Using results from field surveys to predict the effect of open windows on thermal comfort and energy use in buildings

Windows are one of the major means by which building occupants control the indoor environment. This research uses results from field surveys to formulate a method for simulation of office buildings to include the effects of window opening behaviour on comfort and energy use. The paper focuses on: (1) what is general window opening behaviour? (2) how can we frame an “adaptive algorithm” to predict whether windows are open? (3) how can the algorithm be used within a simulation to allow the effects of window opening on comfort and energy use to be quantified? We have found that: (1) the proportion of windows open depends on indoor and outdoor conditions, (2) logistic regression analysis can be used to formulate an adaptive algorithm to predict the likelihood that windows are open, (3) the algorithm when embedded in simulation software provides insights not available using more usual simulation methods and allows the quantification of the effect of building design on window opening behaviour, occupant comfort and building energy use.     

Predictive controllers for thermal comfort optimization and energy savings

The present work is focused on the study of indoor thermal comfort control problem in buildings equipped with HVAC (heating, ventilation and air conditioning) systems. The occupants’ thermal comfort sensation is addressed here by the well-known comfort index known as PMV (predicted mean vote) and by a comfort zone defined in a psychrometric chart. In this context, different strategies for the control algorithms are proposed by using an only-one-actuator system that can be associated to a cooling and/or heating system. The first set of strategies is related to the thermal comfort optimization and the second one includes energy consumption minimization, while maintaining the indoor thermal comfort criterion at an adequate level. The methods are based on the model predictive control scheme and simulation results are presented for two case studies. The results validate the proposed methodology in terms of both thermal comfort and energy savings.     

Thermal comfort analysis of a low temperature waste energy recovery system: SIECHP

The use of a recovery device is justified in terms of energy savings and environmental concerns. But it is clear that the use of a recovery system also has to lead to controlling indoor environmental quality, nowadays a priority concern. In this article, experimental research has been carried out whose aim is to study the thermal comfort provided by a combined recovery equipment (SIECHP), consisting of a ceramic semi-indirect evaporative cooler (SIEC) and a heat pipe device (HP) to recover energy at low temperature in air-conditioning systems. To characterize this device empirically in terms of thermal comfort (TC), Fanger's predicted mean vote (PMV), draught rate, and vertical air temperature difference were used in this study as the TC criteria.     

The impact of indoor thermal conditions,system controls and building types on the building energy demand

It is possible to evaluate the energy demand as well as the parameters related to indoor thermal comfort through building energy simulation tools. Since energy demand for heating and cooling is directly affected by the required level of thermal comfort, the investigation of the mutual relationship between thermal comfort and energy demand (and therefore operating costs) is of the foremost importance both to define the benchmarks for energy service contracts and to calibrate the energy labelling according to European Directive 2002/92/CE. The connection between indoor thermal comfort conditions and energy demand for both heating and cooling has been analyzed in this work with reference to a set of validation tests (office buildings) derived from a European draft standard. Once a range of required acceptable indoor operative temperatures had been fixed in accordance with Fanger's theory (e.g. −0.5 < PMV < −0.5), the effective hourly comfort conditions and the energy consumptions were estimated through dynamic simulations. The same approach was then used to quantify the energy demand when the range of acceptable indoor operative temperatures was fixed in accordance with de Dear's adaptive comfort theory.     

Energy and comfort performance of thermally activated building systems including occupant behavior

In building simulations it is common practice to use standardized occupant behavior and internal gains. Although this is a valid approach for designing systems, the probabilistic nature of these boundary conditions influences the energy demand and achieved thermal comfort of real systems. This paper analyzes the influence of occupant behavior on the energy performance and thermal comfort of a typical office floor equipped with a thermally activated building system (TABS). A multi-zone TRNSYS model with 10 adjacent zones per orientation for a typical moderate Belgian climate is set up. First, the energy performance and thermal comfort of thermally activated building systems (TABS) are compared with the performance of idealized cooling with standardized user behavior. TABS are able to deliver good thermal comfort but show to have a higher energy demand. Secondly, probabilistic occupant behavior was implemented in the TABS simulations. The influence of the occupancy rate, the shading device use and switching of the lights are analyzed by defining user profiles. It is shown that occupant behavior may have an important influence on the cooling demand and thermal comfort. However, as long as good solar protection is foreseen and operated in a correct way, TABS are able to cope with different user behavior modeled in this paper. In this case, normal daily stochastic processes do not considerably affect the cooling demand and thermal comfort during summer.     

Assessment of monitored energy use and thermal comfort conditions in mosques in hot-humid climates

In harsh climatic regions, buildings require air-conditioning in order to provide an acceptable level of thermal comfort. In many situations buildings are over cooled or the HVAC system is kept running for a much longer time than needed. In some other situations thermal comfort is not achieved due to improper operation practices coupled with poor maintenance and even lack it, and consequently inefficient air-conditioning systems. Mosques represent one type of building that is characterized by their unique intermittent operating schedule determined by prayer times, which vary continuously according to the local solar time. This paper presents the results of a study designed to monitor energy use and thermal comfort conditions of a number of mosques in a hot-humid climate so that both energy efficiency and the quality of thermal comfort conditions especially during occupancy periods in such intermittently operated buildings can be assessed accurately.     

Energy use and thermal comfort in a rammed earth office building

A two-storey rammed earth building was built on the Thurgoona Campus of Charles Sturt University in Albury-Wodonga, Australia, in 1999. The building is novel both in the use of materials and equipment for heating and cooling. The climate at Wodonga can be characterised as hot and dry, so the challenge of providing comfortable working conditions with minimal energy consumption is considerable. This paper describes an evaluation of the building in terms of measured thermal comfort and energy use. Measurements, confirmed by a staff questionnaire, found the building was too hot in summer and too cold in winter. Comparison with another office building in the same location found that the rammed earth building used more energy for heating. The thermal performance of three offices in the rammed earth building was investigated further using simulation to predict office temperatures. Comparisons were made with measurements made over typical weeks in summer and winter. The validated model has been used to investigate key building parameters and strategies to improve the thermal comfort and reduce energy consumption in the building. Simulations showed that improvements could be made by design and control strategy changes.     

Climate change,thermal comfort and energy: Meeting the design challenges of the 21st century

This paper addresses the dual challenge of designing sustainable low-energy buildings while still providing thermal comfort under warmer summer conditions produced by anthropogenic climate change—a key challenge for building designers in the 21st century. The main focus is towards buildings that are ‘free running’ for some part of the summer, either being entirely naturally ventilated or mixed-mode (where mechanical cooling is only used when thought to be essential). Because the conditions in these buildings will vary from day to day it is important to understand how people react and adapt to their environment. A summary is made of recent developments in this area and of the climate data required to assess building performance. Temperatures in free running buildings are necessarily closely linked to those outside. Because the climate is changing and outside summer temperatures are expected to increase, the future will offer greater challenges to the designers of sustainable buildings aiming to provide either entirely passive or low-energy comfort cooling. These issues are demonstrated by predictions of the performance of some case study buildings under a climate change scenario. The examples also demonstrate some of the important principles associated with climate-sensitive low-energy design.     

Evaluation of thermal comfort using combined CFD and experimentation study in a test room equipped with a cooling ceiling

This paper reports a full-scale experimental campaign and a computational fluid dynamics (CFD) study of a radiant cooling ceiling installed in a test room, under controlled conditions. This research aims to use the results obtained from the two studies to analyze the indoor thermal comfort using the predicted mean vote (PMV). During the whole experimental tests the indoor humidity was kept at a level where the condensation risk was minimized and no condensation was detected on the chilled surface of the ceiling. Detailed experimental measurements on the air temperature distribution, surface temperature and globe temperature were realized for different cases where the cooling ceiling temperature varied from 16.9 to 18.9 °C. The boundary conditions necessary for the CFD study were obtained from the experimental data measurements. The results of the simulations were first validated with the data from the experiments and then the air velocity fields were investigated. It was found that in the ankle/feet zone the air velocity could pass 0.2 m/s but for the rest of the zones it took values less than 0.1 m/s. The obtained experimental results for different chilled ceiling temperatures showed that with a cooling ceiling the vertical temperature gradient is less than 1 °C/m, which corresponds to the standard recommendations. A comparison between globe temperature and the indoor air temperature showed a maximum difference of 0.8 °C being noticed. This paper also presents the radiosity method that was used to calculate the mean radiant temperature for different positions along different axes. The method was based on the calculation of the view factors and on the surface temperatures obtained from the experiments. PMV plots showed that the thermal comfort is achieved and is uniformly distributed within the test room.     

Primary energy and comfort performance of ventilation assisted thermo-active building systems in continental climates

This article presents a simulation study comparing the primary energy and comfort performance of ventilation assisted thermo-active building systems (TABS) relative to a conventional all-air (VAV) system in a compact office building featuring good thermal envelope performance, heat recovery, and solar gain control for the continental climate of Omaha, Nebraska with pronounced heating and cooling periods. TABS heating is accomplished using a geothermal heat pump and TABS cooling using a geothermal heat exchanger without an additional vapor compression cycle required. It was found that the coordination of the TABS and VAV systems is crucial, i.e., supply air temperature and active layer temperature setpoints and reset schedules greatly affect the performance of the overall system. The small contribution of TABS in the heating case shows the need for the adaptation of the ventilation system configuration to the TABS system. Annual cooling energy demand for the ventilation assisted TABS is higher than for the pure VAV system, which is due to lower occupied period room operative temperatures and thus a higher comfort provided. While a 4% useful energy penalty for the combined TABS/VAV was recorded, the VAV case requires 20% more delivered energy than the TABS case because of the displacement of compressor driven coil loads with low-exergy cooling through the ground heat exchanger in the TABS case. A primary energy intensity of 189 kWh/m² a was recorded for the TABS case; in contrast, the conventional all-air (VAV) equipped building incurs a primary energy intensity of 229 kWh/m²a, which represents a penalty of 20%. Clear advantages of the TABS approach can be observed with respect to thermal comfort: during summer cooling periods, the mean radiant temperature of the TABS case is on average 2 K below that of the VAV case. Moreover, the VAV system is associated with a fairly constant predicted mean vote (PMV) value of 0.75, which is quite warm, while the TABS equipped system reveals an average of 0.56, which results in only 12% instead of 17% of people dissatisfied. Based on these results, ventilation assisted thermo-active cooling systems appear to be a very promising alternative to conventional all-air systems offering both significant primary energy as well as thermal comfort advantages provided the TABS is mated with low-exergy heating and cooling sources.     

A field study of occupant thermal comfort and thermal environments with radiant slab cooling

This paper presents the findings of a field study of occupant thermal comfort and thermal environments with a radiant slab cooling system. The study combined field measurements and questionnaires based on the ASHRAE RP-921 project protocol. A total of 116 sets of data from 82 participants were collected in summer and winter. The results reveal that occupant whole-body thermal sensations with radiant cooling were consistent with the PMV model. The main advantage of radiant cooling for thermal comfort was found to be reduced local thermal discomfort with reduced vertical air temperature difference as well as reduced draft rate. The survey results revealed that 14–22% of participants in the study reported local cold discomfort in the arm–hand and the leg–foot regions. The results indicated that there may be lower limits on air speeds acceptable to occupants. Statistical analysis indicated that occupant thermal votes were free of significant correlation with personal, contextual and psychological factors. Suggestions to improve the questionnaire and the field survey process are offered.     

Simulation of energy use, human thermal comfort and office work performance in buildings with moderately drifting operative temperatures

Annual primary energy use in a central module of an office building consisting of two offices separated with a corridor was estimated by means of dynamic computer simulations. The simulations were conducted for conventional all-air VAV ventilation system and thermo active building system (TABS) supplemented with CAV ventilation. Simulations comprised moderate, hot–dry and hot–humid climate. Heavy and light wall construction and two orientations of the building (east–west and north–south) were considered. Besides the energy use, also capability of examined systems to keep a certain level of thermal comfort was examined. The results showed that with the moderate climate, the TABS decreased the primary energy use by about 16% as compared with the VAV. With hot–humid climate, the portion of the primary energy saved by TABS was ca. 50% even with the supply air dehumidification taken into account. The TABS working in a moderate climate kept the predicted percentage of dissatisfied (PPD) <10% during 60–80% of the working hours per year. Optimization of the TABS's control strategy (circulation pump dead-band, water supply temperature) resulted in significant reduction of the annual working hours with PPD > 10%; 1.4% in comparison to 17.5% h/yr. The highest estimated loss of occupants’ productivity related to their thermal sensation hasn’t exceeded 1% in whole year average.     

Flow patterns and thermal comfort in a room with panel,floor and wall heating

Thermal comfort aspects in a room vary with different space heating methods. The main focus in this study was how different heating systems and their position affect the indoor climate in an exhaust-ventilated office under Swedish winter conditions. The heat emitters used were a high and a medium–high temperature radiator, a floor heating system and large wall heating surfaces at low temperature. Computational fluid dynamics (CFD) simulations were used to investigate possible cold draught problems, differences in vertical temperature gradients, air speed levels and energy consumption. Two office rooms with different ventilation systems and heating needs were evaluated. Both systems had high air exchange rates and cold infiltration air.     

Urban Physics: Effect of the micro-climate on comfort,health and energy demand

The global trend towards urbanisation explains the growing interest in the study of the modification of the urban climate due to the heat island effect and global warming, and its impact on energy use of buildings. Also urban comfort, health and durability, referring respectively to pedestrian wind/thermal comfort, pollutant dispersion and wind-driven rain are of interest. Urban Physics is a well-established discipline, incorporating relevant branches of physics, environmental chemistry, aerodynamics, meteorology and statistics. Therefore, Urban Physics is well positioned to provide key-contributions to the current urban problems and challenges. The present paper addresses the role of Urban Physics in the study of wind comfort, thermal comfort, energy demand, pollutant dispersion and wind-driven rain. Furthermore, the three major research methods applied in Urban Physics, namely field experiments, wind tunnel experiments and numerical simulations are discussed. Case studies illustrate the current challenges and the relevant contributions of Urban Physics.     

Effects of radiant temperature on thermal comfort

The aim of this paper is to investigate the local differences between body segments caused by high radiant temperature, and to analyze the interior surface temperatures for different wall and ceiling constructions with their effect on thermal comfort. For the segment-wise thermal interactions between human body and its surrounding, simulations have been conducted by appropriately modifying Gagge 2-node model to multi-segment case to demonstrate the local differences. Simulation results are found to be in good agreement with experimental and simulation results reported in the literature. To calculate the interior surface temperatures of the wall and ceiling, the sol–air temperature approach is used for convenience. It is shown in the paper that the body segments close the relatively hot surfaces are more affected than others and interior surface temperatures of un-insulated walls and ceilings exposed to a strong solar radiation reach high levels, all of which cause thermal discomfort for the occupants in buildings.     

Experimental evaluation of a climate façade: Energy efficiency and thermal comfort performance

The results of an extensive experimental campaign on a climate façade with a mechanically ventilated air gap, carried out at the Department of Energetics at the Politecnico di Torino, are presented. Measurements were performed utilizing the TWINS (Testing Window Innovative Systems) test facility, which consists of two outdoor cells, one used for reference purposes, and the other which adopts different active façade configurations. The energy efficiency of the façade and the thermal comfort implications have been evaluated considering the ability to pre-heat the ventilation air in the winter season, and the ability to remove part of the solar load during the summer season; the normalized daily energy passing through the façade and the normalized surface temperature of the inner glass were analysed. The improvement in performance obtained by varying the configuration and operative conditions (changing the air flow rate, the shading device and the internal glazing) has been investigated.     

Impact of adaptive comfort criteria and heat waves on optimal building thermal mass control

This article investigates building thermal mass control of commercial buildings to reduce utility costs with a particular emphasis on the individual impacts of both adaptive comfort criteria and of heat waves. Recent changes in international standards on thermal comfort for indoor environments allow for adaptation to the weather development as manifested in comfort criteria prEN 15251.2005 and NPR-CR 1752.2005 relative to the non-adaptive comfort criterion ISO 7730.2003. Furthermore, since extreme weather patterns tend to occur more frequently, even in moderate climate zones, it is of interest how a building's passive thermal storage inventory responds to prolonged heat waves. The individual and compounded effects of adaptive comfort criteria and heat waves on the conventional and optimal operation of a prototypical office building are investigated for the particularly hot month of August 2003 in Freiburg, Germany. It is found that operating commercial buildings using adaptive comfort criteria strongly reduces total cooling loads and associated building systems energy consumption under conventional and building thermal mass control. In the case of conventional control, total operating cost reductions follow the cooling loads reductions closely. Conversely, the use of adaptive comfort criteria under optimal building thermal mass control leads to both lower and slightly higher absolute operating costs compared to the optimal costs for the non-adaptive ISO 7730. While heat waves strongly affect the peak cooling loads under both conventional and optimal building thermal mass control, total cooling loads, building energy consumption and costs are only weakly affected for both control modes. Passive cooling under cost-optimal control, while achieving significant total cost reductions of up to 13%, is associated with total energy penalties on the order of 1–3% relative to conventional nighttime setup control. Thus, building thermal mass control defends its cost saving potential under optimal control in the presence of adaptive comfort criteria and heat waves.     

Integrated modeling of pedestrian energy exchange and thermal comfort in urban street canyons

An open-air scale model is used to quantify pedestrian radiative and convective energy exchanges in street canyons of varying geometry, as well as surface-atmosphere energy exchanges above the urban canopy. A semi-empirical model based on measured data in summer is developed to link between the two levels, for the prediction of pedestrian energy exchange within a given street canyon based on climatic conditions above the street array. The relationships identified in the semi-empirical model are then tested with an independent data set from the winter season, demonstrating that the semi-empirical model may be used to predict the effect of street geometry on pedestrian comfort under varying seasonal conditions. Finally, the estimation of pedestrian energy exchange by street geometry is refined to include the effects of humidity and evaporative heat loss along with radiation and convection, and results are used to correlate between physiological energy exchange and thermal sensation, which is a more direct measure of human thermal comfort. The results reinforce previous findings, which indicate that in a hot-arid climate, compact street canyons can substantially reduce overall pedestrian thermal discomfort if their axis orientation is approximately north–south, while in east–west oriented canyons the effect of street proportions is much less pronounced.     

The effects of roof covering on the thermal performance of highly insulated roofs in Mediterranean climates

While the EU Directive 2002/91/CE on the Energy Performance of Buildings (EPBD) clearly establishes regulations for the thermal insulation of buildings for saving energy in winter, the summer strategy is described by a little more than qualitative provisions. As a consequence, in the national requirements, the high insulation of the building envelope is considered as the principal strategy to control energy consumption even in summer, regardless of the different climates. This approach leads to a homologation of the building trade, and imposes construction technology and materials which do not adhere to the traditional way of making buildings, like in Southern Europe. Here, the “over insulation” of buildings runs the risk of reducing the effectiveness of traditional passive cooling strategies (thermal mass, air permeability of the roof covering, roof ventilation) and could have adverse effects on internal comfort. In this paper, we focus on the effects of over insulation on the thermal performance of roofs in summer, by analyzing experimental data from monitoring a full-scale mock-up in Italy. Results show how an increase in insulation thickness reduces the effectiveness of traditional passive cooling strategies, as an effect of the thermal decoupling between the interior and the upper layers of the roofs.     

Virtual Building Dataset for energy and indoor thermal comfort benchmarking of office buildings in Greece

The knowledge of building stock energy data of a country is a very significant tool for energy benchmarks establishment, energy rating procedures and building classification boundaries determination, according to the Directive 2002/91/EC and its implementation in EU Member States. The lack of building energy databases in many EU Countries, including Greece, and the difficulties of collecting them lead to the investigation of other potential solutions. The aim of this paper is to present a method of a Virtual Building Dataset (VBD) creation for office buildings in Greece. The philosophy of VBD is based on the creation and simulation of random office buildings that could be found or built in Greece, taking into account the Greek constructional and operational characteristics of office buildings and Greek legislation. The VBD consists of 30,000 buildings (10,000 in each climatic zone) with their detailed constructional and operational data and of their simulation outputs: the annual specific energy consumption for heating, cooling, artificial lighting, office equipment and an indoor thermal comfort indicator. Based on VBD results the energy and indoor thermal comfort benchmarks for office building sector in Greece are assessed and presented.