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Heat transmission across an enclosed space is determined by the type of filling gas, the temperatures and long-wave emissivities of all surfaces that define the space, and the heat flow direction. The ASHRAE Handbook of Fundamentals provides the thermal resistances (R-values) of enclosed airspaces with only five effective emittance values (E) for vertical, horizontal, and 45° airspaces. ASHRAE R-values do not include the case of 30° sloped airspaces. In addition, ASHRAE R-values ignore the impact of the airspace aspect ratio (A) on R-values. However, many previous studies, as well as this study, have shown that A can have a significant effect on the R-value. Previously, correlations were developed for determining the R-values for vertical (90°) airspaces subjected to horizontal heat flow, horizontal (0°) airspaces subjected to up and down heat flow, 45° airspaces subjected to up and down heat flow, and 30° airspaces subjected to downward heat flow. To the authors’ knowledge, no such correlation existed for determining the R-value of 30° airspaces subjected to upward heat flow, which is developed in this paper. The potential increase in R-value by placing a thin layer of varied emittance on both sides in the middle of the airspace was also considered. Architects and building designers can use the developed correlation to compute the R-values of airspaces of various values for A and E and various operating conditions. This correlation along with the previous correlations can be included in the current energy models (e.g., EnergyPlus, ESP-r, DOE, and Design Builder).

Many parts of the building envelopes contain enclosed airspaces. Also, the insulating glass units in fenestration systems, such as curtain walls, windows, and skylight devices, contain enclosed spaces that are normally filled with air or heavy gas such as argon, xenon, or krypton. The thermal resistance (R-value) of an enclosed space depends mainly on the type of the filling gas, emissivity of all surfaces that bound the space, the size and orientation of the space, the direction of heat flow through the space, and the respective temperatures of all surfaces that define the space. Assessing the energy performance of building envelopes and fenestration systems, subjected to different climatic conditions, requires accurate determination of the R-values of the enclosed spaces. In this study, a comprehensive review is conducted on the thermal performance of enclosed airspaces for different building applications. This review includes the computational and experimental methods for determining the effective R-value of enclosed reflective airspaces. Also, the different parameters that affect the thermal performance of enclosed airspaces are discussed. These parameters include the following: (a) dimensions, (b) inclination angles, (c) directions of heat flow, (d) emissivity of all surfaces that bound the space, and (e) operating conditions. Moreover, numerical simulations are conducted using a previously developed and validated model to investigate the effect of the inclination angle, direction of heat transfer, and the coating emissivity on the R-values of enclosed spaces when they are filled with different types of gases.

Cool roofs use reflective materials or coatings to reflect a portion of the incident solar radiation. This results in a lowering the surface temperature of the cool roof compared to black roofs, and thus helps reduce the cooling energy loads during the summer season. The research reported in this paper was conducted to assess experimentally and numerically the performance of cool and black roofs that were subjected to the hot, humid and dusty climate of Jubail Industrial City (JIC). This paper focused on characterizing one of the important properties of reflective coating material (RCM), which is its solar reflectivity. In this study, the effect of dust/dirt accumulation on the solar reflectivity of the RCM was investigated at different exposure times to the natural weathering conditions of JIC. The test results showed that dust and dirt can significantly contribute in reducing the solar reflectivity of the RCM. As such, a number of cleaning processes were conducted on the surface of the RCM so as to increase its solar reflectivity. The effect of each cleaning process on the solar reflectivity of the RCM was investigated. Finally, this paper provides a test protocol and procedure for characterizing the dust concentration/intensity on the surfaces of the RCM and cleaning this material after different exposure times to a natural and polluted climate.

The heat generation from recent advanced computer chips is increasing rapidly. This creates a challenge in cooling the chips while maintaining their temperatures below the threshold values. Another challenge is that the heat generation in the chip is not uniform where some chip components generate more heat than other components. This would create a large temperature gradient across the chip, resulting in inducing thermal stresses inside the chip that may lead to a high probability to damage the chip. The locations in the chip with heat rates that correspond to high heat fluxes are known as hotspots. This research study focuses on using thermoelectric modules (TEMs) for cooling chip hotspots of different heat fluxes. When a TEM is used for cooling a chip hotspot, it is called a thermoelectric cooler (TEC), which requires electrical power. Additionally, when a TEM is used for converting a chip’s wasted heat to electrical power, it is called a thermoelectric generator (TEG). In this study, the TEMs are used for cooling the hotspots of computer chips, and a TEC is attached to the hotspot to reduce its temperature to an acceptable value. On the other hand, the other cold surfaces of the chip are attached to TEGs for harvesting electrical power from the chip’s wasted heat. Thereafter, this harvested electrical power (HEP) is then used to run the TEC attached to the hotspot. Since no external electrical power is needed for cooling the hotspot to an acceptable temperature, this technique is called a sustainable self-cooling framework (SSCF). In this paper, the operation principles of the SSCF to cool the hotspot, subjected to different operating conditions, are discussed. As well, considerations are given to investigate the effect of the TEM geometrical parameters, such as the P-/N-leg height and spacing between the legs in both operations of the TEC mode and TEG mode on the SSCF performance.

Significant research effort has gone into developing bottom-up, physics based, urban building energy modeling (UBEM) tools, which allow evaluating district-wide energy demand and supply strategies. In order to reduce the simulation inputs required in UBEM, groups of buildings are typically classified into representative “archetypes”. This approach necessarily simplifies the real diversity of occupant behaviors and construction variations, reducing in turn the variety of predicted building energy demands. To further understand the limitations of archetype-based modeling, this paper evaluates four characterization methods of increasing complexity, by comparing simulation results to measured Energy Use Intensity (EUI) distributions of 336 residential buildings in a district in Kuwait City. The first two methods follow a typical deterministic approach, organizing buildings into one and four archetypes respectively, while the third method introduces probabilistic uncertainty modeling for occupant related parameters. The fourth method introduces a new “Bayesian” calibration technique for archetype parameters, and applies it to occupant parameters in method three. In a first step, frequency calibrated distributions for occupancy, lighting power density, plug load density and cooling set points are generated through parametric modeling from a test set consisting of about half of the 336 buildings. The resulting joint distribution of parameters is then sampled using Latin Hyper Cube (LHC) for the probabilistic simulation of the remaining urban model. The comparison of simulated EUI distributions with measured data suggests that the proposed probabilistic Bayesian calibration leads to significantly closer predictions, with a maximum error in the 10th and 90th percentiles of 15% against 55%, 60% and 29% for the other three methods.

Life cycle impacts in buildings includes operational carbon for heating, cooling, hot water, ventilation, lighting, on the one hand, and embodied carbon for material supply, production, transport, construction and disassembly, on the other. Improved operational carbon has increased the percentage of embodied carbon in the total life cycle of buildings. Kuwait is looking at enhancing the sustainability of its built environment, as there is an urgent need to expand and build new cities. This research analyses the sustainability of the Middle Eastern built environment in order to provide the most appropriate strategies to respond to this demand. Therefore, this paper looks at different alternatives to the current construction methodologies, such as cement replacement in concrete or rammed earth structural systems. The impact of three envelope and energy upgrades on the whole life cycle environmental performance of a Middle Eastern residential neighborhood is evaluated. Simulations are performed through urban modeling, resulting in a distribution of the embodied and operational impacts of buildings for the different design options. Based on the results showing embodied carbon can be lowered by 200 kgCO2e/m2, this paper offers guidelines for building codes and governments.

Numerical simulations are conducted in this paper to investigate the hygrothermal performance of white and black roofing systems with and without Phase Change Materials (PCMs). The roofs considered in this paper are three roofing systems, namely, reference roof without drywall, reference roof with drywall but without PCM, and roofing system with PCM drywall of different melting temperatures. These roofing systems are subjected to the weather conditions of Kuwait city. In order to find out whether white roofs could lead to moisture-related problems, the numerical simulations are conducted for a period of 5 years. In case of the moisture accumulation is still increasing after 5 years on year-to-year basis of comparison of moisture, the period of simulation will be extended accordingly. The results show that no risk of condensation and mould growth occur in black and white roofing systems with and without PCM. In addition, the results show that white roofs experience an increase in the heating energy loads compared to black roofs. However, the decrease in the cooling energy loads for white roofs are typically much greater than the increase in the heating energy loads. As such, white roofs result in a net energy savings compared to black roofs. Furthermore, the results show that the months of the highest total energy loads for different roofing systems occur in July and August. The main outcome of this paper shows the capabilities of using reflective materials with different short-wave solar absorption coefficients and PCMs with different melting temperature for enhancing the energy performance of the roofing systems.

Many previous studies by the authors of this paper and others have shown that installing white/reflective/cool roofing systems resulted in energy savings. The amount of energy savings depended on the longwave thermal emissivity and the short-wave solar reflectivity of the rooftop surfaces. The question is “what is the percentage energy savings for the whole building as a result of using cool roofing systems instead of conventional/black roofing systems? To answer this question, three-dimensional energy simulations are conducted for typical Saudi buildings when they are subjected to the natural weathering conditions of the Eastern Province of Saudi Arabia. Several Window-to-Wall Ratios (WWRs) having different thermal resistances (R-values) and Solar Heat Gain Coefficients (SHGCs) are considered in the study. The windows are located in the different main solar orientations. To investigate the effect of the area ratio of the roof to the walls on the potential energy saving due to using cool roofs, one storey and two-storey are considered in this study. Results showed that using reflective materials with lower short-wave solar absorption coefficients in the roofing systems have resulted in a decrease in the yearly total energy loads of one-storey building and two-storey building.

Between 2000 and 2015, annual electric peak demand in Kuwait has doubled to 15000 MW and the Ministry of Energy and Water expects this number to double once more by 2030 attributing 70% of this growth to new housing projects. Within this context, this manuscript evaluates the effect of incorporating PCM-wallboards in low-rise air-conditioned residential heavyweight buildings in Kuwait. Using an EnergyPlus single-zone model, a parametric study is performed considering several window-to-wall ratios (WWRs), different solar orientations and some PCM-wallboards configurations. The main study goals are to: (i) explore the validity of a single PCM-wallboard solution that can be universally applied throughout residential buildings in Kuwait; (ii) evaluate the impact of PCMwallboard on the reduction of both cooling demand and peak-loads; (iii) provide some guidelines for incorporating PCM-wallboards in Kuwait. Following an extensive parametric study, a 4 cm thick PCM-wallboard with a melting-peak temperature of 24 °C yielded the lowest annual cooling demand across a variety of room orientations and WWRs assuming cooling setpoint of 24 °C. Its implementation led to annual cooling energy savings of 4%–5% across all the case-studies. Regarding the impact throughout the year, cooling demand and peak-loads can be reduced by 5%–7% during summer months. The average daily cooling loads can be reduced by 5%–8%. Keywords: PCM-wallboards; residential buildings; hot arid climate; cooling energy demand; dynamic simulation

This paper presents the results of a series of parametric analysis to investigate the factors that affect the effectiveness of using simultaneously building thermal capacitance and ice storage system to reduce total operating costs (including energy and demand costs) while maintaining adequate occupant comfort conditions in buildings. The analysis is based on a validated model-based simulation environment and includes several parameters including the optimization cost function, base chiller size, and ice storage tank capacity, and weather conditions. It found that the combined use of building thermal mass and active thermal energy storage system can save up to 40% of the total energy costs when integrated optimal control are considered to operate commercial buildings.

This paper presents a simulation environment that can evaluate the benefits of using simultaneously building thermal capacitance and ice storage system to reduce total operating costs including energy and demand charges while maintaining adequate occupant comfort conditions within commercial buildings. The building thermal storage is controlled through pre-cooling strategies by setting space indoor air temperatures. The ice storage system is controlled by charging the ice tank and operating the chiller during low electrical charge periods and melting the ice during on-peak periods. Optimal controls for both building thermal storage and ice storage are developed to minimize energy charges, demand charges, or combined energy and demand charges. The results obtained from the simulation environment are validated using laboratory testing for an optimal controller.

This paper presents an assessment of the electricity generated by photovoltaic (PV) grid-connected systems in Kuwait. Three years of meteorological data are provided for two main sites in Kuwait, namely, Al-Wafra and Mutla. These data and a PV grid-connected system mathematical model are used to assist a 100 kWp grid-connected PV system proposed for both sites. The proposed systems show high energy productivity whereas the annual capacity factors for Mutla and Al-Wafra are 22.25% and 21.6%, respectively. Meanwhile the annual yield factors for Mutla and Al-Wafra are 1861 kWh/kWp/year and 1922.7 kWh/kWp/year, respectively. On the other hand the cost of the energy generated by both systems is about 0.1 USD/kWh which is very close to the price of the energy sold by the Ministry of Electricity and Water (MEW). Furthermore the invested money is recovered during the assumed life cycle time whereas the payback period for both sites is about 15 years. This work contains worthwhile technical information for those who are interested in PV technology investment in Kuwait.

This work studies the effect on Embodied Energy (EE) of concrete when Ordinary Portland Cement (OPC) is partially substituted with natural Pozzolanic Volcanic Ash (VA) at the material and the building scale. The work aims to demonstrate potential improvements to the EE of buildings by comparing the EE of the cement mix with VA replacement to that of baseline case of traditional concrete. Embodied Energy Coefficients (EEC) express the EE of each building product in Mega Joules (MJ) per kg of material. Hardened cement paste made with up to 50% of the OPC replaced by volcanic ash with a mean particle size of either 17 μm or 6 μm is considered. Replacement of OPC with volcanic ash decreases the EEC, however the mix design must be engineered considering the volcanic ash composition to maintain the optimum mechanical strength. Grinding the volcanic ash from 17 μm to 6 μm led to increased compressive strength when replacing up to 40% of OPC with 6 μm sized volcanic ash. An average of 16% decrease in EEC values can be achieved when 40% OPC was replaced with VA. On a building scale, the initial EE is the energy consumed related to the extraction, production, and transportation of materials. For buildings with an average Structural Material Quantities (SMQ, expressed in mass of material per area) value of approximately 2000 kg/m2, a 16% decrease in EE value was observed among a sample set of 26 residential and commercial buildings when 50% of OPC is replaced with VA. The demonstrated reduction in EE values were calculated when natural supplementary cementitious materials (SCM) such as volcanic ash are used as a partial replacement to OPC, and it can be adapted to design and build energy-efficient systems tailored for structural and non-structural applications.