6. Electric Water Heaters
6. Electric Water Heaters
After the space-heating system, domestic water heaters consume the second-largest amount of energy in most Canadian houses. Depending on the type of house and on the number and lifestyles of the occupants, hot water consumption may account for more than 20 per cent of the total annual energy consumption in the home. Many Canadian homes have electric water heaters to supply hot water for household use.
An electric water heater (Figure 15) usually consists of a tank, thermostats, two electric resistance elements (which are submerged inside the tank), and inlet and outlet pipes for cold and hot water respectively. Internal thermostats regulate the temperature of the water.
Tanks are typically insulated on the exterior with mineral wool insulation and lined on the inside with a thin epoxy or ceramic glass layer. When hot water is needed, the elements are activated, which then heat the water until it reaches the correct temperature. Essentially, electric water heaters are large closed electric kettles. In the past, water temperature was generally maintained at between 60oC (140oF). Today, this temperature has been somewhat lowered to prevent young children from burning themselves.
Figure 15: Electric Water Heater
The submerged electric resistance heating elements found in water heaters are very efficient, providing about 99 per cent of the available heat to the surrounding water. Even so, older water heating systems lose considerable heat as a result of standby losses.
REDUCING STANDBY LOSSES
The term "standby loss" refers to heat lost from the water in a domestic water heater and its distribution system to the surrounding air. It is a function of the temperature difference between the water and the surrounding air, the surface area of the tank, and the amount of insulation encasing the tank.
You should consider the following options in order to reduce standby losses:
- Insulation of the tank with an approved insulating blanket.
It is extremely important not to insulate over any controls and to follow the manufacturer's instructions. - Installation of a heat trap above the water heater. A heat trap is a simple piping arrangement that prevents hot water from rising up in the pipes, thereby minimizing the potential for this loss.
- Insulation of the hot water pipes to reduce heat loss from the pipes themselves. Pipe insulation is available in a variety of materials and thicknesses, with easy application to most hot water pipes. Use insulation with an RSI (insulation value) of at least 0.35 (R-2) over as much of the pipe as you can easily access.
- Placement of the water heater over a layer of rigid thermal insulation to reduce heat loss through the bottom of the tank. This is particularly applicable to electric water heaters or to external storage tanks for integrated space and water-heating systems.
Before carrying out any of the steps listed above, check with your local installer or electricity utility representative to ensure that you will not compromise the safety or operation of the appliance.
Increased Efficiency Water Heaters
If you are in the market to buy or rent a new electric water heater, increased tank insulation and heat traps are options that are available to help you save even more energy.
The hot water can also come from a heat pump electric water heater. This is often a ground-source heat pump with an additional condenser or heat exchanger. For more information, consult the NRCan booklet entitled Heating and Cooling with a Heat Pump.
It should be noted that electric water heaters are regulated by existing efficiency standards which are being evaluated in various regions of Canada.
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Source: Natural Resources Canada (NRCan) - Office of Energy Efficiency