Optimization of the performance of absorption systems during transient operations such as start-up and shut-down is particularly important for small-capacity chillers and heat pumps to minimize lifecycle costs. Dynamic models in the literature have been used to study responses to step changes in a single parameter, but more complex processes such as system start-up have not been studied in detail. A robust system-level model for simulating the transient behavior of an absorption chiller is developed here. Individual heat and mass exchangers are modeled using detailed segmental models. The UA-values and thermal masses of heat exchangers used in the model are representative of a practical operational chiller. Thermal masses of the heat exchangers and energy storage in the heat exchanging fluids are accounted for to achieve realistic transient simulation of the heat transfer processes in the chiller. The pressure drop due to fluid flow across the heat exchangers is considered negligible in comparison to the pressure difference between the high- and low-side components (~ 1.5 MPa). In components with significant mass transfer effects, reduced-order models are employed to decrease computational costs while also maintaining accurate system response. Mass and species storage in the cycle are modeled using storage devices. The storage devices account for expansion and contraction of the refrigerant and solution in the cycle as the system goes through start-up, shut-down, and other transient events. A counterflow falling film desorber model is employed to account for the heat and mass transfer interactions between the liquid and vapor phases, inside the desorber. The liquid film flows down counter to the rising vapor, thereby exchanging heat with the counterflowing heated coupling fluid. A segmented model is used to account for these processes, and a solver is developed for performing rapid iteration and quick estimation of unknown vapor and liquid states at the outlet of each segment of the desorber. Other components such as the rectifier, expansion valves and solution pump are modeled as quasi-steady devices. System start-up is simulated from ambient conditions, and the coupling fluid temperatures are assumed to start up to their steady-state values within the first 90 s of simulation. It is observed that the system attains steady-state in approximately 550 s. The evaporator cooling duty and COP of the chiller during steady-state are observed to be 3.41 kW and 0.60, respectively. Steady-state parameters such as flow rates, heat transfer rates and concentrations are found to match closely with results from simulations using corresponding steady-state models. Several control responses are investigated using this dynamic simulation model. System responses to step changes in the desorber coupling fluid temperature and flow rate, solution pumping rate, and valve setting are used to study the effects of several control strategies on system behavior. Results from this analysis can be used to optimize start-up and steady state performances. The model can also be used for devising and testing control strategies in commercial applications.

Increased standards of living and indoor comfort demands have led to an increase in the demand for air-conditioning in buildings in South Africa. Conventional vapor compression systems use refrigerants that damage the ozone layer and contribute significantly to the global warming effect. Therefore, there is an urgent need to implement environmentally cleaner ways of satisfying this air-conditioning demand and absorption cooling systems have shown great potential to do so. This project is concerned with finding the technical and economic effectiveness of solar powered absorption cooling systems for South African climatic conditions. Solar cooling systems are made up of a solar collector array, water storage tank, absorption chiller and cooling tower for heat rejection. In this study, two complete systems, one utilizing an open wet cooling tower and another using a dry cooler were studied and their technical and economical performance analyzed. One system was installed at Netcare Moot Hospital in Pretoria and comprised of a solar collector array made up of 52 evacuated tube collectors, two 6000 litre hot water storage tanks, 35kW LiBr-water absorption chiller, and a wet cooling tower. This system was coupled to an existing vapor compression chiller so that cooling is provided even when no solar energy is available. The installation controlled and remotely monitored through the internet and parameters logged through a Carel Building Management System. The other system is at Vodacom World in Midrand, Johannesburg and is an autonomous solar heating and cooling system aimed at maintaining the building environment at comfort conditions throughout the year. It is made up of a 116m2 evacuated tube collector array, a 6500litre hot water storage tank, 35kW LiBr-Water absorption chiller, 1m3 of cold water storage, a dry cooler for the chiller, and two underground rock storages to pre-cool the supply air to the building and the dry cooler respectively. Long term system performance studies were carried out by varying the system control strategy for the chiller, hot water storage tank, existing vapor compression chiller (in the case of the Moot Hospital installation), hot water storage tank, dry cooler (for the Vodacom installation) and the system Coefficient of Performances were calculated and life cycle cost analysis carried out. Due to the fact that solar availability and cooling demand are approximately in phase, solar powered absorption cooling presents a great opportunity for reducing peak electrical cooling energy demand. It was also discovered that the economic effectiveness of the system increases with the absorption chiller capacity, and it‟s more advisable to operate the solar absorption cooling system with a vapor compression chiller as a backup for facilities that require uninterrupted cooling. The solar autonomous system is oversized for most of the year since it is designed to cover the peak cooling loads. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

This study addresses 5 uncertainties that exist in the operation of HVAC systems, which will presumably affect the actual energy consumption of the HVAC system in comparison to the consumption under idealized bahavior. We consequently add these parameters and their uncertainty range into the source code, eventually resulting in an EnergyPlus program in which the HVAC operation uncertainty is embedded as so-called model form uncertainty. The upgraded EnergyPlus is tested for each parameter uncertainty separately, and to show the impact of each uncertainty albeit for hypothetical uncertainty ranges of the parameters.

The thesis presents a comprehensive overview of the context and significance of ventilation cooling techniques and their feasibility in the United States. Passive cooling is one of the more architecturally interesting ways by which architects could make buildings energy efficient. There is great interest in passive systems since they can lead to a huge reduction of energy costs and support more sustainable building solutions. A number of ventilation system options are available to fill the need for a lower cost alternative to active [conventional] systems. It is the non-residential sector where energy consumption is of most concern and integrating passive natural ventilation in new non-residential buildings is receiving a lot of attention internationally and the U.S. building industry. Interest in improving air quality by passive ventilation is also increasing. / Department of Architecture

Commissioning of HVAC systems has potential for significant improvements in occupant satisfaction, comfort and energy consumption, but is very labour-intensive and expensive as practiced at this time. Previous investigators have capitalized on digital control systems' capability of logging and storing data and of interfacing with external computers for open loop control by developing methods of automated fault detection and diagnosis during normal operation. Some investigators have also considered the application of this technique in commissioning. This thesis investigates the possibility of utilizing first principles and empirical models of air-handling unit components to represent correct operation of the unit during commissioning. The models have parameters whose values can be determined from engineering design intent information contained in the construction drawings and other data available at commissioning time. Quasi-dynamic models are developed and tested. The models are tested against design intent information and also against data from a real system operating without known faults. The results show the models agree well with the measured data except for some false positive indications, particularly in the damper and fan models, during transients. A procedure for estimating uncertainty in the instrumentation and the models is developed. The models are also tested against artificial faults and are able to detect all of the faults. Methods of diagnosing the faults are discussed.

This thesis aims at preparing a user-friendly software tool for the prediction and analysis of the noise generated in Heating, Ventilating and Air Conditioning (HVAC) Systems elaborating the standardized prediction formulae and data coming from the research studies. For the analysis portion of the software, different types of indoor noise criteria are introduced and implemented in the software to ease the investigation of the level and the quality of the sound perceived by the occupant in a room through such criteria. General software structure and implementation of HVAC elements are explained by different userinterface samples in the thesis. Several case studies are presented to demonstrate the capabilities of the tool prepared in VISUAL BASIC programming language within the scope of the study.

Retail centres are a visible sign of developed capitalist societies and make an appreciable contribution to these economies. For the firms involved in supplying air conditioning maintenance to retail centres, governance structures (that incorporate the make-or-buy decision and the decision concerning the nature of the exchange relationship) are fundamental business decisions. The absence of literature in this area creates a research opportunity to undertake a theoretical and empirical investigation into the determinants of the governance of air conditioning maintenance in Australian retail centres. The research objectives revolve around a microeconomic theory (Transaction Cost Economics) and two related theories – one from strategic management (Resource-Based Theory) and one from a power-based perspective (Resource Dependency Theory). In terms of the make-or-buy decision, an integrative framework of vertical integration is developed that aims to create a clearer understanding of the conditions under which Transaction Cost Economics (TCE) and Resource-Based Theory (RBT) are dominant. This approach is encouraged by the similarity of the assumptions made in TCE and RBT concerning rationality and which envisage a short term approach to profits. If a wider view is taken, that includes supply chains in which firms take a longer term approach to profits, then Resource Dependency Theory (RDT) can also be considered as a complementary theory to TCE. In order to test TCE on the issue of the nature of the exchange relationship, TCE's contractual schema is developed, along with a new type of asset specificity (Ongoing Asset Specificity). Case studies and a nationwide postal survey are used to collect data from multiple sources, comprising 51 interviews, the collection of documentary information, as well as 18 completed case study questionnaires and 205 useable survey questionnaires. Multiple research methods allow the relative strengths of different methods to be combined to more effectively test the hypotheses. Pattern matching and regression analysis are the main techniques used to analyse the data. The results provide a successful testing of the integrative framework of vertical integration. That is, this framework is shown to be more powerful in accounting for the make-or-buy decisions in the supply chains in this thesis, than the singular deployment of either TCE or RBT. With regard to the nature of the exchange relationship decision, the results also support the development of TCE's contractual schema and Ongoing Asset Specificity. Through the incorporation of these developments, TCE outperforms RDT across all of the internal and external exchanges in the supply chains in this thesis. In total, it is concluded that transaction costs and production costs can both be key determinants of the governance of air conditioning maintenance in the chain that supplies this activity to Australian retail centres. Moreover, and in this chain, upstream exchange relationships are not determined by downstream external exchange relationships. The implications of the results for practice - in more mainstream construction, and concerning the make-or-buy decision, particularly concern trades in close physical and intellectual proximity to the main contractor’s key activity of planning and coordinating site activity. Here, the results indicate that main contractors would benefit from focusing on the possibility of hold-up and not production cost improvements. With respect to external relationships, the results show that even when clients have an ongoing requirement for an activity, a discrete exchange can be both economical and effective. This suggests that calls by some government sponsored reports for all clients buying services from main contractors to seek a relational exchange are not justified. In terms of the firm's internal relationships and upstream external relationships, the evidence from this thesis is that these relationships should not necessarily be determined by the firm’s downstream external relationships. Here, for example, main contractors might not allow their exchanges with their staff and subcontractors to be determined by exchanges with their clients. More specifically, this thesis suggests that main contractors can prosper from developing relational exchanges with their staff, core subcontractors and suppliers despite engaging in discrete and arms-length exchanges with their clients. This finding may encourage main contractors to help move mainstream construction away from any "command and control" image.

Single leaf in pocket on back end paper. / Bibliography: p. 475-488. / xxviii, 488 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study aims to develop a robust set of tools to model the performance of a range of composite coil configurations, to develop an operational model to predict the steady state performance of single and multizone air conditioning systems and to use the computational model as an exploratory tool to examine the performance of a series of candidate design solutions. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1996?

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 177-192) Also available in print.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 115-119). Also available on the Internet.