Paul Strachan

Practical application of uncertainty analysis

Uncertainty analysis, based on Differential Sensitivity Analysis and Monte Carlo Analysis, has been used in several research projects in order to estimate reliability of results, especially in empirical validation-based projects where both measured and predicted uncertainty bands need to be evaluated. However, such analyses have been time-consuming, involving either repetitive manual changing of the input parameters followed by a simulation run, or involving the writing of specific programs to automate the process. Their use has, in consequence, been restricted. This paper reviews the sources of uncertainty in the predictions from thermal simulation programs. It then describes how uncertainty analysis has been incorporated into the thermal simulation program ESP-r. An example of its application is given.

Simulation-assisted control in building energy management systems

Technological advances in real-time data collection, data transfer and ever-increasing computational power are bringing simulation-assisted control and on-line fault detection and diagnosis (FDD) closer to reality than was imagined when building energy management systems (BEMSs) were introduced in the 1970s. This paper describes the development and testing of a prototype simulation-assisted controller, in which a detailed simulation program is embedded in real-time control decision making. Results from an experiment in a full-scale environmental test facility demonstrate the feasibility of predictive control using a physically-based thermal simulation program.

Building-integrated photovoltaic and thermal applications in a subtropical hotel building

Effective cooling of a PV panel is able to increase the electricity output of the solar cells. This paper describes a comparative study of three different options in applying large-scale building-integrated PV technology in a coastal city at the South China Sea. The computational model was based on a 260 m2 mono-crystalline silicon PV wall on a 30-storey hotel building. The numerical analysis was via the ESP-r building energy simulation software. The results showed that the different design options exhibit short-term electrical performance differences, but have similar long-term electricity yields. However, some design options perform much better in reducing the air-conditioning loads of the building.

Comparison of the simplified methods of the ISO 13790 standard and detailed modelling programs in a regulatory context

The CEN standards that support the European Energy Performance of Buildings Directive requirement for calculation of the energy consumption of buildings allow various methods to be used for the same calculation. The impact of using the different methods within the updated ISO 13790 standard for space heating and cooling energy calculations was examined with a parametric analysis of a common building specification. The impact was assessed by considering the energy band, which would be assigned for the building based on the calculation results. The standard describes three different methods that can be used for the calculations: a monthly quasi-steady state method, a simplified hourly method and detailed simulation. For most cases studied, differences in the building rating given by the various methods were a maximum of one band. More significant differences were noticed in some cases. Parameter values in the monthly method were determined, which would lead to improved matching.

Whole model empirical validation on a full-scale building

This paper describes an empirical validation study undertaken on two identical full-size buildings within the scope of the IEA ECB Annex 58 project. Details of the experimental configuration and monitoring are included, together with results from measurements and from predictions made by 21 modelling teams using commercial and research simulation programmes. The two-month, side-by-side experiment was undertaken on buildings with high levels of thermal mass and in a period with high solar gains. The detailed specification and associated measurement data provide a useful empirical validation dataset for programme testing. Results from the modelling demonstrate good agreement between measured data and predictions for a number of programmes, in both absolute predictions of temperatures and heat inputs as well as dynamic response. On the other hand, a significant number of user input errors resulted in poor agreement for other programmes, especially in the blind validation phase of the modelling methodology.

Photovoltaic-integrated building facades

Photovoltaic (PV) cells, when integrated within a building facade, offer the possibility of generating electric power and heat for local use or export. This paper reports on a project to investigate the practical operational efficiencies that might be delivered from such facades. The results from laboratory experiments and computer simulations are presented: the former were used to develop an empirical relationship between cell temperature and power output; the latter were undertaken to assess operational efficiencies under a range of climate conditions representative of the UK.

Experience of using building simulation within the design process of an architectural practice

The tracer gas method is one of the most widely used methods for measuring flow rates for building air infiltration and ventilation. The accuracy of this method depends vitally on the spatial uniformity of the tracer/air mixing. However, information on this critical problem has been scarce, largely due to the practical difficulty in experimentally obtaining data. In the last decade a new tool for building research has emerged, namely computational fluid dynamics or CFD. A study of tracer/air mixing has been carried out using a time dependent CFD method, supported by conceptual/dimensional analysis. In this study, 12 cases of tracer/air mixing in simulated tracer decay tests were computed. Each case had a different zonal volume or other boundary or initial conditions. By comparing these results, it was found that there were many factors affecting tracer/air mixing and, contrary to a previous report, there does not exist a universal critical value of air change rate below which satisfactory mixing is guaranteed, although lower air change rates are generally beneficial to mixing. In addition, it has been demonstrated that smaller building zones and higher inlet air flow velocities have positive effects on tracer/air mixing while the initial tracer concentration level has no effect. Finally a statistical parameter of concentration spread coefficient for assessing tracer mixing has been introduced.

An empirical validation of modelling solar gains through a glazing unit using building energy simulation programs

Empirical validation of building energy simulation tools is an important component in assessing the reliability of the simulation software. An experiment performed in conjunction with the International Energy Agencys Task 34/Annex 43 was used to assess the performance of four building energy simulation codes used to model an outdoor test cell with a glazing unit. The experiment was run for a 20-day period during October 2004, and experimental cooling powers were compared with predictions from (1) EnergyPlus, (2) DOE-2.1E, (3) TRNSYS-TUD, and (4) ESP-r. Detailed code inputs for optical and thermophysical properties as well as the impact of thermal bridges were quantified through experiments and simulations; numerous statistical parameters and sensitivity analyses were implemented to facilitate a thorough comparison of predicted and experimental cooling powers. The mean percentage differences for all four codes were: 1.9% for EnergyPlus, −3.6% for DOE-2.1E, −6.2% for TRNSYS-TUD, and 3.1% for ESP-r. The implications of various modeling procedures as well as a detailed discussion of the results are provided, specifically concerning the sensitivity of the code cooling power predictions to the selection of convective heat transfer coefficients and algorithms.

Trends in office internal gains and the impact on space heating and cooling demands

Internal gains from occupants, equipment and lighting contribute a significant proportion of the heat gains in an office space. Looking at trends in Generation-Y, it appears there are two diverging paths for future ICT demand: one where energy demand is carefully regulated and the other where productivity enhancers such as multiple monitors and media walls causes an explosion of energy demand within the space. These internal gains scenarios were simulated on a variety of different building archetypes to test their influence on the space heating and cooling demand. It was demonstrated that in offices with a high quality facade, internal gains are the dominant factor. As a case study, it was shown that natural ventilation is only possible when the ICT demand is carefully regulated.

Data mining analysis of building simulation performance data

Detailed simulation studies of building performance can result in large data sets, particularly where statistical information on annual energy or environmental performance is required. Key performance indicators such as the number of hours above a certain temperature can easily be extracted. However, it is difficult for users to explore such datasets and understand the underlying reasons why a building performs in a certain way. This is especially true in climate responsive buildings which involve complex interactions of ventilation, solar gains, internal gains and thermal mass, for example. Data mining techniques have traditionally been employed in the financial and marketing sectors to elicit patterns within the data. This paper describes how the different data mining techniques may be employed in helping to analyse building performance data. Clustering is identified as a particular useful analysis technique and its potential is illustrated through a number of case studies.