Week 9 - Use in practice: issues

Question 1

Describe three principal issues faced by engineers when deploying detailed energy simulation tools in practice.

Answer 1

Managing the application of simulation (who does what, when and where).

Implementation of a performance assessment method whereby each step in the process is clearly controlled (model definition, calibration, simulation commissioning, results analysis, mapping to design decisions etc.)

Quality assurance of models and the results they produce.

Question 2

In relation to integrated building performance simulation, identify three progressively detailed input levels and the performance assessments then made possible.

Answer 2

Cumulative model description: ‘Early’, ‘Intermediate’ and ‘Detailed’:

Early

1. pre-existing database: implied performance indicators (e.g. material hygrothermal and embodied energy data etc)
2. geometry: visualisation, photomontage, shading, insolation
3. constructional attribution: embodied energy, material quantities, time constants
4. operational attribution: casual gains, electricity demands
5. boundary conditions thermal: photo-realistic imaging, illuminance distribution, no-systems thermal and visual comfort levels

Intermediate

1. special material: selectricity generation (photovoltaics), daylight levels (switchable glazings)
2. control system: daylight utilisation, energy performance, system response
3. flow network: natural/mechanical ventilation, heat recovery
4. HVAC network: psychrometric analysis, component sizing

Detailed:

1. CFD domain: indoor air quality
2. electrical network: renewable energy integration, load control
3. enhanced resolution: thermal bridging
4. moisture network: local condensation, mould growth and health.

Question 3

In relation to energy systems simulation, select five principal program input parameters, state the nature of a related uncertainty and suggest what action might be taken to reduce this uncertainty.

Answer 3

1. Climate: A stochastic system that is inherently uncertain. Micro-climate phenomena - e.g. wind hollows can have significant impact.
2. Lighting: Clouds and pollution, will impact on the sky luminance distribution.
3. Glazing: The thermo-optical properties of glazing may exhibit a significant variation both within a given sample (e.g. from centre to edge) and between samples (e.g. uncertainty in convective heat exchange, particularly with solar shading devices).
4. Form and fabric: The translation from design intent to on-site realisation gives rise to many uncertainties in relation to final dimensions, construction composition and tightness. Each of these factors can impact significantly on the final performance of the design.

Ventilation: The quantification of a building’s leakage distribution is an inherently uncertain task and there exists scant guidance on the likely ranges to be found in practice. Likewise, the determination of surface pressure distribution is dependent on the ameliorative effect of local wind shelter phenomena that are the subject of considerable uncertainties. An otherwise sophisticated program may well provide results that are inaccurate and inapplicable. A sensitivity analysis, giving the variation of the results when input data are changed, is usually required.

5. Occupant interactions: The physiological and psychological processes that give rise to particular occupant responses to their environment are not well understood and few models exists for use in predicting how people interact with ventilation, lighting and heating/cooling systems. The levels of heat and moisture production can vary significantly, both between individuals and as a function of the context.

Question 4

Describe the steps involved in undertaking a performance assessment using an integrated energy simulation program. For each step give an example of the required action and the related knowledge.

Answer 4

1. Establish a computer representation corresponding to a base case design.
2. Calibrate this model by compare predictions to some reference case using reliable techniques (e.g. inter-model comparison).
3. Locate representative boundary conditions (e.g. of temperature, wind and solar irradiance) of appropriate severity (e.g. typical or extreme).
4. Undertake integrated simulations (e.g. covering energy, mass and momentum balance) using suitable programs.
5. Express multi-variate performance (e.g. peak load, energy demand, environmental emissions) in terms of suitable criteria.
6. Identify problem areas (e.g. overheating) as a function of criteria acceptability.
7. Analyse simulation results (e.g. examine flow-path magnitudes) to identify cause of problems (e.g. excessive solar gain).
8. Identify solutions (e.g. change control system) by associating problem causes with appropriate design options.
9. For each solution, establish a reference model
10. Iterate from step 4 until the overall performance is satisfactory (e.g. thermal comfort is attained for acceptable energy consumption).

Question 5

Identify five performance entities that might be displayed in an ‘Integrated Performance View’ and describe how together they might be used to refine the overall performance of a design.

Answer 5

1. fuel and power consumption;
2. environmental emissions;
3. thermal comfort;
4. visual comfort; and
5. installed plant capacity.

Taken together, these performance entities allow a balance to be struck between comfort requirements, energy use and environmental impact.