In most previous studies that have been conducted on converting waste heat energy from exhaust gases into useful energy, the engine waste heat recovery system has been placed along the exhaust flow pipe where the temperature differs from the temperature just behind the exhaust valves. This means that an important fraction of the energy from the exhaust gases is still lost to the environment. The present work investigates the potential thermodynamic analysis of an integrated exhaust waste heat recovery (EWHR) system based on a Rankine cycle on an engine's exhaust manifold. The amount of lost energy contained in the exhaust gases at the exhaust manifold level, at average temperatures of 500 °C and 350 °C (for petrol and diesel), and the thermodynamic composition of these gases were determined. For heat to occur, a temperature difference (between the exhaust gas and the working fluid) at the pinch point of 20°C was considered. A thermodynamic analysis was performed on different configurations of EWHR thermal efficiencies and the selected suitable working fluids. The environmental and economic aspects of the integrated EWHR system just behind the exhaust valves of an internal combustion engine (ICE) were analysed. Among all working fluids that were used when the thermodynamic analysis was performed, water was selected as the best working fluid due to its higher thermal efficiency, availability, low cost and environmentally friendly characteristics. Using the typical engine data, results showed that almost 29.54% of exhaust waste heat can be converted. This results in better engine efficiency and fuel consumption on a global scale by gaining an average of 1 114.98 Mb and 1 126.63 Mb of petrol and diesel respectively from 2020 to 2040. It can combat global warming by recovering 56.78 1 011 MJ and 64.65 1 011 MJ of heat rejected from petrol and diesel engines, respectively. A case study of a Volkswagen Citi Golf 1.3i is considered, as it is a popular vehicle in South Africa. This idea can be applied to new-design hybrid vehicles that can use the waste heat to charge the batteries when the engine operates on fossil fuel. / Dissertation (MSc)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MSc / Unrestricted

<div>With the United States being the world’s second largest consumer of primary energy, research into areas of significant consumption can provide large impacts in terms of the global energy consumption. Buildings account for 41% of U.S. total energy consumption with the residential sector making up a majority. Household appliances account for the second largest site energy consumption at 27%, after the HVAC system for the U.S. residential sector. Federal appliance standards have been instrumental in improving efficiencies but have been increasing aggressively to where it is unknown what suitable technologies can support this rate of increase. Thermally integrating residential appliances by leveraging waste heat recovery goes outside standards and has not been adequately explored by connecting all residential appliances. Limited studies exist focused only on single appliances connected to waste heat recovery or being thermally integrated. Preliminary modeling on waste heat availability from five major appliances, namely refrigerator-freezer, clothes dryer, clothes washer, dishwasher, and cooking oven was conducted. Conservative estimates predict the total amount of heat recovery to be around 2,000 kWh/year; clothes dryer - 137 kWh/year, clothes washer - 60 kWh/year, 1,500 kWh/year- refrigerator-freezer, 27 kWh/year – dishwasher, and 178 kWh/year – cooking oven. The cooking oven presents technical challenges coupled with safety concerns. The clothes dryer and refrigerator-freezer can deliver useful water temperatures and reduce compressor power consumption, up to 20%. The dishwasher has better opportunity as a heat sink to offset the internal heater, 0.17 kWh of electricity/cycle for heating wash water. The clothes washer drains large volumes of water available for heat recovery and can offset the impact of using high temperature washes with improved wash performance. </div><div>Modelica appliance models have been developed for four of these five appliances. The Modelica models capture individual use and the predictions of the RF and DW were compared against available experimental data. The individual models have been connected to a simple storage tank model to simulate the integrated appliance system. An integrated appliance prototype was designed and fabricated for the collection of experimental data. Comparisons made between the experimental data and the integrated appliance simulation results adjusted the modeling approach and improved agreement with collected data. After tuning, ideal modifications to each appliance are made and reflected in a new integrated model. A parametric study is conducted on ideal improved, thermally capable appliances under a 1-week schedule for two different tank sizes. For 300L and 150 L tank sizes, the appliance total energy for the week is roughly 30.5 kWh compared to a baseline appliance system with no thermal resource sharing at 33.8 kWh. At an electricity cost of $0.15/kWh, the cost savings for the integrated system is a little over $0.40/week. Furthermore, the savings is completely diminished when considering the required auxiliary power to support the exchange of heat between each appliance and storage tank. The impact of tank size should be explored further to identify a critical tank size where the system savings is no longer available. Accounting for all the domestic hot water needs of the home would generate an improved picture where integrated appliances have technical feasibility. </div><div><br></div>

The combination of the continuously growing demand of energy in the world, the depletion of oil and its sharp price increase, as well as the urgent need for cleaner and more efficient fuels have boosted the global trade of liquefied natural gas (LNG). Nowadays, there is an increasing interest on the design philosophy of the LNG receiving terminals, due to the fact that the existing technologies either use seawater as heating source or burn part of the fuel for regasifying LNG, thus destroying the cryogenic energy of LNG and causing air pollution or harm to marine life. This investigation addresses the task of developing novel systems able to simultaneously regasify LNG and generate electric power in the most efficient and environmentally friendly way.    Existing and proposed technologies for integrated LNG regasification and power generation were identified and simple, efficient, safe and compact alternatives were selected for further analysis. A baseline scenario for integrated LNG regasification and power generation was established and simulated, consisting of a cascaded Brayton configuration with a typical small gas turbine as topping cycle and a simple closed Brayton cycle as bottoming cycle. Various novel configurations were created, modeled and compared to the baseline scenario in terms of LNG regasification rate, efficiency and power output. The novel configurations include closed Rankine and Brayton cycles for the bottoming cycle, systems for power augmentation in the gas turbine and combinations of options. A study case with a simple and compact design was selected, preliminarily designed and analyzed according to characteristics and costs provided by suppliers. The performance, costs and design challenges of the study case were then compared to the baseline case. The results show that the study case causes lower investment costs and a smaller footprint of the plant, at the same time offering a simple design solution though with substantially lower efficiencies.

The building sector is responsible for approximately 40 % of the total energy usage in Sweden. In office buildings the heating, ventilation and air conditioning system can account for up to 55 % of the energy usage. In order to reduce the energy usage of the heating, ventilation and air conditioning system different control methods are often used. One of these control methods is demand controlled ventilation, where the ventilation system is controlled with regard to occupancy with the help of motion and/or CO2 sensors. The aim of this thesis was to determine the energy savings potential of a heat recovery unit as well as demand controlled ventilation in an office building. The effect of longer intervals between sensor control signals to the ventilation system was also investigated. This is done by creating schedules, gathered from actual building occupancy, that are being used to control the occupancy and ventilation in a building model in the building performance simulation software IDA ICE. As a reference building, the fifth floor of the LU1 section of the natural science building at Umeå University is used. The reference building consists of 40 offices for which the occupancies are known. The average occupancy for all the offices combined throughout the investigated time period is determined to be 34.8 %. The results from the simulations indicate that an energy savings potential of 52.98 % can be achieved by a heat recovery unit with an efficiency of 80 % or 95 %, when compared to not having a heat recovery unit. When implementing demand controlled ventilation an energy savings potential of 2.8-11.0 % can be achieved, with the energy savings potential decreasing when the efficiency of the heat recovery unit increases. Finally, it is shown that longer intervals between sensor control signals to the ventilation system leads to a small increase in energy usage and poorer indoor air quality.

No description available.

The aim of this study is to investigate the heat recovery potential in supermarket refrigeration systems using CO2 as refrigerants. The theoretical control strategy to recover heating demand from refrigeration system is explained thoroughly and the heat recovery process from two existing supermarket using CO2 booster units is analyzed and evaluated. The measured data of refrigeration systems is obtained through Iwmac interface, processed using Excel and Refprop. The aim is to see what control strategy is used in these systems and weather it matches the theoretical one and at what level heat is recovered from the system. Besides, a simulation model is made by EES to investigate the potential of higher rate of heat recovery in the supermarkets. The simulation results are compared with field measurement and validated by measured values. Then, the ability of refrigeration system to do heat recovery at quite high rates for covering the total heating demand without using parallel heating system is evaluated and efficiency of the system is calculated. At the next step the heat recovery potential at other refrigeration solutions such as R404A conventional and CO2-ammonia cascade systems are studied and the results are compared to booster units. Finally, the potential for selling heat from the refrigeration system in supermarket to district heating network is investigated. Two different scenarios are made for such purpose and the results are evaluated. The heat recovery control strategy of existing supermarkets does not match the theoretical strategy and regarding the capacity of the system, heat is recovered to low extent. Simulation shows that heat can be recovered to higher extent at quite high heating COP of 3-5. Additionally the other heat recovery solutions for R404A conventional and CO2-ammonia cascade systems are found to be competitive to CO2 booster system.  The analysis of selling heat to district heating network shows that CO2 booster system is capable of covering the demand at reasonable heating COP as the first priority and selling the rest to district heating network at heating COP of 2 as second priority.

By partly replacing the use of primary energy sources with waste heat recovery, climate and environmental goals for the future will be closer at hand. This thesis investigates the waste heat potential of Alfa Laval’s vacuum brazing furnaces in Ronneby and alternative ways of integrating the furnace’s waste heat into the building’s HVAC system. The main challenge was the low-temperature qualities associated with the cooling water, which constituted an obstacle to recovering waste heat without any additional equipment, such as a heat pump. Tests and analyses performed in this thesis are, therefore, mainly aimed at raising the temperature quality of the cooling water. A test was conducted on the cooling system to calculate the energy losses with regards to the cooling water. In one 11-hour cycle, 1546 kWh of electricity was used to heat the furnace. Out of that, 1360 kWh was cooled off to the atmosphere. Additionally, a test on the furnace’s clean-up cycle was performed. The maximum cooling water temperature reached during this test was 44 C. This shows excellent potential in the possibility of recovering the waste heat without any additional equipment. Further, this thesis aims to broaden the knowledge around areas concerning increased cooling water temperatures, which, during the writing, seemed to have a gap in documented sources. The results of this thesis indicate that a temperature quality increase of the furnaces’ cooling water is possible. Cooling system changes have also been suggested, which is necessary for an efficient and safe heat recovery.

A modeling tool was developed capable of evaluating the thermal performance of a commercial building, for the purpose of objectively quantifying the impacts of both operational changes and technological retrofits. The modeling tool was created using a steady state energy balance approach, discretized into half hour time steps to capture the time varying characteristics of the rate of heat transfer through the building envelope, the ventilation systems, appliance heat gains, heat generated by electricity consumption, solar energy transfer and space heating through exhaust gas energy recovery with the TEG POWER system. Several experimental facilities were used to validate the modeling tool, and to provide inputs to the case studies presented. Data from two separate commercial baking operations was collected, and was shown to be in agreement with the model predictions with a 7% error. Several energy conservation measures were simulated, including switching to idealized methods of exhaust ventilation, sealing and insulating appliances, shutting down appliances during unoccupied hours, and the inclusion of exhaust gas energy harvesting. Implementing all four conservation measures at a single restaurant had the effect of reducing electricity consumption by 14% or approximately 17,700 kWh (64 GJ), and reducing natural gas consumption by 60% or approximately 18,200 m3 (608 GJ) annually. In contrast, proceeding directly to the energy harvesting solution, and bypassing other conservation measures, only allowed for 20% of the total potential energy savings to be realized. If the concepts identified are implemented across 2000 comparable restaurants in Ontario, there is a potential to reduced electricity consumption by 44.4 million kWh and natural gas consumption by 33.7 million cubic meters annually. The measures would effectively eliminate 65,500 metric tonnes of CO2 emissions every year. / Thesis / Master of Applied Science (MASc)

no abstract provided by author / M.S.

The purpose of this study is to develop and demonstrate a novel process for heat recovery from hot exhaust gases. This process involves direct contact of a hot gas with a countercurrently flowing vibrofluidized bed of cold solid. Based on a simple heat-transfer model, an "apparent" heat-transfer coefficient between the air and solid was calculated. The temperature profile of the air as a function of heat-exchanger length was used to determine the "apparent" area for heat transfer in the model. Analysis, based on factorial-design experiments, showed that increasing the airflow rate and applied vibrational intensity, as well as decreasing the baffle height of the system served to increase the "apparent" heat-transfer coefficient. Increasing the solid flow rate produced higher heat-transfer coefficients only when the baffle was lowered past a certain "critical" height. Under optimum conditions investigated, a gas-to-bed heat-transfer coefficient of about 270 W/m²-K was obtained with a heat exchanger length of 0.71 m. "Cold-flow" experiments of the system were used to explain the heat-transfer trends. A condition analogous to "flooding" determined the operating range of the "flowing" vibrofluidized-bed heat exchanger. As a result of this work, significant progress has been made on the evolutionary development of a vibrofluidized-bed heat exchanger to be used for future heat recovery. / M.S.