Safety & Energy Articles from FEC

The Rural Missouri NEWS Service
Jim McCarty 573-635-6857, ext. 3402

2007 Safety Articles | 2009 Safety Articles

May 2008

Cool savings for air conditioning season

Imagine summer without air conditioning. True, your parents or grandparents got by with oscillating fans. And even today, one-third of U.S. homes do not have air conditioning.

Today, our appetite for air conditioning consumes about 5 percent of all electricity generated at an annual cost of more than $11 billion, according to the U.S. Department of Energy.

Choosing high-efficiency air conditioners and taking other actions to keep your home cool could reduce this energy use by as much as 50 percent. The most efficient room air conditioners on the market are up to 70 percent more efficient than more standard room air conditioners. While the upfront cost of such units is high, they more than pay for themselves in the energy they save.

Here’s some tips for getting the most from the dollars you spend on air conditioning.

How air conditioners work

Air conditioners operate much like refrigerators. The U.S. Department of Energy explains it this way:

A cold indoor coil, called an evaporator, cools your house. A hot outdoor coil, known as a condenser, releases the collected heat outside. Both sets of coils are formed as serpentine tubes, usually made of copper, surrounded by aluminum fins. A pump, called a compressor, moves a refrigerant between the evaporator and the condenser, forcing the refrigerant through the tubes and fins in the coils.
The liquid refrigerant evaporates in the evaporator coil, pulling heat out of indoor air and cooling the house. The hot refrigerant gas is pumped outdoors into the condenser where it reverses back to a liquid and gives up its heat to the air flowing over the condenser’s tubing and fins.

Room or central air conditioning?

The basic types of air conditioners are room (also known as window) and central units, which come in two styles: split-system and packaged. Room air conditioners cool rooms rather than an entire house, whereas central units circulate cool air through a system of supply and return ducts in walls, floors or ceilings.

Most central air conditioners are split systems in which an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system units, the indoor cabinet also contains a furnace or the air-handling components of a heat pump.

In a packaged central unit, the evaporator, condenser and compressor are all located in one cabinet, usually on a roof or on a concrete pad next to the house’s foundation. Packaged units are ideal for situations where indoor space is at a premium; they also are often used in small commercial buildings. In packaged systems, air supply and return ducts come from indoors through the exterior wall or roof to connect with the packaged unit outside. Packaged units often include electric heating coils or a natural gas furnace, which eliminates the need for a separate furnace indoors.

The Missouri Department of Natural Resources offers these pluses and minuses for room versus central air conditioners from its Web site at www.dnr.mo.gov/energy/residential/residential.htm:

Room A/C Pluses

They allow for zoned cooling, which can save substantial amounts of electricity and money
They’re less expensive to buy than a central unit

Room A/C Minuses

You don’t have the convenience of whole-house cooling
They’re noisier

Central A/C Pluses

They provide whole-house air conditioning, which is desirable if many rooms are used on a fairly constant basis

Central A/C Minuses

They cost more to buy, install and run
They’re more likely to require tune-up and maintenance from a contractor versus your doing your own maintenance

Measuring air conditioning efficiency

The efficiency of room and central air conditioning units is measured differently. The U.S. Department of Energy explains that a room air conditioner’s efficiency is measured by the energy efficiency ratio (EER). The EER is the ratio of the cooling capacity (in British thermal units – Btu – per hour) to the power input (in watts). The required cooling capacity depends on the size of the room being cooled; the amount of insulation; the outdoor temperature; and the desired indoor temperature. The higher the EER, the more efficient the unit. Look for units with an EER of 10 or above.

For central units, efficiency is measured by the seasonal energy efficiency ratio (SEER). National minimum standards increased in 2006 for central air conditioners and now require a SEER of at least 13. Some Energy Star-qualified units have SEERs reaching nearly 17. Before 1979, SEERs of central air conditioners ranged from 4.5 to 8.0.

When buying a unit, look for the bright yellow EnergyGuide label that gives the EER or SEER and calculates how much electricity the unit will use in a year.

Sizing air conditioners

The common rating term for air conditioning size is the “ton,” which is equal to 12,000 British thermal units (Btu) of heat removed per hour. The energy required to lower the temperature of 1 pound of water 1 degree Fahrenheit is equivalent to one Btu.

Another way of understanding the relationship between a ton and a Btu is that it would take 12,000 Btu of heat to melt 1 ton of ice.

The size of a unit depends on these U.S. Department of Energy guidelines:

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 house from the outside
How much heat the occupants and appliances in your home generate

Two groups, the Air Conditioning Contractors of America (ACCA) and the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), publish calculations for sizing central air conditioners. Reputable contractors will use one of these procedures to size your new central unit.

Insist your contractor use the ACCA’s Manual J® residential load calculation procedure. This is the official standard for residential load calculation and is required by many building codes around the country.

Sizing for concrete homes

One construction technique used in framing new homes is to use insulated concrete forms. These Styrofoam forms interlock to create a wall structure that is filled with concrete to create the exterior walls. This type of framing is an important factor in sizing your air conditioning unit. According to the Portland Cement Association, insulated concrete walls can result in heating and air conditioning equipment being downsized by as much as 15 percent to 40 percent in concrete-framed homes compared to identical wood-framed homes.

Jeff Barber, a housing and environmental design specialist for the Southwest Region of the University of Missouri Extension, says the Air Conditioning Contractors of America’s Manual J and the American Society of Heating, Refrigerating, and Air Conditioning Engineers’ (ASHRAE) Handbook of Fundamentals don’t adequately account for the better insulating properties and lower air infiltration of walls with greater thermal mass, such as those made from concrete.

Instead, he recommends HVAC Sizing for Concrete Homes, a software program that provides an alternative means of estimating heating and cooling system needs for concrete homes. The software was developed through the U.S. Department of Housing and Urban Development, using U.S. Department of Energy calculations and various ASHRAE standards. For more information about sizing heating and cooling equipment for concrete homes, contact your local University of Missouri Extension office or a licensed heating, ventilation and air conditioning (HVAC) contractor.

Bigger isn’t better

According to the U.S. Department of Energy, a large air conditioner doesn’t provide the best cooling. Buying an oversized unit costs you in these ways:

It costs more to buy a larger unit.
The larger-than-necessary unit cycles on and off more frequently. This reduces efficiency and causes indoor temperatures to fluctuate more. Frequent cycling also inhibits moisture removal.
A larger unit uses more electricity and creates added demands on electrical generation.

Room air conditioner basics

Sizing tips
A common mistake is to buy an air conditioner that is too large. The thought is that it will provide better cooling. In fact, an oversized air conditioner is actually less effective and wastes energy, plus it can wear out more quickly.

According to Energy Star, the government’s program for setting efficiency standards in equipment, appliances and materials, air conditioners remove both heat and humidity from the air. It’s true an oversized until can cool a room quickly, but it will remove only some of the humidity, leaving the room with a damp, clammy feeling. A properly sized unit will effectively remove humidity as it cools.

Here’s what Energy Star recommends for sizing a room air conditioner:

For square and rectangular rooms, multiply the length of the area by its width
For triangular areas, multiply the length by the width and divide by 2
For other shaped areas, ask an air conditioning sales person or contractor to determine the square footage
Use the square footage and accompanying chart to determine the correct cooling capacity as measured in British thermal units (Btu) per hour

Area to be Cooled (square feet) - Capacity Needed (Btu per hour)

100 to 150 - 5,000
150 to 250 - 6,000
250 to 300 - 7,000
300 to 350 - 8,000
350 to 400 - 9,000
400 to 450 - 10,000
450 to 550 - 12,000
550 to 700 - 14,000
700 to 1,000 - 18,000
1,000 to 1,200 - 21,000
1,200 to 1,400 - 23,000
1,400 to 1,500 - 24,000
1,500 to 2,000 - 30,000
2,000 to 2,500 - 34,000

Make these adjustments as necessary:

If the room is heavily shaded, reduce capacity by 10 percent
If the room is sunny, increase capacity by 10 percent
If more than two people regularly occupy the room, add 600 Btu for each additional person
If the unit is used in a kitchen, increase capacity by 4,000 Btu
If you are mounting an air conditioner near the corner of a room, look for a unit that can send the airflow in the right direction

Proper power
In the United States, 110 volts, 115 volts and 120 volts are used interchangeably to describe the most common voltage range. Likewise, 220 volts, 230 volts and 240 volts refer to one voltage range. Small room air conditioners generally can operate on 110- to 120-volt circuits. However, according to the U.S. Department of Energy, large room units rated at 115 volts may require a dedicated circuit, and units rated at 230 volts may require a special circuit.

Of course, don’t take any chances with electricity. Consult with a licensed electrician about the proper electrical hook-up for your room air conditioner.

Proper mounting
If you are mounting your air conditioner near the corner of a room, look for a unit that directs its airflow in the desired direction for your room layout. If you need to mount the unit at the narrow end of a long room, look for a fan control known as “Power Thrust” or “Super Thrust” that sends the cooled air farther into the room.

Other features to look for:

A filter that slides out easily for regular cleaning
Logically arranged controls
A digital readout for the thermostat setting
A built-in timer

Central air conditioner basics

Efficiency standards
The U.S. Department of Energy implemented new efficiency standards for residential central air conditioners in January 2006. Since then, central units have been required to have a seasonal energy efficiency ratio (SEER) of 13 or higher.

Units manufactured after Jan. 23, 2006, are 30 percent more efficient than the previous minimum standard of SEER 10. The government predicts that from 2006 through 2030 the SEER 13 standard will save the equivalent energy consumed by nearly 26 million households and save consumers $1 billion.

Properly sizing a central unit
Factors such as square footage, number and placement of windows, exterior shading, insulation, air leaks and number of appliances and occupants affect the size of a central unit. Your contractor should use the calculation in the Air Conditioning Contractors of America’s Manual J. This is the official standard for residential load calculation and is required by many building codes around the country.

Retire your over-the-hill unit and save
That “good as new” 10-year-old unit may not be as good as you think it is. Chances are it’s using much more energy than necessary to cool your home.

Nearly half of the average home’s energy bill during the summer goes to cooling it, according to Energy Star, a joint program of the U.S. Environmental Protection Agency and U.S. Department of Energy. If every room air conditioner sold in the United States were Energy Star-qualified, it would prevent 1.2 billion pounds of emissions or the equivalent of emissions from 100,000 cars. In fact, if sized and installed correctly, Energy Star-qualified heating and cooling equipment:

Can save you up to 20 percent on your annual energy costs
Will use 25 percent to 40 percent less energy than a new conventional system

Smart air conditioning use saves $$$$

Yes, there’s a price to pay for a house cooled by air conditioning. But by using air conditioning wisely, you can reduce that price. Here’s how, according to the Missouri Department of Natural Resources and the U.S. Department of Energy:

Set your thermostat as high as comfortably possible
Use a programmable thermostat to adjust the setting on your air conditioner at night or when no one is home; avoid using the air conditioner when you are not home
Use a fan with your window air conditioner to spread cool air effectively through your home
Don’t set your thermostat at a colder setting than normal when you turn on your air conditioner; it won’t cool your house any faster and could result in excessive cooling and unnecessary expense
Don’t place lamps or TVs near your air conditioner’s thermostat; the heat from the appliances will cause the air conditioner to run longer
Shade your existing condenser with a screen or foliage so it’s not in direct sunlight or place it on the north side of your house if you are adding a new unit. Doing so may reduce your energy cost by 1 percent to 2 percent. However, don’t obstruct air flow around the unit.
Locate a room air conditioner in a window or wall near the center of the room and on the shadiest part of the house; seal gaps between the unit and the window with foam weatherstripping.

Checking up on your air conditioning contractor

Bob Vila, nationally known home improvement and remodeling expert, knows a thing or two about air conditioning. Here are some suggestions from him, the U.S. Department of Energy and Energy Star for a maintenance checklist for your air conditioning contractor:

Check for correct amount of refrigerant. Too much or too little will make your system less efficient, increase energy costs and reduce the life of the equipment
Test for refrigerant leaks using a leak detector. The performance and efficiency of your air conditioner is greatest when the refrigerant charge exactly matches the manufacturer’s specification
Capture any refrigerant that must be evacuated from the system instead of releasing it to the atmosphere; your contractor should know the federal rules about proper disposal of ozone-destroying chlorofluorocarbons and hydrochlorofluorocarbons, the two most common types of air-conditioning refrigerants
Measure air flow through the evaporator coil. Dirty coils may restrict air flow
Clean and adjust blower components to provide proper system air flow for greater comfort. Air flow problems can reduce your system’s efficiency by up to 15 percent
Clean evaporator and condenser coils. Dirty coils reduce the system’s ability to cool your home and cause the system to run longer, increase energy costs and reduce the life of the unit; remove debris around condenser coils and trim foliage back at least 2 feet from the condenser
Verify the correct electric control sequence and make sure 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
Check the accuracy of the thermostat
Check for and seal duct leaks in central systems
Readjust coil fins if they are bent
Check your return air grilles and supply air registers for proper sizing and placement

Your contractor can show you how to inspect, clean or change air filters. Do this at least once a month during the season of use. A dirty filter can increase energy costs and damage your equipment, leading to early failure.

Also have your contractor show you how to use a “fin comb” to adjust bent coil fins back to their original shape.

Reduce your need for AC

The easiest way to save money and energy from cooling is to reduce the need for air conditioning. Here are some tips from the American Council for an Energy-Efficient Economy:

Shade or improve windows – Consider horizontal trellises for your east and west-facing windows. Protect south-facing windows with deciduous trees or climbing foliage so you can take advantage of low-angle sun in the winter. New windows on those walls that get the most summer sun should have low-e glazings to block unwanted heat gain.
Cool with air movement and ventilation – Circulating air with fans will help cool your house, reduce your air conditioning usage by as much as 30 percent and use very little energy doing it. A ceiling fan in summer can make a room feel as much as 7 degrees cooler by creating a “wind chill” effect. Adjust your ceiling fan so it turns counterclockwise and blows air downward. Think about stepping out of a shower and then sitting directly under a ceiling fan. Do you want to feel cool or warm? Adjust the fan accordingly.
Portable fans also can be effective in moving air. Even mild air movement of 1 mph can make you feel 3 or 4 degrees cooler.
House or attic fans can be an effective way to cool your entire house without central air conditioning. These fans suck air through the house, inducing a strong draft in rooms where windows are open as it pulls cooler, outdoor air inside. However, before switching on the house fan, consider the temperature and humidity level outside. A house fan may pull in unwanted humidity, resulting in more work for your air conditioner.
Insulate and tighten your house – Make checking insulation levels and air leaks between your living space and the attic your highest priority.
Get rid of inefficient appliances – Inefficient appliances emit a lot of heat. Old refrigerators are prime suspects. Also replace incandescent light bulbs, which give off more heat energy than light energy, with compact fluorescents, and unplug electronic equipment not being used.
Consider cool exterior finishes – Use light-colored or other cool roofing and siding products that can reduce your peak cooling demand by 10 to 15 percent.

What about portable air conditioners and dehumidifiers?

Portable air conditioners are free-standing floor units that don’t have to be installed in a window. They can be effective in either supplementing a central unit or cooling a single room.

If the portable unit is operating as a true air conditioner through a heat exchange process, then it needs venting through one or two exhaust hoses. These can be easily installed in a room window with a window kit or to another location. If the portable unit is simply removing humidity from the air, thus making it feel cooler, then exhaust hoses are not required.

It’s true that removing moisture from the air – dehumidifying – makes us feel more comfortable. To boost efficiency in air conditioners, according to the Missouri Department of Natural Resources, many highly efficient air conditioners do not dehumidify effectively.

If you need to remove moisture from your house – evidenced by musty smells, a clammy feeling to the air, condensation on windows and wet stains on the wall or ceiling – look for Energy Star-qualified dehumidifiers. Look for units that remove the most pints of water per hour.

Useful air conditioning and summer cooling Web sites and contacts

The Web sites below offer helpful information on air conditioning. Also consider a call to your local University of Missouri Extension office. Some extension agents have training in efficient housing design, including sizing air conditioners. And don’t forget your local cooperative, which may offer tips and incentives for switching to more efficient air conditioners.

www.acca.org/energystar - The Air Conditioning Contractors of America can help locate a contractor in your area who sells and installs Energy Star-qualified units

www.ashrae.org - The American Society of Heating, Refrigeration, and Air Conditioning Engineers offers publications on air conditioning

www.energystar.gov - Check out Energy Star for qualified products and access to installers

www.ari.org - The Air Conditioning and Refrigeration Institute offers consumer brochures

www.energystar.gov/index.cfm?fuseaction=sizing.showIntro#insulated - Answer the questions on this Energy Star page to help calculate what size central air conditioning unit you will need

www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12420 - The U.S. Department of Energy’s Energy Efficiency and Renewable Energy department offers guidance on sizing a room air conditioner

hes.lbl.gov/ - This Home Energy Savers site includes an energy calculator and other useful information about saving energy in your home; it is sponsored by the Environmental Energy Technologies Divisions of Lawrence Berkeley National Laboratories

www.dnr.mo.gov/energy/residential/residential.htm - The Missouri Department of Natural Resources Energy Center includes summer cooling tips

www.cement.org/bookstore/profile.asp?itemid=CD044 - This site offers a software program, HVAC Sizing for Concrete Homes, that provides an alternative means of estimating heating and cooling system needs for homes built with insulated concrete forms

www.consumerreports.org/cro/appliances/heating-cooling-and-air/air-conditioners/reports/sizing-worksheet/index.htm - Consumer Reports offers a handy online calculator for helping properly size an air conditioner

www.touchstoneenergysavers.com - From the nation’s Touchstone Energy Electric Co-ops, this is your one-stop connection to valuable tools, resources and information to help you create a more energy-efficient home.

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