Dynamically determining input signals to a complex system, to increase performance and/or reduce cost, is a difficult task unless users are provided with feedback on the consequences of different input decisions. For example, users self-determine the set point schedule (i.e. temperature thresholds) of their HVAC system, without an ability to predict cost--they select only comfort. Users are unable to optimize the set point schedule with respect to cost because the cost feedback is provided at billing-cycle intervals. To provide rapid feedback (such as expected monthly/daily cost), mechanisms for system monitoring, data-driven modeling, simulation, and optimization are needed. Techniques from the literature require in-depth knowledge in the domain, and/or significant investment in infrastructure or equipment to measure state variables, making these solutions difficult to implement or to scale down in cost. This work introduces methods to approximate complex system behavior prediction and optimization, based on dynamic data obtained from inexpensive sensors. Unlike many existing approaches, we do not extract an exact model to capture every detail of the system; rather, we develop an approximated model with key predictive characteristics. Such a model makes estimation and prediction available to users who can then make informed decisions; alternatively, these estimates are made available as an input to an optimization tool to automatically provide pareto-optimized set points. Moreover, the approximation nature of this model makes the determination of the prediction and optimization parameters computationally inexpensive, adaptive to system or environment change, and suitable for embedded system implementation. Effectiveness of these methods is first demonstrated on an HVAC system methodology, and then extended to a variety of complex system applications.

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.

This thesis has improved Baltazar's methodology for potential energy savings estimation from retro-commissioning/retrofits measures. Important improvements and discussions are made on optimization parameters, limits on optimization parameter values, minimum airflow setting for VAV systems, space load calculation, simulation of buildings with more than one type of system, AHU shutdown simulation, and air-side simulation models. A prototype computer tool called the Potential Energy Savings Estimation (PESE) Toolkit is developed to implement the improved methodology and used for testing. The implemented methodology is tested in two retro-commissioned on-campus buildings with hourly measured consumption data. In the Sanders Corps of Cadets Center, the optimized profiles of parameter settings in single parameter optimizations can be explained with engineering principles. It reveals that the improved methodology is implemented correctly in the tool. The case study on the Coke Building shows that the improved methodology can be used in buildings with more than one system type. The methodology is then used to estimate annual potential energy cost savings for 14 office buildings in Austin, TX with very limited information and utility bills. The methodology has predicted an average total potential savings of 36% for SDVAV systems with electric terminal reheat, 22% for SDVAV systems with hot water reheat, and 25% for DDVAV systems. The estimations are compared with savings predicted in the Continuous Commissioning assessment report. The results show it may be helpful to study the correlation by using generalized factors of assessment predicted energy cost savings to estimated potential energy cost savings. The factors identified in this application are 0.68, 0.66, and 0.61 for each type of system. It is noted that one should be cautious in quoting these factors in future projects. In the future, it would be valuable to study the correlation between measured savings and estimated potential savings in a large number of buildings with retrocommissioning measures implemented. Additionally, further testing and modifications on the PESE Toolkit are necessary to make it a reliable software tool.

This research demonstrates the usage of numerical acoustics to model sound and vibrational energy propagation in HVAC ducts and plenums. Noise and vibration in HVAC systems propagates along three primary paths that can be classified as airborne direct, airborne indirect and structure-borne. The airborne direct path was simulated using acoustic FEM with special boundary conditions to handle the diffuse acoustic field loading and the baffled termination. The insertion loss for a number of different plenum geometries was compared to published measurement results. Results were in good agreement both below and above the cutoff frequency. Additionally, the airborne indirect path, often termed breakout noise by the HVAC community, was assessed using Statistical Energy Analysis (SEA). This path was examined experimentally by placing a loudspeaker inside the air handler and measuring the sound power transmitted through the walls. SEA results compared favorably with the measured results in one-third octave bands even at low frequencies. Finally, the structure-borne path was considered by exciting the walls of the aforementioned air handler using an electromagnetic shaker. The panel vibration and the sound power radiated from the panels were measured. Results were compared with the SEA with good agreement provided that SEA loss factors were determined experimentally.

Air-to-air energy recovery wheels are now widely used in industry and buildings; however, the effectiveness of water vapor exchange in these regenerative wheels appears to be much lower than may be economically feasible. The purpose of this research is to investigate the feasibility of using agglomerated desiccant particle coatings to improve the performance of regenerative wheels used in HVAC air-to-air heat and moisture exchange and energy recovery applications. Desiccant particles coated on wheels lose most of their water vapor sorption capacity due to the method of coating. Desiccant agglomerates can be made by mixing starch, fine silica gel particulate, and water within an agglomerating device. The desiccant particle agglomerating process improves the desiccant mass transfer properties by increasing the overall surface area of desiccant particles; and also by creating a much rougher surface that can increase the likelihood of turbulent flow, and therefore, increasing the overall mass transfer rates. The industrial desiccant coating process involves submerging the desiccant into a coating agent and then applying this mix to the substrate or the matrix of the energy wheel. This process was improved in this research by ensuring the particles are applied after the coating agent is applied to ensure that the agglomerates or desiccant particles are not submerged by the coating material. Because testing energy wheels under steady state operating conditions has proved to be difficult, time consuming and costly in the past, a small parallel flow test cell is used to measure the transient response of coated substrate aluminum sheets after a step change in the inlet air humidity or temperature. Using a previously developed theoretical model, the time constants for these inlet step change responses are then used to predict the sensible and latent effectiveness of a regenerative energy wheel coated with the same agglomerated particles, which is rotated at a known operating speed and wheel face velocity. When the new desiccant coatings are used, it is shown that the latent heat effectiveness for a typical wheel could be up to 85%. It is found that the steady state air flow pressure drop readings for the test cell shows that agglomerated particles coated on the surfaces within the test cell implies some transitional turbulent flow behavior compared to similar substrate surfaces coated in a conventional manner with desiccant particles (e.g. up to 60% higher pressure drop at a channel Reynolds number of 300) in the same test cell. This implied enhanced turbulence flow friction factor in the test cell suggests a somewhat similar enhancement for increased mass and heat transfer coefficients for the test cell or coated wheel matrices. The transient results for humidity step changes for air flow through the test cell reveals that the adsorption and desorption response time constants are much larger for the agglomerated coated substrate surfaces than the conventional industrial coated surfaces. These data imply much higher moisture or latent heat effectiveness values for wheels coated with agglomerated particles. When the new desiccant coatings are used, it is shown that the latent heat effectiveness for a typical wheel could be better than 80% or 20% higher than currently available typical energy wheels. With improvements to the desiccant particle agglomerating process, desiccant coating process and particle coating and testing methods, this thesis shows that significant improvements may be practical for the design, testing and operation of regenerative heat and moisture exchange wheels.

The purpose of this research is to develop and verify a simplified and concise building simulation model suitable for high-level applications such as preliminary design or for embedding into adaptive control systems. An actual complex modern building and its energy system has been monitored. The monitored energy performance of this building has been compared with the empirical performance predicted by two simulation modeling programs and, alternatively, by a simplified single-zone model. This project is composed of several related tasks. The first component is the monitoring of the energy consumption rates, pertinent environmental data, and load indicators of the new Klaus Advanced Computing Building on the Georgia Institute of Technology's Atlanta campus. The Klaus building was chosen because it represents a typical non-residential building. Subsequently, these findings have been compared with results from DOE-2 and eQUEST, well established energy simulation modeling programs. These comparisons allow for an empirical verification of the modeling program for Atlanta conditions. Finally, a simplified single-zone building model has been developed, and its predictions compared with the empirical data and with the results of the more complex programs. The results verify both the more complex programs and the single-zone model, and also demonstrate the use of a single-zone model for future work and predictions.

Systems based on the vapor compression cycle are the most widely used in a variety of air conditioning applications. Despite the vast growth of modern control systems in the field of air conditioning systems, industry standard control is still thermostat based on-off control, in other words cycle control. This thesis proposes an approach to find the optimal profiles for the expansion valve and the evaporator fan for an air conditioning system for a given period of on-off cycle of the compressor. The research will consist of two phases, the development of a simulation model and an experimental analysis. In this thesis, the profiles for the expansion valve and the evaporator fan are parameterized by an S-curve equation so that the optimization problem will have less numbers of parameters. The first step is a simulation model that predicts startup/shutdown characteristics. This model is used as a tool to understand the effect that the S-curve parameters has on the system cycle efficiency. Several key vapor compression system dynamics are identified as causes for increasing/decreasing system's cyclic efficiency. Refrigerant migration and fan delay at shutdown are determined as crucial issues that have an effect on the A direct search optimization algorithm, namely the simplex search algorithm, is then used to search for the optimal S-curve parameters. Valve/fan strategies that ultimately resulted in a better superheat control are assessed as the most energy efficient. Extensive experimental tests conducted on a 3-ton residential air conditioner are then presented to intuitively understand the effect of expansion valve and evaporator fan cycling in a real system. A real time optimization method is explored and the feasibility, recommendations for a successful online method are proposed. The heuristics for the expansion valve and evaporator fan profiles from the optimization results could be easily hard coded into any commercial air conditioning system to perform the much preferred cycle control. Thus a significant improvement in the energy performance was observed without the use of any advanced control techniques.

Scania has identified a problem among certain costumers in very dusty environments. The air filters for their truck’s climate system need extensive maintenance, replacement or manual cleaning, because of dust frequently loading up the filters. In this thesis the problem has been analyzed in order to find a solution. The process was initiated by the usage of the black box method, where needed transformations were found, resulting in three needed technical systems. Thereafter, brainstorming was used to find concepts for each technical system. Concepts were compared and ranked against each other. For the most critical of the three systems, the cleaning action, prototypes were built of the four highest ranked concepts. These prototypes were then used to compare the performance between the concepts. The selected filter cleaning device consists of a method to analyze filter blockage, alert the driver when cleaning is needed and a system to clean the filter for the Scania climate system. The system consists of a pressure sensor used to measuring filter blockage, an air pulse system which cleans the filter and a controller unit to control the cleaning cycle and to inform the driver. The air pulse system has two main parts, a pulse valve and an air tank. The pulse valve is used for releasing the air accumulated in the air tank. The complete system is supplied with 8.5 bar from the internal air pressure system in the truck and a 24 V power supply, also located in the truck. A suggestion on how a final implementation can be done has been developed, with a minimized number of variants and modifications of parts already in production. A proof of concept was built and mounted in a truck to validate the complete system. Numbers on cleaning performance and sound levels have been produced. The proof of concept manages to remove the restriction created from dust by approximately 50 %. Aside from developing a suitable filter cleaning device, figures on when the filter needs to be cleaned have been identified. To keep a good working environment within the cab a pressure drop over the filter of 936 Pa is recommended as a point of cleaning. This is to maintain the needed airflow of at least 123 m3/h with two persons seated in the cab to not exceed regulated levels of CO2 within the truck cab.

abstract: The ability to shift the photovoltaic (PV) power curve and make the energy accessible during peak hours can be accomplished through pairing solar PV with energy storage technologies. A prototype hybrid air conditioning system (HACS), built under supervision of project head Patrick Phelan, consists of PV modules running a DC compressor that operates a conventional HVAC system paired with a second evaporator submerged within a thermal storage tank. The thermal storage is a 0.284m3 or 75 gallon freezer filled with Cryogel balls, submerged in a weak glycol solution. It is paired with its own separate air handler, circulating the glycol solution. The refrigerant flow is controlled by solenoid valves that are electrically connected to a high and low temperature thermostat. During daylight hours, the PV modules run the DC compressor. The refrigerant flow is directed to the conventional HVAC air handler when cooling is needed. Once the desired room temperature is met, refrigerant flow is diverted to the thermal storage, storing excess PV power. During peak energy demand hours, the system uses only small amounts of grid power to pump the glycol solution through the air handler (note the compressor is off), allowing for money and energy savings. The conventional HVAC unit can be scaled down, since during times of large cooling demands the glycol air handler can be operated in parallel with the conventional HVAC unit. Four major test scenarios were drawn up in order to fully comprehend the performance characteristics of the HACS. Upon initial running of the system, ice was produced and the thermal storage was charged. A simple test run consisting of discharging the thermal storage, initially ~¼ frozen, was performed. The glycol air handler ran for 6 hours and the initial cooling power was 4.5 kW. This initial test was significant, since greater than 3.5 kW of cooling power was produced for 3 hours, thus demonstrating the concept of energy storage and recovery. / Dissertation/Thesis / M.S. Mechanical Engineering 2012

Le secteur du chauffage, de la ventilation et de la climatisation (Heating Ventilation and Air-Conditioning,HVAC) se doit, comme toute industrie d’envergure, de maîtriser la fiabilité de ses produits pour garantir un service optimal au client, réduire les délais de développement et maîtriser ses coûts. Pour ce faire, il est indispensable de connaitre et savoir appliquer les outils de fiabilité prévisionnelle, expérimentale et opérationnelle. Seule une méthodologie robuste permettant de définir une stratégie de qualification permet de garantir la tenue de l’objectif de fiabilité.La première partie de ce travail définit les problématiques ayant attrait à la fiabilité et fait l’inventaire des méthodes existantes dans des domaines connexes et surtout dans le domaine HVAC.Dans un second temps la méthodologie de qualification est proposée, avec un focus sur l’exploitation du retour d’expérience, la définition des objectifs de fiabilité et tous les plans d’essais possibles. Enfin, des exemples concrets mis en place chez CIAT (UTC) sont détaillées dans une dernière partie. / The heating, ventilation and air conditioning (HVAC) field, as any other large industry, must control the reliability of its products in order to guarantee an optimal service to customers, reduce development limits and master its costs. To achieve it, predicted, experimental and operational reliability tools should be known and well applied. Only a strong methodology leading to a qualification strategy can ensure the holding of the reliability target. The first part of this work defines reliability terms and inventories existing methods in related fields and specifically in HVAC. Following that, the qualification methodology is detailed, focusing on feedback, definition of reliability targets and possible test plans. Finally, specific examples implemented at CIAT (UTC) are detailed in final part.