Brochure

18
6-189.9
UNIT SELECTION
Selection Procedure
In order to properly select a unit heater it is necessary to have the
following basic information.
1. Heating output capacity
Model size output is to be matched against the heat loss to be
replaced.
2. External static pressure (blower units only)
The external static pressure (E.S.P.) is determined using the
ASHRAE Guide for duct losses or provided by the design
engineer.
3. Accessory internal static pressure (Nozzles, transitions,
filters, etc.) (blower units only)
The critical accessories are those that add internal static
pressure (I.S.P.) to the unit. Once these items are determined,
the total pressure drop can be determined (if applicable).
4. Heat exchanger material
The heat exchanger type is determined by the application.
The standard heat exchanger material is aluminized steel.
A 409 stainless steel heat exchanger and burner is
recommended when the combined entering/return air to the
unit is below 40°F or in high humidity applications.
5. Type of fuel
Either natural or propane gas determined by the design
engineer.
6. Gas controls
Either single stage, two stage, or mechanical modulation as
determined by the design engineer.
7. Main power supply voltage to unit
8. Altitude at which unit is to be installed
With this information a basic unit can be selected as shown in the
following example.
Selection Example Conditions (Propeller Unit)
In the following example, select a unit heater to meet the following
conditions:
1. Heating output capacity = 156,000 Btu/Hr per design engineer
2. External Static Pressure = 0.0
3. Internal Static Pressure = 0.0. No static producing accessories
are required
4. Heat exchanger and burner = 409 Stainless Steel
5. Gas Type = Natural
6. Gas Controls = Single Stage Intermittent Pilot Ignition (IPI)
7. Supply Voltage: 460V/60Hz/3Ph
8. Altitude: 1,000 feet
Selection Example Solution (Propeller Unit)
With the information listed above, the basic model, using the
information in this catalog and the Model Nomenclature shown on
page 26, can be selected as shown in the following example:
1. Determine the Model and Input Rating (MBH):
Using the Heating output capacity, the Furnace Input Rating is
determined from Table 7.1. The closest model to 156,000
Btu/Hr output has an Btu/Hr Input rating of 200,000 Btu/Hr so the
Furnace Input Rating = 200. The corresponding model for a 200
size, propeller, power vented unit heater is PDP. The model and
size are a PDP200.
2. Determination of Heat Exchanger/Burner/Drip Pan Material:
From item #4 in the example, the Heat Exchanger and Burner
required are 409 Stainless Steel. Thus, the Heat Exchanger
Material = S from the Model Nomenclature on page 26. The
burner is an option placed on the order.
3. Determine the development sequence:
From item #6 in the example, the IPI results in the Development
Sequence = E from the Model Nomenclature on page 26.
4. Determine Power Code Required:
Referring to Table 7.2, it can be seen that the supply voltage
from the 7.2 example conditions is not available (460V). A
transformer kit selected later in this example must be used.
In this instance, from Table 7.2 select the 115V/60Hz/1Ph power
code (PC) = 01 unit.
5. Determine the control type:
From items #5 and #6 in the example conditions, the gas type is
Natural Gas and controls are single stage IPI. Given the supply
voltage listed from the example conditions (460V) and by
looking up the supply voltage of 460V/60Hz/3Ph in Table 14.2 for
propeller units, it directs us use to a unit voltage of 115V. We
then refer to Tables 14.1 and 14.2, locate the single-stage
options and select the appropriate Control Code (CC) of 30.
Remember a step-down transformer will be selected later in this
example.
At this point we have a full model number of:
PDP200SE0130SBAN
6. Determination of transformer:
To operate a 115V/60Hz/1Ph unit on 460V/60Hz/3Ph supply
power a unit step down transformer must be selected. By
referring to Table 14.1 we see that a 460V to 115V step down
transformer is required.
7. Altitude:
Since deration of gas fired unit heaters is only required for
units to be installed at 2,000 ft or greater, no high altitude kit is
required.
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