Today's systems are designed to meet stricter environmental, indoor air capability and user requirements. Many of the gains in Hvac system efficiency have come as the ensue of improvements in the operating efficiency of key system 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 found tools have helped system engineers found Hvac systems that perform more efficiently.
Although there are many private advances that have helped to heighten Hvac system operating efficiency, much of the wide improvement can be attributed to five key factors:
Differential Pressure Sensor
- The amelioration 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, construction owners were satisfied with the carrying out 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 found changes
Several found and carrying out changes have helped heighten chiller performance. To heighten the heat change 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 Electromechanical operate systems have been replaced by microprocessor-based electronic controls that provide greater precision, reliability and flexibility. changeable frequency drives operate the speed of the compressor, resulting in an growth in part-load performance.
Increased power efficiency is not the only advantage of the new generation of construction chillers; these chillers offer great refrigerant containment. Although older chillers routinely may have lost 10 percent to 15 percent of the refrigerant payment per year, new chillers can limit losses to less than 0.5 percent. Lower leak rates and great purge systems sell out the quantity of non-condensable gasses found in the refrigerant system -- a key factor in maintaining chiller carrying out over time.
Another requisite amelioration is in boiler operation: the change of pneumatic and by hand controls with microprocessor-based systems. As a rule of thumb, the systems can be staggering to perform power 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 carrying out more accurately than pneumatic-based systems. By modulating the boiler's carrying out accurately, the systems help to contend the permissible fuel-to-air ratio and track the load located on the boiler by the Hvac system.
Microprocessor-based systems offer any additional advantages, together with remote monitoring and operating capabilities, automatic operate sequences, monitoring of steam flow, and reduced maintenance costs. One way the systems can help sell out maintenance costs is through their capability to contend permissible fuel-to-air ratio. By maintaining the permissible ratio, the systems sell out the rate at which soot collects on boiler tubes, thus decreasing the frequency of required tear down and cleaning. Retention the boiler tubes clean of soot also helps to heighten the thermal efficiency of the boiler.
Direct digital controls
A major change in the Hvac field is the wide implementation of direct digital controls (Ddc). Introduced more than 15 years ago, Ddc systems have come to be the business thorough for operate systems found today. With the capability to provide literal, and literal, operate of climatic characteristic and air and water flows, the systems have widely replaced pneumatic and galvanic operate systems.
Ddc systems help construction owners save power in any ways. Their accuracy and precision nearly eliminate the operate problems of offset, overshoot, and hunting ordinarily found in pneumatic systems, resulting in great regulation of the system. Their capability to retort 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 simple or automatic calibration ensures that the operate systems will perform as designed over time, with minuscule or no loss of accuracy.
Ddc systems also offer any other advantages. Because the operate strategies are software-based, the systems can be of course modified to match changes in occupant requirements without costly hardware changes. Ddc systems also are ideal for applications that advantage from remote monitoring and operation.
Energy-efficient motors
Today's Hvac systems are making use of energy-efficient motors. Energy-efficient motors offer a moderate but requisite growth in full-load operating efficiency over thorough motor designs. For example, an energy-efficient 10 hp motor operates at about 93 percent efficiency; a thorough motor of the same size is typically rated at 88 percent. Similarly, a 50 hp energy-efficient motor is rated at approximately 94 percent efficiency in dissimilarity to the 90 percent efficiency rating of a 50 hp thorough motor.
This growth in operating efficiency accompanies a first-cost growth for the motors. How rapidly this additional first cost is recovered depends on two factors: the loading of the motor, and the amount of hours the motor is operated per year.
The closer the motor is operated to its full-load rating and the greater the amount 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 period for the additional first cost is typically between three and six months.
The aggregate of constant loading and long hours of carrying out have made Hvac applications well-suited for the use of energy-efficient motors. Energy-efficient motors ordinarily are found driving centrifugal circulation pumps and system fans. With these loads, the 4 percent or 5 percent growth in the electrical efficiency of the drive motor translates to a requisite power savings, particularly when the systems operate 24 hours per day, year round.
A side advantage of energy-efficient motor found is its higher power factor. Expanding the power factor of a drive motor reduces the current draw on the electrical system, frees additional distribution capacity and reduces distribution losses in the system. Although Expanding the power factor isn't adequate of a advantage to explicate the cost differential of the higher efficiency motor, it's an leading consideration, particularly for large users of electricity where system capacity is limited.
Although the motors have demonstrated themselves to be very cost-effective in new applications, their use in existing applications is a minuscule 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 growth operating efficiency, changeable frequency drives have had the most dramatic results. Applied to system components ranging from fans to chillers, the drives have demonstrated themselves to be very flourishing in reducing system power requirements during part-load operation. And with most systems operating at part-load capacities 90 percent or more of the time, the power 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 system motor 20 hp and larger can advantage from the factory 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 dissimilarity is used to sell out the operating speed of the tool 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 sell out the power requirements at partial flow, the savings are significantly less.
Another area where changeable frequency drives have improved the operating efficiency of an Hvac system is with centrifugal pumps found in hot and chilled water circulation systems. Typically, these pumps provide a constant flow of water to terminal units. As the request for heating or cooling water decreases, the operate valves at the terminal units throttle back. To keep the pressure in the system constant, a bypass valve between the provide and return systems opens. With the flow rate remaining nearly constant, the load on the pump's galvanic drive also remains nearly constant.
Variable frequency drives regulate the pressure in the system 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 found capacity 90 percent of the time, the savings produced by reduced speed carrying out 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 during part-load operation. When changeable frequency drives are applied to these chillers, they regulate the carrying out 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 growth in part-load efficiency translates into a 15 percent to 20 percent growth in the chiller's seasonal efficiency.
Energy conservation isn't the only advantage of changeable frequency drives. A strain is located on an galvanic motor and the mechanical system 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 sell out these stresses by beginning systems at reduced voltages and frequencies in a soft start, resulting in increased motor and tool life.
Finally, the most leading element in an energy-efficient Hvac system is how the system is operated. No matter how sophisticated the system, or how wide its energy-conserving features, the system's carrying out depends upon the way in which it's operated and maintained. Operating personnel must be properly trained in how best to use the system and its features. Maintenance personnel must be trained and qualified with the permissible tools to keep the system operating in the way it was designed. Maintenance cannot be deferred.
Energy-efficient Hvac systems offer the factory boss the capability to heighten system carrying out while reducing power requirements. But they advantage construction owners only as long as they are taken care of. If factory managers select to ignore maintenance requirements, they may soon find systems malfunctioning to the point where they have of course increased the requirement for energy.
The Elements Of An productive Hvac systemdifferential pressure sensor
