Michael A. Humphreys

ADAPTIVE THERMAL COMFORT AND SUSTAINABLE THERMAL STANDARDS FOR BUILDINGS

Abstract The origin and development of the adaptive approach to thermal comfort is explained. A number of recent developments in the application of the theory are considered and the origin of the differences between adaptive thermal comfort and the ‘rational’ indices is explored. The application of the adaptive approach to thermal comfort standards is considered and recommendations made as to the best comfort temperature, the range of comfortable environments and the maximum rate of change of indoor temperature. The application of criteria of sustainability to thermal standards for buildings is also considered.

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

Abstract 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.

Thermal comfort: use of controls in naturally ventilated buildings

Abstract 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.

Development of an adaptive window-opening algorithm to predict the thermal comfort, energy use and overheating in buildings

This investigation of the window-opening data from extensive field surveys in UK office buildings demonstrates: (1) how people control the indoor environment by opening windows; (2) the cooling potential of opening windows; and (3) the use of an ‘adaptive algorithm’ for predicting window-opening behaviour for thermal simulation in ESP-r. It was found that when the window was open the mean indoor and outdoor temperatures were higher than when closed, but it was shown that nonetheless there was a useful cooling effect from opening a window. The adaptive algorithm for window-opening behaviour was then used in thermal simulation studies for some typical office designs. The thermal simulation results were in general agreement with the findings of the field surveys. The adaptive algorithm is shown to provide insights not available using non adaptive simulation methods and can assist in achieving more comfortable, lower energy buildings while avoiding overheating.

Twentieth century standards for thermal comfort: Promoting high energy buildings

The urgent need to reduce anthropogenic greenhouse gas (GHG) emissions in a bid to meet increasingly stringent GHG targets has focused the attention of scientists on the built environment. The reason is that nearly 50% of all the energy in the developed world is consumed in buildings and it is here that the easiest savings can be made. Although the theoretical trend in building regulations is to favour lower carbon buildings, in reality new buildings have typically become more energy profligate year after year. Much of this results from increased mechanization, poorer building fabric and design, and the resource consumption patterns. Modern thermal comfort standards are partly responsible for increased levels of energy consumption in buildings as well as for encouraging unhealthier, less comfortable buildings because they drive the designers towards higher use of air-conditioning. A first step towards the radical overhauling of our approach to the artificial conditioning of buildings is to revise these standards. This article describes the evolution of the current standards and the problems inherent in the buildings they shape and serve and then proceeds to propose new methods of regulating thermal comfort in a warming world in which the cost of energy is rising.

Twenty first century standards for thermal comfort: fostering low carbon building design and operation

Nearly 50% of energy consumed in the developed world is consumed in buildings. Despite regulation intent, many new buildings are energy profligate. Thermal comfort standards are partly responsible for this increase in consumption. In this volume, Roaf et al. have described the evolution of current comfort standards and problems inherent in buildings they shape, and have discussed two new methods of regulating thermal comfort in buildings which recognize human adaptation and have potential for reduced energy demand. These new methods incorporate adaptation through a fixed heating and cooling threshold approach (similar to Japanese Cool-Biz) or through heating and cooling setpoints calculated based on outdoor conditions (using CEN standard equations). The impact on comfort and energy demand of these new approaches is investigated for a London office building. Variables such as future climate, future building upgrades, setback temperatures, internal gains and ventilation are also explored. Adoption of the new approaches gave a 50% reduction in heating and cooling energy for the simulated office. The new approach together with optimized setback temperatures, ventilation strategies and higher efficiency equipment gives predicted heating and cooling energy demand close to zero. Recommendations for future regulation, design and operation of buildings are proposed.

Considering the impact of situation-specific motivations and constraints in the design of naturally ventilated and hybrid buildings

A simple logical model of the interaction between a building and its occupants is presented based on the principle that if free to do so, people will adjust their clothing or available building controls with the aim of achieving or restoring comfort and reducing discomfort. These adjustments are related to building design in two ways: first, the freedom to adjust depends on the availability and ease of use of control options; second, the use of controls affects building comfort and energy performance. The values of constraints are quantified for a range of existing buildings in Europe and Pakistan. The integration of the model within a design flow is proposed and the impact of different levels of constraints demonstrated. It is proposed that to minimize energy use and maximize comfort in naturally ventilated and hybrid buildings the designer should take the following steps: (i) provide unconstrained low-energy adaptive control options where possible, (ii) avoid problems with indoor air quality which provide motivations for excessive ventilation rates, (iii) incorporate situation-specific adaptive behaviour of occupants in design simulations, (iv) analyse the robustness of designs against variations in patterns of use and climate and (v) incorporate appropriate comfort standards into the operational building controls.

Towards an adaptive model for thermal comfort in Japanese offices

ABSTRACT This study investigates the seasonal adaptation to temperature that occurs in Japanese offices, with a view to suggesting an adaptive model for them. Temperatures were measured in 11 office buildings and thermal comfort transverse surveys of occupants were conducted for over a year in the Tokyo and Yokohama areas of Japan. A total of 4660 samples were collected from about 1350 people. The occupants were found to be highly satisfied with the thermal environment in their offices. Even though the Japanese government recommends the indoor temperature setting of 28°C for cooling and 20°C for heating, the comfort globe temperature was found to be 2.6°C lower in cooling mode and 4.3°C higher in heating mode, in line with actual indoor temperatures. The monthly and seasonal variation in the comfort temperature was found to be significantly lower than those in dwellings. The comfort temperature is related primarily to the indoor temperature, but an adaptive relationship can be derived to estimate the indoor comfort temperature from the prevailing outdoor temperature for similar office buildings.

Development of a window opening algorithm based on adaptive thermal comfort to predict occupant behavior in Japanese dwellings

Window opening behavior and thermal comfort were monitored in relation to the thermal environment over a 4 year period in the living rooms and the bedrooms of dwellings in the Kanto region of Japan. 36 144 sets of physical and subjective data were collected from 243 residents of 120 dwellings. This paper explores relationships between the different variables in the data. The likelihood of windows being open depended on the three modes of operation of the dwelling, free running (FR), heating (HT) or cooling (CL). In the FR mode, the likelihood was much higher than in either the CL or the HT modes. The likelihood that a window is open correlated well with both indoor temperature and outdoor air temperature in the FR Mode. The indoor comfort temperature correlated well with the running mean of the outdoor temperature. Window opening behavior as predicted by logistic regression analysis is in agreement with the measured data. The deadband of window opening was narrower, and the constraint on window opening was smaller than had previously been found in studies in office buildings. Equations are given to quantify these relations and to enable window opening and comfort temperature to be predicted from outdoor temperature.

Principles of Adaptive Behaviours

This short chapter introduces the causal relationship between the behaviour of building occupants, their comfort and the energy used by the buildings. It suggests that much of the behaviour is motivated by the desire of the occupants to make themselves comfortable and to optimise the environment. The provision of comfortable conditions in domestic buildings in hot-humid climates is highlighted. An annex also introduces ways in which the comfort-related behaviour can be understood and allowed for in predictive simulations of indoor temperature and energy use.