joe1234
Member
Join Date: Sep 2008
Posts: 7
Trane XE1000 Condenser Noise Level
Hi.
I have a 10 year old rane XE1000 which is very noisy. It works just fine, but it has progressevly gotten noiser.
Anyone know what the db decible noise level of this unit is? I looked through my manual and it does not say.
I like to know what the db is since I am shopping for another condenser and want to compare.
Thank you,
Joe
mike n mike n is online now
Member
Join Date: Jan 2008
Posts: 230
Shhhh;
I am sure somewhere in the technical data you may find the noise levels although I have not seen but maybe that is because I haven't looked. First let us deal with what you have there are many reasons why an outdoor unit might be noisy.
Bad bearings or loose components on a condensor fan, liquid refrigerant flooding back into a compressor, outdoor coil dirty causing both condensor and fan to overwork.
Put in a new filter, clean your coils and lubricate and tighten your condensor fan motor and blade (if it can be lubricated).
Restart the system and see if it is any quieter and know if you do purchase new equipment anything you get is going to be alot quieter than what you have and the more you spend on efficiency the more the manufacturers are willing to do concerning noise reduction and warranty improvement.
Sunday, September 21, 2008
Saturday, September 20, 2008
Hmeowners Cries for Help
I have a 3-year-old home with a walkout basement. The air conditioner is on the master bedroom side of the house and mounted up on a rack that holds it off the ground and level with the first floor. When the air conditioner kicks on, it makes a very loud sound. It wakes me up every time it kicks on and keeps me awake while it is running. Is there anyway to mask/reduce the noise so it isn't so noticeable in the bedroom.
The location of the outdoor unit does not concern me as much as the noise if we are talking about normal start up noise it may be that you have a lower quality unit. If we are talking about noise that sounds like metal on metal (clanking) then we need to think about a damaged compressor or refrigerant floodback on start up.
Look at the system airflow first because that is the easiest and cheapest to remedy. Is the filter clean or are there any other airflow obstructions.
I have a 3-year-old home with a walkout basement. The air conditioner is on the master bedroom side of the house and mounted up on a rack that holds it off the ground and level with the first floor. When the air conditioner kicks on, it makes a very loud sound. It wakes me up every time it kicks on and keeps me awake while it is running. Is there anyway to mask/reduce the noise so it isn't so noticeable in the bedroom.
The location of the outdoor unit does not concern me as much as the noise if we are talking about normal start up noise it may be that you have a lower quality unit. If we are talking about noise that sounds like metal on metal (clanking) then we need to think about a damaged compressor or refrigerant floodback on start up.
Look at the system airflow first because that is the easiest and cheapest to remedy. Is the filter clean or are there any other airflow obstructions.
Wednesday, September 10, 2008
Air Conditioning more complex everyday
Air conditioning is a pretty simple process right, well the latest problem the engineers are trying to solve is that since the government has mandated that system efficiencies have to be increased how do we achieve that.
The first path was to make the coils larger, simple right. Of course that creates another problem, that's right how we gonna get that big unit in the small space where the old one was.
So to solve that problem they are developing new coils that expand the surface area for heat transfer integral to the tubing so they can start reducing the overall size of the coils.
I think that is great, the only thing I worry about is if they can't keep the coils from leaking for 5 years now because the copper is so thin how much tougher is it going to be to repair a leak now. I guess they don't want us to fix them just sell 'em a new one.
The first path was to make the coils larger, simple right. Of course that creates another problem, that's right how we gonna get that big unit in the small space where the old one was.
So to solve that problem they are developing new coils that expand the surface area for heat transfer integral to the tubing so they can start reducing the overall size of the coils.
I think that is great, the only thing I worry about is if they can't keep the coils from leaking for 5 years now because the copper is so thin how much tougher is it going to be to repair a leak now. I guess they don't want us to fix them just sell 'em a new one.
Monday, September 8, 2008
Striving for Super Efficiency
Striving for Super Efficiency
The three basic components used in the manufacture of microchannel coils are parallel flow aluminum tubes (purple in illustration above), enhanced aluminum fins (red), and header manifolds (green). These components are combined by alternating tube and fin sections — a layer of tube atop a layer of fin atop a layer of tube, etc. This combination of fins and tubes is captured at both ends by the header manifolds. (Illustration courtesy of Johnson Controls.)
Manufacturers Continue to Tweak, Improve Upon Design of Condenser Coils
Long ago, the industry determined that the combination of copper tubing and aluminum fins provided the most efficient transfer of thermal heat in condenser coils.
Manufacturers of residential units are not necessarily on that same page — or that line of thinking — today.
Most manufacturers, if not all, are revising, have revised, or continue to revise their outdoor coil construction. One of the main objectives, of course, is to increase heat transfer efficiency, as energy efficiency is high on every homeowner’s wish list.
In the end, each manufacturer believes it has engineered and/or perfected — at least up to now — the most-efficient coil design. Some, like Goodman Manufacturing, have made changes as a direct result of the efficiency offered from R-410A refrigerant.
The NEWS asked major manufacturers to discuss the residential condenser coil changes that are occurring in the marketplace. Though not all responded, those that did provided great detail as to what’s happening with the component.
MICROCHANNEL TECHNOLOGY
Many years ago York engineers were concerned about 3 major issues concerning the industry.
“The first was efficiency, whether it was a 12 SEER or 13 SEER minimum,” said Andy Armstrong, director of marketing, Johnson Controls-Unitary Products. “We were confident that condenser coils would be challenged with new efficiencies.”
The second issue to address, he explained, was size. “The industry’s answer to efficiency has always been tied to bigger heat transfer surfaces,” he said. “Both application size restrictions and raw material usage made bigger and bigger coils an untenable long-term solution.”
The last issue involved sustainability. “We needed to make products that used less materials to begin with, and then, after use were easier to recycle and reuse,” said Armstrong.
In the case of Johnson Controls and York, they turned to microchannel technology, technology that has been used in the automotive industry for some time now. According to believers in the design, heat transfer efficiency and improvement in reliability are achieved through a higher level of corrosion resistance. (Johnson Controls uses the name MicroChannel.)
“Today, Johnson Controls believes that MicroChannel technology is the solution to all three challenges,” said Armstrong.
“With better heat transfer efficiency, MicroChannel allows us to economically reach the efficiency levels demanded by our customers. Not only do we reach higher efficiency levels, we reach them in a much smaller footprint. And from a sustainability standpoint, MicroChannel allows us to use far fewer raw materials.”
STATING ITS CASE
Enlarge this picture
Goodman said its unit with SmartCoil™ and R-410A refrigerant use 25 percent less refrigerant and the overall unit requires 15 percent less volume.
Johnson Controls is so convinced it has the answer, a year ago it produced a white paper on the subject, titled “Microchannel Technology: Benefits of Microchannel Technology in HVAC Applications.” (For the full report, go to www.us-ac.com.)
In the white paper, it states three basic components are used in the manufacture of microchannel coils: parallel-flow aluminum tubes, enhanced aluminum fins, and header manifolds.
According to the Johnson Controls’ report, these components are combined by alternating tube and fin sections — a layer of tube atop a layer of fin atop a layer of tube, and so forth. It said this combination of fins and tubes is captured at both ends by the header manifolds.
“Separator plates are located within the header manifolds to segment the coil assembly into two distinct sections: a desuperheating section, where the refrigerant gas transitions from gas to liquid, and a subcooling section, where the liquid refrigerant is further cooled below its saturated temperature,” it states in the report.
The manufacturer’s report also points out several advantages of microchannel technology when compared to traditional copper tube and aluminum fin designs. Per Johnson Controls, that list includes improved heat transfer properties, smaller size and weight, improved durability and serviceability, improved corrosion protection, and reduced refrigerant charge up to 50 percent. The report goes on to state its case and proof for each advantage it listed.
“Looking towards the future, January 2010, one of the current refrigerant options, R-22, can no longer be used in the manufacture of HVAC equipment and will be entirely replaced with R-410A, a more environmentally friendly refrigerant,” it states in the white paper. “Microchannel addresses all of the current and foreseeable future challenges in the HVAC industry.”
Armstrong was just as definitive. “Although R-410A refrigerant is better for the environment than R-22, no one would argue that the less we use any greenhouse gas, the better,” he said.
“With our current MicroChannel 5-ton 13 SEER product, we use one-half as much refrigerant as our closest competitor and one-third as much as another. When considering energy and time used in recovery, this statistic alone has dramatic effects for this industry and our environment.”
He added, “When the Johnson Controls-built unit has completed its useful life, an all-aluminum coil is far easier to recycle than its tube-and-fin counterparts. With an eye on the future, Johnson Controls engineers have taken a smaller box to a higher level.”
The three basic components used in the manufacture of microchannel coils are parallel flow aluminum tubes (purple in illustration above), enhanced aluminum fins (red), and header manifolds (green). These components are combined by alternating tube and fin sections — a layer of tube atop a layer of fin atop a layer of tube, etc. This combination of fins and tubes is captured at both ends by the header manifolds. (Illustration courtesy of Johnson Controls.)
Manufacturers Continue to Tweak, Improve Upon Design of Condenser Coils
Long ago, the industry determined that the combination of copper tubing and aluminum fins provided the most efficient transfer of thermal heat in condenser coils.
Manufacturers of residential units are not necessarily on that same page — or that line of thinking — today.
Most manufacturers, if not all, are revising, have revised, or continue to revise their outdoor coil construction. One of the main objectives, of course, is to increase heat transfer efficiency, as energy efficiency is high on every homeowner’s wish list.
In the end, each manufacturer believes it has engineered and/or perfected — at least up to now — the most-efficient coil design. Some, like Goodman Manufacturing, have made changes as a direct result of the efficiency offered from R-410A refrigerant.
The NEWS asked major manufacturers to discuss the residential condenser coil changes that are occurring in the marketplace. Though not all responded, those that did provided great detail as to what’s happening with the component.
MICROCHANNEL TECHNOLOGY
Many years ago York engineers were concerned about 3 major issues concerning the industry.
“The first was efficiency, whether it was a 12 SEER or 13 SEER minimum,” said Andy Armstrong, director of marketing, Johnson Controls-Unitary Products. “We were confident that condenser coils would be challenged with new efficiencies.”
The second issue to address, he explained, was size. “The industry’s answer to efficiency has always been tied to bigger heat transfer surfaces,” he said. “Both application size restrictions and raw material usage made bigger and bigger coils an untenable long-term solution.”
The last issue involved sustainability. “We needed to make products that used less materials to begin with, and then, after use were easier to recycle and reuse,” said Armstrong.
In the case of Johnson Controls and York, they turned to microchannel technology, technology that has been used in the automotive industry for some time now. According to believers in the design, heat transfer efficiency and improvement in reliability are achieved through a higher level of corrosion resistance. (Johnson Controls uses the name MicroChannel.)
“Today, Johnson Controls believes that MicroChannel technology is the solution to all three challenges,” said Armstrong.
“With better heat transfer efficiency, MicroChannel allows us to economically reach the efficiency levels demanded by our customers. Not only do we reach higher efficiency levels, we reach them in a much smaller footprint. And from a sustainability standpoint, MicroChannel allows us to use far fewer raw materials.”
STATING ITS CASE
Enlarge this picture
Goodman said its unit with SmartCoil™ and R-410A refrigerant use 25 percent less refrigerant and the overall unit requires 15 percent less volume.
Johnson Controls is so convinced it has the answer, a year ago it produced a white paper on the subject, titled “Microchannel Technology: Benefits of Microchannel Technology in HVAC Applications.” (For the full report, go to www.us-ac.com.)
In the white paper, it states three basic components are used in the manufacture of microchannel coils: parallel-flow aluminum tubes, enhanced aluminum fins, and header manifolds.
According to the Johnson Controls’ report, these components are combined by alternating tube and fin sections — a layer of tube atop a layer of fin atop a layer of tube, and so forth. It said this combination of fins and tubes is captured at both ends by the header manifolds.
“Separator plates are located within the header manifolds to segment the coil assembly into two distinct sections: a desuperheating section, where the refrigerant gas transitions from gas to liquid, and a subcooling section, where the liquid refrigerant is further cooled below its saturated temperature,” it states in the report.
The manufacturer’s report also points out several advantages of microchannel technology when compared to traditional copper tube and aluminum fin designs. Per Johnson Controls, that list includes improved heat transfer properties, smaller size and weight, improved durability and serviceability, improved corrosion protection, and reduced refrigerant charge up to 50 percent. The report goes on to state its case and proof for each advantage it listed.
“Looking towards the future, January 2010, one of the current refrigerant options, R-22, can no longer be used in the manufacture of HVAC equipment and will be entirely replaced with R-410A, a more environmentally friendly refrigerant,” it states in the white paper. “Microchannel addresses all of the current and foreseeable future challenges in the HVAC industry.”
Armstrong was just as definitive. “Although R-410A refrigerant is better for the environment than R-22, no one would argue that the less we use any greenhouse gas, the better,” he said.
“With our current MicroChannel 5-ton 13 SEER product, we use one-half as much refrigerant as our closest competitor and one-third as much as another. When considering energy and time used in recovery, this statistic alone has dramatic effects for this industry and our environment.”
He added, “When the Johnson Controls-built unit has completed its useful life, an all-aluminum coil is far easier to recycle than its tube-and-fin counterparts. With an eye on the future, Johnson Controls engineers have taken a smaller box to a higher level.”
Saturday, September 6, 2008
In the South Air Conditioning is Art
Air conditioning artist named
Earlier this year, in the cold of winter, the Air Conditioning Tribute Committee announced a call for entries for artists to pay tribute to the most important of summer-time inventions — the air conditioner.
The response was positive, and the committee had a tough choice ahead, narrowing the submissions to just one winner.
But the committee members labored (in the cool air of the meeting room) and decided the entry that best captured the appreciation of air conditioning was the one submitted by Augusta, Ga., artist Thomas Lyles. The committee will meet with Lyles this month to complete the details.
Lyles, a native of Gadsden, presented a blueprint of his concept. His work, when complete, will showcase the winning poetry entry along with multiple mosaic scenes against the backdrop of industrial ductwork.
The artwork will include sound, working air vents and a video screen. People will be able to hear, see and feel the message of his work.
The next phase of the Air Conditioning Tribute Project involves area schoolchildren and the public. Friday, the committee announced an essay/poetry contest. The submissions will be used in conjunction with the exhibit next summer, and the winning students will receive cash prizes for themselves and their classrooms.
The student categories are elementary, middle and high school. The student must attend school in Etowah County. Entries should be no more than 400 words and capture the South’s thankfulness for the invention of the air conditioner.
In the adult category, entries by anyone with an Etowah County connection will be accepted.
The deadline for submissions is Nov. 23.
Categories and prizes:
• Elementary school — $100 for the winning student, $100 for classroom
• Middle school — $200 for the winning student, $200 for classroom
• High school — $200 for the winning student, $200 for classroom
• Adult (18 and older) — $500 for the winning adult
Complete details for the contest are available at the Hardin Center in downtown Gadsden and online at www.culturalarts.org.
Earlier this year, in the cold of winter, the Air Conditioning Tribute Committee announced a call for entries for artists to pay tribute to the most important of summer-time inventions — the air conditioner.
The response was positive, and the committee had a tough choice ahead, narrowing the submissions to just one winner.
But the committee members labored (in the cool air of the meeting room) and decided the entry that best captured the appreciation of air conditioning was the one submitted by Augusta, Ga., artist Thomas Lyles. The committee will meet with Lyles this month to complete the details.
Lyles, a native of Gadsden, presented a blueprint of his concept. His work, when complete, will showcase the winning poetry entry along with multiple mosaic scenes against the backdrop of industrial ductwork.
The artwork will include sound, working air vents and a video screen. People will be able to hear, see and feel the message of his work.
The next phase of the Air Conditioning Tribute Project involves area schoolchildren and the public. Friday, the committee announced an essay/poetry contest. The submissions will be used in conjunction with the exhibit next summer, and the winning students will receive cash prizes for themselves and their classrooms.
The student categories are elementary, middle and high school. The student must attend school in Etowah County. Entries should be no more than 400 words and capture the South’s thankfulness for the invention of the air conditioner.
In the adult category, entries by anyone with an Etowah County connection will be accepted.
The deadline for submissions is Nov. 23.
Categories and prizes:
• Elementary school — $100 for the winning student, $100 for classroom
• Middle school — $200 for the winning student, $200 for classroom
• High school — $200 for the winning student, $200 for classroom
• Adult (18 and older) — $500 for the winning adult
Complete details for the contest are available at the Hardin Center in downtown Gadsden and online at www.culturalarts.org.
Wednesday, September 3, 2008
Air conditioning could 'heat up' London
Air conditioning could 'heat up' London
The large scale installation of air conditioning to combat rising temperatures in London could make conditions in the capital even hotter – according to a draft report on climate change issued by the mayor’s office.
The draft London climate change adaptation strategy issued by Mayor of London Boris Johnson states: “In order to avoid unsustainable adaptation, when considering possible adaptation options, the wider implications of the action should be assessed over the lifetime of the action.
“For example, air conditioning is not considered to be a sustainable adaptation action except in extreme circumstances (because of the large energy demands),”
A particular concern raised by the report is the effect on the ‘urban heat island’ within London by waste heat from air conditioning systems.
This is where heat generated in the city by traffic, air conditioning systems and other energy uses adds to the heat being radiated from the buildings and roads, further raising temperatures in the area and meaning there is little let up during a heat wave.
The report says the contribution to the urban heat island by human activity – known as anthropogenic - is thought to be “minimal across” the whole of London at the moment, but significant in high density areas.
The report said: “In Westminster and the City of London modelling suggests that the anthropogenic contribution, calculated using the total energy demand for buildings and traffic, may be a significant contribution to urban heating.
“If the use of air conditioning were to become widespread, the area affected by a significant anthropogenic contribution would increase.”
The effect of an urban heat island cam lead to an increase in mortality rates as people are less able to recover from the hot temperatures they experience during the day as the heat does not decrease significantly at night.
"It can also increase the demand for cooling and upset sleep patterns, while also putting pressure on water supplies and damaging temperature sensitive infrastructure. The increased reliance on electric cooling can also lead to blackouts.
The report said London had to look carefully at measures to limit the use of air conditioning and continue introducing further energy efficiency approaches.
Other issues highlighted included the threat of rising sea levels, wetter weather, a higher chance of heat waves and increased risks of flooding. Measures under consideration include better urban design and improved flood defences.
Mr Johnson said: ‘We need to concentrate efforts to slash carbon emissions and become more energy efficient in order to prevent dangerous climate change. But we also need to prepare for how our climate is expected to change in the future.”
The large scale installation of air conditioning to combat rising temperatures in London could make conditions in the capital even hotter – according to a draft report on climate change issued by the mayor’s office.
The draft London climate change adaptation strategy issued by Mayor of London Boris Johnson states: “In order to avoid unsustainable adaptation, when considering possible adaptation options, the wider implications of the action should be assessed over the lifetime of the action.
“For example, air conditioning is not considered to be a sustainable adaptation action except in extreme circumstances (because of the large energy demands),”
A particular concern raised by the report is the effect on the ‘urban heat island’ within London by waste heat from air conditioning systems.
This is where heat generated in the city by traffic, air conditioning systems and other energy uses adds to the heat being radiated from the buildings and roads, further raising temperatures in the area and meaning there is little let up during a heat wave.
The report says the contribution to the urban heat island by human activity – known as anthropogenic - is thought to be “minimal across” the whole of London at the moment, but significant in high density areas.
The report said: “In Westminster and the City of London modelling suggests that the anthropogenic contribution, calculated using the total energy demand for buildings and traffic, may be a significant contribution to urban heating.
“If the use of air conditioning were to become widespread, the area affected by a significant anthropogenic contribution would increase.”
The effect of an urban heat island cam lead to an increase in mortality rates as people are less able to recover from the hot temperatures they experience during the day as the heat does not decrease significantly at night.
"It can also increase the demand for cooling and upset sleep patterns, while also putting pressure on water supplies and damaging temperature sensitive infrastructure. The increased reliance on electric cooling can also lead to blackouts.
The report said London had to look carefully at measures to limit the use of air conditioning and continue introducing further energy efficiency approaches.
Other issues highlighted included the threat of rising sea levels, wetter weather, a higher chance of heat waves and increased risks of flooding. Measures under consideration include better urban design and improved flood defences.
Mr Johnson said: ‘We need to concentrate efforts to slash carbon emissions and become more energy efficient in order to prevent dangerous climate change. But we also need to prepare for how our climate is expected to change in the future.”
Monday, September 1, 2008
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.
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.
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