During the schematic design phase of a project, the project team will develop rough construction drawings that offer an overview of a project's features. While the level of detail is much less than the later stages of design, it is enough to generate construction cost estimates and allow the team to ensure that the design concepts fit within the project budget.
During this phase, the team will typically consider many design options and the decisions they make will inform the later stages of design. This process of selecting different design options and concepts has a good amount of overlap with activities described in the conceptual design section of this site. In fact, many projects will effectively merge the conceptual and schematic phases together and refer to this combined process as "schematic design."
The schematic design documents developed by the team include architectural floor plans and elevation drawings, as well as engineering plans for the HVAC, electrical and plumbing systems. The architectural drawings will convey the basic layout of the building, and the engineering drawings will include system capacities and approximate locations. Detailed aspects of the design are generally not included until the design development phase.
BEM practitioners can be highly impactful during this phase by helping to analyze the energy and comfort impacts of each of the design options being considered by the team. Read on for more guidance on BEM analysis that can inform the major architectural and engineering decisions made during schematic design.
Architectural design activities
During the schematic design phase, the architects begin to integrate the project's space needs and design goals into a set of floor plans. This is a highly iterative process where much coordination occurs between the architect and the building owner. Often, several options are presented to the building owner showing different designs and space layout, and the owner's feedback is used to refine the design. In addition to floor plan drawings, this information may also be presented in other formats such as 3D renderings or models.
Many of the key design decisions are made during this stage. Decisions about the building's form and elevation/facade design can have large impacts on the building's performance and BEM analysis can be very informative in the decision making process.
Progression of main design concepts
During this phase, the design concepts that were identified during the conceptual design phase will continue to be explored, vetted, and selected for inclusion in the building design. BEM analysis can support the architectural team by evaluating:
- Constructions and thermal mass options
- Fenestration and daylighting options
- Natural ventilation design features
- Passive solar design features
Develop preliminary floor plans
A primary goal of the schematic design phase is to develop floor plan drawings that include the space type needs for the building as defined when creating the building program. The physical locations of the various space types are designed for functionality, flow, occupants' experience, and many other factors.
The BEM practitioner, or mechanical engineer, will ultimately use the floor plan layout as the basis for performing load calculations and early-stage energy modeling. Because the schematic design phase considers many options, the BEM analysis can provide feedback on how each option performs relative to one another. Helpful modeling tasks may include:
- Analysis of energy and comfort impacts of different programming layouts
- Analysis of the impact of locations of special zones such as conference rooms, equipment rooms, and others
- Analysis of how HVAC loads differ for different programming layouts and how this may impact architectural needs such as shaft sizes, equipment room sizes, and plenum heights
Develop preliminary facade design and elevation drawings
The elevation drawings show the building's facade design and call out construction material types, window sizes and locations, locations of other openings such as doors and louvers, shading, and other features.
The facade is an essential element that defines the building's character, provides protection from the elements, and contributes to its energy efficiency. BEM analysis can contribute to the facade design process in a number of ways:
- Window-to-wall ratio parametric studies to determine performance impacts of different window areas including solar gains and daylighting potential
- Shading feature design analysis
- Analysis of potential for natural ventilation and passive cooling with operable windows
- Analysis of thermal performance of different wall construction materials
- Analysis of thermal performance of different glazing performance specifications
The BEM studies may analyze whole-building performance using a simple box model, or they may be focused studies on a specific building orientation or room type using shoebox models.
Engineering design activities
The engineering team collaborates closely with the architects to ensure that the building systems meet the functional needs of the building. The mechanical (HVAC) engineers consider aspects such as indoor air quality and comfort; the electrical engineers consider power and lighting needs. System selections often consider the tradeoffs between equipment cost and energy efficiency (operational costs), and also how the system choice may impact compliance with the energy code.
HVAC system energy will account for a significant proportion of a building's total energy use. The amount will vary depending on the architectural design (e.g. massing and facade design), the planned usage of the building and the amount of internal gains. Energy analysis is crucial at this stage to ensure that the performance of building systems is considered in the design.
HVAC load calculation analysis is a process to determine the heating, ventilation, and air conditioning requirements for each space and system within the building. Loads analysis helps the HVAC engineers design all aspects of the system including system sizes (heating and cooling capacity), flow rates for air and water, ductwork and diffuser sizes, etc. However, during schematic design, the goal is not to design every element of the system yet. Schematic design load analysis focuses on determining overall heating and cooling capacities so that approximate sizes for boilers, chillers, and air handling systems can be identified (and included in cost estimation processes). This big-picture sizing information is also used to coordinate with the architects so that they can allocate sufficient space for equipment rooms, mechanical shafts (to route large ducts vertically between floors), and ceiling plenum cavities (to run ducts and other system features above the ceilings).
Loads analysis is similar in many ways to whole-building BEM except that, where BEM analysis focuses on calculating performance over a period of time (e.g. an annual analysis), loads analysis is focused just on calculating performance at peak conditions (e.g. the hottest and coldest days of the year).
Loads analysis is often performed by the HVAC engineering team, often by a member of the team who also performs BEM analysis. Often the BEM practitioner (whether they are part of the HVAC design team, or an external consultant) will be consulted at this stage to identify ways to reduce the loads in the building. Reducing the loads can result in smaller system capacities (saving first costs, reducing the size of equipment rooms, vertical shafts, and plenum height), improved thermal comfort, and significant operational energy cost savings.
- Load reduction modeling
HVAC systems selection
The choice of HVAC system may be based on many factors:
- Efficiency - some system types are inherently more efficient than others. Projects that have set performance goals may be more likely to evaluate a range of low-energy system types.
- Cost - system costs may vary based on their complexity to manufacture and to install. An analysis of first costs vs. ongoing operational costs (e.g. payback analysis or life cycle cost analysis) is important to understand the true cost implications of selecting a system type.
- Expertise - some design firms may have more experience with a certain system type and therefore may be likely to select that system over an alternative type.
- Capacity - some system types have the ability to provide more cooling or heating per square foot of area than others. It is important to understand the amount of loads in each space and ensure that the system can meet the load density (load per square foot).
BEM analysis that can help to inform the system selection:
- Compare the performance of different system options
Read more about different HVAC system type options: HVAC system types
Lighting systems selection
During schematic design, the lighting system design will focus on analyzing the building space types, determining desired illuminance levels, selecting lighting fixture types, and selecting desired control options for the lights.
BEM analysis that can inform the lighting system design:
- Test strategies to reduce lighting power density and quantifying energy impacts
- Analyze the impact of lighting control strategies such as occupant sensor and daylight sensor controls
Develop schematic design drawings
The schematic design drawings and supporting documentation are at a high level, but with sufficient detail to begin estimating the construction costs.
HVAC drawings include approximate sizes and locations for major equipment such as chillers, boilers, cooling towers, and air handling units. Major duct runs are typically depicted as single lines, but with the duct dimensions called out. Vertical ductwork (through shafts) are generally drawn in 2D to demonstrate they will fit within the architectural shaft spaces. The HVAC specifications and other supporting documents will indicate the basis of design and include information such as design set point temperatures, assumptions of thermal properties of the building envelope used for load calculations, description of any special features of the system including planned control strategies.
BEM analysis is not typically a key component when drafting the design documents, however the load calculation process and system selection analysis that precedes the drawing phase is of utmost importance to selecting appropriate system types and ensuring the accuracy of the system sizes shown on the drawings.
Energy (and other metrics) estimation
During the schematic design phase, many fundamental design decisions are made that will have significant impacts on the performance of the building. As the design progresses to later stages (design development and construction documents), it becomes increasingly difficult to change these early decisions without significant and costly redesign. Therefore, it is important that the energy and other performance metrics be estimated during schematic design to understand how the building performs relative to specific project performance goals, code compliance, or beyond-code program performance. If BEM analysis shows the project is not meeting the performance goals or complying with the code, changes can be made rather easily at this stage.
A typical approach during SD is to use simple box models to capture a baseline performance (often a code-minimum baseline), and then test various design strategies against the baseline to determine how each measure, or combinations of multiple measures impacts the performance.
Integrated design strategies
Many design decisions affect both the architectural and engineering designs, especially for high-performance buildings. It is important for the architectural and engineering teams to coordinate when developing big-picture strategies and continuing this collaboration as the strategies are developed.
Thermal comfort strategy
Design concepts to explore include:
- Natural ventilation
- Ceiling fans
- Mechanical cooling
- Radiant systems
- Occupant control
Indoor air quality strategy
Design concepts to explore include:
- Mechanical ventilation
- Natural ventilation
- Source control
- Demand control ventilation
Thermal load control strategy
Design concepts to explore include:
- Exterior shading
- Interior shading
- Glazing selection and area
- Cool roof
- Thermal mass
Daylighting and visual comfort strategy
Design concepts to explore include:
- Electric lighting
- Shading devices
- Task lighting vs. ambient lighting
- Narrow building
- Top lighting
- Side lighting
Relevant ASHRAE Standard 209 cycles
Several ASHRAE Standard 209 cycles are applicable to the schematic design phase, including:
- Cycle 2 - Conceptual design modeling
- Cycle 3 - Load reduction modeling
- Cycle 4 - HVAC system selection modeling