Exploring the Control of the Position of the Isotherms of the Heat Pump Cycle in an Air Handling Unit: An Experimental study

The use of heat pumps in the building heating and cooling supply chain is increasing, and air-to-air heat pumps are increasingly being installed in modern air handling units. The energy conversion modes of such devices are constantly changing due to the constant change in the state of the outdoor air (temperature, humidity). Flexibility, the ability to efficiently and rationally respond to ambient air parameters, is an important feature of choosing the operating mode of energy transformers and their control. The overall seasonal efficiency of the air handling unit depends on it. Modern commercial heat pumps have two control degrees of freedom. They have a variable-speed compressor and an electronic expansion valve. This combination of control components once made it possible to increase the seasonal efficiency of heat pumps. For a long time, the possibility of controlling the cycle in this way prevailed, and only electronic control tools were improved. Little attention is paid to how the changes in the thermodynamic cycle are combined with the energy demands of air preparation corresponding to the outdoor temperature. It would be relevant to look for additional components of the heat pump circuit that could control its operating cycle, which could increase the efficiency indicators of the air preparation process. The article’s authors seek to introduce an additional component into traditional measures of heat pump control, providing the third degree of freedom of the control cycle. For this purpose, studies are being conducted to experimentally assess the impact of the volume of the heat pump system on the shifts of the isotherms of its thermodynamic operating cycle. The results show that the system volume parameter has the potential for regulation capabilities in controlling the operation of a heat pump, so it is worthwhile to further develop and study such a technological solution in more detail

Energy Efficiency Improvement Potential in Historical Brick Building

Energy efficiency in historical heritage buildings is viewed as a taboo because these buildings usually are law-protected and no energy efficiency measures that would change the appearance of building are allowed. In this paper we look at a potential of increasing energy efficiency level in historical buildings. Measurements to determine energy efficiency of a historical brick building have been done, which also give the possibility to determine the potential of energy efficiency measures in this building

Mathematical Model of Packed Bed Solar Thermal Energy Storage Simulation

Mathematical model has been developed to assess the effects of using phase change materials (PCM) in fully mixed water accumulation tank. Packed bed system of spheres with diameter of 40 mm have been considered as an option to increase energy storage density. A continuous phase model has been applied to analyse the influence of phase change during a charging and discharging processes. The methodology for calculating energy mass flow, density of water, heat transfer between layers, temperature for each time step and energy transferred to PCM is given. Single type of PCM with melting temperature of 55 °C and multiple type PCM system (65°, 55°, 45° and 35° C) are compared. It is found that multiple type PCM system compared to only water and single type PCM systems, provide lower return temperatures and higher energy density

Storage of Solar Energy by Application of Thermally Stratified Phase Change Materials. Experimental Research and Optimization

Main aspect when solar thermal energy storage (TES) is considered is thermal storage capacity in form of sensible heat, latent heat or chemical energy. In case of solar systems, solar TES provide a solution for mismatch between energy supply and energy demand. Higher capacity reduces the size of the system and increases overall efficiency [1]. Water is used in almost every system as working fluid due to characteristics like nontoxicity, abundance, high specific heat and suitability for wide range of heating applications [2]. Since the temperatures that occur in solar heat storage is above 0 °C and below 100 °C, no phase change of water can occur and energy is stored only as sensible heat. Wide variety of phase change materials (PCM) have been created and accepted as suitable to make use of latent heat storage (LHS). While use of phase change materials in latent thermal heat storage have been studied thoroughly, a lot less studies have been looking into use of different melting temperature phase change materials to enhance the efficiency of solar system. Solar systems in many cases are used in existing buildings where available space is limited. By increasing efficiency and energy density, it is possible to store more and take less space

Storage of Solar Energy in Fully Mixed Medium by Application of Phase Change Materials

Numerical calculation has been used to assess the effect of using PCM in fully mixed water accumulation tank. Packed bed sys-tem of spheres with diameter of 40 mm have been considered as option to increase energy storage density. Random close pack-ing factor of 63% have been chosen, since author believes that if PCM spheres would be introduced on the site, it would be dif-ficult to use tools like shakers to reduce the volume of voids. Change of specific heat for PCM before and after phase change has been taken into account in energy equations. Four types of PCM are used, described by their melting temperature in degrees Celsius – 65, 55, 35 and 25. Multiple type PCM system is found to provide better solution compared to both water alone and single type PCM systems, since it can work at lower temperatures and provide higher energy density compared to water alone system

Conceptual Design of Experimental Solar Heat Accumulation System with Phase Change Materials

The research on solar heating systems often is faced with choice of carrying out experiments in real systems with changing parameters or to use modelling software with constant parameters but many undefined parameters or assumptions. The design of experimental system for simulating solar heat accumulation is proposed in this paper. The proposed design allows testing of phase change materials which provide higher thermal density compared to water. Results from computational fluid dynamic simulations carried out by other studies have been analysed for implementation into designing of the tank. All of these factors have been taken into account to create a system that resembles real case and can simulate for a long periods of time

Modelling of phase change in spheres for applications in solar thermal heat storage systems

Thermally stratified solar energy accumulation tanks are an effective technique that is widely used in solar collector systems. Thermal energy storage (TES) systems using phase change materials (PCM) is another technology that can be applied to accumulation tanks to improve thermal energy density. To analyze the impact of placing PCM inside the tanks, it is crucial to understand the parameters that describe the processes that take place in each of the PCM sphere. In this study COMSOL Multiphysic is used to analyze the energy accumulation in PCM through thermal conductivity, which is one of the first steps to full simulate PCM in stratified water environment. The assumption stated by other studies that for low Rayleigh numbers the thermal conductivity is the dominant heat transfer principle is tested by comparing the model to experimental data. The simulation results showed that the thermal conductivity method can be successfully used to model the process until the material has melted, suggesting that additional effects has to be considered to increase the accuracy of model

Historic Brick Building Exterior Wall Insulation Materials

In Latvia there are a great number of old brick buildings of historic value and which is an evidence of the architecture of that time. These buildings are monuments of masonry traditions and culture and a significant part of housing stock. With building standards becoming ever higher, old buildings struggle to keep up. To reduce energy consumption of old buildings, an increase of heat resistance for envelope is required

Experimental study on the optimisation of staged air supply in the retort pellet burner

The use of biofuels for heating purposes is beneficial from a greenhouse gas emission point of view. But combustion of solid biofuels typically is related with high emission rates of CO, NOx, PAHs, VOCs and particle matter. The most important factor that is affecting the formation of harmful emissions is the way the combustion process is organised. The amount of air injected and approach for the air supply system, are the most important factors affecting combustion process. Air staging is one of the most effective technical solutions for achieving complete combustion and low emissions. The main idea of air staging is to inject air into different zones of a combustion process. The main goal of this study is to optimise pellet combustion process in a 500 kW boiler with staged air supply. The research is based on on-site experiments and application of scientific instrumentation. Fly-away unburned fuel particles were discovered during the on-site experiments. Reduction of the amount of fly-away particles was set as a target function for the optimisation. The amount of emissions (CO, NOx and particle matter) and the amount of incombustibles in fly ashes were identified. Two different solutions with applied secondary air supply nozzles were analysed. The results of the study show that even small changes in the way the combustion air is injected can significantly affect the combustion process

Experimental Study on the Optimisation of Staged Air Supply in the Retort Pellet Burner

The use of biofuels for heating purposes is beneficial from a greenhouse gas emission point of view. But combustion of solid biofuels typically is related with high emission rates of CO, NOx, PAHs, VOCs and particle matter. The most important factor that is affecting the formation of harmful emissions is the way the combustion process is organised. The amount of air injected and approach for the air supply system, are the most important factors affecting combustion process. Air staging is one of the most effective technical solutions for achieving complete combustion and low emissions. The main idea of air staging is to inject air into different zones of a combustion process. The main goal of this study is to optimise pellet combustion process in a 500 kW boiler with staged air supply. The research is based on on-site experiments and application of scientific instrumentation. Fly-away unburned fuel particles were discovered during the on-site experiments. Reduction of the amount of fly-away particles was set as a target function for the optimisation. The amount of emissions (CO, NOx and particle matter) and the amount of incombustibles in fly ashes were identified. Two different solutions with applied secondary air supply nozzles were analysed. The results of the study show that even small changes in the way the combustion air is injected can significantly affect the combustion process