When it comes to HVAC systems, the efficiency of the main components has improved a lot during recent years, and new technology has also played an important role in increasing the overall efficiency of systems. Better-performing systems have also been manufactured with the use of computer-assisted design tools. Stricter requirements for the user and stricter guidelines for indoor air quality have meant that today’s systems are more environmentally friendly.
Five major factors are responsible for much of the improved efficiency of HVAC systems, although many other factors have played a part too.
* The introduction and use of low kW/ton chillers.
* More widespread use of Boiler control systems that are more efficient.
* DDC (Direct digital control) systems are being used more widely.
* More use of energy-efficient motors.
* More effective use of variable frequency drives.
For many years, an operating range of 0.8 to 0.9 kW/ton was considered acceptable for chillers; an operating efficiency of over 1.0 kW/ton at a full load was more normal for an older system.
Today, efficiency has increased by close to 50 percent, with current HVAC systems having chillers with a 0.50 kW/ton rating. Another bonus of the newer chillers is that the operating efficiency doesn’t decrease as quickly as before.
Chiller Design Changes
The size of the heat exchangers has also increased, a design change that has contributed significantly to the overall performance of modern chillers. More reliability, increased flexibility, and better precision can also be enjoyed due to the replacing of the older electromechanical controls with electronic controls that use a microprocessor. Due to the compressor’s speed being controlled by a variable frequency drive, part load performance is also better in today’s newer systems.
An improvement in refrigeration containment is also a benefit of using these new and improved chillers. The amount of refrigerant charge lost each year is typically less than 0.5 percent, a big improvement on older chillers that routinely lost between 10 and 15 percent in a typical year. And the chiller performs much more efficiently over time, thanks to fewer non-condensable gases, because of an improved purge system and lower leakage rates. Today’s boilers to are a lot more efficient than they were, partly due to a microprocessor-based control system replacing the older manual and pneumatic controls. In general, a newer system should save you between 5 to 7 percent in energy costs over an older pneumatic system. Because the operation of the boiler is regulated more precisely with a microprocessor-based system, you’ll enjoy these energy bills savings over an older system. The more precise modulation means that the load placed on the boiler is more precisely maintained, and the fuel to air ratio is better monitored. It means that less soot accumulates on the boiler tubes, and you won’t have to clean the system as much. Your boiler’s thermal efficiency is also greatly improved when the boiler doesn’t collect all that unwanted soot. The ability to operate your HVAC system remotely is another advantage of a more up-to-date microprocessor operating system. You can also monitor steam flow and enjoy the convenience of automated control sequences.
Direct Digital Controls
Over 15 years ago, the HVAC industry saw the introduction of DDC or Direct Digital Controls. With these, you can regulate the flow of water and air more precisely, and the system has become standard across the industry, a big improvement on the pneumatic and electric systems. A pneumatic system has problems with overshoot, hunting, and offset, and the implementation of DDC systems has eliminated these issues, allowing homeowners and businesses to save money. Control activities are also better coordinated because they can respond to an almost unlimited number of sensors. Over time, a DDC system won’t lose much of its accuracy or precision, and a range of more complex control instructions can be carried out than with an older pneumatic system. Another benefit of DDC systems is that they eliminate the need for potentially expensive changes to hardware when changing occupant requirements mean modifications to the system. And as mentioned before, the ability to operate the system remotely is a big plus.
Energy Efficient Motors
Although the level of operating efficiency is modest when your system uses an energy-efficient motor, it nonetheless makes a big difference. A standard 10 HP motor operates about 88 percent efficiency, although you can expect that rating to increase to about 93 percent with the same size energy-efficient motor. A 50 HP standard motor has an energy-efficient rating of about 90 percent, while the same energy-efficient motor has around 94 percent. However, it does mean a first cost increase for the motor and a boost in operating efficiency. The number of hours that the motor operates in a year and the loading will determine how quickly the extra first cost is recouped. The first cost differential will be recovered more quickly if a motor is used more hours in a year and operated at or close to its full load rating. You can assume it will take between 3 and 6 months to recoup the losses if the motor is constantly running near full load or close to it. Energy-efficient motors are especially well suited for use in HVAC systems because of the long hours of use and the continual loading involved. If you have a recently installed system fan or circulation pump, you may find that an energy-efficient motor drives it. If your system is operating all day, every day, or you run it a lot, you should enjoy a noticeably lower energy bill, thanks to the drive motor’s 4 to 5 percent increase inefficiency. An increase in power is another benefit of using an energy-efficient motor. It means fewer system distribution losses, extra capacity for distribution, and less drawing on the electrical system. Users of large amounts of electricity can benefit from this increased power, especially when there are limitations on system capacity. However, the increased power factor of a higher efficiency motor generally doesn’t justify the extra cost. In general, it will take you between 5 to 10 years to recoup the extra cost of replacing an older motor with a higher-efficiency motor. It makes it hard to justify using them in existing applications. Since being used in HVAC systems, variable frequency drives have been beneficial in lowering system energy requirements when operating in a part load mode. These drives have been responsible for providing the most significant results for new technology for boosting operating efficiency and have been used in various settings, from chillers to fans. And it usually just takes between one and two years to recoup the extra cost, when most systems are operating about 90 percent of the time with a part load capacity.
The savings are more with a larger motor, is the general rule of thumb. It generally makes financial sense to install a variable frequency drive in any system with a motor of at least 20 HP.