10 Strategies to Improve HVAC Chiller Performance
HVAC chiller installations consume the most energy in commercial buildings today. Yet still, when appropriately addressed, improving them can save you thousands of dollars every year. Based on scientific proof, the following are ten strategies proven to enhance chiller performance. These techniques range from retrofitting compressors to using chilled-water resets and anything in between that can lower energy expenses. So here we begin!
Compressor Retrofit or VFD
The chiller compressor is responsible for most of the system’s energy usage. Retrofitting outdated compressors or adding variable frequency drives (VFDs) can significantly boost efficiency. When changing a compressor, opt for a more modern technology such as variable speed or scroll rather than older fixed speed types. This trivial exchange can decrease energy consumption by as much as 9%. If retrofitting is not an option, installing a VFD will save about 20% of energy because it allows the compressor to change its speed according to load requirements.
Chilled Water Reset
Traditionally, chilled water is maintained at a fixed temperature regardless of building load. Chilled water resets can be based on the outside air temperature or system demand as a more advantageous method. Raising the chilled water setpoint during part-load situations reduces the chiller compressor’s cooling capacity request. According to the U.S. Department of Energy, increasing the chilled water temperature by a few degrees Fahrenheit can improve chiller performance by 1-2 percent while complying with cooling objectives.
Condenser Water Reset
If your chiller plant utilizes cooling tower water, condenser water reset offers similar efficiency gains. During low building load or mild outdoor temperatures, the condenser water setpoint can be lowered 2-4°F. Hence, this reduces the pressure of condensation and, therefore, enables less work to be done by the chiller compressor. Studies found that if the temperature is lowered by one degree Fahrenheit, there would be an energy saving of about 1-2% due to the condenser water reset.
Heat Exchanger Cleaning
Neglecting to clean evaporator and condenser coils reduces heat transfer and increases power consumption over time. Each year, biofilms, minerals, and particulates accumulate within the chiller’s heat exchangers, driving up head pressure and hindering thermal transfer. An overwhelmed condenser reduces efficiency by 10% or more if severely fouled. Regular cleaning restores performance. Develop a proactive maintenance plan for annual coil cleaning for open cooling towers or closed loops every three years for preventive upkeep. Before cleaning, isolate equipment to avoid cross-contamination.
Electronic Expansion Valve
Most chillers use a fixed orifice thermostatic expansion valve (TXV) to meter refrigerant flow. Replacing this mechanical valve with an electronic expansion valve (EEV) provides finer evaporator superheat control and excellent stability at part-load conditions. An EEV responds faster than a TXV to precisely regulate superheat levels and reduce head pressure, lowering energy costs by up to 14%. In addition, valve settings may also be optimized for confidential contracts during EEV commissioning. This upgrade is worth considering, especially for variable speed systems.
Air-Cooled Condenser Fans
In chiller applications using air-cooled condensers, motorized fan controllers consume a fair amount of power. However, the ECMs or variable-speed drives (VSDs) can help achieve fan speed changes that align with their requirements. Variable fan operation saves energy by not running each at full speed. Retrofit ECM/VFDs often achieve total chiller power savings of approximately 6%. For new chillers, specify premium fans like plug fans, which promote increased air flow with lower horsepower requirements.
Free Cooling or Economizer Cycle
Buildings in mild climate zones can take advantage of accessible cooling technologies. On dry, calm days, the compressor can be shut off entirely when the outdoor wet-bulb temperature is lower than the return chilled water. Unlike the outdoor air used, which is passed through an air- or water-side economizer to meet thermal demands, This allows for rejecting “free” heat without using any mechanical means of cooling. Free cooling strategies reduce energy consumption during the year by between 20% and 50%, depending on the climatic conditions. It is essential to ensure that controls include smart economizer lockouts to protect against system failures.
Chiller Sequencing and Plant Optimization
Proper staging and load-matching of chillers within the plant is critical for high-part load efficiency. Using sequencing logic, a programmable logic controller automatically allocates operating chillers and matches their capacity to thermal demand. Cooling towers, condenser water pumps, and other auxiliary plant components should also be optimized in sync with the chillers. Advanced sequencing controls yield up to 20% savings from properly distributing loads across efficient operating ranges.
Pump and Fan VFDs
Applying variable frequency drives to circulation pumps and air handlers permits modulating flow rates according to need. Oversized systems often move excess air or water, which results in tremendous wastage of power. For example, at lower loads, different variable frequency drives automatically reduce their speeds if fitted into such pumps, reducing energy consumption by 30%. The retrofitting process should commence with minor equipment and move to larger equipment before anything else happens.
Controls Upgrades
Newly developed controllers utilize advanced control algorithms and digital sensors, allowing more precise and responsive chiller operation. Replace aging controls and pneumatic devices with direct digital controls integrated with a building automation system. Up-to-date control platforms perform complex setpoint resetting, demand limiting, and optimum start/stop sequencing out of the box. Staying on top of software updates also addresses functional or efficiency problems. Modern controls create an opportunity to optimize approaches like those discussed here for an additional savings boost.
Summing Up
Optimizing HVAC Chiller performance is key to reducing costs, improving efficiency, and ensuring reliable operation. Implementing these ten strategies can significantly enhance your system’s performance, but the real game-changer lies in leveraging IoT solutions for continuous monitoring and predictive maintenance.
At Avigna, we specialize in providing IoT-driven solutions to help you achieve optimal efficiency and prevent costly downtime. Connect with us for a free IoT consultation and discover how your operations can gain a boost with IoT.
