Air-conditioning for thermal comfort was introduced into Thailand fifty years ago. With highly luminous sky and high solar radiation, air-conditioned buildings are heavily shaded by internal shading devices to reduce solar gain. Buildings with curtained walling are even perceived to possess aesthetic value by many developers. Heat reflective glazing is typically used with the result that daylight cannot penetrate and electric lighting is used. Inadvertently, such buildings are subject to high external load due to heat gain through glazing. However, Thailand is in the tropical zone where northern and southern facades of a building could be effectively shaded by simple fixed shading devices. The use of multiple slat external shading device with small width is practical for tall buildings. Such device does not cause significant wind loading, allows daylight from sky to pass through, and allow viewing from the interior to the exterior scene. This paper presents results of a simulation and experimental study on the use of such devices on windows under different types of glazing, different ratios of window area to wall area, and with and without insulation on walls. With proper arrangement, glazing that allows more daylight penetration is shown to offer energy and monetary savings over its cost, and the cost of air-conditioning energy. This paper illustrates that it is possible to maximize benefits from utilizing appropriate window area to wall area, and from utilizing suitable glazing and wall insulation.