Minimization of Peak Currents in a Household

The requirements for electrical current vary considerably during a normal day. For example, when a family wakes up in the morning, the lights come on, everyone takes a shower, has breakfast, gets ready for the day, and leaves for school or work. Meanwhile, the hot water heater turns on to replace the hot water used for showers, the refrigerator turns on to cool down after it has been opened for breakfast items, the microwave or stove is turned on to cook breakfast, and the air conditioner turns on to cool down the house. The result is a large demand for electrical current in a short time to operate all these appliances simultaneously. The process is repeated in the evening. After everyone leaves, the demand goes back down. When this scenario is multiplied by millions of homes across the country, the consequence is that the power company must design their generating and distribution systems to provide enough capacity to handle the periodic surges of power that occur at various times while allowing the systems to remain idle for much of the day or night. This adds considerably to the cost of electric power which is in turn passed on to the consumer.
 
Clearly, it would be advantageous to spread out the use of electric current over time to the greatest extent possible to minimize the surges in the requirements for electric current. This would enable power companies to lower costs and to retain excess capacity to reduce brownouts and blackouts.
 
The Fairfield University School of Engineering proposes to design and fabricate a system that will monitor and control the use of electric current in a household and keep the level of current below a specified amount at any given time during the day. For example, suppose the temperature in the room rises above the desired level. The thermostat on the air conditioner tells the compressor and fan to turn on to cool the room. Suppose, at the same time, the water temperature in the hot water tank drops below the desired level. The thermostat in the hot water heater tells the heater element to turn on to heat the water. While many of these appliances have thermostats and timers, they all operate independently. By controlling them from a central location, the timing can be adjusted so that they do not come on at the same time.  In our example, the water heater can be made to turn on during the time period that the air conditioner is off.
 
This can be accomplished without extensive rewiring by using existing wireless technology. A subsystem that monitors the current and contains a relay to open or close the electrical circuit to the power line is inserted between the appliance and the power line. For most appliances, this can be accomplished by plugging the subsystem into the wall and plugging the appliance into the subsystem. For other appliances, the subsystem can be hard wired into the power line. The subsystem monitors the current and wirelessly transmits the data to a central control unit. The central control unit monitors all the appliances and determines which are on at a given time. If the overall current level is at or near the desired upper limit, the central control unit wirelessly transmits a signal back to the subsystem to keep the relay open and not allow the appliance to be turned on.
 
The central control unit allows priorities to be placed on the different appliances by the user (i.e., the water heater should be turned on in preference to the air conditioner) and allows for an override if necessary (i.e., to allow the freezer to run after a power outage to bring the temperature down as fast as possible).
 
The Fairfield University School of Engineering has a unique opportunity to test and verify this system. A dormitory unit consisting of four apartments is dedicated to the study of electrical power generation and control, and considerable data already exists on current usage vs. time. We propose to design and fabricate sufficient subsystems and central control units to equip each of the four apartments. We will take data with these units in place for a sufficient time to attain a statistically significant comparison in order to see if the potential for savings exists.
 
The initial estimate of manufacturing cost is $10-$15 for the subsystem and $40-$50 for the central control unit. It is anticipated that the power companies would give rebates to the customers if this concept proves to be feasible in reducing power.