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Section 1 Evaluating Design Solutions

Section 2 Evaluating Detailed Design



 


 

Description:  The purpose of this unit is to enable you to evaluate design solutions which can satisfy client needs within the given constraints which relate to Services.

Author: Gates MacBain Associates


Section 1 Evaluating Design Solutions


Aims and Objectives


At the end of this section you should be able to:
  • Evaluate detailed designs.

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 

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.  


Sensitivity Analysis 

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.    


Value Engineering 

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.  


Evaluation Tools 

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.


Websites


Publications

  • Churcher, D. (2008) Design Activities and Drawing Definitions (BG 6/2009), 2nd edition. BSRIA
  • Longmaid, J (2004). A Practical Guide to system selection (BG 9/2004). BSRIA 
  • Pennycook, K. (2007). A Quality Control Framework (BG4/2007), 2nd edition. BSRIA
  • CIBSE (2007). Environmental Design – CIBSE Design Guide A. CIBSE
  • CIBSE (2006). Tests for Software Accreditation and Verification. CIBSE TM33
  • CIBSE (1998). Building Energy and Environmental Modelling. CIBSE AM11


Self-Assessment Task

  • You are going to carryout an evaluation of building services design. Produce a list of documents and tools you would require to do so.




Section 2 Evaluating Detailed Design


Aims and Objectives

At the end of this section you should be able to:
  • Evaluate detailed designs for their ability to satisfy client’s needs within the identified constraints.


In this section, we will explore some examples of how detailed design and evaluation is carried out in building services engineering design.  


Evaluation of HVAC 

The calculation tools should be used to assess heat losses. The tools can be CIBSE Simple Model, Reference Model or the Basic Model to obtain a quantitative comparison between the three models. However, to evaluate the reliability of manual methods, computer based simulation tools, such as thermal models and Computer Fluid Dynamics (CFD), could be used to assess building heat losses based on hourly external data and corresponding building performance.   

The simulation process can be further refined by carrying out sensitivity analysis by changing parameters. For example, we can vary the ventilation rates and examine space temperature variation. Similarly the simulation can be used to evaluate lightweight and heavyweight buildings, naturally and mechanically ventilated buildings, etc.  


Ventilation Requirements 

Ventilation provision can be evaluated to ensure that it is adequate to meet occupancy and other ventilation requirements such as indoor air quality. For this purpose, the engineer could use calculation tools to assess ventilation and infiltration rates which would also inform heating load calculations. The engineer should also estimate hot water demand.To support/verify the manual calculations, the engineer could use CFD and physical models.  


Pre-heat Requirements 

The engineer should use dynamic tools to analyse the thermal inertia of the building during cold spells and when in intermittent operation. Computer based simulation tools, such as thermal models could be used to analyse building thermal response and assess pre-heat requirements, based on hourly external data.   


Controls 

For appropriate design of controls, the engineer should use dynamic simulation tools in order to analyse load diversity and pre-heat requirements based on external conditions, building fabric and application. Sensitivity analysis can evaluate the effect of varying the fabric or window characteristics on pre-heat period during long periods of cold weather. The load diversity analysis could identify integrated solutions for heating for example covering base load, peak load and contingency load with a combination of Low and Zero Carbon (LZC) technologies and boiler units.


Stand-by Capacity 

The engineer should assess standby capacity by carefully considering risk assessment, risk of oversizing etc. as well as zoning, circuit design and various pumping choices.  


Heat Sources 

The engineer should select heat sources and heating plants as well as tools for sizing them. Dynamic simulation tools could be used for plant sizing based on hourly building thermal performance. Such tools could also be used to check coordination of systems and avoid conflict of services e.g. heating and cooling at the same time, open windows for ventilation while heating is in operation etc.  


Evaluation of Lighting 

The calculation tools should be used to assess the daylight availability and distribution based on building form and orientation, location, time of year. However, to evaluate the reliability of manual methods, computer based simulation tools to do dynamic analysis such as by changing shading options and window orientation, the effect on space daylight distribution can be explored. Similarly, control settings can be changed to assess its effect on lighting diversity.   


Positioning, Interaction and Controls 

Calculation tools can be used to assess number of luminaires required and their positioning. Similarly, positioning of controls should be evaluated in terms of energy efficiency. Overall performance of lighting as a result of controls can be used to adjust daylighting/electric lighting use. Conflict and interaction with other services has to be evaluated. For example, solar gains and internal heat gains for heating, cooling and ventilation services design, electric load for electrical services design, etc.   


Energy Sources  

Detailed analysis on sizing the mains, electricity supply from grid and/or from renewables has to be carried out in the light of  voltage distribution, power generation, earthing, etc.   


Design Review 

The overall system design should be reviewed against targets and client requirements and the design intent such as achieving required performance, energy efficiency at part load and performance of controls. The aim is to confirm that the energy targets and the internal thermal comfort requirements are met at part load as well as to ensure that the controls are able to respond effectively to the changes in the internal environment without effecting energy efficiency. 

Dynamic simulation models can be used for this purpose. For example, we can vary the system efficiency and examine energy use; or examine heating load variation for variable solar gain. We can also examine energy use for variable occupancy and solar gains. Integrated solutions will require the fine tuning of controls to make sure that variable load is covered without compromising the systems’ efficiency.   


Evaluating Final Design   

This involves checking 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   

Evaluation will confirm that the final solution maps with the original design intent. The tasks to be performed could include value engineering and checking compliance with the building regulations.   

Simulation results from previous design tasks should be aggregated to check overall building performance and compliance with the building regulations, based on hourly external data. This exercise as well value engineering might highlight some problem areas requiring certain changes. These changes also will be evaluated.   The resources listed contain a more detailed explanation of evaluation techniques and tools.


Websites


Publications

  • Churcher, D. (2008) Design Activities and Drawing Definitions (BG 6/2009), 2nd edition. BSRIA
  • Longmaid, J (2004). A Practical Guide to system selection (BG 9/2004). BSRIA 
  • Pennycook, K. (2007). A Quality Control Framework (BG4/2007), 2nd edition. BSRIA
  • CIBSE (2007). Environmental Design – CIBSE Design Guide A. CIBSE
  • CIBSE (2006). Tests for Software Accreditation and Verification. CIBSE TM33
  • CIBSE (1998). Building Energy and Environmental Modelling. CIBSE AM11


Self-Assessment Task

  • In continuation to the task set in the previous section, select a service and produce a checklist of performance targets.







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