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.     

加拿大卡尔加里市Okotoks小镇太阳能小区建设

简要介绍了北美目前最大的跨季太阳能储存项目——加拿大0kotoks小镇的太阳能小区建设，对其太阳能供热系统的工作原理及利用土壤床作为储能体进行大规模跨季节太阳能储存的方法进行了分析。该项目根据不同季节可利用太阳能数量的不同，分别设置了短期（临时）太阳能储箱（STTS）及跨季节太阳能储存箱（BTES），以提高太阳能的利用率。其中，BTES的效率可达50％以上。小区太阳能家用热水系统（DWH）可满足住户60％的热水需求，而太阳能采暖系统则可满足90％采暖要求；建成后每幢住宅每年可减排5t温室气体，整个小区可减排260t／年。     

A national field survey of house temperatures

Information about temperatures in houses is of importance in assesing the value of various energy conservation measures and gives an indication of the standards of thermal comfort enjoyed by the occupants. In the present paper results are discussed of the most extensive survey of domestic dwelling temperatures to have been taken in the U.K. During February and March 1978, when the outside temperature was close to the average for the heating season, spot measurements of the wet- and dry-bulb temperatures were made in each room of 1000 homes nationwide. On the same occasion, an interview was conducted with an adult member of the household to obtain information on thermal comfort conditions and heating patterns. The globe temperature was measured in the room where the interview took place (usually the living-room). Interviews were conducted both during the daytime and in evenings, and at weekends as well as on weekdays. The mean of the living-room temperatures recorded was 18.3°C, mean kitchen temperature 16.7°C and mean temperature of the warmest bedroom 15.2°C. The average dwelling temperature was 15.8°C. The major sources of variance in temperature were the type and operation of the heating system, the dwelling age, household income, the time of day and geographical location. Household composition was a minor factor. The living-room temperature was relatively insensitive to the above-mentioned factors and had the appearance of being held at a level more or less independent of that in the rest of the dwelling. Centrally-heated houses ran 3°C warmer on average than non-centrally-heated houses. However, the difference in mean temperatures in the living-rooms between the two categories was only 1.5°C dry-bulb and 0.9°C globe temperature. Although strong correlations between a number of the explanatory variables, such as dwelling age and heating system type, means that a deeper analysis is required before a firm causal model can be proposed, the results provide an important new basis for assessing energy conservation options in domestic space heating.     

Thermal analysis of the architecture of old and new houses at Ghadames

The study suggests improvements in the design of new houses to conserve energy and enhance indoor thermal comfort. Summer temperature records show that a new house has an average indoor temperature of 35°C with the ambient average 31°C. The traditional house in the old city recorded 28°C for the same period. Winter temperatures in both types of houses were similar (12°C) when not occupied. Architectural features of the two houses were compared to identify those responsible for difference in the thermal performance. Larger exposed surface and window areas, higher overall heat transfer coefficient and weaker thermal coupling with the ground for the new houses seems to contribute to their inferior thermal performance.     

One-year Measurement of Indoor Climate and Energy Consumption of Super-insulated Houses in a Mild Climate Region of Japan

Two super-insulated houses were constructed near Sendai City in accordance with the Canadian R-2000 manual (Canadian Home Builders' Assoc., 1987). Shelter performance, thermal environment, air quality and energy consumption of these two houses were investigated for one year. The two super-insulated houses were very airtight compared with other houses. The one-year measurement of room temperature and humidity for one super-insulated house showed that the daily mean temperature for the dining-living room and the master bedroom was 15°C-20°C during the winter and 22°C-28°C during the summer. Absolute humidity for these rooms was less than 5 g/kg (DA) during the winter. The indoor environment of the two super-insulated houses during the heating season was more thermally comfortable, compared with that of ordinary houses in Japan. During the summer, the indoor temperature in these two houses was stable during the day and did not decrease at night even if the outdoor air temperature dropped. The CO₂ concentration in these two houses was lower than that of other airtight houses due to continuous mechanical ventilation. The space heating energy consumption for one super-insulated house was less than that of ordinary houses in Tohoku District in which only the living-dining room was heated.     

Assessing impacts of summertime overheating: some adaptation strategies

The UK is predicted to experience warmer summers in the future, but the domestic building stock in England was not designed to cope with this change. The Standard Assessment Procedure (SAP) 2009 is used to assess the current state of the English building stock in terms of its vulnerability to overheating. The English Housing Survey 2009 provided data for 16 150 dwellings which are weighted to represent the housing stock. SAP predicts 82% of dwellings are currently at ‘slight’ risk of overheating and 41% at medium to high risk. If summer temperatures become 1.4°C warmer, then 99% of properties are predicted to have a medium to high risk of overheating. Several potential adaptations to the housing stock were considered to reduce overheating. Although ventilation strategies had the largest positive effect, the use of solar shading and shutters which allow secure ventilation could reduce vulnerability to overheating in the current climate. In a warmer climate, although some dwellings would still be at slight risk, the results suggest that solar shading strategies could reduce the percentage of those at medium to high risk to 6%. Future energy efficiency programmes will need to include adaptation measures to prevent overheating.     

Overheating in Scotland: contributing factors in occupied homes

ABSTRACT

There is growing awareness of the overheating risks in new-build properties in the UK. However, this tends to be considered a problem principally for the southern regions in the UK, only becoming a serious issue in the north of England in the medium-term and in the long-term for Scotland. This notion tends to be largely predicated upon climate change predictions, differences in latitude and summer air temperatures. This paper describes the results from Building Performance Evaluation (BPE) studies over a two-year period from 26 occupied new-build homes across Scotland which demonstrated incidences of overheating. Results suggest that low-energy buildings are susceptible to overheating despite northerly latitudes, with 54% of houses studied overheating for more than six months annually, and 27% of homes overheating for less than 10% of the year. Evidence indicated that commonly used prediction tools do not appear to anticipate overheating adequately. This paper maps common overheating causes due to design and the role of occupants, identifying the risks due to the regulatory system, prediction and procurement processes, and design and construction. A common finding was that design and occupancy factors appear to have a greater impact on overheating more than location and climatic factors.     

Heat requirements and energy use in British houses

Housing data likely ranges of insulation levels are combined to give estimates of the heating requirements for conventional houses and small flats to be built in Britain in 1977–1987. After allowance for non-solar heat gains, requirements of 65–120 kWh/day for 4–6 person houses and of 8–47 kWh/day for small flats are predicted. The 65 kWh/day lower limit for houses will be improved on in the case of very well insulated houses using modified construction techniques.Data are collated showing average incidental heat gains from appliances, water heating, and other sources. The effects of these on annual heating energy use and on mean power requirements are assessed, and annual heating energy use per kW of design heat loss is calculated for a range of levels of incidental gains at three British locations; Pembroke, Croydon and Edinburgh. The typical solar contribution to this heating energy is also calculated.Mean-to-peak power variations are considered, showing that on average a heating system operates at 20–30% of the house design heat loss; this is the level at which energy use efficiency is most significant.The theoretical predictions of heating energy use are shown to give reasonable agreement with actual use as measured in field trials, despite the wide variability of the latter. The variation of total solar heating with orientation of a house with windows on two opposite sides is studied in the Appendix, showing a variation of ±15% in winter and ±6% in spring and summer for a particular house design.     

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.     

东北地区太阳能农宅设计和研究

针对东北地区的气候特点和农村的自然条件,根据太阳能房的工作原理,通过对农村住宅进行合理的户型设计和构造设计,有效利用太阳能解决冬季农宅采暖和夏季降温,并对太阳能产生的经济效益进行分析,通过试点工程表明,太阳能住宅设计大大提高了农宅的热工性能,既降低了冬季农宅的采暖能耗,也调节了夏季的室内温度,达到了节能、环保、经济的目的,走可持续发展的道路是可行的。     

Energiespeicherbeton – ein Beton mit integriertem Latentwärmespeichermaterial

Energy storage concrete – a concrete with integrated latent heat storage material. In times of solar architecture and increased utilisation of renew‐able energy, building components with high thermal heat storage capability are becoming increasingly important. One of the areas future research in building physics and building services will focus on is the development of energy storage units. A particularly interesting research area is latent heat storage. This essay describes the development of a concrete with integrated latent heat storage material (phase change material, PCM) as part of a thesis. This innovative concrete offers significantly improved thermal characteristics. For example, it was possible to more than double the heat capacity within a temperature range of 10 Kelvin around the melting point of the PCM. The PCM has a melting point between approx. 22 °C and 35 °C, depending on application. A highly versatile material such concrete offers a wide range of application options. In principle, it is possible to use latent heat storage concrete to supplement heating systems, to extend the scope of passive solar systems, or to protect against overheating in summer.     

Analysis of thermal performance of building attached sunspace

The thermal performance of a sunspace attached to a living room located in Amman-Jordan has been investigated. Six configurations that differ by the ratio of glazed surface area to opaque surfaces area are studied. A novel configuration that utilizes an inclined front surface is thermally investigated. The effect of orientation of the sunspace, opaque wall and floor absorption coefficients and number of glass layers on the thermal performance is evaluated. Results show that the sunspace reduces the heating load during the winter, while it creates a serious overheating problem during summer. The contribution of reducing heating requirements increases with increasing the ratio of glazed surface to opaque surface area. Also, the optimal contribution was obtained when the sunspace was oriented to the south. Two passive cooling techniques are proposed and evaluated to overcome the summer overheating problem. Additionally, a passive heating technique is proposed to minimize the thermal losses during winter nights. Internal shading and night ventilation successfully minimize the overheating problem. Employing the three passive techniques with sunspace, results show that as high as 42% reductions in annual heating and cooling load can be achieved. Utilizing an inclined front surface with double layer of glass can further reduce heating and cooling load requirements.     

Energy conservation effect of new HVAC system for condominiums with solar collectors integrated with the balcony handrail

Energy consumption in Japan's houses has been increasing rapidly over the past decades. Furthermore, installation of 24-h ventilation systems in houses became mandatory last year, which will probably increase the heating, ventilation, and air conditioning (HVAC) energy consumption in Japan's houses. Regardless of these situations, natural energy utilization to reduce HVAC energy has not spread, especially in condominiums in Japan. In this study, we propose a new HVAC system for condominiums that makes use of solar heat, outdoor cool air by integrating elements in condominiums such as the balcony handrail, the 24-h ventilation system, and under-floor space. As a first step in the development of this system, we carried out experiments and computational fluid dynamics (CFD) studies on a solar heat collector integrated with the balcony handrail to determine its specification and to obtain information on its heat collection performance. As a second step, we calculated dynamic thermal load on a model condominium to evaluate the energy-saving performance and thermal comfort of the proposed system. The calculation results show that the proposed system has a high performance, both for energy saving and thermal comfort.     

Scaling of free convection heat transfer in a triangular cavity for Pr > 1

Unsteady natural convection inside a triangular cavity subject to a non-instantaneous heating on the inclined walls in the form of an imposed temperature which increases linearly up to a prescribed steady value over a prescribed time is reported. The development of the flow from start-up to a steady-state has been described based on scaling analyses and direct numerical simulations. The ramp temperature has been chosen in such a way that the boundary layer is reached a quasi-steady mode before the growth of the temperature is completed. In this mode the thermal boundary layer at first grows in thickness, then contracts with increasing time. However, if the imposed wall temperature growth period is sufficiently short, the boundary layer develops differently. It is seen that the shape of many houses are isosceles triangular cross-section. The heat transfer process through the roof of the attic-shaped space should be well understood. Because, in the building energy, one of the most important objectives for design and construction of houses is to provide thermal comfort for occupants. Moreover, in the present energy-conscious society it is also a requirement for houses to be energy efficient, i.e. the energy consumption for heating or air-conditioning houses must be minimized.     

Determinants of winter indoor temperatures in low income households in England

The objective of this study is to quantify the extent to which variation in heating season indoor temperatures is explained by dwelling and household characteristics and increased by energy efficiency improvements in low income households. A survey of dwellings in the Warm Front home energy efficiency scheme was carried out in five urban areas of England. Half-hourly living room and main bedroom temperatures were recorded for 2–4 weeks over two winters. For each dwelling, regression of indoor on outdoor temperature was used to obtain estimates of daytime living room and night time bedroom temperatures under standardized conditions (outdoor temperature of 5 °C). The results indicate that the median standardized daytime living room temperature was 19.1 °C and the median standardized night time bedroom temperature 17.1 °C. Temperatures were influenced by property characteristics, including its age, construction and thermal efficiency and also by the household number of people and the age of the head of household. Dwellings that received both heating and insulation measures through the Warm Front scheme had daytime living room temperatures 1.6 °C higher than pre-intervention dwellings, night time bedroom temperatures were 2.8 °C higher. Warm Front energy efficiency improvements lead to substantial improvements of both living room and bedroom temperatures which are likely to have benefits in terms of thermal comfort and well-being.     

An assessment of roof space solar gains in a temperate maritime climate

New Zealand has a temperate maritime climate. Despite mild winters compared to nations with continental climates, New Zealand houses have been reported to often be at temperatures below internationally recommended levels. Sources of additional heating are therefore of interest to many New Zealand home occupants. Roof space solar gains have been identified as one possible source of heating. This paper investigates the energy gains available in New Zealand homes from ventilation systems drawing air from the roof cavity. Three New Zealand houses were monitored and a computer-based thermal building simulation developed to quantify the heating and cooling energy that might be transferred by home ventilation systems. The computer model simulating the temperature in the roof space and occupied spaces was constructed using MATLAB, and used publicly available weather station data as the inputs. A good match between measured and modelled results was obtained. Small heating and cooling benefits are possible at certain times from pumping roof space air into the living areas of some New Zealand houses. The magnitude of these benefits, however, is not significant compared with the space heating required to maintain reasonable indoor temperatures over the New Zealand winter.     

An active and passive solar house

The majority of the world's population lives in rural and remote areas in the Third World countries. Many of these areas still do not have regular electric and water supplies. Having the increasing cost of conventional energy in mind, a prototype solar house has been developed in which all the energy requirements of the house are met with solar energy.

Concepts of photovoltaic electric power, thermal heating and passive cooling have been used. All the systems have been functioning satisfactorily. Although the cost of this type of house will be high, such houses can bring considerable improvement in the life-style of rural and remote dwellers in Third World countries.     

An estimate of the time-varying temperature field of the main reflector and subreflector of the Shanghai 65 m radio telescope under solar illumination

The time-dependent temperature fields of the reflectors of the Shanghai 65 m radio telescope are investigated numerically, taking account of the non-uniform heating of the reflector surfaces due to solar illumination and the constantly changing ambient air temperature. This paper utilizes a ray casting algorithm to calculate the borderline separating the reflector areas in shadow and in sunshine, aiming to provide an accurate calculation of the solar energy absorbed. Then a ray tracing algorithm is utilized to calculate the total solar energy that is reflected by the main reflector area and received by the subreflector surface area. Finally, the solar energy is used as the main thermal load on the reflector surface to numerically examine the temperature distribution on both the main reflector and the subreflector. The results illustrate that the time-varying temperature fields of the reflectors of a radio telescope due to asymmetric solar illumination can be accurately simulated utilizing the ray casting algorithm and the ray tracing algorithm. The occurring periods and avoidance zones of the overheating of the subreflector are identified, among which the maximum temperature of the subreflector reaches 144.9°C. These dangerous observation zones should be avoided during the operation of the radio telescope.     

Temperatures and heating energy in New Zealand houses from a nationally representative study—HEEP

The household energy end-use project (HEEP) has collected energy and temperature data from a randomly selected, nationally representative sample of about 400 houses throughout New Zealand. This database has been used to explore the drivers of indoor temperatures and heating energy. Initial analysis of the winter living room temperatures shows that heating type, climate and house age are the key drivers. On average, houses heated by solid fuel are the warmest, with houses heated by portable LPG and electric heaters the coldest. Over the three winter months, living rooms are below 20 °C for 83% of the time—and the living room is typically the warmest room. Central heating is in only 5% of houses. Solid fuel is the dominant heating fuel in houses. The lack of air conditioning means that summer temperatures are affected by passive influences (e.g. house design, construction). Summer temperatures are strongly influenced by the house age and the local climate—together these variables explain 69% of the variation in daytime (9 a.m. to 5 p.m.) living room temperatures. In both summer and winter newer (post-1978) houses are warmer—this is beneficial in winter, but the high temperatures in summer are potentially uncomfortable.     

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.