Low Delta-T Syndrome, what is it?

Challenges related to Low Delta-T Syndrome lead to numerous inefficiencies and a subsequent rise in energy costs.


Central Chilled Water Systems have served as the primary method for large-scale building cooling since their inception in the 1920s, owing to their practicality and efficiency compared to ductless split units. While these systems have demonstrated their capacity for savings and thermal comfort, they can also result in significant financial burdens and occupant discomfort if not optimized according to their original design intent. Indeed, the importance of a combination of well-executed design, meticulous operations, and regular maintenance of chilled water systems cannot be overstated for sustaining a healthy building environment. One notable issue in the design, control, and maintenance of chilled water and HVAC networks is the occurrence of Low Delta-T syndrome.

What is Low Delta-T Syndrome?

Delta-T is defined as the temperature difference between the chilled water supply and return, measured from the ETS room of a central chiller plant. Low Delta-T Syndrome manifests when a building’s Delta-T falls below its optimal setpoint, leading to various drawbacks such as elevated humidity levels and inadequate conditioning of spaces. According to ASHRAE standards, a District Cooling supplier serving properly designed buildings should maintain a Delta-T of approximately 9 degrees Celsius. When this setpoint deviates below the optimal level, it adversely affects the district cooling side, resulting in inefficiencies in the plant’s electricity and chilled water consumption, thereby incurring substantial penalties from local authorities.

Figure 01

Simple diagram of the supply/return chilled water loop

Addressing Low Delta-T Syndrome in Buildings: Tailored Solutions

Based on the comprehensive research conducted at Ark Energy and data collected from buildings actively addressing this issue, it is unequivocally established that there is no universal solution to eradicate low Delta-T syndrome. The measures employed to tackle this problem are typically customized for each specific building, and some of these tailored approaches are outlined below:

1.Replacement of malfunctioning actuator valves and FCUs in tenant spaces

2.Execution of HEX cleaning and chemical dosing

3.Adjustment of improper temperature set-points in AHUs and FAHUs

4.Reconditioning of double regulating valves (DRVs)

5.Recommissioning of Building Management Systems (BMS)

6.Installation of an Energy Control Management System (ECMS) to integrate main BTU meters and control and optimize the three networks of chilled water pumps

7.Installation of BTU submeters to monitor chilled water consumption in tenant spaces

8.Integration of a cloud-based energy management information system (arkEMIS) for high-definition energy data monitoring and automated abnormal drift detection


Building Information Modelling and Energy Simulation for Architecture Design [Journal] / auth. Bonomolo Marina, Di Lisi Simone and Leone Giuliana // MDPI. – Italy : MDPI, March 4, 2021. – 1 : Vol. 11.

Data Driven Energy Centered Maintenance [Book] / auth. Alshakhshir Fadi and Howell Marvin T.. – New York : River Publishers, 2021. – Vol. 1 : pp. 145-153.

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