Trane Performance Air Handlers Manual de instalación descargar pdf (Pagina 83)

100

CAH-SVX01B-EN 83

Start-Up

Trane air handlers use a 0-20 inch range transmitter as standard. To sufficiently cover VAV turndown

on the smallest fans with the above range, a transmitter with an accuracy of 0.25 percent (full scale)

is used as standard. If a field-provided transmitter with a lower accuracy is selected, the range

should be chosen closer to the actual, maximum pressure differential expected for the application.

The transmitter outputs a signal that represents the differential pressure which is used to calculate

airflow. To adequately calculate and display the airflow for the smaller fans, ensure that the analog

input is programmed with enough decimal places to sufficiently represent the pressure differential

being measured. For instance, Rover should be used to increase the number of decimal places

being used (to a maximum of 4) on an MP-580/581 controller in lieu of the default zero.

Note that the adjustment of the “Zero” and “Span” controls on the transmitter itself are not

required at time of installation. The transmitter is factory-calibrated to the range selected and

cannot be significantly adjusted to “tighten” the range closer to the pressure being read for the

given application. The adjustments are primarily provided to account for any drift that may occur

over time.

Transmitter Calibration

The transmitter is factory-calibrated to a specific pressure range with a 0-20 inch w.g. range being

used in most cases. To check calibration and to adjust if necessary, consult the transmitter

manufacturer or the factory for specific procedures.

The transmitter outputs a linear, 4-20 mA signal representing a differential pressure measurement.

With this measurement, the airflow through the fan can be calculated using the following equation:

Constant Factor K

The constant factor K is unique for each fan and is primarily a function of the area and the geometry

of the fan inlet. Pre-engineered factors are available from the factory for fan types where the airflow

measurement system is available.

Field-obtained factors can provide maximum accuracy. To obtain the factor in the field, measure

the differential pressure being output from the transmitter while measuring the airflow through the

system. Once these two values have been measured, simply solve for K using the following

equation:

CFM = K * SQRT(DP)

Where:

CFM = Airflow (ft

/min.) assuming a standard air density of 0.075 lbm/ft

K = A constant factor that’s unique for each fan. See next section for more information.

DP = Differential pressure (inches w.g.) being measured by the transmitter.

Significant differences in elevation and/or temperature will affect the density of air. For air at

a constant, non-standard density, a field-obtained K factor can be used. Alternatively, the

following equation can be used to continuously correct the equation above:

ACFM = CFM * SQRT(0.075/ρ)

Where:

ACFM = Actual airflow (ft

/min) corrected for non-standard air density.

ρ = Density (lbm/ft

) of the air at the inlet to the fan.

Note: Alternative units, including SI, can be used in place of the IP units above although the

K-factor must be converted appropriately.

K = ACFM/SQRT(DP)

Where:

K = Field-provided constant factor.

ACFM = Actual airflow (ft

/min) being measured at the air density being measured.

DP = Differential pressure (inches w.g.) being measured by the transmitter.

1 2 ... 78 79 80 81 82 83 84 85 86 87 88 ... 99 100

Comentarios a estos manuales

Sin comentarios

Trane Performance Air Handlers Manual de instalación Pagina 83

Comentarios a estos manuales

Relacionado con productos y manuales para Acondicionadores de aire del sistema de división Trane Performance Air Handlers