Thermal Comfort Conditions In Buildings Research Articles

Hybrid nanocomposite of vanadium dioxide and carbon nanotubes embedded in a gypsum binder for thermal energy storage

This investigation studied the heat storage capacity of a gypsum blinder with a hybrid nanocomposite (NH) of vanadium dioxide and multiwall carbon nanotubes (VO2/MWCNT). The influence of the NH in the hydration kinetics and hydrated products was determined. The effect of the incorporated amount of NH in the wettability, mass loss by humectation-drying cycles, thermal conductivity, specific heat (Cp) and gypsum thermal performance at 40 °C was determined. Characterization techniques exhibited that the presence of VO2/MWCNT did not modify hydration kinetics and phases development, water drop angle or compressive strength. Nevertheless, gypsum blinders mass loss increased with the presence of the nanocomposite after 6 humectation-drying cycles. According to the thermal properties, it was found that the NH addition increased gypsum blinders thermal conductivity and Cp values. Finally, it was concluded that gypsum with VO2/MWCNT promotes self-thermal regulation properties without affecting its performance. The usage of VO2/MWCNT embedded in a gypsum as a construction material would provide thermal comfort conditions in buildings.

ASHRAE Likelihood of Dissatisfaction: A new right-here and right-now thermal comfort index for assessing the Likelihood of dissatisfaction according to the ASHRAE adaptive comfort model

The assessment of local and short-term thermal discomfort in buildings has been widely investigated, and different metrics are available in the literature to predict the likelihood of dissatisfied people. These metrics are named right-here and right-now discomfort indexes and constitute the basis for evaluating long-term thermal comfort conditions in buildings. Well-known examples are the Predicted Percentage of Dissatisfied (PPD) part of the Fanger comfort model included in the ISO standard 7730 and the Overheating risk index (NaOR), built upon the EN adaptive thermal comfort model. This study proposes a new index for use with the ASHRAE adaptive thermal comfort model to fill a gap in the literature and standard. It is called the ASHRAE Likelihood of Dissatisfaction (ALD) and is obtained from a logistic regression of the right-here and right-now thermal comfort field data contained in the 1990s ASHRAE RP-884 database. The recent release of another, more extensive database of thermal comfort field studies, the ASHRAE Global Thermal Comfort Database II, provides an opportunity to validate ALD with an independent dataset and assess its generalisability. The successful external validation of ALD and its agreement with NaOR give support to the reliability of the novel right-here and right-now index and open to the possibility to use it for assessing short-term thermal comfort conditions in buildings, calculating long-term thermal comfort indices based on the ASHRAE adaptive model, optimising both the design of new buildings and renovations and for assessing the operational thermal comfort performance of existing buildings.

Towards a Computational Fluid Dynamics-Based Fuzzy Logic Controller of the Optimum Windcatcher Internal Design for Efficient Natural Ventilation in Buildings

Recently, increased attention has been given to the coupling of computational fluid dynamics (CFD) with the fuzzy logic control system for obtaining the optimum prediction of many complex engineering problems. The data provided to the fuzzy system can be obtained from the accurate computational fluid dynamics of such engineering problems. Windcatcher performance to achieve thermal comfort conditions in buildings, especially in hot climate regions, is considered as one such complex problem. Windcatchers can be used as natural ventilation and passive cooling systems in arid and windy regions in Saudi Arabia. Such systems can be considered as the optimum solution for energy-saving and obtaining thermal comfort in residential buildings in such regions. In the present paper, three-dimensional numerical simulations for a newly-developed windcatcher model have been performed using ANSYS FLUENT-14 software. The adopted numerical algorithm is first validated against previous experimental measurements for pressure coefficient distribution. Different turbulence models have been firstly applied in the numerical simulations, namely, standard k-epsilon model (1st and 2nd order), standard Wilcox k-omega model (1st and 2nd order), and SST k-omega model. In order to assess the accuracy of each turbulence model in obtaining the performance of the proposed model of the windcatcher system, it is found that the second order k-epsilon turbulence model gave the best results when compared with the previous experimental measurements. A new windcatcher internal design is proposed to enhance the ventilation performance. The fluid dynamics characteristics of the proposed model are presented, and the ventilation performance of the present model is estimated. The numerical velocity profiles showed good agreement with the experimental measurements for the turbulence model. The obtained results have shown that the second order k-epsilon turbulence can predict the different important parameters of the windcatcher model. Moreover, the coupling algorithm of CFD and the fuzzy system for obtaining the optimum operating parameters of the windcatcher design are described.

Performance analysis of domed roof integrated with earth-to-air heat exchanger system to meet thermal comfort conditions in buildings

In the present study, an integrated cooling system consisting an earth-to-air heat exchanger (EAHE) and a domed roof is investigated numerically to meet the thermal comfort conditions and supply the cooling demand for a building. Simulation of airflow in the EAHE and a test room with the domed roof is performed with ANSYS FLUENT software three-dimensionally, and the thermal behavior of the system is modeled with the code developed in MATLAB software. Furthermore, for verifying the numerical results of EAHE modeling, an experimental study is conducted. The impact of both geometric and environmental parameters on the system performance is also investigated. The obtained results reveal that the system is capable of providing thermal comfort conditions, according to adaptive thermal comfort standard (ATCS), for the test room with a maximum cooling demand of about 1000 W alone and without consuming electric energy by using three pipes with a length of 35 m and a diameter of 0.4 m. The application of the proposed system instead of the split inverter air conditioner and the evaporative cooler to provide a similar cooling load can reduce the electrical energy consumption up to 0.360 kW h, and 0.200 kW h, respectively. In addition, the environmental analysis indicates that the utilization of this system instead of the split inverter air conditioner and evaporative air cooler with similar capacities leads to respective 361.89 kg and 216.06 kg reduction in CO2 emissions for summer months. Finally, the application of the proposed integrated system for a two-story building with domed roof is evaluated. The results show the ability of the system to provide thermal comfort for the two-story building with a maximum cooling demand of approximately 300 W for each floor using two pipes with a length of 35 m and a diameter of 0.4 m.

Performance analysis of wind catcher integrated with shower cooling system to meet thermal comfort conditions in buildings

In this study, natural ventilation and cooling of a two-floor building connected to a wind catcher were studied in which a shower cooling system has been used to reduce ambient air temperature. The capability of the system to meet thermal comfort conditions based on adaptive thermal comfort and ISO/EN 7730 standards was evaluated under different operating conditions. In order to estimate the air change per hour and air flow simulation around and inside the test building, ANSYS FLUENT 6.3 software was utilized and the air temperature at the outlet of the shower cooling system was computed using a thermodynamic model. The results showed that for the wind velocity beyond 0.4 m/s, the ACH value for the rooms could be set in the range of 3–20 h−1 with the regulation of window's aperture. Under this condition, the temperature and relative humidity of air stream into the building did not change with the wind velocity. Also, it was found that when three buildings are situated in one direction, ACH value for the middle building is less than others. As the ACH value increases, thermal comfort conditions are met for larger values of required cooling demands. Although electrical energy consumption of the proposed system is already lower than evaporative air coolers, it cannot compete with split inverter air conditioners where the relative humidity of ambient air is high.

An MAS-based subjective model for indoor adaptive thermal comfort

The achievement of high level personalized sets of comfort parameters is contemplated within the more general context of so-called smart buildings, where people, by means of the new communication technologies, become active actors to the process of the singling out and control of the best indoor conditions. This dynamic intelligence approach would usefully contribute to better energy-efficient and environment-friendly management of buildings. Multi-agent schemes are suitable tools in this aim, since they are able to manage the user–building–plant system, where adaptivity of people to indoor conditions is suitably achieved. In this article, a contribution to the development of the classical Fanger's model is presented, embodying a user's personal preferences referring to his/her cognitive–emotive–relational ambit. The proposed algorithm is based on a particular multi-agent aimed at the assessment of subjective indoor comfort. Such a subjective–adaptive model is meant herein as a tool for achieving an optimal control of thermal comfort conditions in buildings.

Short-term airing by natural ventilation - implication on IAQ and thermal comfort

The need to improve the energy efficiency of buildings requires new and more efficient ventilation systems. It has been demonstrated that innovative operating concepts that make use of natural ventilation seem to be more appreciated by occupants. Among the available ventilation strategies that are currently available, buoyancy driven, single-sided natural ventilation has proved to be very effective and can provide high air change rates for temperature and Indoor Air Quality (IAQ) control. However, to promote a wider distribution of these systems an improvement in the knowledge of their working principles is necessary. The present study analyses and presents the results of an experimental evaluation of airing performance in terms of ventilation characteristics, IAQ and thermal comfort. It includes investigations of the consequences of opening time, opening frequency, opening area and expected airflow rate, ventilation efficiency, thermal comfort and dynamic temperature conditions. A suitable laboratory test rig was developed to perform extensive experimental analyses of the phenomenon under controlled and repeatable conditions. The results showed that short-term window airing is very effective and can provide both acceptable IAQ and thermal comfort conditions in buildings. Practical Implications This study gives the necessary background and in-depth knowledge of the performance of window airing by single-sided natural ventilation necessary for the development of control strategies for window airing (length of opening period and opening frequency) for optimum IAQ and thermal comfort in naturally ventilated buildings.

Five Years of Laboratory and In Situ Test Experiences to Verify Therms Comfort Conditions in an Innovative Hybrid Ventilated Building

Climatisation and natural ventilation concepts are today, in most countries, considered to be an essential aspect of the building project. In fact they are utilised to guarantee summer thermal comfort and indoor air quality control. Also there are many other advantages including low energy use, reduction of noise levels and easy plant maintenance. In recent years the use of hybrid ventilation systems in office buildings has been developed. The achievement of thermal comfort conditions in buildings is an important aim in order to satisfy occupants. To achieve a high level of life quality a study of climatic parameters of the ambient air is needed. International Standard ISO 7726 and ASHRAE Standard 55-81 define the values of parameters affecting thermal comfort in offices. The aim of the present work is to evaluate the fluid dynamic phenomena connected to the running of the air conditioning and natural ventilation systems in an innovative office building, constructed in central Italy, aimed at achieving energy optimisation with good thermal comfort.This building has been monitored and the main fluid dynamic data of the air have been recorded. In addition the recorded values have been related to external parameters including solar radiation, wind speed and wind direction, to verify the indoor conditions in relation to the energy use of the building and to outdoor conditions.This research has been accomplished using automated monitoring for indoor data acquisition, a microclimatic station and a meteorological station equipped with the probes needed to measure the external environmental parameters. The experimental data corresponding to a monitoring period are reported. Results verified the performance of the measuring system developed for this project. They also provided information about the ventilation behaviour and thermal comfort conditions in the building under various sets of climatic conditions.

The validity of ISO-PMV for predicting comfort votes in every-day thermal environments

One of the uses of ISO 7730 (predicted mean vote, PMV) is to predict the thermal sensations of people in buildings. This application is examined, using the ASHRAE database of field-studies. Taking these world-wide data as a single distribution, PMV is free from serious bias. There exist, however, underlying biases in relation to all contributing variables, and a further bias related to the outdoor temperature. These biases often combine to produce a substantial bias in PMV. In surveys of individual buildings, PMV often differs markedly and systematically from the actual mean vote, both for naturally ventilated (NV) and for air-conditioned (AC) spaces. Possible origins of the biases are discussed, and it is shown that it would be possible to modify PMV substantially to reduce them. Environmental consequences of the use of PMV are discussed. It is concluded that ISO 7730 in its present form can be seriously misleading when used to estimate thermal comfort conditions in buildings.

Recent research on an indirect evaporative cooler (IEC) Part 2: thermal performance of a non-conditioned building coupled with an IEC

The thermal performance of a non-conditioned building fitted with an indirect evaporative cooler (IEC) has been investigated in terms of hourly, monthly and seasonal discomfort index. The effect of various design parameters of the IEC on the discomfort index has been investigated for three different climatic areas of India, i.e. hot–dry, warm, humid and composite. The analysis has shown that the IEC is effective for creating thermal comfort conditions in buildings in dry–hot and composite climates. © 1997 by John Wiley & Sons, Ltd.