Thursday, January 16, 2014

Reducing water wastage while waiting for your hot water

This small plumbing modification was needed to stop/reduce wasting cold water down the drain while waiting for the hot water from the hot water tank to reach the hot water outlets which are located in the bathrooms and kitchen.

In my case, I have a 200 litres hot water tank installed in the washroom on the 2nd floor. The furthest hot water outlet is located approximately 25 meters away of pipes. The piping is 22mm insulated acorn pipe (20mm internal diameter). Calculating the volume of water stored in the pipe which will need to be displaced for the hot water to reach the outlet using the supplied measurements, it equates to about 0.78 litres of water. Using the below formula,

V = 3.142 x 0.01m (pipe radius) x 25 (pipe length) = 0.78 litres

In practice the wasted water will be much higher. I measured the water in a measuring tank and I actually displaced 4/5 litres until the water coming out from the tap was comfortable hot enough. The difference between the calculated & actually displaced water is mainly due to heat losses in the 25m pipe run (even though the pipe is well insulated).
Now this is only if you need hot water once a day which is not the case (at least at my house) were we're a family of five. It's obvious that a large amout of water which will be wasted on a daily basis just in 'waiting' for the hot water.

The solution was easy, I installed a valve just outside my ground floor bathroom (furthest point) which is used/opened to direct the hot water back up to the roof tank using an already existing plumbing. In my case I used the water pipe which is used to pump the well water to the roof tank. Since the hot water plumping circuit is on a pressure pump, there was absolutely no problem for this solution to work since the pressure pump will come on and push the water back to the tank.

The picture below is showing the 'return' red valve which is used to return cold water back to the roof tank until the hot water reaches the valve (downstairs). It is easily accessible by just opening a window and opening the valve for a some time. 

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