Emerson Fluid Chiller Guía para resolver problemas descargar pdf (Pagina 45)

Regulators

Emerson Climate Technologies

HP Parallel Piping

Hot Gas Bypass

Demand continues to mount for improved comfort

conditioning combined with lower operating costs. New

architectural designs have created real problems for

contractors and engineers to maintain humidity con-

trol at reduced loads, and to control load variations.

Refrigeration and air conditioning systems are usu-

ally designed to provide a given capacity at maximum

conditions. These operate with little uctuation through-

out a narrow load range. However, only the larger size

machines make any provisions for operation at reduced

capacity. In some systems, integral cylinder unloading,

gas engine drives with variable speed control, or even

several smaller systems, provide a logical solution.

Function – Hot Gas Bypass Method

Many manufacturers now recommend use of a

modulating control valve to provide a metered ow of

compressor discharge gas to the system low side, in a

proportion that will balance the system capacity to the

load demand. This is commonly known as the hot gas

bypass method. It permits full modulation of capacity

on all types of reciprocating compressors, and extends

capacity reduction below the last step of cylinder unload-

ing.

The system must provide a means of bypassing high

pressure refrigerant to the system low pressure side, to

maintain operation at a given minimum suction pres-

sure. Proper bypass control can be accomplished by a

modulating type pressure regulator, which opens on a

decrease in valve outlet pressure.

Operation of Bypass Valves

Bypass pressure regulators are grouped into the fol-

lowing categories:

1. Direct acting conventional port valves (gure 3)

2. Direct acting balanced port valves (gure 4). Any of

these regulators are available with either an adjust-

able setting, or a xed, non adjustable setting.

Figure 4: Balance port CPHE adjustable eld-serviceable

hot gas bypass regulator.

Additional Refrigerant

On most systems, an added refrigerant charge will be

required. It is essential to have enough to completely ll

the condenser for the lowest ambient condition. To accu-

rately determine the added refrigerant charge required

to ll the condenser, nd the total length of condenser

tubing in feet, and multiply by pounds of refrigerant per

foot for a given size tubing.

Factory Settings

The HeadMaster Control is factory-set to provide

an average condensing temperature consistent with

good system performance. The complete type number

includes the service reference code, port size, connec-

tion size and style. When ordering, be sure to specify

the complete type number.

UL File No. SA5312

CSA File No. LR44005

Figure 3: DGRE adjustable hot gas bypass regulator.

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