Low Delta T Syndrome.

by Bruno Carvalho
The concept of Delta T, or temperature difference, plays a crucial role in the operational efficiency of heating and cooling systems. When the temperature difference between the supply and return flow is inadequately low, Low Delta T syndrome occurs, resulting in various problems.
Operational Heat Exchanger Contamination: Operational contamination of the heat exchanger is one of the main causes of Low Delta T. Accumulation of deposits, sediments, and impurities in the heat exchangers reduces the efficiency in heat transfer between the system fluid and the heating or cooling medium. This diminishes the temperature difference between the supply and return flow, impairing the overall system capacity.
Incorrectly Sized Control Valves: Improperly sized control valves can restrict water flow in the system, causing a drop in temperature difference. If the valves are not adjusted correctly to handle thermal demands, the system may struggle to reach and maintain the desired temperature, leading to Low Delta T.
Lack of Hydronic Balancing: Hydronic balancing refers to the balanced distribution of water flow in different system components, such as radiators, coils, and heat exchangers. Lack of hydronic balancing can result in flow imbalances, leading to temperature variation between the supply and return flow.
Fluctuations in Differential Pressure: Variations in the differential pressure within the system can also affect Delta T. Inadequate fluctuations can cause instability in water flow, leading to irregular temperature distribution and contributing to Low Delta T syndrome.
The negative effects of Low Delta T extend beyond thermal efficiency. The need for additional pumps and generators to compensate for the low temperature difference results in increased energy consumption, impacting the operational costs of the system.
The most common causes found in chilled water installations operating with Low Delta T are listed below:
  • Low ambient temperature setpoint, outside design conditions;
  • Inoperative control valves;
  • Lack of sensor calibration;
  • Lack of interlocking valve with the air conditioner;
  • Leakage in closed control valve (close-off);
  • Dirty air filter;
  • Incrustation in coil (water or air);
  • Lack of balancing or rebalancing;
  • Improperly selected coils;
  • Improperly selected control valves;
  • Inverted hydraulic connection of the air conditioner;
  • Replacement of air conditioners and control valves without respecting the original design Delta T;
  • Uncontrolled process loads (industry).
Preventive maintenance, regular system monitoring, and implementation of proper design and operation practices are essential to prevent Low Delta T syndrome and optimize the energy performance of heating and cooling systems.
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