Engineering Manual

Determine the Corrected Capacity
The corrected cooling / heating capacity is different from the rated cooling / heating capacity. The corrected capacity includes changes in
unit performance after considering design temperatures, available capacity that can be allocated from the outdoor unit, pressure drop due
to refrigerant line length, defrost operation in heating mode, and (if applicable) altitude. Depending on the location of the building, additional
capacity correction factors may need to be applied.
Using the Outdoor Unit Cooling and Heating Capacity Tables
Rated cooling capacity ratings are obtained with air entering the indoor unit at 80ºF dry bulb (DB) and 67ºF wet bulb (WB), and outdoor ambi-
ent conditions of 95ºF dry bulb (DB) and 75ºF wet bulb (WB). Rated heating capacity ratings are obtained with air entering the indoor unit at
70ºF dry bulb (DB) and 60ºF wet bulb (WB) and outdoor ambient conditions of 47ºF dry bulb (DB) and 43ºF wet bulb (WB).
To evaluate the total outdoor unit capacity at design conditions perform a selection using LATS Multi F software (preferred method) or refer-
ence the Performance Data Capacity Tables found in the Multi F outdoor unit section in this manual. All design temperatures are not explicitly
shown in the charts, therefore, interpolation may be necessary to calculate the capacity for specific design conditions. Based on the premise
that capacity follows a linear curve, the following formula can be applied:
(y - y1) / (y2 - y1) = (x - x1) / (x2 - x1)
Where
y = Missing Capacity (Capacity at the Design Temperature).
1
y1 = Capacity at Lower Temperature (Smaller value of the two nearest published TC datapoints).
y2 = Capacity at Higher Temperature (Higher value of the two nearest published TC datapoints).
x = Design Temperature (Temperature not shown in published capacity tables).
2
x1 = (Smaller value of the two nearest published temperature datapoints).
x2 = (Larger value of the two nearest published temperature datapoints).
1
Median between two published Total Capacity [TC] Btu/h datapoints in the capacity table.
2
Median between two nearest published temperature datapoints.
EQUIPMENT SELECTION PROCEDURE
Using the Indoor Unit Cooling and Heating Capacity Tables
The datapoints shown in the indoor unit cooling and heating capacity charts are based on (and convey) an indoor unit operating with maxi-
mum possible refrigerant flow from the outdoor unit and before any derates are applied. In other words, the capacities displayed reflect what
the indoor unit would produce if it was the only indoor unit that required capacity, and the outdoor unit did not have to allocate any capacity to
another indoor unit.
System operation with a combination of indoor units is not conveyed in these charts, however, the information can be used to calculate
indoor unit allocated capacity (without using the system combination tables). Simply calculate by using the formula:
Where
Qidu(combi) = Qodu(rated) x Qidu(rated)
   ΣQidu(rated)
• The formula can be used to find individual indoor unit capacity for Multi F MAX systems.
• A more accurate method to determine expected capacity would be to apply the outdoor unit’s corrected capacity instead of rated
capacity.
Qidu(combi) = Individual Indoor Unit Combination Capacity.
Qodu(rated) = Outdoor Unit Rated Capacity.
Qidu(rated) = Individual Indoor Unit Rated Capacity.
ΣQidu(rated) = Total Connected Indoor Unit Rated Capacity.
Outdoor Units
LMU18CHV LMU24CHV LMU36CHV LMU540HV
Rated Capacity (Btu/h)
Cooling 15,600 19,200 34,000 52,500
Heating 17,000 26,400 41,000 58,000
Connectable Indoor
Units
Minimum No. of Connectable Indoor Units 2 2 2 2
Maximum No. of Connectable Indoor Units 2 3 4 8
Maximum Capacity Index 24,000 33,000 48,000 73,000
Table 98: Rated Outdoor Unit Capacity.
Due to our policy of continuous product innovation, some specications may change without notication.
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176 | APPLICATION GUIDELINES
Multi F and Multi F MAX Indoor Unit Engineering Manual
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