This article was originally published in the May/June 1998 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online May/June 1998
Taking Control of Energy Use
by Lori Marsh
The smart house has been touted for decades. With today's information technology, this elusive goal might be on its way to realization. But it's time to find out--will these systems save energy?
for example), a homeowner can put his or her home into coming home mode. The drapes in the front windows open, certain house lights turn on, and others turn off. The heat or air conditioning kicks in to bring the air temperature within a certain range. The hot tub preheats. Anything that can be turned on or off can be controlled.
Advanced home control systems go by several names, including smart home, home automation and integrated home systems. By any name, these systems conveniently control home electronics and appliances including audio/video, home office, telecommunications, intercom, security, lighting, HVAC, and lawn sprinklers. Control systems can also provide information--residents can find out how much electricity they've used on specific appliances or systems, and utilities can read meters remotely. The systems can be accessed from remote locations by phone or computer, allowing residents to turn on the heat, for example, on their way home from work.
A control system can make sophisticated decisions, limited only by the sensitivity of its sensors. With occupancy sensors in every room, lighting levels and air temperatures can be controlled based upon whether or not someone is there. With rain gauges, thermometers, wind speed, and light level sensors, decisions can become weather dependent. For example, one could program a lawn sprinkler system to turn on if total rain in the previous week had been less than 1/2 inch. A rain gauge could then turn the irrigation off once 1/4-inch of water had been sprinkled.
Some home control systems combine with special utility rates to save ratepayers money. But there are still questions about the bottom line for energy professionals--will these systems save energy?
It isn't yet clear how much energy home control systems can save; the units themselves actually use energy. A home control system with occupancy sensors can turn off lights in empty rooms, but lighting usually makes up only a small portion of residential energy use. Obviously, such a system will save more energy for people who habitually leave lights on in empty rooms than for those who diligently turn off lights. In fact, energy consumption could actually increase if the residents use the home control system to increase security by turning on more lights than they used before. The control systems themselves draw loads as low as 15 watts.
In the past, the home control industry grew primarily because of demands from home security and home entertainment customers. J.P. Freeman Company, which consults for the home automation industry, estimated in a 1997 market research report that consumers spent $2.7 billion on home automation in 1996. The same report further estimates that the industry will experience an annual growth rate of 29% until 2005, passing $27 billion.
Most homeowners are not ready to make the necessary investment in a whole-house control system. According to USA Today, this investment typically runs about 2% of the cost of a new 3,000 ft2 house, or between $4,000 and $6,000. But increasing numbers of homeowners are attracted to smaller investments that control specific systems or appliances.3% Rule of Thumb Space heating and cooling are the largest energy consumers in most homes, so they represent a lot of potential energy savings from automation.
A sophisticated HVAC control system allows residents virtually infinite flexibility in scheduling air temperatures within the home to match their lifestyle. However, temperature changes for periods of less than four or five hours typically do little to save energy. In this time, energy is either released or stored in the thermal mass of the home, and this change in stored energy must be overcome when the air temperature changes back. It takes a sophisticated thermostat to program a setback pattern that significantly reduces system energy use without disrupting the occupants' lifestyle.
The actual savings due to thermostat setbacks will vary depending on weather conditions, the thermal efficiency of the house envelope, and the thermal mass of the structure. Still, a rule of thumb is 3% savings for every °F of setback. Using this assumption, reducing the winter setpoint by 5°F would reduce heating energy consumption by 15%.Motors--An Unmined Bonanza Another type of home control that may offer significant energy savings is a motor controller. Worldwide, there are over 700 million motors in service, and this number increases by some 50 million each year. While most of these motors are in commercial applications, any controller that improves the efficiency of motor operation could still save considerable residential energy.
Coast Energy Management Incorporated (CEMI) has introduced a line of motor controllers called Power Planners that increase the efficiency of induction motors when they are running at less than full loads. Induction motors are found in refrigerators, freezers, air conditioners, heat pumps, washing machines, clothes dryers, dishwashers, pool and well pumps, and many other household appliances. Of course, the greatest savings are available from appliances that operate the most hours per year--such as refrigerators and freezers.
Power Planners monitor the load on a motor and provide it with only as much current and voltage as it needs. The amount of savings realized will depend on how loaded the motor actually is. When a motor is operating near its rated capacity, there is little energy to be saved. However, if a motor is oversized for an application, it will draw more energy than it needs. In such situations, the Power Planner can realize significant savings.
Older refrigerators and freezers use more electricity than newer units; if the efficiency improvement with Power Planner were the same for all appliances, then the older units would save the most energy in absolute terms. According to labs monitoring by for BC Hydro, a public utility in Canada, energy savings will vary from 10%35%, depending on how well the refrigerator motor is sized to its load.
The Power Planner I, the model for most residential applications, retails for $49.95. Assuming an annual energy use of 1,000 kWh (a reasonably efficient refrigerator) a 20% savings would represent 200 kWh annually. At 8¢/kWh, that equals $16 a year for a 32% return on the investment.Is TOU For You? The potential for saving money with a sophisticated controller can be further enhanced with time-of-use (TOU) rates. While electric rates vary from one utility to another, the concept behind a TOU rate is the same. The utility charges the least for electricity when system-wide demand is low, a moderate price when demand is moderate, and a premium price as the system reaches its capacity.
One rate plan offered to residential customers in the Roanoke, Virginia area by American Electric Power (AEP) contains only two price levels, on- and off-peak. In AEP's two-tier schedule, the rate that applies at any given time is determined by the time of day and day of the week (weekend and holiday hours are all off-peak). The hours selected as off-peak are based on the historical demand profile on the AEP system.
AEP offers the TranstexT controller to take advantage of TOU rates. The device allows the user to specify appliance use as a function of a real-time price signal. Up to 16 electric appliances are controlled, with each appliance plugged into an addressable relay, which in turn plugs into an electrical outlet. The user can specify, for example, whether the water heater is on or off at each price level, or when a clothes dryer can operate. The customer could load clothes into the dryer and turn it on, but the dryer would not actually operate until the low-price signal was received.
The utility is also testing a price plan that further refines the rate schedule. This is the four-tiered plan currently being tested on 200 customers in the Roanoke area. This plan uses the TranstexT to interpret real-time price information not only to turn appliances on and off based on when they are used, but also to change thermostat setpoints based on the systemwide demand. The rate that applies at any given time is based on the actual demand that the AEP grid is experiencing. The TranstexT calls AEP about once per day on the customer's normal phone line to determine what rate will be in effect at what time. Special thermostats allow customers to select heating and cooling setpoints for each time of day, for each of the four utility rates. For example, a customer could designate 6:00 am to 7:00 am as morning. For that hour, the heat would be set to 72°F if the pricing signal was P1 (least expensive), 70°F at P2, 68°F at P3, and 65°F at P4. Similar decisions can be made for the other time periods, and for the cooling mode.
The TranstexT system also offers billing information. At the push of a button, it will display the home's total energy consumption within the current billing period, the cost of that energy under the special residential service variable spot price, and what the cost would have been under the standard residential schedule. It will also project the total bill for the month based on the current usage history. This allows the customer to adjust setpoints based on usage to date. Energy use data are reset monthly, when the meter is remotely read.
Dale Moore, senior analyst with AEP, reports an average financial savings of 10% for customers on the TranstexT system. Customers have saved some energy: on average, energy consumption has declined 4%. She attributes the savings to increased customer awareness of energy use and the ease of controlling both the water heater and the heating and cooling setpoints on the HVAC equipment.Savings on Demand Some utilities offer their residential customers the option of a billing rate that includes a demand component. The utility typically establishes the customer's peak demand based on the highest demand the customer sustains for at least 15 minutes, any time of the month. Customers on this rate structure who sustain relatively constant demand end up paying the least per kilowatt-hour. These customers can achieve significant dollar savings by using demand controllers, such as the timers that many utilities install on water heaters to turn them off during peak periods.
Air conditioning, heat, hot water, and clothes drying account for about 80% of the electrical demand in a typical all-electric home. The goal of demand control is to prevent unnecessary coincidental operation. For example, the controller would not allow backup resistance heat on a heat pump and water heater elements to run simultaneously. Each would wait its turn.
Microprocessor-based controls make demand control within the home practical and affordable. Demand control technology lets a homeowner manage the home's major electrical loads minute to minute. Ideally, the homeowner's comfort and convenience are not affected, but peak electrical demand is leveled out.
The Energy Sentry, manufactured by Brayden Automation of Fort Collins, Colorado is one example of a residential demand controller. The equipment includes a simple dial with which the homeowner sets the allowable electrical demand in kW. The manufacturer makes recommendations for this setting, depending on what equipment is present and the energy use history of the client. Typically, the Energy Sentry controls heat pumps (compressor and strip heat); other electric heaters such as baseboards, furnaces, or radiant heaters; electric clothes dryer heating elements; electric water heaters; and pool pumps. The allowable demand must be set higher than the peak demand of the largest piece of equipment. The demand controller acts as a traffic cop for electricity, alternating which piece or pieces of equipment may operate.
If the allowable demand is set too low, too many appliances will be left waiting their turn and equipment will have a tendency to cycle on and off frequently. If the occupants observe such cycling, they are advised to increase the allowable demand.
Energy Consultants Incorporated (ECI) of Virginia Beach, Virginia, is the largest-volume Energy Sentry dealer in the United States. William Kee, the company's president, reports that ECI has installed demand controllers in approximately 2,300 homes in Virginia and North Carolina in areas where the local utility offers a rate structure with a demand component. Kee says that his company has tracked the energy performance of every home in which it has installed a controller. For each home, Kee mails a monthly report showing what the cost of energy would have been under the standard residential rate, versus what the bill was with the demand rate. For a year after installation, any customer not satisfied with the controller can have it removed and receive a full refund. Less than 1% of the customers have requested that a controller be removed. Based upon Kee's extensive records, the average annual savings to these customers is about $600. At an installation cost of $2,000, that represents a 30% simple return on investment. Kee does not believe that the Energy Sentry significantly alters total energy consumption, since it does not control how much a piece of equipment operates--just when it operates.
Lori Marsh is an associate professor in the Department of Biological Systems Engineering at Virginia Polytechnic Institute and State University and an extension specialist for the Virginia Cooperative Extension Service.
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