Hourly indoor thermal comfort and air quality acceptance with passive climate control methods

Nowadays, the effect of permeable coverings on conditioning of indoor air in real buildings, has become of special interest in the process of achieving a sustainable built environment. In these studies, the first hour of occupation is usually selected, because it is then that the strong effect of coverings is felt, due to the low ventilation rate that prevails during the unoccupied period. In this context, an hourly study enables us to understand the behaviour during working periods and the effect of coverings on indoor thermal comfort conditions, air quality acceptance and peaks of energy consumption.Results showed that permeable coverings reduce energy consumption and peak loads and this effect is controlled by air renewal. Consequently, during the summer season, indoor thermal comfort and acceptance of indoor air conditions were found to be better with permeable coverings. In winter, in offices with impermeable coverings inadequate operative conditions of heating, ventilation, and air-conditioning (HVAC) induced a slight improvement on indoor air conditions, during the period of occupation. Further studies are required to assess the real effect of building materials and their use, and substitution of the current HVAC systems with this type of passive method. In particular, a suitable method to determine the adequacy of coverings and their active thickness needs to be developed.     

采用室内热舒适性控制的变风量空调系统节能控制研究

在对变风量空调系统及控制系统分析的基础上,利用ＤＤＣ控制器可采集多点和多种信号的优点,提出采用室内热舒适性控制取代室内温度控制的控制方案。仿真试验结果证明,同常规的室内温度控制方案相比,室内热舒适性控制方案可以较好地改善室内的热舒适性,同时,在保证室内热舒适性前提下,采用室内热舒适性控制方案不仅能够保证控制的稳定性,而且有较好的节能作用。     

Fuzzy control system for thermal and visual comfort in building

In the era of informational and technological breakthrough, the automatically controlled living and working environment is expected to become a commonly used service. This paper deals with dynamically controlled thermal and illumination responses of built environment in real-time conditions. The aim is to harmonize thermal and optical behaviour of a building by coordinating energy flows that pass through the transparent part of the envelope. For this purpose, a test chamber with an opening on the southern side was built. Changeable geometry of the opening is achieved by the automated external roller blind. A fuzzy control system enables the positioning of the shading device according to the desired indoor set points and the outdoor conditions. Through the experiments, the fuzzy controllers were tuned and gradually improved. Some sets of the experiments are presented here to illustrate the process.     

Cooling strategies,summer comfort and energy performance of a rehabilitated passive standard office building

One of the first rehabilitated passive energy standard office buildings in Europe was extensively monitored over two years to analyse the cooling performance of a ground heat exchanger and mechanical night ventilation together with the summer comfort in the building. To increase the storage mass in the light weight top floor, phase change materials (PCM) were used in the ceiling and wall construction. The earth heat exchanger installed at a low depth of 1.2 m has an excellent electrical cooling coefficient of performance of 18, but with an average cooling power of about 1.5 kW does not contribute significantly to cooling load removal. Mechanical night ventilation with 2 air changes also delivered cold at a good coefficient of performance of 6 with 14 kW maximum power. However, the night air exchange was too low to completely discharge the ceilings, so that the PCM material was not effective in a warm period of several days. In the ground floor offices the heat removal through the floor to ground of 2–3 W m⁻² K⁻¹ was in the same order of magnitude than the charging heat flux of the ceilings. The number of hours above 26 °C was about 10% of all office hours. The energy performance of the building is excellent with a total primary energy consumption for heating and electricity of 107–115 kW h m⁻² a⁻¹, without computing equipment only 40–45 kW h m⁻² a⁻¹.     

Effect of thermal insulation using leather and carpentry wastes on thermal comfort and energy consumption in a residential building

In this work, we investigate the effect of the thermal insulation by leather wastes (wet-blue chrome shavings and buffing dust) and carpentry wastes (wood shavings and sawdust) on the energy consumption of a model building using the average climatic data of the city of Casablanca (Morocco). For this study, we used the dynamic thermal simulation tool “TRNSYS 16” which predicts the thermal behavior of building and systems associated with it. Using this software, we evaluated the effect of the above material wastes on thermal comfort and building energy consumption. The type and the thickness of the materials were considered as variants to choose the better solution. The average temperatures of building supposed thermally insulated compared to those obtained without insulation clearly show the thermal insulation ability of tested materials during the cold and warm periods of the year. Increasing the thickness of the insulator makes locals increasingly comfortable. Because of their performance, leather and carpentry wastes can compete with conventional insulating materials such as polystyrene and cork.     

Adaptive thermal comfort model for different climatic zones of North-East India

Thermal comfort standards ISO 7730 and ASHRAE 55-2004 are based on the experimental results conducted in climatic chambers and the adaptive opportunities are usually limited in these experiments. However, in naturally ventilated buildings, adaptive opportunities are not fixed and occupants always have the liberty to modify the opportunities in order to feel comfortable. A comfort survey has been carried out in three different climatic zones of North-East India in four different seasons of a year. Climatic parameters corresponding to actual mean vote (AMV) are recorded during the survey and the values are used to calculate the predicted mean vote (PMV) using ISO 7730 calculation procedures. Results show that the PMV deviates from AMV values. A corrective term ‘adaptive coefficient’ is calculated based on PMV and AMV values and least square method to assess the different adaption used for thermal comfort. Theoretical adaptive models of thermal comfort have been developed based on these adaptive coefficients for the region. The adaptive coefficient values are varying for different seasons and also for different climatic zones. This reflects the various levels of adaptation in different seasons in a particular climatic zone. This adaptive coefficient can be used as a reference to thermal comfort assessment of the buildings and also can be used as dynamic control of the set temperature in the air conditioning system, which will results enormous energy saving. Result of this study also contributes towards the debate over the applicability of PMV model to naturally ventilated building.     

Evaluation of the cost efficiency of an energy efficient building

This paper presents quantitative results on the economics of different levels of thermal insulation for a building envelope. Results are calculated on the basis of an example building in Germany, which is a recently built single family house with materials commonly used in light-weight constructions. Defining the cost efficiency of an energy efficient building allows one to identify solutions which are already economically viable as well as to determine specific costs of the investment in an advanced sustainable building.     

The analysis of security cost for different energy sources

Global concerns for the security of energy have steadily been on the increase and are expected to become a major issue over the next few decades. Urgent policy response is thus essential. However, little attempt has been made at defining both energy security and energy metrics. In this study, we provide such metrics and apply them to four major energy sources in the Korean electricity market: coal, oil, liquefied natural gas, and nuclear. In our approach, we measure the cost of energy security in terms of supply disruption and price volatility, and we consider the degree of concentration in energy supply and demand using the Hirschman–Herfindahl index (HHI). Due to its balanced fuel supply and demand, relatively stable price, and high abundance, we find nuclear energy to be the most competitive energy source in terms of energy security in the Korean electricity market. LNG, on the other hand, was found to have the highest cost in term of energy security due to its high concentration in supply and demand, and its high price volatility. In addition, in terms of cost, we find that economic security dominates supply security, and as such, it is the main factor in the total security cost. Within the confines of concern for global energy security, our study both broadens our understanding of energy security and enables a strategic approach in the portfolio management of energy consumption.     

Analysis of the thermal performance and comfort conditions produced by five different passive solar heating strategies in the United States midwest

This paper presents a summary of the thermal performance of five different passive solar test-cells (Direct Gain, Trombe-wall, Water-wall, Sunspace, and Roofpond) and a control test-cell during the 2002–2003 heating season in Muncie, Indiana. The results discussed in this article correspond to the initial phase of a longer study (data were collected from December of 2002 until August of 2004). The project’s original intent was to identify any barriers to achieving thermal comfort within a space when passive solar heating systems are employed in severe winter climates with predominant overcast sky conditions. Because of the original intent of this project, the test-cells were arranged with their smaller facades oriented to the north and south and the longer facades facing east and west. This arrangement permitted to study temperature differences throughout the day (diurnal operative temperature swings) and also simultaneous temperature differences throughout the space (a simultaneous comparison of four points instrumented within each cell to detect variations between the south side and the north side of the test-cells).The results of this phase of the study show that the Direct Gain strategy had the largest diurnal variations of temperature with an average operative temperature swing of 7.8 °C and a maximum variation during the reported period of 10.3 °C. By contrast, the Roofpond strategy had the smallest diurnal variations of temperature with an average operative temperature swing of 1.2 °C and a maximum variation during the reported period of 1.4 °C. In terms of the simultaneous variations in the operative temperature between the south side and the north side of the test-cells, the Direct Gain strategy showed again the highest variations with an average simultaneous operative temperature difference between the south and north sides of the test-cell of 2.9 °C and a maximum variation during the reported period of 3.7 °C. The Roofpond strategy, on the other hand, had the smallest variations with an average simultaneous operative temperature difference between the south and north sides of the test-cell of 0.1 °C and a maximum variation during the reported period of 0.2 °C. The conclusions of this study demonstrate that diurnal variations of the operative temperature are primarily determined by the type of passive solar strategy utilized (with direct gain producing the highest temperature swings and the indirect gain strategies producing the smallest temperature swings) and by the thermal storage capacity of the system (with a higher thermal storage producing a smaller temperature swing). The simultaneous variations of the operative temperature inside the test-cells during the daytime were mostly influenced by the type of passive solar strategy utilized (with direct gain producing the highest simultaneous differences in temperature between the south and north sides of the test-cell and the indirect gain strategies producing the smallest temperature swings).     

Online performance evaluation of alternative control strategies for building cooling water systems prior to in situ implementation

This paper presents the online test and evaluation of the performance of five practical control strategies (fixed set-point control method, fixed approach control method, two near optimal strategies and one optimal strategy) for building cooling water systems to identify the best strategy for future field validation. All of these strategies were tested and evaluated in a simulated virtual environment similar to the situation when they are actually implemented in practice. A virtual building system representing the real building and its central chilling system was developed and used to test the operational performance of the system controlled by different strategies. The packages of each control strategy are separately computed by the application program of Matlab, as the control optimizers to identify the necessary control settings for the given condition based on the collected operation data. The data exchanger between the virtual building system and the control optimizer was managed by a software platform through a communication interface. The results showed that the optimal control strategy is more energy efficient and cost effective than the other strategies, and its computational cost is manageable and can satisfy the requirements of practical applications. This strategy is being implemented in a super high-rise building for field validation.     

隔断式工位空调系统气流组织与人体热舒适评价

采用K-ε湍流模型对采用隔断式工位空调的典型办公室工作微环境进行数值模拟,分析工位空调在人体周围所形成的非均一环境参数场,并进一步研究非均匀环境对人体热舒适的影响.在不同工位送风参数下对房间和人体周围环境参数的分布状况及吹风感和热舒适性进行研究.模拟结果发现:工位空调送风可以使室内温度呈现分区分布,工位送风效率高,可以...     

An investigation of the potential for natural ventilation and building orientation to achieve thermal comfort in warm and humid climates

The aim of this study was to analyze the most important factor, the climatic conditions with respect to thermal comfort in buildings. The impact of building location and climate and orientation on thermal comfort were investigated.With the help of dynamic computer simulations the different hourly weather data were analyzed. First of all the climate determines the amount of solar radiation and mean outside temperature that a building is exposed to. The climate also influences the amount of energy that is used for heating and cooling but also the amount of energy that is used for lighting. There is solar excess which determines the amount of solar energy that is unwanted in the building. With growing amounts of glass and a glazing system that allows large solar heat gains,the impact of orientation is substantial. A detailed analysis was conducted to evaluate the potentials for improving thermal comfort. Detailed results are given in sample graphics and tables in the study. In a tropical climate the improvement in comfort by NV range between 9% and 41% (Kuala Lumpur in April). For a subtropical climate the improvements vary between 3% and 14%. In a temperate climate the improvements vary between 8% and 56%. The results showed that NV has a good potential in tropical and temperate climates but not in subtropical climates. Especially in Hong Kong it seems to be very difficult to apply NV. The results showed that in particular in the hottest period (summer) the potential for comfort improvements is rather small. The design of climate responsive building envelopes should take this into consideration.     

The early design model for prediction of energy and cost performance of building design options

In order to encourage the use of computer modelling in building environmental analysis, it is necessary to provide a model developed from the designer's point of view. Detailed simulation models require a high degree of expertise and familiarity, further, there is also a need for detailed information not available in the early stages of the design process. Simplified models play an important role in the early stages of a design to achieve an integrated design: firstly, they are easy to use and, secondly, they require information easily available at the start of a design. In the Early Design Model (EDM) the solar gain utilisation factor has been determined as a continuous function of thermal mass. The differences between the annual energy predictions of EDM and SERI-RES ranges from 0.1% to 4.6% for time constants ranging from 378 to 2.52 hours. The differences between the two sets of predictions on monthly basis ranges from m 3.6% to m 6.48% (EDM's predictions being larger) during the heating season, and from +2.86% to a maximum of +51% (EDM's predictions being smaller) in the remaining part of the year. In addition to energy predictions, EDM incorporates a facility which gives cost indications.     

Simple tool to evaluate energy demand and indoor environment in the early stages of building design

A simplified building simulation tool to evaluate energy demand and thermal indoor environment in the early stages of building design is presented. Simulation is performed based on few input data describing the building design, HVAC systems and control strategies. Hourly values for energy demand and indoor temperature are calculated based on hourly weather data. Calculation of the solar energy transmitted through windows takes into account the dependency of the total solar energy transmittances on the incidence angle, shades from far objects and shades from the window recess and overhangs. Several systems including heating, cooling, solar shading, venting, ventilation with heat recovery and variable insulation can be activated to control the indoor temperature and energy demand. Predicted percentages of dissatisfied occupants are calculated for a given time period to support decisions concerning the thermal indoor environment. The simplified building simulation tool gives reliable results compared to detailed tools and needs only few input data to perform a simulation. The tool is therefore useful for preliminary design tasks in the early design stages where rough estimates of the building design are given and rough estimates of energy use and thermal indoor environment are needed for decision support.     

A numerical simulation tool for predicting the impact of outdoor thermal environment on building energy performance

A building affects its surrounding environment, and conversely its indoor environment is influenced by its surroundings. In order to obtain a more accurate prediction of the indoor thermal environment, it is necessary to consider the interactions between the indoor and outdoor thermal environments. However, there is still a lack of numerical simulation tools available for predicting the interactions between indoor and outdoor microclimate that take into account the influences of outdoor spatial conditions (such as building forms and tree shapes) and various urban surface materials. This present paper presents a simulation tool for predicting the effect of outdoor thermal environment on building thermal performance (heating/cooling loads, indoor temperature) in an urban block consisting of several buildings, trees, and other structures. The simulation tool is a 3D CAD-based design tool, which makes it possible to reproduce the spatial forms of buildings and constructed surface materials in detail. The outdoor thermal environment is evaluated in terms of external surface temperature and mean radiant temperature (MRT). Simulated results of these temperatures can be visualized on a color 3D display. Building heating/cooling loads and indoor air temperature (internal surface temperature) can also be simulated. In this study, a simulation methodology is described, and a sensitivity analysis is conducted for a wooden detached house under different outdoor conditions (building coverage, adjacent building height, surrounding with trees or no-trees). Simulation results show that the simulation tool developed in this study is capable of quantifying the influences of outdoor configurations and surface materials on both indoor and outdoor environments.     

A reversible thermal panel for spacecraft thermal control (evaluation of effectiveness and reliability of new autonomous thermal control device)

The current trend in spacecraft design toward high‐density packing of the payload electronics and increased waste heat flux will require the development of lightweight high thermal conductive materials and innovative thermal control techniques. Additionally, new challenging missions will require new techniques to adapt to a variety of environmental conditions. In this study, a new passive thermal control device—a Reversible Thermal Panel (RTP) based on high thermal conductive graphite sheets and shape memory alloy—is proposed. The RTP changes its function reversibly from radiator to solar absorber by deploying/stowing a reversible fin. Thermal analyses were conducted to predict the fundamental thermal performance of the RTP. A breadboard model of the RTP based on the graphite sheets and aluminum alloys was fabricated, and the thermal vacuum test was conducted with the reversible fin deployed and stowed. The desired variability in thermal performance of the RTP due to deploying or stowing the reversible fin was demonstrated. Comparison of the predicted results with test results indicated a good agreement. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(5): 350–367, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20060     

Experimental results of different control strategies in a solar air-conditioning system at part load

In this article, different control strategies used in a solar cooling installation are presented and compared, publishing real working data from three summer periods, with the system working at part load.The facility consists of two solar fields that feed a heating system during the winter and a 35 kW Li-Br absorption chiller during the summer period to cool part of an office building.The improvements obtained using control based on critical radiation and a variable flow mass have been compared on the solar plant with a conventional constant flow control. In the same way, the improvements obtained in the yields of a cooling production plant have been compared when programming three different controls: the first one with fixed flow masses, the second adapting the temperature on the condenser as a function of the generator temperature (constant flow mass), and the third adapting the condenser temperature and the flow mass on the generator as a function of the system loads.     

Optimization of control strategies for stand-alone renewable energy systems with hydrogen storage

This paper presents a novel strategy, optimized by genetic algorithms, to control stand-alone hybrid renewable electrical systems with hydrogen storage. The strategy optimizes the control of the hybrid system minimizing the total cost throughout its lifetime. The optimized hybrid system can be composed of renewable sources (wind, PV and hydro), batteries, fuel cell, AC generator and electrolyzer. If the renewable sources produce more energy than the one required by the loads, the spare energy can be used either to charge the batteries or to produce H₂ in the electrolyzer. The control strategy optimizes how the spare energy is used. If the amount of energy demanded by the loads is higher than the one produced by the renewable sources, the control strategy determines the most economical way to meet the energy deficit. The optimization of the various system control parameters is done using genetic algorithms. This paper explains the strategy developed and shows its application to a PV–diesel–battery–hydrogen system.     

Numerical analysis and field measurements of the airflow patterns and thermal comfort in an indoor swimming pool: a case study

Public indoor swimming pools are a very popular type of sports facility. They need to ensure good indoor air quality and thermal comfort of the occupants (TCO) while reducing their energy consumption. The objectives of this study are to develop a numerical code, based on the zonal method; to investigate the indoor airflow patterns; and to determine the TCO in the indoor swimming pool. The numerical simulation, performed using the TRNSYS software (version 17), is validated against intensive field measurements, carried out in the public indoor swimming pool located at Bishop’s University (Sherbrooke, Quebec, Canada), of the temperature, velocity, and relative humidity of the air as well as the surface temperature of the walls, ceiling, and floor. The developed code is then used to study the indoor flow patterns and to evaluate the TCO using three indexes: the humidex chart, the predicted mean vote (PMV), and the predicted percentage of dissatisfied (PPD). The results show a hot-humid rather uncomfortable atmosphere is prevailing in the occupied parts of the studied indoor swimming pool. The calculated airflow rates show that, due to the position of the ventilation inlets and outlets, most of the ventilation air circulates in the upper part of the building causing an insufficient air renewal in the occupied parts of the studied indoor swimming pool.     

Numerical evaluation of various thermal management strategies for polymer electrolyte fuel cell stacks

Thermal management is one of the key factors required to ensure good performance polymer electrolyte fuel cell (PEFC) stacks. The choice of the thermal management strategy depends on the specific application, size, weight, design, complexity, and cost. In this work, we investigate various alternative thermal management strategies for PEFC stacks, e.g., forced convection in specially design cooling plate/channel with either (i) liquid or (ii) air as the coolant; (iii) edge-air cooling with fins and; combine oxidant and coolant flow (open-cathode) with (iv) forced and (v) natural convection air cooling. A three-dimensional two-phase model, comprising of the equations of conservation of mass, momentum, species, energy and charge, is employed to quantify the performance of various cooling strategies. The results demonstrate that thermal management is essential to ensure good stack performance. Liquid cooling, as expected, performs the best compared to air cooling, whereas natural convection cooling is just marginally able to maintain a stack with large number of cells from steep drop in performance. Finally, results presented in this paper can provide useful design guidelines for selection of a suitable thermal management strategy for a PEFC stack and its near-to- or optimum cooling condition.