Page 12 ZC-KI6-VSS1709
EQUIPMENT SIZING AND SELECTION
Procedure
1. Conduct a complete heat loss / heat
gain calculation.
2. Determine inlet water temperature
3. Select Air Handler
4. Determine zones within the space.
Three is typical but it can be 2 or 4.
5. Select # outlets per room
6. Determine Duct Layout
Heat Loss / Heat Gain
Room by room calculations need to be
completed using HRAI, ASHRAE, or
another approved sizing methods.
Air Handler Selection
The selected air handler must be sized
according to the following rules:
a) Heating capacity must be between
100% and 140% of the heat loss.
(110% to 140% for combo systems
130°F water temp)
b) Cooling capacity must be between
75-100% of the heat gain. Note that
slightly under-sizing the cooling
equipment improves efficiency and
provides better humidity control.
Zoning ensures the space will be
comfortable even on the hottest days.
When using a boiler system, select a
boiler with an output that meets or
exceeds the heat loss of the space being
heated. If the boiler is serving additional
loads, size the boiler to meet the total
combined load.
For combo heating systems, use an
approved sizing method such as the
Unified Combo Guidelines published by
HRAI.
Define Zones
The space served by the air handler
should be divided up into zones. Three is
typical. Each of these zones is to be
served by a single main duct by the air
handler. Zones can represent areas such
as the basement, main floor and second
floor. In some applications, it may be
desirable to divide the area into east
facing, west facing and basement zones
depending on solar gain. Zoning based
on usage is also acceptable: office, living
and sleeping areas for example.
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