What is delta-T and how it affects energy efficiency?

Simply put, delta-T refers to the temperature difference between the chilled water entering the air handler unit (AHU) evaporator or chilled water coil and the leaving refrigerant or water. It is a crucial factor in determining the performance and energy efficiency of not only the AHU, but the HVAC system as a whole.

Here’s how Delta-T Works

1. Cooling Capacity: The delta-T directly impacts the cooling capacity of the HVAC system. A larger temperature difference means that more heat is being removed from the building, resulting in a higher cooling capacity. Conversely, a smaller delta-T indicates that less heat is being removed, leading to lower cooling capacity.
2. Energy Efficiency: The delta-T affects the energy efficiency of the HVAC system. A larger temperature difference means the HVAC system can achieve the desired cooling effect more efficiently. This is because a larger delta-T allows the evaporator coil to operate at a higher heat exchange rate, extracting more heat from the building’s air. As a result, the compressor, which consumes a significant amount of energy, doesn’t have to work as hard to achieve the desired cooling effect.
3. System Performance: The delta-T also impacts the overall performance of the HVAC system. If the temperature difference across the evaporator coil is too high, it may indicate that the system is oversized for the cooling load of the building. This can result in short cycling, where the system turns on and off frequently, leading to energy wastage and wear and tear on the equipment. On the other hand, if the delta-T is too low, it may suggest that the system is undersized or that there are issues with the refrigerant flow or air distribution. In such cases, the HVAC system may struggle to meet the cooling demands of the building efficiently.
4. Pumping Energy: Another aspect affected by the delta-T is the pumping energy required to circulate the chilled water through the evaporator coil. A higher temperature difference can reduce the pumping energy since less water flow is needed to transfer the same amount of cooling. Conversely, a smaller delta-T may require higher water flow rates, resulting in increased pumping energy consumption.
   
   

Improve Energy Efficiency with Delta-T as a Metric

To improve energy efficiency and system performance, facility managers should consider the following measures:

1. Regular Maintenance: Ensure the evaporator coil is clean and free of debris, as dirt and dust can hinder heat transfer and reduce the delta-T. Regular maintenance, including steam coil cleaning and replacing air filters, can prevent clogging and maintain optimal performance with delta-T.
2. Balancing Load and Delta-T: Evaluate the load requirements of the building and ensure that the system is appropriately sized. Oversized or undersized equipment can lead to inefficient operation and reduced delta-T. Proper load calculations and system design are essential to achieve optimal cooling and energy efficiency.
3. System Optimization: Engage an HVAC professional to assess and optimize the system’s components, including the evaporator coil, refrigerant charge, airflow, and controls. Ensuring these elements are calibrated correctly can help maximize the delta-T and overall system performance.

By understanding and managing the delta-T across the HVAC chilled water evaporator coil, facility managers can improve energy efficiency, reduce operational costs, enhance occupant comfort, and prolong the lifespan of the HVAC system. Consulting with energy professionals or HVAC experts, like WTI Pure Air, is recommended to implement the most effective strategies for your specific institutional facility. Contact us today for more info on HVAC condition assessments, deep coil cleaning and restoration!