How Temperature reset works in Central Air Systems

What is it?

There is a controller in the air-side tab that lets the user determine whether the supply air temperature from the central air handling unit is constant or gets reset based on a specific criteria.

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Why do I care?

The temperature control strategy for an all-air system will have an impact on the amount of energy the system uses, because it will decide at each time step whether more air is delivered at a milder temperature or less air is delivered at a colder temperature to each zone.

Systems affected

These controls can be applied to all the systems with variable centrally supplied airflow and supply temperature, including:

  • VAV (all types)
  • Underfloor Air Distribution
  • Displacement Ventilation

Control options summarized

There are 4 options you can choose from in the dropdown:

  1. Constant supply air temperature - (default). The HVAC system always just supplies air to the zones at the temperature you nominated in the controller directly above.
  2. Minimize heating energy. This is often colloquially known as "supply air temperature reset". The central air handling unit adjusts the supply air temperature up so that it's whatever is needed for the zone with the most cooling required. We called this "Minimize heating energy" because the bias is towards supplying milder air where possible so there is less reheat throughout the building. (link to E+ manual on this control)
  3. Minimize cooling energy. This solution essentially tries to match the cooling supply air setpoint (off the air handling unit) with the outside air, with the idea being that if the supply air is as close as possible temperature as outside, cooling energy will be reduced. (link to E+ manual on this control)
  4. Minimize fan energy. This solution tries to match the heating supply air temperature (off the air handling unit) with the outside air. The most common observed effect was to reduce fan energy.
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