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A study is presented where potential optical errors in parabolic troughs are divided into two groups: random and nonrandom. It is shown that the intercept factor is a function of both random and nonrandom errors as well as geometric parameters such as concentration ratio and rim angle. Three error parameters, universal to all collector geometries, that is, “universal” error parameters which combine random and nonrandom errors with collector geometric parameters, are derived analytically. The mathematical derivation of these universal error parameters is presented. A numerical technique, a detailed ray-trace computer routine which maps rays from elemental reflector surfaces to the absorber surface, is used to validate the existence of the universal error parameters. The universal error parameters are made up of one universal random error parameter, σ* ( =σC), and two universal nonrandom error parameters, β* ( = βC) and d* (=(dr)y/D). The use of universal error parameters for comprehensive optical analysis of troughs is also presented.

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In most commercial buildings and industrial plants HVAC systems consume large amounts of energy, and usually offer the most significant potential for savings. Liquid conventional chillers play a very important role in providing these savings. Proper design, installation, and maintenance of these systems are therefore the key steps leading to improved efficiency which benefit both the customers and the utilities. To effectively materialize this concept two steps have been followed here. In the first section of this paper conventional chillers of different types have been modelled and simulated using a software (DOE2). The chillers are rated for a generic building and meteorological weather of San Diego. Performance parameters such as the part/full‐load efficiencies, the number of occurrences during peak hours and load frequencies are then calculated. These results gave typical performance values (curves) which can be used to compare screw, centrifugal, and reciprocating chillers among each other within a predefined scope. In the following section the field data of 39 conventional chillers and the manufacturers specifications of some of them are collected and analysed. This gave an overall view of their actual field performance and their deviation from the manufacturers' specifications. Comparison of the simulated and collected data also provided better vision of the expected performances versus the actual performances, and pinpointed some major drawbacks in the design and sizing methodology. The results also led to important conclusions regarding the status quo and the possibilities in the immediate future. Preferred chiller types and methods of providing the required cooling energy recommended by the simulation results are compared with the existing ways of providing energy in order to conform the eventual promises and quantify the room for efficiency.