Today systems are designed to meet environmental requirements, indoor air quality and more stringent user. Many of the HVAC system efficiency gains have come as the result of improving operational efficiency of key system components. Other useful are the results of the use of technologies that are new, or new to the HVAC field. The use of computer-aided design tools have helped reclosable HVAC design system running more efficiently.
Although there are many individual advances that have helped to improve the operating efficiency of the HVAC system, much of the overall improvement can be attributed to five key factors:
-The development of coolers, low kW/ton; 2,220-the use of control systems of high efficiency boilers;
-The application of direct digital control (DDC) systems;
-The use of energy-efficient motors; and,
-The combination of variable frequency drives pump, fan motors and chillers.
For years, building owners were satisfied with the performance and efficiency of refrigerators that operated in the range of -0.9 .8 kW/ton new. As they age, real operating efficiencies fall to more than 1.0 kW/ton fully loaded.
Today, new coolers are installed with efficiency at full rated load of 0.50 kW/ton, an increase of 50 percent. Equally impressive are the part load efficiencies of the new generation of chillers. Although the operational efficiency of the chiller almost all elderly falls quickly away with reduced load, operational efficiency of new refrigerators didn’t get off just as quickly.
Chiller design changes
construction and operation of several changes have helped improve the performance of the chiller. To improve the characteristics of heat transfer of refrigerators, manufacturers have increased the size of the units heat exchangers. Electromechanical control systems have been replaced by microprocessor electronic controls that provide greater precision, reliability and flexibility. Variable frequency control the speed of the compressor, increasing part load performance.
increased energy efficiency, is not the only advantage of the new generation of refrigerators; These coolers provide better containment refrigerant. Although the older coolers routine may have lost the 10 percent to 15 percent of the refrigerant charge every year, new chillers can limit losses to less than 0.5 percent. The lowest loss rate and finest blowdown systems reduce the amount of non-condensable gases found in a coolant system a key factor in maintaining performance over time.
Another significant development is the boiler in operation: the replacement of pneumatic controls and manuals with microprocessor-based systems. As a general rule, the systems may be required to achieve energy savings of 5 percent to 7 percent compared to conventional pneumatic systems.
microprocessor control systems to achieve their savings first as the result of their ability to modulate the operation boiler more accurately compared to pneumatic systems-based. By modulating operation boiler with precision, the systems help to maintain the proper fuel-air ratio and trace the load placed on the boiler by the HVAC system.
Microprocessor systems offer several additional benefits, including remote monitoring and operational capabilities, automatic control sequences, steam flow monitoring, and reduced maintenance costs. One way in which systems can help reduce maintenance costs is through their ability to maintain the proper fuel-air ratio. Keeping the correct ratio, the systems reduce the rate at which the soot collects on boiler pipes, thereby reducing the frequency of required tear down and cleaning. Keep the boiler pipes clean of soot also helps to improve the thermal efficiency of the boiler.
direct digital controls
A major shift in the HVAC field is the generalized application of digital controls (DDC). Introduced more than 15 years ago, the DDC systems have become the industry standard control system design for today. With the ability to provide accurate and precise temperature control and air and water flows, systems have largely replaced pneumatic and electric control systems.
DDC systems help building owners to conserve energy in different ways. Their accuracy and almost eliminate problems offset control, overrun, and commonly found in pneumatic systems, resulting in better system setting. Their ability to respond to a nearly unlimited number of sensors results in better coordinated control activities. This also allows the systems to run more complex control strategies that could be done with air controls. Finally, their simple or automatic calibration ensures that the control systems will perform as designed, with little or no loss of precision.
DDC systems also offer many other benefits. Elements of an HVAC system control strategies are based on the software, the systems can be easily modified to adapt to changes in the requirements of occupants without expensive hardware changes. DDC systems are ideal for applications that benefit from monitoring and remote operation.
energy efficient motors
Today HVAC systems are making use of energy-efficient engines. Energy-efficient motors offer a moderate but significant increase operational efficiency at full load on standard models. For example, a motor 10 hp energy efficient works out to about 93 percent efficiency; a standard engine of the same size is typically rated at 88 percent. Similarly, an energy-efficient motor 50 hp is estimated at around 94 percent efficiency in contrast to the 90 percent efficiency rating of a standard motor 50 hp. 2,220 this increase operational efficiency accompanies a first increase cost of the engines. How quickly this extra initial cost is retrieved depends on two factors: the motor load, and the number of hours the engine is operated by year. 2,220 More motor runs at full load and the greater the number of class hours per year is activated the motor faster, the differential of the first cost is recovered. For most applications where the motor runs continuously at or near full load, the amortization period for the first additional cost is usually between three and six months.
HVAC applications the combination of constant load and working long hours made it particularly suitable for the use of energy-efficient engines. High energy efficiency motors commonly found driving circulation pumps and centrifugal system fans. With these loads, the 4 percent or 5 percent increase in electrical motor efficiency results in significant energy savings, especially when systems work 24 hours a day, all year round.
A side benefit of energy efficient engine design is its major power factor. Increasing the power factor of a driving motor reduces the current draw on the electrical system, free extra distribution capability and reduce distribution losses in the system. Although the increase in the power factor ISNA enough of a benefit to justify the cost differential higher efficiency motor, important consideration, particularly for large users of electricity the system capacity is limited.
Although the engines have proven to be very cost effective in new applications, their use in existing applications is a little harder to justify. In most cases, the cost to replace an existing one, drive motor with greater efficiency will not be retrieved for five to 10 years or more.
Among the improvements in HVAC systems that have helped to increase operational efficiency, variable frequency drives have had the most dramatic results. Applied to the components of the system ranging from fans to coolers, the units have proven to be very effective in reducing energy demand during partial load operation. And with most operating systems at part load capacity of 90 percent or more of the time, the energy-saving products by frequency inverter quickly recoup their investment, typically within one to two years. 2,220 In general, the larger the engine, the greater the savings. As a general rule, most HVAC systems engine 20 HP and can benefit from the installation of a frequency converter.
variable frequency drive applications
variable frequency drives produce their savings by varying the frequency and voltages. This variation is used to reduce the speed of operation of the equipment controls to meet the requirements of load. The reduced operating speed, the drive motor power consumption falls quickly. 2,220 For example, a centrifugal fan, when operating at 75 percent of stream, draws only about 40 percent of full load power. At 50% flow, the power required for the fan reduces to less than 15 percent of full load power. While traditional damper control systems or control palette, also reduce the partial flow, energy savings requirements are significantly less.
Another area where the variable frequency drives improved operational efficiency of an HVAC system is with centrifugal pumps hot water circulating systems and chilled. Typically, these pumps provide a steady stream of water to Terminal units. As the demand for heating or cooling water decreases, the check valves at Terminal units remove the gas. To maintain constant pressure in the system, a bypass valve between supply and return systems opens. With the remaining nearly constant flow, the load on the pump electric motor remains almost constant.
variable frequency regulating pressure in the system in response to different needs by slowing down the pump. As with centrifugal fans, the required power from the falls as the load and the speed decreased. Again, because most systems work well below design capacity 90 percent of the time, the savings produced by the low speed operation are significant, typically recover the cost of the unit in one or two years.
A third question is variable frequency drive centrifugal chillers. Coolers are sized to peak cooling loads, although these loads occur only a few hours per year.
With conventional control systems which close input palette chiller, cooling efficiency falls off significantly during partial load operation. When variable frequency are applied to these coolers, regulate the functioning of the chiller reducing the speed of the compressor. The result is near full load operating efficiency over a wide range of cooling loads. This increase in efficiency at part load translates into a 15 percent to 20 percent increase of the chiller seasonal efficiency.
Energy conservation the only advantage of variable frequency drives. A strain is placed on an electric motor and mechanical system that pushes each time a pump, fan or chiller starts at full voltage: motor winding warms, straps slip, drive chains stretch and high pressure grew in circulation systems. Variable frequency drives to reduce these solicitations by reduced voltages and frequencies systems starting from a soft start, resulting in increased motor life and equipment.
Finally, the most important element in an HVAC system with low energy consumption is how the system is running. No matter how sophisticated the system, or as its power-saving features large, System performance depends on how used and maintained. Operational staff must be properly trained how to make the best use of the system and its features. Maintenance personnel must be trained and equipped with the tools to keep the operating system in the way it was designed. Maintenance cannot be deferred.
energy efficient HVAC systems offer the facility managers the ability to increase system performance, reducing the energy requirements. But they benefit from building owners only insofar as they are taken care of. If facility managers choose to ignore the needs of maintenance, may soon find faulty systems to the point where they have actually increased energy requirements