Sample Specification
H Series
Refrigerated Compressed Air Dryers
General
Vendor shall supply one packaged, fully assembled refrigerated type dryer. Dryer is to be complete with: heat exchangers, separator,
automatic condensate drains and interconnecting piping, and a refrigeration system and controls completely wired, piped and mounted on
a structural steel frame ready for start-up after utility connections are made. (Air-cooled models with remote condensers will require
refrigeration and electrical connections at site.)
Description
An air-to-air heat exchanger shall be provided so that half of the heat load in the incoming air is removed by the outgoing air, minimizing
refrigeration capacity and energy requirements. The heat exchanger shall be a shell and tube type with extended surfaces on the outside
of the tubes and smooth surfaces on the inside. Inlet air is to be routed through the tubes where a combination of moisture condensation
and twisted tape turbulence enhancers increases the heat transfer coefficient. The increased heat transfer coefficient inside the tubes
balances the extended surface on the outside of the tubes, increasing heat exchanger efficiency and minimizing pressure drop. Turbulence
enhancers shall resist fouling and are to be removable so that tube cleaning, if necessary, can be accomplished. A prefilter shall not be
required upstream of the dryer. Dry, filtered outlet air is routed on the shell side to take advantage of the extended surface without threat
of fouling.
The air-to-refrigerant heat exchanger shall be a shell and tube type with removable heads. Refrigerant is to be routed in multiple passes
on the tube side. Cross sectional area of the tubes is to be varied (smaller where the refrigerant is mostly a liquid, greater where it is a gas)
to increase the velocity of the refrigerant through the heat exchanger and ensure quick response to changing loads. Twisted tape turbulence
enhancers shall be used in gas phase passes to promote refrigerant droplet evaporation. Removable heads are to be baffled, flat head
style to minimize oil or liquid refrigerant accumulation.
The separator/filter shall be of the filter cartridge type in a top access pressure vessel. Vessel internals are to be painted. Filter cartridges
shall contain two stages. The first stage is to be a cleanable, stainless steel separator core for removal of bulk liquids. The second stage
is to be a replaceable coalescing type filter sleeve capable of collecting all droplets three microns in size and larger and maintaining this
high efficiency at reduced flows. Efficient liquid removal prevents an increase in the outlet dew point by preventing liquid carryover and reevaporation. The second stage shall also act as an in-depth filter media capturing all solid particles three microns in size and larger.
All pressure vessels shall be built and stamped in accordance with the ASME boiler and pressure vessel code. Interconnecting piping
is to be welded by ASME qualified welders and is to be hydrostatically tested as a complete assembly with all other pressure vessels
attached, per that code. Heat exchangers, separator and interconnecting piping shall be fully insulated and the insulation protected with
a durable shroud.
The dryer is to be supplied with three, rebuildable automatic condensate drains. One drain is supplied for each heat exchanger and
one for the separator. Drains are to discharge automatically and are to be routed to a common piping connection at the frame edge. Each
drain is to be supplied with an isolation valve.
A non-cycling, direct expansion refrigeration system shall be supplied and include Copeland semi-hermetic, direct coupled, suction gas
cooled refrigeration compressor(s) with oil pressure pump, oil strainer and oil sight glass (one compressor, 7.5 through 40 HP; two
compressors, 50 HP and larger).
The control system shall allow automatic and continuous operation at all load conditions from zero (0%) load to full (100%) load while
tolerating large load swings, in the specified ambient range, without adjustment. Outlet dew point shall be maintained at ± 3°F (± 1.7°C)
within the specified pressure dew point at all loads. A three valve control system shall be supplied and include: a hot gas by-pass valve
to control pressure in the evaporator; a thermal expansion valve (TXV) to control superheat; and a liquid injection (desuperheating) valve
to control the return gas temperature. Control valves shall be preceded by a strainer and are serviceable without removing valve bodies
from the line.
By-pass gas shall be routed into the suction piping downstream of the evaporator. This enables a constant evaporator temperature to
be maintained by preventing interference with TXV heat load control. It also prevents refrigerant floodback at low loads. Units with 20 HP
and larger condensing units shall be supplied with compressor unloaders that work in conjunction with the hot gas by-pass valve to control
evaporator pressure.
A PLC (programmable logic control) shall be provided to: monitor all critical operating conditions; indicate operating status and fault
conditions; protect compressor from adverse operating conditions; stage compressor unloaders; and set message flags and alarm contacts.
Control functions shall include: monitoring refrigerant head and suction pressures and compressor oil pressure and shutting off the
compressor if a fault condition occurs; monitoring refrigerant suction pressure and staging compressor unloaders.
A back-lit LCD display shall be furnished and indicate: dryer operating mode and compressor status; inlet air, refrigerant suction and
refrigerant head pressures; power consumption (indicates approximate % on units supplied with unloaders); and fault messages for: high
and low refrigerant pressure, low oil pressure, high evaporator temperature, motor over-temperature, and motor starter open. An alarm
light and contacts for remote alarm shall be provided to indicate that a fault condition exists.
The control panel shall include: on/off and operating mode selector switches, power-on and general alarm lights and operator interface.
An equipment mounted inlet pressure gauge shall be provided.
To ensure refrigeration system reliability, the refrigeration system shall include: crankcase oil heater; sight glass with moisture indicator;
suction filter and liquid filter/dryer with replaceable cores; suction accumulator with blow out plug capable of holding one-half of the
refrigerant charge; and an automatic pump-down system to prevent liquid from slugging the compressor on start-up. Refrigeration lines
shall be sil-brazed, securely mounted, and isolated with vibration eliminators or loops. All cold lines shall be fully insulated. The refrigeration
system shall be charged with refrigerant, leak tested, and full load tested prior to delivery.
The electrical system shall be provided with an across-the-line, full voltage, magnetic motor starter. All wires shall be numbered,
terminated on a terminal strip, and enclosed in wiring trays. All electrical components are UL and CSA approved. Electrical construction
shall be NEMA 4.
For serviceability, dryer shall be supplied with: manual isolation valves on hot gas by-pass and liquid lines; high and low side service taps;
refrigerant sight glasses with moisture indicators; and an oil sight glass.
Performance Statement
Dryer shall be capable of drying ____________ scfm (m3/min, m3/h) of ____________ compressed air (gas, other) to a pressure dew
point of _________ °F (°C) at inlet conditions of _________ psig (kgf/cm2) and _________ °F (°C) (saturated) and the dryer condenser
operating
Water-cooled models:
with ____________ °F (°C) _____________ cooling water (glycol solution, other).
or
Air-cooled models:
in a _____________ °F (°C) maximum ambient temperature.
At the above conditions the pressure drop across the dryer shall be no greater than ____________ psid (kgf/cm2).
HCS-H
7/97
®
INTERNATIONAL
Division Of Hansen Inc.
Canonsburg, PA 15317-1700 U.S.A.
Tel 724-745-1555 Fax 724-745-6040
sales@hankisonintl.com