Towards Nearly Zero Energy Buildings in Lebanon: Bioclimatic Design and Experimental Strategies

In the coastal climate of Lebanon, summer internal comfort relies heavily on air-conditioning. Lebanon also suffers from a chronic shortage in electricity supply, where unorganized private sector provides up to 28% of the needed power, through what are referred to as neighbourhood generators. Within this context, numerous local and international bodies are promoting low energy construction by issuing specific construction codes. Although they aim at reducing energy consumption within new builds, each publication recommends different envelope U-values. Located on the eastern shores of the Mediterranean, Lebanon coastal climate is placed under the general category of warm temperate climates where summers are hot with minimal to no precipitation. The built environment in Lebanon is largely comprised of heavyweight materials such are concrete, stones, and/or their combined derivatives. This is an important observation, since heavyweight construction is usually recommended in hot climates for attenuating internal summer heat. A review related to building studies focussed on reducing cooling or heating loads reveal at least four research methods including monitoring of actual structures; software simulation; calibrated simulation; and monitoring of purpose-built models. For similar or hotter climates, the majority of publication claim that externally-placed wall insulations have better effects on internal temperature than internally-placed ones. In contrast, a highly and internally-insulated house in Lebanon has won local and international sustainable awards by claiming that internal peak temperatures with no mechanical cooling are considerably cooler than the outdoors peak temperature. The combination of all these factors raises the fundamental research question of finding the best performing wall-construction composition and materiality that will minimise internal overheating, and thus reduce or eliminate cooling energy loads for summer comfort in apartment buildings in Lebanon. To reach this aim, the research starts by monitoring existing apartment buildings, followed by calibrated software-based temperature simulation. Next, in order to reduce the uncertainties found while monitoring the apartments, three test cells with different double masonry walls and insulation configurations are built and their internal temperatures are monitored for a full summer season. They are maintained under a strictly-controlled environment. Later, these test cells are computationally simulated and calibrated. Results show that the best method for studying heavyweight construction is through full scale test cells, since each of the applied methods showed different results for the best performing construction with the least summer overheating. More so, performance ranking of the different constructions is not consistent throughout the different methods. As seen in the literature, temperature software calibration method is feasible but requires initial data to be modified. Final results, based on the test cells, showed that the un-insulated double masonry wall test cell did lead to minimum overheating when compared to the three test cells with different insulation locations within similar double masonry walls. The outer insulated, which in the literature review is always seen as the better performing, ranked only second with a 40% difference when using the overheating degree hours above 30oC as a performance indicator. This is due to the increased capacity of the unobstructed (un-insulated) double masonry walls to store and release heat into the room and the outdoor. The contribution to knowledge is threefold: (1) a thorough understanding of the summer temperature behaviour of heavyweight construction in Lebanon; (2) a detailed assessment of temperature software allowed showing both their expectations and limitations in simulating heavyweight construction; (3) finally proving that un-insulated double masonry wall can provide least summer overheating when compared to differently insulated double masonry walls in the climate of Lebanon.