This is in continuation to the unit: Design Strategies; Design Parameters; and Optimum Solutions in which we looked into identifying the client needs, relevant legislation, standards and constraints as well as establishing reliable design parameters and feasibility studies.
In this unit, we will investigate how detailed design can be evaluated to satisfy client needs.
Design Process and Relevant Stages
Once the client needs are identified, the design team maps these with the regulations, standards and codes of practice to establish design parameters. Concept designs are developed and checked for compliance with health and safety and other pertinent legislation. The design is then evaluated using both manual and simulated tools.
These processes can be mapped with both RIBA Plan of Work 2007 (Stage D & E) as well as with CIBSE Design Compass (Deign Development stage). Following table will show this clearly.
Building Services design stage – Design development
Review system performance and check predicted system performance
Check performance, energy efficiency at part load and performance of controls.
Check that the final design meets the client requirements in terms of quality, performance, reliability and cost as well as required energy targets and compliance with regulations
| || |
RIBA Stage D
Development of concept design to include structural and building services systems
RIBA Stage E
Preparation of technical design(s)
Evaluation is the process of making judgements on the proposed design and make changes and/or improvements where needed. Evaluation has to be objective keeping in mind the overall intent of the design activity. Whole-building approach should be used in evaluation. The individual services should be evaluated on their own as well. Typically different solutions have different strength and weaknesses when an evaluated against the design criteria and target values.
A number of documents are required to carry out an evaluation, some of which are listed below.
- Client needs as detailed in the design brief
- Constraints including site conditions, regulations and standards
- Performance targets in terms of energy efficiency, use of renewable technologies and comfort requirements
- Design parameters and details including
- Architectural, structural or other associated drawings
- Evaluation of previously carried out projects
- Minutes of meetings
- Design assumptions
- Future climate change scenarios
At evaluation stage, sensitivity analysis and value engineering are carried out. These are defined below.
It provides information regarding viability of a system by varying input variables and studying their effects on the system such as changing climate variables and studying their effect on systems’ energy performance.
It is a structured process in which an effort is made to provide design solutions in the most cost-effective way. To do so, every aspect of the design is reviewed in detail against the functions of the building. ‘Value’ is value-for-money which means that the design meets the user requirements without over-specification and at the lowest possible cost.
Manual calculations can be used for evaluation of design solutions. However, these manual calculation procedures have certain limitations. Values of design parameters are often uncertain or unknown at the time calculations are made due to:
- Lack of detailed knowledge regarding building design/operation
- Uncertainty regarding thermal/optical properties of materials, building quality, etc.
- Unpredictability of the future climate
Hence, besides manual calculations, a number of computer-based tools should be used for evaluation of the design. These tools improve the exploratory power to vary the design parameters and hence evaluate the effect on the systems and hence fall into the category of dynamic tools.
The uncertainties can also e handled by using appropriate design margins or allowances.
Simulation or Modelling
Simulation is the act of imitating a situation or a process such as a flight simulator can help to train pilots in an environment which imitates and hence is closer to the real-world situations. It involves creating a model for a theoretical and physical process which can then be run on a computer. Different design parameters can be variables as an input. The model then gives a likely output or the effect on the systems’ performance.
It is a proven fact through extensive research that simulation or modeling can be used as a tool to reduce the uncertainties at the design stage. However, any simulation must be used with care and with complete understanding of assumptions and processes.
Simplified Building Energy Model (SBEM)
Buildings must be evaluated to find the lowest energy consumption solution. SBEM is a simulation software developed by BRE to carry out calculations of energy use and CO2 emissions of a building. The tools consider building geometry, construction, use and HVAC and lighting equipment and provide an analysis of building’s energy consumption.
The tool is based upon National Calculation Method (NCM) and makes extensive use of databases to ensure compliance with regulations. It provides consistent and reliable evaluation of energy use in buildings and should not be considered as a design-tool.
SBEM is applicable to buildings other than dwellings.
The engineer should be using assessment methods to evaluate the option selected earlier. The evaluation should be based on results from detailed calculations
The resources listed contain a more detailed explanation of evaluation techniques and tools.