Multi F Engineering Manual

EQUIPMENT SELECTION PROCEDURE
Select the Equipment
Determine the Number of Zones
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pump systems or a Multi F MAX system, the designer will be able to combine spaces with similar load profiles located near or adjacent to
each other into “thermal zones.” After combining like spaces into zones that will be served by a single (or grouped) indoor unit(s), calculate
the peak cooling and heating loads for each zone.
Choosing the Appropriate Indoor Units
Determine the appropriate indoor unit capacity that satisfies the given zone load calculations, and choose how many (and which styles of)
indoor units will be required. See the table on the next page for allowable indoor unit to outdoor unit connections, and the maximum number
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CFM, featured airflow specifications, and static pressure (if applicable) for each indoor unit.
Avoid oversizing indoor units in an attempt to increase the air exchange rate in the space. Multi F and Multi F MAX systems are designed
for minimum airflow over the coil to maximize latent capacity while cooling, maintain a comfortable, consistent discharge air temperature
while heating, and minimize fan motor power consumption. In extreme cases, oversizing the indoor units will affect outdoor unit size selec-
tion and compromise the outdoor unit’s ability to effectively match the space load(s).
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1. At least two indoor units must be connected to the outdoor unit.
2. Total connected indoor unit nominal capacity must be a minimum 40% and a maximum of 133% of outdoor unit nominal capacity.
3. To calculate the connected total indoor unit nominal capacity, simply sum up the nominal capacities of all indoor units.
• For high static duct and vertical-horizontal air handling indoor units, a 1.3 multiplier must first be applied before adding to the sum of
other indoor units.
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To choose the multi-zone system that is the most appropriate for the space, as with traditional air-conditioning systems, follow similar
protocols outlined in Manual J from the Air Conditioning Contractors of America (ACCA; see www.acca.org).
1. Obtain the design conditions, and calculate the maximum cool and heat loads for the structure.
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• Determine number of zones.
• Determine total number of indoor units (refer to zone load calculations when choosing indoor units).
• Determine number of indoor units allocated to each outdoor unit, considering allowable indoor unit connections, both indoor unit and
outdoor unit capacities, and system piping capabilities.
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• System Combination Tables.
• Capacity Tables (it will be necessary to interpolate).
• Capacity Coefficient Factors (such as refrigerant line length derates, design condition derates, defrost operation derate [heating mode],
altitude derate [if applicable]).
4. Compare corrected capacities to load calculations.
5. Reselect equipment if necessary.
Obtain Design Conditions, Calculate Maximum Cool / Heat Loads
Obtain the winter outdoor / indoor temperature and summer and winter outdoor / indoor temperature design parameters for the location in
which the system is installed. Determine if summer or winter design gains, relative humidity, and building features like skylights, orientation,
number of occupants, etc., would change the total heat loss / gain and sensible / latent heat gain, and then calculate the maximum cool and
heat loads for the space (using Manual J or energy modeling programs).
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APPLICATION GUIDELINES | 185
Application Guidelines
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