Analysis of energy and comfort impacts of different programming layouts
BEM can be used to analyze energy and comfort impacts of floor plans representing alternative programming layouts. As discussed below, the arrangement of spaces of different usage types can affect performance in several ways.
See also these related topics:
- Analysis of the impact of locations of special zones
- Analysis of how HVAC loads differ for different programming layouts
Impact of Programming Layouts
Programming layout decisions can affect a building’s energy consumption as well as the thermal and visual comfort of its occupants. The variation in performance of different layouts is often due to the varying impact of exterior exposure for different space occupancy types. Therefore, savings opportunities will also be affected by design choices for building form and massing, orientation and fenestration design.
Keep in mind that the impacts described here will vary between projects. Impacts depend on climate: hot vs. cold or sunny vs. cloudy. Impacts will also depend on the mix of occupancy types and their characteristics such as their relative occupant density, plug loads, comfort requirements, illuminance requirements, or usage schedules.
Energy impacts
- Heating and cooling. Heating and cooling loads and the associated energy consumption can vary between space layout options, especially if spaces have significantly different comfort requirements, internal heat gains or usage schedules.
- HVAC distribution. The energy used by fans and pumps to deliver heating, cooling and ventilation air can be affected by space layout through the impact on the length of distribution paths and flow requirements
- Daylighting. The potential lighting energy savings for automatic lighting control can vary significantly depending on the illuminance requirements and occupancy schedule of spaces with access to daylight.
- Lighting. In some cases, total installed lighting power can be reduced through space layout that minimizes floor area with high illuminance requirements or permits efficient lighting design strategies such as task/ambient lighting.
- Natural ventilation. Potential savings from natural ventilation depend on the location of occupied spaces relative to exterior operable openings. The layout may affect both the amount of floor area that can be served by natural ventilation as well as the performance of the natural ventilation in those spaces. See natural ventilation design features.
Thermal comfort impacts
A primary programming decision that affects thermal comfort is the location of occupants relative to exterior walls, windows and operable openings. Programming decisions can also affect the opportunity for comfort through personal comfort controls or local control of air movement. Decisions that affect thermal comfort also affect energy consumption through the impact on air temperature setpoint requirements.
- Mean radiant temperature. The interior surface temperature of walls and windows is a significant factor in the mean radiant temperature experienced by occupants in perimeter areas.
- Direct sun. Direct solar radiation through windows onto occupants has a major impact on their comfort.
- Operable openings. Access to operable windows may improve occupants’ perception of thermal comfort. [1][2]
- Personal comfort controls. Layouts that enable the use of personal comfort controls, either single-occupant spaces or other systems that allow individual control of air temperature and/or air movement, can significantly improve occupant thermal comfort. [3]
- Air movement. Space layouts that allow the use of ceiling fans or other means of local control of air movement, can provide improved comfort. [4][5]
Visual comfort impacts
Programming decisions, combined with fenestration design and lighting design, affect occupant visual comfort. The primary layout decision is the location of occupants relative to windows and skylights, which affects opportunities for views as well as potential for discomfort due to glare. Energy may be affected due to loss of daylighting savings or the impact on heating and cooling loads caused by occupant operation of window shades in response to glare.
Resilience and passive survivability
Space layout and the location of occupants relative to operable openings can affect the ability of occupants to use the building during periods when heating, cooling or ventilation are not available.
Other impacts
Programming decisions can affect appropriate HVAC system type selections. The approach to perimeter heating and cooling might vary depending on the occupancy of perimeter areas and the associated comfort requirements. The opportunity to use HVAC systems with limited peak heating or cooling capacity, such as radiant systems, can also be affected by programming layout.
Programming layouts may also affect transport energy for elevators.
Layout Alternatives
This section describes several space layout alternatives to consider for improved energy and comfort performance.
Locate circulation and temporarily occupied spaces at the perimeter
Space layouts that move occupants away from exterior walls, for example by locating circulation or temporarily occupied spaces at the perimeter offer potential for improved occupant comfort and lower energy consumption.
- Thermal comfort may be improved by reducing the mean radiant temperature impact of exterior surfaces and reducing the potential for drafts caused by cold windows. In addition, it is less likely that direct sun will cause discomfort.
- Energy savings are then possible because occupants may feel comfortable over a wider range of air temperatures, cooler in winter and warmer in summer. Temperature setpoints in the perimeter circulation area may also be relaxed relative to space layouts that place occupants near windows.
- Visual comfort may be improved due to less glare from bright surfaces.
Avoid workstations on east and west orientations
Layouts that avoid placing workstations near east or west facing facades will avoid thermal and visual comfort problems caused by direct sun in the morning and afternoon. For south-facing spaces, direct sun can be controlled with fixed shading devices such as overhangs or light shelves.
Group spaces with similar needs
Space layout can facilitate energy savings by grouping together spaces that are expected to operate on the same schedule. Significant savings can be achieved by shutting off or setting back heating, cooling, ventilation and lighting for portions of the building when it is not needed.
Configure furniture for daylight penetration
The height and material choice for partitions in spaces such as offices can affect energy performance. Daylight penetration can be enhanced with low partitions, use of materials that transmit light, and orientation of partitions to avoid blocking light from windows. Furniture configuration may also enhance or inhibit natural ventilation airflow.
Minimize HVAC distribution paths
The energy consumed for moving air for cooling, heating and ventilation depends on the pressure loss in ducts, and that pressure loss depends on several factors that can be affected by space programming, including duct length, duct size, and the number of turns and fittings. And in multi-zone systems like common VAV reheat systems, the pressure loss along a single path from the air handler to the most distant zone (i.e. the path with the greatest pressure loss) can dictate the required fan power. Some layout issues to consider:
- Locate air handlers and air shafts centrally to provide roughly equal duct paths to each zone
- Provide multiple shafts or air handlers to reduce duct length
- Allow space for adequate duct size
- Use a zonal type HVAC system type such as fan coils or variable refrigerant flow systems that require less duct length
Take advantage of natural ventilation
The airflow provided by natural ventilation can vary significantly based on space configuration. For example, layouts that include operable openings on two or more walls (cross ventilation) provide more wind-driven airflow than a space with operable openings on only one wall (single-sided ventilation). See natural ventilation design features.
Guidance on Modeling Approach
BEM can be used to explore the impact of alternative programming layouts. The following are examples of model inputs that might vary between alternatives.
- Thermostat setpoints based on thermal comfort needs
- Fan power based on air distribution system impacts
- Daylight control inputs based on space configuration and illuminance requirements
- Operating schedules for alternatives that allow for partial shutdown
- Natural ventilation inputs for layouts that affect natural ventilation performance
Appropriate inputs
A study of programming options will likely happen early in design when many design details are still to be determined, especially details of HVAC and lighting systems. Therefore, many assumptions will be necessary.
Thermal zoning. Some simplification is likely appropriate, but the models should include enough thermal zones to represent the variety of space occupancy types included in the alternative programming layouts. The model should separate zones for areas with significantly different exterior loads, internal loads or operating schedules. For this type of study, the zoning pattern is likely more detailed than for a typical simple box model. Read more about thermal zoning strategies.
Internal loads. Make sure that internal load inputs are appropriate for each space type rather than simply using the same assumptions for all zones.
- Number of occupants (or occupant density) and occupancy schedule
- Lighting power and schedule
- Daylighting control inputs
- Plug load power and schedule
Zone HVAC. Inputs should be appropriate for each space type.
- Cooling and heating thermostat setpoints
- Outdoor air ventilation rate requirement
- Zone terminal unit characteristics such as VAV box minimum flow setpoints (if appropriate)
HVAC system. Design details are likely not available at this early stage. For guidance on appropriate inputs see airside HVAC assumptions for early-stage models and waterside HVAC assumptions for early-stage models. Other considerations:
- Fan power inputs account for differences in air distribution among alternatives
- HVAC operating schedules account for any differences among alternatives
Other modeling considerations
Some BEM software offer advanced capabilities that may be useful for comparing the impact of programming alternatives.
- Thermal comfort calculations, such as mean radiant temperature and operative temperature, for each zone.
- Visual comfort and glare calculations for each zone.
- Operable shades, which could be modeled to represent the impact of occupant control of shades in response to direct sun or glare.
Guidance on Presenting Results
Where alternatives affect thermal comfort, visual comfort or daylighting, a useful presentation approach is to superimpose information about performance metrics on the building floor plan.
General BEM results that are typically found useful are described in this page: Analyzing Model Outputs. Other important considerations:
Additional Resources
- ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy.
- Sonta, et al. “Data-driven optimization of building layouts for energy efficiency”. Energy and Buildings, Volume 238, 2021
References
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