Herbert Eppel

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.

Application of passive downdraught evaporative cooling (PDEC) to non-domestic buildings

The applicability of Passive Downdraught Evaporative Cooling (PDEC) for reducing energy consumption in hot dry climates is reviewed. A new EC Joule project explaining the application of PDEC in non-domestic buildings is described. The building performance assessment methodology which employs dynamic thermal simulation programs for thermal analysis, and computational fluid dynamics (CFD) codes for airflow modelling is discussed. The role which wind tunnel tests and field measurements have in producing improved models is noted. Preliminary results from CFD benchmark trials are presented.

Passive Downdraught Evaporative Cooling I. Concept and Precedents

This is the first of a series of four papers that describe a 3-year EU-funded research project into the application of passive downdraught evaporative cooling to non- domestic buildings. In this paper various evaporative cooling techniques are reviewed. By spraying fine drop lets of water at the top of atria, a downdraught of air cooled by evaporation can be produced. Such direct eva porative cooling using an evaporation tower appears to be a suitable approach for partly displacing the need for air-conditioning in hot, dry climates. It can satisfy fresh air requirements and reduce or eliminate demand for mechanical cooling. Examples of this cooling technique in Southern Europe and the Middle East have already demonstrated its operation and potential energy sav ings. However, limitations, primarily due to control of the system, have been identified. This introductory paper presents the theoretical basis of evaporative cooling, reviews some historical precedents, and discusses their relative strengths and weaknesses. Three further papers in this series will disseminate the main findings of the project.

Passive Down-Draught Evaporative Cooling: Thermal Modelling of an Office Building

Two simulation-based methods of predicting the dynamic thermal performance of non-domestic buildings in hot dry climates, conditioned by Passive Downdraught Evaporative Cooling (PDEC), have been evaluated. In the PDEC system analysed, microscopic droplets of water were evaporated in ambient air and the resulting cool dense air delivered passively, through controlled openings, to occupied areas. The first method predicts the annual hours of PDEC operation, the water usage and the frequency of occurrence of different internal temperatures. The second method, which requires a thermal model with an integrated airflow network, provides insight into the airflow control strategies. Both methods demonstrated that an office building, in Seville, would need support from a mechanical cooling system to remain comfortable. However, the predicted energy use and carbon dioxide production was just 25% of that for a conventional airconditioned building.

Passive Downdraught Evaporative Cooling

This is the second in a series of four papers that describe a 3-year EU-funded research project into the application of passive downdraught evaporative cooling (PDEC) to non-domestic buildings. The paper describes the use of computational fluid dynamics (CFD) for modelling PDEC. It describes the modelling techniques used and application to investigate the performance of a hypothetical office building in Seville. From the CFD analysis it is concluded that: (i) CFD is invaluable for analysing the ventilation performance of PDEC buildings, (ii) wind buffering and appropriate aperture sizes are essential to maintain well-regulated flows, and (iii) a top-down ventilation strategy performs equally well in upflowing mode, e.g. during night venting.

Passive Downdraught Evaporative Cooling II. Airflow Modelling

This is the second in a series of four papers that describe a 3-year EU-funded research project into the application of passive downdraught evaporative cooling (PDEC) to non-domestic buildings. The paper describes the use of computational fluid dynamics (CFD) for modelling PDEC. It describes the modelling techniques used and applica tion to investigate the performance of a hypothetical office building in Seville. From the CFD analysis it is con cluded that: (i) CFD is invaluable for analysing the venti lation performance of PDEC buildings, (ii) wind buffering and appropriate aperture sizes are essential to maintain well-regulated flows, and (iii) a top-down ventilation strategy performs equally well in upflowing mode, e.g. during night venting.