In the US, temperatures have started to drop and colder weather is on the horizon. This is the best time to start thinking about what can be done to save energy in preparation for seasonal changes —starting with a chiller water supply temperature reset.
Resetting chiller water supply temperature —in accordance with the season— can increase the efficiency of the overall HVAC system and create monetary savings. In fact, the utility Georgia Power states that efficiency increases by 1 percent for each degree Fahrenheit raised in the chilled water supply above 42°F in centrifugal chillers. They also suggest that increasing the chilled water supply’s temperature in hot and humid climates should be possible and still maintain building comfort. This is a conservative estimate, with other sources claiming between 1.5 and 2 percent without impacting occupant comfort.
In cooler months, increasing the chilled water supply temperature makes logical sense if the cooling load is less than the design load. Within a building’s HVAC system, the chilled water supply is sent to the building’s air handling units (AHUs), which use the chilled water to achieve set points on how cold the air supplied to the space needs to be. The system works as a loop, so when the water returns from the AHU to the chiller plant, the heat exchanger doesn’t have to work as hard to reduce the temperature of the water, if the water supply temperature set point has been risen. This tactic lessens the workload and energy consumption of the compressor.
One of our clients recently experienced the benefits of this strategy first-hand. The onsite building engineer increased the water supply temperature setpoint from 41°F to 43°F, timed with a change in seasons. The result was an immediate chiller plant power reduction of 22 percent.
The air-side of the system can also be used to bring about change to the water-side of the system. If air temperature is adjusted to be lower, the chilled water valve at the AHU will keep the door open longer allowing more water to flow through it. This results in more water being pumped throughout the entire system. On the flip side, if the setpoints at the AHU are raised, less water needs to be circulated, which reduces the burden on the system’s pumps and reduces energy consumption. Our BuildingIQ 5i Platform works on the AHU level of an HVAC system, creating the energy reductions outlined in this scenario, while also using predictive analytics to coordinate these actions based on variables such as energy pricing, occupant behavior, weather forecasts, and more.
A campus installation that uses a central plant to supply cooling to multiple buildings began using our cloud-based 5i platform to implement control at the AHU level. Two water pipes run between the central plant and each building that it is supplying. The system is set up so that it can measure exactly the amount of water that is supplied to each building from the chiller plant —this helps them divide energy costs between buildings. When the AHU temperature setpoints were optimized by the 5i platform, the data clearly showed that they could satisfy cooling needs, while reducing the amount of circulated water. This decreased the stress on the overall system and pumps, leading to energy savings.
BuildingIQ’s effectiveness of generating energy savings by making intelligent adjustments at the AHU level based on machine learning, advanced modeling, and predictive analytics has been proven over and over in installations around the world. We believe that applying this same technique to smartly move the chilled water supply setpoints could create significant energy savings as well. Using cloud-based platforms to adjust the water-side and air-side set points in real-time with the common goal of overall building energy reductions may prove to the be future of HVAC energy management.
Dr. Estatio Gutierrez is Director of Optimization at BuildingIQ. Estatio obtained his Doctor of Philosophy (PhD), Mechanical Engineering in 2015. The focus of his dissertation was urban weather modeling focused on the impacts of air conditioning systems in the urban environment. He also has studies in atmospheric sciences and meteorology.