Energy conservation is an important part of any national energy strategy. Energy conservation in a country like Palestine without energy resources of its own, is even more important. Energy conservation in buildings, by using proper insulation material, will reduce imported energy and reduce fossil fuel combustion and its polluting products.

Building insulation will reduce the running cost of space heating at the expense of an increase in the initial investment by the added insulation material. The high cost of fuel and electricity in Palestine, as shown in Table 1, is expected to favor the economics of buildings insulation. All monetary values mentioned in the paper are in US dollars.

Energy consumption for space heating forms more than 60% of the household energy consumption in Palestine. Houses are heated using kerosene or gas stoves, or central heating systems. Boilers in the central heating systems burn diesel, light fuel oil, or LPG.

The Palestinian territories extend from coastal Gaza Strip at the Mediterranean Sea to the mountain ranges in the West Bank with elevations reaching 1000 m above sea level. In contrast the Jordan valley, in the east, drops to 300 m below sea level.

The Palestinian territories can be divided into three climatic zones for space heating purposes. Table 2 shows the characteristics of each climate zone.

Almost no space heating is required in the Jordan valley, while little heating is needed in the coastal region. The heating season in the mountain region of West Bank, with 1354 degree days, extends from October to April.

Building materials employed in newly constructed houses are stones, concrete, bricks and the required iron bars for reinforcement. Wall structures, vary from one region to another. In general, stone and concrete walls are used in the West Bank mountain regions, while brick is more commonely used in the coastal region and the Jordan valley.

Table 3 lists some typical wall structures for buildings in Palestine and their thermal characteristics, including the conductance U-value, and thermal resistance.

Wall I, which is the most common structure in the West Bank, consists of a 7 cm-thick stone layer followed by 20 cm-thick concrete layer and a 3 cm internal plaster layer. In order to improve the thermal resistance of the structure and reduce heating loads, some new houses employ wall IV or wall V. Wall III is the most common type in the Gaza Strip and Jordan Valley. Wall II is used in many rural areas in the West Bank to reduce the cost of construction by eliminating the outer stone layer.

Heat losses from a building at steady-state are computed as losses through walls and ceiling, plus ventilation and air infiltration.

Air ventilation and infiltration are not affected by wall insulation, while heat losses through walls decrease with increasing resistance or decreasing conductance. Hence, only wall losses will be considered in the insulation thickness optimization analysis that will follow.

The annual energy requirement for space heating, E_h, can be determined using the degree days, DD, the wall conductance, U, and the efficiency of the heating system, ? as given by the following equation

(1)

E_h=86400UDD/?

The life cycle cost analysis employed in this paper computes the heating cost over the lifetime of the building.

The total heating cost over a lifetime of N years is evaluated in present value dollars using the present worth factor PWF. The PWF, which depends upon the inflation rate, g, and the interest rate, I, is adjusted for inflation as shown below.

As insulation thickness increases the heating load decreases, and hence the cost of fuel and total cost of heating. On the other hand, the insulation cost increases as its thickness increases. The total cost of fuel and insulation material will show a minimum when plotted versus the insulation thickness as shown in Fig. 1 for wall I. The insulation thickness at the minimum total cost is taken as the optimum insulation thickness.

The optimum insulation thicknesses for the various wall types specified in Table 3 were computed using Eq. (13) and the values of the parameters in Table 4. Table 5 presents the results for the various walls and for two types of insulation, rock wool and polystyrene.

In order to account for different values of the interest and inflation rates, the optimum insulation thickness for wall I is plotted versus the PWF, as shown in Fig. 2, for the two types of insulation. For example, an interest rate of 8% and inflation rate of 10% the PWF is 9.05 and the optimum insulation thickness is 0.067 m for polystyrene.

Life cycle savings per meter square of wall area are computed as the difference between the cost of heating the uninsulated building and the cost of insulating the building. Table 6 presents the total saving over 10 years for insulated walls in the West Bank. Such savings are proportional to the fuel cost and to the PWF; any increase in the fuel cost will increase the savings. The payback period is calculated as the insulation cost divided by the annual savings per square meter of wall, also given in Table 6.

The effect of degree days and wall thermal resistance on the optimum insulation thickness are illustrated in Fig. 3. Colder climates having higher degree days require larger layers of insulation, as shown in the figure. At a given number of degree days, buildings having higher thermal resistance require less insulation.

Comparing our results with a similar analysis for Jordan at a similar number of degree days shows that in our case the optimum insulation thickness is much larger than that in Jordan. This results from the much higher fuel prices in Palestine, which are about twice as high as in Jordan, and from the lower insulation cost in Palestine, which is about one third that of Jordan.

The optimum insulation thickness which minimizes the life cycle cost was computed for different wall structures. Savings over a lifetime of 10 years were computed for different wall structures and number of degree days. Even for climates with as few as 500 degree days, savings will be realized by adding insulation. The savings in cold climates as in mountain ranges of the West Bank can be as much as 22 $/m² of wall area over lifetime of 10 years.

Payback periods are 1–1.7 years for rock wool insulation, and 1.3–2.3 years for polystyrene insulation, depending on the type of wall.

Generalized charts for obtaining the optimum insulation thickness were prepared as a function of wall thermal resistance and number of degree days.

Insulation of buildings in Palestine is shown to be economically feasible and should be implemented, as it will save money and reduce imported energy.