Calculation of Outdoor Air Fraction through Economizer Control Types during Intermediate Season

  • Hong, Goopyo (Dept. of Architectural Engineering, Yonsei Univ.) ;
  • Hong, Jun (Dept. of Architectural Engineering, Yonsei Univ.) ;
  • Kim, Byungseon Sean (Dept. of Architectural Engineering, Yonsei Univ.)
  • Received : 2016.11.17
  • Accepted : 2016.12.20
  • Published : 2016.12.31


Purpose: In this study, we examined outdoor air fraction using historical data of actual Air Handling Unit (AHU) in the existing building during intermediate season and analyzed optimal outdoor air fraction by control types for economizer. Method: Control types for economizer which was used in analysis are No Economizer(NE), Differential Dry-bulb Temperature(DT), Diffrential Enthalpy(DE), Differential Dry-bulb Temperature+Differential Enthalpy(DTDE), and Differential Enthalpy+Differential Dry-bulb Temperature (DEDT). In addition, the system heating and cooling load were analyzed by calculating the outdoor air fraction through existing AHU operating method and control types for economizer. Result: Optimized outdoor air fraction through control types was the lowest in March and distribution over 50% was shown in May. In case of DE control type, outdoor air fraction was the highest of other control types and the value was average 63% in May. System heating load was shown the lowest value in NE, however, system cooling load was shown 1.7 times higher than DT control type and 5 times higher than DE control type. For system heating load, DT and DTDE is similar during intermediate season. However, system cooling load was shown 3 times higher than DE and DEDT. Accordingly, it was found as the method to save cooling energy most efficiently with DE control considering enthalpy of outdoor air and return air in intermediate season.


Supported by : National Research Foundation of Korea(NRF)


  1. 2014 Energy Consumption Survey, Korea Energy Economics Institute.
  2. J.H. Huh, "Building Energy Management", KIASEBS, Vol.4 No.2, pp. 18-24
  3. G. Wang, L. Song, Air handling unit supply air temperature optimal control during economizer cycles, Energy and Buildings, 49 (2012) 310-316.
  4. C.S.P. W.J.Suh, Issues and Limitations on the Use of a Whole Building Simulation Tool for Energy Diagnosis of a Real-life Building, AIK, 28(1) (2012) 273-283.
  5. Y. Yao, L. Wang, Energy analysis on VAV system with different air-side economizers in China, Energy and Buildings, 42 (8) (2010) 1220-1230.
  6. A.A. Chowdhury, M.G. Rasul, M.M.K. Khan, Modelling and analysis of air-cooled reciprocating chiller and demand energy savings using passive cooling, Applied Thermal Engineering, 29 (8-9) (2009) 1825-1830.
  7. J.E. Son, K.H. Lee, Cooling energy performance analysis depending on the economizer cycle control methods in an office building, Energy and Buildings, 120 (2016) 45-57.
  8. C.H.C. Steven T. Taylor, Economizer High Limit Controls and Why Enthalpy Economizers Don't Work, ASHRAE, 52 (11) (2010).
  9. L.S. Gang Wang, Energy Analysis, Optimal High-Limit Control and Engineering Approach of Air-Side Economizers, ASHRAE Transactions, 120 (2014) 383-396.
  10. M.L. G. Wang, Optimal Outside Air Control for Air Handling Units with Humidity Control, Proceedings of International Conference for Enhanced Building Operations (2006).