A case study for influence of building thermal insulation on cooling load and air-conditioning system in the hot and humid regions

Ensuring the effective thermal insulation in regions, where the cooling requirement of building with respect to heating requirement is dominant, is very important from the aspect of energy economy. In this study, the influence of thermal insulation on the building cooling load and the cooling system in case of air-conditioning by an all-air central air-conditioning system was evaluated for a sample building located in Adana, based on the results of three different types of insulation (A, B and C-type buildings) according to the energy efficiency index defined in the Thermal Insulation Regulation used in Turkey. The operating costs of the air-conditioning system were calculated using cooling bin numbers. Life-cycle cost analysis was carried out utilizing the present-worth cost method. Results showed that both the initial and the operating costs of the air-conditioning system were reduced considerably for all three insulation thicknesses. However, the optimum results in view of economic measurements were obtained for a C-type building. The thickness of thermal insulation for the buildings in the southern Turkey should be determined according to the guidelines for a C-type building.     

Sizing windows to achieve passive cooling, passive heating, and daylighting in hot arid regions

The study aims to demonstrate a process for sizing the windows of a passive solar house case study that involves a multi-decision problem. The initial design was created in an earlier stage, during which, decisions on broader issues such as building orientation, form design, and the appropriate spatial organization of the building were made. It applies a variety of methods to generate and evaluate design alternatives such as rules of thumb and LCR method for passive heating; earth cooling and cross ventilation rules of thumb for passive cooling; and dylighting factor for daylighting. At the end, the study makes preliminary performance estimates between two alternatives to choose a final solution.     

Improvement of thermal performance of mortars by using heat storage aggregate made with industrial by-product to reduce cooling load

The usage of waste materials as building materials can be an important method to reduce energy consumption and decrease natural resource usage in the construction industry. In this work, phase change materials (PCMs) were incorporated with industrial by-product materials as an aggregate to produce mortars, which can improve the energy efficiency and improve the environment of buildings. Bottom ash (BA), a by-product from coal-fired power plants, was directly impregnated into paraffin, a PCM, to produce a heat storage aggregate (HSA). The raw materials of the HSA production were characterized by X-ray diffraction, scanning electron microscope, and differential scanning calorimeter. The mortar mixes had a water to cement ratio of 1:2 and a sand to cement ratio of 2.5:1. Six mixtures were prepared with different HSA amounts of 0%, 10%, 20%, 30%, 40%, and 50% by volume. The compressive strength, density, and thermal properties of the mortars were investigated. The results and analyses showed that the compressive strength and density of the mortars decreased with increasing HSA amounts. The thermal conductivity of HSA mortars slightly decreased for increasing levels of HSA. In addition, HSA mortars showed a significant increase in time lags when the HSA content increased, up to approximately 165% to 197% higher than that of the control mortars. HSA levels in mortars can play an important role in improving the heat conductance into buildings.     

Further progress in the research of fin‐based passive cooling technique for the free‐standing silicon photovoltaic panels

The paper deals with a passive air‐based cooling technique of photovoltaic (PV) panels in operating conditions. Cooling technique is done by specific type of using aluminium fins, and its main purpose is to increase the electrical efficiency of the PV panel. An increase in electrical efficiency can be achieved because of temperature degradation effect, where the PV panel yields less power at higher operating temperatures (the PV panel's efficiency can drop by up to 0.5%/°C). To confirm a cooling technique, a medium‐sized PV system was used in a 2‐month experiment. The experiment was done in realistic operating conditions, and all working parameters were thoroughly measured. After the analysis of the data, no significant raise in electrical efficiency was recorded throughout the experiment. A numerical approach was conducted, based on gained experimental data. Developed numerical model gave explanations of experimental results and provided an insight in heat flow through the PV cell. Later on, developed numerical model was used to propose new cooling variations of the fin‐based technique and to further examine the overall potential of air based passive cooling techniques. It was shown that cooling effect by up to 5°C is a realistic expectation for this technique in described operating conditions.     

Performance assessment of a passive core cooling design for cylindrical lithium‐ion batteries

Battery thermal management (BTM) system is an indispensable component for large‐sized lithium‐ion battery packs used in aerospace and automotive applications. Besides providing a proper temperature range for batteries to operate, thus improving their efficiency, lifespan, and safety, the BTM system also needs to be well designed with considering the cost, weight, and practicability. In this paper, an internal passive BTM system is proposed for the cylindrical Li‐ion batteries. The design embeds a phase change material (PCM) filled mandrel inside the battery to achieve the cooling effect. A thermal test cell is first fabricated and tested in a wind tunnel under different cooling scenarios, and it is also used to verify a numerical thermal model. The proposed BTM system is further examined through the model and found to be able to create a preferable environment for batteries to operate. Specifically, the core BTM system consumes less PCM and achieves lower temperature rises and more uniform temperature distributions than an external BTM system. The proposed design can also exert its full latent heat to manage the heat generated from the battery without having a thermally conductive matrix, which is usually composite with PCM in external BTM systems. In addition, experiments show that the battery equipped with the proposed BTM system is ready for intensive cycling tests.     

Parametric analysis of space cooling systems based on night ceiling cooling with PCM‐embedded piping

A parametric analysis is conducted for space cooling systems based on cold water flowing, during the night, within regularly arranged pipes embedded in a layer of phase change material (PCM), located among the structural layers of the ceiling. The introduced PCM layer in conjunction with night cooling add to the usual ceiling cooling systems offers the advantages of low energy consumption, high cool storage capacity, operation under reduced night electricity price, smoothing of electricity consumption by eliminating daily peak loads, improved thermal comfort and elimination of ceiling dripping. Our parametric analysis is based on a transient three‐dimensional finite‐difference solution of the related heat‐transfer problem for various values of all the main system parameters. PCM phase change process is simulated by using the effective thermal capacity function, which is determined experimentally for PCM suitable for air‐conditioning applications. Our tests showed that the main parameters of the system are pipe spacing, PCM layer thickness, pipe depth within the ceiling, cooling water inlet temperature, night cooling duration and PCM properties (thermal conductivity, phase change heat and ends of phase change temperature range). The effect of all the above parameters is analysed and suggestions are made for selecting the proper combinations of their values in order to obtain the lowest energy consumption in conjunction with the highest level of thermal comfort. Copyright © 2010 John Wiley & Sons, Ltd.     

Applying support vector machine to predict hourly cooling load in the building

In this paper, support vector machine (SVM) is used to predict hourly building cooling load. The hourly building cooling load prediction model based on SVM has been established, and applied to an office building in Guangzhou, China. The simulation results demonstrate that the SVM method can achieve better accuracy and generalization than the traditional back-propagation (BP) neural network model, and it is effective for building cooling load prediction.     

Integration of multiple passive load mitigation technologies by automated design optimization—The case study of a medium‐size onshore wind turbine

The present work considers the application to a medium‐size onshore wind turbine of passive load mitigation technologies, first individually and then integrated together. The study is conducted with the help of a comprehensive automated design optimization procedure, which eases the generation and comparison of consistent solutions, each satisfying the same overall requirements. Passive load mitigation is here obtained by inducing bend‐twist coupling to the blades. The coupling is generated by rotating the fibers of anisotropic laminates, by the aerodynamic sweeping of the blade and by offsetting the spar caps in opposite directions on the pressure and suction sides. The first two solutions yield significant benefits, while the third, for this particular wind turbine, is ineffective. In addition, the typical power losses associated with bend‐twist coupled blades are reduced by a novel regulation strategy that varies the fine pitch setting in the partial load region. After having considered each load mitigation technology by itself, fiber rotation and sweeping are combined together and used to design a rotor with a larger swept area. The final design generates cost of energy savings thanks to a large‐diameter, highly coned, soft‐in‐bending rotor that results in lower turbine costs and a higher energy capture compared with the baseline design.     

Energy and thermal performance of heat pipe/cooling coil systems in hot‐humid climates

The objective of this study is to evaluate the magnitude of reduction in cooling and reheat energy when a heat pipe system is incorporated with the cooling coil of an air‐conditioning system. The heat pipe/cooling coil (HP/CC) system performance is determined by several parameters that are related to both the air‐conditioner cooling coil and the heat pipe physical characteristics as well as the condition of the air entering and leaving the system. In order to appreciate the impact of these parameters and their relative influence on energy consumption and the required indoor air conditions, a simple mathematical model incorporating the parameters of HP/CC is formulated. The model describes the overall system performance at varying entering and leaving air conditions. The model is then applied to a case study as an example of an application to investigate these relationships for a better understanding of the system behaviour and the influencing design parameters. It is evident that due to the coupling nature of the heat pipe and the cooling coil actions, a unique system performance will be obtained for each combination of heat pipe effectiveness and cooling coil by‐pass factor. A proper selection of both the heat pipe and the cooling coil characteristics is found to be necessary for a satisfactory performance under the given operating conditions. Copyright © 2000 John Wiley & Sons, Ltd.     

Three-dimensional transient cooling simulations of a portable electronic device using PCM (phase change materials) in multi-fin heat sink

Transient three-dimensional heat transfer numerical simulations were conducted to investigate a hybrid PCM (phase change materials) based multi-fin heat sink. Numerical computation was conducted with different amounts of fins (0 fin, 3 fins and 6 fins), various heating power level (2 W, 3 W and 4 W), different orientation tests (vertical/horizontal/slanted), and charge and discharge modes. Calculating time step (0.03 s, 0.05 s, and 0.07 s) size was discussed for transient accuracy as well. The theoretical model developed is validated by comparing numerical predictions with the available experimental data in the literature. The results showed that the transient surface temperatures are predicted with a maximum discrepancy within 10.2%. The operation temperature can be controlled well by the attendance of phase change material and the longer melting time can be conducted by using a multi-fin hybrid heat sink respectively.     

机坪辐射对机场建筑空调冷负荷的影响

从民用机场建筑地理位置,建筑结构的生,探讨机坪辐射现象对候机楼为主的民用机场建筑空调冷负荷的影响,宽阔,平坦的,大面积的停机坪在夏季强烈阳光照射下形成一个巨大的发射平面,与阳光共同形成机坪辐射,而这种辐射所形成的最大负荷与建筑物的温差传热最大值出现在同一时段,形成空调系统的高峰负荷,因此,机坪辐射对机场建筑空调冷负荷的影响应是一个不容忽视的因素,对于候机楼等机坪周边机场建筑的空调冷负荷,材料选择以及空调送风系统的布置等,除了考虑一般影民用建筑空高冷负荷的因素外,应充分考虑机坪辐射的影响。     

Numerical simulation of steam–water two‐phase flow under dynamic load

A separated‐phase physical model for steam–water two‐phase flow on a rotating platform was developed. The mesh generation for a horizontal pipe was conducted, and the finite volume method was used to discretize the equations. Equations were solved with the SIMPLE algorithm after setting the initial and boundary conditions. Predicted results were compared with experimental data, and they agreed well with each other. The results showed that the fluid outlet pressure and pressure drop in the test section increased with increasing dynamic load. However, the effective heat transferred to the fluid decreased with the increase of dynamic load. The developed model can be used to simulate the gas–liquid two‐phase flow under different gravity or rotary conditions.     

Properties and performance of advanced reflective paints to reduce the cooling loads in buildings and mitigate the heat island effect in urban areas

High reflective coatings and paints spread on the roof and walls can be very useful to reduce the cooling loads in buildings to ensure thermal comfort in the built environment. The solar reflectance of construction and cooling materials was measured with a spectrophotometer. A surface temperature monitoring campaign compared the thermal profiles of typical Italian construction materials with an innovative sustainable white paint, obtained with a special mixture of milk and vinegar of very high solar reflectance. Two building-integration cool-roof campaigns were run in the experimental building, Casa Intelligente of ENEA, in which indoor and outdoor air temperature and roof surface temperatures were monitored. This campaign, run in the summer of 2005 and 2006, allowed us to verify the influence of cool roofs to mitigate indoor air temperatures and to compare the behaviour of different cool-roof technologies.     

Development and energy evaluation of phase change material composite for building energy‐saving

Phase change materials (PCMs) contributed to building energy‐saving and thermal comfort through increasing the thermal capacity of building envelopes. In this study, a phase change material composite was developed by using the PCMs mixture of capric acid (CA) and lauric acid (LA) as the primary phase change energy storage agent and using the solid waste fly ash as a carrier material. The results showed that for Guangdong, the ideal PCMs mixture should have a transition temperature of 25.5^oC, which could be obtained by using a mass ratio of CA/LA of 4:6. Then, experiment results also indicate that the optimum adsorption ratio of 2:1 (FA/PCMs) was detected for the synthesis of this FA/PCMs composite, which has the latent heat of 45.38 J/g and exists excellent thermal reliability. Moreover, simulation results by using EnergyPlus show that the proposed composite has a good building energy‐saving effect.     

Characteristics of solidification and melting in the water‐saturated porous medium cooled from the top (response of solid–liquid interface due to time‐varying cooling temperature)

This paper describes the response of a solid–liquid interface in a water‐saturated porous box to a time‐varying cooling temperature. Spherical soda glass beads with an average diameter of 5 mm constitute a porous matrix. The lower boundary of the matrix is kept at 8°C at all times during the experiments, while the upper plate is set at a temperature, lower than the liquids 0°C. After a steady state is reached, the cooling temperature is varied periodically with a fixed amplitude of 4°C. The solid–liquid interface positions are measured and the characteristic amplitudes and the phase delays are determined for different periods ranging from one hour to ten hours at four different cooling temperatures. It has been found that the amplitude of the interface is proportional to the cooling temperature period length, and that a thicker solid layer causes larger phase delays. The proposed one‐dimensional model has been found appropriate for predicting the response of the horizontally averaged position of the solid–liquid interface. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 330–341, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20015     

Fatigue and extreme load reduction on two‐bladed wind turbines using the flexible hub connection

The load reduction potential in regular operation and the design drivers of a flexible hub connection on two‐bladed turbines are presented in this paper. Developed for the two‐bladed Skywind 3.4 MW wind turbine, the flexible hub connection integrates an additional, multidirectional elasticity between the hub mount and the nacelle carrier to reduce the load transfer into the support structure. The stiffness and damping properties of the interface connection determine the load amplitudes of the system and influence the overall turbine dynamics. Consequently, the design relevant operating scenarios change due to a potential dynamic instability, resonance, or violation of deflection margins in comparison with a nonflexible hub connection. The system's capability to reduce fatigue and ultimate loads is assessed in several turbulent inflow conditions and transient operating states, while taking into account the operating limits of displacements. A permutation of the dynamic coupling parameters is conducted to characterize the sensitivity of load characteristics to the design variables. By identifying the critical operating conditions, it is possible to provide design guidelines for an effective optimization strategy.     

Development of the three-dimensional Numerical Generation of Response Factors (NGRF) method of conductive temperatures in passive cooling earth-contact components

This paper reports on the development and application of a method for the numerical prediction of temperatures within passive cooling components. In previous studies the basic idea was presented in an alternate form for the prediction of earth-contact heat transfer. The new method is demonstrated to be fast, accurate and flexible as a result of incorporating elements of the response factor method into a finite volume technique based numerical model. Initially, a ‘pre-processing’ procedure is required to generate a certain number of hours for use as a time series by the response factor technique in the second stage of the method. It is here shown that even a reduced number of temperature response factors, e.g. 50 h, is sufficient to obtain accurate predictions of the component’s hourly temperature profile up to 1 year ahead.This study develops the equations addressing temperature profiles in structural components. The ‘state of the art’ of the presented method corresponds in the way that the conductive temperature response factors are calculated being numerically in the three-dimensional space. The method solves the three-dimensional earth-contact temperature profiles, which interact with indoors and outdoors temperature profiles. Once the numerical temperature response factors time series of an earth-contact component’s grid node have been generated then its future thermal performance due to any surrounding temperature variation can be predicted fast and accurately. The structural earth-contact passive cooling components’ response factors are generated by a three-dimensional numerical model, with no need of past experimental data and stored to be used at any time in future. The method is given the name NGRF (Numerical Generation of Response Factors). The way that the temperature response factors are determined in the three-dimensional space targets in the improvement of the prediction of earth-contact temperature profiles.     

Energy performance of a hybrid space-cooling system in an office building using SSPCM thermal storage and night ventilation

Thermal performance of a hybrid space-cooling system with night ventilation and thermal storage using shape-stabilized phase change material (SSPCM) is investigated numerically. A south-facing room of an office building in Beijing is analyzed, which includes SSPCM plates as the inner linings of walls and the ceiling. Natural cool energy is charged to SSPCM plates by night ventilation with air change per hour (ACH) of 40 h⁻¹ and is discharged to room environment during daytime. Additional cool-supply is provided by an active system during office hours (8:00-18:00) necessary to keep the maximum indoor air temperature below 28 °C. Unsteady simulation is carried out using a verified enthalpy model, with a time period covering the whole summer season. The results indicate that the thermal-storage effect of SSPCM plates combined with night ventilation could improve the indoor thermal-comfort level and save 76% of daytime cooling energy consumption (compared with the case without SSPCM and night ventilation) in summer in Beijing. The electrical COPs of night ventilation (the reduced cooling energy divided by fan power) are 7.5 and 6.5 for cases with and without SSPCM, respectively.     

Development of a thermally enhanced frame wall with phase‐change materials for on‐peak air conditioning demand reduction and energy savings in residential buildings

This paper presents the development of a thermally enhanced frame wall that reduces peak air conditioning demand in residential buildings. A frame wall that integrates a highly crystalline paraffin phase‐change material (PCM), via macro‐encapsulation, was developed, constructed, and evaluated. This prototype wall is referred to as phase‐change frame wall (PCFW). Results from field testing show that the PCFW reduced wall peak heat fluxes by as much as 38%. For a period of several days that included walls facing different directions, the average wall peak heat flux reduction was approximately 15% when PCFWs with a 10% concentration of PCM (based on indoor sheathing weight) were used and approximately 9% when a 20% PCM concentration was used. The average space‐cooling load was reduced by approximately 8.6% when 10% PCM was applied and 10.8% when 20% PCM was used. The level of insulation in the PCFWs that were tested was 1.94m²K/W (R‐11). Copyright © 2005 John Wiley & Sons, Ltd.     

High performance cooling of a HVDC converter using a fatty acid ester-based phase change dispersion in a heat sink with double-layer oblique-crossed ribs

The paper concerns with a high performance cooling method for a HVDC converter using fatty acid ester-based phase change dispersion (PCD) in a heat sink with double-layer oblique-crossed ribs. Thermo-physical properties of PCDs were first characterized under both solid and liquid states, and the cooling performance of the heat exchanger was then experimentally examined, by heating two copper blocks clamped closely to the aluminium heating surfaces. A three-dimensional Euler-Euler multiphase approach was further performed to evaluate the thermal performance under different operating conditions including heating power, flowrate and PCD concentration. The results showed that the viscosity of PCD can be a 100 times that of water, but the increased pumping power was only ~17.01% on average. The use of the PCD achieved a lower temperature of heat sink and fluid than that of water under the same set of conditions due to the latent heat of the PCM, thus enabling a safer and cooler environment for temperature-sensitive HVDC components such as insulated gate bipolar transistors (IGBT). An optimal set of working conditions was proposed and a flowrate of 8 L/min under a heating power of 1.1 kW and a PCM concentration of 25% was recommended for industrial cooling operations.