Geoff Levermore

Analyses and algorithms for new test reference years and design summer years for the UK

With the increasing use of simulation for building design, test reference years (TRYs) are required for energy analyses and design summer years (DSYs) for assessing natural ventilation in the summer. Previously TRYs and DSYs only existed for three sites in the UK. Also the data was derived from weather data up to 1995. More sites were required and also updated data, as a number of warm years had occurred after 1995. The opportunity was also taken to improve the derivation of the TRY using just the Finkelstein-Schafer statistic and also to improve the algorithm for smoothing between months. New programs had to be written for filling missing values in the lower-quality raw data. This paper describes these programmes, the quality assurance procedures and analyses the years produced. A comparison is made between the 14 sites demonstrating the link between dry bulb temperature, solar radiation and latitude.

A review of the IPCC Assessment Report Four, Part 1: the IPCC process and greenhouse gas emission trends from buildings worldwide

The Intergovernmental Panel on Climate Change, (IPCC), Fourth Assessment Report, AR4, Climate Change 2007 consists of three volumes based on the work of three IPCC Working Groups (WGs). WG1 considered the scientific basis of climate change and what the climate models are showing. WG2 considered the consequences of climate change and possible adaptation to it. WG3 considered how the climate change could be mitigated. This paper briefly outlines the history of the IPCC, its purpose and outputs, including the AR4 and its relation to the Kyoto Protocol, and the IPCC authoring process. The paper then reviews the trends in carbon emissions, especially from the built environment (which are a major source of greenhouse gas, GHG, emissions in the world), and the potential mitigation reductions in carbon emissions that are considered possible and the scenarios on which they are based. Practical application: Climate change is an important topic for building services engineers, resulting in the UK in the new, performance-based Building Regulations Part L. This paper outlines the history and relevance of the IPCC for building services engineers as well as reviewing the world trends in carbon emissions from buildings and the future scenarios on which they are based. The paper emphasises the importance of buildings and building services in the context of climate change.

Climate change and future energy consumption in UK housing stock

This paper examines the likely effects on gas and electricity consumption and carbon emissions from heating and cooling systems in existing dwellings up to 2080, assuming a widespread uptake of cooling systems. This area of research is highly sensitive to the myriad of possible inputs and thus holds a wide range of predicted outcomes. However, general trends have been found, showing significant sensitivity to ventilation rate, U-values, occupant behaviour and location. Heating demand will still be dominant over cooling demand in UK dwellings by the 2080s, based on an UKCIP02 A1F1 weather scenario. A national worst case scenario for the 2050s, shows a 10 megatonne CO2 emissions saving on present levels largely due to a 20% reduction in gas consumption. Practical applications: The balance of heating and cooling demand causes more modest changes in CO 2 than first anticipated. Despite first perceptions of future energy use in housing and climate change, heating appears to remain the major load rather than cooling, even into the 2080s. These predictions of future CO 2 emissions will be useful to those in the building industry planning appropriate proportionate climate adaptation and climate mitigation measures. Also, the prediction of changes to future energy demands from the housing sector will be of interest to energy providers considering future demands for heating and cooling and may feed into larger bottom-up energy models.

New algorithm for generating hourly temperature values using daily maximum, minimum and average values from climate models

The use of building simulation programmes for predicting building performance is increasing all the time especially with the advent of cheap, fast computers. Hourly weather data, in particular outdoor dry bulb temperature (DBT) and solar radiation values, are required for simulation programmes for building performance. When hourly values are not available there are algorithms for generating hourly temperature values from daily values. These use the daily maximum temperature TMAX, and daily minimum temperature, TMIN. However, climate prediction models, such as HadCM3 and HadRM3 also provide the daily average dry-bulb temperature TAVE as well as the daily maximum and minimum. The average temperature is important for selecting weather years and also because the average temperature is often different from the average of the maximum and minimum, assumed in the simpler algorithms. Buildings being designed now will need to perform under future weather conditions with climate change, so the downscaling of daily values from climate prediction models to hourly values is required. This paper describes a new, more accurate algorithm for generating hourly temperature values in the UK that uses all three temperature parameters from climate change models, and demonstrates the improvement of the quality of the generated values against traditional algorithms that use just the daily maxima and minima. Practical application: The proposed algorithm for generating hourly DBT values from daily maximum, minimum and average values is intended primarily for deriving hourly data for running building simulation programmes, as some weather stations and future climate prediction models only provide daily values of weather parameters. Climate change is affecting all aspects of human life, and as well as being affected by climate change, buildings can also affect the degree of climate change, since well-designed buildings will require less energy to run, thus minimising the amount of carbon dioxide emitted. As the climate is predicted to change significantly in the next 100 years, if buildings are designed to last, it is important for designers to know how buildings will respond and perform then. Building simulation programmes are useful for this, but they require hourly weather data which are not provided by most climate prediction models. By having a quality-assured algorithm for down-scaling the raw daily values to hourly values, data from climate prediction models, such as HadCM3 and HadRM3 can be used for building simulations for any location in the world. The hourly DBTs derived from using the algorithm suggested in this paper may also be used in conjunction with other hourly weather data, such as wet-bulb temperature, solar irradiance, cloud cover and wind speed, derived from the same dataset.

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.

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.

An examination of UKCIP02 and UKCP09 solar radiation data sets for the UK climate related to their use in building design

The climate is changing, both globally and in the UK. To adapt effectively, engineers and planners need as much information as possible on how the climate will evolve. The UK Climate Impacts Programme (UKCIP) provided this in 2002 with UKCIP02 and the latest data UKCP09, which provides data to a resolution of 5 km square grids over the UK. Data sets from these were used in this study along with the historical measured data for three locations — Bracknell (London), Manchester and Edinburgh — to analyse critically the likely changes that may occur in the key climate variables, that is temperature, sunshine duration and solar irradiation. These parameters have an important bearing on the design and function of buildings and building services. Sunshine duration is the main variable that is used to obtain solar radiation in the UKCP09 5 km grid data. For the grids containing Bracknell, Manchester and Edinburgh, most of the UKCP09 data sets for the years 2050 and 2080 showed abnormally elongated sunshine duration, that is from sunrise to sunset, for clear days. In contrast, the latest historic measured data sets indicate only a third of the above sunshine duration. Note that the latter data are used in cooling load design calculations and for the generation of sol-air temperatures.1 Of particular note was the anomalous occurrence in UKCP09 of late evening sunshine duration. For Bracknell and Edinburgh, the sunshine duration at hour ending 20 and beyond showed substantial amount of predicted sunshine. As a result of this work, corrective action has been proposed for UKCP09 data. Furthermore, a very significant increase was also noted in solar irradiation for UKCP09. For the historic measured data for Bracknell, the clear day noon irradiation is 818 Wh/m 2. For the UKCP09 grid containing Bracknell the 2080 High Emission scenario data gives an average value of 1002 Wh/m2, an increase of 23%. The same trend occurs for Edinburgh, (a present value of 789 Wh/m 2 and the predicted value of 948 Wh/m2, an increase of 20%). Note that compounded with presently found increase of 4—5°C increase for the above locations, the substantial increase in irradiation will have a much more pronounced increase in the cooling load of buildings. An evaluation of the change in the character of solar radiation was also undertaken. This was done by noting the change in the diffuse fraction of global irradiation. For Bracknell and Edinburgh historic data and UKCP09 data 2080 High Emission data set show a drastic decrease, respectively from 0.37 to 0.13 and from 0.33 to 0.14. Diffuse fraction may be used as an indicator of the prevailing sky clarity. If the predictions come true a drastic decrease in the diffuse fraction of this magnitude signifies a radical shift in the character of solar climate for the future. The current solar climate of Bracknell is known for its above average turbidity, the latter stemming from the following factors: inland location, high-density housing, proximity to Heathrow airport and M25 London orbital motorway. Whether such an extreme shift in the sky clarity will occur within a matter of 60—70 years is open to discussion. Practical applications: To adapt effectively against the challenge posed by climate change engineers need to know the extent to which the basic climate variables such as temperature and solar radiation will change. This work has used basic data from the UKCP09 project to analyse the extent of the above change with respect to the basic and other derived data. It was shown that for Scottish and English locations a temperature rise of up to 4—5°C may occur between the present age and the year 2080 for High Emission scenario. It was also shown that the corresponding irradiation strength may increase around 22%. Furthermore, it was also found that if these predictions come true then a drastic decrease in the diffuse fraction of irradiation will produce a radical shift in the character of solar climate. The resulting higher proportion of beam irradiation will have to be handled with care in design of overhangs and other shading contraptions to prevent an excessive increase in cooling load of buildings.

A low cost, easily fabricated radiation shield for temperature measurements to monitor dry bulb air temperature in built up urban areas:

Temperature measurements for UK and world cities are often taken at local airports. These are usually on the outskirts of the urban areas and so not subject to the urban heat island (UHI) effect. Hence they are not representative of urban and city area temperatures. As most buildings are built in urban and city areas, designers need to know these temperatures. It is therefore very important to study the UHI effect and adjust the weather data used for design to include the UHI effect. This paper emanates from a project to measure the UHI effect in Greater Manchester, UK. With the advent of miniature temperature sensors and data loggers a simpler and cheaper shield was designed and produced. This paper describes the construction and testing of a new, low cost radiation shield that can accommodate a new, low cost combined miniature temperature sensor and data logger. The shield and data loggers are both tested and shown to give very reliable results. Practical application: The low cost, easily fabricated radiation shield with its miniature sensor—logger was designed to measure the dry bulb air temperature in Greater Manchester to investigate the UHI effect. The shield is designed to be mounted, with two stainless steel bands, on a lamppost column, typically at 4 m height. A telescopic pole can be used to unhook the sensor—logger for data collection. The shield can also be used to measure the dry bulb air temperature around buildings by fixing it to an external wall. Tests have shown the shield to perform well in comparison to a Stevenson screen and to greatly reduce any influence of solar irradiance.

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.

A Review of the IPCC Assessment report Four, Part 2, Mitigation options for residential and commercial buildings

The Intergovernmental Panel on Climate Change, (IPCC), Fourth Assessment Report, AR4, Climate Change 2007 consists of three volumes based on the work of three IPCC Working Groups (WGs). WG1 considered the scientific basis of climate change and what the climate models are showing. WG2 considered the consequences of climate change and possible adaptation to it. WG3 considered how the climate change could be mitigated. Within this WG3 volume is chapter 6 on the mitigation options for residential and commercial buildings. This paper reviews this chapter which discusses how the potential savings of greenhouse gases can be achieved through technical fixes and policies. The technical fixes are based on existing technology although it is recognised that existing building refurbishment is a major issue to be addressed and that there are a number of policies that can help achieve these reductions although some are in their infancy. Part 1 of this paper (The IPCC process and Greenhouse Gas Emission trends from Buildings worldwide) considered the history of the IPCC and the trends in emissions, particularly from buildings. Practical application: Climate change is an important topic for building services engineers, resulting in the UK in the new, performance-based Building Regulations Part L. This paper reviews the technical options that have been identified by the IPCC as potentially carbon mitigating for buildings. The context of the world situation is also considered and the policies considered by the IPCC as relevant to buildings and plant that will ultimately affect the design of building services engineers in the UK and overseas.