January 1, 1999
By Jim Sawers, P.Eng., Reid Crowther & Partners
The following is an adapted version of a paper presented at the Green Buildings Challenge conference in Vancouver in October.The very nature of engineering, architecture and construction is such that ...
The following is an adapted version of a paper presented at the Green Buildings Challenge conference in Vancouver in October.
The very nature of engineering, architecture and construction is such that every problem has more than one solution. As a result the evaluation of alternative solutions has long been an important part of the industry. The nature of building technology design and decision making was well put by Ove Arup, founder of the consulting engineering firm of the same name. He said, “Engineering is not a science. Science studies particular events to find general laws. Engineering design makes use of these laws to solve particular problems. In this it is more closely related to art or craft; as in art, its problems are under-defined, there are many solutions, good, bad, or indifferent. The art is, by a synthesis of ends and means, to arrive at a good solution. This is a creative activity, involving imagination, intuition and deliberate choice.”
In moving towards environmental building design, however, the problem we face is that traditional models cannot effectively evaluate the complex and often ill-defined decisions inherent in evaluating green technologies.
The use of green building technologies has, in the past, been limited by the inflexibility of the traditional evaluation methods. These tools have been primarily financial models–an alternative is selected purely for its economic benefit. However, the nature of green building technologies is such that benefits are often subjective rather than objective or purely financial. It is important, therefore, that we should develop an evaluation tool that effectively deals with the “soft” benefits of green building technologies and approaches if they are ever to be more widely implemented and given the opportunity to prove themselves.
The need for an improved evaluation methodology is also evident from the increased reporting of dissatisfied green building owners and occupants. In an article in the U.S. publication HPAC magazine of February 1998, J. H. Heerwagen and J. A. Wise noted that, in a green manufacturing plant and office, only 40 per cent of all workers perceived their new green building as “healthier” than the old building from which they had moved.
The green building technology evaluation model we are proposing draws on techniques used in information technology (IT) project evaluation and in the field of value management. The most significant influences we have drawn from these sources are:
— the use of a value hierarchy to establish and weigh decision criteria
— an expanded definition of project “costs” and “benefits”
— the use of a decision matrix and sensitivity analysis.
Green Building Technologies Model
The stages of green building technology evaluation are:
Stage 1: Key Objectives. Each participating stakeholder presents their perception of what the project needs to achieve. The deliverable is a list of agreed project objectives.
Stage 2: Sorting Objectives. The identified objectives are structured into a value hierarchy or tree. The top of the tree is the overriding raison d’tre of the entire project. This is then progressively broken down into sub-objectives. In this exercise the expanded definition of costs and benefits must be emphasized.
Stage 3: Assign Importance Weights. Importance weights are assessed for each branch of the value tree and the final weights are calculated by “multiplying through the tree.” The weights should also be checked for consistency.
Stage 4: Evaluation. Each option is assessed and a decision matrix used to obtain an aggregate rating for each option.
Stage 5: Sensitivity Analysis. The sensitivity of the evaluation to changes in the chosen importance weights and option scores is tested.
Stage 6: Cost/Value Ratio. The estimated capital cost for each proposal is then compared to the aggregate rating and the decision is made as to which option represents the greatest value for money.
In the design of a green building, the stakeholders might arrive at the value hierarchy illustrated in Figure 1.
In turn, the criteria weightings shown might be developed. These criteria may then, for example, be used to compare using a traditional overhead mixing air distribution system with using a displacement ventilation system. The decision matrix of Figure 2 might then result.
In this example, the six identified rating criteria are interpreted as follows.
Strategic Alignment. The extent to which the alternative approach or technology will support or enhance the strategic goals or values of the organization.
Competitive Advantage. The extent to which the alternative will give the organization an advantage over its competition.
Technological Risk. The extent to which the alternative technology is proven and reliable.
Sustainability. The extent to which the alternative and the benefits it offers can be sustained over the life of the project. This criteria addresses issues such as flexibility, maintainability and ease of operation.
Energy impact. The extent to which the alternative will reduce energy consumption.
Environmental impact. The extent to which the alternative reduces the impact on the external environment and/or improves the indoor environment.
The criteria for any particular project will, of course, vary with the nature of the project and the needs of its sponsors and users. The value tree could be extended and modified to suit particular circumstances.
The scoring of design alternatives against the rating criteria is a key step and perhaps the least well defined in the literature. In some cases, quantitative decisions can be made; in others only qualitative scoring is possible. In all cases, a reference point is required to normalize scoring.
The Green Buildings Challenge model uses a reference point (score of 0) for the normal industry practice, say ASHRAE Standard 90.1. A score of 5 is set as the “best” condition. Thus a scoring scale for energy impact might be as follows.
In the case of a rating criteria such as environmental impact, measurement is not quite so direct. Using elements of the LEED system, a scoring scale for environmental impact might be as follows (again the reference point (score of 0) is normal industry practice and 5 is best condition).
The proposed evaluation model was developed as a result of the inability of traditional evaluation techniques to deal effectively with the “soft” benefits of green building technologies. Using it intelligently will help practitioners to encourage clients to adopt green building technologies in their buildings. Without the use of these technologies, local, national and international energy and environmental goals simply will not be met. CCE
Jim Sawers, P.Eng. is Vice-President Building Engineering, Reid Crowther & Partners Ltd., Calgary.