Kevin J. Lomas

Sensitivity analysis techniques for building thermal simulation programs

Three sensitivity analysis techniques, differential sensitivity analysis (DSA), Monte Carlo analysis (MCA), and stochastic sensitivity analysis (SSA), are appraised using three detailed finite difference simulation programs, ESP, HTB2, and SERI-RES. The applicability of the methods to simpler programs is considered. Domestic-scale, passive solar buildings are used as vehichles for testing the methods. The sensitivities, in both hourly and daily average predictions, due to the uncertainties in over 70 input parameters, are compared for DSA and MCA. The sensitivities of the predictions to changes in a reduced set of inputs are compared for DSA and SSA. It was found that in this case SSA had drawbacks. It is suggested that, at present, DSA is used to obtain the sensitivities of predictions to individual input parameter uncertainties and that MCA is used to obtain the total sensitivities in the predictions. With further work, it may be possible to extract individual sensitivities from MCA, which would make this the preferred technique.

Empirical validation of building energy simulation programs

Abstract The largest-ever exercise to validate dynamic thermal simulation programs (DSPs) of buildings has recently been completed. It involved 25 program/user combinations from Europe, the USA and Australia, and included both commercial and public domain programs. Predictions were produced for three single-zone test rooms in the UK. These had either a single-glazed or double-glazed south-facing window, or no window at all. In one 10-day period the rooms were intermittently heated and in another 10-day period they were unheated. The predictions of heating energy demands and air temperatures were compared. The observed interprogram variability was highly likely to be due to inherent differences between the DSPs, rather than the way they were used. Predictions of the difference in performance of two rooms were no more consistent than predictions of the absolute performance of a single room. By comparing the predictions with the measurements and taking due account of experimental uncertainty, the DSPs that are likely to contain significant internal errors are distinguished from those which, in these tests, performed much better. The likely sources of internal error are discussed. It is recommended that empirical validation exercises should consist of an initial blind phase in which program users are unaware of the actual measured performance of the building, and then an open phase in which the measurements are made available. The work has produced five empirical validation benchmarks, which have significant practical benefits for program users, vendors and potential purchasers. There is considerable scope for improving the predictive ability of DSPs and so suggestions for further work are made.

GIS-based decision support for solar energy planning in Urban environments

This paper describes the development of a solar energy planning system, consisting of a methodology and decision support software for planners and energy advisers. Intended primarily to predict and realise the potential of solar energy on an urban scale, the system will support decisions in relation to the key solar technologies: solar water heating, photovoltaics and passive solar gain. The prototype discussed here relates to the first of these. Based on a methodology for predicting the solar energy potential of domestic housing stock, it is implemented as a relational database application linked to a customised geographical information system (GIS). The methodology takes into account baseline energy consumption and projected energy saving benefits. To support this, the system incorporates a domestic energy model and addresses the major problem of data collection in two ways. Firstly, it provides a comprehensive set of default values derived from a new dwelling classification scheme that builds on previous research. Secondly, novel GIS tools enable key data to be extracted from digital urban maps in different operational modes. The paper concludes with a discussion of possible planning scenarios to illustrate how the system may be deployed at various levels of granularity to assist targeting of individual properties or city neighbourhoods, or for whole-city projections.

Carbon reduction in existing buildings: a transdisciplinary approach

Closed access. This editorial was published in the journal, Building Research and Information [© Taylor & Francis (Routledge) and the definitive version is available at: http://dx.doi.org/10.1080/09613210903350937

Predicting the urban solar fraction: a methodology for energy advisers and planners based on GIS

This paper describes the development of the underlying methodology of a solar energy planning (SEP) system for energy advisers and policy makers. The methodology predicts the baseline energy consumption of domestic properties and determines the potential for reducing this using the three key solar technologies of passive solar design, solar water heating and photovoltaic (PV) systems. A new dwelling classification system has been developed to address the major problem of data collection for city-wide domestic energy modelling. The system permits baseline energy demands to be estimated using assumed values or more accurately calculated using dwelling survey data. The methodology integrates existing models with new approaches to both identify suitable dwellings for installing solar water heating and PV systems and to quantify the potential energy savings and reductions in carbon dioxide emissions. Guidance on improving estate layouts to enhance passive solar conditions is also given. Results can be presented using a geographical information system (GIS). The paper concludes with a discussion of possible planning scenarios to illustrate how the methodology may enable planners to consider the urban-scale application of solar energy with greatly increased confidence.

Solar radiation transport through slat-type blinds: A new model and its application for thermal simulation of buildings

Although external and internal slat-type blinds (such as venetian blinds) are used frequently to reduce the solar load on windows, there are no detailed calculation models for such shading devices within detailed thermal simulation models (DSMs). A new calculation model (GLSIM-BLIND) has been written to either simulate blind systems accurately at each simulation time-step, or to simulate blinds approximately using simplified daily effective shading factors for each radiation component. In addition, the program calculates annual or monthly effective total solar transmittance values, or effective shading factors, which can be used in thermal calculations or in simple dynamic programs. The model can be used for a wide range of different blind systems and blind control strategies. It is suitable for optimising blind arrangements during the design phase of a building. This article shows the theoretical basis of the new calculation technique and demonstrates its application in thermal building simulations.

Putting solar energy on the urban map: a new GIS-based approach for dwellings

This paper describes some aspects of prototype software designed to assist local authority planners and energy advisers in their efforts to increase the uptake of solar hot water systems in cities. To estimate the potential yield from installed systems, the Solar Energy Planning system implements an adaptation of the method for calculating the thermal performance of solar heating systems for domestic hot water in BS5918. A much-enhanced version of the BREDEM-8 domestic energy model provides the basis for predicting the delivered energy savings. Reductions in CO2 emissions can also be quantified. A trial of the prototype in an urban area of Leicester, UK, is illustrated and some encouraging results are reported.

Design strategy for low-energy ventilation and cooling within an urban heat island

Natural ventilation is a proven strategy for maintaining thermal comfort in non-domestic buildings in the UK. The energy consumption and thus the carbon dioxide emissions that contribute to global warming are lower than in conventional air-conditioned buildings. However, the ambient temperatures in the UK have risen over the last decade and new climatic data for use in the design of naturally ventilated buildings has been published. Using these data and dynamic thermal modelling, it is shown that passive stack ventilation alone was unlikely to maintain summertime comfort in a proposed University College London building within an urban heat island. The stack ventilation strategy was evolved by the introduction of passive downdraught cooling. This low-energy technique enables cooled air to be distributed throughout the building without mechanical assistance. The underlying principles of the technique were explored using physical models and the anticipated performance predicted using thermal modelling. The architectural integration is illustrated and the control strategy described. The resulting building is believed to be the first large-scale application of the passive downdraught cooling technique; construction began in late 2003.

The radiation transfer through coated and tinted glazing

The incidence angle dependent transmittance and absorptance of special glazing containing coated or tinted glass are conventionally modelled using a simple application of the Fresnel equations, treating the glazing as if it were clear glass. This simplified approach leads to only a rough approximation of the true transmission and can result in an inaccurate assessment of the solar energy gains in highly glazed spaces such as atria and in commercial buildings where special glazing is popular. An improved calculation technique has been developed which is based on the fundamental optical behaviour of radiation in thin films and in substrates. It considers the physical effects of coherent and incoherent layers, interference, and absorption. The main feature of the model is its applicability to any combination of coating and glass, with no limitation on the number or sequence of the layers. This paper shows the theoretical basis of the calculation technique and demonstrates its ability to produce wavelength and incidence angle dependent properties of special glazing. The validity of the predictions is illustrated by comparison with measurements.

The U.K. applicability study: an evaluation of thermal simulation programs for passive solar house design

Abstract The predictions of three detailed thermal simulation programs, ESP, HTB2 and SERIRES, are compared for a range of passive solar dwellings subjected to U.K. weather conditions. From the variations in predictions, the Simulation Resolution (SR) of the programs was estimated. SR values are given for predictions of annual heating energy demands and internal air temperatures. The influence of internal convective heat transfer and glazing algorithms on inter-program variability is shown. The wider utility of SR for interpreting the significance of program predictions is discussed.