Manual Equipment Selection Procedures - LG MULTI F Engineering Manual
Multi f; multi f max with lg red heat pump outdoor unit
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F
MULTI
WITH
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MULTI
MAX
To use the manual equipment selection procedure in choosing 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:
• 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 with LGRED heat pump systems
or a Multi F MAX with LGRED 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 8 for allowable indoor unit to outdoor unit connections, and the maximum number of connectible
indoor units on each Multi F with LGRED and Multi F MAX with LGRED 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 with LGRED 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.
For allocated capacity information, see the combination tables in the "Multi F / Multi F MAX with LGRED Combination Data Manual" on
www.lg-dfs.com. For performance data, see "Multi F / Multi F MAX with LGRED Performance Data Manual" on www.lg-dfs.com.
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MANUAL EQUIPMENT
SELECTION PROCEDURE
INTRODUCTION | 7
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