Dissertations / Theses on the topic 'Air conditioning – Design and construction'

This thesis details a study of strategies used to limit the flow generated noise encountered in the outlet diffusers of high velocity heating, ventilation and air conditioning (HVAC) duct systems. The underlying noise rating criterion is drawn from the specifications covering ocean going aluminium fast ferries. Although directed primarily towards the fast ferry industry the results presented herein are applicable to other niche high velocity HVAC applications. Experimental tests have been conducted to prove the viability of a high velocity HVAC duct system in meeting airflow requirements whilst maintaining acceptable passenger cabin noise levels. A 50 mm diameter circular jet of air was expanded using a primary conical diffuser with a variety of secondary outlet configurations. Noise measurements were taken across a velocity range of 15 to 60 m/s. An optimum outlet design has been experimentally identified by varying the diffuser angle, outlet duct length and the termination grill. A 4 to 5 fold reduction in required duct area was achieved with the use of a distribution velocity of 20 to 30 ms-1, without exceeding the prescribed passenger cabin noise criteria. The geometric configuration of the diffuser outlet assembly was found to have a pronounced effect on the noise spectrum radiating from the duct outlet. The development of a numerical model capable of predicting the flow induced noise generated by airflow exiting a ventilation duct is also documented. The model employs a Large Eddy Simulation (LES) CFD model to calculate the turbulent flow field through the duct diffuser section and outlet. The flow-generated noise is then calculated using a far field acoustic postprocessor based on the Ffowcs-Williams and Hawkings integral based formulation of Lighthill???s acoustic analogy. Time varying flow field variables are used to calculate the fluctuating noise sources located at the duct outlet and the resulting far field sound pressure levels. This result is then used to calculate the corresponding far field sound intensity and sound power levels. The numerical acoustic model has been verified and validated against the measured experimental results for multiple outlet diffuser configurations.

Finned-tube heat exchangers are predominantly used in space conditioning systems, as well as other applications requiring heat exchange between two fluids. One important widespread use is in residential air conditioning systems. These residential cooling systems influence the peak demand on the U.S. national electrical system, which occurs on the hot summer afternoons, and thereby sets the requirement for the expensive infrastructure requirement of the nations power plant and electrical distribution system. In addition to this peak demand, these residential air conditioners are major energy users that dominate residential electrical costs and environmental impact. The design of finned-tube heat exchangers requires the selection of over a dozen design parameters by the designer. The refrigerant side flow and heat transfer characteristics inside the tubes have been thoroughly studied. However, the air side flow around the tube bundle and through the fin gaps is much more complex and depends on over a dozen design parameters. Therefore, experimental measurement of the air side performance is needed. First this study built an experimental system and developed methodology for measuring the air side heat transfer and pressure drop characteristics of fin tube heat exchangers. This capability was then used to continue the goal of expanding and clarifying the present knowledge and understanding of air side performance to enable the air conditioner system designer in verifying an optimum fin tube condenser design. In this study eight fin tube heat exchangers were tested over an air flow face velocity range of 5 ?? ft/s (675-1600cfm). The raw data were reduced to the desired heat transfer and friction data, j and f factors. This reduced heat transfer and friction data was plotted versus Reynolds number and compared. The effect of fin spacing, the number of rows and fin enhancement were all investigated. The heat transfer and friction data were also plotted and compared with various correlations available from open literature. The overall accuracy of each correlation to predict experimental data was calculated. Correlations by C.C. Wang (1998b, 1999) showed the best agreement with the data. Wangs correlations (1998b, 1999) were modified to fit the current studys data.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.
ENGLISH ABSTRACT: The thesis was initiated by a Consulting Engineering Company (KV3) as a research project to investigate various options in which the efficiency and energy utilisation of conventional air conditioning systems may be enhanced by using alternative and renewable energy. Initially, eight options had been identified and through a process of determining the degree of commercialisation the alternative options were reduced to three. These options, referred to as the sustainable cooling alternatives, are active mass cooling, night flushing and roof cooling system. The roof cooling system comprised a roof-pond, roof-spray, pump and storage tank. The roof cooling system was mathematically and experimentally modelled. The roof cooling experiment was performed under a variety of weather conditions with the roof-pond and storage tank temperatures continuously recorded. The experimentally recorded temperatures were compared to the temperatures generated by the theoretical simulation calculations for the same input and weather conditions. Good agreement was found between the mathematical and experimental model. The largest discrepancy found between the simulated temperature and the experimental temperature was in the order of 1 ºC. A one-room building has been assumed to serve as a basis to which the sustainable cooling alternatives could be applied to for theoretical simulation. The one-room building had four façade walls and a flat roof slab. Night flushing, active mass cooling and the roof cooling system were applied to the one-room building such that the room air temperature and space cooling load could theoretically be simulated. The theoretical simulations were also repeated for the case where the roof-pond and roof-spray were applied as standalone systems to the one-room building. The theoretical simulation calculations were performed for typical summer weather conditions of Stellenbosch, South Africa. Under base case conditions and for a room thermostat setting of 22 ºC the peak cooling load of the one-room building was 74.73 W/m². With the application of night flushing between the hours of 24:00 and 07:00, the room cooling load was reduced by 5.2% by providing 3.9 W/m² of cooling and reducing the peak room temperature by 1.4 ºC. The active mass cooling system was modelled by supplying water at a constant supply temperature of 15 ºC to a pipe network embedded in the roof slab of the one-room building. The sea may typically be considered as a cold water source for buildings situated at the coast. The active mass cooling system reduced the peak cooling load of the one-room building by 50% by providing 37.2 W/m² of cooling and reducing the peak room temperature by 6.7 ºC. When the roof-spray and roof-pond systems were applied as standalone systems to the oneroom building, the peak cooling load of the one-room building could be reduced by 30% and 51% respectively. This is equivalent to 22.3 W/m² of peak cooling by the roof-spray and 38 W/m² of peak cooling by the roof-pond. The roof-spray reduced the peak room temperature by 3.71 ºC while the roof-pond reduced the peak room temperature by 5.9 ºC. Applying the roof cooling system to the one-room building produced 46 W/m² of peak cooling which resulted in a 61.1% reduction in peak cooling load. The roof cooling system reduced the peak temperature by 8 ºC. By comparing the sustainable cooling alternatives, the roof cooling system showed to be the most effective in reducing the one-room building peak cooling load. Over a 24 hour period the roof cooling system reduced the net heat entry to the one-room building by 57.3%. In a further attempt to reduce the peak cooling load, the sustainable cooling alternatives were applied in combinations to the one-room building. The combination of night flushing and roof-spray reduced the peak cooling load by 36% while a combination of night flushing and active mass cooling reduced the peak cooling load by 55%. Combining night flushing with the roof-pond also yielded a 55% peak cooling load reduction. The combination of roofpond, active mass cooling and night flushing provided 51 W/m² of cooling which corresponded to a 68% reduction in peak cooling load. Utilising the sustainable cooling alternatives in a combination in the one-room building gave improved results when compared to the case where the sustainable cooling alternatives were employed as standalone systems. It is illustrated by means of a sensitivity analysis that the ability of the roof cooling system to produce cool water is largely influenced by ambient conditions, droplet diameter and roofspray rate. Under clear sky conditions, an ambient temperature of 15 ºC, relative humidity of 80%, a roof-spray rate of 0.02 kg/sm² and a roof-pond water level of 100mm, water could be cooled at a rate of 113 W/m². The roof-spray energy contributed to 28 W/m² whilst the night sky radiation was responsible for 85 W/m² of the water cooling. It must however be noted that the water of the roof cooling system can never be reduced to a temperature that is lower than the ambient dew point temperature.
AFRIKAANSE OPSOMMING: Die tesis is geïnisieer deur ‘n Raadgewende Ingenieurs Maatskappy (KV3) as a navorsingsprojek om verskeie opsies te ondersoek waarmee die effektiwiteit en energie verbruik van konvensionele lugversorgingstelsels verbeter kan word deur middel van alternatiewe en hernubare energie. Agt opsies is oorspronglik geïdentifiseer en deur middel van ‘n proses waarby die graad van kommersialisering van hierdie alternatiewe maniere bepaal is, kon die opsies verminder word tot drie. Hierdie opsies, ook verwys na as die volhoubare verkoelingsalternatiewe, sluit in aktiewe massa verkoeling, dakverkoeling en nagventilasie. Die dakverkoelingstelsel bestaan uit dakwater, ‘n dakspuit, ‘n pomp en ‘n stoortenk. Die dakverkoelingstelsel is wiskundig en eksperimenteel gemodelleer. Die dakverkoelingseksperiment is uitgevoer onder ‘n verskeidenheid van weersomstandighede. Die dakwater asook die stoortenk se water temperatuur is voortdurend aangeteken. Dieselfde weer- en insetkondisies is gebruik vir die simulasie berekening en die temperature van die stoortenk se water en die dakwater is vergelyk met die temperatuurlesings van die eksperimentele werk. Die temperature van die eksperimentele lesings het goed vergelyk met die temperatuur simulasie berekeninge. Die grootste verskil tussen die simulasie en eksperimentele temperatuur was in die orde grootte van 1 ºC. ‘n Een-kamer gebou is aangeneem om as basis te dien waarop die volhoubare verkoelingsalternatiewe aangewend kon word vir teoretiese simulasie. Die een-kamer gebou het uit vier buite mure en ‘n horisontale beton dak bestaan. Nag ventilasie, aktiewe massa verkoeling en die dakverkoelingstelsel is toegepas op die een-kamer gebou en die kamer se verkoelingslas asook die kamer se lugtempertuur is teoreties gesimuleer. Die teoretiese simulasies is ook herhaal vir die geval waar die dakwater and dakspuitstelsel apart aangewend is op die een-kamer gebou. Die teoretiese simulasie berekeninge is uitgevoer vir tipiese somer weersomstandighede vir Stellenbosch, Suid Afrika. Onder basisgeval omstandighede, waar die een-kamer gebou gesimuleer is, sonder enige volhoubare verkoelingsalternatiewe en ‘n termostaat verstelling van 22 ºC, is die piek verkoelingslas bereken as 74.73 W/m². Met die toepassing van nagventilasie tussen die ure 24:00 en 07:00 was die piekverkoelingslas van die kamer verminder met 5.2% deur 3.9 W/m² se verkoeling te verskaf en die piekkamer temperatuur te verminder met 1.4 ºC. Aktiewe massa verkoeling is gesimuleer deur water teen ‘n konstante temperatuur van 15 ºC te verskaf aan ‘n pypnetwerk, geïnstalleer in the beton dak, van die een-kamer gebou. Geboue geleë aan die kus kan tipies seewater oorweeg as ‘n bron van koue water. Aktiewe massa verkoeling het die piekverkoelingslas van die een-kamer gebou verminder met 50% deur 37.2 W/m² se verkoeling te verskaf en die piekkamer temperatuur te verminder met 6.7 ºC. Wanneer die dakspuit- en dakwaterstelsel aangewend is op die een-kamer gebou as enkel staande stelsels, is die piekverkoelingslas verminder met 30% en 51% onderskeidelik. Dit is ekwivalent aan 22.3 W/m² se verkoeling vir die dakspuitstelsel en 38 W/m² se verkoeling vir die dakwaterstelsel. Die dakspuitstelsel het die piekkamer temperatuur verminder met 3.71 ºC terwyl die dakwaterstelsel ‘n 5.9 ºC verlaging in piekkamer temperatuur tot gevolg gehad het. Die dakverkoelingstelsel het 46 W/m² se piekverkoeling verskaf wat ‘n 61.1% vermindering in piekverkoelingslas tot gevolg gehad het. Die ooreenstemmende piek temperatuur vermindering is 8 ºC. Deur die verskeie volhoubare verkoelingsalternatiewe met mekaar te vergelyk, word getoon dat die dakverkoelingstelsel die mees effektiefste manier is om die een- kamer se piekverkoelingslas te verminder. Oor ‘n tydperk van 24 uur het die dakverkoelingstelsel die totale energievloei na die een-kamer gebou met 57.3% verminder. In ‘n verdere poging om die piekverkoelingslas te verminder, is die volhoubare verkoelingsalternatiewe toegepas in kombinasies op die een-kamer gebou. Die kombinasie van nagventilasie met die dakspuitstelsel het die piekverkoelingslas met 36% verminder, terwyl ‘n kombinasie van nagventilasie en aktiewe massa verkoeling ‘n 55% vermindering in piekverkoelingslas tot gevolg gehad het. Die kombinasie van dakwater en nagventilasie het ook ‘n piekverkoelingslas vermindering van 55% teweeggebring. Die kombinasie van dakwater, aktiewe massa verkoeling en nagventilasie het 51 W/m² se verkoeling veskaf, wat ooreenstem met ‘n 68% vermindering in piekverkoelingslas. Deur die volhoubare verkoelingsalternatiewe in kombinasies toe te pas op die een-kamer gebou, kon beter resultate verkry word toe dit vergelyk is met die geval waar die volhoubare verkoelingsalternatiewe as enkelstaande stelsels toegepas is. Dit is geïllustreer deur middel van ‘n sensitiwiteitsanalise dat die vermoë van die dakverkoelingstelsel om koue water te produseer, beïnvloed word deur buitelug kondisies, waterdruppel deursnee en dakspuit massa vloeitempo. Onder die oop hemelruimteomstandighede, ‘n buitelug temperatuur van 15 ºC, ‘n relatiewe humiditeit van 80%, ‘n dakspuit massa vloeitempo van 0.02 kg/sm² en dakwatervlak van 100 mm, kon water verkoel word teen ‘n tempo van 113 W/m². Die dakspuit gedeelte het 28 W/m² bygedra terwyl die nagruim radiasie sowat 85 W/m² se verkoeling verskaf het. Daar moet egter kennis geneem word dat die water temperatuur van die dakverkoelingstelsel nooit verminder kan word tot onder die buitelug doupunttemperatuur nie.

Buildings represent more than 40% of final global energy consumption, among which 50%-60% of energy consumption is attributed to Heating, Ventilation and Air Conditioning (HVAC) systems. The application of phase change material emulsions (PCMEs) in air conditioning systems is considered to be a potential way of saving energy because with their relatively higher energy storage capacity, they are able to reduce flow rate whilst delivering the same amount of cooling energy. PCMEs can also simultaneously act as cold energy storage to shift peak-load to off-peak time and improve coefficient of performance of systems. However, one of the main barriers affecting the application of PCME is the difficulty in maintaining stability in the emulsions without experiencing any temperature stratification during phase change process. To this end, an innovative energy efficient phase change emulsion has been developed and evaluated. The emulsion (PCE-10) which consists of an organic PCM (RT10) and water has a phase change temperature range of 4-12°C with heat capacity of twice as much as that of water thus making it a good candidate for cooling applications. Particular attention was also paid to the selection of the surfactant blends of Tween60 and Brij52 since they are capable of minimizing the effect of sub-cooling as well as ensuring stability of the emulsion. For the purpose of testing the performance of developed PCE-10 in fin-and-tube heat exchangers, series of theoretical and experimental studies have been carried out to understand the rheological behaviour and heat transfer characteristics of the developed PCE-10 in a fin-and-tube heat exchanger. Both experimental and theoretical results were fairly close and showed that the PCE-10 did enhance the overall heat transfer rate of the heat exchanger. In order to evaluate the potential of the integrated system, whole building energy simulation was carried out with a building simulation code TRNSYS. It was found out that the required volumetric flow rate of PCE-10 was 50% less than that of water which is equivalent to 7% reduction in total energy consumption when providing the same amount of cooling power. Despite its potential in cooling systems, the viscosity of the developed sample was found to be much higher than water which could contribute to high pressure drop in a pumping system. Its thermal conductivity was also found to be about 30% lower than the value for water which could influence heat transfer process. There is therefore the need to enhance these thermophysical properties in any future investigations.

The project was carried out at Karlstad University during the spring of 2014 as a degree project for a Degree of Bachelor of Science in Innovation and Design Engineering and consists of 22.5 ECTS. The supervisor was lecturer Lennart Wihk from Karlstad University. The examiner was professor Leo de Vin. The project was conducted for Swegon AB and dealt with developing a user interface for systems regulating climate parameters in indoor environments, such as hotel rooms or office environments. The area of focus has been on developing the user interface with regard to end users, giving it the right functions and making it easy to understand. Suggestions about how user interfaces of this type could look was to be delivered to Swegon. The project started with creating a foundation. This was done through literature studies, benchmarking and interviews. The information gained here was used to put together a list of requirements which was later used as a guide when developing and evaluating concepts. Idea generation-methods were used to generate concepts and the concepts were developed further to later be voted on by employees at Swegon. The votes were evaluated and two concepts were developed, based on the the voting outcome. The concepts are inspired by wishes from the end users (expressed in the interviews) and are developed with regard to principles of design. The concepts were made into prototypes, in the form of 3D-printed models. The results of the project, in short: • Two image boards. One with thoughts about functions of existing climate related user interfaces written on it, and one with thoughts of different ways of illustrating air-temperature written on it. • Explanations of and reflections about functions of four different types of user interfaces for heating, ventilation and air conditioning (HVAC) systems. • Four product semantic analyses (PSA). Three of existing user interfaces for Swegon HVAC systems and one of a concept for a user interface for HVAC systems. • Interviews with six potential end users, written down to a large extent. • A compilation of the six interviews, written down in English. • An interview with an employee at Swegon service, regarding installation of user interfaces for HVAC systems, written down to a large extent. • A functional analysis, which in this project works as a requirements specification. • 10 ideas of concepts. • Two voting-systems which are developed for use when voting for several elements which can be combined to make up a holistic concept. The voting-systems are inspired by the "morphological analysis" described by Johannesson et al. (2009). • Two final concepts of user interfaces for HVAC systems with thorough descriptions in a table in this report. The concepts are developed with respect to end users and design principles. • Simplified versions of each of the two final concepts as CAD-models and as 3D-prints.

Studies on design for control optimization of air-conditioning (a/c) system for better performance in Hong Kong are reported in this thesis. Typical plant configuration data was collected from an in-depth survey of a/c systems and control used in Hong Kong. Control performance has been used for the first time as an objective for optimizing a/c system designs. The study investigates and illustrates that optimization of a/c systems for application in the Hong Kong by simulation is promising and flexible. The accuracy of simulation is enhanced by using the survey data. The survey shows that some a/c control systems and their control strategies are not well considered in the design stage and their operation and set-up are not properly addressed. Hence, there exists optimization opportunities in the a/c system design and control strategies for a/c systems used in Hong Kong. Parameters affecting the control performance of a/c systems were investigated by carrying out experiments. Identified parameters are the objective function of optimization, controller settings, control valve and drive and, in case of direct digital control, sampling rate. The influence of these factors on the control performance is an essential consideration for the entire optimization process. Strategies in applying the findings in optimizing an a/c system for control performance by simulation were developed and suggested. This study provides platform for further simulation study of optimization in both methodologies and control strategies for a/c system design and operation.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2020
Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 105-108).
The Direct Evaporative Closed Air Loop (DECAL) system is a novel high efficiency liquid desiccant air-conditioning (LDAC) system which runs primarily on thermal energy rather than electricity. It is designed for residential cooling in hot and humid climates where demand is growing rapidly and incumbent direct-expansion system performance is poor. Unlike other LDAC systems, DECAL is modular. This allows the indoor hardware to remain small and non-intrusive, and offers increased flexibility to install the system in existing building stock without costly changes to the structure. This work lays out the basic operating cycle of the DECAL system and shows its thermodynamic merits in terms of ideal system performance against other LDAC systems. Design studies show DECAL offers improved thermal efficiency, especially in humid climates. The ideal thermal coefficient of performance (COP[subscript th]) is 1.24 at the design point ambient condition of 35C, 60% RH.
A mathematical model is built to better characterize performance and optimize the system design. With transport inefficiencies included, the optimal system electrical and thermal COP (COP[subscript e] and COP[subscript th]) are 46.3 and 0.759 respectively for a LiCl system at the design point. These results show the DECAL system could reduce electrical consumption by over 85% from present day best-in-class systems using low-grade thermal energy. A benchtop scaled test of the closed air loop is constructed to validate the model. Experimental test results agree well with the model predictions for evaporative cooling effectiveness and sensible heat exchange, as well as pressure drop. The drying effect of the LAMEE is lower than anticipated. This is likely due to crystallization of liquid desiccant in the pores of the membrane, resulting in a high vapor diffusion resistance. Adjusting for this effect, full system test measurements match the system model well.
The benchtop rig testing verified that the closed air loop is capable of generating a sensible cooling effect, but further testing is required to demonstrate modelled figures of merit are achievable.
by Ross A. Bonner.
S.M.
S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering

This work deals with the preparation, thermo-hydraulic characterisation, and performance analysis of silica gel coated highly conductive surface enhancing structures to be used as tube inserts in a prototype of an innovative water-cooled sorption rotor. The candidate inserts under investigation comprise highly porous aluminium foam inserts, twisted-in wire brushes, and flocked structures, that are investigated for their flow impedance, heat transfer performance, and cyclic dehumidification performance. The conducted analysis comprises experimental testing of insert specific pressure drop and heat transfer performance in a purpose built test rig, that led to the preselection of the foam structures and a twisted-in aluminium wire brush insert for desiccant coating and further investigation. Cyclic heat and mass transfer tests were performed in a purpose-built small-scale test rig, that simulated the dehumidification process of a desiccant rotor with and without employing water-cooling. The experimental analysis is complemented by a numerical investigation of the cyclic heat and mass transfer performance of the brush and metal foam type structures, modelled as two-dimensionally axis-symmetric porous media. The geometry based functions of the insert specific flow characteristics are derived from two- and three-dimensional pore scale computational fluid dynamics models, that are calibrated against experimental data. The validity of fundamental modelling assumptions was confirmed by a decent agreement between numerical and experimental steady-state heat transfer results. The heat and mass transfer investigation showed that the investigated structures were capable of effectively removing heat during the dehumidification half-cycle. The thermal mass was shown to be a critical design parameter in achieving acceptable dehumidification performance.

The aim of this thesis is to develop a computer program to design and simulate air conditioning-comfort application of a selected building, for a year period, on an hourly basis. In order to carry out this study, a computer program named AHUSIM.m, is prepared with Matlab computing language. The design and simulation procedure starts with preparing the inputs like indoor, outdoor design states, zone cooling and heating loads, along with the general data for conditioning-comfort equipment. The program, in light of these input data, performs the plotting of the psychrometric processes -including the design and off design processes- on psychrometric charts, air conditioning-comfort system selection and calculating the response of this selected system at varying load conditions for a year. The program also calculates the energy requirements of parts of the selected system throughout the year. Furthermore, it lists dimensions of the parts of the air conditioning-comfort unit, the outdoor supply air and total air flow rates, air and water inlet and exit states. Using numerical tools for heating, ventilating and air conditioning (HVAC) process design and simulation, can improve energy economy and comfort which are the main criteria of HVAC engineering. In such an attempt, major concern is the interaction between the comfort and energy consumption. The program, by designing the system and deciding its behavior throughout a year
provides a means of automatic control considering comfort and energy economy. This program also provides a tool for comparison of different techniques for putting limits to the relation between comfort and energy consumption.

Includes abstract.
Includes bibliographical references (p. 127-129).
Faults and inefficiencies in air conditioning installations account for between 2% and 11% of allenergy consumed by commercial buildings in the United States each year. Diagnostics systems havebeen proven to improve the performance of air conditioning plants but the high costs of purchasing,retrofitting and maintaining such a system results in limited market adoption of such systems.This thesis discusses the design, implementation and results of low-cost remote monitoring anddiagnostic platform for use in air conditioning installations. The design of the various hardwarecomponents is presented along with the structure of the framework developed for each device. The thesis also contains information regarding the selection, integration and installation of the various types of sensors required on the various installations. A specially-designed protocol was also developed to handle communication between the hardware devices. Both the physical configuration and details of the protocol structure are presented in detail in this thesis. The mechanism through which the device uploads data to a server is also described in this thesis and includes details on both the hardware and the server technologies used in the upload process. The system has been installed on two different sites in Cape Town, South Africa and has produced meaningful diagnostic information since November 2007.

Enhanced Finned-Tube Condenser Design and Optimization Susan W. Stewart 173 pages Directed by Dr. Sam V. Shelton Finned-tube heat exchangers are widely used in space conditioning systems, as well as any other application requiring heat exchange between liquids and gases. Their most widespread use is in residential air conditioning systems. Residential systems dictate peak demand on the U.S. national grid, which occurs on the hot summer afternoons, and thereby sets the expensive infrastructure requirement of the nations power plant and electrical distribution system. In addition to peak demand, residential air conditioners are major energy users that dominate residential electrical costs and environmental impact. The only significant opportunity for electrical power use reduction of residential air conditioners is in technology improvement of the finned-tube heat exchangers, i.e., condenser and evaporator coils. With the oncoming redesign of these systems in the next five years to comply with the regulatory elimination of R-22 used in residential air conditioners today, improvement in the design technology of these systems is timely. An air conditioner condenser finned-tube coil design optimization methodology is derived and shown to lead to improved residential air conditioner efficiency at fixed equipment cost. This nonlinear optimization of the 14 required design parameters is impractical by systematic experimental testing and iteration of tens of thousands condenser coils in an air conditioning system. The developed methodology and results can be used in the redesign of residential systems for the new mandated environmentally friendly refrigerants and to meet increasing regulatory minimum system efficiencies. Additionally, plain fins and augmented fins, (louvered), are compared using the developed model and optimization scheme to show the effect of the augmentation on system performance. Furthermore, an isolated condenser model was developed using condenser entropy generation minimization as the figure of merit to minimize the model complexity and computation time. Isolated model optimizations are compared with the system model optimum designs.

Industry practitioners and researchers recognize project scope definition as a factor of project success in terms of cost and schedule. The Construction Industry Institute developed the Project Definition Rating Index (PDRI) as a tool to aid in the effectiveness of scope development. The Air Force has adopted use of this tool, though has yet to validate its effectiveness empirically. The objective of this study is to provide that empirical validation by comparing the cost, schedule, and budget estimate performance metrics of Air Force military construction (MILCON) projects that used the PDRI against those that did not. Project data for 263 (100 PDRI and 163 non-PDRI) MILCON projects worth $3.9 Billion were analyzed. The projects that used the PDRI performed better on all three metrics, with statistically significant results on both cost and schedule growth. This study provides empirical evidence of how the use of formal scope definition tools can improve performance for Air Force MILCON projects. When compared to previous research, the study also contributes to a broader understanding of scope definition in the design and construction industry.

This thesis is concerned with an experimental and theoretical investigation of domestic heat pumps. The development of heat pumps in the 1970's did not meet the original expectations and this thesis examines the reasons why. The items considered included cycling and unsteady conditions created whilst matching the heat pump's output to meet a space heating load. A detailed study was made of the hermetically sealed refrigerant compressor, the heat exchangers, and the refrigerant pressure and temperature control systems. In addition to the conventional heat pump a study was made of the advantages gained from modular designed heat pumps. The application of heat pumps to U.K. dwellings and climatic conditions was studied together with the suitability of thermostatic control. Initial studies were made of the operation of a demonstration unit. This showed how intermittent operation would reduce a heat pump performance and was followed by the development of a computer model which simulated the complete refrigerant circulation system. This allowed a study to be made of a heat pump performance at part load conditions. A computer model of the complete refrigerant cycle was developed which aided in the design and construction of a heat pump which used refrigerant R12. This was followed by the construction of a second test rig using R 134(a). The completed R 134(a) test rig was installed in an environmental chamber which could simulate outdoor weather conditions. Results from the test rigs indicated that the performance was greatly affected by on/off cycling an item that was further investigated.

Air-cooled condensers are routinely designed for a variety of applications, including residential air-conditioning systems. Recent attempts at improving the performance of these heat exchangers have included the consideration of microchannel tube, multilouver fin heat exchangers instead of the more conventional round tube-plate fin designs. In most packaged air-conditioning systems, however, the condenser surrounds the compressor and other auxiliary parts in an outdoor unit, with an induced draft fan at the top of this enclosure. Such a configuration results in significant mal-distribution of the air flow arriving at the condenser, and leads to a decrease in performance. This work addresses the issue of mal-distribution by adapting the air-side geometry to the expected air flow distribution. A microchannel tube, multilouver fin condenser is first designed to transfer the desired heat rejection load for an air-conditioning system under uniform air flow conditions. Tube-side pass arrangements, tube dimensions, and fin and louver geometry are varied to arrive at a minimum mass, 2.54 kg condenser that delivers the desired heat load of 14.5 kW. The design model is then used to predict the performance of the condenser for a variety of air flow distributions across the heat exchanger. It is found that for a 50% air flow mal-distribution, the required condenser mass increases to 2.73 kg. The air-side geometry (fin density and height) of the condenser is then systematically changed to optimally distribute the air-side surface area across the condenser to best address the mal-distributed air flow. It is found that linear fin density and height variations from the mean value of 40% and 20%, respectively, keeping the mean fin density and height the same, reduce the required condenser mass to 2.65 kg even for this mal-distributed air-flow case. The influence of geometry variations on heat transfer coefficients, fan power and other performance measures is discussed in detail to guide the judicious choice of surface area and tube-side flow area allocations for any potential air flow mal-distribution. The results from this study can be used for the design of air-cooled condensers under realistic flow conditions.

District-heating and/or cooling systems are gradually becoming popular all over the world for heating and/or cooling of large premises. Current conventional practice for the DHC underground distribution networks is to place the supply and the return pipelines side-by-side in air-filled trencRe's. However, t present investigation has shown that by optimising the location of the pipelines, the thermal insulation provided by the air around the pipes can be maximised. This is achieved by placing the hot pipeline above the cold one, the exact position depending upon the temperatures involved. For most purposes, it is recommended that the displacement ratio for the hot pipe is to be at -0.7 or -0.08 and that of the cold pipe at 0.05 or 0.67 for district heating or cooling respectively [i. e. the hot and cold pipes being placed in the upper and lower halves of the trench respectively]. Each chapter is presented in such a way that it can be read independently of the others as far as possible.

The cleaning technology for exhaust air is an area under constant development. In collaboration with Ozone Tech Systems the project resulted in a lab scale test rig for air cleaning units. The test rig was designed primarily to investigate the mechanisms of an UV reactor as well as the life times of a hydrogen sulphide absorption bed and an activated carbon bed. The thesis consisted in the design of the system, the acquisition of units and the construction of the system followed by the modelling of the pollutant elimination in the UV reactor. Fluid dynamics of the process flow is neglected, while the light distribution is numerically calculated. Two separate pollutants were considered, one being volatile organic compounds represented by acetaldehyde, and the other being hydrogen sulphide, chosen due to their prevalence in exhausts. An experimental plan is developed to validate the model, find model parameters and finally to investigate process parameters in the UV reactor.
Luftföroreningar är ett mycket aktuellt problem, och tekniken för att rena luftströmmar är under ständig utveckling. I samarbete med Ozone Tech Systems designades och byggdes en testrigg för att undersöka olika luftreningsenheter. De primära målen var att undersöka mekanismerna i en UV reaktor samt livslängden för två lika packade bäddar; en absorptionsbädd för divätesulfid samt en adsorptionsbädd av aktiverat kol. Examensarbetet bestod av designmomentet, införskaffande av rätt enheter och konstruktionen av systemet. Även numerisk modellering av UV-reaktorn ingick i projektet, och denna gjordes med störst avseende på UV-ljusets fördelning i reaktorn medan flödesdynamiken försummades.Två olika föroreningar valdes p. g. a. deras frekventa förekomst i luftströmmar som ska renas; divätesulfid och flyktiga organiska ämnen (representerade här av acetaldehyd). Rapporten presenterar även en experimentell plan för att validera modellen, hitta modellens semiempiriska parametrar, samt till slut för att med hjälp av faktoriell design undersöka interaktionen mellan olika faktorer i UV-reaktorn.

Two design analysis programs that model the performance of solar heated and passively cooled homes in the climate of BURUNDI are presented. The new programs, SOLBUDI and COLBUDI, are based on the design analysis programs SOLASEC and COOLASEC which have been modified to account for skylights, solar heat gains on wall and roof surfaces, as well as nocturnal radiation effects on the roof. Additionally, Bjumbura (∼ 800 meters in altitude) weather data and the thermal properties of building materials commonly used in Burundi are incorporated into the programs. Typical weather data for cities at mid-altitudes (∼ 1500 meters) and high altitudes (>2000 meters) are also presented. Due to the great variation in altitude (700 meters - 2600 meters) and climate in Burundi, both heating and cooling are required, hence the need for both heating (SOLBUDI) and cooling (COLBUDI) design analysis programs. Skylights, east windows, and west windows are the best sources of solar gain in Burundi due to the high solar angles, which are present all seasons. Thus, solar gains through these apertures must be controllable to prevent overheating during the warm season.

An examination of contemporary office buildings in the warm humid region of Kenya revealed the predominance of highly glazed lightweight buildings that are prone to overheating and rely on costly and unsustainable active climate control systems. In the midst of growing energy demand and a potential deficit in supply, the influx of these poorly designed buildings has intensified the need to explore viable climate-responsive design alternatives suitable to local conditions that can extend occupant comfort and reduce the need for energy intensive environmental control systems. This view is shared by the Kenyan government which has set ambitious targets to develop and enforce national codes for energy efficiency and conservation in buildings by 2030. However, despite the clear and urgent need, research shows that little work has been developed to date that can be applied to the Kenyan context and climate. In this research, ways of improving the thermal comfort and performance of office buildings in the warm humid city of Mombasa (latitude 4°S) were explored. The work was developed through a series of field studies of local vernacular and modern case study buildings and subsequent computer simulations. From this, vernacular Swahili-inspired design strategies were derived and the application of the potentially most significant mitigation strategy to typical local office buildings examined further. Although other work exists elsewhere that may be comparable to parts of this study, this is the first effort that brings together the post occupancy evaluation of buildings in Mombasa, a thorough investigation of the effectiveness of the vernacular strategies found in Swahili architecture, and the validation of the application of these strategies to modern offices. Initial findings derived from a parametric study revealed external shading to be the most effective design strategy as it alleviated solar heat gain transmitted through glazing into buildings, resulting in a significant reduction in discomfort hours. Subsequently, using a series of dynamic computer simulations run for a typical office building in Mombasa, the average monthly solar heat gain coefficient (SHGC) values were derived for a typical year. These previously unavailable latitude (and hemisphere) specific solar path indices were deemed critical in the provision of essential data for effective external shading device design. The findings indicated that low SHGC values of under 0.5 gave the general indication of low percentage of discomfort hours (under 10%). Additionally, estimates of potential annual cooling energy savings of up to 60% were made based on the reduction of SHGC values for shading elements of practicable size. The application of these study findings to two local office buildings revealed that the derived SHGC values and energy estimates provide useful references when considered for similar type office buildings on similar latitudes. For both buildings, it was predicted that energy savings of 15% to 61% could be achieved from the application of suitably sized external shading devices. It was suggested that this type of information would encourage designers to use external shading devices as a method of maintaining thermal comfort, conserving energy and lowering operating costs in office buildings. Finally, recommendations for the incorporation of minimum shading standards in building regulations have been made and presented in a design guidance document.

Thesis (M.S. in Engineering Science)--Naval Postgraduate School, June 1990.
Thesis Advisor(s): Howard, Richard M. Second Reader:Pagenkopf, Eric L. "June 1990." Description based on title screen as viewed on October 19, 2009. DTIC Descriptor(s): Remotely piloted vehicles, vertical takeoff aircraft, ducted fans, velocity, flight testing, measurement, recovery, aircraft, hazards, demonstrations, fabrication, cycles, flight, vertical orientation, test vehicles, unmanned, safety, takeoff, shipboard, engines, reinforced plastics, propeller blades, propellers, static tests, tilt, thrust, horizontal orientation DTIC Indicator(s): UAV (Unmanned Air Vehicles), tilt, ship launched, shrouded propellers, aeronautical engineering, archytas aircraft, model tests. Author(s) subject terms: Unmanned Air Vehicle (UAV), Vertical Takeoff and Landing (VTOL), ducted fan, Remotely Piloted Vehicle (RPV) Includes bibliographical references (p. 93-94). Also available in print.

Design Build is rapidly becoming one of the most commonly used project delivery methods in the construction industry. The United States Corp of Engineers (USACE) has started implementing its own version of Design Build with the introduction of Military Transformation in April 2005. Per the Department of the Army (2008) Military Transformation is a term employed by the Corps to implement the use of alternate project delivery method as a means of achieving best value. The United States Air Force (AF) and the Air Force Reserve Command (AFRC) are expected to establish a target of 75% of all future Military Construction Projects (MILCONs) executed when using the Design Build method. The use of this delivery method results in significant changes to the relationships between the various parties associated with facility project delivery compared to the traditional Design Bid Build method. AFRC construction project procedures and requirements must also change.

This research explores technological interventions to reduce energy use in the domestic sector, a notable contributor to the global energy footprint. In the UK elevated challenges associated with renovating an outdated, poorly performing housing stock render a search for alternatives to provide immediate energy saving at low cost. To solve this problem, this thesis takes a holistic design approach to designing and implementing a spatiotemporal heating solution, and aims to investigate experiences of comfort, thermal comfort concepts for automated home heating, users’ interactions and experiences of living with such a system in context, and the underlying utility of quasi-autonomous spatiotemporal home heating. The mixed-methods research process was employed to explore and answer four questions: 1) what is the context within which these home heating interfaces are used, 2) to what extent can spatiotemporal automated heating minimise energy use while providing thermal comfort, 3) how are different heating strategies experienced by users, and 4) How do visibility of feedback, and intelligibility affect the user experience related to understanding and control? Ideation techniques were used to explore the context within which the designs are used with regard to all factors and actors in play and resulted in a conceptual model of the context to be used as a UX design brief. This developed model used mismatches between users’ expectations and reality to indicate potential thermal comfort behaviour actions and mapped the factors within the home context that affected these mismatches. Potential user inclusion through participatory design provided stakeholder insight and interface designs concepts to be developed into prototypes. The results of a prototype probe study using these prototypes showed that intelligibility should not be an interface design goal in itself, but rather fit in with broader UX design agenda regarding data levels, context specificity, and timescales. Increased autonomy in the system was shown not to directly diminish the experience of control, but rather, control or the lack of originated from an alignment of expectations and reality. A quasi-autonomous spatiotemporal heating system design (including a novel heating control algorithm) was coupled with the design of a smartphone interface and the resultant system was deployed in a low-technology solution demonstrating the potential for academic studies to explore such automated systems in-situ in the intended environment over a long period of time. Assessment of the novel control algorithm in an emulated environment demonstrated its fitness for purpose in reducing the amount of energy required to provide adequate levels of thermal comfort (by a factor of seven compared with EnergyStar recommended settings for programmable thermostats), and that these savings can be increased by including occupants’ thermal preference as a variable in the control algorithm. Field deployment of that algorithm in a low-tech sensor-based heating system assessed the user experience of the automated heating system and its mobile application-based control interface, as well as demonstrated the user thermal comfort experience of two different heating strategies. The results highlighted the potential to utilise the lower energy-use “minimise discomfort” strategy without compromising user thermal comfort in comparison to a “maximise comfort” strategy. Diverse heating system use behaviours were also identified and conceptualised alongside users’ experiences in line with the developed conceptual model. A rich picture analysis of all previous findings was utilised to provide a model of the design space for home automated heating systems, and was used to draw interface design guidelines for a broader range of home automation control interfaces. The work presented here served as important first steps in demonstrating the importance of assessing UX of automated home heating systems in situ over elongated periods of time. Novel contributions of (i) conceptual model of automated systems’ domestic context and thermal comfort behaviours within, (ii) nudging this behaviour by selecting a “minimise discomfort” heating strategy over “maximise comfort”, (iii) using UX to influence user expectations and subsequently energy behaviour, and (iv) inclusion of thermal preference in domestic heating control algorithm were all resultant of examining naturally occurring behaviours in their natural setting. As such, they are important exploratory discoveries and require replication, but provide new research directions that would allow reduction of domestic energy use without compromise.

This thesis considers the development of a Hammerstein-bilinear approach to non-linear systems modelling, analysis and control systems design, which builds on and extends the applicability of an existing bilinear approach. The underlying idea of the Hammerstein-bilinear approach is to use the Hammerstein-bilinear system models to capture various physical phenomena of interest and subsequently use these for model based control system designs with the premise being that of achieving enhanced control performance. The advantage of the Hammerstein-bilinear approach is that the well-structured system models allow techniques that have been originally developed for linear systems to be extended and applied, while retaining moderate complexity of the corresponding system identification schemes and nonlinear model based control designs. In recognition of the need to be able to identify the Hammerstein-bilinear models a unified suite of algorithms, being the extensions to the simplified refined instrumental variable method for parameter estimation of linear transfer function models is proposed. These algorithms are able to operate in both the continuous-time and discrete-time domains to reflect the requirements of the intended purposes of the identified models with the emphasis being placed on straightforward applicability of the developed algorithms and recognising the need to be able to operate under realistic practical system identification scenarios. Moreover, the proposed algorithms are also applicable to parameter estimation of Hammerstein and bilinear models, which are special cases of the wider Hammerstein-bilinear model class. The Hammerstein-bilinear approach has been applied to an industrial heating, ventilation and air conditioning (HVAC) system, which has also been the underlying application addressed in this thesis. A unique set of dynamic control design purpose oriented air temperature and humidity Hammerstein-bilinear models of an environmentally controlled clear room manufacturing zone has been identified. The greater insights afforded by the knowledge of the system nonlinearities then allow for enhanced control tuning of the associated commercial HVAC control system leading to an improved overall control performance.

The thesis explores the technical feasibility of an alternative method of decoupling air-conditioning systems function within the context of ecological issues. The system is a variant of dedicated outdoor air systems to separate dehumidification and cooling in air conditioning equipment. The project specifically investigates locating these components within the building envelope. Placement in the envelope moves the systems closer to fresh air and offers architectural expression for components that are normally out of sight. Designers, engineers, building science, mechanical, structural, biologist, and architectural engineers ideally as agents offer beneficial improvement to the system. The reduction in size of components into the building envelope offers risk. The thesis design space uses historical works, biological analogues, and past work to ground the technical understanding of the topic. Specific use of biological inspired design realizes translation from other systems to improve the alternative decoupled air conditioning system. The thesis develops prototype models for lighting analysis and for sensible and latent heat calculations. Psychrometric charts serve as tools to understand the thermodynamic air-conditioning process in conventional direct expansion vapor compression and solar liquid desiccant air conditioning systems. Data, models, and sketches provide tools for improvements to the 'thick' building envelope. Finally, the diagrams translate into functional decompositions for modifications to improve the system. The thesis probes the constraints in the areas of cost, fabrication, and technology that may not yet exist for selective improvement rather than a barrier to development of the thesis.