Today's systems are designed to meet stricter environmental, indoor air capability and user requirements. Many of the gains in Hvac ideas efficiency have come as the ensue of improvements in the operating efficiency of key ideas components. Other gains are the ensue of the use of technologies that are whether new, or new to the Hvac field. Even the use of computer-aided institute tools have helped ideas engineers institute Hvac systems that perform more efficiently.
Although there are many personel advances that have helped to enhance Hvac ideas operating efficiency, much of the comprehensive revision can be attributed to five key factors:
- The improvement of low kW/ton chillers;
- The use of high-efficiency boiler operate systems;
- The application of direct digital operate (Ddc) systems;
- The use of energy-efficient motors; and,
- The matching of changeable frequency drives to pump, fan and chiller motors.
For years, building owners were satisfied with the execution and efficiencies of chillers that operated in the range of 0.8 to 0.9 kW/ton when new. As they age, actual operating efficiencies fall to more than 1.0 kW/ton at full load.
Today, new chillers are being installed with full load-rated efficiencies of 0.50 kW/ton, a near 50 percent increase. Equally impressive are the part-load efficiencies of the new generation of chillers. Although the operating efficiency of nearly all older chillers rapidly falls off with decreased load, the operating efficiency of new chillers does not drop off nearly as quickly.
Chiller institute changes
Several institute and execution changes have helped enhance chiller performance. To enhance the heat exchange characteristics of the chillers, manufacturers have increased the size of the units' heat exchangers. Electromechanical operate systems have been replaced by microprocessor-based electronic controls that furnish greater precision, reliability and flexibility. changeable frequency drives operate the speed of the compressor, resulting in an increase in part-load performance.
Increased vigor efficiency is not the only benefit of the new generation of building chillers; these chillers offer great refrigerant containment. Although older chillers routinely may have lost 10 percent to 15 percent of the refrigerant charge per year, new chillers can limit losses to less than 0.5 percent. Lower leak rates and great purge systems cut the quantity of non-condensable gasses found in the refrigerant ideas -- a key factor in maintaining chiller execution over time.
Another needful improvement is in boiler operation: the exchange of pneumatic and manual controls with microprocessor-based systems. As a rule of thumb, the systems can be startling to perform vigor savings of 5 percent to 7 percent over conventional pneumatic-based systems.
Microprocessor-based operate systems perform their savings primarily as the ensue of their capability to modulate the boiler's execution more accurately than pneumatic-based systems. By modulating the boiler's execution accurately, the systems help to contend the permissible fuel-to-air ratio and track the load settled on the boiler by the Hvac system.
Microprocessor-based systems offer several added advantages, including remote monitoring and operating capabilities, automated operate sequences, monitoring of steam flow, and reduced maintenance costs. One way the systems can help cut maintenance costs is through their capability to contend permissible fuel-to-air ratio. By maintaining the permissible ratio, the systems cut the rate at which soot collects on boiler tubes, thus decreasing the frequency of required tear down and cleaning. Keeping the boiler tubes clean of soot also helps to enhance the thermal efficiency of the boiler.
Direct digital controls
A major convert in the Hvac field is the comprehensive implementation of direct digital controls (Ddc). Introduced more than 15 years ago, Ddc systems have become the manufactures suitable for operate systems institute today. With the capability to furnish precise and precise operate of climatic characteristic and air and water flows, the systems have widely replaced pneumatic and electric operate systems.
Ddc systems help building owners save vigor in several ways. Their accuracy and precision nearly eliminate the operate problems of offset, overshoot, and hunting commonly found in pneumatic systems, resulting in great regulation of the system. Their capability to answer to a nearly unlimited range of sensors results in great coordinated operate activities. This also allows the systems to perform more involved operate strategies than could be performed with pneumatic controls. Finally, their uncomplicated or automated calibration ensures that the operate systems will perform as designed over time, with wee or no loss of accuracy.
Ddc systems also offer several other advantages. Because the operate strategies are software-based, the systems can be authentically modified to match changes in occupant requirements without costly hardware changes. Ddc systems also are ideal for applications that benefit from remote monitoring and operation.
Energy-efficient motors
Today's Hvac systems are production use of energy-efficient motors. Energy-efficient motors offer a moderate but needful increase in full-load operating efficiency over suitable motor designs. For example, an energy-efficient 10 hp motor operates at about 93 percent efficiency; a suitable motor of the same size is typically rated at 88 percent. Similarly, a 50 hp energy-efficient motor is rated at roughly 94 percent efficiency in variation to the 90 percent efficiency rating of a 50 hp suitable motor.
This increase in operating efficiency accompanies a first-cost increase for the motors. How rapidly this added first cost is recovered depends on two factors: the loading of the motor, and the whole of hours the motor is operated per year.
The closer the motor is operated to its full-load rating and the greater the whole of hours per year the motor is operated, the quicker the first-cost differential is recovered. For most applications where the motor is run continuously at or near full load, the payback duration for the added first cost is typically in the middle of three and six months.
The blend of constant loading and long hours of execution have made Hvac applications well-suited for the use of energy-efficient motors. Energy-efficient motors commonly are found driving centrifugal circulation pumps and ideas fans. With these loads, the 4 percent or 5 percent increase in the electrical efficiency of the drive motor translates to a needful vigor savings, particularly when the systems operate 24 hours per day, year round.
A side benefit of energy-efficient motor institute is its higher power factor. Addition the power factor of a drive motor reduces the current draw on the electrical system, frees added distribution capacity and reduces distribution losses in the system. Although Addition the power factor isn't adequate of a benefit to elucidate the cost differential of the higher efficiency motor, it's an prominent consideration, particularly for large users of electricity where ideas capacity is limited.
Although the motors have demonstrated themselves to be very cost-effective in new applications, their use in existing applications is a wee more difficult to justify. In most instances, the cost to replace an existing, operating motor with one of higher efficiency will not be recovered for five to 10 years or longer.
Of the improvements in Hvac systems that have helped to increase operating efficiency, changeable frequency drives have had the most dramatic results. Applied to ideas components ranging from fans to chillers, the drives have demonstrated themselves to be very thriving in reducing ideas vigor requirements while part-load operation. And with most systems operating at part-load capacities 90 percent or more of the time, the vigor savings produced by changeable frequency drives rapidly recover their investment, typically within one to two years.
In general, the larger the motor, the greater the savings. As a rule of thumb, nearly any Hvac ideas motor 20 hp and larger can benefit from the facility of a changeable frequency drive.
Variable frequency drive applications
Variable frequency drives produce their savings by varying the frequency and voltage of the motor's electrical supply. This variation is used to cut the operating speed of the equipment it controls to match the load requirements. At reduced operating speed, the power draw of the drive motor drops off rapidly.
For example, a centrifugal fan, when operated at 75 percent flow, draws only about 40 percent of full-load power. At 50 percent flow, the power requirement for the fan decreases to less than 15 percent of full-load power. While conventional operate systems, such as damper or vane control, also cut the vigor requirements at partial flow, the savings are significantly less.
Another area where changeable frequency drives have improved the operating efficiency of an Hvac ideas is with centrifugal pumps found in hot and chilled water circulation systems. Typically, these pumps furnish a constant flow of water to final units. As the interrogate for heating or cooling water decreases, the operate valves at the final units throttle back. To keep the pressure in the ideas constant, a bypass valve in the middle of the furnish and return systems opens. With the flow rate remaining nearly constant, the load on the pump's electric drive also remains nearly constant.
Variable frequency drives regulate the pressure in the ideas in response to varying demands by slowing the pump. As with centrifugal fans, the power required by the pumps falls off as the load and speed are decreased. Again, because most systems operate well below institute capacity 90 percent of the time, the savings produced by reduced speed execution are significant, typically recovering the cost of the unit in one to two years.
Chiller loads
A third application for changeable frequency drives is centrifugal chillers. Chillers are sized for peak cooling loads, although these loads occur only a few hours per year.
With conventional operate systems that close vanes on the chiller inlet, chiller efficiency falls off significantly while part-load operation. When changeable frequency drives are applied to these chillers, they regulate the execution of the chiller by reducing the speed of the compressor. The ensue is near full-load operating efficiency over a very wide range of cooling loads. This increase in part-load efficiency translates into a 15 percent to 20 percent increase in the chiller's seasonal efficiency.
Energy conservation isn't the only benefit of changeable frequency drives. A strain is settled on an electric motor and the mechanical ideas it drives every time a pump, fan or chiller is started at full-line voltage: Motor winding becomes heated, belts slip, drive chains stretch and high-pressure is advanced in circulation systems. changeable frequency drives cut these stresses by beginning systems at reduced voltages and frequencies in a soft start, resulting in increased motor and equipment life.
Finally, the most prominent element in an energy-efficient Hvac ideas is how the ideas is operated. No matter how sophisticated the system, or how comprehensive its energy-conserving features, the system's execution depends upon the way in which it's operated and maintained. Operating personnel must be properly trained in how best to use the ideas and its features. Maintenance personnel must be trained and qualified with the permissible tools to keep the ideas operating in the way it was designed. Maintenance cannot be deferred.
Energy-efficient Hvac systems offer the facility boss the capability to enhance ideas execution while reducing vigor requirements. But they benefit building owners only as long as they are taken care of. If facility managers pick to ignore maintenance requirements, they may soon find systems malfunctioning to the point where they have authentically increased the requirement for energy.
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