Improve Indoor Thermal Environment Research Articles

Integrating the Living Wall with Mechanical Ventilation to Improve Indoor Thermal Environment in the Transition Season

A living wall, when integrated with a mechanical ventilation system, can effectively improve the indoor thermal environment and reduce indoor CO2 concentration during the transition season. In this study, a control experiment was conducted to analyze the effect of a living wall integrated with mechanical ventilation (LW-V) on indoor air quality. During the experiment, indoor air temperature, relative humidity, indoor air speed, and CO2 concentration were measured, while the skin temperature was monitored and subjective questionnaires were administered to 60 subjects. The results show that the indoor environment was effectively improved by employing the LW-V system, with the average indoor temperature decreasing by 1.45 °C, while relative humidity increased by 19.1%. Due to the plant photosynthesis, CO2 concentrations were reduced by 13.83 ppm. Meanwhile, the mean skin temperature was reduced by 0.18 °C and was closer to the neutral mean skin temperature. Questionnaire analysis reveals the LW-V system improved overall air freshness sensation and thermal comfort level by 1.09 and 0.53, respectively. The LW-V system improved the indoor thermal environment as well as air quality during the transition season significantly.

Combining use of natural ventilation, external shading, cool roof and thermal mass to improve indoor thermal environment: Field measurements and simulation study

Thermal mass, natural ventilation, external shading and cool roof are commonly regarded as passive cooling measures. Combined use of these passive cooling measures could achieve a more comfortable indoor environment, and further reduce the building energy demand. The aim of this paper was to assess the short and long-term performances of individual and combination passive measures in a cooling-dominated region of China experimentally and numerically. The field measurement revealed that natural ventilation, external shading and cool roof can reduce the internal wall and indoor air temperatures. The mean air temperatures in the test chamber were 1.3, 2.0, and 1.1 °C lower than that in reference chamber. The combined use of natural ventilation, external shading and cool roof can maintain the daily indoor air temperature within the range of 26.2 and 28.1 °C. The mean air temperature in the test chamber was reduced by 2.8 °C. Long-term simulation results confirmed that applying combination mode of natural ventilation, cool roof and external shading, the indoor temperature, varying from 21.9 to 28.1 °C, is greatly improved compared with the case operated natural ventilation only, particularly during peak temperature hours. The effect of specific heat capacity on indoor air temperature is complex. Increasing the specific heat is not always beneficial to indoor thermal environment. Further, the greater the heat transfer coefficient leads to the higher indoor air temperature through entire summer. The maximum indoor air temperature is reduced by 2.6 °C when the heat transfer coefficient changes from 1.0 to 0.1 W/m2·K.

A zoned group control of indoor temperature based on MPC for a space heating building

The traditional regulation of district heating (DH) system are mainly based on the central control in heat plants and/or in the substations. But the end-user control is becoming increasingly important in saving DH energy consumption. In view of this, a novel zoned group control method of indoor room temperature based on model predictive control (MPC) for a space heating building is proposed. Firstly, a room temperature simulation model based on IDA Indoor Climate and Energy (IDA-ICE) is developed for the experimental room, where the simulation result is validated by the measurements. But it is still difficult to use this model in the predictive control. Therefore, a resistor capacitor (RC) room temperature simulation model with parameters identified by IDA-ICE is proposed. A room temperature controller based on RC-MPC is developed and tested in the experimental room for model validation. Secondly, a DH building in Dalian, China is chosen for the case study. The IDA-ICE simulation results show that the temperature distribution in different rooms of the building is clearly uneven without end-user control. Corresponding targeted control strategies according to the temperature distribution should be used in different zones (cluster of rooms) to improve indoor thermal environment. Therefore, a zoned group control model based on RC-MPC for DH building room temperature is developed in MATLAB/Simulink, which adopts IDA-ICE for parameter identification in RC simulation model and utilizes RC model to predict the room temperature trajectory in the MPC controller. Results show that the proposed model can achieve active and dynamic room temperature control for different zones more precisely according to the changing heat load distribution. It is not necessary to define every room a group, instead, many rooms with similar conditions can be grouped in the same cluster, and temperature differences between rooms can be controlled within a reasonable range.

Research on a novel air conditioning system for improved indoor thermal environment control

Research on a novel air conditioning system for improved indoor thermal environment control

Experimental Investigation of Indoor Thermal Comfort under Different Heating Conditions in Winter

Owing to historical reasons, only a few locations in the Guangdong province use heating to enhance interior thermal conditions. With the variation in climate and increase in people’s lifestyle requirements, winter heating has become increasingly necessary. However, a literature review revealed that only a few studies have investigated the heating requirements during winter in the Guangdong province. In this study, we compared the thermal comfort of radiant floor heating with wall-mounted air conditioner heating. A Guangzhou University climate chamber was used in several investigations. The findings revealed that the thermal neutral temperatures of radiant heating and air conditioner heating were 22.0 °C and 23.0 °C, respectively, about 1 °C variation in temperature. Additionally, in the research on thermal reactions and local skin temperature measurements, the impact of local thermal discomfort on the overall thermal experience was also considered. The findings showed a direct relationship between the local thermal discomfort caused by radiant heating and general thermal sensation. Thermal sensation of the subjects mainly originated from the lower extremities and was significantly affected by Va (air velocity). The relationship between the local thermal discomfort of convective heating and general thermal sensation was weak and mainly caused by the uneven thermal environment. Thus, in south China, for lowering energy usage, radiant floor heating should be used to create an improved indoor thermal environment in winter.

Association between Indoor Temperature in Winter and Serum Cholesterol: A Cross-Sectional Analysis of the Smart Wellness Housing Survey in Japan.

Issuance of the WHO Housing and health guidelines has paralleled growing interest in the housing environment. Despite accumulating evidence of an association between outdoor temperature and serum cholesterol, indoor temperature has not been well investigated. This study examined the association between indoor temperature and serum cholesterol. We collected valid health checkup data of 2004 participants (1333 households), measured the indoor temperature for 2 weeks in winter, and divided participants according to whether they lived in a warm (average bedroom temperature ≥ 18℃), slightly cold (12-18℃) or cold house (＜12˚C). The relationship between bedroom temperature and serum cholesterol was analyzed using multivariate logistic regression models, adjusting for demographics, lifestyle habits and the season in which the health checkup was conducted, with a random effect of climate areas in Japan. The sample sizes for warm, slightly cold, and cold houses were 206, 940, and 858, respectively. Compared to those in warm houses, the odds ratio of total cholesterol exceeding 220 mg/dL was 1.83 (95%CI: 1.23-2.71, p=0.003) for participants in slightly cold houses and 1.87 (95%CI: 1.25-2.80, p=0.002) in cold houses. Similarly, the odds ratio of LDL/non-HDL cholesterol exceeding the standard range was 1.49 (p=0.056)/1.67 (p=0.035) for those in slightly cold houses and 1.64 (p=0.020)/1.77 (p=0.021) in cold houses. HDL cholesterol and triglycerides were not significantly associated with bedroom temperature. Besides lifestyle modification, improving indoor thermal environment through strategies such as installing high thermal insulation and appropriate use of heating devices may contribute to better serum cholesterol condition.

An optimal control method for small-scale GSHP-integrated air-conditioning system to improve indoor thermal environment control

ON/OFF controlled ground-source heat pump (GSHP) is often integrated with small-scale central air-conditioning system (ACS) for villas. Chilled-water temperature (CHWT) in this system usually oscillates in a large range due to the ON/OFF switch of the compressor. As it may be too high or too low, the cooling output of the air-handling unit (AHU) in its adjustable range may not be coincident with the indoor cooling demand, which may lead to unsatisfactory room temperature control performance. This study proposes an optimal control method for this system to improve the control robustness of the room temperature. Usually, the variation of indoor cooling-load is transferred to the chilled-water resulting in changing water temperature. In this method, the optimal chilled-water return (CHWR) temperature is calculated on the basis of the estimated sensible heat load and total cooling-load of the concerned rooms. Then, this CHWR temperature is reset following up the ON and OFF states of the compressor to regulate the variation range of the CHWT. Thus, the cooling output of the AHU in its adjustable range can always follow up the changing of indoor cooling demand. This method is tested on a simulation platform and a real ACS. The test results show good temperature control performance can be achieved. The experimental results demonstrate that the maximum deviation of room temperature is reduced by 2°C and the energy consumption of the GSHP and fan can be reduced by 30.12% at light cooling-load. The application performance shows this method can be easily realized in a common building automation system.

A new method to improve indoor environment: Combining the living wall with air-conditioning

Indoor plants can improve indoor thermal environment, relieve the anxiety, and reduce the CO2 concentration especially in enclosed rooms with air-conditioning and heating. However, owing to the space limitation and the light requirement, it is very difficult to maintain traditional large-scale plantings indoors. To improve indoor planting efficiency and thermal environment, the living wall was introduced to be combined with air-conditioning. Two identical rooms were built to analyze the efficiency of combining a living wall with air-conditioning. One room contained a living wall and air-conditioning, while the other room only with air-conditioning was served as a reference. The indoor thermal environment and CO2 concentration were monitored, while the 64 participants were questioned to display their subjective feelings in two rooms. The results showed that combining the living wall lowered the relative humidity by 2.6%, maintained the indoor air speed at 0.20 m/s∼0.30 m/s and reduced the CO2 concentration by approximately 10%, while it increased the uniformity of these environmental parameters. The average skin temperature in the room with the living wall was 0.2 °C higher than that in the referred room and closer to the neutral mean skin temperature. The living wall significantly improved the subjective evaluation on indoor environment, especially in air movement and air freshness, with the thermal comfort level from 0.13 (Slightly higher than ''Neutral (0)'') to 0.73 (Slightly lower than ''Comfortable (+1)'').

Experimental study on a modular thermo-activated building system for improving indoor thermal environment and energy saving

Thermo-activated Building Systems is an energy-efficient envelope insulation technology. In this paper, the Modular Thermo-activated Building Systems (MTABS) is proposed to enable flexible installation and maintenance of embedded pipe. Two scaled-down experimental rooms of the same size were built, in which the normal energy-saving wall (NW) and the MTABS wall were applied to the south-facing wall respectively. The MTABS for impacting on the indoor thermal environment and energy saving were measured in continuous low-grade heat injection mode under winter outdoor conditions in Hefei, and were analyzed in comparison with the NW. Experimental results show that MTABS can effectively improve the indoor thermal environment. The average temperature difference between indoor and outdoor of MTABS is 6.72 °C higher than that of NW; when the heat source temperature is 25 °C, the cumulative daily heat fluxes of MTABS is 44.0 kWh·m-2, which providing auxiliary indoor heating while significantly reduces energy consumption.

Improving Indoor Thermal Environment of Residential Buildings Under Typical Space Heating Methods in Xinjiang, China

In order to improve the thermal environment of residential buildings in winter for Xinjiang, this research conducted a field test and a survey of residential buildings under typical heating methods. The results show that the indoor temperature and humidity are dynamically changing, and the variation of central heating and gas wall-mounted furnace fluctuated less than that of coal heating. Furthermore, the thermal environment evaluation shows that the thermal comfort level under gas wall-mounted furnace heating are the highest, which belongs to category Ⅰ. For the central heating and coal stove, only 12% and 26% of buildings achieve to category Ⅱ. Moreover, it is found that the acceptable temperature range of coal furnace heating residents can be as low as 19.5°C, while that of central heating and gas wall-mounted furnace heating is 20.3°C~25.7°C, which relate to the clothing insulation of residents under different heating methods. In addition, all residents almost have the same habit of window opening behaviour during heating period, and 72% of residents open windows for ventilation. Correspondingly, 62% of residents feel dry during heating season, which induce xerosis cutis, dry mouth and other uncomfortable symptom, and can be improved by using humidifier, planting plants and so on.

Thermal design method of building wall considering solar energy utilization and thermal insulation

This study makes a breakthrough out of the original thermal design idea which is mainly aim to improve thermal insulation performance of building wall, putting forward thermal design method of building wall to consider solar energy utilization and insulation simultaneously. Firstly, a day is divided into daytime and nighttime, and the expressions of indoor heat gain through the wall during such two periods are derived respectively according to the harmonic response method. The weighted sum of daytime and nighttime heat gain, then, could be used as the evaluation index of wall thermal performance. Taking this index as objective function and wall thermal resistance as well as heat capacity per unit wall area having the corresponding thickness of the thermal resistance as variables, a method for determining the optimum wall thermal resistance and heat capacity is proposed. Finally, for the room without heating measures in Lhasa area, using the typical weather data in winter as input conditions, the optimal matching curve of wall thermal resistance and heat capacity taking into account both the effect of solar energy utilization and insulation is calculated, so are the optimal value of them under different indoor temperatures (0–12 °C, interval of 2 °C). The results show that, in Lhasa area, the south wall has great potential to improve indoor thermal environment by using solar energy. From the perspectives of wall’s “carrier” role of utilizable climatic resources, the higher thermal insulation performance doesn’t always bring better results.

Improved indoor air temperature and humidity control using a novel direct-expansion-based air conditioning system

Many approaches have been tried to obtain an improved indoor thermal environment in small-to medium-sized buildings located in hot-humid climates when using direct-expansion (DX)-based air conditioning (A/C) systems. However, inadequacies still existed in these approaches. Therefore, to address these problems, a novel DX-based A/C system with a two sectioned cooling coil (TS-DXAC) has been proposed. In this paper, a control strategy to operate the TS-DXAC system for achieving an improved indoor air temperature and humidity control in hot and humid climates is presented. Firstly, the detailed configurations of the TS-DXAC system and the control strategy of the TS-DXAC system are presented. The developed strategy included two control algorithms, i.e., Algorithm I and Algorithm II, enabling the TS-DXAC system to be operated under two different indoor conditions, i.e., hot-humid, and hot-dry, respectively. Secondly, a test TS-DXAC system was set up and the controllability tests for the control strategy were carried out. This is followed by presenting the experimental results and related discussions. The experimental results demonstrated that in all the tests, indoor air temperature could be directly controlled at the two indoor conditions, while indoor air temperature and relative humidity could be simultaneously controlled over a relatively long period at a hot-humid indoor condition using Algorithm I. The control strategy enabled the TS-DXAC system to respond the changes in either indoor settings or cooling loads by outputting variable sensible and latent cooling capacities at a higher energy efficiency compared to conventional On-Off controlled DX A/C systems. However, to improve the control sensitivity under Algorithm I, consideration should be given to the variable speed operation of the compressor in the TS-DXAC system.

Thermal comfort assessment of naturally ventilated public hospital wards in the tropics

Natural ventilation, which is a common method used in tropical climate countries, can provide a high rate of airflow to maintain good indoor air quality and thermal comfort. However, the use of natural ventilation alone as passive cooling strategy is insufficient to improve indoor thermal environment. Thus, this study aims to determine the existing thermal comfort conditions in a naturally ventilated public hospital ward by using three methods: simulation works, objective measurements and field surveys. The combination of all these methods in measuring thermal comfort is essential in acquiring the most accurate results and has yet to be implemented in any public hospital in the tropics on the basis of the literature review conducted. The simulation results presented that more than half of the total occupants in the ward feel discomfort, with a predicted mean vote (PMV) between 1.0 and 1.6 and a predicted percentage of dissatisfied between 40% and 56%. On-site measurements recorded the same PMV reading, indicating slightly warm and warm, on the basis of the ASHRAE Standard 55 assessment scale. By contrast, the results of the survey questionnaire showed a different perception of the occupants, with 82% of the respondents voting in the range of warm to hot scale. The thermal conditions in the naturally ventilated ward studied for two months in 2020 were found to be uncomfortable and required further improvement. Knowledge of the climatic characteristics and the current state of the indoor thermal environment will help the building owners strategise an appropriate bioclimatic design approach.

Improving indoor thermal environment in a traditional building of Danihe Village, China with additional solar house

A considerable chunk of population in China live in rural areas. To create a suitable living environment in winter, many of them resort to additional solar house to improve the indoor thermal environment. Most of the previous studies focus on how the additional solar house changes the environment, but few try to optimize the size of that house. Therefore, this paper carries out field measurement and numerical simulation to evaluate the indoor thermal environment of a traditional building of Danihe Village, an important residential settlement in Xi’an, northwestern China’s Shaanxi Province, and explores the most suitable size of the additional solar house for improving the indoor thermal environment of the building in winter. The results show that the width of the additional solar house should be controlled within the range of 600–2400 mm, which provides the residents indoor with the best thermal environment. The research results offer a guide for improving indoor thermal environment and reducing indoor energy cost in future.

Effect of north wall internal surface structure on heat storage-release performance and thermal environment of Chinese solar greenhouse

Chinese solar greenhouse (CSG) is an energy-saving agricultural building which is used to grow vegetables in winter. The north wall of CSG plays an crucial role in concerning the production yield and quality during the winter months. To improve the thermal performance of north wall, different internal surface structures (ISS) with same materials were compared. Based on the field experiment and the proposed valuation, the dynamic heat storage-release characteristics of the north walls have been analyzed and discussed. The results showed that compared with the flat wall and the striped wall, the alveolate wall has better properties of heat storage and thermal insulation. Moreover, relative humidity in this type of greenhouse is more suitable for growing crops. The alveolate wall can improve indoor thermal environment and reduce the sensitivity to external environment. The obtained results can provide a basis for the scientific construction of the CSG north wall. It has significant potential for the area in high latitude, high altitude and long winter.

Evaluating the improvement effect of low-energy strategies on the summer indoor thermal environment and cooling energy consumption in a library building: A case study in a hot-humid and less-windy city of China

Public buildings such as libraries consume a vast amount of cooling energy for maintaining a comfortable and stable indoor environment in summer, especially in the hot-humid climate. This study used a case study approach to discuss the effect of low-energy strategies that can be applied to improve indoor thermal environment and cooling energy consumption of library buildings in hot and humid cities like Nanning City (a southern city, China). The use of cooling window shutters (a shutter with the effects of shading and evaporative cooling) and ceiling fans for generating airflow was considered as applicable energy-saving measures in this study, and a university library was selected as the study building in which the two energy-saving measures were employed. The SET* and annual cooling load before and after the adoption of the proposed measures were quantitatively investigated with a building energy consumption simulation software (DesignBuilder). Simulation results showed that the daytime SET* values can be reduced by 3.0 °C and 4.5 °C respectively on a typical summer day after the use of the cooling shutters and ceiling fans. Moreover, the cooling loads can also be decreased by 8.4% and 16.6% respectively. Particularly, the combination of these two measures enabled the daytime SET* value and annual cooling load lower by 7.0 °C and 60.8% respectively.

Study on Indoor Thermal Environment of Traditional Dwellings in the Watery Town in Suzhou in Winter

Traditional dwellings have their own characteristics and values in the construction of indoor thermal environment. In order to analyze the current situation of thermal environment of dwellings in Southern Region of the Yangze River. This paper takes traditional dwellings in the watery town in Suzhou as the research object, and studies the indoor thermal environment in winter through field measurement of indoor and outdoor temperature and relative humidity of dwellings in winter, questionnaire survey and PMV-PPD thermal evaluation system. The results show that the average indoor temperature is 7.5°C, humidity of residential is 72%, the average predicted thermal sensation vote is -2.79, the predicted dissatisfaction is over 90%, and the indoor thermal environment dissatisfaction in public questionnaire survey is 20.83%, which is far from the predicted dissatisfaction PPD. It shows that the vote of hot feeling underestimates the residents' tolerance for the environment, and corrects the deviation of PMV value through adaptive coefficient. The revised aPMV value is greater than PMV value, but the thermal and humidity environment level is still Class III, which does not meet the living conditions. Water source heat pump can be used as a heating method in winter to improve the thermal environment, which can provide reference for improving indoor thermal environment of residential buildings in water towns.

Dynamic heat preservation at night for a Trombe wall with a built-in panel curtain in Western China

Integrating the design of insulation, heat storage, and solar heating can help to improve indoor thermal environment during winter in Western China. However, insulation at night is often overlooked for Trombe walls (TWs). The present study considers a panel curtain installed in the cavity to enhance the preservation of heat of TWs at night. The effects of the structural parameters related to insulation inside the cavity on the TWs were analyzed in Western China and a design approach for insulation inside the cavity was proposed. In addition, the indoor air temperature of a TW with a built-in panel curtain (CTW) room was analyzed. The results indicate that the heat efficiency in the nighttime can be significantly improved by setting a panel curtain in the air cavity. Low emissivity film should be attached to the closed cavity side. The emissivity of the panel curtain’s exterior surface plays an important role in the closed cavity and the effect is more significant with low emissivity. The optimum thickness depends on the climate, i.e., 0.02–0.06 m for a large solar radiant heat loss ratio (SHLR), 0.02–0.05 m for a medium SHLR, and 0.02–0.04 m for a low SHLR. The thickness of the circulated cavity should be larger than 0.07 m, and the effect varies within a small range when the thickness exceeds 0.1 m. A panel curtain can significantly improve the indoor air temperature in a CTW room.

Thermal comfort in winter incorporating solar radiation effects at high altitudes and performance of improved passive solar design\u2014Case of Lhasa

The solar incidence on an indoor environment and its occupants has significant impacts on indoor thermal comfort. It can bring favorable passive solar heating and can result in undesired overheating (even in winter). This problem becomes more critical for high altitudes with high intensity of solar irradiance, while received limited attention. In this study, we explored the specific overheating and rising thermal discomfort in winter in Lhasa as a typical location of a cold climate at high altitudes. First, we evaluated the thermal comfort incorporating solar radiation effect in winter by field measurements. Subsequently, we investigated local occupant adaptive responses (considering the impact of direct solar irradiance). This was followed by a simulation study of assessment of annual based thermal comfort and the effect on energy-saving potential by current solar adjustment. Finally, we discussed winter shading design for high altitudes for both solar shading and passive solar use at high altitudes, and evaluated thermal mass shading with solar louvers in terms of indoor environment control. The results reveal that considerable indoor overheating occurs during the whole winter season instead of summer in Lhasa, with over two-thirds of daytime beyond the comfort range. Further, various adaptive behaviors are adopted by occupants in response to overheating due to the solar radiation. Moreover, it is found that the energy-saving potential might be overestimated by 1.9 times with current window to wall ratio requirements in local design standards and building codes due to the thermal adaption by drawing curtains. The developed thermal mass shading is efficient in achieving an improved indoor thermal environment by reducing overheating time to an average of 62.2% during the winter and a corresponding increase of comfort time.

Importance of Behavioral Adjustments for Adaptive Thermal Comfort in a Condominium with HEMS System

The energy use in residential dwellings has been increasing due to increasing use of modern electric appliances to make the lifestyle easier, entertaining and better. One of the major purposes of indoor energy use is for improving indoor thermal environment for adjusting thermal comfort. Along with the use of passive means like the use of mechanical devices, the occupants in any dwellings use active means such as the use of natural ventilation, window opening, and clothing adjustment. In fact, the use of active means when the outdoor environment is good enough might be more suitable to improve indoor thermal environment than the use of mechanical air conditioning units, which necessarily require electricity. Therefore, the people in developing countries like Nepal need to understand to what extent the occupants can use active means to manage their own indoor thermal comfort. The use of active means during good outdoor environment might be an effective way to manage increasing energy demand in the future. We have made a field survey on the occupants’ adaptive behaviors for thermal comfort in a Japanese condominium equipped with Home Energy Management System (HEMS). Online questionnaire survey was conducted in a condominium with 356 families from November 2015 to October 2016 to understand the occupants’ behaviors. The number of 17036 votes from 39 families was collected. The indoor air temperature, relative humidity and illuminance were measured at the interval of 2-10 minutes to know indoor thermal environmental conditions. The occupants were found using different active behaviors for thermal comfort adjustments even in rather harsh summer and winter. Around 80% of the occupants surveyed opened windows when the outdoor air temperature was 30⁰C in free running (FR) mode and the clothing insulation was 0.93 clo when the outdoor air temperature was 0⁰C. The result showed that the use of mechanical heating and cooling was not necessarily the first priority to improve indoor thermal environment. Our result along with other results in residential buildings showed that the adaptive behaviors of the occupants are one of the primary ways to adjust indoor thermal comfort. This fact is important in enhancing the energy saving building design.