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Thermal insulation is one of the most effective energy-conservation measures in buildings. Despite the widespread use of insulation materials in recent years, little is known regarding their optimum thickness under dynamic thermal conditions. Insulated concrete blocks are among the units most commonly used in the construction of building walls in Saudi Arabia. Typically, the insulation layer thickness is fixed at a value in the range 2.5–7.5 cm, regardless of the climatic conditions, type and cost of insulation material, and other economic parameters. In the present study, a numerical model based on a finite-volume, time-dependent implicit procedure, which has been previously validated, is used to compute the yearly cooling and heating transmission loads under steady periodic conditions through a typical building wall, for different insulation thicknesses. The transmission loads, calculated by using the climatic conditions of Riyadh for a west-facing wall, are fed into an economic model in order to determine the optimum thickness of insulation ( L opt ). The latter corresponds to the minimum total cost, which includes the cost of insulation material and its installation plus the present value of energy consumption cost over the lifetime of the building. The optimum insulation thickness depends on the electricity tariff as well as the cost of insulation material, lifetime of the building, inflation and discount rates, and coefficient of performance of the air-conditioning equipment. In the present study, the effect of electricity tariff on the computed optimum insulation thickness is investigated. Different average electricity tariffs are considered; namely, 0.05, 0.1, 0.2, 0.3 and 0.4 SR/kWh (designated as Cases 1–5, respectively; 1 US$ = 3.75 Saudi Riyals). Results using moulded polystyrene as an insulating material show that the values of L opt are: 4.8, 7.2, 10.9, 13.7 and 16.0 cm for Cases 1–5. Under the conditions of optimal insulation thickness for each electricity tariff, Case 1 gives the lowest total cost of 17.4 SR/m 2 , while Case 5 gives the highest total cost of 53.1 SR/m 2 . Corresponding thermal performance characteristics in terms of yearly total and peak transmission loads, R -value, time lag and decrement factor are presented.

The solar-radiation variation over horizontal surfaces calculated by the ASHRAE clear-sky model is compared with measurements for Riyadh, Saudi Arabia. Both model results and measurements are averaged on an hourly basis for all days in each month of the year to get a monthly-averaged hourly variation of the solar flux. The measured data are further averaged over the years 1996–2000. The ASHRAE model implemented utilizes the standard values of the coefficients proposed in the original model. Calculations are also made with a different set of coefficients proposed in the literature. The results show that the ASHRAE model calculations generally over-predict the measured data particularly for the months of October → May. A daily total solar-flux is obtained by integrating the hourly distribution. Based on the daily total flux, a factor Φ (

A photovoltaic grid-connected (PVGC) system has been installed at the Solar Village in Riyadh. Because a PVGC system can use the utility grid as a store, the PVGC system does not need storage batteries.This will result in an initial cost reduction by about 40% as compared with an equivalent PV stand-alone system. The electric power is supplied from the PV generator or utility grid, or from both the PV generator and utility grid simultaneously. During the day time and if the load near the PVGC system is turned OFF, all the available power generated by the PV generator is supplied to the grid. The utility peak load during hot weather in the Riyadh region coincides with the maximum incident solar radiation, and hence the PVGC system produces the highest power, which can be used for load shaving and fossil-fuel conservation.