Kamel Ghali

Experimental and Numerical Investigation of the Effect of Phase Change Materials on Clothing During Periodic Ventilation

A numerical and experimental investigation is conducted of periodic ventilation pro cesses in fabric containing microcapsules of phase change materials (PCM). When PCMS are added to textiles, they release heat as the liquid changes to a solid state and absorb heat as the solid returns to a liquid state. In this work, PCMS are incorporated in a numerical three-node fabric ventilation model to study their transient effect on body heat loss during exercise when subjected to sudden changes in environmental conditions from warm indoor air to cold outdoor air. The results indicate that the heating effect lasts approxi mately 12.5 minutes depending on PCM percentage and cold outdoor conditions. Heat released by PCMS decreases the clothed-body heat loss by an average of 40-55 W/m2 for a one-layer suit depending on the frequency of oscillation and crystallization temperature of the PCM. The experimental results reveal that under steady-state environmental condi tions, the oscillating PCM fabric has no effect on dry resistance, even though the measured sensible heat loss increases with decreasing air temperature of the chamber. When a sudden change in ambient conditions occurs, the PCM fabric delays the transient response and decreases body heat loss.

Empirical Evaluation of Convective Heat and Moisture Transport Coefficients in Porous Cotton Medium

The air penetration within a porous clothing system on a moving human being is an important physical process that considerably affects the heat and moisture resistance of the textile material. This effect of the coupled convection heat and mass exchange within the clothing system is experimentally investigated and theoretically modeled to determine the heat and mass transfer coefficients between the air penetrating the void space and the solid fiber as a function of the velocity of penetrating air. Experiments were conducted inside environmentally controlled chambers to measure the transient moisture uptake of untreated cotton fabric samples as well as the outer fabric temperature using an infrared pyrometer. The moisture uptake was conducted at three different volumetric flow rates of 0.0067, 0.018 and 0.045 m 3 /sec/m 2 of fabric area to represent airflow penetrations that could result from slow, medium, and vigorous walking, respectively. The theoretical analysis is based on a two-node adsorption model of the fibrous medium. A set of four coupled differential equations were derived describing time-dependent convective heat and mass transfer between the penetrating air and the solid fiber in terms of relevant unknown transport coefficients

The Energy Saving Potential and the Associated Thermal Comfort of Displacement Ventilation Systems Assisted by Personalised Ventilation

This study examined the effect of assisting displacement ventilation (DV) systems with personalised ventilation modules on the segmental and overall comfort of the human body during transient load variations and the associated energy saving of the combined system. A transient thermal space model has been developed for the DV system aided by the personalised task ventilator. The model was coupled with a human bioheat model to predict the segmental skin and core temperature and to assess segmental and overall thermal comfort. A case study of a typical office including six occupants was considered to assess the energy savings associated with operation of the DV system with and without personalised ventilation for the same comfort level. Higher room air temperatures in the occupied zone of the order of 26℃ (78.8°F) were found acceptable for the combined system resulting in a thermal comfort of 1.4 on a scale of −4 (very uncomfortable) to +4 (very comfortable). The DV system aided by the personalised ventilator used 27% less energy over nineteen hours of daily operation when compared to a standalone DV system providing the same level of comfort. Higher room temperatures exceeding the limit of 26℃ were found not to be beneficial in terms of energy saving.

The influence of wind on outdoor thermal comfort in the city of Beirut: A theoretical and field study

This article studies the outdoor comfort in the city of Beirut to improve the quality of open spaces and better explain the peoples tolerance and acceptance of outdoor environmental conditions. Field experiments were conducted to develop statistical correlations for thermal sensation and thermal comfort of people in the outdoors to environmental parameters. A transient bioheat model was developed to study the effect of wind speed and frequency in the physiological responses of the human body and its effect on the overall body thermal sensation and comfort state. The model was experimentally validated and simulated for three different wind frequencies of 0.15, 0.25, and 0.35 Hz, representing a range of wind frequencies encountered during an average summer day. For each of these wind frequencies, simulations were performed for two air velocity ranges: V1 = 0.5 m/s to 2.8 m/s (1.64 ft/s to 9.18 ft/s) and V2 = 0.5 m/s to 1.8 m/s (1.64 ft/s to 5.9 ft/s) at air temperatures of 30°C and 34°C (86°F and 93.2°F) and relative humidity of 40% and 70%. The numerical results showed that for velocity range V1, the overall comfort improved from –1.15 to –0.82 with the increase of wind frequency, while at velocity range V2, comfort improved from –1.27 to –0.99 with wind frequency for the same air temperature and relative humidity. It is concluded that the positive effect of wind frequency and velocity amplitude in making people more tolerant of outdoor conditions decreases with the increase in air temperature and relative humidity.

Optimal location and thickness of insulation layers for minimizing building energy consumption

This work aims to optimize the position and thickness of insulation layers in building external wall for climates in the coastal Mediterranean zone and in the inland plateau of Lebanon. A space and an air-conditioning system performance models are developed to predict the space and system loads and associated thermal comfort of occupants. A genetic algorithm is used for the optimization of the life cycle cost of the insulation based on energy load while including the productivity loss associated with thermal discomfort during transient periods. For continuous operation of building HVAC system, adding insulation reduces life cycle cost by 20% over current thermal code requirements. During intermittent operation, locating the insulation at the inner side of the walls results in 15% reduction in energy load compared to locating it on the outer wall. The optimum thickness varied between 3 cm and 5 cm depending on wall orientation climate season.

Experimental and Theoretical Study of an Optimized Integrated Solar Desalination and Air Conditioning Unit

The objective of this work is to model and optimize the operation of a combined air conditioning unit and solar distiller still to enhance distillate output and system performance to meet a specified cooling load and fresh water needs of a residential application. Simulation models have been developed for the solar distiller and cooling coil of the combined system. The developed models were experimentally validated. The combined distiller and cooling coil model predicted well the condensate volume over half-hour intervals with less than 5%. A computationally efficient optimization tool of the combined system operation is developed using statistical correlations for solar still performance parameters based on data generated by the validated simulation model. The optimization problem of the combined solar distiller and air conditioning system operation is solved for a residential application of peak cooling load of 5.4 kW with distilled water demand of 100 l/day over 10 hr of combined system operation. It is found that the optimal operation total energy consumption varied between 21.34 and 23.80 kWh/day. The fresh water energy cost ranged from 0.11 to 0.12 kWh/liter over the cooling season and is found lower than the cost of stand-alone water production from atmosphere machines.

Simplified Model of Contaminant Dispersion in Rooms Conditioned by Chilled-Ceiling Displacement Ventilation System

The aim of this paper is to develop and experimentally validate a simplified model to predict carbon dioxide transport and distribution in rooms conditioned by chilled-ceiling displacement ventilation (CC/DV) system for known supply thermal and flow conditions and chilled-ceiling temperature. The transport model of carbon dioxide considers upward convective flow by the rising thermal wall and source plumes, the CO2 lateral diffusion into plume-adjacent air layers, and vertical CO2 diffusion in air inside and outside the plumes. Experiments were performed for different supply air CO2 concentrations, supply air flow rates, and strengths of heat sources. Experimental measurements of the vertical profile of air temperature, and carbon dioxide concentration compared well with values calculated by the model. The indoor air quality is assessed based on levels of carbon dioxide concentration in the radiant-cooled space. The model can be put to practical use in finding the maximum acceptable fraction of return air to be mixed with the supply while the air quality in the breathing zone remains acceptable.

Modulated air layer heat and moisture transport by ventilation and diffusion from clothing with open aperture

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Strategies for reducing energy consumption in existing office buildings

This work establishes viable low-cost building system energy conservation measures (ECMs) while maintaining thermal comfort and good indoor air quality for existing office buildings in Mediterranean climate, taking an eight-storey office prototype building for analysis. The low-cost ECMs explored include raising indoor temperature cooling set point, lighting control, air economizer, night purging, and utilization of condensate drain to cool the direct expansion unit condenser to improve the overall system coefficient of performance. A standard system audit methodology and advanced energy modelling techniques were used to replicate the building base case. It is found that the building electrical energy consumption can be reduced by more than 16% energy without compromising thermal comfort when implementing the low-cost ECMs with minimal disruption and installation cost on existing building systems.

Low-mixing coaxial nozzle for effective personalized ventilation

The aim of this work was to study the performance of a novel coaxial nozzle for personalized ventilation that can be used as an add-on to ceiling diffuser. The coaxial nozzle minimizes air entrainment between the central fresh air stream and the room air. It allows effective delivery of clean air to the breathing zone while the recirculated conditioned air is supplied to the space by the associated ceiling diffuser. Detailed 3-D Computational Fluid Dynamics (CFD) simulations were performed and numerical results on velocity, temperature, and CO2 concentration fields agreed well with experimentally measured values. The effect of the jet flow rate, temperature, and inclination angle on air quality at the breathing zone of the occupant was then investigated. The proposed coaxial personalized ventilation achieved high air quality in the breathing zone demonstrated by a personal exposure effectiveness of 32% at fresh airflow rate of 10 L s−1 per person. It contributed also to the attainment of temperature differences up to 2℃ between the occupant’s microenvironment and the rest of the room air leading to considerable energy savings compared to the mixed convection air conditioning.