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Mixed-mode ventilation and air conditioning as alternative for energy savings: a case study in Beirut current and future climate


The aim of this work is to assess the use of mixed-mode ventilation for a typical office building in Lebanon and consequently reduce Heating Ventilation and Air Conditioning (HVAC) energy consumption in the observed current and under the future projected climatic conditions. Mixed-mode cooling is considered a compromise between the insufficient natural ventilation and the expensive year round-operated HVAC. A control algorithm is set for windows and HVAC system to ensure mixed-mode operation. Dynamic simulations are performed on a typical office building in Beirut City under the mixed-mode operation in the present and the future using commercial IES-VE software. The results of the software were validated against measured HVAC and total energy consumption of the typical office base case with conventional mechanical system. The results of the simulations are evaluated in terms of potential reduction in energy consumption under the present and the future weather data. Finally, a lifecycle cost analysis is performed for the proposed system, and its payback period is computed. Under present construction practices and weather data, 31% annual energy savings were achieved using mixed-mode system. Under future 2050s projected weather data, annual energy savings of 21% was attained with a payback period of 3.8 years.

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C n :

System running cost

CO2 :

Carbon dioxide


Coefficient of performance

dbt omax m :

Monthly mean maximum temperature under current weather conditions (°C)

dbt omin m :

Monthly mean minimum temperature under current weather conditions (°C)


Greenhouse gases


Hadley Center Coupled Climate Model


Heating ventilation and air conditioning

I h,o :

Current hourly solar horizontal irradiation energy (Wh/m2)


Integrated Environmental Solutions–Virtual Environment


Intergovernmental Panel on Climate Change


Middle East and North Africa

N :

Holding period of the NPV

n :

Running year


Net present value


North West Orientation


Parts per million

r :

Discounted rate of return

r o :

Current relative humidity data (%)


South East Orientation

T in :

Indoor temperature


Typical meteorological year

T op :

Indoor operative temperature


Outdoor temperature (°C)

T HL :

Adaptive cooling upper limit set-point temperature (°C) defined in the ASHRAE 55 Adaptive Comfort Model (2013)

T LL :

Adaptive heating lower limit set-point temperature (°C) defined in the ASHRAE 55 Adaptive Comfort Model (2013)

T AC :

Mechanical system air conditioning set point temperature (°C)

T He :

Mechanical system heating set point temperature (°C)

t omdb :

Monthly mean of the current dry bulb temperature

t omwb :

Monthly mean of the current wet bulb temperature


Overall heat transfer coefficient (W/m2/K)


Urban Heat Island Effect

Δ t mwb :

Monthly mean change in wet bulb temperatures (°C)

Δ I h,m :

Monthly percentage mean change in solar horizontal irradiance (%)


  • Agami Reddy, T. (2006). Literature review on calibration of building energy simulation programs: uses, problems, procedures, uncertainty, and tools. ASHRAE Transactions, 112(1), 226–240.

    Google Scholar 

  • Aggerholm, S. (2002). Hybrid ventilation and control strategies in the annex 35 case studies. Denmark: Danish Building and Urban Research.

    Google Scholar 

  • Al-Tamimi, N. A., & Fadzil, S. F. S. (2011). The potential of shading devices for temperature reduction in high-rise residential buildings in the tropics. Procedia Engineering, 21, 273–282.

    Article  Google Scholar 

  • Alves, C. A., Duarte, D. H., & Gonçalves, F. L. (2015). Residential buildings’ thermal performance and comfort for the elderly under climate changes context in the city of São Paulo, Brazil. Energy and Buildings, 114, 62–71.

    Article  Google Scholar 

  • Annan, G., Ghaddar, N., & Ghali, K. (2014). “Natural ventilation in Beirut residential buildings for extended comfort hours.International Journal of Sustainable Energy, in press, 1–18.

  • ASHRAE. (2013a). ASHRAE handbook fundamentals. Chapter 18 nonresidential cooling and heating. Atlanta: American Society of Heating, Refrigerating, and Air Conditioning Engineers.

    Google Scholar 

  • ASHRAE. (2013b). ASHRAE standard 55–92. Thermal environmental conditions for human occupancy. Atlanta: American Society of Heating, Refrigerating, and Air Conditioning Engineers.

    Google Scholar 

  • Azhar, S., & Brown, J. (2009). BIM for sustainability analyses. International Journal of Construction Education and Research, 5(4), 276–292.

    Article  Google Scholar 

  • Belcher, S. E., Hacker, J. N., & Powell, D. S. (2005). Constructing design weather data for future climates. Building Services Engineering Research and Technology, 26(1), 49–61.

    Article  Google Scholar 

  • Bianco, V., Manca, O., & Nardini, S. (2009). Electricity consumption forecasting in Italy using linear regression models. Energy, 34(9), 1413–1421.

    Article  Google Scholar 

  • Brager, G. S. & de Dear, R. (2001). Climate, comfort, and natural ventilation: a new adaptive comfort standard for ASHRAE standard 55. Proceedings, Moving Thermal Comfort Standards into the 21st Century, Windsor, UK, April 2001.

  • Cardinale, N., Micucci, M., & Ruggiero, F. (2003). Analysis of energy saving using natural ventilation in a traditional Italian building. Energy and Buildings, 35(2), 153–159.

    Article  Google Scholar 

  • Carlucci, S., & Pagliano, L. (2012). A review of indices for the long-term evaluation of the general thermal comfort conditions in buildings. Energy and Buildings, 53. doi:10.1016/j.enbuild.2012.06.015.

  • Costa, A. (2014). Effect of a global warming model on the energetic performance of a closed loop solar thermal energy system. Revista Ciência e Tecnologia, 17(31), 29–34.

    Google Scholar 

  • De Dear, R. J., & Brager, G. S. (2002). Thermal comfort in naturally ventilated buildings: revisions to ASHRAE standard 55. Energy and Buildings, 34(6), 549–561.

    Article  Google Scholar 

  • De Reyck, B., Degraeve, Z., & Vandenborre, R. (2008). Project options valuation with net present value and decision tree analysis. European Journal of Operational Research, 184(1), 341–355.

    Article  MATH  Google Scholar 

  • Deuble, M. P., & de Dear, R. (2012). Mixed-mode buildings: a double standard in occupants’ comfort expectations. Building and Environment, 54, 53–60.

    Article  Google Scholar 

  • EN15251, CEN Standard. (2007). Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics, Thermal environment, lighting and acoustics. Paris: AFNOR.

    Google Scholar 

  • Ezzeldin, S., & Rees, S. J. (2013). The potential for office buildings with mixed-mode ventilation and low energy cooling systems in arid climates. Energy and Buildings, 65, 368–381.

    Article  Google Scholar 

  • Ezzeldin, S., Rees, S., Cook, M. (2008). Energy and Carbon Emission Savings due to Hybrid Ventilation of Office Buildings in Arid Climates. PLEA 2008 – 25th Conference on Passive and Low Energy Architecture, Dublin, 22nd to 24th October 2008.

  • Ezzeldin, S., Rees, S., & Cook, M. (2009). Performance of mixed-mode cooling strategies for office buildings in arid climates. In Proceedings of the 11 th International IBPSA Conference, Glasgow, Scotland, July 2009.

  • Ghaddar, N., & Bsat, A. (1998). Energy conservation of residential buildings in Beirut. International Journal of Energy Research, 32(2), 523–546.

    Article  Google Scholar 

  • Ghaddar, N., Ghali, K., & Najm, A. (2003). Use of desiccant dehumidification to improve energy utilization in air-conditioning systems in Beirut. International Journal of Energy Research, 27(15), 1317–1338.

    Article  Google Scholar 

  • Griffiths, M., & Eftekhari, M. (2008). Control of CO2 in a naturally ventilated classroom. Energy and Buildings, 40(4), 556–560.

    Article  Google Scholar 

  • Habchi, C., Ghali, K., & Ghaddar, N. (2015). Displacement ventilation zonal model for particle distribution resulting from high momentum respiratory activities. Building and Environment, 90, 1–14.

    Article  Google Scholar 

  • Habchi, C., Chakroun, W., Alotaibi, S., Ghali, K., & Ghaddar, N. (2016). Effect of shifts from occupant design position on performance of ceiling personalized ventilation assisted with desk fan or chair fans. Energy and Buildings, 117, 20–32.

    Article  Google Scholar 

  • Haddad, E. A., Farajallah, N., Camargo, M., Lopes, R. L., & Vieira, F. V. (2014). Climate change in Lebanon: higher-order regional impacts from agriculture. The Region, 1(1), 9–24.

    Article  Google Scholar 

  • Holmes, S. H. & Reinhart, C.F. (2011). Climate change risks from a building owner’s perspective: assessing future climate and energy price scenarios. Proceedings of Building Simulation 2011:12th Conference of International Building Performance Simulation Association, Sydney, 14–16 November.

  • Humphreys, M. A., & Nicol, J. F. (1998). Understanding the adaptive approach to thermal comfort. ASHRAE Transactions, 104, 991–998.

    Google Scholar 

  • IES Virtual Environment (2015). Integrated Environmental Solutions. Glasgow G20 0SP, United Kingdom.

  • Ineichen, P. (2006). Comparison of eight clear sky broadband models against 16 independent data banks. Solar Energy, 80(4), 468–478.

    Article  Google Scholar 

  • Inkarojrit, V. & Paliaga, G. (2004). Indoor climatic influences on the operation of windows in a naturally ventilated building. In Proceedings of the 21st international conference on passive and low energy architecture (pp. 19–22), September19–22 2004, Netherlands.

  • Intergovernmental panel on Climate Change (IPCC) (2016) HADCM3 (Hadely Center Coupled Climate Model). Hadley Centre for Climate Prediction and Research, Last accessed, January 2016.

  • IPCC (Intergovenmental Pannel on Climate Change) (2014) Climate change, in:IPCC Fifth Assessment Synthesis Report, Geneva, 2014.

  • Jentsch, M. F., Bahaj, A. S., & James, P. A. (2008). Climate change future proofing of buildings—Generation and assessment of building simulation weather files. Energy and Buildings, 40(12), 2148–2168.

    Article  Google Scholar 

  • Jentsch, M. F., James, P. A., & Bahaj, A. S.. (2010). Climate Change adapted simulation weather data: implications for cities in hot, arid climates of the Middle East. In proceedings of World Renewable Energy Congress XI, 25–30 September 2010, pp 644–649, Abu Dhabi, UAE.

  • Ji, Y., Lomas, K. J., & Cook, M. J. (2009). Hybrid ventilation for low energy building design in south China. Building and Environment, 44(11), 2245–2255.

    Article  Google Scholar 

  • Johns, T. C., Gregory, J. M., Ingram, W. J., Johnson, C. E., Jones, A., Lowe, J. A., Mitchell, J. F. B., Roberts, D. L., Sexton, B. M. H., Stevenson, D. S., Tett, S. F. B., & Woodage, M. J. (2003). Anthropogenic climate change for 1860 to 2100 simulated with the HadCM3 model under updated emissions scenarios. Climate Dynamics, 20(6), 583–612.

    Article  Google Scholar 

  • Jylhä, K., Jokisalo, J., Ruosteenoja, K., Pilli-Sihvola, K., Kalamees, T., Seitola, T., Hyvönen, M. M. R., Laapas, M., Drebsand, A., & Drebs, A. (2015). Energy demand for the heating and cooling of residential houses in Finland in a changing climate. Energy and Buildings, 99, 104–116.

    Article  Google Scholar 

  • Kalogirou, S. A. (2001). Use of TRNSYS for modelling and simulation of a hybrid pv–thermal solar system for Cyprus. Renewable Energy, 23(2), 247–260.

    Article  Google Scholar 

  • Kalvelage, K., Passe, U., Rabideau, S., & Takle, E. S. (2014). Changing climate: the effects on energy demand and human comfort. Energy and Buildings, 76, 373–380.

    Article  Google Scholar 

  • Krichak, S. O., Breitgand, J. S., Samuels, R., & Alpert, P. (2011). A double-resolution transient RCM climate change simulation experiment for near-coastal eastern zone of the eastern Mediterranean region. Theoretical and Applied Climatology, 103(1–2), 167–195.

    Article  Google Scholar 

  • Lelieveld, J., Berresheim, H., Borrmann, S., Crutzen, P. J., Dentener, F. J., Fischer, H., Feichter, J., Flatau, P. J., Heland, J., Holzinger, R., Korrmann, R., Lawrence, M. G., Levin, Z., Markowicz, K. M., Mihalopoulos, N., Minikin, A., Ramanathan, V., De Reus, M., Roelofs, G. J., Scheeren, H. A., Sciare, J., Schlager, H., Schultz, M., Siegmund, P., Steil, B., Stephanou, E. G., Stier, P., Traub, M., Warneke, C., Williams, J., & Ziereis, H. (2002). Global air pollution crossroads over the Mediterranean. Science, 298(5594), 794–799.

    Article  Google Scholar 

  • Makhoul, A., Ghali, K., & Ghaddar, N. (2013). Desk fans for the control of the convection flow around occupants using ceiling mounted personalized ventilation. Building and Environment, 59, 336–348.

    Article  Google Scholar 

  • Meteonorm Software (2015) Meteotest, Bern, Switzerland.

  • Nikolaidis, Y., Pilavachi, P. A., & Chletsis, A. (2009). Economic evaluation of energy saving measures in a common type of Greek building. Applied Energy, 86(12), 2550–2559.

    Article  Google Scholar 

  • Olesen, B. W., & Brager, G. S. (2004). A better way to predict comfort: the new ASHRAE standard 55–2004. ASHRAE Journal.

  • Pagliano, L., & Zangheri, P. (2010). Comfort models and cooling of buildings in the Mediterranean zone. Advances in Building Energy Research, 4(1), 167–200.

    Article  Google Scholar 

  • Pan, Y., Huang, Z., Wu, G., & Chen, C. (2006). The application of building energy simulation and calibration in two high-rise commercial buildings in Shanghai. Proceedings of SimBuild, 2006 Conference, 2–4 August 2006, MIT, Cambridge, Massachusetts. IBPSA-USA.

  • Payne, W. V., & Domanski, P. A. (2002). A Comparison Of An R22 And An R410A Air Conditioner Operating At High Ambient Temperatures. International Refrigeration and Air Conditioning Conference. Paper 532. July 2–5, 2002, Purdue University, USA.

  • Pedrini, A., Westphal, F. S., & Lamberts, R. (2002). A methodology for building energy modelling and calibration in warm climates. Building and Environment, 37(8), 903–912.

    Article  Google Scholar 

  • Peng, C., & Elwan, A.F. (2013). “How hot can the university campus get in 2050?: environmental simulation of climate change scenarios at an urban neighborhood scale.” In Proceedings of the Symposium on Simulation for Architecture and Urban Design (p. 5). Society for Computer Simulation International. April 2013.

  • Pérez-Lombard, L., Ortiz, J., & Pout, C. (2008). A review on buildings energy consumption information. Energy and Buildings, 40(3), 394–398.

    Article  Google Scholar 

  • Pfafferott, J., Herkel, S., & Wambsganß, M. (2004). Design, monitoring and evaluation of a low energy office building with passive cooling by night ventilation. Energy and Buildings, 36(5), 455–465.

    Article  Google Scholar 

  • Pollock, M., Roderick, Y., McEwan, D., & Wheatley, C. (2009). “Building simulation as an assisting tool in designing an energy efficient building: a case study.” Proceedings of the Eleventh International IBPSA Conference, Glasgow, Scotland, July 27–30, 2009.

  • Radhi, H. (2009). A comparison of the accuracy of building energy analysis in Bahrain using data from different weather periods. Renewable Energy, 34(3), 869–875.

    Article  Google Scholar 

  • Republic of Lebanon, Ministry of Public works and transport (2005). Climatic zoning for buildings in Lebanon. United Nations Development Programe.

  • Rijal, H. B., Tuohy, P., Nicol, F., Humphreys, M. A., Samuel, A., & Clarke, J. (2008). Development of an adaptive window-opening algorithm to predict the thermal comfort, energy use and overheating in buildings. Journal of Building Performance Simulation, 1(1), 17–30.

    Article  Google Scholar 

  • Ruble, I., & Nader, P. (2011). Transforming shortcomings into opportunities: can market incentives solve Lebanon's energy crisis? Energy Policy, 39(5), 2467–2474.

    Article  Google Scholar 

  • Schulze, T., & Eicker, U. (2013). Controlled natural ventilation for energy efficient buildings. Energy and Buildings, 56, 221–232.

    Article  Google Scholar 

  • Seager, R., Ting, M., Held, I., Kushnir, Y., Lu, J., Vecchi, G., Huang, H., Harnik, N., Leetmaa, A., Lau, N., Li, C., Velez, J., & Naik, N. (2007). Model projections of an imminent transition to a more arid climate in southwestern North America. Science, 316(5828), 1181–1184.

    Article  Google Scholar 

  • Skeiker, K. (2004). Generation of a typical meteorological year for Damascus zone using the Filkenstein–Schafer statistical method. Energy Conversion and Management, 45, 99–112.

    Article  Google Scholar 

  • Taleb, H. M. (2015). Natural ventilation as energy efficient solution for achieving low-energy houses in Dubai. Energy and Buildings, 99, 284–291.

    Article  Google Scholar 

  • Tuohy, P. G., Rijal, H. B., Humphreys, M. A., Nicol, J. F., Samuel, A., & Clarke, J. A. (2007). Comfort driven adaptive window opening behaviour and the influence of building design. In: 10th IBPSA Conference on Building Simulation 2007, September 3–6, Beijing.

  • Ürge-Vorsatz, D., Eyre, N., Graham, P., Harvey, D., Hertwich, E., Jiang, Y., Kornevall, C., Majumdar, M., McMahon, J. E., Mirasgedis, S., Murakami, S., & Novikova, A.. (2012). Energy end-use: building. Global Energy Assessment-Toward a Sustainable Future, Chapter 10, 649–760.

  • Wang, H., & Chen, Q. (2014). Impact of climate change heating and cooling energy use in buildings in the United States. Energy and Buildings, 82, 428–436.

    Article  Google Scholar 

  • Wang, L., & Greenberg, S. (2015). Window operation and impacts on building energy consumption. Energy and Buildings, 92, 313–321.

    Article  Google Scholar 

  • Weitzman, M. L. (2001). Gamma discounting. American Economic Review, 260–271.

  • Williams, D., Elghali, L., Wheeler, R., & France, C. (2012). Climate change influence on building lifecycle greenhouse gas emissions: case study of a UK mixed-use development. Energy and Buildings, 48, 112–126.

    Article  Google Scholar 

  • Yana Motta, S. F., & Domanski P. A. (2000). “Performance of R-22 and its alternatives working at high outdoor temperatures.” (2000). International Refrigeration and Air Conditioning Conference. Paper 464, July 25–28, 2000, Purdue University, USA.

  • Yassine, B., Ghali, K., Ghaddar, N., Srour, I., & Chehab, G. (2012). A numerical modeling approach to evaluate energy-efficient mechanical ventilation strategies. Energy and Buildings, 55, 618–630.

    Article  Google Scholar 

  • Yi, C. Y., & Peng, C. (2014). Microclimate change outdoor and indoor coupled simulation for passive building adaptation design. Procedia Computer Science, 32, 691–698.

    Article  Google Scholar 

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Correspondence to Nesreen Ghaddar.

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Daaboul, J., Ghali, K. & Ghaddar, N. Mixed-mode ventilation and air conditioning as alternative for energy savings: a case study in Beirut current and future climate. Energy Efficiency 11, 13–30 (2018).

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  • Climate change
  • Adaptive comfort
  • Control algorithm
  • Mixed-mode ventilation