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

Abstract

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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Abbreviations

C n :

System running cost

CO2 :

Carbon dioxide

COP:

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)

GHG:

Greenhouse gases

HADCM3:

Hadley Center Coupled Climate Model

HVAC:

Heating ventilation and air conditioning

I h,o :

Current hourly solar horizontal irradiation energy (Wh/m2)

IES-VE:

Integrated Environmental Solutions–Virtual Environment

IPCC:

Intergovernmental Panel on Climate Change

MENA:

Middle East and North Africa

N :

Holding period of the NPV

n :

Running year

NPV:

Net present value

NW:

North West Orientation

ppm:

Parts per million

r :

Discounted rate of return

r o :

Current relative humidity data (%)

SE:

South East Orientation

T in :

Indoor temperature

TMY:

Typical meteorological year

T op :

Indoor operative temperature

T OUT :

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

U-value:

Overall heat transfer coefficient (W/m2/K)

UHIE:

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 (%)

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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). https://doi.org/10.1007/s12053-017-9546-z

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Keywords

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