Derivation of the adaptive equations for thermal comfort in free-running buildings in European standard EN15251

The equation for thermal comfort for buildings in the free-running mode (Annexe A2) in European Standard EN15251 rests on the data collected in the EU project Smart Controls and Thermal Comfort (SCATs). Many of these data were from naturally ventilated office buildings which were in free-running mode outside the heating season. Using the data from these buildings a relationship between indoor comfort and outdoor climate was developed for free-running buildings. This paper describes the data and the methods of analysis used to estimate the comfort conditions in the variable environment of free-running buildings. The paper also describes how the indoor comfort conditions were related to the running mean of the outdoor temperature, and addresses the effects of air movement and humidity. The paper considers the proportions of people likely to be comfortable if the temperature differs from the neutral temperature. The differences between the adaptive comfort charts in EN15251 and ASHRAE 55-2004 are discussed.     

Comparison of thermal comfort algorithms in naturally ventilated office buildings

With the actual environmental issues of energy savings in buildings, there are more efforts to prevent any increase in energy use associated with installing air-conditioning systems. The actual standard of thermal comfort in buildings ISO 7730 is based on static model that is acceptable in air-conditioned buildings, but unreliable for the case of naturally ventilated buildings. The different field studies have shown that occupants of naturally ventilated buildings accept and prefer a significantly wider range of temperatures compared to occupants of air-conditioned buildings. The results of these field studies have contributed to develop the adaptive approach. Adaptive comfort algorithms have been integrated in EN15251 and ASHRAE standards to take into account the adaptive approach in naturally ventilated buildings. These adaptive algorithms seem to be more efficient for naturally ventilated buildings, but need to be assessed in field studies. This paper evaluates different algorithms from both static and adaptive approach in naturally ventilated buildings across a field survey that has been conducted in France in five naturally ventilated office buildings. The paper presents the methodology guidelines, and the thermal comfort algorithms considered. The results of application of different algorithms are provided with a comparative analysis to assess the applied algorithms.     

Influence of the internal inertia of the building envelope on summertime comfort in buildings with high internal heat loads

The aim of this study was to assess the influence of thermal mass placed on the inner side of the building envelope, described as the dynamic internal areal heat capacity (International Standard ISO 13786), on the summertime thermal comfort in buildings characterised by high internal heat loads.To that aim, simultaneous monitoring was carried out on rooms with high internal heat loads (school classrooms), varying the internal inertia of the envelope through the introduction of an insulating panel on the interior side. Analytical assessment was performed in order to include different inertia values and combinations of both external and internal heat loads.The study allowed the threshold values of internal areal heat capacity to be determined with respect to the different periodic transmittance values of the walls, assessed according to the adaptive thermal comfort model described in Standard EN15251.These values could be adopted in energy saving regulations which, being based on semi-stationary calculation models, tend to consider the performance of building envelopes as analogous even if there is different thermal inertia.     

Development of an adaptive thermal comfort equation for naturally ventilated buildings in hot-humid climates using ASHRAE RP-884 database

The objective of this study was to develop an adaptive thermal comfort equation for naturally ventilated buildings in hot-humid climates. The study employed statistical meta-analysis of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) RP-884 database, which covered several climatic zones. The data were carefully sorted into three climate groups including hot-humid, hot-dry, and moderate and were analyzed separately. The results revealed that the adaptive equations for hot-humid and hot-dry climates were analogous with approximate regression coefficients of 0.6, which were nearly twice those of ASHRAE and European standards 55 and EN15251, respectively. The equation using the daily mean outdoor air temperature had the highest coefficient of determination for hot-humid climate, compared with other mean temperatures that considered acclimatization of previous days. Acceptable comfort ranges showed asymmetry and leaned toward operative temperatures below thermal neutrality for all climates. In the hot-humid climate, a lower comfort limit was not observed for naturally ventilated buildings, and the adaptive equation was influenced by indoor air speed rather than indoor relative humidity. The new equation developed in this study can be applied to tropical climates and hot-humid summer seasons of temperate climates.     

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.     

Comparison of low-energy office buildings in summer using different thermal comfort criteria

Sustainable low-energy office buildings attempt to harness the buildings architecture and physics to provide a high quality working environment with the least possible primary energy consumption. A promising approach to condition those buildings in summer employs the utilization of the building's thermal storage activated by natural heat sinks (e.g., ambient air, ground water or soil) through night ventilation or thermally activated building systems (TABS). However, a certain room temperature cannot be guaranteed as occupants may influence the room energy balance by window opening, internal heat gains or sun shading control. Between 2001 and 2005, monitoring campaigns were carried out over 2 or 3 years in 12 low-energy office buildings which are located in three different summer climate zones in Germany. These climate zones are defined as summer-cool, moderate and summer-hot. The weather at the building site and the room temperatures in several office rooms were monitored by different scientific teams. The raw data are processed for data evaluation using a sophisticated method to remove errors and outliers from the database and to identify the time of occupancy. The comfort in all office rooms in each building is evaluated separately. For data presentation, these separate comfort votes per office room are averaged using the median instead of the arithmetic mean in order not to overestimate extremely cold or hot room temperatures. A comfort evaluation in these 12 low-energy office buildings indicates clearly, that buildings which use only natural heat sinks for cooling provide good thermal comfort during typical and warm summer periods in Germany. However, long heat waves such as during the extreme European summer of 2003 overstrain passively cooled buildings with air-driven cooling concepts in terms of thermal comfort.     

Resilience of naturally ventilated buildings to climate change: Advanced natural ventilation and hospital wards

Naturally ventilated buildings have a key role to play mitigating climate change. The predicted indoor temperatures in spaces with simple single-sided natural ventilation (SNV) are compared with those in spaces conditioned using a form of edge in, edge out advanced natural ventilation (ANV) for various UK locations. A criterion, for use in conjunction with the BSEN15251 adaptive thermal comfort method, is proposed for determining when the risk of overheating, both now and in the future, might be deemed unacceptable. The work is presented in the context building new, and refurbishing existing, healthcare buildings and in particular hospital wards. The spaces conditioned using the ANV strategy were much more resilient to increases in both internal heat gains and climatic warming than spaces with SNV. The ANV strategy used less energy, and emitted less CO₂ than conventional, mechanically ventilated (MV) alternatives. In a warming world, the ‘life-expectancy’ of passively cooled buildings can be substantially influenced by the internal heat gains. Therefore, resilience to climate change, susceptibility to internal heat gains and the impact of future heat waves, should be an integral part of any new building or building refurbishment design process.     

Thermal comfort in office buildings: Two case studies commented

Air conditioning in offices has become a current practice in North Western Europe. The main reasons for that are high internal loads, solar gains and increased comfort expectations. Hence, the move away from the naturally ventilated cellular office increased thermal comfort complaints.     

A novel personalized thermal comfort control, responding to user sensation feedbacks

This paper presents a novel heating, ventilation, and air conditioning (HVAC) control architecture for office buildings, which uses the predicted mean vote (PMV) index of each occupant as feedback and offers them the opportunity to act on their own comfort level by signalling a possible thermal uncomfortable sensation to a personal user interface. A co-simulation EnergyPlus/Simulink has been used to test this new personalized and adaptive thermal comfort control in an office building for different seasons, up to two employees per office. Simulation results show that such a comfort control algorithm leads to sizeable energy savings as well as comfort improvement for each occupant. Moreover, after processing the order given by the user interface, the control algorithm makes the simulated thermal sensation match the actual thermal sensation of the occupant with a high accuracy, leading to a better consideration of his thermal comfort.     

Design strategy for low-energy ventilation and cooling within an urban heat island

Natural ventilation is a proven strategy for maintaining thermal comfort in non-domestic buildings in the UK. The energy consumption and thus the carbon dioxide emissions that contribute to global warming are lower than in conventional air-conditioned buildings. However, the ambient temperatures in the UK have risen over the last decade and new climatic data for use in the design of naturally ventilated buildings has been published. Using these data and dynamic thermal modelling, it is shown that passive stack ventilation alone was unlikely to maintain summertime comfort in a proposed University College London building within an urban heat island. The stack ventilation strategy was evolved by the introduction of passive downdraught cooling. This low-energy technique enables cooled air to be distributed throughout the building without mechanical assistance. The underlying principles of the technique were explored using physical models and the anticipated performance predicted using thermal modelling. The architectural integration is illustrated and the control strategy described. The resulting building is believed to be the first large-scale application of the passive downdraught cooling technique; construction began in late 2003.     

Categories of indoor environmental quality and building energy demand for heating and cooling

Maintaining suitable indoor climate conditions is a need for the occupants’ well being, while requiring very strictly thermal comfort conditions and very high levels of indoor air quality in buildings represents also a high expense of energy, with its consequence in terms of environmental impact and cost. In fact, it is well known that the indoor environmental quality (IEQ), considering both thermal and indoor air quality aspects, has a primary impact not only on the perceived human comfort, but also on the building energy consumption. This issue is clearly expressed by the European Energy Performance of Buildings Directive 2002/92/EC, together with the most recent 2010/31/EU, which underlines that the expression of a judgment about the energy consumption of a building should be always joint with the corresponding indoor environmental quality level required by occupants. To this aim, the concept of indoor environment categories has been introduced in the EN 15251 standard. These categories range from I to III, where category I refers to the highest level of indoor climate requirement. In the challenge of reducing the environmental impact for air conditioning in buildings, it is essential that IEQ requirements are relaxed in order to widen the variations of the temperature ranges and ventilation air flow rates. In this paper, by means of building energy simulation, the heating and cooling energy demand are calculated for a mechanically controlled office building where different indoor environmental quality levels are required, ranging from category I to category III of EN 15251. The building is located in different European cities (Moscow, Torino and Athens), characterized by significantly different wheatear conditions. The mutual relation between heating and cooling energy demand and the required levels of IEQ is highlighted. The simulations are performed on a typical office room which is adopted as a reference in validation tests of the European Standard EN 15265 to validate calculation procedures of energy use for space heating and cooling.     

Design strategy for low-energy ventilation and cooling within an urban heat island

Natural ventilation is a proven strategy for maintaining thermal comfort in non-domestic buildings in the UK. The energy consumption and thus the carbon dioxide emissions that contribute to global warming are lower than in conventional air-conditioned buildings. However, the ambient temperatures in the UK have risen over the last decade and new climatic data for use in the design of naturally ventilated buildings has been published. Using these data and dynamic thermal modelling, it is shown that passive stack ventilation alone was unlikely to maintain summertime comfort in a proposed University College London building within an urban heat island. The stack ventilation strategy was evolved by the introduction of passive downdraught cooling. This low-energy technique enables cooled air to be distributed throughout the building without mechanical assistance. The underlying principles of the technique were explored using physical models and the anticipated performance predicted using thermal modelling. The architectural integration is illustrated and the control strategy described. The resulting building is believed to be the first large-scale application of the passive downdraught cooling technique; construction began in late 2003.     

Application of adaptive comfort behaviors in Chilean social housing standards under the influence of climate change

Currently, energy performance indicators for buildings are associated with the primary energy source consumption, CO₂ emissions or net energy distribution, which together set the building’s energy efficiency. The evaluation is frequently based on setpoint temperatures and hours of operation. However, these fixed parameters are not suitable for social housing simulation as their performance tends to be in free running, excluding extremely cold or warm conditions. Therefore, a more successful assessment for the efficiency of these buildings is the users’ capability to live within adaptive comfort ranges without air conditioning systems. The aim of this research is to analyze new Chilean standards for sustainable social housing in the context of climate change using the adaptive comfort approach addressed in EN 15251:2007. Using EnergyPlus simulation software, 16 parametric series are analyzed for current conditions and validated against on-site measurements. Meanwhile, a prediction for the climate in 2050 has also been taken into account. The case study is the most widespread low cost dwelling model. The study demonstrates that the period of time within thermal comfort conditions varies substantially if analysis is done using the adaptive comfort standard or the Sustainable Construction Code (CCS) for Chilean housing. Considering climate change, the percentage of time fluctuates from ?19.00% to 24.30%. Concluding that the adaptive comfort model has a greater capacity to positively assess indoor temperatures for social housing in Central-Southern Chile. This research also establishes that it is possible to provide homes where standards are improved within comfort conditions without using artificial means, 99.67% of the time currently and 88.89% in the future.     

Thermal comfort for naturally ventilated houses in Indonesia

For naturally ventilated buildings (NVB) located in the tropical regions, thermal comfort (TC) prediction based on predicted mean vote (PMV) standard has shown some deviations from the observed results. Hot and humid environmental conditions throughout the year and personal adaptation could have an effect on expectation and perception about TC. Through an extensive field survey conducted in residential buildings in Indonesia, 525 sets of data had been gathered. The data analysis revealed that the PMV equation had predicted warmer thermal perception as compared to what people actually felt. Interestingly, it was observed that under hot and humid tropical climate, people indicated preference to cooler environment as compared to what the neutral temperature has shown. The study also investigated the occupant’s adaptive control preferences in creating a more thermally comfortable living environment. The reciprocal effects of occupant’s thermal perception and behavioural adaptation were explored. In tropical free-running buildings where the air temperature and humidity might not be modified easily without mechanical means, the people seemed to prefer higher wind speed.     

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.     

Evaluation of adaptive thermal comfort models in moderate climates and their impact on energy use in office buildings

Thermally Activated Building Systems (TABS) are regarded as top-cooling systems rather than full air-conditioning systems. Therefore, adaptive thermal comfort models (ASHRAE55, ISSO74 or EN15251) are supposed to be applicable to TABS buildings, although the comfort model conditions are not necessarily satisfied. This paper investigates whether, for a moderate climate and with the heating and cooling set points chosen according to the adaptive models, the building’s energy use reduces. After all, applying adaptive models, if appropriate, is thought to lower energy use because higher maximum operative zone temperatures T_op,max are allowed, compared to the conventional ISO7730 model. For purpose of generality, a building with an ideal heating and cooling system is considered. Analysis of moderate climate weather data reveals a low energy reducing potential for the ASHRAE55 and ISSO74 model, because high reference outdoor temperatures hardly occur. EN15251 on the other hand, allows very high T_op,max and will lower the cooling need.A 2-zone building simulation demonstrates a higher cooling need for ASHRAE55 and ISSO74, compared to ISO7730. Because cooling is needed during the whole year, the lower winter T_op,max of these adaptive models causes these unexpected results. With real data of warmer years or varying gains, this conclusion holds.     

Thermal comfort of people in the hot and humid area of China—impacts of season,climate, and thermal history

We conducted a climate chamber study on the thermal comfort of people in the hot and humid area of China. Sixty subjects from naturally ventilated buildings and buildings with split air conditioners participated in the study, and identical experiments were conducted in a climate chamber in both summer and winter. Psychological and physiological responses were observed over a wide range of conditions, and the impacts of season, climate, and thermal history on human thermal comfort were analyzed. Seasonal and climatic heat acclimatization was confirmed, but they were found to have no significant impacts on human thermal sensation and comfort. The outdoor thermal history was much less important than the indoor thermal history in regard to human thermal sensation, and the indoor thermal history in all seasons of a year played a key role in shaping the subjects' sensations in a wide range of thermal conditions. A warmer indoor thermal history in warm seasons produced a higher neutral temperature, a lower thermal sensitivity, and lower thermal sensations in warm conditions. The comfort and acceptable conditions were identified for people in the hot and humid area of China.     

Thermal comfort: use of controls in naturally ventilated buildings

A field study of the thermal comfort of workers in natural ventilated office buildings in Oxford and Aberdeen, UK, was carried out which included information about use of building controls. The data were analysed to explore that what effect the outdoor temperature has on the indoor temperature and how this is affected by occupants’ use of environmental controls during the peak summer (June–August). The proportion of subjects using a control was related to indoor and outdoor temperatures to demonstrate the size of the effect. The results suggest that the use of controls is also related to thermal sensation and their appropriate use is a significant part of adaptive behaviour to modify the indoor thermal conditions. The results make it possible to predict the effect of temperature on the ventilation rate in naturally ventilated buildings.     

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.     

A comparison of the occupant comfort in a conventional high-rise office block and a contemporary environmentally-concerned building

A comparative study of the occupant comfort (neutral) in a conventional high-rise office block and a contemporary environmentally-concerned building for Sheffield UK climate conditions was carried out. A questionnaire was designed for occupants to rate their workplace environment in terms of the thermal, visual, acoustic and overall perception and satisfaction level. The basic physical parameters were measured at the same time, e.g. air temperature, humidity, illuminance and sound level. It is inferred that (1) There is a noticeable difference between the conventional building and environmentally-concerned building in terms of their thermal and visual environment. (2) A clear distinction of the occupant sensation and satisfaction level towards their thermal and visual environment is presented between these two buildings. (3) The effect of basic physical variables on the occupants’ perception and satisfaction level becomes less significant when minimal standards are attained. (4) The acoustic satisfaction level however, was not perceived differently by the occupants of the two building types.