Why hot water recirculation systems save money, water and energy.
You turn on a hot-water faucet and have to wait two minutes for hot water to arrive. It's a common problem with existing homes and getting worse as new homes get bigger. We are also installing more fixtures and appliances that use hot water, the plumbing code is mandating larger-diameter pipes, and new low-flow fixtures ensure that wait times are longer than ever.
Despite its resource intensity, hot water delivery systems are seldom an area of significant focus when constructing a home. As a result, many homes are built with poor performing, inefficient hot water delivery systems that waste large amounts of water and energy.
As an example if you live in a stretched-out single-story home and the water heater is located in the garage, your bathroom may be 50 ft or more away. Lawrence Berkeley National Laboratory concludes that due to the long-wait, about 20% or 3,650 gallons of water is wasted each year.
How quickly and efficiently a hot water system can deliver hot water to the point of use depends on a number of factors. How efficiently a water heater can convert ambient cold water into hot water, how efficiently the hot water is delivered to the intended point of use, and finally, how the hot water is used by a variety of fixtures and appliances.
Both generation and use of hot water can be reduced through simple product selections. Using WaterSense and EnergyStar labeled products adds to both the energy and water efficiency by reducing delivery system water and energy waste. WaterSense hot water delivery system requirements state that no more than 0.5 gallons of water may be stored in any piping or manifold between the hot water source and any hot water fixture, and no more than 0.6 gallons of water may be delivered to a fixture before the hot water arrives. WaterSense also states that recirculation systems must be demand-initiated. They may not be solely timer-or temperature-based.
Demand-initiated recirculation systems have been found to be more energy-efficient than timer-or temperature-based recirculation systems, because hot water is only drawn into the recirculation loop when hot water is needed. Unfortunately, you still have to wait for the hot water to come from the tank to the faucet, which can take minutes and be very inconvenient.
Recirculation systems consist of one continuous hot water supply loop that circulates water throughout the home. The loop is typically located within 10 feet of every fixture, and is insulated so that heat loss is minimized during circulation.
It is important to note that timer-and temperature-based recirculation systems may not be used to meet WaterSense new home specification criteria. However, I have found that a timer/demand switch combination is the most livable solution; the timer is set for when the household rises in the morning and uses the maximum water load for showers, faucets and appliances, then programmed again for water use in the evening when everyone returns. This requires just a few hours of circulation a day. You can use the on-demand switch for all other occasions and to cancel the timer if not required.
For existing homes that do not have hot water circulation, and installing one would be difficult and expensive, there is an alternative. In this configuration the pump returns water to the cold water line as the return.
Water sensor valve recirculation systems work well and are water and energy efficient. An electric pump is placed at the hot water heater outlet, pressurizing the hot water system between 3 and 4 pounds per square inch (psi). The low pressure is because the hot and cold water pressure is balanced at an incoming pressure of around 50 psi. The bypass valve bleeds the hot water line into the cold line until the temperature in the hot water line hits around 100ºF and the valve closes. For best results, the valve should be located at the faucet furthest from the water heater, although in many cases more than one valve is necessary for optimal operational efficiency. The benefit of this system is that it is inexpensive, very effective, doesn't waste any water during recirculation and can be easily retrofitted in existing homes.
For more information please contact Paul Scrivens at www.greenhomeenergyadvisors.com