Numerical analysis of effect of shape-stabilized phase change material plates in a building combined with night ventilation

Effect of shape-stabilized phase change material (SSPCM) plates combined with night ventilation in summer is investigated numerically. A building in Beijing without active air-conditioning is considered for analysis, which includes SSPCM plates as inner linings of walls and the ceiling. Unsteady simulation is performed using a verified enthalpy model, with time period covering the summer season. Effects of the following factors on room air temperature are investigated: the thermophysical properties of the SSPCM, the thickness of SSPCM plate and air change per hour (ACH) at both nighttime and daytime. The results show that the SSPCM plates could decrease the daily maximum temperature by up to 2 °C due to the cool storage at night. The appropriate values for melting temperature, heat of fusion, thermal conductivity and thickness of SSPCM plates need to be considered and calculated according to the climate conditions and building structure. The ACH at night needs to be as high as possible but the ACH at daytime should be controlled.     

An assessment of mixed type PCM-gypsum and shape-stabilized PCM plates in a building for passive solar heating

Thermal performance of two phase change material (PCM) composites, mixed type PCM-gypsum and shape-stabilized PCM plates, has been numerically evaluated in a passive solar building in Beijing with an enthalpy model. Effects of the melting temperature and phase transition zone of the PCM are analyzed and a comparison between the two types of PCM composites is performed. The results show that: (1) for the present conditions, the optimal melting temperature is about 21 °C; (2) PCM composites with a narrow phase transition zone provide better thermal performance; (3) both mixed type PCM-gypsum and shape-stabilized PCM plates effectively shave the indoor temperature swing by 46% and 56%, respectively; (4) the shape-stabilized phase change material (SSPCM) plates respond more rapidly than the mixed type PCM-gypsum and prove to be thermally more effective in terms of utilizing the latent heat.     

Performance of a hybrid heating system with thermal storage using shape-stabilized phase-change material plates

Performance of a hybrid heating-system, combined with thermal storage using shape-stabilized phase-change material (SSPCM) plates, is investigated numerically. A direct gain passive solar house in Beijing is considered, which includes SSPCM plates as the inner linings of walls and the ceiling. Unsteady simulation is performed using a verified enthalpy model, with a time period covering the winter heating-season. Additional heat supply is employed during load hours at late night and early morning (23:00–07:00 in Beijing) or during the whole day necessary to keep the minimum indoor air temperature above 18 °C. The results indicate the thermal storage effect of SSPCM plates, which improves the indoor thermal comfort level and saves about 47% of normal-and-peak-hour energy use and 12% of total energy consumption in winter in Beijing.     

Assessment of Building External Wall Thermal Performance Based on Temperature Deviation Impact Factor under Discontinuous Radiant Heating

As the variation and timely meeting thermal environment requirement of indoor air temperature has a close relationship with the thermal performance of building external wall under discontinuous radiant heating condition, one appropriate assessment method or index for assessing the building external wall thermal performance is very necessary. In order to reasonably evaluate the thermal performance of external wall under discontinuous radiant heating condition and build the direct connections and interactions among the indoor air temperature, external wall inner surface temperature and outdoor air temperature, the first and second impact factors of temperature deviation were established, based on one mathematical model of room heat transfer. For one experimental room and four types of external walls under discontinuous radiant heating condition, both the influence of the external wall inner surface temperature deviation on the indoor air temperature and that of the outdoor air temperature deviation on the external wall inner surface temperature were determined effectively with the first and second impact factors of temperature deviation. In addition, favourable performance for the self-insulation and inner insulation walls were found, due to their superiority in effectively and timely improving the indoor thermal environment under discontinuous radiant heating condition.     

Thermal characteristics of shape-stabilized phase change material wallboard with periodical outside temperature waves

Thermal characteristics of shape-stabilized phase change material (SSPCM) wallboard with sinusoidal temperature wave on the outer surface were investigated numerically and compared with traditional building materials such as brick, foam concrete and expanded polystyrene (EPS). One-dimensional enthalpy equation under convective boundary conditions was solved using fully implicit finite-difference scheme. The simulation results showed that the SSPCM wallboard presents distinct characteristics from other ordinary building materials. Phase transition keeping time of inner surface and decrement factor were applied to analyze the effects of PCM thermophysical properties (melting temperature, heat of fusion, phase transition zone and thermal conductivity), inner surface convective heat transfer coefficient and thickness of SSPCM wallboard. It was found that melting temperature is one important factor which influences both the phase transition keeping time and the decrement factor; for a certain outside temperature wave, there exist critical values of latent heat of fusion and thickness of SSPCM above which the phase transition keeping time or the decrement factor are scarcely influenced; thermal conductivity of PCM and inner surface convective coefficient have little effect on the phase transition keeping time but significantly influence the decrement factor; and the phase transition zone leads to small fluctuations of the original flat segment of inner surface temperature line. The results aim to be useful for the selection of SSPCMs and their applications in passive solar buildings.     

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.     

Performance of shape-stabilized phase change material wallboard with periodical outside heat flux waves

Numerical simulations were carried out to investigate the performance of shape-stabilized phase change material (SSPCM) wallboard with sinusoidal heat flux waves on the outer surface and compared with traditional building materials – brick, foam concrete and expanded polystyrene (EPS). One-dimensional enthalpy equation was solved using control volume-based implicit finite-difference scheme. Time lag (φ), decrement factor (f) and phase transition keeping time (ψ) of inner surface were applied to analyze the effects of PCM thermo-physical properties, inner surface convective heat transfer coefficient and thickness of SSPCM wallboard. The results showed that for SSPCM, there exist two flat segments within one wave length period of inner surface heat flux lines and it has larger time lag and lower decrement factor than those three ordinary building materials. It was found that melting temperature and thermal conductivity of SSPCM have little effects on φ, f and ψ, which is different from the case of temperature waves; for a certain outside heat flux wave, there exist critical values of latent heat of fusion and thickness of SSPCM above which the heat flux wave amplitude can be diminished to zero; inner surface convective heat transfer coefficient is one important factor which significantly influences the decrement factor; and the phase transition zone leads to small fluctuations of the original flat segments of inner surface heat flux line.     

Thermal performance of phase change material energy storage floor for active solar water-heating system

The conventional active solar water-heating floor system contains a big water tank to store energy in the day time for heating at night, which takes much building space and is very heavy. In order to reduce the water tank volume or even cancel the tank, a novel structure of an integrated water pipe floor heating system using shape-stabilized phase change materials (SSPCM) for thermal energy storage was developed and experimentally studied in this paper. The thermal performances of the floors with and without the SSPCM were compared under the intermittent heating condition. The results show that the Energy Storage Ratio (ESR) of the SSPCM floor is much higher than that of the non-SSPCM floor; the SSPCM floor heating system can provide stable heat flux and prevent a large attenuation of the floor surface temperature. Also, the SSPCM floor heating system dampens the indoor temperature swing by about 50% and increases the minimum indoor air temperature by 2°C–3°C under experimental conditions. The SSPCM floor heating system has a potential of making use of the daytime solar energy for heating at night efficiently.     

Thermal performance of phase change material energy storage floor for active solar water-heating system

The conventional active solar water-heating floor system contains a big water tank to store energy in the day time for heating at night, which takes much building space and is very heavy. In order to reduce the water tank volume or even cancel the tank, a novel structure of an integrated water pipe floor heating system using shapestabilized phase change materials (SSPCM) for thermal energy storage was developed and experimentally studied in this paper. The thermal performances of the floors with and without the SSPCM were compared under the intermittent heating condition. The results show that the Energy Storage Ratio (ESR) of the SSPCM floor is much higher than that of the non-SSPCM floor; the SSPCM floor heating system can provide stable heat flux and prevent a large attenuation of the floor surface temperature. Also, the SSPCM floor heating system dampens the indoor temperature swing by about 50% and increases the minimum indoor air temperature by 2°C–3°C under experimental conditions. The SSPCM floor heating system has a potential of making use of the daytime solar energy for heating at night efficiently.     

Experimental investigation of performance of a multi-purpose PV-slat window

This paper reports on experimental investigation of performance of a new type of PV-slat window (PV-SW). The main functions of this PV-SW are as follows: to admit sufficient daylight, to act as a shading device for decreasing direct heat gain through window glazing and to ensure indoor air movement, which improves resident's thermal comfort. To assess the performance of this PV-SW, two test rooms of 1×1×1.5 m³ (H:W:L) volume were built using plywood and gypsum boards. At the first, the PV-SW of 0.5×0.6 m² surface area was located at the south-facing wall whereas the other room was equipped with a commercial transparent slat window of the same size.The PV-SW consists of six PV slats. The photovoltaic cells were connected in series giving a maximum electrical power output of 36 W (12 V×3 A). The circuit was connected to a direct current axial fan, located inside the room, that requires a maximum power of 43 W. The analysis of performance of this PV-SW was investigated based on power output, daylight factor and temperature difference between indoor and ambient.The experimental results showed that this multi-purpose PV-SW is extremely interesting as it can produce power up to 15 W, decrease indoor temperature and provide sufficient light for housing. The maximum indoor illumination was about 750 lx with slats angle of 68°. The room temperature was about 2–3^oC lower than that of room equipped with transparent slats.     

Preparation,characterization and permeation kinetics description of calcium alginate macro-capsules containing shape-stabilize phase change materials

Macro-capsules containing shape-stabilize phase change materials (SSPCM) which have 50 wt% of n-octadecane (OD) and 50 wt% of high-density polyethylene (HDPE) were prepared by using a traditional coating pan with calcium alginate (CA) as the shell material. The surface morphologies and construction, wall permeability and the kinetic release parameters of OD in a solvent of petroleum ether along with the thermal properties of the materials were investigated using a scanning electron microscope (SEM), thermal cycles, the extraction release kinetics, and differential scanning calorimeters (DSC), respectively. The results show the wall thickness of the macro-capsules was about 30–50 μm under the experimental conditions. The surface of the SSPCM after the application of chromic acid is rough and littered with numerous, microscopic holes measuring about 3 μm in diameter. From this one may conclude that either the hydrophilicity of the SSPCM surface or the permeability of the prepared macro-capsules was altered during the process and thus differed from the unmodified samples. In addition to this, the weight loss percentage (WLP) of the macro-capsules was approximately 1.5 times in the unmodified capsules, and 3 times in the modified SSPCM. The addition of the plasticizer glycerin into the wall significantly decreased the impermeability of the macro-capsules. From the parameters of the Power exponent, there are two different release mechanisms, Fickian/quasi-Fickian diffusion and anomalous transport for modified and unmodified SSPCM.     

下沉式日光温室土质墙体的保温蓄热性能

为研究土质墙体下沉式日光温室的保温蓄热性能,对墙体温度及热流的变化进行了实验测试.测试结果表明:白天土质墙体接受太阳辐射并蓄热;夜间墙体内侧表面温度高于室内温度,墙体向室内放热.土质墙体具有良好的保温蓄热性能,可以满足作物生长的需要,.     

局部采暖建筑非采暖房间平均温度模拟分析

局部采暖建筑热负荷与非采暖房间室内平均温度和外围护结构热工参数密切相关。通过对西安、大连、长春三地的典型建筑在不同外围护结构保温方式下全面采暖和局部采暖进行能耗模拟分析后发现：处于不同气候分区的局部采暖建筑,非采暖房间室内平均温度有差别;建筑中功能相同的各非采暖房间,处在中间层的室内平均温度最高,底层次之,顶层最低,热负荷反之;且各非采暖房间室内平均温度难以满足热舒适的要求。局部采暖建筑中,部分房间热负荷高于相同外围护结构保温条件下全面采暖建筑对应房间的热负荷,但建筑热负荷低于全面采暖建筑的建筑热负荷。     

Thermal cycle testing of calcium chloride hexahydrate as a possible PCM for latent heat storage

In order to study the changes in latent heat of fusion and melting temperature of calcium chloride hexahydrate (CaCl₂·6H₂O) inorganic salt as a latent heat storage material, a thousand accelerated thermal cycle tests have been conducted. The effect of thermal cycling and the reliability in terms of the changing of the melting temperature using a differential scanning calorimeter (DSC) is determined. It has been noticed that the CaCl₂·6H₂O melts between a stable range of temperature and has shown small variations in the latent heat of fusion during the thermal cycling process. Thus, it can be a promising phase change material (PCM) for heating and cooling applications for various building/storage systems.     

Preparation of macro-capsules containing shape-stabilized phase change materials and description of permeation kinetics of its wall

Through in situ polymerization, a kind of macro-capsule was prepared by using silica gel as the shell material and shape-stabilized phase change materials (SSPCM) containing 50 wt% of n-octadecane (OD) of high density polyethylene (HDPE) as the core. The surface and its construction of capsules, the permeability of the capsule wall and the release kinetics parameters of the OD in the system of petroleum ether were experimental investigated by a scanning electron microscope (SEM), thermal cycles and the extraction release kinetics. The results showed that the wall thickness of the macro-capsules was about 20–50 μm under the experimental conditions. The SSPCM surface, modified with chromic acid, is rough, and there are many tiny holes about 3 μm in diameter in it. For these reasons, either the hydrophilicity of the SSPCM surface or the cohesion between the core and the wall have been greatly improved, and then, the weight loss percentage (WLP) of the macro-capsules is decreased by about 1.5 and 2.5 times relative to that of un-modified and modified SSPCM, respectively. Additionally, after the macro-capsules were re-sprayed by using a calcium chloride solution, its wall was more compact. From the fitting parameters of the power exponent, there were two different release mechanisms, quasi-Fickian diffusion and anomalous transport for the un-encapsulated SSPCM and the macro-capsules, respectively.     

Numerical model of a building with transparent insulation

An explicit finite difference simulation model is developed to study the thermal performance of an outdoor test-room with one transparently insulated (TI) wall. The thermal behavior of the room is examined under different control strategies for the shading device and for air flow through the TI wall to the room. Simulation results indicate significant energy savings with practically no auxiliary heating required on cold sunny days in Montreal. However, appropriate control strategies are required to prevent overheating of the room and discomfort. Air flow through the TI wall and then into the room succeeds in lowering its room surface temperature to less than 31°C and reducing to zero the auxiliary heating required on any clear day. Blind control is based on several criteria, including outside temperature, room-facing surface temperature of TI wall (not to exceed 29°C) and room air temperature not to exceed a certain maximum.     

应用于日光温室墙体的相变材料热物性优化研究

建立日光温室计算传热模型,以室内空气温度和墙体内表面温度为指标,通过实验方法验证了所建立的传热模型准确性,最后分析相变材料相变温度、相变焓、导热系数、密度等热物性对室内最低温度和相变蓄热率的影响规律,确定被动式相变蓄热墙体和主-被动式相变蓄热墙体的最佳相变材料热物性,阐明了实际应用时相变材料选择原则。研究结果表明,所建立的日光温室传热模型具有较高准确性,可用于日光温室墙体相变材料热物性优化;主-被动式相变蓄热墙体最佳相变材料的相变温度为27 ℃,相变焓为200 kJ/kg,导热系数为0.35 W/（m·K）,密度为440 kg/m³,被动式相变蓄热墙体最佳相变材料的相变温度为26 ℃,相变焓为200 kJ/kg,导热系数为0.35 W/（m·K）,密度为792 kg/m³;最佳相变材料热物性应用时,2种墙体室内最低温度均可达到15.0 ℃,但是被动式相变蓄热墙体的相变蓄热率较主-被动式相变蓄热墙体减小29.5%。本研究可为相变材料在日光温室的高效利用提供参考。     

Thermal load levelling of heat flux through an insulated thermal storage water wall

This communication presents an investigation of the thickness distribution of a given total thickness of the insulation inside and outside a thermal storage water wall for acheiving the maximum load levelling of the heat flux entering through the wall. Analysis is based on the solution of the heat conduction equation for the temperature distribution in the insulated wall subjected to periodic solar radiation and atmospheric air on one side and in contact with room air at constant temperature (corresponding to air-conditioned rooms) on the other side. an explicit solution for a temperature distribution satisfying the apporpriate boundary conditions at the surface has been derived to obtaing a periodic heat flux through the storage water wall. It is found that for a given total thickness (cost) of insulation the thicknesses of outside and inside insulation must be equal for best load levelling. Moreover, more load levelling is achieved when the whole of the insulation is outside rather than inside the thermal storage water wall.