Author A is a Doctor in the Department of Mechanical Engineering, Qatar University, Doha, Qatar. Author B is a Professor in the Department of Mechanical Engineering, Qatar University, Doha, Qatar. Author C is a Professor in the Department of Mining Metals and Materials Engineering, McGill University, Montreal, Canada. Three Measures to Reducing Energy Consumption of Space Conditioning Systems in Hot Climate Mohamad Kharseh, PhD Mohammed Alkhawaja, PhD Ferri Hassani, PhD ABSTRACT Because of the increasing cost of energy and the awareness of the impact of global warming, reducing fossil-energy consumption has become a key area for actions during the last decades. There is strong popular belief that the climate change is anthropogenic and attributed to fossil fuel consumption. Heating and cooling systems in residential and commercial buildings are the major energy consumer. In hot and country like Arabian Peninsula, the share of air conditioning systems excesses the half energy consumption. It is worth to mention that in such region 100 % of energy consumption coms from fossil fuel. This provides the challenge to study energy consumption of buildings and find methods to increase the performance of such systems. Current paper shows the impact of different measures on reducing the cooling load of the buildings in hot climate. The examined measures are (1) U-value of the external shell, (2) indoor set-temperature, and (3) lighting efficacy. For this aim, a common type of residential house in Doha, was chosen as case study. The cooling load of the case study estimated using a simulation model bases on Hourly Analysis Program. The calculations show that different measures have different impact on the annual cooling loading of the building. It was also shown that the effect of each measure depends on the construction thermal quality of the building. A brief economic comparison between the examined measured was done as well. INTRODUCTION Heating and cooling systems account for more than 30 % of the world’s total energy consumption [1,2]. In hot and underdeveloped country like Qatar, air conditioning systems are expected to be even more than half national energy consumption. In Saudi Arabia, for instance, the air conditioning systems are the largest energy consumption sector and account for 65 % of total energy consumption in buildings [3,4]. Although building regulations are changing with the time toward reduce the thermal loads of buildings, the energy demand for heating and air conditioning systems is increasing worldwide. The increase in the thermal load of the building is attributed to the increasing standards of living. For example, in non-OECD nations, as developing nations mature, the amount of energy used in the building sector is rapidly increasing. On the other hand, the traditional building designs were, in both developed and developing countries, effective in reducing heating and cooling loads. Unfortunately, in modern designs, many elements of reducing thermal load have been discarded. The thermal quality of building envelope (TQBE) refers to the performance of the building shell as a barrier to unwanted heat transfer between the interior of the building and the outside environment. The TQBE plays the fundamental role in determining the thermal load of building. For instance, high TQBE can reduce heat losses from building to the point