Equipment Selection Procedure - LG MULTI F Series Engineering Manual

EQUIPMENT SELECTION PROCEDURE

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.
2. Select the equipment (choosing the appropriate indoor units and outdoor unit):
• 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.
3. Determine the corrected capacity for the indoor units and outdoor unit using LATS Multi F software (preferred method) or:
• System Combination Tables.
• Capacity Tables (it may 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).
Select the Equipment
Determine the Number of Zones
Multi F heat pump systems can cool or heat, but not simultaneously. When designing larger-capacity Multi F heat pump systems or a Multi
F MAX system, the designer may 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, choose how many (and which styles of) indoor
units will be required. See Table 96 for allowable indoor unit to outdoor unit connections, and the maximum number of connectable indoor
units on each Multi F and Multi F MAX outdoor unit. When choosing, also consider the cooling and heating CFM, featured airflow specifica-
tions, 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 may affect outdoor unit size selection and
compromise the outdoor unit's ability to effectively match the space load(s).
For proper system operation:
1. At least two indoor units must be connected to the outdoor unit.
2. Total connected indoor unit nominal capacity should 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 24,000 and 36,000 Btu/h 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 smaller indoor units.
• When two 24,000 Btu/h or one 24,000 Btu/h and one 36,000 Btu/h high static duct and / or vertical-horizontal air handling indoor units
are the only connected indoor units, the multiplier is 1.2.
342 | APPLICATION GUIDELINES
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