Determining the Number and Location of Zones - Verasys - LIT-12012331 - General System Information - Verasys System - 4.0

Verasys System Changeover Bypass Zoning System Design Application Note

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Verasys System
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Application Note
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You can have a minimum of three zones and a maximum of 24 of zones within a single air handler. The primary precaution when applying the COBP Zoning System is selecting the zoning. Ensure no zone is at the maximum (design) heating or cooling load when another zone requires the opposite air temperature to satisfy its load.

For example, depending on the wall, ceiling, and floor material and location within the building (top or middle floor), a typical floor of a building usually has several distinct temperature or control zones uniquely affected by the outdoor load. These zones are shown in the following figure.

Figure 1. Outdoor Load Locations and Zones

Depending on the size of the building and partition layout, some of the zones may overlap or may not require zoning.

For example, in Figure 1, if Zone 11 consists of multiple conference or computer rooms, additional zoning is required. If Zone 5 is a corridor, no zoning is required. Similarly, Zones 7 and 8 can comprise a single zone if no external windows and partitions exist between them. Some zones can be divided into multiple offices with full partitions between them, and so they require separate damper assemblies because of the different internal loads, but the same external load.

Generally, the greater the number of individual zones, the greater the comfort. The designer has to evaluate the specific building, balancing the costs of multiple zones to match the building requirements.

It is important to recognize purely internal zones, such as Zone 11 in Figure 1, which can contain separate offices, conference rooms, and computer rooms. If the internal zones have high cooling requirements and the external zones (1,2,3) are on or near the design heating load, applying a single zoning system to this arrangement of zones can result in poor zoning system performance. It can also result in problems meeting the preferred comfort levels of the occupants.

Serve the interior zones with cooling only loads with a separate RTU that can zone between multiple rooms with a similar profile. System performance may be compromised. Frequent change-over from the heating to the cooling mode occurs during the heating season if internal zones combine on the same air conditioning unit serving perimeter zones. The exposure to the sun has a large effect on the loading of the building. With the building zoned as shown in the following section, for best control, put Zones 6, 7, 8, 9, and 10 on one RTU and Zones 1, 2, 3, 4, and 5 on another RTU. Put Zone 11 on a separate single zone constant volume RTU.

See Appendix: Example Zoning Designs for multiple building layout scenarios and zoning recommendations.