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HOT WATER RECIRCULATION

            
By Solarbair, LLC © July 25, 2010

In homes with average to long hot water wait times, having no hot water recirculation system is inefficient because time, water, energy and money must be flushed down the drain each time hot water is required.  Traditional type residential hot water recirculation systems are also inefficient.   Worst case scenario the pump runs 24/7 and the hot water lines are un-insulated.   The energy is consumed by the pump is just the tip of the iceberg amounting to approximately $21 annually.  The heat lost from the piping is what really consumes energy.  Often times the pump is also oversized in which case hot water rushing through the lines erodes the pipe and leaks result.

Some modifications can be made to reduce the waste associated with traditional recirculation.  The pump can be controlled by a timer and set to stop running when there is no demand for hot water, for instance from 11:00 PM to 6:00 AM.  The pump can also be controlled by a temperature sensor, turning on only when water in the lines has cooled.  In some cases the hot water will circulate without a pump simply because hot water rises and cool water descends.  Insulation can be added to the hot water lines to reduce the heat loss. Even with the above efficiencies added traditional hot water recirculation wastes energy.  Heat lost off the piping can amount to over $100 annually even if the hot water lines are insulated and upwards of $300 if they are not.  Perhaps the whole idea of recirculation should be re-thought.

This is where D’mand type systems come into play.  Push a button just before using a fixture and the hot water is circulated on demand.   D’mand systems pump the cool water out of the hot line and back to the water heater at a greater rate than would be discharged from the fixture.  When the hot water from the water heater reaches the fixture the pump automatically turns off.   Viola, the wait for hot water is reduced and water is not wasted down the drain.  Pumping energy is negligible at about $2 per year since the pump only runs for a minute or so per use.  Heat loss from the piping is actually the same or less than it would be with no circulation system at all.  Because the room temperature water in the hot line is circulated back to the water heater as opposed to running down the drain, less cool water from the city or well is introduced.  This results in a slight reduction in overall heat loss most likely enough to offset the energy used by the pump.   Water is saved along with the energy required to process, deliver and treat it.

 

There are two downsides to D’mand systems.  First, there will still be a wait (probably shorter than without the pump) for the hot water to be circulated. Second, the cooled water from the hot water line will now be in the cold water line.  If you then fill a glass from the cold tap you might be drinking water which was once heated.  Since hot water leaches elements from tanks and piping more than cold water you may end up ingesting more of these elements.  A solution to this issue is to have a dedicated line through which the hot water returns to the water heater or to drink filtered water.  

If you have a tank-less or on-demand water heater you may have thought hot water recirculation was out of the question.  With a tank-less water heater and a standard recirculation system either the recirculation flow rate is high enough to activate the water heater and it has to run almost constantly (not good), or the flow rate is too low, the heater does not turn on and unheated water is circulated doing no good at all.  The D’mand system comes to the rescue again.  An adequately sized D’mand system will move enough water to activate a tank-less heater but only when needed.  Since about a gallon of water flows through most tank-less water heaters before they get up to temperature, water savings realized by the addition of a D’mand system will be even greater with the tank-less option.

Some D’mand systems have remote wireless activation buttons available.  If the pump is installed at the furthest fixture a remote button can be installed at fixtures along the way.  The pump can then be activated to make hot water available immediately at the remote location.

If you are in the planning stages of a new home or are considering a remodel it is a good idea to locate the water heater centrally to reduce the wait for hot water.  Reducing the size and length of the hot water lines can also help reduce waste.

                

To see products available, Google “D’mand system.”  For information and the costs associated with hot water recirculation see:
www.builditsolar.com/Projects/Conservation/Recirc/RecircEnergy.htm   

www.chilipeperapp.com.