Yingxin Zhu

People who live in a cold climate: thermal adaptation differences based on availability of heating

Are there differences in thermal adaptation to cold indoor environments between people who are used to living in heating and non-heating regions in China? To answer this question, we measured thermal perceptions and physiological responses of young men from Beijing (where there are indoor space heating facilities in winter) and Shanghai (where there are not indoor space heating facilities in winter) during exposures to cold. Subjects were exposed to 12°C, 14°C, 16°C, 18°C, 20°C for 1 h. Subjects from Beijing complained of greater cold discomfort and demonstrated poorer physiological acclimatization to cold indoor environments than those from Shanghai. These findings indicate that peoples chronic indoor thermal experience might be an important determinant of thermal adaptation.

A General Model for Analyzing the Thermal Performance of the Heat Charging and Discharging Processes of Latent Heat Thermal Energy Storage Systems

During melting of phase change materials (PCM) encapsulated in a container, the solid PCM sinks to the bottom or floats to the top of the container according to the gravitational force and buoyancy resulting from the difference between solid and liquid densities. Compared with the solidification process, the melting process has a quite different behavior. Although the heat transfer characteristics of melting processes in various typical kinds of containers have been studied, the general model for analyzing the thermal performance of both melting and solidification processes of latent heat thermal energy storage (LHTES) systems composed of PCM capsules has not been presented in the literature. The present paper describes such a model which can be used to analyze the instantaneous temperature distribution, instantaneous heat transfer rate, and thermal storage capacity of a LHTES system. For solidification, the model is validated with the results in the literature. The thermal performance during melting of a LHTES system composed of PCM spheres is analyzed as an example. The model is not limited to a specific system or a specific PCM, so it can be used to select and optimize system design and to simulate the thermal behavior of various typical LHTES systems.

Modeling of thermal processes for internal melt ice-on-coil tank including ice-water density difference

The internal melt ice-on-coil tank with horizontal tubes is used widely for thermal storage. Its discharge process is greatly affected by the ice-water density different. The existing models developed for internal melt ice-on-coil tanks are concentric cylinder models which are applicable to tanks with vertical tubes or when all the water in the tank is frozen, but they do not describe the effect of the ice-water density difference on discharge. This paper introduces an eccentric cylinder model developed especially for the discharge process in a tank with horizontal tubes. The model is simple and is suitable for system simulation. Experimental validation proved the reliability of the model.

Heat transfer processes during an unfixed solid phase change material melting outside a horizontal tube

The melting of an unrestrained phase change material (PCM) around a horizontal tube arises in many applications such as ice storage for HVAC (Heating, Ventilating and Air Conditioning) systems. The instantaneous heat transfer rate during the melting process must be known for optimal system design and operation of the application. A theoretical model was developed to analyze the heat transfer during the melting process. A series of experiments on internal melting of unrestrained ice around a fixed horizontal tube were reported. The temporal geometric shape, melting rates under various experimental conditions were determined using a photograph technique. The experimental results were used to validate the theoretical model. The validation results show that the model accurately predicts the solid PCM melting rate.

Prediction Model of Human Thermal Sensation Under Low-Air-Pressure Environment

Passengers in aircraft cabins experience a low-air-pressure environment in most time of the flying period. So the influence of low air pressure on passengers’ comfort needs further research. The most commonly used model to predict human comfort is predicted mean vote (PMV) model. But PMV is designed for standard atmospheric environment, not for low-pressure environment. Researchers have confirmed that under low-pressure environment, human body heat loss through convection will decrease while through evaporation will increase. Thus, PMV model is not suitable for prediction under low-pressure environment and needed to be revised. The main purpose of this study was to investigate human body heat loss under low-pressure environment through both theoretical derivation and experimental validation, thus the model to predict human thermal comfort under low-air-pressure environment could be promoted. The heat loss was divided into four parts: convection heat loss, skin evaporation heat loss, radiation heat loss, and respiration heat loss. From theoretical derivation, following conclusion could be obtained. Radiation heat loss is more related to temperature, and the influence of air pressure is not significant. The convection heat loss will decrease and skin evaporation heat loss will increase under low pressure environment. Heat loss through respiration increases under low-pressure environment. The total heat loss will increase under low-pressure environment. Experimental validation was conducted with six experiment conditions: 22 and 27 °C (1.0/0.9/0.8 atm). Thirty subjects were recruited, and thermal sensation was significantly lower under low-pressure environment than standard pressure environment. Linear regression was analyzed between the value of thermal sensation vote and human thermal storage rate. Instead of the value PMV model predicted which was significantly higher than thermal sensation vote, the new model developed was more effective in predicting human thermal comfort under low-pressure environment.

Dynamic Modeling of Encapsulated Ice Tank for HVAC System Simulation

Dynamic system simulation facilitates the optimization of thermal storage system design and operation. The models used for system simulation should minimize solution time, accurately simulate process response, and should apply to a variety of products made by different manufacturers. This paper introduces an ice tank software model used for the thermal storage and HVAC dynamic system simulation called TSTORS. It is a time dependent model for an encapsulated ice tank. Three groups of experiments with three different systems verify that the model applies to different types of encapsulated ice tanks with different diameter ice balls. The model is also applicable to other ice tanks with such designs as non-spherical capsules or built-in metal cores in the ice balls. For such tanks, the parameters needed for the model can be obtained from data provided by the manufacturers.

Thermal Environment and Passengers’ Comfort in Aircraft Cabin

Passengers’ comfort is becoming more and more important in aircraft cabins. In this study, thermal environment parameters on 10 airlines (1 international and 9 domestic) including 23 aircrafts and 6 different aircraft types were measured with 155 subjective questionnaires regarding passengers’ comfort collected. Thermal environment parameters contained air temperature and relative humidity, wall temperature, radiant temperature, air velocity, noise, illumination, and absolute pressure. The questionnaires collected basic information of passengers (age, height, weight, and clothes level) and their evaluation of the environment (thermal comfort, perceived air quality, and symptoms). The results showed that air temperature was between 23 and 27 °C and average level of humidity was 26.3 %. Wall temperature was slightly lower than air temperature, but radiant temperature was very close. Air velocity was generally below 0.2 m/s, which was imperceptible for passengers. Average noise level was 82.5 dB (A weighted sound pressure level). The illumination changed greatly, and air pressure dropped when taking off and rose when landing and at cruise period; low pressure between 77 and 90 kPa was maintained. Subjective questionnaire assessment showed passengers were satisfied with the environment, and they believed noise and air pressure contributed most to their comfort level. More than 15 % of the passengers reported drowsiness and symptoms related to humidity (dry eye, nose, and throat). Deep analysis indicated that the longer the fight, the less comfortable passengers felt. Seasonal factor showed no significant influence on comfort level.

Spatial Distribution of Thermal Environment Parameters and its Impact on Passengers’ Comfort in 14 Boeing 737 Aircraft Cabins

Passengers’ comfort in air craft cabin is related to many factors. Besides the level of thermal environment parameters, its spatial distribution in aircraft cabin and the place where passengers sit should also matters. In this investigation, a total of 14 Boeing 737 aircrafts including 7 airlines were measured. Each airline had two aircrafts, starting from Qingdao and returning right away after landing. Large-scale subjective questionnaire investigation regarding passengers’ comfort was conducted on each flight. As a result, 979 questionnaires were collected. Thermal environment parameters’ measurement contained air temperature and relative humidity, wall temperature, radiant temperature, air velocity, noise, illumination, and absolute pressure. The questionnaires collected basic information of passengers (age, height, weight, and clothes level) and their evaluation of the environment (thermal comfort, perceived air quality, and symptoms). The main purpose of this study is to investigate the spatial distribution of thermal environment parameters and find its relationship with passengers’ comfort. Thus, different parts in aircraft cabin including both horizontal (front, middle, and back) and vertical (head, knee, and feet) were measured. The passengers’ evaluation was also divided according to the place they sat (front, middle and back, window, middle and aisle). The results showed that the uniformity of air pressure and noise in aircraft cabin was quite good. Air velocity was under 0.2 m/s which was imperceptible for passengers. Air temperature was between 24 and 29 °C in all flight, and the deviation in each flight was below 3 °C. The average relative humidity was from 20 to 30 %, and the lowest was between 5 and 20 %. The difference between air temperature and black globe temperature was less than 1.4 °C. Spatial distribution of air temperature, black globe temperature, and relative humidity was relatively small (<3 °C, <10 %) on different cross-sections, while on the same cross-section, difference was smaller (<1 °C, <2 %). For vertical direction, temperature at the head was higher than the feet but within 2 °C. Wall temperature changed greatly during the flight especially the floor, usually 1–7 °C lower when taking off. Floor temperature near the window seat was generally lower than middle and aisle seat. Passenger was satisfied with cabin environment. Overall evaluation of environment showed no difference among passengers at front, middle, and back. However, passengers at window seat and middle seat showed more comfortable than those at aisle seat.

Using Natural Ventilation in Office Buildings Under Subtropical Climate: A case Study in Shenzhen

Although thermal comfort standards indicate that in hot climates natural ventilation can offset the temperature above which air conditioning becomes necessary, actual applications remain scarce. This paper details the results of the post-occupancy evaluation of an office building in the subtropical Chinese city of Shenzhen, which uses natural ventilation through user-controlled windows to reduce yearly air-conditioning time by 35 %. Investigation of the indoor environment and thermal comfort of occupants showed overall satisfaction. Electricity consumption of the office part of the building was found to be 60.2 kWh/m2.a, which is below the standard deviation band of a statistical sample of 57 Shenzhen office buildings. These results support the feasibility of using natural ventilation in mixed-mode buildings in subtropical climates for increased energy efficiency.

Bridging the gap: The need for a systems thinking approach in understanding and addressing energy and environmental performance in buildings

Innovations in materials, construction techniques and technologies in building construction and refurbishment aim to reduce carbon emissions and produce low-energy buildings. However, in-use performance consistently misses design specifications, particularly those of operational energy use and indoor environmental quality. This performance gap risks reducing design, technology, sustainability, economic, health and well-being benefits. In this paper, we compare settings of the Chinese and the UK buildings sectors and relate their historical context, design, construction and operation issues impacting energy performance, indoor environmental quality, occupant health and well-being. We identify a series of key, common factors of ‘total’ building performance across these two settings: the application of building regulations, the balance between building cost and performance, skills, construction and operation. The dynamic and complex interactions of these factors are currently poorly understood and lead to building performance gaps. We contend that a systems approach in the development of suitable building assessment methods, technologies and tools could enable the formulation and implementation of more effective policies, regulations and practices. The paper illustrates the application of the approach to the UK and Chinese settings. A full application of a systems approach may help to provide a more dynamic understanding of how factor interactions impact the ‘total’ building performance gaps and help address its multiple causes.