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Large buildings, such as consumer and institutional facilities, consume large amounts of energy. Such establishments require efficient HVAC systems that can support their functions. It is not surprising that HVAC systems consume the most energy in such establishments. With all their components, HVAC systems are complex mechanical equipment. Reducing energy consumption is of utmost importance in HVAC system optimization, but requires specialist knowledge.
Facility managers are looking for the most energy-saving HVAC components such as chillers, pumps, and cooling towers. But the key to HVAC optimization does not only depend on its parts. These individual components cannot achieve efficiency for the entire HVAC system. A holistic approach that considers all components is the key to maximizing the HVAC system.
The term ‘optimization’ has been mainstream in facilities management industries. Nowadays, optimization has become misleading. Toback stated, “Some vendors say the solution is a piece of hardware. Some say it is software, while others say it is a cloud-based dashboard. But the truth is central plant optimization is not a single thing. It is an overall methodology that starts with a good design and construction. It integrates automation and optimization. It provides maintenance and monitoring throughout a building’s lifecycle.” To optimize the HVAC system, one must look at it as a whole. Focusing on the components that consume the most energy in the system.
HVAC system optimization can be a challenging task. It requires knowledge of the different parts of the HVAC system. Knowing how much energy each part consumes. But worry not – for today, we give you a complete guide for your HVAC system optimization. Expert help is great, but you can also do some simple tasks to help maximize your HVAC system.
Know Your HVAC System Components
In general, HVAC systems are composed of eight parts.
- Thermostat. It is the most visible part of the HVAC system, and it regulates the temperature of your HVAC. It can be set manually or programmed in advance to keep the area in which it is located at the desired temperature. It also automatically adjusts to meet the desired temperature programmed.
- Furnace. It is the key component of your HVAC system. It is the largest part of your HVAC system that occupies considerable space. The furnace heats the supply of air distributed to various areas of the building through the HVAC system optimization.
- Heat exchanger. Networx stated, “It switches on when a thermostat activates the furnace to produce warmer temperatures in winter. It pulls in cool air, heats it, and circulates the resulting heated air via your ducts and out through the vents.” The heat exchanger is located inside your furnace unit’s housing.
- Evaporator coil. This component’s function is opposite to the heat exchanger. It functions as an ‘air cooler’ when the thermostat is set in lower temperatures. It is located in a metal closure on the furnace’s exterior (top or side). As stated by Networx, “The evaporator coil works similarly to an automobile radiator to produce cool air. It is then circulated through the ductwork.”
- Condensing unit. This component is connected to the evaporator coil. It is installed outside the building and filled with refrigerant gas. According to Networx, “When the refrigerant has been cooled to a liquid by heat exchange with the exterior air, the condensing unit pumps the liquid to the evaporator coil to be evaporated into a gas once more.”
- Refrigerant lines. It carries refrigerant substance to the condensing unit vaporized in a gas form. Then, it returns the gas to the evaporator coil in liquid form. Refrigerant lines are narrow tubes made of copper or aluminum that make them durable to heat and cold.
- Ductwork. Networx stated, “Ductwork refers to the system of ducts that transports air warmed or cooled by the system to the various areas of a building. Ducts are commonly made of lightweight aluminum. But they may also be manufactured from steel, flexible plastic, polyurethane, fiberglass, or fabric.”
- Vents. These are the outlets that transfer the heated or cooled air from the duct system to various building areas. Vents are made of safe metals and are located on the ceiling. These components direct the treated air downward to the occupants of an establishment. According to Networx, vents “may be manually controlled or even closed, to control the amount of heating or cooling and the area of the room to which it will be directed.”
HVAC System Optimization
The goal of HVAC system optimization is to make mechanical systems work all the time efficiently. As stated by Toback, “For true optimization, the solution must automatically control HVAC equipment as a holistic system 24/7 so that it uses the least amount of energy without sacrificing performance.” The first step to optimizing your HVAC system is to assess the basic rules of optimization.
- Measurement is the initial step. Measuring the energy consumption of each unit of your HVAC system is the key to optimization. According to Toback, “It is impossible to accurately predict and report the impact of varying conditions on the entire system.” Hence, measuring each piece of equipment will certainly help in your optimization strategy. Again, what you cannot measure, you cannot optimize.
- Optimize systems as a whole, not just individual components. HVAC system optimization is a holistic process. Installing the most efficient components or saving energy only in one subsystem does not optimize the whole HVAC system.
- Optimization must be automatic, dynamic, and continuous. Toback wrote, “To achieve maximum efficiency, optimization must be a real-time dynamic process, not a static set-and-forget process. Operational control must be automatic and based on real-time inputs and adjustments.”
Toback states that optimization fails to meet expectations. Due to the solution not delivering the closed-loop optimization in real-time. According to them, “Products sold as being able to “optimize” vary widely. From efficient components to component-based efficiency tools to systemwide HVAC optimization. No standard definition for “HVAC optimization” is guiding the industry. Engineers do not get the energy and cost savings they expect from the products they specify.”
Efficiency Strategies for your HVAC System
Some HVAC system optimization
can reduce your system’s energy consumption. But these strategies fall short when utilized alone. Thus, it is important to deploy these steps altogether.
- Energy management and analytic dashboard solutions. This strategy provides a necessary insight into how the central plant’s units are consuming energy. Some of these components can recommend a few ways to save energy. It meets the requirement for the basic rules of optimization. But it does not meet the strategy of true optimization. That is, automatically reacting to system conditions even before the energy is wasted.
- Fault detection and diagnosis (FDD). It automatically detects and diagnoses performance faults. This is an essential tool that ensures HVAC systems stay healthy in the long run. According to Toback, “On its own, FDD has drawbacks. FDD rules can be applied to any sensor, meter, valve, or pump in a chiller plant. It has alarms notifying the operations team whenever key values drift from a specified range. However, operations teams cannot easily prioritize the FDD-armed sensors that are critical to system reliability and savings over those that are not.”
- Chilled and condenser-water resets. This strategy is standard practice for systematic central plant operations. Chillers run better when refrigerant lift and compressor work are minimized. This is done by specifying warmer chilled water setpoints and a colder condenser water setpoint. But note that resets must be done carefully. Consider the impact of reset on the total system’s energy consumption. Toback wrote, “Energy savings may be lost if the chilled-water pumps or cooling tower fans must work harder to compensate. For example, increasing the chilled-water supply temperature decreases the log-mean temperature differential. It also affects the associated heat-transfer quantity of the air handling unit’s cooling coil. That which often requires more chilled-water flow and pumping energy to meet the same cooling load and humidity requirements.”
- Install variable frequency drives (VFDs). Many facilities utilize the primary optimization strategy of installing VFDs. These VFDs use proportional-integral-derivative (PID)-based controls all throughout a chiller plant. According to Toback, “PID loops are industry-standard ways to control individual components. But they typically focus only on individual components. Thus, they fail to deliver systemwide benefits no matter how many are installed.” These PID loops require considerable tuning to provide a smooth and stable run. Toback added, “System hunting is common with PID-based optimization. It occurs especially when using temperature or pressure setpoints. Significant latency can occur between when a specific setpoint is sent and when a resulting change in sensor feedback is realized. This often causes enough frustration to goad operators into turning off the optimization system.”
Another practice is retro-commissioning an HVAC system to bring the central plant back to its original condition. It can provide one-time energy efficiency gains. But the HVAC system performance will only drift over time. Often years later, when the central plant’s next retro-commissioning cycle occurs.
Air Filtration
In addition to “atmospheric dust,” airborne particulates can include pollen, mold (fungal) spores, animal dander, insect proteins, pesticides, lead, and infectious bacteria and viruses. Designers can integrate features into the ventilation system that will provide benefits for the school occupants as well as the efficiency and longevity of the HVAC system. In addition, these features can reduce the need for expensive cleaning of the ductwork and air handling units.
Filter Efficiency
- Air filters should have a dust-spot rating between 35% and 80% or a Minimum Efficiency Rating Value (MERV) of between 8 and 13. The higher the rating, the better the protection for the equipment and the occupants.
Pressure Drop
- Design more filter surface area into ventilation systems. Since different filter media are approximately proportional in their efficiency/pressure drop ratio, the most effective method for reducing pressure drop is to design more filter surface area into the filter system. This can be done by the specification of a filter with larger amounts of surface area, such as a pleated filter or bag filter.
Monitoring Pressure
- Consider installing a simple pressure differential sensor across all filter banks. This will prevent building personnel from having to guess whether the filter is ready for replacement. Sensors with a range of zero to 1.0 in. w.g. can save money and the environment by preventing premature disposal of filters that still have a useful life and can prevent health and maintenance problems caused by overloaded filters that have blown out. The sensors should be easily visible from a standing position in an easily accessed location near the air handling unit.
HVAC Optimization with AKCP
AKCP offers HVAC system solutions for all your needs. With over 30 years of experience, our company is the world’s oldest and largest manufacturer of networked wired and wireless sensor solutions.
Differential Air Pressure Sensor installed on the Air Handling Unit Filter. When pressure drop across the filter is high filters are dirty and require maintenance. Sensors are wireless with 10-year battery life. Wireless Pipe Pressure Sensors monitor the water or gas pressure and temperature on the input and discharge lines from the AHU.
In chilled water-cooling systems having sufficient water in the cooling tower is essential. With wireless tank depth pressure sensors, you can easily monitor and be alerted if the water level drops below the required levels. Flow meters can be installed to check for water loss, ensuring inflow and outflow are equal.
Air Handling Unit Monitoring also includes control of systems. Variable Frequency Drives controlling the compressor motor can improve efficiency and lower operating costs. Utilizing a VFD to vary the motor speed also allows better matching of the hydraulic energy generated by the chiller to the demand load. This not only reduces electrical energy consumption. It can also provide more precise control of chilled water temperature. AKCP can interface to VFDs via RS485 and control their speed based on data input from our wireless sensors.
Conclusion
HVAC system optimization is crucial for high-performance buildings. HVAC systems consume a lot of energy. Thus, it is essential to reduce energy consumption while maximizing the performance of your HVAC system. HVAC system optimization requires a holistic approach rather than focusing on the individual components. The design process and continuous monitoring are essential to maximizing the performance of your system. Always remember the basic rules of HVAC system optimization.
Reference Links:
https://www.networx.com/article/know-your-hvac-system-components-and-how