Engineering Manual

EQUIPMENT SELECTION PROCEDURE
Select the Equipment
Determine the Number of Zones
Multi F and Multi F with LG RED 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, and choose how many (and which styles of)
indoor units will be required. See Table 90 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 indoor units, also consider the cooling and heating 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 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 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.
• When high static duct and / or vertical-horizontal air handling indoor units are the only connected indoor units, the multiplier is 1.2.
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).
For allocated capacity information, see the combination tables in the "Multi F / Multi F MAX Combination Data Manual" on www.lg-dfs.com. For
performance data, see "Multi F / Multi F MAX Performance Data Manual" on on www.lg-dfs.com. Also refer to the appropriate manuals on www.
lg-dfs.com for combination and capacity data for Multi F with LG RED / Multi F MAX with LG RED units.
Due to our policy of continuous product innovation, some specications may change without notication.
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184 | APPLICATION GUIDELINES
Multi F and Multi F MAX Indoor Unit Engineering Manual
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