Servicios de Red inteligente, Tarificación adicional y Números cortos

5 8 1

where: A = damper opening (sq Et)

= maximum air quantity thru bypass

h design pressure drop (in. wg) thru bypassed equipment

Temperature control with bypassed air is

with either a face and bypass damper or a bypass damper alone. However, the face and bypass damper arrangement is recommended, since the bypass area becomes very large, and it is difficult to accommodate the required air flow thru the bypass at small partial loads. Even where a con-trolled face and bypass damper is used, leakage ap-proaching of design air quantity passes thru the face damper when the face damper is closed.

This air quantity normally is, included when the fan is selected.

See for systems having a variable air flow to determine fan selection and brake horsepower requirements.

FANS

Properly designed approaches and discharges from fans are required for rated fan performance

ir to minimizing noise 6

indicate several possible layouts for varying degrees of fan performance. In addition, these fig-ures indicate recommended location of double width fans in plenums.

Fans in basement locations require vibration iso-lation based on the blade frequency. Usually cork or rubber isolators are satisfactory for this service.

On upper floor locations, however, spring mounted concrete bases designed to absorb the lowest natural frequency are recommended.

The importance of controlling sound and vibra-tion cannot be overstressed, particularly on upper floors. The number of fans involved in one location and the horsepower required for these fans directly determines the quality of sound and vibration con-trol needed.

Small direct connected fans, due to

oper-ating speed, are generally by

rubber or cork.

In addition, all types fans must have

connections to discharge ductwork and, where must have flexible connections to the in-take ductwork. Details of a flexible connection arc shown in Fig. 8.

Unitary equipment should be located near col-umns or main beams to limit the floor tion. Rubber or cork properly loaded usually gives the required deflection for efficient operation.

FAN MOTOR AND DRIVE

A proper motor and drive selection aids in long life and minimum service requirements. Direct drive fans are normally used on applications where exact air quantities are not required, because ample energy (steam or hot water, etc.) is available at more than enough temperature difference to compensate for any lack of air quantity that exists. This ap-plies, for example, to a unit heater application.

Direct drive fans are also used on applications where system resistance can be accurately determined.

However, most air conditioning applications use belt drives.

V-belts must be applied in matched sets and used on balanced sheaves to minimize vibration prob-lems and to assure long life. They are particularly useful on applications where adjustments may be required to obtain more exact air quantities. These adjustments can be accomplished by varying the pitch diameter on adjustable sheaves, or by changing one or both sheaves on a fixed sheave drive.

Belt guards are required for safety on all V-belt drives, and coupling guards are required for direct drive equipment. Figure 9 illustrates a two-piece belt guard.

The fan motor must be selected for the maximum anticipated brake horsepower requirements of the fan. The motor must be large enough to operate within its rated horsepower capacity. Since the fan motor runs continuously, the normal over-load allowed by should be reserved for drive losses and reductions in line voltages. Normal torque motors are used for fan duty.

APPARATUS CASING

The apparatus casing on central station equip-ment must be designed to avoid restrictions in air flow. In addition, it must have adequate strength to prevent collapse or bowing under maximum oper- , ating conditions.

‘ I O N

SINGLE INLET FAN SINGLE INLET FAN

NOTES

P L A N V I E W P L A N V I E W

- F

1

NOTE 3 E L E V A T I O N V I E W E L E V A T I O N V I E W D I M E N S I O N S :

DOUBLE INLET FAN

NOTES

P L A N V I E W

ELEVATION VIEW (SECTION)

DIAMETER OF FAN INLET E MAXIMUM PREFERRED

X C

. F 36” MINIMUM FOR ACCESS DOOR

I N L E T C O N N E C T I O N S

B E S T G O O D

T R A N S F O R M A T I O N I N 7 ” P R E F E R R E D , IN 4” PERMITTED NOTE 68 7

D I M E N S I O N S : TO

F A N D I S C H A R G E O P E N I N G , L A R G E S T D I M E N S I O N

D I S C H A R G E C O N N E C T I O N S

NOTES:

Fan should be centered in casing to provide good flow 5. Use square elbow for best results, with take-off

conditions. in opposite direction to fan rotation.

2. All equipment should be centered for best performance. G. Slope of 1” in 4” recommended for low velocity.

Angle is used to determine distance between 7. Slope of 1” in 7” recommended for high velocity.

equipment and fan.

4 . m i n i m u m . V a n e s p a c i n g d e t e r m i n e d f r o m Chart 6.

FIG. AND

TYPICAL VANE LOCATION

NOTE I

I

NOTE I

NO

FROM CHART 6. VANE SPACING

A T O

B LONGEST DIMENSION OF OUTLET OPENING

NOTES:

1. Transformations to supply duct have maximum slope of 3. Do not install ducts so that the air flow is counter to

1” in 7”. fan roration. If necessary, turn fan section.

2 . S q u a r e e l b o w s w i t h d o u b l e t h i c k n e s s v a n e s m a y b e substituted.

4 . T r a n s f o r m a t i o n s a n d u n i t s s h a l l b e a d e q u a t e l y ported so no weight is on the flexible fan connection.

I” FLANGE AND HEM ALTERNATE

POSITION OF B O L T

IMPREGNATED FABRIC

20 U.S. GAGE STEEL

RECTANGULAR OUTLET)

SEALING COMPOUND APPLIED

BETWEEN FLEXIBLE CONNECTION SHEET METAL SCREWS SEALING COMPOUND APPLIED

AND FAN BEFORE ASSEMBLY l ON 12” CENTERS BETWEEN FLEXIBLE CONNECTION

AND CASING BEFORE ASSEMBLY 5 ” F L A N G E

r

B A N D I R O N -\ -SEALING COMPOUND APPLIED BETWEEN FABRIC, BAND AND 18 US. GAGE STEEL, BEFORE ASSEMBLY *

*REQUIRED ON HIGH PRESSURE SYSTEMS ONLY,

( FA N

FLEXIBLE

SHEAVE SECTION A-A

DIMENSIONS REQUIRED FOR CONSTRUCTION

EXPANDED METAL AND

CENTER LINE OF SHEAVE AT

S T A R T U P

HEM REVERSED IN THIS SECTION

a s a

together, i n

or on 12 in. ken-perpendicular to air flow arc the casing. Side walls It roof over I t

mental reinforcing shown in Diagonal

braces in 1 I also

The rccommcntled construction of apparatus casings connections between equipment com-ponents (except when in the ducts) is 18 U.S. steel or aluminum.

in contact with galvanized at connections to spray type equipment requires that the inside of

casing with an isolating material for distance in. from the point of contact.

FIG. 10 APPARATUS CASING SEAMS