermal mass for walls that soak up warmth in the daytime and slowly radiate it as the temperature around them drops.
A somewhat oversized evacuated-tube solar water heater system supplies enough sunshine- heated water to supply all of the hot water needs of the house.
Normally a much smaller system is sized to provide about 70% of water heating needs, with gas supplying the backup water heating. But in the desert, with the guaranteed sunshine virtually every day, it is possible to supply the all of the comforts of hot water and electricity with climate-friendly solar power. Solar electricity can supply the last few degrees of water heating boost if needed.
In some ways, even with the increased energy needs, because of its abundant sunshine, it is actually easier to build a zero carbon home in the desert.