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The project selection problem has attracted significant attention among construction project participants. Typically, a contractor can execute one or more projects from available projects. This study introduces a new strategy to help contractors in evaluating and selecting suitable construction projects. The new strategy is based on identifying multiple criteria that affect construction projects as well as developing and using a model that supports decision based on the analytic hierarchy process. Furthermore, a fuzzy risk analysis model is proposed to analyze and quantify some of the identified criteria to help contractors select minimally risky projects. Market conditions, financial resources, project conditions, time delays, and cost overruns are five identified criteria that control the selection. Through identifying 70 subsidiary factors, the effects and importance of the first three criteria were determined through a field survey, while time delay and cost overrun criteria were analyzed and quantified through the risk analysis model. The new strategy was applied on a real case study comprising two HVAC system projects in the construction industry (project 1 in Egypt and project 2 in Saudi Arabia). Criteria and causes that yield different effects on the new strategy to support contractor decision and selection control are discussed in detail. Risk factors were ranked according to their importance, and their effects on both time and cost were clarified. The results obtained from the investigated case study showed 55.5% support for project 2, and only 44.5% support for project 1. This strategy is applicable to other case studies in different countries with different projects, criteria, and execution activities.

The time and costs associated with HVAC system installation are significant percentages of the total time and cost of construction projects. Furthermore, these systems affect many of the other construction activities. They are complicated, and their installations face many risks, which may lead to time and cost overruns for the project. Therefore, more attention should be paid to how these systems are installed in construction projects. The main objective of this study was to identify the main activities associated with HVAC system installation in construction projects, as well as the risk factors that affect them. Other objectives included conducting an analysis and assessment of the effects of these risk factors on time and cost objectives. Multi-stage field surveys were used in this study. The major risk sources were qualified in terms of their severity, probability of occurrences, and impacts on time and cost objectives. Three activities associated with HVAC system installation were identified: (a) air distribution duct work, (b) chilled water distribution pipe work, and (c) HVAC equipment installation. Fifty-five risk factors that affect each specific activity and that are common to all activities were also identified and categorized into four groups. Two agreement analysis tests and a full statistical analysis were conducted. A high degree of agreement between all partners was obtained. The time and cost percentages of the three activities were determined. A detailed discussion and analysis indicated that approximately 50% of the key risks belonged to common risks that affected all activities, while the most important risky activity was chilled water distribution pipe work. Furthermore, the analysis emphasized that the number of risk factors increased as the expected duration of the activity increased; however, this relationship did not exist in the case of cost. Ultimately, the obtained results indicate that the expected time and cost overruns caused by the effects of risk factors on HVAC system delivery are approximately 10–20% and 5–10%, respectively.

Desiccant systems have found applications in a very large variety of industrial and daily usage products including the new HVAC installations. The dehumidifier is one of the essential parts of those systems, which severely affects the whole system performance. This paper theoretically and experimentally studies the performance of the cross flow dehumidifier, which has been less studied than the counter flow dehumidifier, although it is more applicable in practice. Channel gauze structured packing was used in the dehumidifier and a LiCl aqueous solution was used as the liquid desiccant. The humidity reduction and dehumidifier effectiveness were adopted as the dehumidifier performance indices. The effects of the dehumidifier inlet parameters, including inlet air and desiccant flow rates, inlet air and desiccant temperature, inlet desiccant concentration and inlet air humidity ratio, on the two indices were investigated. The characteristics of the dehumidifier performance agreed well with the other studies reported in the open literature.

Reduction of energy consumption is a major concern in vapor compression cooling systems, especially in areas with very hot weather conditions. In hot weather conditions, performance of these systems decrease sharply and electrical power consumption increases considerably. Evaporative condensers enhance the heat rejection process by using the cooling effect of evaporation and therefore improve energy-usage efficiency. This paper presents an extensive review of the state of the art of evaporative condensers used in residential cooling systems: refrigeration, air-conditioning, and heat pump systems. The paper primarily concentrates on the energy consumption of residential cooling systems worldwide and its related problems. In addition, the paper covers the operation principles of evaporative-condensers, theory of heat rejection, and water evaporation rate. Finally, comparison between different types of condensers is presented. It is found that by using evaporative-cooled condenser instead of air-cooled condenser, the power consumption can be reduced up to 58% and the coefficient of performance can be improved by about 113.4% with systems of different cooling capacities ranging from 3 to 3000 kW.

An idea that improves the wettability over the surfaces of a cylindrical dehumidifier channel was proposed and experimentally proved. Fibrous sheets were attached to the inner surfaces of the channel. The capillary effect of fibers sustains the complete wetting of the heat and mass transfer surfaces. The air to be dehumidified and cooled flows upward in the annulus space between the two layers of fibrous sheets, which are saturated with the downward flowing desiccant solution. The permeability of the fibrous sheet was determined experimentally. It was 2.43 × 10 −10 m 2 . The measured solution flow rate due to the capillary suction of the sheets was Γ in,min = 1.12 kg/h m. The liquid desiccant tested was H 2 O/CaCl 2 with salt concentration ratios ranging from 35 to 40%. The measured distribution of the solution flow rate along the circumference of the sheets at the outlet showed 5% deviation from the average flow rate. This is a good indication for the good wettability of walls inside the dehumidifier. Feeding the solution by this mechanism has many advantages over spray feeding. Beside sustaining complete surface wetting, it also prevents channel blockage with solution, which is a main factor in increasing the air pressure drop. About 95% of the air pressure drop is saved in this study by avoiding these problems. A simple theoretical model for the heat and mass transfer processes inside the dehumidifier was developed and experimentally validated. In general, there is good agreement between the predicted and measured data. The developed model was utilized to study the effect of the different parameters on the dehumidifier performance. For a 1 m height dehumidifier with an inlet specific humidity and air temperature of 0.0234 kg v /kg a , and 35 °C, respectively, the predicted outlet air specific humidity was 0.0102 kg v /kg k and the corresponding outlet air temperature was 27.4 °C. The inlet solution temperature and salt concentration were 25 °C and 40%, respectively.

Calcium chloride solution is a cheap desiccant. It is unstable at certain solution concentrations and dehumidified air temperatures. The aim of this research is to stabilize it by mixing with calcium nitrate in different weight combinations. The physical properties of a proposed liquid desiccant such as density, viscosity, and vapor pressure were obtained. Heat and mass transfer analysis between a thin liquid layer of the proposed desiccant and the air flowing through rectangular channel has been studied. The different factors affecting the dehumidification process of air were studied.