Work from a building floorplan that ideally shows the dimensions of the building shape. If the building is simple (e.g., rectangular), simply knowing the dimensions of the building or the rough aspect ratio is good enough. Three default options are available for simple building shapes:
- Square – One Zone
- Rectangular 1x2 – 2 Zone
- Square – 4 Zone
Use the Custom option if the building has a more complex shape (e.g., has wings or irregular shapes), do your best to approximate the shape of the floorplan.
Make sure that the sketch is oriented correctly when entering the overall shape in the tool interface. The uppermost zones should be north-facing facades, and the lowermost should be south-facing facades. If the building is not oriented perpendicular to a north-south axis, assign a new north-south axis for the building (as close as possible to true north-south) that is perpendicular to the major lines of the building's shape.
Your initial building shape sketch should involve filling in all pixels with a single one-digit integer value (e.g., 1). This will initially define the floorplan as a single zone (in this case, as Zone 1). Later, you will split this into more zones. Around all the edges of your sketch, select the “Edge” option to enter Es, which indicate that there is a border with the building envelope. If your sketch is a section of a floorplan, do not include Es at the edge where there is no envelope border.
The final step is to define the specific zones. This step takes some subjective decision-making and modeling discretion. The following are several tips and guidelines to consider.
- You may only define up to nine zones. A typical floor of a commercial building may have up to 40 thermostatically controlled zones, therefore some merging of true zones into modeled zones may be unavoidable. To create the zone, click the colored icon to the left of the Zone Name field and then begin to draw with your cursor on the zone map below. Enter a name associated with each zone to help you remember what they conceptually represent. Each zone should be assigned a Zone Type. This helps to pre-define default values for densities of lighting, people, and electric equipment. If nothing in the list is a good proxy for the actual zone type, pick something reasonably close, and then you will have the option to modify the default values to better represent the zone of interest. Even if the zone type is a good match, you may decide to modify the default values in the table if you have prior knowledge about the density of lighting, equipment and people. A final entry in the table is the Window-Wall %. This value can be set differently by zone, so that different window fractions can be defined on different exterior-facing facades. Pictures of the building, Google Street View and architectural drawings are good sources to visually estimate these values.
- Think about your zoning in terms of two types of space segregation: orientation and space usage.
- One good strategy is to start by segregating in terms of orientation. Change the values in the cells you have defined such that 1s are located along the south-facing perimeter, 2s on the east-facing perimeter, 3s on the north-facing perimeter, 4s on the west-facing perimeter, and 5s in the interior. Some buildings with narrow shapes may not have a true interior, so the numbering can start with 1–4.
- How “deep” to define the perimeter is a matter of user discretion as well. Having building floorplans available that indicate the depth of interior partitions can help with this. For example, if the building footprint is a 100’ by 100’ square that you have represented by a 20×20 pixel space in your sketch, each pixel will be a 5’×5’ square of the actual footprint. If the building drawing indicates that exterior zone partitions are typically about 15’ from the perimeter walls, then the perimeter zones should each be three pixels deep. 15’ is a good assumption for exterior zone depth if you do not have drawings that show room partitions. If you are zoning an open floorplan, using the five-orientation approach is still recommended because there will still be multiple HVAC zones, and those closer to the perimeter will preferentially develop loads that reflect envelope-driven heat transfer.
- Once this 4–5 zone map has been developed, add any zone definition complexity (by adding Zones 6–9) that results from differences in space usage. Space usage may refer to anything that affects the density or schedules of lighting, electrical equipment, or people, occupied/unoccupied thermostat setpoints, and other details such as the VAV minimum airflow requirements. These may take the conceptual form of spaces like a conference room, courtroom, auditorium, kitchen, lobby, corridor, restroom, data center, or any other such usage type that varies from the predominate space usage (e.g., office or retail space).
- Sometimes buildings have separate cooling-only HVAC systems serving high density loads like data centers, transformer rooms and electrical closets. If these spaces are conditioned independently of main HVAC systems, it is recommended to exclude them from the zoning floorplan and thus the model. These zones and their connected systems are not often a target of re-tuning and the high internal loads of these zones may cause the AHU you are defining to run closer to 24/7 if they are connected. As a consequence of excluding these zones, however, you may not be able to properly calibrate your model against metered electricity.