Analysis of the impact of locations of special zones
Decisions regarding the location of spaces with special needs can affect building energy performance. Special zones in this space-layout context are spaces with significantly different usage compared to the predominant space types. These special zones may be different in terms of characteristics such as:
- Usage schedules
- Indoor environmental quality requirements (e.g. air quality or thermal comfort)
- Internal heat gains (e.g. occupant density or special equipment)
Examples of special zones include:
- Conference rooms. Highly variable loads compared to other zones.
- Computer room and electrical rooms. High heat gain, typically 24 hours per day.
- Mechanical rooms.
- Kitchens. High heat gain, exhaust air requirements.
- Labs. Air flow requirements, exhaust ventilation requirements, sometimes specific temperature and humidity requirements.
BEM can be used to evaluate the energy impacts of the location of special zones.
See also these related topics:
- Analysis of energy and comfort impacts of different programming layouts
- Analysis of how HVAC loads differ for different programming layouts
Impact of Programming Layouts
The location of special zones can affect the building energy performance in a number of ways.
Impact on efficiency of HVAC operation
The choice of location for special zones often leads to their being served by the same HVAC systems as other zones. As a result, the special zones can affect HVAC operating efficiency when they have significantly different usage hours or significantly different patterns of heating, cooling or ventilation demands compared to other zones.
The impact of different usage hours can be significant unless the HVAC system is designed to operate efficiently when serving only a portion of the building during normally unoccupied hours.
Special zones with different patterns of heating, cooling or ventilation demands can affect the control of the HVAC system. For example, the highly varying loads in a conference room can lead to changes in system supply air temperature setpoints, which then affect the demand for airflow and reheat energy in all zones served by a typical VAV reheat system. The magnitude of this impact might vary depending on the location of the conference room, especially with respect to solar exposure.
Impact on opportunities for efficient design strategies
In some cases, the choice of physical location for special zones might enable, or preclude, the use of efficient design strategies. Some examples of potential efficiency strategies related to special zones:
- Separate HVAC system for special zones
- Passive ventilation or cooling, which might require exterior exposure
- Heat recovery to capture waste heat from special zones
- Transfer air to or from special zones
Alternatives
BEM can be used to assess a number of different strategies to mitigate the energy impact of special zones.
Separate HVAC system
Locate special zones so that it is practical to serve them with a separate HVAC system, especially when those zones have different operating schedules or load patterns compared to other zones. Often the most efficient strategy is to allow systems to be shut off.
HVAC system selection
Choose an HVAC system that minimizes the efficiency impact of special zones. Some HVAC systems allow individual zones to be shut down while others continue to operate efficiently. Examples include zonal systems such as variable refrigerant flow systems or fan coils. Variable air volume systems can be designed to allow shutoff of air to some zones, with some limits.
Location of special zones relative to solar exposure
Place rooms such as conference rooms strategically, considering factors like solar exposure to potentially reduce energy consumption. Solar heat gain through windows added to high peak internal loads in spaces such as conference room result in high peak cooling loads and the associated air distribution system design impacts. In addition, the operational efficiency of the overall HVAC system can be affected by the cooling demand created by solar heat gain coincident with a full conference room, causing HVAC control action such as reduced supply air temperature that leads to overcooling or excess reheat energy consumption in other zones.
Thermal mass
Locate special zones with highly variable heat gains, such as conference rooms, in areas with high thermal mass to dampen the space loads and reduce the associated impact on HVAC controls.
Access to outside
Locate special zones such as computer rooms, electrical, and mechanical rooms where they have access to outdoor air for passive cooling and ventilation.
Access for heat recovery
Locate zones with high gain such that heat can be recovered for uses such as space heating or water heating.
Transfer air
Strategically locate special zones that either require transfer air for exhaust air makeup or can be a source of transfer air for other zones. A common example is locating a dining room with high outdoor air ventilation requirement adjacent to a kitchen with high exhaust air requirement.
Guidance on Modeling Approach
In addition to the guidance on the energy and comfort impacts of programming decisions, here are additional considerations for evaluating some of the strategies described above.
Account for part-load performance
When evaluating the impact of strategies such as using separate systems for special zones, the goal is to get an accurate estimate of HVAC system performance over a range of operating conditions. Make sure that the approach used to model the HVAC systems accounts for part-load performance and uses appropriate operating schedules.
Understand HVAC system operation
When analyzing layouts to minimize the HVAC control impact of special zone location, make sure to understand how the proposed HVAC system works and how its controls are modeled. For example, make sure to understand control inputs related to supply air flow, outdoor air ventilation and supply air temperature control. For more information, see HVAC systems.
Check simulation results
Check simulation results to make sure that the modeled system controls behave as expected. For example, check hourly outputs such as zone air temperature, supply air flow and supply air temperature to understand how the BEM software is controlling the modeled system.
Guidance on Presenting Results
In addition to presenting energy results, also present any impacts on peak heating and cooling loads and associated HVAC sizing impacts.
General BEM results that are typically found useful are described in this page: Analyzing Model Outputs. Other important considerations:
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