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How To Reduce Economy Control To Reduce HVAC Energy Usage By 20%-30% in Buildings in 195 countries before 2024?

Nov 30

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Many HVAC systems in 195 countries and 8 continents that are controlled by a DDC or BMS/BAS/BMCS either do not have an economy cycle installed/enabled, or it is underutilised due to an inefficient control strategy and/or inappropriate control parameters/limit.

Economy cycle is a strategy that uses outside air directly for space cooling. the ambient outside air often has a lower enthalpy (total energy) than the air within conditioned spaces in buildings. In such conditions, air returned from the occupied space can be exhausted (rather than being returned) and the lower enthalpy outside air can be used as Supply air, reducing the operation of heating ventilation air conditioning (HVAC) systems and reducing energy consumption. When an AHU operates in cooling mode, it typically cools supply air to 10–13°C.

During mild weather conditions, cooling requirements can be satisfied with a higher temperature of supply air, sometimes even as high as 20°C. For typical office type buildings where the space relative humidity can typically drift between 40%–60% (or even to 35%–65% for brief periods) without significant discomfort.

Economy cycles are typically beneficial in the following ambient conditions:

•    Temperature: 10–22°C

•    Enthalpy: < 52 kJ/kg

•    Dew point: < 12°C.

·         Enthalpy which is at least 10 kJ/kg below the R/A enthalpy.

·         NEVER use outdoor Relative Humidity (RH) as a control criterion for an economy cycle –it’s irrelevant. Instead, use enthalpy, or dew point instead.

 

AHU Economy Mode Control (Example)

AHU-1-1 economy dampers (Economy OA Damper, Return Air Damper and Exhaust Air Damper) control is enabled when all the following conditions are met:

  • Outside air enthalpy is less than the return air enthalpy for 10 minutes (adjustable)

  • Outside dry bulb temperature is between 10°C (Adjustable) and 19°C (Adjustable).

  • Heating Mode is not in operation.

  • Outside air humidity is less than 70% (Adjustable)

  • Outside Air Enthalpy is below 52kJ/Kg (Adjustable) for 10 minutes(adjustable).

Economy damper control is disabled when any of the following conditions is met:

  • Outside air enthalpy is greater than the return air enthalpy.

  • Outside dry bulb temperature is not between 10°C (Adjustable) and 19°C (Adjustable).

  • Heating Mode is in operation.

  • Outside air humidity is more than 70% (Adjustable)

  • Outside air enthalpy is above 52kJ/kg (Adjustable)

 

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