A Pump Is Used To Maintain Rate Of Flow The Elements Of An Efficient HVAC System

You are searching about A Pump Is Used To Maintain Rate Of Flow, today we will share with you article about A Pump Is Used To Maintain Rate Of Flow was compiled and edited by our team from many sources on the internet. Hope this article on the topic A Pump Is Used To Maintain Rate Of Flow is useful to you.

The Elements Of An Efficient HVAC System

Today’s systems are designed to meet stringent environmental, indoor air quality and user needs. Many of the gains in HVAC system efficiency have come from improvements in the efficiency of key system components. Other gains are the result of the use of technologies that are either new or new to the HVAC field. The use of computer-aided design tools has also helped system engineers design HVAC systems that operate more efficiently.

Although there are many individual advances that have helped improve HVAC system efficiency, the overall improvements can be attributed to five major factors:

– development of low kW/ton chillers;

– use of high-efficiency boiler control system;

– Use of Direct Digital Control (DDC) system;

– use of energy-efficient motors; and,

– Matching of variable frequency drives for pump, fan and chiller motors.

Over the years, building owners have been satisfied with the performance and efficiency of chillers operating in the range of 0.8 to 0.9 kW/ton when new. With age, the actual efficiency drops to more than 1.0 kW/ton at full load.

Today, new chillers are being installed with a full load-rated efficiency of 0.50 kW/ton, an increase of nearly 50 percent. The part-load efficiency of the new generation of chillers is equally impressive. While almost all older chillers degrade rapidly with reduced load, newer chillers do not degrade nearly as quickly.

Changes in chiller design

Several design and operation changes have helped improve chiller performance. To improve the heat transfer characteristics of chillers, manufacturers have increased the size of the heat exchangers of the units. Electromechanical control systems have been replaced by microprocessor-based electronic controls that provide greater accuracy, reliability, and flexibility. Variable frequency drives control compressor speed, resulting in increased part-load efficiency.

Increased energy efficiency is not the only benefit of new generation building chillers; These chillers provide good refrigerant containment. Although older chillers routinely lost 10 percent to 15 percent of the refrigerant charge per year, newer chillers can limit losses to less than 0.5 percent. Low leakage rates and better purging systems reduce the amount of non-condensable gases found in the refrigerant system – a key factor in maintaining chiller performance over time.

There is another significant development in boiler operation: replacing pneumatic and manual controls with microprocessor-based systems. As a rule of thumb, the systems are expected to achieve 5 percent to 7 percent energy savings over traditional pneumatic-based systems.

Microprocessor-based control systems offer savings as a result of their ability to more precisely modulate boiler operation than pneumatic-based systems. By precisely modulating boiler operation, the systems help maintain the proper fuel-to-air ratio and track the load placed on the boiler by the HVAC system.

Microprocessor-based systems offer many additional advantages, including remote monitoring and operating capabilities, automated control sequences, monitoring of steam flow, and lower maintenance costs. One way systems can help reduce maintenance costs is through the ability to maintain the correct fuel-to-air ratio. By maintaining the correct ratio, the systems reduce the rate of soot accumulation on the boiler tubes, thus reducing the frequency of necessary teardowns and cleanings. Keeping the boiler tubes free of soot helps improve the thermal efficiency of the boiler.

Direct digital controls

A major change in the HVAC sector is the widespread implementation of Direct Digital Controls (DDC). Introduced more than 15 years ago, the DDC system has become the industry standard for control system design today. With the ability to provide accurate and precise control of temperature and air and water flow, the systems have largely replaced pneumatic and electrical control systems.

DDC systems help building owners save energy in several ways. Their accuracy and precision virtually eliminate the control problems of offset, overshoot, and hunting commonly found in pneumatic systems, resulting in better system regulation. Their ability to respond to an almost unlimited range of sensors results in better coordinated control activities. This allows systems to perform more complex control strategies than can be done with pneumatic control. Finally, their simple or automatic calibration ensures that the control systems will function as designed over time, with little or no loss of accuracy.

DDC systems offer many other benefits as well. Because the control strategy is software-based, the system can be easily modified to match changes in resident requirements without costly hardware modifications. DDC systems are also ideal for applications that benefit from remote monitoring and operation.

Energy-efficient motors

Today’s HVAC systems use energy-efficient motors. Energy-efficient motors offer a moderate but significant increase in full-load operating efficiency compared to standard motor designs. For example, an energy-efficient 10 hp motor operates at about 93 percent efficiency; A standard motor of the same size is usually rated at 88 percent. Similarly, a 50 hp energy-efficient motor is rated at approximately 94 percent efficiency compared to the 90 percent efficiency rating of a 50 hp standard motor.

This increase in operating efficiency is accompanied by an increase in the first cost of the motors. How quickly this additional first cost is recovered depends on two factors: motor loading and the number of hours the motor is operated each year.

The closer the motor is operated to its full-load rating and the more hours the motor is operated per year, the sooner the first-cost difference is recovered. For most applications where the motor is continuously operated at or near full load, the payback period for the additional first cost is typically between three and six months.

The combination of continuous loading and long hours of operation makes HVAC applications well suited for the use of energy-efficient motors. Energy-efficient motors are commonly found driving centrifugal circulation pumps and system fans. With these loads, a 4 percent or 5 percent increase in the drive motor’s electrical efficiency translates into significant energy savings, especially when systems are operating 24 hours a day.

A side benefit of energy-efficient motor design is high power factor. Increasing the power factor of the drive motor reduces the current draw on the electrical system, freeing up excess distribution capacity and reducing distribution losses in the system. Although increasing the power factor is not enough to justify the price difference for a high efficiency motor, it is an important consideration, especially for large power users where system capacity is limited.

Although the motors have proven themselves to be very cost-effective in new applications, their use in existing applications is somewhat difficult to justify. In many instances, the cost of replacing an existing, working motor with a higher efficiency one will not be recovered for five to 10 years or more.

Among the improvements in HVAC systems that have helped increase operating efficiency, variable frequency drives have had the most dramatic results. Applied to system components ranging from fans to chillers, the drives have shown themselves to be very successful in reducing system power requirements during part-load operation. And while most systems operate at part-load capacity 90 percent or more of the time, the energy savings produced by variable frequency drives recover their investment quickly, typically within one to two years.

In general, the larger the motor, the greater the savings. As a rule of thumb, almost any HVAC system motor 20 hp and larger can benefit from the installation of a variable frequency drive.

Variable frequency drive applications

Variable frequency drives save the motor by changing the frequency and voltage of its power supply. This variation is used to reduce the operating speed of the devices it controls to match the load requirements. At low operating speeds, the drive motor’s power draw drops off rapidly.

For example, a centrifugal fan, when operated at 75 percent current, draws only 40 percent of full-load power. At 50 percent current, the fan’s power requirement is less than 15 percent of full-load power. Conventional control systems, such as damper or vane control, also reduce energy requirements at partial flow, reducing savings significantly.

Another area where variable frequency drives have improved HVAC system efficiency is in centrifugal pumps found in hot and cold water circulation systems. Generally, these pumps supply a constant flow of water to the terminal units. As demand for hot or cold water decreases, the control valves in the terminal units throttle back. To keep the pressure constant in the system, a bypass valve opens between the supply and return system. As the flow rate remains nearly constant, the load on the pump’s electric drive also remains nearly constant.

Variable frequency drives control the pressure in the system in response to varying demands by decelerating the pump. As with centrifugal fans, the power required by pumps decreases as load and speed decrease. Again, since most systems operate at less than 90 percent of design capacity, the savings from low-speed operation are significant, typically recouping the unit cost in one to two years.

Chiller load

A third application for variable frequency drives is centrifugal chillers. Coolers are sized for peak cooling loads, even if these loads are only a few hours per year.

With conventional control systems that close the vanes at the chiller inlet, chiller efficiency drops significantly during part-load operation. When variable frequency drives are applied to these chillers, they regulate the operation of the chiller by reducing the speed of the compressor. This results in near full-load efficiency over a wide range of cooling loads. This increase in part-load efficiency increases the seasonal efficiency of the chiller by 15 to 20 percent.

Energy conservation is not the only benefit of variable frequency drives. The electric motor is stressed and the mechanical system that drives it every time a pump, fan or chiller is started at full-line voltage: motor windings heat up, belts slip, drive chains stretch, and high-pressure develops in circulating systems. . Variable frequency drives reduce these stresses by starting the system in a soft start at lower voltages and frequencies, resulting in longer motor and equipment life.

Ultimately, the most important factor in an energy-efficient HVAC system is how the system is operated. No matter how sophisticated the system, or how extensive its energy-saving features, the system’s performance depends on the way it is operated and maintained. Operating personnel should be properly trained on how to best use the system and its features. Maintenance personnel must be trained and equipped with the proper tools to keep the system operating as designed. Maintenance cannot be deferred.

Energy-efficient HVAC systems give facility managers the ability to improve system performance while reducing energy requirements. But they only benefit building owners as long as they are taken care of. If facility managers choose to ignore maintenance requirements, they may soon find system failures where they have actually increased energy requirements.

Video about A Pump Is Used To Maintain Rate Of Flow

You can see more content about A Pump Is Used To Maintain Rate Of Flow on our youtube channel: Click Here

Question about A Pump Is Used To Maintain Rate Of Flow

If you have any questions about A Pump Is Used To Maintain Rate Of Flow, please let us know, all your questions or suggestions will help us improve in the following articles!

The article A Pump Is Used To Maintain Rate Of Flow was compiled by me and my team from many sources. If you find the article A Pump Is Used To Maintain Rate Of Flow helpful to you, please support the team Like or Share!

Rate Articles A Pump Is Used To Maintain Rate Of Flow

Rate: 4-5 stars
Ratings: 7201
Views: 89082146

Search keywords A Pump Is Used To Maintain Rate Of Flow

A Pump Is Used To Maintain Rate Of Flow
way A Pump Is Used To Maintain Rate Of Flow
tutorial A Pump Is Used To Maintain Rate Of Flow
A Pump Is Used To Maintain Rate Of Flow free
#Elements #Efficient #HVAC #System

Source: https://ezinearticles.com/?The-Elements-Of-An-Efficient-HVAC-System&id=6345195