One of the primary goals of sustainable building systems is the conservation of resources used during the life of the building. Plastic piping systems have many advantages and applications for those interested in the conservation of both energy and water.
Reclaimed, Gray Water and Rainwater Systems
Reclaimed water is wastewater a city or municipality has treated to a level where it can be used to irrigate, fight fires and uses other than drinking. This is currently done in areas of the southwest where water is a critical resource to conserve. This water is commonly carried in purple colored plastic pipe back to buildings for reuse. The purple color of the pipe visually warns workers that it is not potable water.
Potable and Reclaimed “Purple“ Water Pipes
Gray water, is wastewater generated from processes such as washing dishes, laundry, showers and bathing. This water, instead of being discharged directly to the sewer is reused in the building for tasks such as toilet and urinal flushing or for irrigation greatly reducing the use of potable water. Plastic pipe systems are ideal to handle and contain gray water that may have a variable composition.
Rainwater is a commodity that can be collected from a building's roof or property and used in a manner similar to, or in addition to, gray water. Plastic pipes can be used in these applications to collect, transport and distribute rainwater.
Because gray water may contain pathogens and may become septic if left standing, discharge must occur in a timely manner. Above ground discharge or spray irrigation of gray water is not suitable for this reason. Gray water used for irrigation is sent through special perforated sub-surface PVC and Polyethylene pipes which are specifically listed in the code for this important purpose.
High Efficiency Irrigation Systems
Sustainable building systems call for a reduction in the use of water for irrigation. One technique is to use low-volume irrigation systems such as drip irrigation. Drip irrigation systems can be a combination of plastic pipes, generally with repositionable flexible ends that deliver low pressure water directly to plant roots reduce waste. Polyethylene is commonly used as the flexible pipe – commonly called “funny” pipe in the industry. Systems exist that minimize fertilizer use by adding measured amounts directly to the water used in irrigation. Green roofs, systems where plants are used to reduce rapid runoff during storms and reduce the heat island effect, will need irrigation to thrive in dry weather. High efficiency plastic pipe irrigation systems can meet that goal.
Geothermal Ground Loops
Because the temperature of the Earth below the frost line remains a relatively constant 50-70 F temperature year round, a heat pump can be used to heat or cool a building more efficiently than conventional methods. The most common system uses a long buried loop of thermally fused Polyethylene pipe filled with a water based solution. These systems are 50% more efficient than traditional methods such as air conditioners and furnaces. Also called a ground source heat pump, these systems can even be set up to produce hot water.
Underfloor hydronic heating commonly uses flexible PEX plastic pipe to efficiently heat a building by using the entire floor as a radiator. This system can save energy over traditional baseboard and forced-air heating and can be used in conjunction with geothermal ground loops.
Higher Efficiency Hot Water Distribution Systems
Plastic pipes used for the distribution of hot water in a building, such as CPVC and PEX have been shown in studies1,2 to waste less energy and water than alternative metal pipe systems. This is due to the insulating properties of plastic and the thicker walls of CPVC and PEX pipe. PEX pipe is also ideal for use in manifold, or “home run” systems, where a single smaller diameter pipe runs directly from the heater manifold directly to the fixtures. In this way, the wait times – and waste associated with flushing cold water down the drain - are minimized.
1 Evaluation of Residential Hot Water Distribution Systems by Numeric Simulation. Robert Wendt, et al Buildings Technology Center Oak Ridge National Laboratory
2 Performance comparison of residential hot water systems. NAHB Research Center, Inc.