Making the Most Efficient use of Eletricity in the Home

Heating, air conditioning, lighting, cooking and refrigeration were the first elements easily identified as major power burners in private dwellings, and as such received a great deal of attention.

Subsequent regulation has been directed toward building and insulation standards for climate control and hot water systems, especially for homes built to Energy Star and other efficiency and green building standards. However, there are many other sources of energy waste.Often over-looked are the insidious consumers of electricity - products that appear to have been turned off, but which in fact continue to burn many watts while they lie idle in standby mode. Chargers (wall warts), DVD players, set-top boxes, and TVs all fall into this category.

Again, as recent government legislation and programs have focused on setting maximum no-load and standby power consumption limits, designers of such equipment must find new solutions to match the demands of the regulations.In order to understand the true nature of electricity consumption in private homes by the many miscellaneous and hard-to-identify sources, several new studies are being undertaken, including one by the Lawrence Berkeley National Laboratory Berkeley, California, which focussed on electrical equipment in thirteen new, unoccupied homes in California. In this research, spot metering was performed of all the builder-installed electrical appliances in both operating and standby modes. Results showed that the average power consumption of these unoccupied homes was equal to 800kWh/yr - with about half of this electricity being consumed by equipment in low power modes. The mean low power consumption (approximately 440 kWh/yr) translates to a continuous standby power of about 50 watts —without anyone living in the house! It should also be noted that several devices exhibited higher than expected standby consumption: a gas fireplace, 5 watts; a structured wiring panel/power supply powering video cameras and a broadband router, 20 watts; and a garage door opener, 5.4 watts.

Given the rapid development of new consumer products, it is safe to assume that home-owners will demand a plethora of other devices, such as home entertainment systems and wired and wireless networking equipment that could be equally wasteful in their consumption of standby and no-load power. To take just one example; some large screen televisions use as much power as a refrigerator. Digital television adapters (DTAs) present an illuminating example of the interaction between new technology and government regulation. From February 2009, approximately 30 million of them will be required in the US homes that are not connected to cable or satellite television. Currently, ENERGY STAR is working on specifications that will introduce a 1 watt sleep mode maximum and a mandatory auto power down mode after a few hours of inactivity.To build upon this theme, as public awareness of global warming has increased, regulatory agencies around the world are putting increasingly strict energy efficiency guidelines and regulations into place. Moreover, agencies are moving away from the existing patchwork of individual regional and national standards towards global, harmonized standards.

The most obvious example concerns external power supplies (EPS): many authorities, including the European Commission, CECP (China), the Australian Greenhouse Office, and KEMCO (Korea), plan to adopt the same specifications as those laid down by ENERGY STAR and the California Energy Commission (CEC) regulations. Lastly, some bodies are shifting from asking for voluntary compliance to imposing mandatory implementation of the standards. In the USA, many States have followed the lead of the CEC and have already implemented mandatory requirements. This EPS spec shows yet another important regulatory trend. As well as demanding a 0.5 watt maximum no-load power consumption for low power adapters, it calls for an average minimum active mode efficiency over a wide load range, as illustrated in Figure 1. (See bottom)For power supply designers, these new demands mean that once-acceptable design practices have become unacceptable in the realms of no-load power, standby power, and overall power supply efficiency. In the emerging regulatory environment, designers are required to give up old design habits and employ new techniques in order to meet these more stringent requirements.Achieving such massive improvements in energy efficiency is a real challenge, but there is good news. Recent developments in integrated circuit technology are enabling power supplies that achieve a constantly high efficiency over the operating power range, and an extremely low standby consumption - at no extra cost.

Until recently, many power supplies, both internal and external, used a line frequency transformer with a linear regulator. This traditional approach rarely achieves much above 50% efficiency, wasting many watts, even under a no-load condition. Moreover, the dramatic rise in the price of copper in recent years has removed the cost advantage of linear supplies. The result is that virtually all new power supplies are today designed using switching techniques.

One manufacturer of power conversion ICs is Power Integrations, In 1998, the company introduced its EcoSmart®. technology which enables a switched-mode power supply design to operate with much higher efficiency when in standby and no-load conditions. Through integration, external components are eliminated, lowering system cost and improving reliability considerably. ICs with Power Integrations' EcoSmart technology include circuitry on the chip that senses when a power supply is in a low-power state (no-load or standby). The device then takes one or more steps to improve the efficiency of the power supply in this state. It lowers the "duty cycle"; that is, it limits the supply of power to the load, drawing less current from the electric utility.

Secondly it "cycle skips", waiting for the device to "wake-up", thus using electric energy only during this short period. This effectively lowers the average operating frequency of the power supply, reducing the switching losses and improving efficiency while in low-power operation As an example of what this new breed of power conversion chips can achieve, Figure 2 (at bottom) shows a power supply constructed using EcoSmart - in this case a TinySwitch-III® regulator. Its highlighted bias winding and use of only three external components cut the standby consumption for the circuit from 300mW to just 30mW. So, an additional component cost of just 1 cent achieves a saving in energy consumption of 27 cents per year. More, the On/Off control methodology results in a standby mode that draws less than 1 watt from the mains (see Figure 3 at bottom).

The figure also shows that this design provides a remarkably consistent efficiency performance over the full power operating range, matching the current regulatory trend of demanding greater efficiency across the entire active power range.A goal once proposed was the 'zero electricity consumption' house, one whose reduced power requirement could be met by photovoltaic supplies. Although great progress has been made thanks to intelligent building design, there is still some way to go due of the growth in power consumption by other miscellaneous items, such as door openers, security cameras, and other energy using products (EuP). The use of high efficiency switching power supplies is therefore now a 'must' for all electronics equipment designers. By replacing wasteful linear supplies with switching power supplies design engineers can easily meet new regulations aimed at energy efficiency.