AEG CGA 75 WOK Specifications download pdf (Page 8)

UH-PRC002-EN8

Application

Considerations

natural gas is not available, Trane units

may be ordered directly from the factory

for use on LP (propane) gas.

Gas heat content varies by fuel type and

location. The standard gross heating

value for natural gas is 1,000 Btu per

cubic foot, and for propane, 2,500 Btu

per cubic foot. Significant variations

selections. To account for variations in

the gross heating value of the fuel, adjust

the total heat input required and select

the unit on the basis of the adjusted load

using the following formula:

Adjusted load = Calculated load x

gross heat value (Btu/cu ft)

Actual gross heat value (Btu/cu ft)

Low Temperature Rise

Trane recommends against the setup of

a unit which will result in a temperature

rise of less than 30°F. With such low

temperature rises, the flue gases passing

through the heat exchanger are cooled

to condensate before reaching the flue

outlet. This condensate is corrosive and

will result in shortened heat exchanger

life.

Air Density

Catalog performance data is based on

elevations up to 2,000 feet above sea

level. Above 2,000 feet the unit’s heating

capacity must be derated four percent

for each 1,000 feet above sea level, and

special orifice selections are required.

Table PAF-1 contains correction factors

that can be applied to the unit’s

cataloged heating capacity, fan rpm, and

fan bhp to obtain actual values for

elevations above 2,000 feet.

Corrosive Atmospheres

Corrosion of heat exchangers and draft

diverters have two basic variables –

moisture (condensation) and sulphur.

These two ingredients form to make

sulfuric acid in the combustion process.

Condensation occurs commonly in

makeup air systems, using large

amounts of fresh air, when air

temperatures entering the heat

exchanger drop to 40°F or below. This

reaction can also occur in recirculating

systems where some quantity of outside

air is introduced upstream of the

exchanger. The sulphur will always be

present as an integral component of the

gas. The resulting concentration of the

acid is governed by the amount of

sulphur in the gas. This concentration

varies from gas to gas and

geographically within the same type

of gas.

Beyond sulfuric acid corrosion there is

the area of chlorinated or halogenated

hydrocarbon vapor corrosion. This type

of corrosion occurs when substances are

mixed with combustion air that will

cause the formation of hydrochloric or

hydrofluoric acid when burned. These

basic substances are found in

degreasers, dry cleaning solvents, glues,

cements, paint removers and aerosol

propellants. Specific chemicals included

in this group are trichloroethylene,

perchloroethylene, carbon tetrachloride,

methylene chloride, methyl chloroform

and refrigerants 11, 12, 21, 22 and 114.

If sufficient PPM content of these

corrosives is present, none of the

common heat exchanger materials will

hold up. The dilemma becomes whether

to place the gas heating equipment

outside of the area to be conditioned, or

use equipment in the space which does

not burn a fuel such as gas (i.e. electric or

hydronic).

Units should not be installed in areas

with corrosive or inflammable

atmospheres. Locations containing

solvents or chlorinated hydrocarbons

will produce corrosive acids when

coming in contact with burner flames.

This reaction will greatly reduce the life

of the heat exchanger and may void the

warranty. For added protection against

heat exchanger corrosion, optional 409

and 321 stainless steel construction is

available. On units using outside air, with

entering air temperature below 40°F,

condensation of flue gas in the heat

exchanger is possible. In these cases,

stainless steel heat exchangers are

recommended.

Careful review of the job application with

respect to use, probable contaminants

within a conditioned space or the

amount of fresh air to be brought in, will

help to make the proper selection of heat

exchanger material. This review will help

to eliminate problems before they begin.

NOTE: When installing duct furnaces in

parallel or in series, minimum clearance

requirements must be considered. This is

required for serviceability of the gas

valve and the high limit. “All duct

furnaces are approved in blow-thru

applications only.”

All duct furnaces are AGA approved

upstream or downstream of the cooling

coil. Recommend optional field installed

drain pan when installed on the

downstream side of the cooling coil.

NOTE: Downstream denotes cooling coil

ahead of the fan section.

When used in conjunction with filters,

cooling coils and an air handler, the duct

furnace can become part of a built-up

heating and cooling system.

Gas Heating Value

The majority of gas heating units are

installed in applications where natural

gas is readily available. In areas where

General

Propeller fan unit heaters and centrifugal

fan unit heaters are designed for use in

space heating applications. The units are

typically used in areas with high ceilings,

and are exposed in the space to be

heated. Unit heaters offer low installed

cost, and are able to heat large volume

areas without requiring extensive duct

systems.

Duct furnaces are designed for use in

ducted applications with a separate air

handling device such as a horizontal

blower assembly. By utilizing a separate

air source, greater application flexibility

in airflow delivery can be obtained.

Multiple duct furnaces can be used with

an air handling unit to provide zone

heating.

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AEG CGA 75 WOK Specifications Page 8

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