Monitoring energy efficiency in the home

A typical application of Pico products is in monitoring energy efficiency both for environmental reasons and also for cost savings. This application note looks at the energy consumption of a domestic home, but the methods and equipment used are equally suitable for studying energy use in office or industrial applications.

Using Pico signal conditioning products a three bedroom house was wired up with sensors for temperature, humidity, light levels and electrical power consumption. All the sensors were then connected to an Enviromon data logger. The Enviromon was an ideal choice for this application as the network cable allowed easy connection of all the sensors to the single data logger. Data from the logger is remotely downloaded to a computer using a telephone modem. This enables several locations to be monitored without regular site visits.

Water Heating

The traces below shows three of the temperature sensors in the house and also the overall electric power consumption of the house. The mains power (in kW) shows a big jump when the electric storage heaters turn on and a second jump from the electric water heater.

The temperature sensor on the hot water tank showed up an immediate problem. The water heating is controlled by both a thermostat and time clock. The clock was set to start heating at 2am and finish at 8am. The red trace below shows the heating of the water. The peak in mains power consumption (approx 2am) shows when the heating starts, by 3.45 the water is hot and the thermostat cuts the heater out. The hot water however is not required until 6am, so for over 2 hours the water slowly cools dropping in temperature by 8%. This represents wasted energy. The rapid temperature drop suggests the insulation of the water tank could be improved, but a instant improvement can be made by changing the time clock settings.

energy efficiency

With the aid of the data logger we can see that the water takes 1 hour 45 min to heat from cold. The time clock was reset to start at 4.15am and as expected the water was hot by 6am.

energy efficiency

Standby power

Our monitoring of the house showed that electric power consumption never dropped below 150W even with all lights and the refrigerator turned off. The main culprit was devices with remote controls left on 'standby' such as the television, video and hi-fi. In particular the television drew nearly 20W in standby mode. Some badly designed products use almost the same amount of power in standby as in normal operation. Another cause of power wastage was mains power adaptors. These small DC power supplies commonly used around the house (for phone chargers, electronic games, computer modems, answer phones, clock radios etc) all use a few watts when plugged in, even if they are not supplying any power. Over the course of a year this adds up to a considerable waste of power (over 1000kWH).

Some manufacturers of electronic products are beginning to address the problem of standby power and clearly label products with standby power ratings. The only way to eliminate this wastage is to turn off such products at the mains when they are not required.

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