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Master
Bedroom
Large
WIndow
• Are in use around the same time of day. For example, it often
makes sense to assign all bedrooms to a single zone because
they are occupied only during the night time when other rooms
in the home are not occupied.
• Have similar heating and cooling needs.
• Are physically separated from other areas.
• Are on the same level of the home. For example, the rooms on
the upstairs level often have a different heating or cooling
demand when compared to rooms downstairs. The differences
can be due to the tendency for heat to rise, different use of
occupancy, and the roof heat load.
• Have similar exposures to external heating gains and losses.
For example, it often makes sense to assign rooms with large
amounts of glass and western or southern exposure to the same
zone.
• The homeowner intends to "set back" at the same time.
• Let you avoid extremely small zones that would cause the
airflow through the unit to become extremely low when only 1
zone requires conditioning.
If possible, discuss these considerations with the homeowner. Get
the homeowner's input before making initial zone assignments.
Mark your preliminary zone assignments on the Floor Plan
Worksheet provided in the Appendix. Fig. 6 shows an example of
zoning assignments marked on a floor plan worksheet.
At this point, consider your zone assignments to be preliminary.
The next task helps you check whether the zone assignments are
feasible.
B. Sizing the Equipment
TASK 3—CALCULATE BLOCK LOAD ESTIMATES AND
ZONE LOAD ESTIMATES
Using the information that you gathered in Task 2, calculate both
heating and cooling load estimates for the entire home. These
estimates are used primarily for sizing the heating and cooling
equipment for the system.
Bath
Bath
Bedroom
Bedroom
Fig. 6—Example of Zoning Assignments
Kitchen
Informal
Dining
Room
Living Room
Shaded
The standard Btu load calculations used for non-zoned systems
apply equally well to zoned systems. Use a reliable method with
which you are comfortable.
After you have tentatively defined the zones for a home, calculate
individual peak heating and cooling load estimates (in Btu's) for
each of the zones. Use a reliable method with which you are
comfortable to calculate the peak zone load estimates. Refer to the
information that you gathered in Task 2.
The peak zone load estimates are used to determine whether the
zone assignments you have made make sense. They also are used
to size the zone dampers and ductwork.
When a zone is recovering from being set back, the system must
supply additional capacity beyond the zone's losses to change the
temperature. The farther the desired setback, the more capacity
must be added.
For zones that will be set back and that need reliable recovery,
multiply their calculated zone loss by a recovery factor of 1.25.
Use the larger zone load estimate when determining the size of the
damper and duct required for the zone.
TASK 4—SIZE HEATING AND COOLING EQUIPMENT
Zone Perfect Plus is designed for use with a furnace or fan coil in
conjunction with a condensing unit or heat pump with a thermo-
static expansion valve (TXV). Zone Perfect Plus operates within
an airflow range of 1.5 to 6 tons in the cooling mode.
How to determine the appropriate size of heating and cooling
equipment is a challenge that is subject to much debate. In a
residential zoning system, there is a very good possibility that a
system will use all zones on a given day. For that reason, we
recommend that you select the size of heating and air conditioning
units based on either the home's block heating load or block
cooling load (whichever is greatest). Select the size of the air
handling unit based on the unit with the largest required CFM.
However, because the system has the capability to not condition
some zones at any given time, and because it is essential to
—6—
N
Utility
Room
Family Room
Shaded
Zone 1
Zone 2
Zone 3
Zone 4
A98342
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