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Air Conditioners
Air Conditioning Basics
Are you considering buying a new air conditioner? Or, are you dissatisfied with the operation of your current air conditioner? Are you unsure whether to fix or replace it? Are you concerned about high summer utility bills? If you answered yes to any of these questions, this information page can help. With it, you can learn about various types of air conditioning systems and how to maintain your air conditioner, hire professional air conditioning services, select a new air conditioner, and ensure that your new air conditioner is properly installed. RETURN TO TOP OF PAGE
Understanding Air Conditioners
Many people buy or use air conditioners without understanding their designs, components, and operating principles. Proper sizing, selection, installation, maintenance, and correct use are keys to cost-effective operation and lower overall costs. RETURN TO TOP OF PAGE
How Air Conditioners Work
Air conditioners employ the same operating principles and basic components as your home refrigerator. An air conditioner cools your home with a cold indoor coil called the evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and condenser coils are serpentine tubing surrounded by aluminum fins. This tubing is usually made of copper. A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils. The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling the home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid giving up its heat to the air flowing over the condenser's metal tubing and fins. RETURN TO TOP OF PAGE
Types of Air Conditioners
The basic types of air conditioners are room air conditioners, split-system central air conditioners, and packaged central air conditioners. Room Air Conditioners Room air conditioners cool rooms rather than the entire home. Since they provide cooling only where they're needed, room air conditioners are less expensive to operate than central units, even though their efficiency is generally lower than that of central air conditioners. Smaller room air conditioners (i.e., those drawing less than 7.5 amps of electricity) can be plugged into any 15- or 20-amp, 115-volt household circuit that is not shared with any other major appliances. Larger room air conditioners (i.e., those drawing more than 7.5 amps) need their own dedicated 115-volt circuit. The largest models require a dedicated 230-volt circuit. RETURN TO TOP OF PAGE
Central Air Conditioners
Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers. A central air conditioner is either a split-system unit or a packaged unit. In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners, this indoor cabinet also contains a furnace or the indoor part of a heat pump. The air conditioner's evaporator coil is installed in the cabinet or main supply duct of this furnace or heat pump. If your home already has a furnace but no air conditioner, a split-system is the most economical central air conditioner to install. In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner also is used in small commercial buildings. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors. RETURN TO TOP OF PAGE
Maintaining Existing Air Conditioners
Older air conditioners (older than 12-15 years) may not be very efficient to use. However, if you choose to make your older air conditioner last requires you to perform proper operation and maintenance.
Air Conditioning Problems
One of the most common air conditioning problems is improper operation. If your air conditioner is on, be sure to close your home's windows and outside doors. Other common problems with existing air conditioners result from faulty installation, poor service procedures, and inadequate maintenance. Improper installation of your air conditioner can result in leaky ducts and low air flow. Many times, the refrigerant charge (the amount of refrigerant in the system) does not match the manufacturer's specifications. If proper refrigerant charging is not performed during installation, the performance and efficiency of the unit is impaired. Service technicians often fail to find refrigerant charging problems or even worsen existing problems by adding refrigerant to a system that is already full. Air conditioner manufacturers generally make rugged, high quality products. If your air conditioner fails, it is usually for one of the common reasons listed below:
• refrigerant leaks. If your air conditioner is low on refrigerant, either it was undercharged at installation, or it leaks. If it leaks, simply adding refrigerant is not a solution. A trained technician should fix any leak, test the repair, and then charge the system with the correct amount of refrigerant. Remember that the performance and efficiency of your air conditioner is greatest when the refrigerant charge exactly matches the manufacturer's specification, and is neither undercharged nor overcharged.
• inadequate maintenance. If you allow filters and air conditioning coils to become dirty, the air conditioner will not work properly, and the compressor or fans are likely to fail prematurely.
• electric control failure. The compressor and fan controls can wear out, especially when the air conditioner turns on and off frequently, as is common when a system is oversized. Because corrosion of wire and terminals is also a problem in many systems, electrical connections and contacts should be checked during a professional service call. RETURN TO TOP OF PAGE
Regular Maintenance
An air conditioner's filters, coils, and fins require regular maintenance for the unit to function effectively and efficiently throughout its years of service. Neglecting necessary maintenance ensures a steady decline in air conditioning performance while energy use steadily increases.
Air Conditioner Filters
The most important maintenance task that will ensure the efficiency of your air conditioner is to routinely replace or clean its filters. Clogged, dirty filters block normal air flow and reduce a system's efficiency significantly. With normal air flow obstructed, air that bypasses the filter may carry dirt directly into the evaporator coil and impair the coil's heat-absorbing capacity. Filters are located somewhere along the return duct's length. Common filter locations are in walls, ceilings, furnaces, or in the air conditioner itself. Some types of filters are reusable; others must be replaced. They are available in a variety of types and efficiencies. Clean or replace your air conditioning system's filter or filters every month or two during the cooling season. Filters may need more frequent attention if the air conditioner is in constant use, is subjected to dusty conditions, or you have fur-bearing pets in the house. RETURN TO TOP OF PAGE
Air Conditioner Coils
The air conditioner's evaporator coil and condenser coil collect dirt over their months and years of service. A clean filter prevents the evaporator coil from soiling quickly. In time, however, the evaporator coil will still collect dirt. This dirt reduces air flow and insulates the coil which reduces its ability to absorb heat. Therefore, your evaporator coil should be checked every year and cleaned as necessary. Outdoor condenser coils can also become very dirty if the outdoor environment is dusty or if there is foliage nearby. You can easily see the condenser coil and notice if dirt is collecting on its fins. You should minimize dirt and debris near the condenser unit. Your dryer vents, falling leaves, and lawn mower are all potential sources of dirt and debris. Cleaning the area around the coil, removing any debris, and trimming foliage back at least 2 feet (0.6 meters) allow for adequate air flow around the condenser.
Coil Fins
The aluminum fins on evaporator and condenser coils are easily bent and can block air flow through the coil. Air conditioning wholesalers sell a tool called a "fin comb" that will comb these fins back into nearly original condition if they are not damaged severly.
Sealing and Insulating Air Ducts
An enormous waste of energy occurs when cooled air escapes from supply ducts or when hot attic air leaks into return ducts. Recent studies indicate that 10% to 30% of the conditioned air in an average central air conditioning system escapes from the ducts. For central air conditioning to be efficient, ducts must be airtight. Hiring a competent professional service technician to detect and correct duct leaks is a good investment, since leaky ducts may be difficult to find without experience and test equipment. Ducts must be sealed with duct "mastic." The old standby of duct tape is ineffective for sealing ducts. Obstructions can impair the efficiency of a duct system almost as much as leaks. You should be careful not to obstruct the flow of air from supply or return registers with furniture, drapes, or tightly fitted interior doors. Dirty filters and clogged evaporator coils can also be major obstructions to air flow. The large temperature difference between attics and ducts makes heat conduction through ducts almost as big a problem as air leakage and obstructions. Ducts in attics should be insulated heavily in addition to being made airtight. RETURN TO TOP OF PAGE
Buying New Air Conditioners
Today's best air conditioners use 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model.
Sizing Air Conditioners
Air conditioners are rated by the number of British Thermal Units (Btu) of heat they can remove per hour. Another common rating term for air conditioning size is the "ton," which is 12,000 Btu per hour. RETURN TO TOP OF PAGE
How big should your air conditioner be?
The size of an air conditioner depends on:
• how large your home is and how many windows it has;
• how much shade is on your home's windows, walls, and roof;
• how much insulation is in your home's ceiling and walls;
• how much air leaks into your home from the outside; and
• how much heat the occupants and appliances in your home generate.
An air conditioner's efficiency, performance, durability, and initial cost depend on matching its size to the above factors. Make sure you buy the correct size of air conditioner. Two groups—the Air Conditioning Contractors of America (ACCA) and the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE)—publish calculation procedures for sizing central air conditioners. Reputable air conditioning contractors will use one of these procedures, often performed with the aid of a computer, to size your new central air conditioner. Be aware that a large air conditioner will not provide the best cooling. Buying an oversized air conditioner penalizes you in the following ways.
• It costs more to buy a larger air conditioner than you need.
• The larger-than-necessary air conditioner cycles on and off more frequently, reducing its efficiency. Frequent cycling makes indoor temperatures fluctuate more and results in a less comfortable environment. Frequent cycling also inhibits moisture removal. During humid times of the year, removing moisture is essential for acceptable comfort. In addition, this cycling wears out the compressor and electrical parts more rapidly.
• A larger air conditioner uses more electricity and creates added demands on electrical generation and delivery systems.
Air Conditioner Efficiency
Each air conditioner has an energy-efficiency rating that lists how many Btu per hour are removed for each watt of power it draws. For room air conditioners, this efficiency rating is the Energy Efficiency Ratio, or EER. For central air conditioners, it is the Seasonal Energy Efficiency Ratio, or SEER. These ratings are posted on an Energy Guide Label, which must be conspicuously attached to all new air conditioners. Many air conditioner manufacturers are participants in the voluntary EnergyStar® labeling program. EnergyStar-labeled appliances mean that they have high EER and SEER ratings. In general, new air conditioners with higher EERs or SEERs sport higher price tags. However, the higher initial cost of an energy-efficient model will be repaid to you several times during its life span. Your utility company may encourage the purchase of a more efficient air conditioner by rebating some or all of the price difference. Buy the most efficient air conditioner you can afford, especially if you use an air conditioner frequently and/or if your electricity rates are high. Room Air Conditioners—EER Room air conditioners generally range from 5,500 Btu per hour to 14,000 Btu per hour. National appliance standards require room air conditioners built after January 1, 1990, to have an EER of 8.0 or greater. Select a room air conditioner with an EER of at least 10.0. The Association of Home Appliance Manufacturers reports that the average EER of room air conditioners rose 47% from 1972 to 1991. If you own a 1970s-vintage room air conditioner with an EER of 5 and you replace it with a new one with an EER of 10, you will cut your air conditioning energy costs in half. RETURN TO TOP OF PAGE
Central Air Conditioners—SEER
National minimum standards for central air conditioners require a SEER of 13.0, for single-package and split-systems. But you do not need to settle for the minimum standard—there is a wide selection of units with SEERs reaching 19 and above. Before 1979, the SEERs of central air conditioners ranged from 4.5 to 8.0. Replacing a 1970s-era central air conditioner with a SEER of 6 with a new unit having a SEER of 13 will cut your air conditioning costs by more than half.
Hiring Professional Service
When your air conditioner needs more than the regular maintenance described previously, hire a professional service technician. A well-trained technician will find and fix problems in your air conditioning system. However, not all service technicians are competent. Incompetent service technicians forsake proper diagnosis and perform only minimal stop-gap measures.
Insist that the technician:
• check for correct amount of refrigerant;
• test for refrigerant leaks using a leak detector;
• capture any refrigerant that must be evacuated from the system, instead of illegally releasing it to the atmosphere;
• check for and seal duct leakage in central systems;
• measure air flow through the evaporator coil;
• verify the correct electric control sequence and make sure that the heating system and cooling system cannot operate simultaneously;
• inspect electric terminals, clean and tighten connections, and apply a non-conductive coating if necessary;
• oil motors and check belts for tightness and wear; and
• check the accuracy of the thermostat. RETURN TO TOP OF PAGE
Choosing a Contractor
Choosing a contractor may be the most important and difficult task in buying a new central air conditioning system. Ask prospective contractors for recent references. If you are replacing your central air conditioner, tell your contractor what you liked and did not like about the old system. If the system failed, ask the contractor to find out why. The best time to fix existing problems is when a new system is being installed. When designing your new air conditioning system, the contractor you choose should:
• use a computer program or written calculation procedure to size the air conditioner;
• provide a written contract listing the main points of your installation that includes the results of the cooling load calculation;
• give you a written warranty on equipment and workmanship
Avoid making your decision solely on the basis of price. The quality of the installation should be your highest priority, because quality will determine energy cost, comfort, and durability.
Installation and Location of Air Conditioners
If your air conditioner is installed correctly, or if major installation problems are found and fixed, it will perform efficiently for years with only minor routine maintenance. However, many air conditioners are not installed correctly. As an unfortunate result, modern energy-efficient air conditioners can perform almost as poorly as older inefficient models. Be sure that your contractor performs the following procedures when installing a new central air conditioning system:
• allows adequate indoor space for the installation, maintenance, and repair of the new system
• uses a duct-sizing methodology such as the Air Conditioning Contractors of America (ACCA) Manual D.
• ensures there are enough supply registers to deliver cool air and enough return air registers to carry warm house air back to the air conditioner.
• seals all ducts with duct mastic and heavily insulates attic ducts.
• locates the condensing unit where its noise will not keep you or your neighbors awake at night, if possible.
• places the condensing unit in a shady spot, if possible, which can reduce your air conditioning costs significantly.
• verifies that the newly installed air conditioner has the exact refrigerant charge and air flow rate specified by the manufacturer.
• locates the thermostat away from heat sources, such as windows, or supply registers. If you are replacing an older or failed split system, be sure that the evaporator coil is replaced with a new one that exactly matches the condenser coil in the new condensing unit. (The air conditioner's efficiency will likely not improve if the existing evaporator coil is left in place; in fact, the old coil could cause the new compressor to fail prematurely.)
If you install a new room air conditioner, try to:
• locate the air conditioner in a window or wall area near the center of the room and on the shadiest side of the house.
• minimize air leakage by fitting the room air conditioner snugly into its opening and sealing gaps with a foam weatherstripping material.
Paying attention to your air conditioning system saves you money and reduces environmental pollution. Notice whether your existing system is running properly, and maintain it regularly. Or, if you need to purchase a new air conditioner, be sure it is sized and installed correctly and has a good EER or SEER rating. RETURN TO TOP OF PAGE
Heat Pumps
Heat Pump Basics
There are two common types of heat pumps: air-source heat pumps and geothermal heat pumps (GHPs). Either one can keep your home warm in the winter and cool in the summer. An air-source heat pump pulls its heat indoors from the outdoor air in the winter and from the indoor air in the summer. A GHP extracts heat from the indoor air when it's hot outside, but when it's cold outside, it draws heat into a home from the ground, which maintains a nearly constant temperature of 50° to 60°F. An air-source heat pump can provide efficient heating and cooling for your home, especially if you live in a warm climate. When properly installed, an air-source heat pump can deliver one-and-a-half to three times more heat energy to a home compared to the electrical energy it consumes. This is possible because a heat pump moves heat rather than converting it from a fuel, like in combustion heating systems. How They Work You might be wondering how an air-source heat pump uses the outdoor winter air to heat a home. Believe it or not: heat can be harvested from cold outdoor air down to about 40°F. And this can be accomplished through a process you're probably already familiar with—refrigeration. Basically, a heat pump's refrigeration system consists of a compressor, and two coils made of copper tubing, which are surrounded by aluminum fins to aid heat transfer. The coils look much like the radiator in your car. Like in a refrigerator or air-conditioner, refrigerant flows continuously through pipes, back and forth from the outdoor coils. In the heating mode, liquid refrigerant extracts heat from the outside coils and air, and moves it inside as it evaporates into a gas. The indoor coils transfer heat from the refrigerant as it condenses back into a liquid. A reversing valve, near the compressor, can change the direction of the refrigerant flow for cooling as well as for defrosting the outdoor coils in winter. When outdoor temperatures fall below 40°F, a less-efficient panel of electric resistance coils, similar to those in your toaster, kicks in to provide indoor heating. This is why air-source heat pumps aren't always very efficient for heating in areas with cold winters. Fuel-burning furnaces generally can provide a more economical way to heat homes in cooler U.S. climates. The efficiency and performance of today's air-source heat pumps is one-and-a-half to two times greater than those available 30 years ago. Indoor Air Quality Concerns All of us face a variety of risks to our health as we go about our day-to-day lives. Driving in cars, flying in planes, engaging in recreational activities, and being exposed to environmental pollutants all pose varying degrees of risk. Some risks are simply unavoidable. Some we choose to accept because to do otherwise would restrict our ability to lead our lives the way we want. And some are risks we might decide to avoid if we had the opportunity to make informed choices. Indoor air pollution is one risk that you can do something about. In the last several years, a growing body of scientific evidence has indicated that the air within homes and other buildings can be more seriously polluted than the outdoor air in even the largest and most industrialized cities. Other research indicates that people spend approximately 90 percent of their time indoors. Thus, for many people, the risks to health may be greater due to exposure to air pollution indoors than outdoors. In addition, people who may be exposed to indoor air pollutants for the longest periods of time are often those most susceptible to the effects of indoor air pollution. Such groups include the young, the elderly, and the chronically ill, especially those suffering from respiratory or cardiovascular disease. http://www.epa.gov/iaq/pubs/insidest.html RETURN TO TOP OF PAGE
Increasing airflow in central heat pumps
The capacity and the efficiency of a heat pump depend upon adequate airflow. There should be about 400 to 500 cubic feet per minute (cfm) airflow for each ton of the heat pump's air-conditioning capacity. Efficiency and performance deteriorate if airflow is much less than 350 cfm per ton. An ideal duct system has both a supply register and a return register for every room. Most homes, however, have only one or two return registers for the entire house. Air from other rooms must find its way back to these registers to be reheated or re-cooled. Obstructions in return air are a common air circulation problem, particularly from closed interior doors to rooms with no return-air register. Blockage of supply or return air ducts and registers can pressurize or depressurize portions of the home, resulting in poor performance and increased air leakage through the building envelope. Restrictions to airflow have the greatest impact on the return-air side of the system, so repairs should start with the return ducts. Air from every supply register must have an unobstructed pathway back to a return register. You can install louvered grilles through walls or doors, ducts between rooms, and/or additional return ducts and registers to improve air circulation. Technicians can increase the airflow by cleaning the evaporator coil, increasing fan speed, or enlarging the ducts—especially return ducts. Enlarging ducts may seem drastic but in some cases, might be the only remedy for poor comfort and high energy costs.
Improving Performance
Poor installation, duct losses, and inadequate maintenance are more of a problem for heat pumps than for combustion furnaces. A growing body of evidence suggests that most heat pumps have significant installation or service problems that reduce performance and efficiency. According to a report on research funded by Energy Star‚ more than 50 percent of all heat pumps have significant problems with low airflow, leaky ducts, and incorrect refrigerant charge RETURN TO TOP OF PAGE
Adjusting refrigerant charge
Room heat pumps and packaged heat pumps are charged with refrigerant at the factory. They are seldom incorrectly charged. Split-system heat pumps, on the other hand, are charged in the field, which can sometimes result in either too much or too little refrigerant. Split-system heat pumps that have the correct refrigerant charge and airflow usually perform very close to manufacturer's listed SEER and HSPF. Too much or too little refrigerant, however, reduces heat-pump performance and efficiency. For satisfactory performance and efficiency, a split-system heat pump should be within a few ounces of the correct charge, specified by the manufacturer. When the charge is correct, specific refrigerant temperatures and pressures listed by the manufacturer will match temperatures and pressures measured by your service technician. Verify these measurements with the technician. If the manufacturer's temperatures and pressure's don't match the measured ones, refrigerant should be added or withdrawn, according to standards specified by the EPA. Refrigeration systems should be leak-checked at installation and during each service call. Manufacturer's say that a technician must measure airflow prior to checking refrigerant charge because the refrigerant measurements aren't accurate unless airflow is correct. http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12300
Installing a New Heat Pump
A heat pump's performance and energy efficiency not only depend on the selection and planning of the equipment but also on careful installation. Consumers and home builders alike tend to accept the lowest bid for heating and air-conditioning work. This unfortunate choice can often leave a system lacking 10 to 30 percent in the materials and labor necessary to optimize heat-pump performance. Rather than just accepting the lowest bid, it's best to research the performance records of local contractors, and get involved in the planning and decision-making about your new heat pump system. You can avoid most of the common comfort and performance problems from improper installation by following these guidelines:
• Make your home as energy-efficient as you can with proper insulation, energy-efficient windows, and an effective air barrier, etc. Then your contractor can install a smaller pump system with shorter duct lengths. In an energy-efficient home, it isn't necessary to run ducts all the way out to exterior walls to install registers near the exterior walls.
• Install the ducts inside your home's insulation and air barrier, if possible. Research shows that this strategy is a major energy saver.
• Insulate your ducts to R-8 if they must be located in an attic or crawl space beyond the home's air barrier and insulation.
• Locate the outdoor unit on the north side of your home if possible. If not, pick a shady spot. There should be no obstructions within 10 feet of the sides with openings and the top.
• Specify that the measured air leakage through your new ducts be less than 10 percent of your system's airflow. Air leakage of 5 percent or less is possible with careful workmanship.
• Tell your contractor that you want a return register in every room.
• Don't use building cavities as ducts. Building-cavity return ducts are notoriously leaky and often cause comfort, energy, and moisture problems.
• Pull on ductwork after installation to make sure it is fastened and sealed well. (Seal duct joints with mastic. http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12300 RETURN TO TOP OF PAGE
Maintaining and Servicing
Heat-pump performance will deteriorate without regular maintenance and service. The difference between the energy consumption of a well-maintained heat pump and a severely neglected one ranges from 10 to 25 percent. Regular Maintenance
• Clean or replace filters regularly (every few weeks, depending on operating time and amount of dust in the environment).
• Clean outdoor coils as often as necessary (when dirt is visible on the outside of the coil).
• Remove plant life and debris from around the outdoor unit.
• Clean evaporator coil and condensate pan every 2 to 4 years.
• Clean the blower's fan blades.
• Clean supply and return registers and straighten their fins.
Professional Service
• Inspect ducts, filters, blower, and indoor coil for dirt and other obstructions.
• Diagnose and seal duct leakage.
• Verify adequate airflow by measurement.
• Verify correct refrigerant charge by measurement.
• Check for refrigerant leaks.
• Inspect electric terminals, and if necessary, clean and tighten connections, and apply nonconductive coating.
• Lubricate motors, and inspect belts for tightness and wear.
• Verify correct electric control, making sure that heating is locked out when the thermostat calls for cooling and vice versa.
• Verify correct thermostat operation. http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12300 RETURN TO TOP OF PAGE
Operating a Heat Pump
Like combustion heating systems, you control heat pumps using thermostats. If you leave and return at regular times everyday, you'll save money by using automatic thermostats, which minimize energy use during the times the home is unoccupied. However, choosing an automatic thermostat's reactivation time requires considering the duration of heat-pump operation necessary to restore a comfortable temperature. During the heating season, some homeowners also set their thermostats back 10°F, manually or automatically, when they leave home or go to bed. A two-stage thermostat controls the heating. The first stage activates the refrigeration system. If it's too cold outside for the refrigeration system to counteract the home's heat loss, then the thermostat's second stage activates the electric resistance coils. An outdoor thermostat will prevent the less efficient electric resistance heat from coming on until the outdoor temperature falls below 40°F. An outdoor thermostat also will prevent auxiliary heat from activating when an automatic thermostat is warming the house after a set-back period. Use setback thermostats that are only for heat pumps. A defrost control tells the reversing valve when to send hot refrigerant outdoors to thaw the outdoor coil during the winter. During the 2-to-10-minute defrost cycle, auxiliary heat takes over, reducing the heat pump's overall efficiency up to 10 percent. The two most common types of defrost controls are time-temperature and demand-defrost. Time-temperature defrost controls activate defrost at regular time intervals for set time periods, whether there is ice on the outdoor coil or not. A demand-defrost control senses coil temperature or airflow through the coil, and only activates defrost if it detects the presence of ice. Obviously, choosing a heat pump with demand-defrost will pay a significant efficiency dividend. For greater efficiency, don't locate a thermostat near a heat source or cold draft because they can cause a heat pump to operate erratically. This includes shading thermostats from direct sunlight. Also, do not turn the thermostat beyond the desired temperature. It will not make the heat pump heat or cool your home any faster. It will only waste energy. Residents who duel one another over the thermostat settings, moving it up and down to suit their different comfort levels, cause heat pumps to operate erratically and inefficiently. http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12300 RETURN TO TOP OF PAGE
Selecting a Heat Pump
When selecting an air-source heat pump, consider the following three characteristics carefully: the energy efficiency rating, sizing, and the system's components. Energy efficiency rating In the United States, we rate a heat pump's energy efficiency by how many British thermal units (Btu) of heat it moves for each watt-hour of electrical energy it consumes. Every residential heat pump sold in this country has an EnergyGuide Label, which features the heat pump's heating and cooling efficiency performance rating, comparing it to other available makes and models. The Heating Seasonal Performance Factor (HSPF) rates both the efficiency of the compressor and the electric-resistance elements. The HSPF gives the number of Btu harvested per watt-hour used. The most efficient heat pumps have an HSPF of between 8 and 10. The Seasonal Energy Efficiency Ratio (SEER) rates a heat pump's cooling efficiency. In general, the higher the SEER, the higher the cost. However, the energy savings can return the higher initial investment several times during the heat pump's life. Replacing a 1970s vintage, central heat pump (SEER = 6) with a new unit (SEER=12) will use half the energy to provide the same amount of cooling, cutting air-conditioning costs in half. The most efficient heat pumps have SEERs of between 14 and 18. You'll find the Energy Star® label—sponsored by the U.S Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA)—on heat pumps with an HSPF of at least 7 and a SEER of at least 12. Many new heat pumps exceed these ratings, but looking for this label is a good way to start shopping for one. Sizing When selecting a new heat pump, it's important that you determine the proper size needed for your home. Bigger is not better. Oversizing causes the heat pump to start and stop more frequently, which is less efficient and harder on the components than letting it run for longer cycles. A properly sized heat pump also will provide you with better comfort and humidity control than an oversized one. The heating and cooling capacity of heat pumps is measured in Btu per hour. The cooling capacity is commonly expressed in "tons" of cooling capacity—each ton equaling 12,000 Btu per hour. Correct sizing procedures involve complex calculations, which are best performed by an experienced contractor, who uses sizing methods accepted by the heat pump industry. Don't employ a contractor who guesses the size of the heat pump needed. Rule-of-thumb sizing techniques are generally inaccurate, often resulting in higher than necessary purchase and annual energy costs. System components You and your contractor should discuss options that will help improve your home's comfort and the economy of your heat pump. Regarding ducts, for example, it's important to carefully consider their design and materials, as well as the proper amount of space they require. Check your home's blueprints to see if the architect and builder have planned adequate space for ducts and fans. Heating and cooling contractors complain that they often have to squeeze heating and cooling systems into spaces that are too small, resulting in constricted ducts and inadequate airflow. Except for packaged systems, you'll also need to select the proper type of indoor coil for adequate summer moisture removal. http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12300 RETURN TO TOP OF PAGE
Thermostats
What Is a Thermostat?
It is a temperature-sensitive switch that controls a space conditioning unit or system, such as a furnace, air conditioner, or both. When the indoor temperature drops below or rises above the thermostat setting, the switch moves to the "on" position, and your furnace or air conditioner runs to warm or cool the house air to the setting you selected for your family's comfort. A thermostat, in its simplest form, must be manually adjusted to change the indoor air temperature. RETURN TO TOP OF PAGE
General Thermostat Operation
You can easily save energy in the winter by setting the thermostat to 68°F (20°C) when you're at home and awake, and lowering it when you're asleep or away. This strategy is effective and inexpensive if you are willing to adjust the thermostat by hand and wake up in a chilly house. In the summer, you can follow the same strategy with central air conditioning, too, by keeping your house warmer than normal when you are away, and lowering the thermostat setting to 78°F (26°C) only when you are at home and need cooling. A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save. Another misconception is that the higher you raise a thermostat, the more heat the furnace will put out, or that the house will warm up faster if the thermostat is raised higher. Furnaces put out the same amount of heat no matter how high the thermostat is set—the variable is how long it must stay on to reach the set temperature. In the winter, significant savings can be obtained by manually or automatically reducing your thermostat's temperature setting for as little as four hours per day. These savings can be attributed to a building's heat loss in the winter, which depends greatly on the difference between the inside and outside temperatures. For example, if you set the temperature back on your thermostat for an entire night, your energy savings will be substantial. By turning your thermostat back 10° to 15° for 8 hours, you can save about 5% to 15% a year on your heating bill—a savings of as much as 1% for each degree if the setback period is eight hours long. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates. In the summer, you can achieve similar savings by keeping the indoor temperature a bit higher when you're away than you do when you're at home. But there is a certain amount of inconvenience that results from manually controlling the temperature on your thermostat. This includes waking up in a cooler than normal house in the winter and possibly forgetting to adjust the thermostat (during any season) when you leave the house or go to bed. RETURN TO TOP OF PAGE
Automatic and Programmable Thermostats
In our modern, high-tech society, we don't think much about some of the electronic gadgets in our homes. Take, for example, the ever-present thermostat—a staple of American households for decades. It usually takes the shape of an unassuming box on the wall, but that modest device controls the comfort of your family on the coldest day in January and the hottest day in July.
Thermostats with Automatic Temperature Adjustment
To maximize your energy savings without sacrificing comfort, you can install an automatic setback or programmable thermostat. They adjust the temperature setting for you. While you might forget to turn down the heat before you leave for work in the morning, a programmable thermostat won't! By maintaining the highest or lowest required temperatures for four or five hours a day instead of 24 hours, a programmable thermostat can pay for itself in energy saved within four years. Programmable thermostats have features with which you may be unfamiliar. The newest generation of residential thermostat technologies is based on microprocessors and thermistor sensors. Most of these programmable thermostats perform one or more of the following energy control functions:
• They store and repeat multiple daily settings, which you can manually override without affecting the rest of the daily or weekly program.
• They store six or more temperature settings a day.
• They adjust heating or air conditioning turn-on times as the outside temperature changes. Most programmable thermostats have liquid crystal temperature displays. Some have back-up battery packs that eliminate the need to reprogram the time or clock in case of a power failure. New programmable thermostats can be programmed to accommodate life style and control heating and cooling systems as needed
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Types of Automatic and Programmable Thermostats
There are five basic types of automatic and programmable thermostats:
• electromechanical,
• digital,
• hybrid,
• occupancy, and
• light sensing.
Most range in price from $50 to $200, except for occupancy and light sensing thermostats, which cost around $300. Electromechanical (EM) thermostats, usually the easiest devices to operate, typically have manual controls such as movable tabs to set a rotary timer and sliding levers for night and day temperature settings. These thermostats work with most conventional heating and cooling systems, except heat pumps. EM controls have limited flexibility and can store only the same settings for each day, although at least one manufacturer has a model with separate settings for each day of the week. EM thermostats are best suited for people with regular schedules. Digital thermostats are identified by their LED or LCD digital readout and data entry pads or buttons. They offer the widest range of features and flexibility, and digital thermostats can be used with most heating and cooling systems. They provide precise temperature control, and they permit custom scheduling. Programming some models can be fairly complicated; make sure you are comfortable with the functions and operation of the thermostat you choose. Remember— you won't save energy if you don't set the controls or you set them incorrectly. Hybrid systems combine the technology of digital controls with manual slides and knobs to simplify use and maintain flexibility. Hybrid models are available for most systems, including heat pumps. Occupancy thermostats maintain the setback temperature until someone presses a button to call for heating or cooling. They do not rely on the time of day. The ensuing preset "comfort period" lasts from 30 minutes to 12 hours, depending on how you've set the thermostat. Then, the temperature returns to the setback level. These units offer the ultimate in simplicity, but lack flexibility. Occupancy thermostats are best suited for spaces that remain unoccupied for long periods of time. Light sensing heat thermostats rely on the lighting level preset by the owner to activate heating systems. When lighting is reduced, a photocell inside the thermostat senses unoccupied conditions and allows space temperatures to fall 10° below the occupied temperature setting. When lighting levels increase to normal, temperatures automatically adjust to comfort conditions. These units do not require batteries or programming and reset themselves after power failures. Light sensing thermostats are designed primarily for stores and offices where occupancy determines lighting requirements, and therefore heating requirements. RETURN TO TOP OF PAGE
Choosing a Programmable Thermostat
Because programmable thermostats are a relatively new technology, you should learn as much as you can before selecting a unit. When shopping for a thermostat, bring information with you about your current unit, including the brand and model number.
Also, ask these questions before buying a thermostat:
• Does the unit's clock draw its power from the heating systems's low-voltage electrical control circuit instead of a battery? If so, is the clock disrupted when the furnace cycles on and off? Battery-operated, back-up thermostats are preferred by many homeowners.
• Is the thermostat compatible with the electrical wiring found in your current unit?
• Are you able to install it yourself, or should you hire an electrician or a heating, ventilation, and air conditioning (HVAC) contractor?
• How precise is the thermostat?
• Are the programming instructions easy to understand and remember? Some thermostats have the instructions printed on the cover or inside the housing box. Otherwise, will you have to consult the instruction booklet every time you want to change the setback times?
Most automatic and programmable thermostats completely replace existing units. These are preferred by many homeowners. However, some devices can be placed over existing thermostats and are mechanically controlled to permit automatic setbacks. These units are usually powered by batteries, which eliminates the need for electrical wiring. They tend to be easy to program, and because they run on batteries, the clocks do not lose time during power outages. Before you buy a programmable thermostat, chart your weekly habits including wake up and departure times, return home times, and bedtimes, and the temperatures that are comfortable during those times. This will help you decide what type of thermostat will best serve your needs. RETURN TO TOP OF PAGE
Will installing a programmable thermostat reduce my heating and cooling consumption?
Yes, programmable thermostats can reduce the energy used for air conditioning or heating by 5 to 30%. Programmable thermostats, while not always digital, save money by turning the air conditioner to a higher setting (or heater to a lower setting) when no one is present in the house, or in the evenings when it is cooler. You can achieve the same savings without the programmable thermostat, but you would have to remember to change your thermostat every day when you leave the house, and turn it down every night when you go to bed. In addition, if you are using the thermostat to regulate your heater, you would wake to a cold house. The programmable thermostat does all of the remembering for you once it is set. A sample of a heating schedule you might program into a thermostat is: Wake up 6:00 am - 9:00 am 68°F Leave 9:00 am - 5:30 pm 60°F Evenings 5:30 pm - 11:00 pm 68°F Sleep 11:00 pm - 6:00 am 60°F This way your house is always comfortable and you can save money on heating. You can make a similar schedule for air conditioning. Wake up 6:00 am - 9:00 am 75°F Leave 9:00 am - 5:30 pm 80°F Evenings 5:30 pm - 11:00 pm 75°F Sleep 11:00 pm - 6:00 am 78°F or off
Other Considerations
The location of your thermostat can affect its performance and efficiency. Read the manufacturer's installation instructions to prevent "ghost readings" or unnecessary furnace or air conditioner cycling. Place thermostats away from direct sunlight, drafts, doorways, skylights, and windows. Also make sure your thermostat is conveniently located for programming. RETURN TO TOP OF PAGE
A Note for Heat Pump Owners
When a heat pump is in its heating mode, setting back a conventional heat pump thermostat can cause the unit to operate inefficiently, thereby canceling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice. Recently, however, some companies have begun selling specially designed setback thermostats for heat pumps, which make setting back the thermostat cost effective. In its cooling mode, the heat pump operates like an air conditioner; therefore, manually turning up the thermostat will save you money.
A Simpler Way to Control Your Environment
The best thermostat for you will depend on your life style and comfort level in varying house temperatures. While automatic and programmable thermostats save energy, a manual unit can be equally effective if you diligently regulate its setting—and if you don't mind a chilly house on winter mornings. If you decide to choose an automatic thermostat, you can set it to raise the temperature before you wake up and spare you some discomfort. It will also perform consistently and dependably to keep your house at comfortable temperatures during the summer heat, as well. RETURN TO TOP OF PAGE
Additional Information
What's the most common mistake people make in trying to save energy around the house?
Common mistakes people make include:
• letting the furnace or air conditioner salesperson sell them a unit that's much bigger than they need,
• not getting the ducts checked for leakage when installing a new heating and cooling system,
• thinking that "since heat rises, we only need to insulate the attic." Floors over a basement or crawlspace, walls and windows also matter.
• not using ceiling and portable fans to improve comfort in the cooling season. They use very little electricity. Use them to circulate air in the house, tomake the house feel cooler by doing this, the thermostat setting for your air conditioner can be raised to 85°F, and still maintain the same comfort as the lower setting.
What's the single biggest user of electricity in my house?
If your house has central air conditioning, the air conditioner will probably be the biggest user by far. Although used only a few months of the year, the annual cost can be much greater than the annual cost of your refrigerator, which is typically the next largest user. In hot climates, the annual air conditioner cost can exceed a thousand dollars. You can get a very rough idea of what your air conditioner is costing you by subtracting the electric portion of your bill in a spring month when you aren't using your air conditioner from the electric portion of the bill in the summer when you do use it. This gives you the monthly cost. Multiply this by the number of months you use your air conditioner to arrive at your approximate annual cost. RETURN TO TOP OF PAGE
We have an older house. Which should we do first:
insulate or replace the furnace? Whether you should insulate or replace your furnace first depends on the situation in your house. Factors that influence this decision are the age and efficiency of your furnace, and the amount of insulation currently present in the house. In general it is more cost-effective to upgrade insulation than it is to upgrade your furnace. However, if your furnace is old, and you are planning on replacing it anyway, you might want to upgrade the furnace if you have to choose between the two options. The average lifetime for a furnace is between 15 and 20 years. The efficiency of furnaces has increased over the years, so the older a furnace is, the more likely that furnace is to be inefficient. The average efficiency of new furnaces has increased from 63% in 1972 to 83% in 1995. Older furnaces, and furnaces which are used a lot are more cost-effective to replace than newer or infrequently used furnaces. Also, if you insulate your house at the time of furnace replacement, you might be able to buy a smaller capacity furnace and save money on the price. The same holds true for A/C and other heating and cooling equipment.
Air-sealing ducts
Measurements of heat pump performance indicate that duct leakage wastes 10 to 30 percent of the heating and/or cooling energy in a typical home. It's one of the most severe energy problems commonly found in homes because the leaking air is 20° to 70°F warmer than indoor air in winter and 15° to 30°F cooler in the summer. Duct leakage may cause some minor comfort problems when ducts are located in conditioned areas. But when leaky ducts are located in an attic or crawl space, the energy loss is often large. Some of the worst duct leakage occurs at joints between the air handler, and the main supply and return air ducts. Some main return ducts use plywood or fiberglass duct-board boxes. These boxes frequently leak because their joints are exposed to the duct system's highest air pressures. Heating and air-conditioning contractors often use wall, floor, and ceiling cavities as return ducts. These building-cavity return ducts are often accidentally connected to an attic, crawl space, or even the outdoors, creating serious air leakage. Fiberglass ducts and flex ducts are often installed improperly. These ducts may also deteriorate with age, leading to significant supply-duct leakage. The best heating and cooling contractors have equipment to test for duct leakage. Testing helps locate duct leaks and indicates how much duct sealing is necessary. Do not use duct tape for sealing—its life span is very short, often less than 6 months. RETURN TO TOP OF PAGE
What Causes Indoor Air Problems?
Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the home. High temperature and humidity levels can also increase concentrations of some pollutants. Pollutant Sources There are many sources of indoor air pollution in any home. These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; building materials and furnishings as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices; and outdoor sources such as radon, pesticides, and outdoor air pollution. The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are significant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide than one that is properly adjusted. Some sources, such as building materials, furnishings, and household products like air fresheners, release pollutants more or less continuously. Other sources, related to activities carried out in the home, release pollutants intermittently. These include smoking, the use of unvented or malfunctioning stoves, furnaces, or space heaters, the use of solvents in cleaning and hobby activities, the use of paint strippers in redecorating activities, and the use of cleaning products and pesticides in housekeeping. High pollutant concentrations can remain in the air for long periods after some of these activities. Amount of Ventilation If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Unless they are built with special mechanical means of ventilation, homes that are designed and constructed to minimize the amount of outdoor air that can "leak" into and out of the home may have higher pollutant levels than other homes. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally considered "leaky." http://www.epa.gov/iaq/pubs/insidest.html Indoor Air and Your Health Health effects from indoor air pollutants may be experienced soon after exposure or, possibly, years later. Immediate effects may show up after a single exposure or repeated exposures. These include irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply eliminating the person's exposure to the source of the pollution, if it can be identified. Symptoms of some diseases, including asthma, hypersensitivity pneumonitis, and humidifier fever, may also show up soon after exposure to some indoor air pollutants. The likelihood of immediate reactions to indoor air pollutants depends on several factors. Age and preexisting medical conditions are two important influences. In other cases, whether a person reacts to a pollutant depends on individual sensitivity, which varies tremendously from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well. Certain immediate effects are similar to those from colds or other viral diseases, so it is often difficult to determine if the symptoms are a result of exposure to indoor air pollution. For this reason, it is important to pay attention to the time and place the symptoms occur. If the symptoms fade or go away when a person is away from the home and return when the person returns, an effort should be made to identify indoor air sources that may be possible causes. Some effects may be made worse by an inadequate supply of outdoor air or from the heating, cooling, or humidity conditions prevalent in the home. Other health effects may show up either years after exposure has occurred or only after long or repeated periods of exposure. These effects, which include some respiratory diseases, heart disease, and cancer, can be severely debilitating or fatal. It is prudent to try to improve the indoor air quality in your home even if symptoms are not noticeable. While pollutants commonly found in indoor air are responsible for many harmful effects, there is considerable uncertainty about what concentrations or periods of exposure are necessary to produce specific health problems. People also react very differently to exposure to indoor air pollutants. Further research is needed to better understand which health effects occur after exposure to the average pollutant concentrations found in homes and which occur from the higher concentrations that occur for short periods of time. http://www.epa.gov/iaq/pubs/insidest.html RETURN TO TOP OF PAGE
Source List
Ask an Energy Expert Energy Efficiency and Renewable Energy Clearinghouse (EREC) P.O. Box 3048 Merrifield, VA 22116 (800) 363-3732 Fax: (703) 893-0400 E-mail: doe.erec@nciinc.com
Consumer Energy Information Web Site Energy experts at EREC provide free general and technical information to the public on many topics and technologies pertaining to energy efficiency and renewable energy.
Reading List
"Electronic Thermostats," Radio-Electronics, June 1992.
"Energy Saving Thermostats," Consumer Reports, October 1993."
"Good News on the 'Setback' Front," T. Wilson, Home Energy, Jan-Feb 1991. 2124 Kittredge Street, No. 95, Berkeley, CA 94704, (510) 524-5405.
"Get Comfortable with Your Setback Thermostat" (PDF 805 KB), the California Energy Commission.
"Home Environment," Home Mechanix, February 1992.
"Home Q&A," Home Mechanix, November 1995.
"The Latest in Home Thermostats," Consumers' Research Magazine, February 1990.
"New Electronic Thermostats Save Money," Consumers Digest, January 1989.
"Programmable Thermostats: How to Buy and Install One in Your Home,
" Family Handyman, January 1989. "Smart Thermostats for Comfort and Conservation,
" March 1994, EPRI Journal.
This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. DOE/GO-10097-375 FS 215 March 1997
NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. RETURN TO TOP OF PAGE |
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