Zoning Design Procedures - York Meridian Technical Manual

036-21478-001 Rev. A (0802)

Zoning Design Procedures

General
There are six basic steps to designing an Meridian
Zoning system:
1.) Determining the number and location of zones
2.) Sizing the central unit
3.) Duct Considerations
4.) Room air motion and diffuser selection
5.) Bypass damper sizing
6.) Sizing the zone dampers
Step #1 - Determining The Number And
Location Of Zones
A single air handler unit can have no more than sixteen
zones and no fewer than 3 zones. If the number of zones
exceeds sixteen then more than one Zone Manager will
be required.
The primary precaution to be taken in applying the

Meridian Zoning System is to select the zoning so that
no zone will be at maximum (design) heating (or cool-
ing) load when any other zone requires the opposite
temperature air to satisfy its load. For example, depend-
1 2
10
9 8
Figure 1-2: Zones Affected by the Outdoor Load
Meridian Systems

N
3
4
11
5
7 6
ing on the wall, ceiling and floor material and location
within the building (e.g. top or middle floor), a typical

floor of a building usually has several distinct tempera-
ture or control zones that are affected uniquely by the
outdoor load. These zones are depicted in Figure 1-2.
Depending on the size of the building and partition lay-
out, some of these zones may overlap or be insignifi-
cant from a zoning standpoint. For example, Zone 11
could be multiple conference or computer rooms where
additional zoning would be required, or it could be as
small as a corridor where no zoning is required. Simi-
larly, zones 7 and 8 could have no external windows
and no partitions between them and could be consid-
ered a single zone. Some zones could be divided into
multiple offices with full partitions between them, thus
requiring separate Zone Controllers because of differ-
ent internal loads, but the same external load.
Generally, the greater the number of individual Zone
Controllers, the greater the comfort. The designer will
have to look at the specific building, balancing the costs
of multiple zones with the added comfort possible with
multiple zones, to match the owner's requirements.
It is important to recognize that there are purely inter-
nal zones, such as Zone 11 in Figure 1-2, which may
contain separate offices/conference/computer rooms.
These internal zones could easily have high cooling re-
quirements while external zones (1,2,3, etc.) could be
at or near design heating load. This is a misapplication

of the Meridian , zoning (or any heating/cooling
change-over) system. The interior zones with cooling
only loads should be served by a separate single zone
rooftop HVAC unit (that could be zoned between mul-
tiple rooms with a similar load profile). Supplemental
heat could be added to the perimeter zones and con-
trolled with the auxiliary heat control board from the
Zone Controller. System performance will generally be
compromised and frequent change-over from the heat-
ing to the cooling mode will occur during the heating
season if purely internal zones are combined on the same
air-conditioning unit serving perimeter zones. The ex-
posure to the sun has a large affect on the loading of the
building. With the building zoned as shown below, for
the best control, zones 6, 7, 8, 9 and 10 should be put
on one HVAC unit, and zones 1, 2, 3, 4 and 5 on an-
other HVAC unit. Zone 11 should be on a separate single
zone constant volume HVAC unit.
Zoning Design Guide
13