Design Summer Year Research Articles

Dynamic thermal simulation of advanced natural ventilation in buildings: current and future usage, UK exemplar

ABSTRACT This paper evaluates the use of advanced natural ventilation (ANV) strategies in a range of climatic conditions from four cities in the UK. A prototype ANV system was proposed to determine the most effective case in mitigating overheating. The case was then assessed under identical simulation conditions for all four ANV strategies. The overheating criteria used in the research include the single temperature criterion from CIBSE Guide A and the adaptive thermal comfort overheating criteria from BS EN 15251. Both the current and future ‘Design Summer Year (DSY)’ weather data were used to examine the thermal performances of the proposed design. The findings show that shading, night cooling and heavy weight structures (ceiling) were all useful in mitigating overheating, with night cooling being identified as the most effective measure. The work assessed the use of ANV in both current and future scenarios to quantify the limits of outdoor environmental conditions under which natural ventilation is an effective strategy for achieving thermal comfort. The adaptive thermal comfort overheating criteria were proved to be easier to meet compared with the CIBSE single temperature criterion. With the adaptive overheating criteria, the given design is predicted to not overheat until 2050 in London Heathrow; and for other places evaluated in the UK (Edinburgh, Manchester & Birmingham), the design passes these criteria. The Centre-in ANV strategies proved to be more effective than the Edge-in strategies for space cooling due to the extended structure thermal mass.

Balancing daylight and overheating in low-energy design using CIBSE improved weather files

A new set of CIBSE weather files for building performance simulation was recently developed to address the need for better quality solar data. These are essential for most building performance simulation applications, particularly for daylighting studies and low-energy building design, which requires detailed irradiation data for passive solar design and overheating risk analysis. The reliability of weather data becomes paramount when building performance is pushed to its limits. Findings illustrate how principles of good window design can be applied to a case study building, built to the Passivhaus standard, and how its expected performance is affected by the quality of solar irradiation data. Analyses using test reference years were most affected by changes in the solar radiation model (up to 8.3% points), whereas for design summer years the maximum difference was 1.7% points. Adopting the new model caused overheating risk to be classified as more severe using test reference years than design summer years, prompting a discussion on the design summer year selection method. Irradiance data measured on-site were used as a benchmark to evaluate the new solar radiation model, which was found to significantly improve the accuracy of irradiance data within weather files and so the reliability of overheating assessments. Practical application: CIBSE weather files are widely used for compliance verification of building performance in the UK context. This paper tests how the introduction of a new solar radiation model in weather files will affect daylighting and overheating simulation results. Examples are given on how low-energy building design considerations driven by advanced simulation techniques can help reaching indoor visual and thermal comfort requirements.

Summer performance, comfort, and heat stress in structural timber buildings under moderate weather conditions

PurposeThe purpose of this paper is to examine the Summer performance, comfort, and heat stress in structural timber buildings. The research utilises building simulation as a tool to investigate the performance of the case study buildings under non-extreme weather conditions.Design/methodology/approachThe research explores three UK sites using the test reference year (TRY) weather files for the current and future weather conditions. The study focuses on the Summer performance and heat stress in non-extreme weather conditions; therefore, the Design Summer Year (DSY) weather files are not used for the simulations. The simulation data are calibrated and validated using the measured data from the field study.FindingsThe results revealed the mean predicted temperatures varied from 20.2–20.8°C for the 2000s. The mean temperatures for the 2030s ranged from 23.1 to 24.2°C. Higher temperatures are predicted at the buildings in the Southeast site than the Midlands and the Northwest sites. The results revealed that there is no significant improvement in the thermal environment when the floor area and the floor-to-ceiling height are increased. However, the study showed that the integration of different design interventions can improve the future performance and resilience of the buildings in various weather conditions.Research limitations/implicationsBy applying the wet-bulb globe temperature (WBGT) and the Universal Thermal Comfort Index (UTCI) mathematical models to calculate the heat stress at the buildings, the study proposes the WBGT of 20.0°C and the UTCI of 24.1°C as possible heat stress indicators for occupants of the buildings in the 2030s.Practical implicationsOn the one hand, the results revealed the maximum temperatures in some of the case study buildings exceed the comfort threshold (28°C). On the other hand, the study showed that occupants of the buildings are not prone to extreme Summertime overheating and heat stress under moderate weather conditions. However, different outcomes may be predicted if DSY weather files for the selected sites are considered.Originality/valueThis study is the first reported work to explore building simulation and mathematical equations to investigate Summer performance, comfort and heat stress indexes in timber buildings under moderate weather conditions in different regional sites in the UK.

The urban heat island of London, an empirical model

On top of climate change and its consequent temperature rises, urban areas have the added burden of the urban heat island (the urban area being warmer than the rural area especially at night under calm, cloud-free conditions). The urban heat island intensity (the difference between the rural air temperature and that in the city centre) can be as large as 10K for the major cities such as London. The urban heat island intensity, consequently, can have a significant effect on the sizing of heating, ventilating and air-conditioning plant and its energy consumption. At present, designers have access to empirical factors for design days only in June, July and August from the Chartered Institution of Building Services Engineers Guide. Or they can use the latest Design Summer Year which implicitly includes the urban heat island intensity. However, the empirical model discussed in this paper allows the designer to add on the hourly urban heat island intensity for central London to any recent year’s hourly weather data set from London Heathrow or Bracknell, a more rural site. The model is similar to one for Manchester, suggesting that the model may well be of application to other UK cities. Practical applications: Most buildings that building services engineers and other building designers are involved with are in urban or city centres. However, the weather data for their designs are based on near-rural weather data, which does not include the urban heat island effect. This paper describes the urban heat island effects that a designer needs to consider and the adjustments that can be made, related to London.

Assessing the requirements from ‘BB101’ 2006 and 2018 for a naturally ventilated preparatory school in the UK

In the UK, BB101 is the guidance document for ventilation design of school buildings. There are significant changes proposed in the new version of BB101. The aim of this paper is to examine the requirements of thermal comfort and CO2-based indoor air quality using both versions on a typical naturally ventilated preparatory school design using dynamic thermal simulations. The findings indicate that the new set of requirements on this school building design (both thermal and CO2 concentration) are much more difficult to meet than the requirements from the old version. One of the new thermal comfort criteria may be too difficult to achieve in practice, as the target value was exceeded for all the rooms of the examined design, using both test reference year and design summer year weather data. The ventilation provision for the school design is believed to be adequate. With appropriate ventilation control strategies, the design is able to meet the revised CO2 concentration criteria. Further examinations of the criteria from the new guidance document are needed to make sure the chosen criteria are fit for purpose. The use of future projected design summer year weather data (2020) also adds extra challenges for the preparatory school building to meet the newly proposed adaptive thermal comfort criteria. Practical applications: The research presents a very first assessment of a preparatory school building design using the newly proposed BB101 guidance document. It will assist further exploration on the appropriateness of the new assessment criteria and the use of design summer year weather data in order to explore the implications of the new BB101 guidelines for designers. The method adopted in the research can also be used for other building types to assess overheating in buildings when adaptive comfort criteria are recommended.

Thermal responses of single zone offices on existing near-extreme summer weather data

There have been a number of attempts in the past to define “near extreme” weather for facilitating overheating analysis in free running buildings. The most recently efforts include CIBSE latest release of Design Summer Year (DSY) weather using multiple complete weather years and a newly proposed composite DSY. This research aims to assess how various single zone offices respond to these new definitions of near extreme weathers. Parametric studies were carried out on single zone offices through which four sampling sets of models were employed to examine the thermal responses of dry bulb temperature, global solar radiation & wind speed collectively. London weather data from 1976 to 1995 were used and the overheating assessments were made based on CIBSE Guide A & BS EN 15251. The research discovers that solar radiation and wind both influence the predicted indoor warmth with solar radiation has obvious stronger impacts than wind. No perfect correlation was found from observation and Spearman’s rank order analysis on the ranks between the weather warmth and the predicted indoor warmth. The ranks made using multiple weather parameters show better correlation than some of the dry bulb temperature only metrics. The research also discovers that the Test Reference Year weather behaves warmer than expected. It is also found that a single complete year can not represent the near-extreme consistently and there is no evidence a composite DSY is better statistically. These findings support the notion of using multiple complete warm weather years for overheating assessments.

Evaluation of thermal comfort and cooling loads for a multistory building

The latest UK Climate Projections (UKCP09) show that mean daily temperatures will increase everywhere in the United Kingdom. This will significantly affect the thermal and energy performance of the current building stock. This study examines an institutional fully glazed building and looks into the changes in the cooling loads and thermal comfort of the occupants during the occupied hours of the non-heating period. Furthermore, it investigates the effect of relative humidity (RH) on thermal comfort. The Design Summer Year (DSY) 2003 for London Heathrow has been used as a baseline for this study and the DSY 2050s High Emissions scenario was used to examine the performance of the building under future weather conditions. Results show a 21% increase of the cooling loads between the two examined scenarios. Thermal comfort appears to be slightly improved during the months of May and September and marginally worsen during the summer months. Results of the simulation show that a relative humidity control at 40% can improve the thermal comfort for 53% of the occupied hours. A comparison of the thermal comfort performance during the hottest week of the year, shows that when the relative humidity control is applied thermal comfort performance of the 2050s is similar or better compared to the thermal comfort performance under the baseline.

The Impact of Different Weather Files on London Detached Residential Building Performance—Deterministic, Uncertainty, and Sensitivity Analysis on CIBSE TM48 and CIBSE TM49 Future Weather Variables Using CIBSE TM52 as Overheating Criteria

Though uncertainties of input variables may have significant implications on building simulations, they are quite often not identified, quantified, or included in building simulations results. This paper considers climatic deterministic, uncertainty, and sensitivity analysis through a series of simulations using the CIBSE UKCIP02 future weather years, CIBSE TM48 for design summer years (DSYs), and the latest CIBSE TM49 DSY future weather data which incorporates the UKCP09 projections to evaluate the variance and the impact of differing London future weather files on indoor operative temperature of a detached dwelling in the United Kingdom using the CIBSE TM52 overheating criteria. The work analyses the variability of comparable weather data set to identify the most influential weather parameters that contribute to thermal comfort implications for these dwellings. The choice of these weather files is to ascertain their differences, as their development is underpinned by different climatic projections. The overall pattern of the variability of the UKCIP02 and UKCP09 Heathrow weather data sets under Monte Carlo sensitivity consideration do not seem to be very different from each other. The deterministic results show that the operative temperatures of the UKCIP02 are slightly higher than those of UKCP09, with the UKCP09 having a narrow range of operative temperatures. The Monte Carlo sensitivity analysis quantified and affirmed the dry bulb and radiant temperatures as the most influential weather parameters that affect thermal comfort on dwellings.

An update of the UK’s design summer years: Probabilistic design summer years for enhanced overheating risk analysis in building design

Overheating is increasingly becoming a key issue for building design across the world. In the UK, better building fabric performance and warmer weather can increase the risk of overheating events in badly designed buildings. The impacts of these overheating events could be reduced by adapting building designs at an early design stage using building thermal models using appropriate weather data such as a design summer year. In this work, a method to determine probabilistic design summer years will be presented. These years take into account the return periods of actual events, are presented within a probabilistic framework and therefore include a description of the severity of the year at each location. Practical application: Design summer years are designed to be used to optimise building performance in terms of thermal comfort at design stage. This paper demonstrates a method to create probabilistic design summer years which contain a range of overheating events which can be used to inform designers of the overheating risk to occupants. The proposed method is then used to generate new near extreme weather files for the UK.

Design summer year weather – outdoor warmth ranking metrics and their numerical verification

The existing methods of selecting design summer year weather data rely on the outdoor dry bulb temperature without considering solar radiation and wind which can impact on indoor thermal conditions. This research sets out to examine the existing outdoor warmth ranking metrics and proposes a new warmth ranking metric (solar air temperature), which takes into account not only dry bulb temperature but also solar and wind conditions. Parametric study was carried out using five typical UK dwelling models, by varying parameters associated with building design and operation, a large model population were generated to statistically determine how well the outdoor warmth ranking metrics correlate the predicted indoor warmth. The outdoor warmth ranking was made for the 20 years source weather data (1976–1995) in London and both CIBSE single temperature criterion and BS EN 15251 adaptive criteria were used to judge overheating in buildings. It is found that the predicted indoor warmth are mostly arbitrary in nature and none of the existing and newly proposed outdoor warmth ranking metrics can strictly correlate. The research also discovers the significant differences between the predicted overheating occurrence and severity in the warmth ranking of weather years. Practical application: The parametric methods described in the paper will facilitate academics and industry researchers to assess design summer year weather generated by various methods. The research also provides guidance on assessing both overheating occurrence and severity in buildings to assist decision making.

Future probabilistic hot summer years for overheating risk assessments

As the 2003 Paris heatwave showed, elevated temperatures in buildings can cause thousands of deaths. This makes the assessment of overheating risk a critical exercise. Unfortunately current methods of creating example weather time series for the assessment of overheating are based on a single weather variable, and hence on only one driver of discomfort or mortality. In this study, two alternative approaches for the development of current and future weather files are presented: one (pHSY-1) is based on Weighted Cooling Degree Hours (WCDH), the other (pHSY-2) is based on Physiologically Equivalent Temperature (PET). pHSY-1 and pHSY-2 files were produced for fourteen locations. These were then compared with the existing probabilistic future Design Summer Year (pDSY) and the probabilistic future Test Reference Year. It was found that both pHSY-1 and pHSY-2 are more robust than the pDSY. It is suggested that pHSY-1 could be used for assessing the severity and occurrence of overheating, while pHSY-2 could be used for evaluating thermal discomfort or heat stress. The results also highlight an important limitation in using different metrics to compare overheating years. If the weather year is created by a ranking of a single environmental variable, to ensure consistent results assessment of the building should be with a similar single metric (e.g. hours >28 °C or WCDH), if however the weather year is based upon several environmental variables then a composite metric (e.g. PET or Fanger’s PMV) should be used. This has important implications for the suitability of weather files for thermal comfort analysis.

Overheating Risk of UK Dwellings Under a Changing Climate

Building practitioners assess the overheating risk of buildings via dynamic thermal comfort simulation with hotter than average reference weather years. In the UK, the near-extreme hot summer years called Design Summer Years (DSY) offered by the Chartered Institute of Building Services Engineers (CIBSE) are provided for fourteen locations for the purpose of estimating overheating risk of naturally ventilated buildings. The current DSY is selected based on the third warmest mean summer dry bulb temperature (DryT) during April to September. However, it has been proved that the simple method used for creating DSY leads to obvious problems into the thermal comfort simulations. In this research, a new design summer year termed as a Hot Summer Year (HSY) is created based on weather data generated from the UK Climate Projections weather generator and the Physiological Equivalent Temperature (PET). The effects of using the DSY and the HSY on indoor thermal comfort are analyzed based on a static overheating risk criterion recommended by CIBSE. With the aim of predicting future overheating risk, future HSYs are created for 2050s and 2080s under the high emission scenario for fourteen locations. These are created to investigate overheating risk of dwellings across the UK.

Generating near-extreme Summer Reference Years for building performance simulation

At present, there is no universally accepted method for deriving near-extreme summer weather data for building performance simulation. Existing data sets such as the Design Summer Years (DSY) used in the UK to estimate summer discomfort in naturally ventilated and free running buildings have been criticised for being inconsistent with the corresponding Test Reference Years (TRY). This paper proposes a method for generating Summer Reference Years (SRY) by adjusting the TRY of a given site with meteorological data in order to represent near-extreme conditions. It takes as the starting point that the TRY is robust, being determined on a monthly basis from the most typical months. Initial simulations for the 14 UK TRY locations show promising results for determining building overheating with the SRY. Practical application: The proposed method for deriving near-extreme summer years from multi-year data and the corresponding ‘typical’ weather year (TRY) of a given site is applicable to locations worldwide and facilitates summer overheating assessment of naturally ventilated and free running buildings. The method helps to overcome the previous shortcomings of near-extreme summer year selection procedures by providing a clear relationship to the underlying TRY.

Using the new CIBSE design summer years to assess overheating in London: Effect of the urban heat island on design

The new CIBSE design summer years (DSYs) for London Weather Centre, Heathrow and Gatwick in London are now available for three baseline years: 1976, 1989 and 2003. This study tested how these different design summer years impacted the assessment of overheating in a naturally ventilated office in London. Two office designs were tested, an uninsulated and one retrofitted with insulation and night cooling. The choice of baseline year impacted the level of overheating for both the uninsulated and retrofitted models. Tested in the more severe years, 1976 and 2003, the offices experienced the highest levels of overheating. When an office was retrofitted and night cooled, the choice of location had more of animpact on overheating due to the urban heat island effect. London Weather Centre and Heathrow experienced higher levels of overheating than Gatwick. The study highlights the need for designers to carefully consider how the differences between the weather files will impact their overheating assessment depending on their buildings’ fabric and ventilation design. Practical application: This study provides initial testing of the how the new CIBSE design summer years impact overheating within a naturally ventilated office in London. Initial analysis of the weather files highlights the differences between locations and baseline years. These differences are then shown to have an impact on overheating depending on the building fabric and ventilation strategy. The results highlight how important it is that practitioners understand how both the weather variables and building and ventilation design will impact the predicted levels of overheating.

The relative importance of input weather data for indoor overheating risk assessment in dwellings

The risk of overheating in UK dwellings is predicted to increase due to anthropogenic climate change and local urban climate modification leading to an increased urban heat island effect. Dwelling geometry characteristics such as orientation, aspect, and glazing, and building fabric characteristics such as thermal mass and resistance can influence the risk of overheating. The majority of simulation-based studies have focused on identifying the importance of building characteristics on overheating risk using a small number of weather files, or focus solely on the impact of external temperatures rather than a full set of climatic variables. This study examines the overheating risk in London dwelling archetypes when simulated under different UK climates, both in the present and under ‘hot future’ conditions, with the objective of identifying whether the conclusions drawn from location-specific studies can be generically applied to different cities. Simulations were carried out using the dynamic thermal simulation tool EnergyPlus using 3456 dwelling variants and six different Design Summer Year (DSY) climate files from locations within the UK. In addition, a 2050 Medium Emissions scenario weather file was used to model a particularly hot summer in all locations. The results indicate that weather files can influence the ranking of relative overheating risk between dwelling types, with significant variations in the relative ranking between London, Scotland and the North of England, and the rest of England. These results show that studies examining the overheating risk across the UK need to consider the variability of building performance under regional weather conditions.

Limitations of the CIBSE design summer year approach for delivering representative near-extreme summer weather conditions

Representative, site-specific weather data is a key requirement for building performance simulation. In the UK, such data is available in two formats, Test Reference Years for analysing building services loads under ‘typical’ year conditions and Design Summer Years for estimating summer discomfort of naturally ventilated and free-running buildings. Currently, Design Summer Years are determined as a complete year based on the rank of the average dry bulb temperature from April to September. The simplicity of this approach does not take into account extreme temperature values in individual months or the incident solar radiation, both of which are however of great significance for the summer overheating performance of a building. This paper analyses the implications of this simplified approach for the resulting data. It is shown that there is no consistent relation between the Design Summer Years and the corresponding Test Reference Years and that, for some sites, building performance simulations using Design Summer Year files deliver unreliable results. Practical application: This paper demonstrates that the current approach for deriving Design Summer Years (DSYs) can lead to data series that are not representative for near-extreme summer conditions at a given location. It highlights that a new approach for deriving near-extreme summer years for building performance simulation is needed in order to overcome the inherent shortfalls of the current DSY data.

The design reference year – a new approach to testing a building in more extreme weather using UKCP09 projections

Current practice in building design is to assess a building’s performance using average or typical weather, a test reference year (TRY), and then to see how it performs when ‘stressed’, using a design summer year (DSY). The DSY is an actual year of hourly data which has the third warmest summer in 20 years’ summers. One of the problems with the DSY method is that it does not explicitly take into account solar radiation, or humidity, nor when more extreme weather occurs – it is selected solely on the mean six monthly temperature from April to September. A DSY may actually be cloudier than the average weather of a TRY. This article proposes an alternative approach using a new type of design reference year (DRY) consisting of a year formed from individual more extreme weather months. The DRY is used in simulating the performance of a building and to identify a single critical month for over-heating, or maximum cooling load. This article compares the characteristics of the DSY and proposed DRY using future projected weather data from UKCIP. Practical applications: Building designers are increasingly required by their clients to demonstrate how a proposed building will perform under a future rather than historical climate. This article describes a method of processing the latest future climate projections (UK Climate Impacts Programme’s (UKCIP’s) CP09 data released in June 2009) and generating a design reference year (DRY) for use in building simulation programmes. The DRY is proposed as a replacement for the design summer year (DSY), which has a number of limitations.

The use of UKCP09 to produce weather files for building simulation

Traditionally, hourly weather years such as the test reference years (TRYs) and design summer years (DSYs) have been used for building energy and thermal performance analysis. Until recently, these weather datasets were based on observed measurements, but the need to adapt buildings to the impacts of likely future climate change has introduced a requirement to incorporate climate projections, such as the UK Climate Projections (UKCP09), into building performance analysis. Four research projects, funded by the EPSRC, examined the use of UKCP09 data, and the associated Weather Generator tool, in producing weather files appropriate for building simulation. A methodology called ‘morphing’, previously used to create the currently available to practitioners, UK Climate Impacts Programme (UKCIP02) based, CIBSE Future Weather Years, will also be discussed here as a potential alternative for the production of UKCP09-based weather files. This article reviews all above methodologies developed to produce weather files for building simulation, using the UKCP09 projections, and discusses their benefits and limitations as well as their ease of use by designers. Practical application: This article aims to provide a comprehensive review of the various methodologies currently available for the production of future weather files for building thermal and energy performance simulation using the UKCP09 projections. This analysis aims to provide users with the benefits and limitations associated with each methodology and end product based on their accessibility, consistency with other currently used datasets, computational resources required and spatial availability.

A low-order canyon model to estimate the influence of canyon shape on the maximum urban heat island effect

A simple mathematical model of an urban canyon is developed. The canyon model consists of horizontal and vertical slabs providing thermal storage for heat and absorption of and shielding from solar radiation and long wave radiation to the sky. The model is compared to a horizontal slab in a rural location to examine the effect of the canyon shape. The results show the same trend as measurements by others, with increasing urban heat island (UHI) effect with increasing canyon aspect ratio. The model is then used to determine the maximum UHI effect by producing a simple algebraic equation. This compares well with measurements in Greater Manchester of canyon and rural temperatures although some empirical adjustments are required. The strong influence of cloud cover is shown by the model and measurements as are the canyon shape and the ground temperature. Practical applications: The model is simple and developed in terms applicable to building services engineers, using ventilation rates through the canyon. It also does not require more than the standard weather data available in a CIBSE Test Reference Year or a Design Summer Year. From this model, the UHI effect can be developed to adjust the data from a rural site to that of an urban and city centre site. This is useful for building designers to take account of the UHI effect which they cannot do at present. This would also be useful for UKCP09 data which have been released.

Methodologies for the generation of design summer years for building energy simulation using UKCP09 probabilistic climate projections

Design summer years representing near-extreme hot summers have been used in the United Kingdom for the evaluation of thermal comfort and overheating risk. The years have been selected from measured weather data basically representative of an assumed stationary climate. Recent developments have made available ‘morphed’ equivalents of these years by shifting and stretching the measured variables using change factors produced by the UKCIP02 climate projections. The release of the latest, probabilistic, climate projections of UKCP09 together with the availability of a weather generator that can produce plausible daily or hourly sequences of weather variables has opened up the opportunity for generating new design summer years which can be used in risk-based decision-making. There are many possible methods for the production of design summer years from UKCP09 output: in this article, the original concept of the design summer year is largely retained, but a number of alternative methodologies for generating the years are explored. An alternative, more robust measure of warmth (weighted cooling degree hours) is also employed. It is demonstrated that the UKCP09 weather generator is capable of producing years for the baseline period, which are comparable with those in current use. Four methodologies for the generation of future years are described, and their output related to the future (deterministic) years that are currently available. It is concluded that, in general, years produced from the UKCP09 projections are warmer than those generated previously. Practical applications: The methodologies described in this article will facilitate designers who have access to the output of the UKCP09 weather generator (WG) to generate Design Summer Year hourly files tailored to their needs. The files produced will differ according to the methodology selected, in addition to location, emissions scenario and timeslice.