Improved heating floor thermal performance by adding PCM microcapsules enhanced by single and hybrid nanoparticles

A heating floor is a low-temperature emitter consisting of pipelines in which a fluid circulates between 35°C and 45°C. To ensure energy efficiency, occupant comfort, and building material durability, proper heat management is crucial in buildings. By using phase change materials (PCMs) in building envelopes, the indoor temperature can be regulated through the storage and release of thermal energy, which reduces energy consumption and enhances occupant comfort. In this study, we evaluated numerically a heating floor that incorporates a PCM enhanced by nanoparticles (NePCM). The aim of the numerical analysis is to assess the impact of the addition of single and hybrid nanoparticles in different proportions to the PCM layer on the thermal performance of the PCM-based floor. Therefore, two main objectives are defined. The primary is to take advantage of the storage capacity of a PCM layer by integrating it into the ground; second, to evaluate the hot water temperature levels effect on the floor's performance. Additionally, we address the low thermal conductivity of PCM by enhancing PCM microcapsules with single and hybrid nanoparticles and comparing them to pure PCM. The numerical results obtained show that positioning the PCM microcapsules above the heating tubes (upper position) provides an optimum improvement in thermal performance. Moreover, the addition of hybrid nanoparticles within the base PCM, 1% of Cu mixed with 4% of Al₂O₃, allows an increase of 4°C, which relates to a reduction of 18% in the internal temperature amplitude and a phase shift of 6 h 30 min compared with the conventional heated floor in which there is no PCM.     

Feasibility study on applications of solar chimney and earth tube systems for BEAM/LEED assessment

Building Environment Assessment Method (BEAM) and Leadership in Energy and Environmental Design (LEED) aim to promote better environment performance of buildings in their life time. This study explores innovative solutions to achieve key requirement of Energy Use (EU) and Indoor Environmental Quality (IEQ) from BEAM/LEED assessments by Solar Chimney (SC) or Earth Tube (ET). EnergyPlus is used to perform the simulation of building's ventilation and energy usage under the typical Hong Kong's weather data. It was found that the SC performance is affected by the building's dimension and orientation and is also determined by solar availability and absorber surface temperature. In most simulation cases, SC provided sufficient natural ventilation, but it also increased cooling load to the space when ambient temperature was higher than indoor. The ET performance was affected by the pipe dimension and buried depth. It was found that a single ET could decrease cooling load to the space in the summer design day ‘July 21’ in Hong Kong, but it could not provide sufficient outdoor fresh air. The result also demonstrated that both SC and ET systems had capabilities to help achieve on‐site renewable energy requirements from BEAM/LEED because of their energy saving capacities on ventilation and thermal comfort. Because SC had higher capability to provide sufficient ventilation, SC could more significantly contribute on the sections pertinent to building ventilation in BEAM/LEED assessments. Because ET had higher capability to save cooling energy, ET could more significantly contribute on the sections pertinent to energy saving in BEAM/LEED assessments. Copyright © 2016 John Wiley & Sons, Ltd.     

Impact of the Relationship between Phase Change Temperature and Boundary Temperature on the Thermal Performance of a PCM Wall and the Presentation of PCM Thermal Performance Indexes

In the composite phase change material (PCM) building envelope, the matching relationship between the phase change temperature of the PCM and the wall's boundary temperature significantly affects the energy storage performance of the PCM building envelope. In this paper, a type of concrete hollow block with a typical structure and a common PCM were adopted to produce multiform composite PCM hollow blocks, and the temperature changing hot chamber method was performed to test the thermal performance of the hollow block walls under different temperature conditions. New indexes were proposed for the thermal performance evaluation of the PCM wall. Meanwhile, combined with experimental data, the effective heat capacity model and the enthalpy model were used to analyze the effect of correlations concerning how the relationship between phase change temperature and wall's boundary temperature influenced the thermal performance of PCM wall. Three main impact factors related to temperature were obtained through the analysis. In addition, approaches for improving the thermal performance of a composite PCM wall were put forward. This paper provides the theoretical basis, data reference and practical instruction for the proper use of a PCM wall and ways for improving the thermal performance of a composite PCM wall.     

The effects of changes in the climate on the energy demands of buildings

It is generally accepted that climate changes will have a major effect on our lives. However, buildings will also be faced with climate changes, and these changes will have an impact on indoor comfort, energy demands and the efficiency of building services, especially on those supporting free cooling and free heating. In order to predict the expected changes in a building's thermal response during its lifetime, it is necessary to look at the climate changes predicted for the future. In our study, the climate changes were considered by using simplified mathematical models combined with available test reference years to establish ‘corrected test reference years’. A transient simulation tool, TRNSYS, was used to simulate the indoor climate and the useful energy demand for the heating and cooling of different buildings with different free‐cooling techniques. In order to predict the expected changes in a building's thermal response, the meteorological parameters for the moderate, continental climate region of Slovenia were taken into account. The study shows that during a building's lifetime, significant changes in useful energy demands can be expected—a decrease in the useful energy demand for heating of between 23 and 40% and an up‐to‐38‐times increase in the useful energy needed for mechanical cooling. In buildings without mechanical cooling, the efficiency of the different free‐cooling techniques should be increased by between 100 and 200% to ensure the same living comfort. The results presented in the study confirm that it is necessary to evaluate the consequences of global climate changes from the point of view of energy use in buildings, their construction and the buildings' service installations. Copyright © 2008 John Wiley & Sons, Ltd.     

Characterization of novel shape‐stabilized phase change material mortar: Portland cement containing Na2SO4·10H2O and fly ash for energy‐efficient building

In this work, a novel Na₂SO₄·10H₂O/fly ash shape‐stabilized phase change material mortar (PCM mortar) was prepared for building energy efficiency, in the context of energy conservation and environmental protection. The working, mechanical, and thermal properties of this proposed PCM mortar were investigated. The experiment results showed that the incorporation of PCMs greatly increased the thermal inertia of the mortar, while corresponding compressive strength was little affected. Specifically, when the blending amount of PCMs reached 15%, the thermal storage capacity of mortar sample (PCM‐15) was 6.18 × 10⁴ kJ/m³, which is 2.4 times of that for mortar sample without PCM (OPC) evaluated by theoretical calculations, while the corresponding compressive strength of mortar sample (PCM‐15) still remained above 31 MPa. Furthermore, the effects of PCM mortar on thermal comfort and energy use of buildings were studied by using experiment and simulation methods, respectively. The control experiments showed that PCM mortar can effectively alleviate the influence of outdoor temperature on indoor temperature compared with OPC. Temperature difference between PCM‐15 and OPC board can reach 4.6°C (inner surface) and 8.6°C (outer surface), respectively. Meanwhile, temperature difference of internal space reached 1.2°C. The simulation results showed that the energy consumption per unit building area was reduced by 4.4 and 18.7 kg/m² in Guangzhou and Harbin, respectively, with PCM mortar as the envelope structure. Hence, the proposed PCM mortar showed significant thermal and mechanical properties and had broad application prospects in regulating indoor temperature and constructing energy‐efficient buildings.     

The energy saving index and the performance evaluation of thermochromic windows in passive buildings

The concepts of the energy saving equivalent (ESE) and energy saving index (ESI) are presented in this paper to evaluate the performance of new materials and components in passive buildings. The ESE represents the hypothetical energy that should be input to maintain a passive room at the same thermal state as that when a particular material or component is adopted. The ESI is the ratio of a particular material or component's energy saving equivalent to the corresponding value of the ideal material or component that can maintain the room at an ideal thermal state in passive mode. The former can be used to estimate the effect of the adoption of a certain building component or material on the building's thermal state from an energy standpoint, while the latter can be used to characterize the performance of the actual building component or material from a common standpoint and be used to evaluate the performance of components or materials in different climatic regions or under different operating situations. In this study, the ESI was used to evaluate the performance of a thermochromic window, represented by a single vanadium dioxide (VO₂) glazing, in passive residential buildings in three climatic regions of China (cold zone, hot summer and cold winter zone, and hot summer and warm winter zone).     

Building roof with conical holes containing PCM to reduce the cooling load: Numerical study

The thermal effectiveness of a building’s roof with phase change material (PCM) is presented in this paper. The considered model consists of a concrete slab with vertical cone frustum holes filled with PCM. The objective of incorporating the PCM into the roof structure is to utilize its high latent heat of fusion to reduce the heat gain during the energy demanded peak hours, by absorbing the incoming energy through the melting process in the roof before it reaches the indoor space. The thermal effectiveness of the proposed roof-PCM system is determined by comparing the heat flux at the indoor surface to a roof without the PCM during typical working hours. A parametric study is conducted to assess the effects of the cone frustum geometry, and the kind of PCM used. The n-Eicosane shows the best performance among the examined PCMs, and the conical geometry of the PCM container is the best in term of thermal effectiveness. The results indicate that the heat flux at the indoor surface of the roof can be reduced up to 39% for a certain type of PCM and geometry of PCM cone frustum holes.     

Development and thermal performance of wood-HPDE- PCM nanocapsule floor for passive cooling in building

Cooling demand in the building sector is growing rapidly; thermal energy storage systems using phase change materials (PCM) can be a very useful way to improve the building thermal performance. This work shows the benefits of PCM when incorporated in wood fiber-polymer composite as floor cooling system using nano-encapsulated PCMs. The wood-plastic-NPCM composites were produced using compression molding process and its mechanical and thermal properties were investigated. Two dynamic simulators were employed to investigate synthesized composites thermal performance. Increasing NPCM content in WPC showed that the fluctuations of the simulator temperature was decreased while the heat fluxes through the floor was increased. The variations of ambient maximum temperature have little effect on the air temperature of the simulator with 40% PCM which indicates that the amount of PCM was enough for studied environmental condition. Field experiments were performed using two medium-scale test houses located on Tehran-Iran. It can be concluded that using NPCM helps to reduce heating and cooling demand. Moreover, the natural night ventilation by opening windows reduced the number of hours that the temperature is above 23°C from 499 h/year in case1 (without opening) to 255 h/year in case 2(with opening). This means that natural night ventilation could help reduce the overheating period to about 50% with the use of NPCM.     

Design and transient-based analysis of a power to hydrogen (P2H2) system for an off-grid zero energy building with hydrogen energy storage

In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m² PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m² evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between ?0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.     

Impact of Phase Change Material's Thermal Properties on the Thermal Performance of Phase Change Material Hollow Block Wall

ABSTRACT

Composite phase change material (PCM) hollow block wall (CPCMHBW) can be established by introducing PCM into the holes of generally used hollow block wall, and good thermal insulation performance will probably produce together with the energy storage function from PCM simultaneously. In this article, the impact of PCM's thermal properties on the thermal performance of CPCMHBW has been analyzed, using two-dimensional enthalpy model. The conclusions include: complete melting and freezing processes and a bit amount of remaining PCM which has not melted or solidified, are fundamental and necessary for high performance; furthermore, that the average surrounding temperature equals to PCM's central phase change temperature determines whether the PCM's function can be used; besides, the PCM's total latent heat controls wall's thermal storage level; in addition, relatively low block material's thermal conductivity and Fourier number (better smaller than 1.0 W·m^?1·K^?1 and 59.83) and medium PCM's corresponding values (lies in the ranges 0.2–0.7 W·m^?1·K^?1 and 0.80–2.80) generate optimum thermal performance. Finally, the thermal factors are ranked with the functions in descending order.     

Investigating and analysing the energy and environmental performance of an experimental green roof system installed in a nursery school building in Athens,Greece

This paper deals with the experimental investigation and analysis of the energy and environmental performance of a green roof system installed in a nursery school building in Athens. The investigation was implemented in two phases. During the first phase, an experimental investigation of the green roof system efficiency was presented and analysed, while in the second one the energy savings was examined through a mathematical approach by calculating both the cooling and heating load for the summer and winter period for the whole building as well as for its top floor. The energy performance evaluation showed a significant reduction of the building's cooling load during summer. This reduction varied for the whole building in the range of 6–49% and for its last floor in the range of 12–87%. Moreover, the influence of the green roof system in the building's heating load was found insignificant, and this can be regarded a great advantage of the system as any interference in the building shell for the reduction of cooling load leads usually to the increase of its heating load.     

Impact of voluntary green certification on building energy performance

Credible estimates of energy savings from green buildings are critical for policy makers to examine the cost and benefit of various incentives intended to encourage commercial buildings to go green (e.g. expedited construction permits, government grants, and property tax incentives). Yet, data limitations have hindered reliable estimations. Filling this gap, this study uses a large panel dataset on energy consumption for commercial buildings in Phoenix metropolitan area, Arizona. By tracking building occupants' monthly energy consumption before and after the building's certification as an Energy Star building, we provide new estimates of the environmental gains from private investment in green real estate. Results show that for occupants that occupy space in a certified building in both the pre-certification and post-certification periods, occupants in Energy Star buildings consume 8% less energy. This empirically robust estimate of potential benefit from green-certification provides a quantifiable benchmark against which green-promoting policies can be measured. We also document evidence of heterogeneous treatment effects. Energy savings differ by the building's initial certification points and the building's baseline energy consumption. These results are useful for policy makers to identify targets for green certification.     

A cost‐effective operating strategy to reduce energy consumption in a HVAC system

The operation of the building heating, ventilating, and air conditioning (HVAC) system is a critical activity in terms of optimizing the building's energy consumption, ensuring the occupants' comfort, and preserving air quality. The performance of HVAC systems can be improved through optimized supervisory control strategies. Set points can be adjusted by the optimized supervisor to improve the operating efficiency. This paper presents a cost‐effective building operating strategy to reduce energy costs associated with the operation of the HVAC system. The strategy determines the set points of local‐loop controllers used in a multi‐zone HVAC system. The controller set points include the supply air temperature, the supply duct static pressure, and the chilled water supply temperature. The variation of zone air temperatures around the set point is also considered. The strategy provides proper set points to controllers for minimum energy use while maintaining the required thermal comfort. The proposed technology is computationally simple and suitable for online implementation; it requires access to some data that are already measured and therefore available in most existing building energy management and control systems. The strategy is evaluated for a case study in an existing variable air volume system. The results show that the proposed strategy may be an excellent means of reducing utility costs associated with maintaining or improving indoor environmental conditions. It may reduce energy consumption by about 11% when compared with the actual strategy applied on the investigated existing system. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimisation of night-time ventilation parameters to reduce building's energy consumption by integrating DOE2 and MATLAB

We have developed an algorithm to optimise the fan flow rate by integrating DOE2 (building's energy simulation software) with MATLAB's genetic algorithm. In our developed algorithm, MATLAB can send desired values of optimisation variables for different hours to DOE2 to simulate building's energy use, and it can also receive building's energy consumption and other data from DOE2 for the optimisation. This powerful optimisation tool can be used for finding optimal solution of night-time ventilation fan flow rates and maximising energy savings. Results of optimisation are used to train a neural network to predict fan flow rates for different conditions. Night-time ventilation investigated in DOE2 considers parameters such as (1) night-time ventilation duration, (2) ventilation fan flow rate, (3) outdoor temperature, and (4) temperature difference between outdoor and indoor. Optimisation results show outdoor temperature between 10°C and 18°C and the temperature difference of more than 8°C are appropriate for night-time ventilation.     

Thermal behaviour of a green vs. a conventional roof under Mediterranean climate conditions

The application of green roofs on urban buildings is considered to have a positive impact on their thermal behaviour and local microclimatic conditions. According to the literature, their ability for attenuation of storm water run-off as well as their contribution to the building's thermal protection is among the most important benefits of this technique. However, despite the development of computer models that can assist towards analysing the nature of their behaviour, there is still a relative gap in measured data representing long-term period thermal performance. In this paper, the results of a long-term experimental analysis are presented, which attempt to identify the thermal behaviour of a green roof in comparison with a bare flat roof. The results show that in Mediterranean countries, a green roof can contribute substantially to building's energy conservation mainly during the warm period of the year, while its influence during the cold period is negligible.     

Optimal roof structure with multilayer cooling function materials for building energy saving

Both cool roof and phase change thermal storage are promising technologies in decreasing building energy consumption. Combining these two technologies is likely to further enhance the thermal comfort of the building as well as reduce air condition loads. In this paper, the cooling performance and energy-saving effects of four types of roof (normal roof, phase change material [PCM] roof, cool roof, and cool PCM roof [cool roof coupled with PCM]) were investigated under a simulated sunlight. Experimental results indicate that compared with normal roof, the other three roofs are able to narrow the indoor temperature fluctuation and decrease the heat flow entering into the room. Among them, cool PCM roof gave the best energy-saving effect that can lower the indoor temperature and heat entering into rooms by 6.6°C and 52.9%, respectively. Besides, the PCM location, PCM thickness, and insulation thickness exerted great impacts on the cooling performance of the roof. Placing the PCM on the internal layer beneath the extruded polystyrene (XPS) insulation board can make the indoor temperature 1.2°C lower than that on the middle layer. Although thicker PCM panels or insulation boards can provide a better thermal insulation, 5 mm in PCM thickness and 20 mm in insulation thickness are enough to guarantee the indoor temperature of cool PCM roof system at a comfortable range (22°C-28°C) for a whole day. These findings will give guidance in designing buildings with a light and compact roof structure to decrease energy consumption and improve comfort level.     

Design parameters and control strategies for a combined passive heating and cooling system in Louisville,KY

ABSTRACT

Conventional passive solar systems can significantly reduce a building's heating load. However, the integration of passive heating and cooling systems in the same building and the benefits of actively controlling passive systems has largely been unexplored. The objective of this study was to determine the relative performance of a passive solar heating and sky cooling system operating with a range of control strategies, with the goal of minimising the overall annual energy use for space conditioning. A combined system (CS) and a separate system (SS) were simulated with thermal networks using MATLAB, with weather data for Louisville, KY. The control strategies simulated included: Seasonal, Ambient, Room and Matrix. The highest fraction of energy supplied by ambient sources for the SS was 0.707 with Matrix control, while for the CS, the highest fraction (0.704) was with Matrix temperature control with switchable attributes for heating and cooling.     

夏热冬暖地区居住建筑应对气候变化节能适应性

为研究夏热冬暖地区居住建筑应对气候变化的适应性,运用TRNSYS动态能耗模拟软件对该地区典型居住建筑能耗进行仿真,制定了居住建筑节能星级评估体系。以广州市为例,分析预测了广州2020年、2050年及2080年的气候变化,并提出应对气候变化的节能措施。研究表明：气温上升1℃,4.0、5.5及6.5星级建筑能耗将分别增长25%、20%及20%;在2080年,气温上升近3.5℃,4.0星级建筑CO2年排放量达53 t/m2,将4.0星建筑升级到5.5和6.5星级,每年可相应减排19.5 t/m2和23.2 t/m2;若以4.0星级建筑当前的CO2排放量为控制目标,则需把建筑围护结构热工性能提升到6.5星级水平,可以实现未来70年减排45%。     

Capric-myristic acid/vermiculite composite as form-stable phase change material for thermal energy storage

Phase change materials (PCMs) can be incorporated with building materials to obtain novel form-stable composite PCM which has effective energy storage performance in latent heat thermal energy storage (LHTES) systems. In this study, capric acid (CA)-myristic acid (MA) eutectic mixture/vermiculite (VMT) composite was prepared as a novel form-stable PCM using vacuum impregnation method. The composite PCM was characterized using scanning electron microscope (SEM) and Fourier transformation infrared (FT-IR) analysis technique. Thermal properties and thermal reliability of the composite PCM were determined by differential scanning calorimetry (DSC) analysis. The CA-MA eutectic mixture could be retained by 20 wt% into pores of the VMT without melted PCM seepage from the composite and therefore, this mixture was described as form-stable composite PCM. Thermal cycling test showed that the form-stable composite PCM has good thermal reliability and chemical stability although it was subjected to 3000 melting/freezing cycling. Thermal conductivity of the form-stable CA-MA/VMT composite PCM was increased by about 85% by introducing 2 wt% expanded graphite (EG) into the composite. The increase in thermal conductivity was confirmed by comparison of the melting and freezing times of the CA-MA/VMT composite with that of CA-MA/VMT/EG composite. The form-stable PCM including EG can be used as energy absorbing building material such as lightweight aggregate for plaster, concrete compounds, fire stop mortar, and component of interior fill for wallboards or hollow bricks because of its good thermal properties, thermal and chemical reliability and thermal conductivity.     

Artificial neural networks applications in building energy predictions and a case study for tropical climates

This study presents artificial neural network (ANN) methods in building energy use predictions. Applications of the ANN methods in energy audits and energy savings predictions due to building retrofits are emphasized. A generalized ANN model that can be applied to any building type with minor modifications would be a very useful tool for building engineers. ANN methods offer faster learning time, simplicity in analysis and adaptability to seasonal climate variations and changes in the building's energy use when compared to other statistical and simulation models. The model herein is presented for predicting chiller plant energy use in tropical climates with small seasonal and daily variations. It was successfully created based on both climatic and chiller data. The average absolute training error for the model was 9.7% while the testing error was 10.0%. This indicates that the model can successfully predict the particular chiller energy consumption in a tropical climate. Copyright © 2005 John Wiley & Sons, Ltd.