Water & Electricity Saver for Instantaneous Heater

Important Note & disclamers :  Modification to any water heater is extremely dangerous.  It should only be done if only you are familiar with the device as there are many accidents involving electricity electrocutions if the modification is not done properly.  

The alternative and safe way to achieve the same result is to turn on the tap to switch on the instantaneous heater on a high setting for a few seconds  and then turn off the tap for the water in the heater to be warmed up.

This article is just for reference only.  The author assumes no responsibility whatsoever.

Introduction

In tropical countries,  electrical instantaneous heaters are often used.  This is because residents often need only heating for showers. These heaters do not occupy space. They often save water and electricity as compare to water storage heaters. Also, they are less than 3 KW and can be powered from the usual 13 Ampere power point. This article will describe a device that will further save some water and electricity.

Working Principle

Every Instant water heater has a small heating exchanger. It gets power through a set of micro-switches that select 2 or more heating elements to warm up the water. The modern ones nowadays use electronic TRIACs to control the heater.

 

For these heaters to heat up the water, one needs to first set the selector switch and turn on the water. The water pressure sensor will pick up the pressure and actuate the micro-switches. These switches will turn on the appropriate heater element to heat up the water in the exchanger. The schematic circuit diagram of Aerogas Elegance water heater is as shown below:

 

Water & Electricity Savings

To heat up the water, water must first flow through the heater for the pressure sensors to pick up the pressure. Water amounting to 1.2 litres will be wasted before warm water can flow out of shower head. At the same time, electricity amounting to about 8 Watts-hr will also be wasted. Assuming a household of 4 persons might take 6 showers per day,  a total of about 2,600 litres of water and 17 kWh of electricity can be saved per year. This might sound to be petty savings for one household.  But it is still a sizable saving for a township of more than 10,000 families.

 

How Water and Electricity Can be saved?

To save, one can use this electronic gadget called “Trigger Delay Time Off Timer” as shown in the following:

 

Circuit Description

The gadget operates on 220V AC supply.  The delay time off is triggered started by a button.  The complete schematic diagram is as shown below

For the gadget to work in the seconds range, the default variable resistor must be changed from 50K ohm to 5K ohm. As the heater will consume 9-13 amperes, it is also necessary to add an external relay. The built-in relay has only a 10 ampere rating.

This gadget has an opto-coupler to isolate the trigger button from the 240V Supply. But the button is linked to the neutral terminal of the 240V supply. It does not offer complete electrical isolation. It will be ideal if there is an isolating transformer for electrical isolation.

 Wiring up

Safety Precautions

Important Note: Wiring up will need one to know about safe use of electricity. A wrong wiring such as wrong polarity connection by interchanging the line and neutral wires for example,  can cause shower head or water to be alive. It can be dangerous causing electrical shorts and execution.

Whenever possible, use only push button of plastic material. If metal material is used, its body must be connected to the earth.  Only waterproof push button can be used.

Further, one should always test the integrity of the heater’s earthing system. The method described in this article can be used to test theearthing.

To further protect the heater, it is recommended to install the following:

1) A Thermal fuse to cut the supply to the relay when the heat exchanger reaches an abnormal temperature of 85^oC. This temperature is about twice the normal operating temperature of the heat exchange. The thermal fuse must be of non-metallic type.  It is to be attached to the heat exchanger for proper operation.

2) A surge diode is to protect the relay contacts from electrical arc welding. This will prevent the relay from welding. Heat exchanger is wire wound. They cause inductive current that could cause the relay to use and weld together. The surge diode will clamp the voltage to less than 328 Volts. This is the breakdown voltage of the 400V surge diode.

For information, the thermal fuse and the surge diode would cost less than USD$1/= each. It is good investment for a piece of mind.