Whole Building Design
August 4, 2008
Designing, constructing, or renovating high-performance buildings requires a whole building approach. This approach differs from the traditional design/build process, as the design team examines the integration of all building components and systems and determines how they best work together to save energy and reduce environmental impact.
The quality of the design team will largely determine the success of a building project. These professionals should have experience incorporating energy efficiency features into their building designs. Once the team is selected, conduct a design charrette to define goals and how they will be met. A commissioning plan will help to verify that design and performance goals are met. Select a cost analysis method to guide the decision process.
PROFESSIONALS SHOULD HAVE GREEN DESIGN EXPERIENCEIdentify members of the entire design team before beginning the design process. All those who can influence the building design and how it is constructed should be represented on the design team, including architects, engineers, building owners and occupants, and specialists in areas such as HVAC/IAQ, materials, and energy use. The size of the team and the aggressiveness of the design goals will determine who should be on this team.
Team members should be truly committed to meeting the project goals. The team members must communicate well with one another. The team members must keep one another up to date on design decisions so that when a decision is made that will affect the performance of another team member’s design area, the team can evaluate the consequences up front and make modifications to the design before it is too late. The whole-building design process depends on strong ongoing communication between the team members.
Clearly state the goals of the building’s design and performance in the contracts placed with the design team members and ensure that all members have a solid understanding of these goals. It may be necessary to revise the standard contract used for building projects to include the project goals and the consequences if the design team does not meet these goals. Verify that the design goals and ultimately the performance goals of the building are being met before providing payment for the design team services throughout the design and construction processes.
CONDUCT A DESIGN CHARRETTEThose who specify and configure the components - architects, designers, consultants, engineers, managers, and contractors - must work together closely throughout the design process. Often, they start by participating in a kind of peer review workshop or “design charrette” early in the process.
A charrette is a workshop for generating and discussing ideas in the planning and design process. Holding a design charrette is a good idea when people need to cut across boundaries and work on a large, collaborative project.
Because participants are encouraged to offer design ideas and solutions to problems that are outside their areas of expertise, charrettes are particularly helpful in complex situations calling for new ways of looking at issues. Design charrettes allow participants to propose and consider many different ideas, address organizational differences, reduce adversity, verify decisions, and expedite the design process. Charrettes help participants design buildings in which each component is considered in light of its effect on all the others and on the building as a whole.
The Charrette Process
The charrette process can take several days, depending on the size and complexity of the project. It requires a room large enough to hold the design team as well as areas for smaller, breakout groups. The team can begin each day with a whole group discussion of issues, goals, findings, and approaches; these help to define subsequent goals and issues for breakout groups to discuss and analyze. Ideally, the breakout groups should contain a cross-section of people in the various disciplines represented in the design team. Breakout groups should regularly join the larger group to present their ideas and approaches; these can then be integrated or adapted into the overall design concept.
The goal is not necessarily to prepare a final design but to explore and understand all the design issues. The information shared and the understanding gained by the participants is the most important product. Trained design charrette facilitators can help in forming teams and small groups, obtaining quick agreement on desired outcomes, and keeping everyone involved in the process.
Recording ideas is essential. The most effective way may be to use on-site graphic recording in a somewhat standard format that can easily be compiled in a report. Examples include “fill-in-the-blanks” flip charts that can be scanned into booklets or files for Internet distribution.
Topics to Address in a Greening Design Charrette
Broad topics covered in the design charrette will include the building’s location and microclimate; orientation and envelope; interior spaces; fenestration, daylighting, and lighting; energy and water needs; HVAC equipment; landscaping and exterior spaces; and monitoring equipment and controls, if applicable. Here are some of the specific things that participants can discuss in the charrette:
• Establishing sustainable, whole building design as a goal from the outset (perhaps with assistance from an energy consultant).
• Siting and orienting the building to maximize southern exposures and to respond to local climate conditions, natural landscape features, and nearby services such as transportation and utilities.
• Obtaining energy performance and lighting analyses. The U.S. Department of Energy (DOE) sponsors continued development of a variety of building energy software tools to help ensure that mechanical, electrical, lighting, and other systems are sized and configured to reduce energy demand.
• Specifying energy-reduction targets and green building material requirements in all contracts.
• Selecting contractors for their expertise in energy-efficient design and construction, their experience in monitoring a building’s energy performance, and their commitment to greening.
• Considering the building’s location, envelope, intended use, hours of operation, occupancy levels, and equipment loads in determining HVAC requirements.
• Ensuring that the building envelope has adequate insulation and that windows are sized and located according to the building’s heating and cooling needs.
• Ensuring that the building envelope incorporates high-performance glazing and other energy-efficient materials.
• Including natural ventilation systems, radiative or ground-coupled cooling, geothermal heat pumps, or peak-load shifting through the use of thermal mass, as appropriate.
DETERMINE COMMISSIONING REQUIREMENTS AND PLANSelect the building systems to be covered in the commissioning process. In large and sophisticated buildings, many systems are integrated. Expanding commissioning activities to cover multiple systems may be desirable. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has published guidelines for commissioning HVAC systems. Additional systems that should be considered for commissioning include mechanical, plumbing, electrical, controls, fire management, sprinklers, elevators, and audio-visual systems.
Develop a strategy to implement the building commissioning process. The ASHRAE guidelines provide a good overall model. Ensure that the commissioning strategy encompasses all of the necessary activities in each stage of the process.
Prepare the design documentation and design criteria for the HVAC system, including the following information:
• HVAC system building-commissioning design documentation form.
• HVAC system design criteria.
• HVAC system description.
Use these HVAC system design documents to:
• Verify with the building owner or users the occupants’ anticipated building program requirements and their planned activities and equipment.
• Verify the fire- and life-safety code requirements for the number of occupants.
• Verify with the mechanical engineer the ventilation requirements for the occupants and their equipment so the HVAC system is designed with sufficient capacity to provide outside air for the projected building population and the anticipated heat-producing equipment.
Have the design team and building operators review the documents to confirm that the building is properly designed for its intended uses. The building population and equipment should not be increased beyond the design limits for the HVAC system.
Prepare design documentation and design criteria for the other building systems to be commissioned according to the format used for the HVAC system.
Prepare specifications to describe the commissioning process. The commissioning process should be described in the construction specifications.
Specify the facility startup amount in the commissioning specifications. The facility startup amount is the total dollar amount that the project sponsor allocates to commissioning in the project specifications and is released to the contractor at the successful completion of each phase of the commissioning. This facility startup amount needs to be determined prior to construction commencement and should be allocated to the general contractor for coordination and to specific subcontractors for their commissioning work.
Ensure that the commissioning process is addressed in contract documents and construction meetings. Contract documents should accurately reflect the process agreed upon for building commissioning. The architect should also be asked to describe the commissioning process at any pre-bid or pre-construction conferences and at pre-commissioning meetings.
Form a commissioning team and designate a commissioning authority. The ASHRAE guidelines define the commissioning authority as the qualified person, company, or agency that will plan and carry out the overall commissioning process. There are many options as to who should be selected to serve this role, including the design professional, the contractor, the building owner, or a commissioning consultant/agent. It is often useful to form a commissioning team that works together to commission the building. In this situation, the role of commissioning authority is divided among various members of the commissioning team, with specific members taking the lead in each phase of the project. Another approach is to consider hiring an independent commissioning agent to ensure that the commissioning is performed adequately.
SELECT COST ANALYSIS METHODSince there will usually be a number of acceptable design alternatives for any project, cost/benefit analyses help select the ones that have the best savings potential.
Depending on the aggressiveness of the design, experience has shown that it costs no more than 10 percent more to build high-performance buildings. Some high-performance buildings cost less to construct. Sometimes additional upfront costs can be justified because the investment will reduce operating costs through the life of the building. The added cost, if any, of system investment each year is compared to the cost of fuel saved each year. Total energy costs are, on average, about 50 percent less than those for conventionally designed buildings. In many cases, the right-sizing of mechanical systems through passive solar design offsets the costs for additional windows or controls.
In analyzing alternative building energy efficiency improvements, conversions, or purchases, cost/benefit analysis is used to determine if and when an improvement will pay for itself through energy savings, and to set priorities among alternative improvement projects. Cost/benefit analyses may be conducted using a simple payback analysis or a more sophisticated analysis of total life-cycle costs and savings. Since most electric utility rate schedules are based on both consumption and peak demand, the analyst should be skilled at assessing the impacts of both.
Before beginning any cost/benefit analyses, determine the acceptable design alternatives that can meet the heating, cooling, lighting, and control requirements of the building being evaluated. The criteria for determining whether a design alternative or alternative fuel is “acceptable” should include reliability, safety, conformance with building codes, occupant comfort, noise levels, refueling issues, and even space limitations.
There are several approaches to cost analysis and calculating project payback:
Simple Payback Analysis
A highly simplified form of cost/benefit analysis is called simple payback. In this method, the total first cost of the improvement is divided by the first-year energy cost savings produced by the improvement. This method yields the number of years required for the improvement to pay for itself. For new construction, it can be used to evaluate conventional construction to energy-efficient design alternatives.
In simple payback analysis, the assumption is that the service life of the energy efficiency measure will equal or exceed the simple payback time. Simple payback analysis provides a relatively easy way to examine the overall costs and savings potentials for a variety of project alternatives. However, it does not consider a number of factors that are difficult to predict, yet can have a significant impact on cost savings. These factors may be considered by using a more sophisticated life-cycle cost analysis.
As an example of simple payback, consider the lighting retrofit of a 10,000-square-foot commercial office building. Relamping with T-8 lamps and electronic, high-efficiency ballasts may cost around $13,300 ($50 each for 266 fixtures) and produce annual savings of around $4,800 per year (80,000 kWh at $0.06/kWh). The simple payback time for this improvement would be $13,000/$4,800 annually = 2.8 years. That is, the improvement would pay for itself in 2.8 years, a 36 percent simple return on investment (1/2.8 = 0.36).
Standardized Payback Equations
One option is to take advantage of a building energy measurement and verification guideline that standardizes procedures for quantifying energy savings from energy-efficiency projects. Called the International Performance Measure Measurement and Verification Protocol (available at www.nrel.gov/docs/fy02osti/31505.pdf), this guideline reduces risk and standardizes paperwork. It also enables loans to be bundled together and sold on a secondary market, like mortgages.
Life-Cycle Cost Analysis
Life-cycle costing (LCC) is an analysis of the total cost of a system, device, building, or other capital equipment or facility over its anticipated useful life. LCC analyses allow a comprehensive assessment of anticipated costs associated with a design alternative. Factors commonly considered in LCC analyses are initial capital cost, operating costs, maintenance costs, financing costs, the expected useful life of equipment, and future equipment salvage values. The result of the LCC analysis is generally expressed as the value of initial and future costs in today’s dollars as reflected by an appropriate discount rate.
The first step in performing an LCC analysis is to establish the general study parameters for the project, including the base date (the date to which all future costs are discounted), the service date (the date when the new system will be put into service), the study period (the life of the project or the number of years over which the investor has a financial interest in the project), and the discount rate. When two or more design alternatives are compared or when a single alternative is compared against an existing design, the variables compared must be the same to assure that the comparison is valid. It is meaningless to compare the LCC of two or more alternatives if they are computed using different study periods or different discount rates.
SELECTING THE â€˜BEST' ALTERNATIVESGenerally, all project alternatives should be initially screened using simple payback analyses. A more detailed and costly LCC analysis should be reserved for large projects or those improvements that entail a large investment, since a detailed cost analysis would then be a small part of the overall cost. Both simple payback and LCC analyses will allow priorities to be set based on measures that represent the greatest return on investment. In addition, these analyses provide a preliminary indication of appropriate financing options:
• Energy efficiency measures that have a short payback period of one to two years are the most attractive economically and should be considered for implementation using operating reserves or other readily available internal funds.
• Energy efficiency measures that have payback periods from three to five years may be considered for funding from available internal capital investment monies, or may be attractive candidates for third-party financing through energy service companies or equipment leasing arrangements.
• Frequently, short payback measures can be combined with longer payback measures of 10 or more years to increase the number of measures that can be cost-effectively included in a project. Projects that combine short- and long-term paybacks are recommended to avoid “cream-skimming” (implementing only those measures that are highly cost effective and have quick paybacks) at the expense of other worthwhile measures. A selected set of measures with a combination of payback periods can be financed either from available internal funds or through third-party alternatives.
If simple payback time is 10 or more years, economic factors are very significant and LCC analysis is recommended. In contrast, if simple payback occurs within three to five years, more detailed LCC analysis may not be necessary, particularly if price and inflation changes are assumed to be moderate. Under this assumption, a simple payback analysis will often be within 15 to 20 percent of the payback time estimated from a detailed LCC analysis. In general, detailed LCC analyses may not be justified if the payback of the improvement is less than five years.
In any cost analysis, it is very important to include avoided cost as part of the benefit of the retrofit. When upgrading or replacing building equipment, the avoided cost of maintaining existing equipment should be considered a cost savings provided by the improvement.
WEIGHING SOCIETAL IMPACTSSome factors related to building heating, air conditioning, and lighting system design are not considered in either simple payback or LCC analyses. Examples include the thermal comfort of occupants in a building and the adequacy of task lighting, both of which affect productivity.
Conventional cost/benefit analyses also normally do not consider the societal benefits from reduced energy use (e.g., reduced carbon emissions, improved indoor air quality). In some cases, these ancillary benefits are assigned an agreed upon monetary value, but the values to be used are strongly dependent on local factors. In general, if societal benefits have been assigned appropriate monetary values by a local utility, they are considered in savings calculations. However, the team should discuss this issue with the local utility or consultants working on these issues.
Reprinted from the U.S. Department of Energy’s (DOE’s) newly redesigned Building Technologies Program Website. The site promotes best practices in residential and commercial construction. For more information, visit www.eere.energy.gov/buildings/.
Publication date: 08/04/2008