Overheating in Auckland homes: testing and interventions in full-scale and simulated houses

ABSTRACT

New Zealand dwellings have thermal conditions managed with relatively light regulation. No minimum airtightness standards exist and historical increases in required insulation levels aimed to reduce winter heating energy consumption. A consequence of this policy is an increased potential for overheating in summer. There has been a steady increase in the use of heat pumps, risking heating energy savings being outweighed by cooling energy increases. Internal temperatures and humidity were monitored in the living spaces of three unoccupied, transportable houses over all four seasons of the Auckland climate. The houses are located on the same site and are of identical construction, apart from selected interventions which were tested to explore their potential to mitigate overheating. Results indicate that overheating can be extreme and long lasting. High internal temperatures are very closely connected with solar gains. Internal temperatures reached 32°C in autumn. Roof space temperatures reached 51°C in summertime. Interventions resulted in modest improvements and an airtight construction provided a small thermal benefit. A thermal model for the houses was developed using EnergyPlus and compared with actual measurements and the interventions. Early results point to the further need to reduce solar gain, increase roof-space ventilation and increase mass, where feasible.     

Overheating in English dwellings: comparing modelled and monitored large-scale datasets

ABSTRACT

Monitoring and modelling studies of the indoor environment indicate that there are often discrepancies between simulation results and measurements. The availability of large monitoring datasets of domestic buildings allows for more rigorous validation of the performance of building simulation models derived from limited building information, backed by statistical significance tests and goodness-of-fit metrics. These datasets also offer the opportunity to test modelling assumptions. This paper investigates the performance of domestic housing models using EnergyPlus software to predict maximum daily indoor temperatures over the summer of 2011. Monitored maximum daily indoor temperatures from the English Housing Survey’s (EHS) Energy Follow-Up Survey (EFUS) for 823 nationally representative dwellings are compared against predictions made by EnergyPlus simulations. Due to lack of information on the characteristics of individual dwellings, the models struggle to predict maximum temperatures in individual dwellings and performance was worse on days when the outdoor maximum temperatures were high. This research indicates that unknown factors such as building characteristics, occupant behaviour and local environment makes the validation of models for individual dwellings a challenging task. The models did, however, provide an improved estimate of temperature exposure when aggregated over dwellings within a particular region.     

Meta-analysis of indoor temperatures in new-build housing

ABSTRACT

Despite growing concerns about overheating, a lack of evidence exists on the scale of the problem, particularly in contemporary UK housing. This paper presents the results of a meta-analysis of indoor temperatures in selected low-energy housing. Temperature data recorded at five-minute intervals in 60 dwellings across 19 demonstration projects (2012–14) were collated and analysed to investigate the prevalence of overheating. Findings evidence high summertime temperatures, with 27% of living rooms exceeding 28°C during August. Based on the Chartered Institution of Building Services Engineers (CIBSE) threshold of 5% annual occupied hours > 25°C, 57% of bedrooms and 75% of living rooms were classified as having overheated. Overall, 30% of living rooms exceeded the adaptive comfort threshold of > 3% occupied hours ΔT?≥?1?K. The results suggest a fundamental relationship between ventilation and indoor temperatures. The higher minimum and average summertime temperatures observed in mechanical ventilation with heat recovery (MVHR) homes (p?<?0.05) and lower temperature range (p?<?0.001) suggest the need for greater attention to adequate summertime ventilation provision in airtight homes. The results demonstrate a high prevalence of overheating in exemplary housing, indicating the need for greater efforts to ensure the effective implementation of strategies to minimize overheating and improve ventilation in low-energy homes.     

Evaluating positivist theories of occupant satisfaction: a statistical analysis

An explorative statistical analysis of consistent non-domestic building performance studies is conducted non-domestic buildings (n?=?47) to validate the universal positions of comfort widely cited in industry guidance and standards. The Building Use Studies (BUS) methodology for evaluating occupant satisfaction employed by these studies was tested for reliability and the factor structure explored. The reliability of this method was found to be ‘excellent’ and eight latent variables that characterize a hierarchical factor structure induced. Increased visual display unit use and open-plan arrangements were found to be associated with negative occupant perceptions. This suggests that privacy and personal communication may be defining issues for occupant satisfaction, with implications for space planning. Significantly different perceptions towards air quality and conditions in winter were observed between gender and those familiar with their environments were found to have a tendency to hold more negative perceptions more broadly. It has also been found that perceptions towards seasonal conditions may be improved by providing local control to mechanical services. Such insights highlight the limitations of reliance on positivist theory. Hence, it is recommended that high-performance buildings be provided control and management systems that learn from those occupying the building over time, cautiously adapting service provision accordingly.     

Natural ventilation in practice: linking facade design,thermal performance,occupant perception and control

The action of opening a window is the most intuitive and simple response to controlling overheating in a room. However, it relies on the vagaries of occupant interaction to exploit the passive design potential and achieve comfortable results. An understanding of occupant behaviour is thus of significance in the design and evaluation of naturally ventilated buildings. This paper demonstrates the link between facade design, thermal performance, occupant perception, and window use in naturally ventilated offices in summer, based on a pilot study monitoring offices in Cambridge, UK. Survey results indicate that facade design has a large impact on the occupants' perceived control over and satisfaction with their environments. The research reveals that there is a close connection between perceived control and actual control (with respect to window use), and that occupants with a high level of perceived control more frequently use their windows than others with a low level of perceived control. Positive feedback loops between occupant action and effect reinforce appropriate behaviour and the paper shows that it is possible to derive statistically significant behavioural models to predict window use for different facade conditions.

L'action d'ouvrir une fenêtre est la réponse la plus intuitive et la plus simple au problème du contrôle de la surchauffe d'une pièce. Néanmoins, elle est soumise aux caprices des interactions des occupants pour que soit exploité le potentiel de la conception passive et qu'il en résulte une température agréable. Comprendre le comportement des occupants n'est donc pas sans importance pour la conception et l'évaluation des bâtiments à ventilation naturelle. Cet article démontre le lien existant entre la conception des façades, les performances thermiques, la perception des occupants et l'utilisation des fenêtres dans les bureaux à ventilation naturelle en été, sur la base d'une étude pilote de suivi de bureaux à Cambridge, au Royaume-Uni. Les résultats de cette enquête indiquent que la conception des façades a une incidence importante sur le contrôle perçu de leur environnement par les occupants et sur leur satisfaction à l'égard de ce dernier. L'étude révèle qu'il existe un lien étroit entre contrôle perçu et contrôle réel (par rapport à l'utilisation des fenêtres) et que les occupants qui ont un niveau élevé de contrôle perçu utilisent plus fréquemment leurs fenêtres que ceux qui ont un faible niveau de contrôle perçu. Les boucles de feedback positif entre les actions des occupants et leurs effets renforcent le comportement adapté et l'article montre qu'il est possible d'en retirer des modèles comportementaux statistiquement significatifs permettant de prédire l'utilisation des fenêtres en fonction de l'état des façades.

Mots clés: comportement adaptatif, performances des bâtiments, conception des façades, ventilation naturelle, ventilation nocturne, comportement des occupants, perception des occupants, contrôle des fenêtres, Royaume-Uni     

Dwelling performance and adaptive summer comfort in low-income Australian households

Increasing reliance on air-conditioning to improve summertime comfort in dwellings results in higher energy bills, peak electricity demand and environmental issues. In pursuit of social equity, society needs to develop ways of improving cooling that are less reliant on air-conditioning. Designing homes to emphasize adaptive thermal comfort can reduce this reliance, particularly when combined with improved dwelling thermal performance. A multi-method evaluation of 10 low-income dwellings in the state of Victoria in Australia is presented, including low-energy and ‘standard-performance’ houses. The combination of performance monitoring and householder interviews reveals new insights for achieving summertime comfort. The low-energy houses without air-conditioning were both measured and perceived as more comfortable than the ‘standard-performance’ houses with air-conditioning. The low-energy households achieved improved personal thermal comfort through a combination of improved fabric performance augmented with adaptive comfort activities (e.g., opening/closing windows). This outcome reduces reliance on air-conditioning, reduces living costs and energy consumption, and improves environmental outcomes. There is a need to integrate lessons from adaptive thermal comfort theory and strategies into minimum building performance requirements and standards, as well as wider design strategies. It is evident that adaptive comfort has a role to play in a transition to a low-carbon housing future.     

德国低能耗建筑技术体系及发展趋势

总结归纳了德国低能耗建筑的分类标准,分析了三种不同标准低能耗建筑相应的设计方法与技术系统;介绍了低能耗建筑技术的发展新动向和德国低能耗建筑推广策略与既有建筑节能改造的案例。     

Exposure duration in overheating assessments: a retrofit modelling study

ABSTRACT

A new indicator of overheating risk is introduced that more comprehensively represents heat stress and the way thermal environment is experienced. This indicator is compared with the industry standard overheating assessment approach (CIBSE TM52). This is demonstrated using an energy retrofit simulation case study of a typical London, UK terraced dwelling under different climate scenarios. Overheating was evaluated first according to TM52, then via an assessment of continuously overheated intervals (COIs) that account for the duration where adaptive limits are continuously exceeded. Results for the case study show that, first, extent of overheating can vary greatly based on climate uncertainties. Second, insulation retrofit only contributes to substantial overheating when the space lacks proper ventilation or protection from solar radiation. Nevertheless, overheating cannot be avoided completely under future climate scenarios even with appropriate passive cooling. More importantly, the results show that overheated hours tend to occur consecutively. This implies that violations of TM52 criterion 1 (which currently applies only at the seasonal scale) can occur at the monthly/weekly resolutions. This ‘buried’ information can be revealed via the COI approach to more comprehensively capture how an overheating situation unfolds in a manner more relevant to heat stress and occupants’ thermal experience.     

Overheating in retrofitted flats: occupant practices,learning and interventions

ABSTRACT

The overheating risk in flats (apartments) retrofitted to energy-efficient standards has been identified by previous studies as one that is particularly high. With climate change and rising mean temperatures this is a growing concern. There is a need to understand the kinds of practices, learning and interventions adopted by the occupants of individual homes to try to reduce overheating, as this area is poorly understood and under-researched. This case study focuses on the impact of different home-use practices in relation to the severity of overheating in 18 flats in one tower block in northern England. Internal temperatures monitored in comparable flats show that the percentage of time spent above the expected category II threshold of thermal comfort according to BS EN 15251 can differ by over 70%. Extensive monitoring, covering a full year, including two summer periods, has identified emergent changes in heatwave practices linked with increased home-use skills and understanding among the research participants. Close analysis of design intentions versus reality has identified key physical barriers and social learning opportunities for appropriate adaptation in relation to heatwaves. Recommendations for designers and policy-makers are highlighted in relation to these factors.     

Perceived control in indoor environments: a conceptual approach

Building automation systems provide the potential to optimize the energy consumption of buildings as well as to detect failures in the operation of buildings. The system comprising building form–HVAC–building automation–user is becoming more complex. Providing the occupants with control over the indoor environment is widely accepted for its positive effect on their satisfaction. This paper explores what the term ‘perceived control’ means conceptually and draws implications for its application to the design and management of buildings. Personality- and environmental-psychology emphasize the importance of personal control to humans. The adaptive model of thermal comfort, findings from post-occupancy evaluations and surveys in real buildings also indicate the importance of high levels of perceived control. These models and findings exist in parallel and have not yet been interconnected and translated into models for the built environment. A new conceptual approach to explain perceived control is proposed. Satisfaction with the indoor environment occurs not only when ‘comfort’ is provided but also immediately after a successful control action, even if homeostasis has not yet been achieved (pleasure). Giving control to occupants can result in higher levels of satisfaction.     

Performance benchmarks for non-domestic buildings: towards user perception benchmarks

While the indoor environment can affect occupants' perceptions of their comfort, health and productivity in buildings, little information exists on what would constitute appropriate benchmarks for these matters. If users' perceptions of building performance are to be addressed and improved, then it is essential to have a reliable, standardized set of benchmarks against which to measure them. A pilot study is presented that tested a range of benchmarking approaches using a small dataset of 30 commercial and institutional buildings. The database included the mean scores from each of the 30 buildings for each indoor environmental quality question in the Building Use Studies (BUS) questionnaire, including those on lighting, comfort, noise and the like. This dataset allowed exploration of the construction of potential benchmarks and the demonstration of systems that could be replicated internationally. It was found to be feasible to establish benchmarks from the questionnaire data received. The variety of forms these benchmarks can take is demonstrated; and the advantages and disadvantages of each are described. For example, absolute benchmarks had the advantage of being able to be assessed without the need for a representative sample, while relative benchmarks gave an assessment of how each variable rated against a larger dataset.     

Do ‘green’ buildings have better indoor environments? New evidence

A post-occupancy evaluation (POE) of 12 green and 12 conventional office buildings across Canada and the northern United States was conducted. Occupants (N = 2545) completed an online questionnaire related to environmental satisfaction, job satisfaction and organizational commitment, health and well-being, environmental attitudes, and commuting. In each building on-site physical measurements at a sample of workstations (N= 974) were taken, including: thermal conditions, air quality, acoustics, lighting, workstation size, ceiling height, window access and shading, and surface finishes. Green buildings exhibited superior performance compared with similar conventional buildings. Better outcomes included: environmental satisfaction, satisfaction with thermal conditions, satisfaction with the view to the outside, aesthetic appearance, less disturbance from heating, ventilation and air-conditioning (HVAC) noise, workplace image, night-time sleep quality, mood, physical symptoms, and reduced number of airborne particulates. A variety of physical features led to improved occupant outcomes across all buildings, including: conditions associated with speech privacy, lower background noise levels, higher light levels, greater access to windows, conditions associated with thermal comfort, and fewer airborne particulates. Green building rating systems might benefit from further attention in several areas, including: credits related to acoustic performance, a greater focus on reducing airborne particulates, enhanced support for the interdisciplinary design process and development of POE protocols.

Il a été mené une évaluation après occupation (POE) de 12 immeubles de bureaux verts et 12 immeubles de bureaux classiques répartis à travers le Canada et le nord des Etats-Unis. Les occupants (N?=?2545) ont rempli un questionnaire en ligne portant sur la satisfaction environnementale, la satisfaction au travail et l'implication organisationnelle, la santé et le bien-être, les attitudes environnementales, et les trajets réguliers. Dans chaque immeuble, des mesures physiques in situ sur un échantillon de postes de travail (N?=?974) ont été effectuées, comprenant : les conditions thermiques, la qualité de l'air, l'acoustique, l'éclairage, la taille des postes de travail, la hauteur de plafond, l'accès aux fenêtres et leur occultation, et les finitions de surface. Les bâtiments verts ont affiché des performances supérieures par rapport aux bâtiments classiques similaires. De meilleurs résultats ont été obtenus concernant la satisfaction environnementale, la satisfaction à l'égard des conditions thermiques, la satisfaction à l'égard de la vue sur l'extérieur, l'aspect esthétique, la diminution des perturbations liées aux bruits provenant du chauffage, de la ventilation et de la climatisation (CVC), l'image du lieu de travail, la qualité du sommeil nocturne, l'humeur, les symptômes physiques, et la réduction du nombre de particules en suspension dans l'air. Différentes caractéristiques physiques ont conduit à une amélioration des résultats pour les occupants dans tous les immeubles, concernant notamment les conditions liées à la confidentialité des conversations, les niveaux inférieurs de bruit de fond, les niveaux de luminosité plus élevés, l'accès accru aux fenêtres, les conditions associées au confort thermique, et le nombre moindre de particules en suspension dans l'air. Les systèmes de notation des bâtiments verts pourraient bénéficier d'une plus grande attention apportée à plusieurs domaines, s'agissant en particulier des crédits relatifs aux performances acoustiques, d'un accent accru sur la réduction des particules en suspension dans l'air, d'un soutien renforcé en faveur du processus de conception interdisciplinaire et du développement de protocoles POE.

Mots clés: performances des bâtiments, bilan environnemental, bâtiments verts, environnement intérieur, Leadership in Energy and Environmental Design (LEED), satisfaction des occupants, évaluation après occupation     

Combating overheating: mixed-mode conditioning for workplace comfort

ABSTRACT

Using post-occupancy evaluations of seven mixed-mode buildings – three in Australia and four in India – this paper demonstrates that effective mixed-mode conditioning (instead of year-round air-conditioning) can deliver comfortable workspaces. Occupant feedback reinforces strong associations between overheating, thermal comfort, overall comfort and perceived productivity. However, differing levels of thermal acceptability within and between the Australian and Indian contexts are evident. Occupants in the Indian buildings were found to tolerate a wider range of temperatures when compared with Western contexts where lower temperature limits entrench an energy demand through a greater reliance on air-conditioning. The outcomes from the study suggest that the perception of overheating and consequent risk to building performance can be intensified when occupants perceive limited adaptive opportunity or problems are not rectified quickly, whereas perceived control is less important where building systems are user responsive. Occupants in three of the study buildings also perceived higher-than-anticipated comfort which could be attributable to well-liked attributes, such as break-out spaces, daylight and fresh air included in these buildings. The findings challenge designers and clients to develop user-responsive climate interactive workplaces that capitalize on spatial and mixed-mode environmental control to tackle the question of overheating.     

Performance gaps in energy consumption: household groups and building characteristics

ABSTRACT

The difference between actual and calculated energy is called the ‘energy-performance gap’. Possible explanations for this gap are construction mistakes, improper adjusting of equipment, excessive simplification in simulation models and occupant behaviour. Many researchers and governmental institutions think the occupant is the main cause of this gap. However, only limited evidence exists for this. Therefore, an analysis is presented of actual and theoretical energy consumption based on specific household types and building characteristics. Using a large dataset (1.4 million social housing households), the average actual and theoretical energy consumptions (gas and electricity) of different household types and characteristics (income level, type of income, number of occupants and their age) were compared for each energy label. Additionally, the 10% highest and lowest energy-consuming groups were analysed. The use of combinations of occupant characteristics instead of individual occupant characteristics provides new insights into the influence of the occupant on energy demand. For example, in contrast to previous studies, low-income households consume more gas per m² (space heating and hot water) than households with a high income for all types of housing. Furthermore, the performance gap is caused not only by the occupant but also by the assumed building characteristics.     

Quantifying occupant comfort: are combined indices of the indoor environment practicable?

What are the various ways in which evaluation of the several aspects of the indoor environment might combine to form an occupant's overall assessment of that environment? Data from an environmental survey of 26 offices in Europe (the Smart Controls and Thermal Comfort, or SCATs, project) are used. These show that dissatisfaction with one or more aspects of the indoor environment does not necessarily produce dissatisfaction with the environment overall. Conversely, satisfaction with one or more environmental aspect does not necessarily produce satisfaction with the total environment. Building occupants balance the good features against the bad to reach their overall assessment. Not all aspects are equally important in this subjective averaging process. Satisfaction with warmth and air quality is more important than satisfaction with the level of lighting or humidity. The relative importance of the various aspects differed from country to country, making it impossible to develop an internationally valid index to rate office environments by means of a single number. The best linear index constructed from the data failed to rank the indoor environments of the buildings in the correct order, as defined by the occupants' overall assessments. It is therefore wise to assess each of the several aspects separately rather than rely only on a combined index.     

The building performance sketch

A new approach to the creation of design tools is proposed that addresses the real information needs of designers in the early stages of design of non-residential buildings. Traditional simplified design tools are typically too limited to be of much use, even in conceptual design. The proposal is to provide access to the power of detailed simulation tools at a stage in design when little is known about the final building, but at a stage also when the freedom to explore options is greatest and the ability to improve the design is greatest. The concept of the building performance sketch forms the basis of the proposed design tool. It was derived from consultation with design analysis teams as part of the development of the COMFEN tool for fenestration design. Tools like COMFEN are explored to understand how they were shaped by consultation and how requests from these teams for real-world relevance might shape such tools in the future. The simulation process can effectively utilize some of the as-built, as-occupied and as-managed lessons on behaviours and technical outcomes from the Post-occupancy Evaluation (PoE) of buildings.

Il est proposé pour la création des outils de conception une nouvelle approche répondant aux véritables besoins d'information des concepteurs dans les premières phases de conception des bâtiments non résidentiels. Les outils de conception simplifiée traditionnels sont habituellement trop limités pour être très utiles, même en design conceptuel. Ce qui est proposé est de pouvoir accéder à la puissance d'outils de simulation détaillée à un stade de la conception où l'on sait encore peu de choses concernant le bâtiment final, mais également à un stade auquel la liberté d'exploration des options possibles comme la capacité d'amélioration de la conception sont les plus grandes. Le concept du schéma de performance du bâtiment constitue la base de l'outil de conception proposé. Il découle de la consultation des équipes chargées de l'analyse de la conception dans le cadre du développement de l'outil COMFEN de conception du fenêtrage. Des outils tels que COMFEN sont examinés afin de comprendre comment ils ont été modelés par la consultation et comment les demandes de ces équipes en termes de pertinence réelle pourraient façonner ces outils à l'avenir. Le processus de simulation peut tirer efficacement parti de certaines des leçons, conformes à l'exécution, à l'occupation et à la gestion, en matière de comportements et de résultats techniques, retirées de l'Evaluation Après Occupation des bâtiments.

modèles d'information du bâtiment?bâtiments?processus de conception?outils de conception?début de conception?efficacité énergétique?retour d'information?simulation des performances?évaluation après occupation     

Strategic decision-making for intelligent buildings: Comparative impact of passive design strategies and active features in a hot climate

In the past years, there has been a growing interest among architects and entrepreneurs to include intelligence in buildings, as a way for achieving energy-efficient buildings that comply with stringent energy codes and national goals of reducing dangerous emissions, together with improving corporate image.     

Thermal behavior of building walls in summer: Comparison of available analytical methods and experimental results for a case study

There is a wide variety of thermal analyses that can be used to characterize the thermal behavior of a wall under certain outdoor conditions. The selection of a particular wall configuration for a building project involves not only the outdoor climate, but also the whole building characteristics, orientation, percentage of glazed areas, occupation periods, lifestyles, etc. In this paper we apply common available methods for wall thermal analysis to two particular wall types, a massive brick wall and an insulated brick wall, in order to compare the information given by each method and to evaluate how these methods can help in the selection of a certain type of wall. The studied methods include the estimation of the wall time lag and decrement factor, the harmonically heated slab model, the Athanassouli’s method, and numerical simulations. The study was performed for the walls of a residence for university students and it was built in La Pampa (Argentina). Once the building was finished, the transient thermal behavior of two walls was monitored during one summer week. The experimental results are presented and the fitting with the thermal behavior predicted by each method is discussed. The thermal comfort indicators PMV (predicted mean vote) and PPD (predicted percentage of dissatisfied) were calculated for two flats, at ground floor and first floor respectively.     

Thermal simulation outputs: exploring the concept of patterns in design decision-making

This paper describes the ongoing development of a building performance simulation (BPS) knowledge management scheme for design decision-making. This knowledge management scheme is developed with reference to the patterns of Christopher Alexander and colleagues, which describe commonly recurring abstract problems in architectural design together with successful abstract solutions. As such they form a ‘repository of knowledge’ on architectural design. Patterns have been used in other fields such as software engineering where they also aim at capturing expert knowledge, and their potential to do the same for BPS is explored here. Decision support using simulation is introduced and the concept of patterns described. A pattern structure is developed and some examples given. Interviews with architectural practices investigated whether patterns could support design processes, and the further development of the concept is discussed.