What is Cooling My Office and is it Efficient

Energy Savings Center - HVAC: Packaged Rooftop Air Conditioners

Approximately half of all U.S. commercial floor space is cooled by self-contained, packaged air-conditioning units, most of which sit on rooftops (Figure 1). Also called unitary air conditioners or simply "packaged units," these mass-produced machines include cooling equipment, air-handling fans, and sometimes gas or electric heating equipment. Rooftop units (RTUs) are available in sizes ranging from 1 ton to more than 100 tons of air-conditioning capacity (1 ton of cooling capacity will remove 12,000 Btu of heat per hour).

The three main power consumers in a rooftop unit—compressor, supply fan, and condenser fan—account for approximately 83, 10, and 7 percent, respectively, of the RTU's peak power (Figure 2). However, because supply fans are often used to provide ventilation even when the compressor is not in use, the compressor’s annual energy usage can be as low as 55 percent of the total energy use, with fans accounting for the remaining 45 percent.

What Are the Options?

Efficiency. RTUs of the same capacity are usually available with a wide range of efficiencies. The Air-Conditioning and Refrigeration Institute (ARI) defines efficiency in several different ways:

• EER (energy-efficiency ratio): The ratio of the rate of cooling (Btu per hour, or Btu/h) to the power input (watts) at full-load conditions. The power input includes all inputs to compressors, fan motors, and controls.

•SEER (seasonal energy-efficiency ratio): A seasonally adjusted rating based on representative residential loads. SEER applies only to RTUs with a cooling capacity of less than 65,000 Btu per hour.

• IPLV (integrated part-load value): A seasonal efficiency rating method based on representative annual commercial loads. It applies to RTUs with cooling capacities equal to or greater than 65,000 Btu per hour.

EER is the rating of choice when determining which RTU will operate most efficiently during full-load conditions. SEER and IPLV are better indicators of which RTU will use less energy over the course of an entire cooling season.

The cooling efficiencies of RTUs under 250,000 Btu per hour are certified according to standards published by ARI. (ARI standards also apply to RTUs of 250,000 Btu per hour and over, but ARI has no certification program and does not publish efficiency data for this size range.)

Federal minimum standards. The current U.S. federal standard, last updated in 1992, requires manufacturers to produce equipment at a minimum efficiency of 8.9 EER and 8.3 IPLV for units with a capacity of at least 65 but less than 135,000 Btu/h and at a minimum efficiency of 8.5 EER and 7.5 IPLV for units of at least 135,000 Btu/h but less than 240,000 Btu/h.

Highest available efficiency. Manufacturers of RTUs continue to offer higher-efficiency units. As of 2005, the highest-efficiency RTUs on the market in sizes ranging from 65,000 to 135,000Btu/h have EER values as high as 13.5; units from 135,000 to 240,000 Btu/h have EER values as high as 13.1.

Compressor. Most RTUs use efficient reciprocating compressors, with several control options to consider. RTUs normally handle part-load conditions with simple on/off switches, operated by programmable timers, to stage compressors. As an alternative to completely shutting off the compressor, some units offer multiple valve-operated cylinders within the compressor that can be shut off individually. Effectively, shutting off cylinders creates a smaller cooling unit that is nevertheless operating with the original heat exchangers, and the result is a more efficient RTU. Another option is hot-gas bypass, which allows the compressor to provide reduced cooling at low loads. However, this option reduces capacity without reducing energy consumption.

Condenser. Nearly all RTUs under 20 tons have air-cooled condensers, which are about 20 percent less efficient than the evaporative condensers used in larger and more efficient models. Because evaporating water can remove more condenser heat than a stream of ambient air, lower condenser temperature and pressure are attained, and the compressors can therefore run at lower power. For smaller units, however (below about 20 tons), the energy required for pumping and spraying the water can outweigh the compressor energy savings gained by evaporative cooling. Other potential drawbacks are that the savings from water cooling decrease in humid climates and that evaporative condensers require more maintenance than air-cooled condensers.

Fans. Fans are used to move air across both the condenser and the evaporator. The airflow across the latter is also the supply air for the building. Although fan power use is a small fraction of compressor power use, fans can account for approximately 45 percent of the annual energy use because the fan operates for many more hours than the compressor. Most manufacturers also offer units with high-efficiency fans that increase both EER and IPLV as well as variable-speed fans that improve IPLV.

Economizers. An economizer is an additional dampered cabinet opening that draws air from the outside when outside air is cooler than the temperature inside the building, thereby providing "free" cooling. Many codes, standards, and utility programs already require the use of economizers, and most RTUs have this option. Economizers can reduce energy use by anywhere from 15 to 80 percent depending on conditions, and they are usually cost-effective given their minimal additional cost.

Controls. Programmable digital controls offer flexible settings that can be tailored to the application and are increasingly available as standard equipment. A good example is a seven-day time clock that consistently operates the RTU according to occupancy schedules and nighttime temperature setbacks. Digital controls are also easily tied into a central energy management system for monitoring and control as part of an overall building-control strategy. In addition, many new RTUs come ready to accept inputs from carbon dioxide sensors. These can be used to implement demand-controlled ventilation, an energy-saving strategy that adjusts building ventilation as occupancy changes rather than assuming that the building is always fully occupied.

Cooling coils. Smaller RTUs normally use direct-expansion evaporator coils, in which air is blown over a fin-and-tube heat exchanger that carries the evaporating refrigerant. Larger RTUs can use either direct-expansion or chilled-water coils. In the latter, the cooling water is piped to the RTU from a remote water-chilling unit. A key variable in coil design is the face area, which determines the air velocity over the coil. Most RTUs keep this face velocity below 600 feet per minute to prevent condensed water in the airstream from blowing off the coil and into the duct system.

How to Make the Best Choice

Select the right size. An undersized unit won't be able to provide sufficient cooling, but if a unit is oversized (the more frequent occurrence), it not only costs more but will lead to higher costs for associated ductwork and other auxiliaries. Operating costs increase too, because oversized equipment spends more time at less-efficient part-load conditions. Specifiers and designers commonly overestimate loads because they fail to take into account the reduced air-conditioning loads that result from energy-efficient lighting, and they overestimate plug loads by using nameplate ratings of office equipment in the building.

It is also critical to use diversity factors when calculating internal loads. For example, consider a school: Peak load for the classrooms occurs when the classrooms are full, peak for the auditorium happens during an assembly, and peak for a gym occurs during a basketball game with the stands full. However, peak load for the school is not the sum of these loads, because they do not all occur simultaneously.

Consider high-efficiency levels recommended by CEE. The Consortium for Energy Efficiency (CEE) offers a program known as the High-Efficiency Commercial Air Conditioning & Heat Pumps Initiative. The initiative's goal is to encourage the use of high-efficiency unitary (single-packaged and split-system) central air-conditioning and heat pump equipment in commercial buildings. CEE currently suggests two efficiency levels for commercial equipment that are approximately 22 percent greater than the current federal standard. The CEE specification is promoted by participating utilities through education and rebate programs.

Energy Star is a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy (DOE) that establishes an efficiency specification above the federal standards. Equipment that meets these specifications is awarded the Energy Star label, which helps consumers and others readily identify high-efficiency products. The current efficiency level for Energy Star was set in 2002 and is the same as that of the CEE.

Identify high-efficiency models. ARI is the main source of information about energy-efficient RTU products. The organization maintains directories (available in both print and electronic formats) on its web site that include products from all ARI member-manufacturers.

CEE also maintains a database of equipment efficiency data. that is easy to use.

Evaluate high-efficiency models by performing a cost-effectiveness calculation. The cost-effectiveness of a high-efficiency RTU depends on several factors, including cooling loads, operating hours, and the local cost of electricity. Use the calculation tool for preliminary screening of high-efficiency options. For more accurate predictions of performance, an analysis that accounts for local climate conditions and part-load equipment performance is necessary.

In addition, the Pacific Northwest National Laboratory offers a free life-cycle cost estimation tool that can be used to compare high-efficiency units with standard ones. This tool is more detailed and has the added benefit of displaying results graphically.

Pay attention to design, commissioning, and maintenance. No matter what equipment you choose, it's also important to make sure that the overall system is designed to be efficient (see Figure 3), that it's commissioned to operate as planned, and that it is properly maintained. A low-static-pressure duct system will reduce control problems, noise, and the fan power required. Comprehensive testing, adjusting, and balancing of the installed unit and its controls will maximize installed efficiency and comfort. Conducting regular tune-ups, correcting refrigerant charge, cleaning and adjusting the system to correct airflow and improve heat transfer, and repairing major duct leaks can yield surprising energy savings at low cost. CEE offers installation guidelines for commercial air-conditioning equipment.

What's on the Horizon?

The Energy Policy Act of 1992 mandates that whenever ASHRAE (the American Society of Heating, Refrigeration and Air Conditioning Engineers) updates the voluntary standard 90.1, which applies to commercial units, the DOE must update the federal standards within two years. ASHRAE approved a new version of 90.1 in 1999, thus initiating this process. Federal standards were passed for water-cooled and other equipment in 2001; however, the standards for commercial air-cooled equipment have not been updated yet. Proposed levels can be found at the DOE's web site. A final rule on the new standard is expected by March 2006, with the standards taking effect on January 1, 2010.

Everybody is a Critic

Air conditioning tips missed mark



In response to your front page article dated Aug. 4th, there were errors on "Help your house beat the heat" tips.

It read that insufficient air flow from a central air conditioning system can cause freezing of the condenser coil. Wrong. Poor air flow may cause freezing of the evaporating coil which is affixed to the furnace.

Secondly, the recommendation of monthly filter changes is typically unnecessary. A periodic inspection of clogging should necessitate the purpose of replacement.

A better tip should have been to go outside and inspect your air conditioning unit. While operating, the larger insulated pipe from your home should be sweaty cold. If not, it could be a sign of refrigerant shortage which creates prolonged operation and potential system damage.

First Air Conditioner Guy Says Replace It For $5,000, Second Air Conditioner Guy Fixes It For $250

First Air Conditioner Guy Says Replace It For $5,000, Second Air Conditioner Guy Fixes It For $250
Reader F.'s air conditioner was broken, so he called the company that installed it when the house was built. They came out, charged him $100, and told him that he could repair the unit for $3,000 or replace it for $5,000. It's a good thing he got a second opinion, because the second repair guy fixed the problem for $250.

F. says:

I called the company that installed it 9 years ago, Westminster Mechanical, because it was making a loud noise and the fan was no longer working. They came out yesterday and in minutes declared that all the components need to be replaced. They estimated around $3000 [for the repair] or a new system for around $5000.

So, I called a neighbor in the business and she sent someone out. In about an hour he found a blockage and once again I have air. Do these companies install in new houses so they can slap a sticker with their number on it and years later when you call say it needs to be replaced? Instead it cost me $250, oh plus the $100 I wasted to have the original company tell me to replace it.

It's nearly impossible to say whether or not the first company was trying to mislead you, so we'll concentrate on what you did right. It's certainly not uncommon for companies to try to get unsuspecting homeowners to try to replace an air conditioner or a furnace when, in fact, it just needs a small repair. So, how do you figure out when your repair guy is telling the truth?

First, before you call someone to come in and look at your AC or furnace, do a little research with the BBB and ask your friends to recommend someone that you can trust. Second, if you're told that you may have to replace your equipment or make an expensive repair, thank the representative for his time and start collecting 2 more estimates. If your unit really does have to be replaced, some contractors will waive the fee and offer a free estimate for the new equipment.

If, like F., there was nothing seriously wrong with your AC, an honest contractor will catch it.

We asked the BBB about F.'s case and were told that complaints about AC repair are relatively uncommon, but that they do happen.

"With something like this, it’s hard for the consumer to know if they’re being lied to or not. If an AC repairman were to say to me, “Your flux capacitor is shot,” who am I to argue? That’s why it’s important to research the company first," said Alison Preszler, Media Relations Manager of the BBB.

Indoor Smog?

Inside air more polluted than outside air - study


Over eighty leading professionals in air-conditioning in hot environments on Friday attended an expert seminar in Dar es Salaam.

Participants came from different countries, from such rare fields as architects, building contractors, project engineers and consultants.

The event was organised by Carrier Air Conditioning, at which issues such as current global warming and energy crisis were discussed at length.

A recent press release from Royal Furnishers Ltd said participants also showcased a wide range of products that are designed to suit the growing requirements of the market.

The adverse impact of sub-standard products flooding the domestic market was also discussed.

According to a recent study carried out in Britain, ``the air inside an office is probably ten times more polluted than the outside air`` and we spend 90 percent of our time in enclosed spaces.

Hence, it was important to use air conditioners in places of work for better health of the workers, it said.

The Sidewalk Sale, One more Global Warming Casualty

Council Would Fine Stores if They Cool the Sidewalks

Now the City Council is expected to pass legislation on Thursday that would impose fines on stores that leave their doors wide open with the air conditioning on.

Councilwoman Gale A. Brewer, a Manhattan Democrat who is co-sponsoring the bill, said she gets a lot of mail from residents complaining about these stores. She said electronics stores are the biggest offenders, though there are plenty of other shops on Fifth Avenue, 34th Street and other popular areas that keep their doors open.

“I’m calling it the Clyde Haberman bill,” she said, a reference to the NYC columnist for The New York Times, who has written about the topic on several occasions.

Ms. Brewer and 18 other council members signed on to the bill, which would affect any business with at least 4,000 square feet, or small stores that are part of a chain with five or more stores in the city. The Department of Consumer Affairs would issue a warning to first-time offenders who kept their exterior doors open while an air-conditioning system intended to cool the area was in use.

Stores would be fined $200 for a second offense and $400 for subsequent violations within an 18-month period.

“Hopefully, they will get the message to help save the planet,” Ms. Brewer said. “There’s no use cooling the sidewalk.”

Her timing is good. Thursday is the fifth anniversary of the blackout that left tens of millions of residents in the dark in eight states across the Midwest and Northeast.

Kathryn S. Wylde, president of the Partnership for New York City, a business policy and advocacy group, regretted the need to “legislate common sense” but said, “The energy crisis in terms of global warming and fuel costs suggests that air conditioning should be contained as much as possible.”

According to calculations by Steven Winter Associates, a building systems consultant, a 5,000-square-foot store would pay $380 extra over a summer season if it kept its doors open with the air conditioning on, while a 10,000-square-foot store would spend an additional $1,000.

“The only group that should be opposing this sensible legislation is OPEC,” said Eric A. Goldstein, a senior lawyer at the Natural Resources Defense Council, which worked with the City Council on the legislation.

Another Reason to Do It Yourself

Police warn about thieves posing as repairmen

York Regional Police have issued a warning about three men posing as repairmen after an attempted robbery at a Richmond Hill home Friday.

At about 11:30 a.m., the men knocked on the door of the Yonge Street and 16th Avenue-area home under the guise of Heating and Air Conditioning repair, police said. After forcing their way into the home, the men demanded cash from someone in the home.

The person in the home managed to call to police but was then confronted by the men, who were all holding handguns. With police on the way, the men fled empty-handed. The person in the home was not hurt.

As the men ran north on 16th Avenue, one of them was nearly run over by a vehicle.

Investigators urged the driver of that vehicle and any other witnesses to contact them.

All three would-be robbers are described as black males clad in navy blue golf shirts with patches reading “Heating and Air Conditioning”, long pants and black/orange gloves.

One man, standing five-feet, four-inches tall, was about 20 years old and 160 pounds, has short black hair and was clean shaven.

The other two were five-feet, eight-inches tall with skinny builds and wore their hair in cornrows. One was about 18 years old.

Always ask for identification before allowing anyone into your home and call the company providing the service to confirm the identity of the people at your door, police said.

If you have any information about this case or the people involved, call police at 1-866-876-5423, ext. 6630, Crime Stoppers at 1-800-222-TIPS or leave a tip at www.1800222tips.com

To Repair or not to Repair

Should you fix an ailing A/C unit?

Hot days and a cool economy mean more people consider repairing rather than replacing broken air conditioners.

"With current economic conditions, people are afraid to pay for a replacement when it seems less expensive to repair," says Richard Henderson, president of M.B. Kiser Heating and Air Conditioning in Dallas.

The $5,000 to $15,000 cost of replacing a central air-conditioning system is enough to make homeowners sweat, yet not many are happy with the idea of continually repairing a unit that does not do a good job of cooling.

How does a homeowner know when it is smarter to replace the A/C?

The age of the unit is the first thing to consider in the repair-or-replace debate. Air conditioners start to wear out after about 10 years. That's the lifespan for efficiency recommended by the federal government's Energy Star program.

Yet units may stay in good working order for a few years longer, even in sweltering North Texas where Mr. Henderson estimates A/C units are pressed into service for about 1,750 to 2,000 hours during warm seasons that last from April to October.


Making repairs

The system is bound to fail eventually, and frequent repairs are one sign that replacement is a better option.

"If it costs $200 to repair a 20-year-old unit, you may want to think twice about putting $200 into it over and over," Mr. Henderson says.

Also, consider the type of repairs. Replacing major components is costly, and the piecemeal addition of those crucial parts can cause the whole system to operate less efficiently. Adding a condenser, for instance, can cost $3,000 to $6,000.

New technology and standards also make replacement attractive.

Replacing an ailing unit that uses an old style of refrigerant is likely to be a smarter choice than repairing it, notes Colin Creel, service manager of the Air Comfort Company in Richardson.

Under the U.S. Clean Air Act, an official phase-out of a common air-conditioner refrigerant known as R-22 begins in 2010. R-22 has been in use in home systems for about 40 years, and it is associated with greenhouse gases that can cause global warming. The Environmental Protection Agency predicts the cost of the refrigerant will climb as it gradually disappears from the market.

Newer units also run more efficiently. An air conditioner's ability to cool is measured by what's known as seasonal energy efficiency ratings (SEER). The higher the SEER number, the more efficient the unit. If a unit with a SEER rating of 8 is replaced with one with a 15 SEER rating, a homeowner can reduce energy costs by almost half, estimates Bill Cunningham, a specialist with Lennox.


Payback time

The savings offered by newer units can be substantial if the homeowner is planning to stay in the house long enough to recover the costs of replacing the system.

"If you are going to stay in the house less than five years, it is going to be difficult to pay for A/C replacement," says Mr. Henderson of M.B. Kiser.

A new, high-efficiency system may give the home an edge in a slow housing market, but the cost of the unit might not be recovered during a sale, he says.

Smart homeowners have regular, annual inspections of their cooling system, Mr. Creel of Air Comfort says. "The system needs maintenance. It's like a car."

Inspectors can find the minor problems that shorten the life of the system and detect faulty ductwork, lack of insulation or an improperly sized unit, all of which can lead to an uncomfortable home.


Jessie Milligan is a Fort Worth freelance writer.

When to replace the A/C

• If the air inside is cool but the humidity is high, the unit may be oversize for the job. (Leaky ductwork also can lead to high humidity, so have the repairman look at the ducts first.)


• If the air conditioner runs constantly but doesn't adequately cool the air, there could be several causes. The unit may be undersize for the area you're trying to cool or, depending on the age of the equipment, parts could be failing.

• If repairs are frequent.


• If a major component such as the outside condenser box is failing and the warranty has expired.


• If the unit is more than 10 years old, especially if it uses the old form of refrigerant known as R-22.


SOURCES: Energy Star, M.B. Kiser, the Air Comfort Company, Lennox

Guide to shopping for window units

The new generation of window-unit air conditioners comes with lower prices and high efficiency, making them good choices for cooling one or two rooms, according to recent ratings in Consumer Reports.


1. Expect to pay $100 to $700, although good units can be had for $150 to $240.


2. Pay attention to British Thermal Units or Btu. Choose units that use:

• 5,000 to 6,000 Btu per hour for rooms of 100 to 300 square feet.

• 7,000 to 8,200 Btu per hour for 250 to 550 square feet.

• 9,800 to 12,500 Btu for rooms of 350 to 950 square feet.


3. Pick a model that allows you to control the direction of airflow. The window it is placed in may be off to one side of the room. You want to be able to direct the airflow to the area of the room in use.


4. Look for certification stickers. The Association of Home Appliance Manufacturers (AHAM) or the Canadian Standards Association (CSA) monitor energy efficiency ratings.

Here are room units that Consumer Reports