Conventional residential building energy auditing needed to identify opportunities for energy savings is expensive and time consuming. On-site energy audits require quantification of envelope R-values, air and duct leakage, and heating and cooling system efficiencies. There is a need to advance lower cost automated approaches, which could include aerial and drive-by thermal imaging at-scale in an effort to measure the building R-value. However, single-point in time thermal images are generally qualitative, subject to errors stemming from building dynamics, background radiation, wind speed variation, night sky thermal radiation, and error in extracting temperature estimates from thermal images from surfaces with generally unknown emissivity. This work proposes two alternative approaches for estimating roof R-values from thermal imaging, one a physics based approach and the other a data-mining based approach. Both approaches employ aerial visual imagery to estimate the roof emissivity based on the color and type of roofing material, from which the temperature of the envelope can be estimated. The physics-based approach employs a dynamic energy model of the envelope with unknown R-value and thermal capacitance. These are tuned in order to predict the measured surface temperature at the time of the imaging, given the transient weather conditions prior to the imaging. The data-mining approach integrates the inferred temperature measurement, historical utility data, and easily accessible or potentially easily accessible housing data. A data mining regression model, trained from this data using residences with known R-values, is used to predict the roof R-value in the unknown houses. The data mining approach was shown to be a far superior approach, demonstrating an ability to estimate attic/roof R-value with an r-squared value of greater than 0.88 using as few as nine training houses. The implication of this research is significant, offering the possibility of auditing residences remotely at-scale via aerial and drive-by thermal imaging coupled with utility analysis.

Advanced energy management control systems (EMCS), or building automation systems (BAS), offer an excellent means of reducing energy consumption in heating, ventilating, and air conditioning (HVAC) systems while maintaining and improving indoor environmental conditions. This can be achieved through the use of computational intelligence and optimization. This paper evaluates model-based optimization processes (OP) for HVAC systems utilizing any computer algebra system (CAS), genetic algorithms and self-learning or self-tuning models (STM), which minimizes the error between measured and predicted performance data. The OP can be integrated into the EMCS to perform several intelligent functions achieving optimal system performance. The development of several self-learning HVAC models and optimizing the process (minimizing energy use) is tested using data collected from an actual HVAC system. Using this optimization process (OP), the optimal variable set points (OVSP), such as supply air temperature ( T s ), supply duct static pressure ( P s ), chilled water supply temperature ( T w ), minimum outdoor ventilation, and chilled water differential pressure set-point ( D pw ) are optimized with respect to energy use of the HVAC’s cooling side including the chiller, pump, and fan. The optimized set point variables minimize energy use and maintain thermal comfort incorporating ASHRAE’s new ventilation standard 62.1-2013. This research focuses primarily with: on-line, self-tuning, optimization process (OLSTOP); HVAC design principles; and control strategies within a building automation system (BAS) controller. The HVAC controller will achieve the lowest energy consumption of the cooling side while maintaining occupant comfort by performing and prioritizing the appropriate actions. The program’s algorithms analyze multiple variables (humidity, pressure, temperature, CO 2 , etc.) simultaneously at key locations throughout the HVAC system (pumps, cooling coil, chiller, fan, etc.) to reach the function’s objective, which is the lowest energy consumption while maintaining occupancy comfort.

Heating and cooling is a prime need for various day to day operations and one of the most basic requirements is space conditioning. A huge amount of energy all across the globe is being used for this purpose using various conventional & non-conventional energy based resources. But environmental problems, fast depletion nature and high prices associated with the use of conventional energy sources is becoming a big problem, due to which promotion of non-conventional energy sources becomes important. The use of an in-ground heat exchanger is a unique technique for space conditioning with reduced energy consumption. A lot of research and studies have been done on the design of such systems. This paper presents a study based on the CFD modelling and simulation to analyze the effect on the effective performance of the system by varying the geometry of ducts and using the extended surface to increase the heat transfer rate. Also, a comparative study of performance of earth tube heat exchanger for different cross section of ducts is also presented.

Fossil fuels have been a means of energy source since a long time, and have tended to the needs of the large global population. These conventional sources are bound to deplete in the near future and hence there is a need for producing energy from renewable energy sources like solar, wind, geothermal, tidal etc. Technologies involving renewable energy are a growing subject of concern. Further, the problem is also one of excessive pollution caused by conventional sources of energy and their impact on the environment. In particular, one of the main sources of pollution is harmful gases emitting out of automobiles. Wind energy is one among the renewable energy sources which is implemented in large scale energy production to supplement growing domestic energy needs. Significant amount of research has been done in this field to harness energy to power household and other amenities using wind farms. The aim of this project is to come up with a low cost solution for wind energy harvesting on moving vehicles. The purpose of this study is to consider the use of wind energy along with conventional energy sources to power automobiles. This would help reduce the use of fossil fuels in automobiles and hence reduce the resulting environmental pollution. Also since the turbine adds to the weight of the vehicle the aim also is to minimize the weight of the turbine. Extensive structural analysis is done for this purpose to choose a material which would be both light weight and also be able to withstand the stresses developed. In the current paper the drag force produced in automobiles is harvested by using a convergent divergent nozzle mounted below the chassis of the car. Initially drag analysis is done in order to determine the increase in drag force produced after mounting of the nozzle. It is found from existing literature that the drag increases by 3.4% after the mounting of the nozzle making it possible the mounting of a nozzle beneath the car. Additionally exhaust gases is also allowed to pass through the same duct to increase the mass flow to the turbine and thus generate more energy. This is made to strike the blades of a 2 stage axial flow turbine whose rotation generates energy. The power output from the turbine is the parameter of interest. This energy can also be stored in batteries and be used to run auxiliary equipment of the automobile including the air conditioner. The exhaust gases will be passed through a catalytic converter before striking the blades of the turbine in order to prevent corrosion of the blades. Computational Fluid Dynamics (CFD) is used to validate the concept and also come up with a design that maximizes energy generation by such turbines. Numerical results obtained by simulation are validated by theoretical calculation based on turbines inlet and outlet velocity triangles. The future scope of the project would include the use of multiple nozzles in order to study its performance.

The design of expanders for organic fluids is gaining an increasing attention due to the large opportunities opened by the ORC as a way to recover low grade heat. The possibility of recovering at least a fraction of the energy related to throttling in inverse cycles could have interesting relapses on the market of heating (heat pumps) and refrigeration machines. The main challenge to be faced is the management of a highly wet fluid (typical quality is in the 0–0.6 range), which puts off side dynamic expanders like turbines. For this reason, piston technology is proposed and analyzed. The potential recovery from the throttling of a 20 kW target domestic heat pump cycle is determined by modeling the real expansion cycle with two different codes, a commercial one (largely widespread and very easy to use) and a purposely developed one, which is much more customizable and may include different approaches to the physical behavior of the two–phase expansion. The results show interesting possibility of energy recovery from this generally wasted source, which opens the way to improvements of the heat pump COP from 4% to about 7%, depending on the working (i.e. seasonal) conditions. The analysis also points out the agreement in the results of two different adopted simulation tools (commercial AMESim ® and self-made customizable EES ® ), which can be thus considered valuable in the design, analysis and optimization of the proposed expander. Due to the biphasic nature of the working fluid, the performance of the expander is strongly influenced by the inlet conditions of the fluid from the condenser of the heat pump to the cylinders, such as throttling of the inlet/outlet valves and friction through the ducts. On the whole, this expander technology has very interesting chances to effectively manage fluids under highly wet conditions, like those related to the throttling from upper to lower pressure of inverse cycles.

This study investigates the drying mechanisms of corn when it is exposed to air at elevated temperature and velocity within a cross-flow packed bed dryer. A highly-instrumented laboratory-scale experimental test dryer was constructed to batch-dry samples of 0.03 m 3 (1 ft 3 ) of high moisture corn. This is achieved using a perforated wall drying chamber with forced air at temperatures ranging from 180–240°F. The high temperature, high velocity air entering the column is supplied by a variable speed fan and a variable Wattage electric heating coil through a 0.09 m 2 (1 ft 2 ) square air duct. This device is able to precisely control the drying air temperate and flow rate, while also measuring the temperature and humidity of the air exiting the dryer. In creating and instrumenting this apparatus, tests were performed to analyze both energy use and drying rate to determine the operating conditions that find a balance between energy and time requirements for moisture removal. This study used a variety of supply air temperatures and air flow rates in drying samples of corn at two initial moisture contents (19%MC and 24%MC) to 15%MC. This is done to determine if there are notable differences in energy requirements (Btu/pound water removed) between different operating conditions. This study determined that corn undergoes a significant pre-heating process before peak drying efficiency is achieved. Current grain dryer designs should focus the most energy just after that pre-heating process for highest overall efficiencies. Additionally, this study found an inverse relationship between dry time and energy efficiency, which showed that an optimum balance between those two factors should be identified.

WINDGRABBER™ (WG) is a novel new roof or pole top mounted wind turbine system proposed for product commercialization up to 50 kWe. WG is projected to be cost-attractive in an environmentally friendly manner. The WG system uses the available energy in the wind via (1) a passively yawed air impact inlet air scoop, (2) a flow tube, (3) an air turbine and (4) a multiphased air inlet with an air impact - drag type outlet section. The WG wind turbine system preferentially utilizes a combination enclosed - radial out-flow, cross-flow, reaction-impulse air turbine of squirrel cage configuration, using either a single or double axial flow inlet of centrifugal fan design with backwardly curved, air foil air blades mounted on the discharge end of a flow tube. The WG wind turbine design is based on the air power instead of the wind power equations, combined with duct resistance, wind impact and wind drag calculations, to determine system wind energy conversion effectiveness with respect to the Betz limit, as well as overall system efficiency. Low pressure drop screens may be provided at the various inlets and outlets to protect birds and small mammals from being drawn into rotating components. A currently proposed Phase I – CAE modeling for conceptual design verification, system optimization and 300 watt pilot plant test program, followed by a Phase II – design improvement and scale up to 3,000 watt prototype demonstration program and followed by a Phase III cost reduction, product improvement and scale up to a 5,000 watt commercial demonstration program is currently being considered by BCK Consulting, L.L.C. (BCK) and West Texas A & M University (WTAMU). The history of WG , up to and including its latest developmental status, will be discussed in this paper with projections offered regarding its future product commercialization prospects. Please see ASME paper ES2010-90062 presented previously [Ref.1].

In order to use real-time energy measurements to identify system operation faults and inefficiencies, a cooling coil energy baseline is studied in an air-handling unit (AHU) through an integration of physical models and a data driven approach in this paper. A physical model for an AHU cooling coil energy consumption is first built to understand equipment mechanism and to determine the variables impacting cooling coil energy performance, and then the physical model is simplified into a lumped model by reducing the number of independent variables needed. Regression coefficients in the lumped model are determined statistically through searching optimal fit using the least square method with short periods of measured data. Experimental results on an operational AHU (8 ton) are presented to validate the effectiveness of this approach with statistical analysis. As a result of this experiment, the proposed cooling energy baselines at the cooling coil have ±20% errors at 99.7% confidence. Six-day data for obtaining baseline is preferred since it shows similar results as 12-day.

The heat transfer principle of power maximization in power plants with heat transfer irreversibilities was cleverly extended by Bejan [1] to fluid flow, by obtaining that the energy conversion efficiency at maximum power is η max = 1 / 2 ( 1 − P 2 /P 1 ). This result is analog to the efficiency at maximum power for power plants, η max = 1 − (T 2 /T 1 ) 1 / 2 which was deduced by Curzon and Ahlborn [2]. In this paper, the analysis to obtain maximum power output delivered from a piston between two pressure reservoir across linear flow resistance is generalized by considering the piston cylinder friction, by obtaining relations of maximum power output and optimal speed of the piston in terms of first law efficiency. Expressions to relate the power output, cross sectional area of the chamber and first law efficiency, were deduced in order to evaluate the influence of the overall size constraints and fluid regime in the performance of the piston cylinder system. Flow in circular ducts and developed laminar flow between parallel plates, are considered to demonstrate that when two pressure reservoirs oriented in counterflow, with different and arbitrary cross sectional area, must have the same area in order to maximize the power output of the system. These results introduce some modifications to the results obtained by Bejan [1] and Chen [3]. This paper extends the Bejan and Chen’s work by estimating under turbulent regime the lost available work rate associated with the degree of irreversibilities caused by the flow resistances of the system. This analysis is equivalent to evaluate the irreversibilities in an endoirreversible Carnot heat engine model caused by the heat resistance loss between the engine and its surrounding heat reservoirs. This paper concludes with an application to illustrate the practical applications by estimating the lost available work of an actual steady-flow turbine and the layout pipes upstream and downstream of the same device.

Gas and air-side heat transfer is ubiquitous throughout many technological sectors, including HVAC (heating, ventilating, and air conditioning) systems, thermo-electric power generators and coolers, renewable energy, electronics and vehicle cooling, and forced-draft cooling in the petrochemical and power industries. The poor thermal conductivity and low heat capacity of air causes air-side heat transfer to typically dominate heat transfer resistance even with the use of extended area structures. In this paper, we report design, analysis, cost modeling, fabrication, and performance characterization of micro-honeycombs for gas-side heat transfer augmentation in thermoelectric (TE) cooling and power systems. Semi-empirical model aided by experimental validation was undertaken to characterize fluid flow and heat transfer parameters. We explored a variety of polygonal shapes to optimize the duct shape for air-side heat transfer enhancement. Predictions using rectangular micro-honeycomb heat exchangers, among other polygonal shapes, suggest that these classes of geometries are able to provide augmented heat transfer performance in high-temperature energy recovery streams and low-temperature cooling streams. Based on insight gained from theoretical models, rectangular micro-honeycomb heat exchangers that can deliver high performance were fabricated and tested. High- and low-cost manufacturing prototype designs with different thermal performance expectations were fabricated to explore the cost-performance design domain. Simple metrics were developed to correlate heat transfer performance with heat exchanger cost and weight and define optimum design points. The merits of the proposed air-side heat transfer augmentation approach are also discussed within the context of relevant thermoelectric power and cooling systems.

A blow-down facility for experimental analysis of real gases is under construction at Politecnico di Milano (Italy), in collaboration with Turboden s.r.l. and in the frame of the research project named Solar . Experiments are meant to characterize flow fields representative of expansions taking place in Organic Rankine Cycle (ORC) turbine passages. Indeed, ORC power plants represent a viable technology to exploit clean energy sources, but ORC turbines design tools still require accurate experimental data for validation. A significant improvement of turbine efficiency is expected from detailed investigations on vapour streams; in fact, ORC turbines design tools still require accurate experimental data for validation. The facility is equipped with a straight axis supersonic nozzle as a test section and a batch-closed loop plant has been designed in order to reduce investment and operational costs. Due to the batch operation, the evaluation of the time evolution of main processes involved in the cycle is of great importance. To this purpose a dynamic simulation of the test rig has been carried out using a dynamic simulator based on an object-oriented modeling language, Modelica , allowing an easy development of component models structured with a hierarchical approach. Models include control loop devices, strongly influencing processes duration. This paper presents how the test rig has been modelled, with particular emphasis on the models framework and on simulation procedure; the calculation results are finally discussed. With a lumped parameter approach, a first scheme of the facility has been built by modelling each of the three main plant section (heating, test, condensation) using components included in a self-made library. Several models, not embedded in the Modelica standard libraries, have been created using Modelica code; among them the most important has been the supersonic nozzle. In order to better describe the facility behaviour and the thermal losses, a plant calculation refinement has been carried out by the development of finite volume based one-dimensional models of ducts and reservoirs, either in radial or axial direction; in particular, a novel distributed-parameters model has been built for the heating section. All simulations have been performed using Siloxane MDM and Hydrofluorocarbon R245fa as reference fluids and FluidProp ® to calculate thermodynamic properties. A quasi 1-D steady nozzle flow calculation has also been carried out by implementing FluidProp ® routines in a dedicated Fortran software. Since the unsteady nozzle expansion is well approximated by a sequence of steady states, the computation provides all thermodynamic properties and velocity along the nozzle axis as a function of time. Simulation results have given a fundamental support to both plant and experiments design.

At present all cold air distribution systems are being used widely due to their advantages of smaller ductwork, shorter floor-to-floor height and less energy consumption etc. They are mostly used in VAV (Variable Air Volume) systems or with the radiant panel systems in the office and residential buildings at the supply air dew point temperature of 6∼10°C, rarely used in large space buildings. The technology of stratified air conditioning is one of the energy saving technologies to large space buildings, which has been popularly used in the conventional air supply systems with the supply air dew point temperature of 11∼16°C. In this paper, the cold air distribution system and the stratified air conditioning technology in a large space building are combined to study. With the method of CFD, the indoor thermal environment of a large space workshop is simulated. The velocity and the temperature as well as the relative humidity fields under different air flow modes are presented, analyzed and compared. With the help of numerical simulation results, the optimal airflow mode is proposed, which show that the all cold air distribution with the stratified air conditioning is a good option for large space buildings. All these above will be good references to the application of cold air distribution system and the selection of the airflow mode in large space buildings.

The Power, Water Extraction, and Refrigeration (PoWER) engine has been investigated for several years as a distributed energy (DE) system among other applications for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semi-closed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, low emissions, lower air and exhaust flows (which decrease filtration and duct size) and condensation of fresh water. The present paper describes the preliminary design and its modeling of a modified version of this system as applied to DE system, especially useful in regions which are prone to major grid interruptions due to hurricanes, under-capacity, or terrorism. In such cases, the DE system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is contained in magnitude and scope. The paper describes the rather straightforward system modifications necessary for ice production. However, the primary focus of the paper is on dynamic modeling of the ice making capacity to achieve significant load-leveling during the summer utility peak, hence reducing the electrical capacity requirements for the grid.

Thermal comfort in an area is directly controlled by terminal boxes in variable air volume (VAV) air-handling unit (AHU) systems. The terminal box either modulates airflow or adjusts the discharge air temperature. Reduced air circulation will cause thermal discomfort in a conditioned space if the airflow and discharge air temperature are not suitable. The objective of this study is to identify an optimal value for airflow and discharge air temperature that will maintain room thermal comfort. Optimal room airflow and discharge air temperature is analyzed, and the impact of room airflow and discharge air temperature on thermal stratification is verified through CFD (Computational Fluid Dynamics) simulations.

Terminal boxes are one of the major building HVAC components and directly impact building room comfort and energy costs. Current terminal boxes may cause occupant discomfort and waste energy if they have inappropriate operation control functions. The objective of this study is to develop and implement applicable optimal terminal box control algorithms. The thermal conditions and energy consumption are compared between conventional and improved control algorithms using measured data. The results of this study show that optimal terminal box control algorithms can stably maintain the set room air temperature and reduce energy consumption compared to conventional control algorithms.

Terminal boxes control space conditions in variable air volume (VAV) air-handling unit (AHU) systems. Terminal boxes either modulate airflow with a control damper or adjust discharge air temperature with a reheat coil. Terminal boxes will have a significant amount of simultaneous heating and cooling and AHUs will consume more fan power if the minimum airflow is higher than required. On the other hand, conditioned space will have indoor air quality (IAQ) problems with less air circulation if the minimum airflow is less than required. The objective of this study is to optimize the minimum airflow ratio to improve thermal environment and save energy consumption. In this study, the problem of current fixed minimum airflow ratio of terminal box is analyzed and variable minimum airflow ratio as an alternative is suggested. The results of this study show that variable minimum airflow ratio can stably maintain the set room air temperature and reduce energy consumption for varying heating loads compared to the conventional fixed minimum airflow ratio.

This paper demonstrates the implementation of new innovative technologies during continuous commissioning (CC) practices to improve building operations and reduce energy costs. A 46-year-old typical commercial building with a floor area of about 216,000 square feet was used as a case study building. The new technologies include a fan airflow measurement method for building pressure control and duct static pressure reset, and a recently developed pump water flow station for secondary pump control. The results show that these technologies improve building operation and maintenance and significantly reduce energy costs. The monthly average electricity savings for HVAC is more than 70% per month for the three months of the monitoring period. The total building electricity savings is 36.7% on average. The gas savings is about 48% for the two months of the monitoring period.

This paper provides an overview of the typical variable speed drive (VSD) control for the supply fan in a variable airflow volume (VAV) system. Two new control methods using the fan airflow station (FAS) are presented in this paper. In the first method, the supply fan speed is controlled to maintain a constant system resistance, which is calculated based on the measured fan head, and airflow, which is calculated by the FAS. In the second method, the supply fan speed is controlled to maintain the duct static pressure set point, which is reset based on the airflow ratio measured by the FAS. The innovative methods can be applied to systems with either direct digial control (DDC) or pneumatic control boxes. The case studies show that the new control method can significantly save supply fan power and increase fan efficiency.

Air duct static pressure is usually a control variable maintained by the supply fan for variable air volume (VAV) systems. Typically the air static pressure is set at a constant set point based on design conditions. However, under partial load conditions, terminal box dampers have to be closed more since required airflow is less than the design airflow which directly results in significantly smaller pressure loss. Thus no matter the terminal boxes are pressure dependent or pressure independent, the static pressure set point should be reset to a lower level to reduce the fan energy, the noise in the terminal boxes, and the terminal boxes malfunction. With the static pressure reset, the room condition can also be maintained better at lower fan energy consumption by minimizing simultaneous cooling and heating. This paper proposes to control the static pressure in dual-duct variable air volume systems by using supply fan variable frequency drives (VFDs) and installing hot air dampers in the hot deck. The static pressure set point is reset based on fan airflow measured by fan airflow station (FAS). With regard to affecting factors of space load, availability of terminal box damper position and space cooling demand, this integrated method has advantages over the existing measures such as fixed static pressure, static pressure reset by outside air temperature, static pressure reset by VAV box damper position and static pressure reset by cooling loop output. According to both the model analysis and case building study, it turns out that this method can significantly save fan power.