A review of minimum U-values for Lebanon and the associated effect of Internal gains

Since 2005 various publications have proposed different U-values to be used in Lebanon to reduce the buildings’ energy demand, creating confusion and a lack of specific and authoritative recommendation. Moreover, the various thermal performance guidelines are not easily comparable due to unexplained basic assumptions and guidance on the calculation of internal gains. This study has two interrelated objectives: a) test the most appropriate U-values for the climate of Beirut, b) study the consequence of increased internal gains have on the cooling energy load in low U-value construction. The paper does dynamic thermal simulation of the various U-values from local and international sources. The analysis allows the comparison and ranking of these various U-values based on the overall yearly energy demand for cooling. This is followed by a sensitivity study where a range of increased internal heat gains are inputted onto a low and a high U-value model to demonstrate that an increase in internal gains results in both models having the same cooling loads. Low U-values under this scenario due not result in a lower annual energy load. The study concludes that, although finding the appropriate U-value for hot climates seems uncontroversial, the effect of internal gains must be taken into consideration. Hence the importance of having consistent and harmonized national and regional benchmark values for U-values and internal gains.