G.J. Levermore

The effects of future climate change on heating and cooling demands in office buildings in the UK

As climate change predicts hotter summers and warmer winters in the next 100 years, buildings designed now as well as many existing buildings will need to cope with the future climate. The aim for building designers should be to provide buildings with comfortable environments for occupants without using excessive heating or cooling energy, which will exacerbate carbon emissions. This is particularly important for office buildings, as these are more susceptible to the effects of warmer temperatures, with their relatively high levels of internal heat gains. The productivity of occupants can also be affected if conditions of the workplace are not ideal. Using climate change data from UKCIP02 based on HadRM3 for three main sites in the UK (London, Manchester and Edinburgh), test reference years were selected for 2020s, 2050s and 2080s under various scenarios.1 Using a second-order room model, future energy usage for heating and cooling were estimated for office buildings complying with various editions of the UK Building Regulation, as a test of the buildings’ age against the effects of climate change. The findings show that the fall in heating energy demand is approximately equalled to the rise in cooling demand as a result of climate change up to the 2080s in Heathrow, Manchester and Edinburgh. Natural ventilation alone would not be able to provide enough summer cooling in the UK in the near future. New office buildings, complying with 2002 Building Regulations, perform significantly better than older ones, and their energy and CO2 emissions remain relatively constant with climate change. However, most of the existing office buildings in the UK are older buildings with lower standards of specification, and the challenge is to make these perform more efficiently. Retrofitting them to have similar properties to the 2002 Building Regulations will be sufficient to cope until 2080s, and increasing the ‘weight’ of the building enclosure will reduce the amount of cooling required. This paper also demonstrates that for all-air systems, it will be essential for fans to be sized correctly for the increasing cooling load with future climate. Practical application: This paper aims to provide a comprehensive study and understanding to how various different office buildings in the UK will cope with climate change, especially how climate change will affect the heating and cooling loads, as well as the associated CO2 emissions as a result of meeting the thermal demands. Using a second-order model, this study simulates an office room for three main UK locations, Heathrow (London), Manchester and Edinburgh, under respective climate change data for 2020s, 2050s and 2080s, comparing their thermal energy consumptions with current weather data. Apart from testing the office room with different orientations, construction thermal ‘weight’ and different future climate scenarios, the office room was also made to comply with various Building Regulations, which determine the permitted maximum U-values and glazing area of the external envelope, and the type of glazing used. This represents the office buildings currently in the building stock in the UK, and the analyses conducted are to examine how each will perform in the 21st century. The results from this study would be useful for building designers to know which aspects will affect energy consumption and thus CO2 emissions most in the future, and what should be done with the existing building stock, where most buildings were built to with higher U-values and single glazing, to make them perform efficiently in the face of a warmer climate. Would retro-fitting be adequate, or would they need to be demolished and re-built? As mechanical cooling becomes a necessity in the future, the energy required for running the fans also contribute greatly to the total CO2 emissions in office buildings in the future.

Constructing a future weather file for use in building simulation using UKCP09 projections

In the future with climate change, building designers may need to demonstrate to clients that their buildings will continue to provide a comfortable environment under future weather conditions. Building simulation modelling can be used to this end provided that suitable weather files can be constructed. This article describes the use of the latest climate projections from UKCIP (UKCP09 data) and a method of constructing an hourly weather file for the following parameters: dry-bulb temperature, relative humidity, cloud cover, solar irradiation (direct and diffuse), wind speed and wind direction. For a given future scenario, the approach used first selects appropriate months from 3000 years of UKCP09 data to construct a Test Reference Year (TRY). Unfortunately, the UKCP09 hourly data has no wind or cloud data, and the solar irradiance is uncorrected at low sun angles. This article describes algorithms for calculating wind speed and cloud cover from the UKCP09 data. From this data, a TRY can be constructed and formatted to be suitable for use with commonly used simulation packages. Practical applications: Building professionals increasingly seek reassurance on 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 (UKCP09 data released in June 2009) and generating a Test Reference Year (TRY) with the full complement of weather parameters suitable for use by commonly used building simulation programmes.

Dry-bulb temperature analyses for climate change at three UK sites in relation to the forthcoming CIBSE Guide to weather and solar data

This paper details some important aspects of the forthcoming CIBSE Guide to weather and solar data. This is intended as a key aid to the design of comfortable, energy-efficient and environmentally friendly buildings, especially through the provision of recent hourly weather data for use in simulation. This should help building services engineers and other building design professionals meet the challenge of designing buildings which have little or no air-conditioning, and which use natural ventilation and natural lighting to the full. Source data for the forthcoming Guide are explored further in this paper. For 3 key UK sites, winters have become milder and summers warmer over the last 36 years, although the evidence does not have the same statistical significance for all parts of the country. However, the trends are compatible with the scenarios for climates in the 2020s and 2050s indicated in the 1996 UK Department of the Environment report on Climate Change Impacts.

Variable-air-volume terminal units II: Dynamic model

Variable-air-volume (VAV) air conditioning systems are used extensively in air-conditioned buildings. This paper extends the steady-state measurements described in a previously paper to obtain a dynamic model of one of the pressure-independent terminal units. These have sometimes been difficult to tune due to interaction with other VAV equipment, e.g. the supply fan or other terminal units. Hence validated, dynamic pressure-independent terminal unit models are essential for future investigations of plant interaction. This paper describes the derivation of a representative dynamic model based on a commercially manufactured European terminal unit including the integral flow controller and actuator gear common in Europe. The dynamic terminal unit model contains detailed sub-modules for the flow controller, variable-speed actuator, damper linkages with hysteresis, damper, fan and velocity sensor. The sub-modules are assembled on a readily available simulation platform. Using them, accurate validated results have been obtained, showing that instability can occur. The modules will be useful to simulators wishing to model real VAV systems.

Performance lines and energy signatures: Analysis with reference to the CIBSE Building Energy Code

With the increasing use of building energy management systems (BEMS) and serially interfacable utility meters, performance lines and energy signatures can be very useful management tools. This paper proposes models of intermittent heating, taken from the CIBSE Building Energy Code, boiler efficiency and compensator control to give a better understanding of energy signatures, the heating plant and its control. Using these models the seasonal efficiency of the boiler is determined as 57%, that for the compensator as 70%, and the intermittent heating saving 17% for an example two-storey open-plan office building.

The Urban Heat Island in Manchester 1996–2011

The urban heat island intensity (difference between a semi-rural and urban dry bulb air temperature, urban heat island intensity) has been analysed for Manchester using data from 1996 to 2011. The semi-rural sites were airfields and the urban site was 2 km from the centre of Manchester. Although the urban site was not as developed as the city centre it showed a significant urban heat island intensity. A stochastic model developed from the data showed that the maximum mean daily value would be about 6℃ which compared well with more detailed measurements. However, there was a highly significant trend of increasing urban heat island intensity which by the end of the century could add 2.4 K to the predicted climate change increase. An analysis of the urban morphology showed that the urban site had indeed become more urban over 9 years of the study, losing green spaces which mitigate against the urban heat island intensity. Practical application : The results from this paper will allow building and HVAC designers to consider the increase in the urban heat island in their designs when using future weather data. Although the results are for Manchester, similar trends may well apply to other similar-sized cities. Designers should consider the future weather data available, as their buildings will last for a considerable time so they should be as future-proofed as possible.

Quantifying the effects of climate change and risk level on peak load design in buildings

Good building design aims to balance providing a comfortable internal environment for as much of the time as possible within a variety of constraints. An important factor is the expected weather, but in a changing climate this poses additional challenges to engineers and architects. This paper examines the effects of increased external temperature on the size of the central air conditioning and heating plant for an example building. It is found that for each 1°C rise in external temperatures, the peak cooling load increases approximately by 10%, the chiller power by 14% and fan power for distribution by 30-50%. These are relatively large increases in power needed to counteract rising external temperature and the paper considers the choice of risk level for sizing building plant. From HadRM3 data, the future frequency distribution of higher external temperatures is examined to evaluate the effects on plant size of designing to a fixed percentile of risk. Projected changes in absolute humidity are also discussed. Practical applications: Climate change is an important topic for building services engineers, resulting in the UK in the new, performance-based Building Regulations Part L. New, future weather data will also become available with different climate change scenarios. This paper examines the implications of both climate change and the risk level on the peak load for natural ventilation or air conditioning and heating that is used in the design of systems.

The exponential limit to the cooling of buildings by natural ventilation

In manual heat gain and heat loss calculations the standard linear ventilation and infiltration heat loss formula (/)NV(tai tao), (with a suitable factor to relate to comfort temperature), is used. In the 1986 CIBSE Guide Section A8, Summertime temperatures in buildings, a limiting ventilation heat loss formula is used as the air change rate, N, increases, but, as with older guides, there is no reference or explanation of its derivation,1 although the 1970 Guide offers some explanation. This limiting equation is not used in the 1999 Guide A, Environmental design which is unfortunate. This paper analyses the ventilation heat loss based on a log mean temperature difference heat transfer approach which also shows a limiting heat loss effect like the A8 equation. It is also suggested that an admittance value should be used instead of a constant heat transfer coefficient which gives greater insight into the heat transfer process. Significant reductions in the heat transfer process are found at relatively low air change rates using the more correct formulae, which could have implications for summer natural ventilation, during both day and night.

Influence of display cabinet cooling on performance of supermarket buildings

Energy demand attributable to the operation of supermarkets is thought to be responsible for 1% of UK greenhouse gas emissions. Current building regulations in the UK require the “building related” energy use of new commercial buildings to comply with particular requirements. Supermarket buildings are therefore modelled in considerable detail, according to these protocols to establish their predicted energy demand. Lighting, occupancy, and small electrical energy impacts are included in this modelling. However, a large gap is found between the design outputs of this modelling and the energy performance of the store in operation. One reason for this is that thermal interactions at the refrigeration cabinets are not included in this modelling, as refrigeration is classified as “process energy” rather than “building related.” This paper explores the comparative energy demands of supermarket retail floors simulated both with and without the cooling effect of refrigeration cabinets included in the simulation. The retail floor of a recently built supermarket is modelled using EnergyPlus. Practical applications : It has been shown that the energy demand of the retail floor of a new store could be reduced by 25% by improvement of the envelope, by halving ventilation rates and doubling insulation levels. This has been shown by simulation of the building energy flows with refrigeration cabinets included in the modelling (whereas these are currently excluded as process energy). Changes in modelling protocols, and regulations, to encompass refrigeration energy transfers, could reduce the national load, due to supermarkets, by at least 140 MW in 5 years. Energy costs to the retailer would be reduced by 20%. Additionally, the simulation has shown the contribution of rooflights to the reduction of energy demand to be lower than previously predicted, saving only around 1/3 of design expectations.

Urban heat island analysis of Greater Manchester, UK using sky view factor analysis

The sky view factor has been used as an indicator of the amount of sky that can be seen from the ground in an urban area. It was also found to be correlated to the formation of urban heat island effect. Sky view factors can be calculated by analysing photographs taken with a camera with a fisheye lens. However, calculations of sky view factor can vary; therefore, a detailed and more accurate method was developed in this paper to analyse photos and to calculate sky view factors. This method can process the now available higher resolution black and white JPEG (the commonly used digital photo standard created by the Joint Photographic Experts Group) photos and can give more accurate sky view factor values than the previous methods. Sky view factor values were calculated for 59 sites where air temperatures were measured and logged in Manchester, UK. Urban heat island intensities were calculated and linear relationships between sky view factors and urban heat island intensities were found for both summer and winter. However, the linearity tended to be stronger with sites having sky view factor values smaller than 0.65, i.e. the deeper canyons. Practical application: The new method can be used to calculate sky view factors from photographs taken from a camera with a fisheye lens with the original JPGE format. Compared to the other two methods, this new method can deal with photographs with a higher resolution. The SVF values calculated can then be used with canyon models to estimate the maximum urban heat island effect of a particular building site. The SVFs were found to be useful indicators in Manchester, UK.