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Due to our policy of continuous product innovation, some specications may change without notication.
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68 | PRODUCT DATA
Single Zone Vertical Air Handling Unit Engineering Manual
Equivalent Piping Length for Piping Components
Component Size (Inches)
Elbow (ft.)
1/4 3/8 1/2 5/8 3/4 7/8 1 1-1/8 1-1/4 1-3/8 1-1/2 1-5/8 1-3/4 2-1/8
0.5 0.6 0.7 0.8 1.2 1.3 1.5 1.6 1.8 2.0 2.1 2.3 2.5 2.8
Table 43: Equivalent Piping Length for Elbows.
Altitude Correction Factor
The impact of air density must be considered on systems installed at a significant altitude above sea level, therefore, locally accepted
altitude correction factors must be applied.
Table 44: Outdoor Unit Frost Accumulation Factor (Heating)
1
.
There will be a temporary reduction in capacity when frost / ice accumulates on the outside surface of the outdoor unit heat exchanger. The level of
capacity reduction depends on a number of factors, for example, outdoor temperature (°F DB), relative humidity (RH), and the amount of frost present.
Entering DB (ºF)
19.4 23.0 26.6 32.0 37.4 41.0 44.6
Derate factor
0.98 0.95 0.93 0.86 0.93 0.96 1.0
1
At 85% outdoor air relative humidity.
The frost accumulation factor does not account for effects of snow accumulation restricting airflow
through the outdoor unit coil.
Defrost Correction Factor for Heating Operation
The outdoor unit heating capacity may need to be adjusted for frost accumulation on air-cooled systems. If design day conditions are below
the dewpoint of the surrounding air, frost may not be a problem and no correction factor is needed. In certain weather conditions, however,
frost may form and accumulate on the air-cooled outdoor unit coil and impact the coils ability to transfer heat. If significant frost accumulates
on the outdoor unit coil, a defrost algorithm will start automatically. The timing between defrost periods is determined by the system’s ability
to achieve a target head pressure value.
Capacity and AHRI ratings tables do not factor in capacity reduction when frost has accumulated on the condenser coil, nor during defrost
operation.
Integrated heating capacity values can be obtained using the formula:
A = B x C
Where:
A = Integrated Heating Capacity.
B = Value found in the Capacity Table.
C = Correction Factor for Frost Accumulation Factor (from table at right).
Correction Factors
EQUIPMENT SELECTION PROCEDURE
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