This is out second post in our concise series on enthalpy and its crucial role in HVAC and AHU systems. Our in-house experts have conducted in-depth research to clarify the importance of this key variable, making it more accessible to professionals in the field.”
Waste heat, also known as excess heat, in air treatment refers to the residual thermal energy that is produced by HVAC systems and other industrial processes but is not effectively utilized.
This excess heat is often a byproduct of heating, cooling, and ventilation operations within buildings and can include heat expelled by compressors, condensers, and other mechanical equipment.
In HVAC systems, particularly those involving air handling units (AHUs), waste heat can arise from several sources:
- Heat from Cooling Processes: When air is cooled to dehumidify or lower the temperature, the removed heat must be expelled, typically via condensers. This expelled heat is often released into the environment, constituting waste heat.
- Excess Heat from Heating Operations: During the heating cycle, any heat not transferred to the air for space heating can become waste heat, especially in systems with inefficient heat transfer mechanisms.
- Operational Byproducts: Mechanical operations, such as those involving fans, pumps, and motors within the AHU, generate heat as a byproduct of electrical energy consumption and friction. This heat is often not harnessed and is instead dissipated into the surrounding air.
Does waste heat really need to be wasted?
Understanding and managing waste heat is crucial for improving the energy efficiency of air treatment systems.
Effective waste heat recovery methods, such as heat exchangers or heat recovery ventilators (HRVs), can capture and reuse this thermal energy, reducing the overall energy consumption and enhancing system performance.
By integrating these strategies, HVAC systems can minimize energy loss, lower operational costs, and contribute to more sustainable building practices.
Why measure Enthalpy in AHUs the heat exchanger?
Measuring enthalpy before and after the heat exchanger in Air Handling Units (AHUs) is critical for several reasons, directly impacting the efficiency and effectiveness of the heat exchange process.
Firstly, enthalpy provides a comprehensive measure of the total energy content of the air, including both its temperature and moisture content. By assessing the enthalpy before the heat exchanger, HVAC professionals can accurately gauge the initial energy state of the incoming air.
This baseline measurement is essential for understanding the total thermal energy that the air handling unit needs to manage.
Secondly, by measuring the enthalpy of the air after it passes through the heat exchanger, professionals can determine the exact amount of energy transferred during the process.
This post-exchange measurement reveals how effectively the heat exchanger is performing its role in transferring heat from the incoming air to the outgoing air, or vice versa.
This data is crucial for evaluating the performance and efficiency of the heat exchanger, ensuring that it operates at optimal levels.
Additionally, monitoring enthalpy before and after the heat exchanger helps in identifying potential inefficiencies or issues within the system.
For instance, a smaller-than-expected change in enthalpy could indicate a problem with the heat exchanger, such as fouling, leaks, or inadequate airflow. Early detection of such issues allows for timely maintenance and adjustments, preventing energy losses and ensuring the system runs efficiently.
Furthermore, understanding the enthalpy change also aids in energy management and cost savings. By maximizing the efficiency of heat exchange processes, AHUs can reduce the need for additional heating or cooling, leading to lower energy consumption and operational costs. This efficiency is particularly important in large commercial or industrial settings where HVAC systems play a significant role in overall energy use.
Finally, precise control of enthalpy before and after the heat exchanger contributes to maintaining optimal indoor air quality and comfort. By ensuring that the right amount of heat is transferred, the system can maintain the desired indoor temperature and humidity levels, enhancing occupant comfort and health.
Enthalpy Sensors are key to the process
Measuring enthalpy before and after the heat exchanger in AHUs is essential for assessing system efficiency, identifying maintenance needs, managing energy use, and ensuring optimal indoor air quality.
This practice enables HVAC professionals to optimize performance, reduce costs, and maintain comfortable and healthy indoor environments.
This is possible with reliable, precise sensors that capture temperature, humidity and pressure and can compute and calculate the enthalpy.
Every Andivi Modbus Temperature and Humidity Sensor also comes serial with Enthalpy, Dew point and Density of Moist Air calculation, which can be used at an instant for the applications in AHUs that have been described in this blog post.
Achieving this level of precision is possible with reliable, advanced sensors that accurately capture temperature, humidity, and pressure to compute and calculate enthalpy.
The Andivi Modbus Temperature and Humidity Sensor exemplifies this capability, as it includes built-in calculations for enthalpy, dew point, and the density of moist air. Hence, we also address the sensor as an Enthalpy Sensor. These sensors provide real-time, actionable data that can be instantly applied to optimize the performance of AHUs, ensuring efficient heat exchange and maintaining ideal indoor air conditions as described in this blog post. By leveraging such sophisticated sensors, AHU systems can achieve superior energy efficiency, cost savings, and enhanced indoor comfort.
Enthalpy Sensors are also available with BACnet protocol.
Why is Enthalpy in Free Cooling relevant for Air Handling Units (AHUs)
Enthalpy is crucial in free cooling for Air Handling Units (AHUs) because it provides a comprehensive measure of the total energy content of the air, including both temperature and humidity.
By comparing the enthalpy of indoor and outdoor air, HVAC systems can optimize the use of natural cooling, reducing reliance on mechanical refrigeration and enhancing energy efficiency.
This approach ensures that free cooling is applied only when the outdoor air has a lower energy content than indoor air, preventing unnecessary humidity from entering the indoor environment.
Continuous monitoring of enthalpy throughout the day and night further refines this process, leading to significant energy savings and maintaining optimal indoor air quality. We have written about it in the blog post: The Importance of Enthalpy in Free Cooling for Air Handling Units (AHUs).
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This article was conceptualized by Danijel Mursic, a mechanical engineer and thermodynamics expert with over 30 years of experience in the AHU and HVAC sector and former CEO of Menerga Slovenija.