Product Brochure

16
6-175.7
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 (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 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 or two stage, as determined by the
design engineer.
7. Main power supply voltage to unit
Selection Example Conditions (Propeller Unit)
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
7. Supply Voltage: 460V/60Hz/3Ph
With the information listed above, the basic model, using the
information in this catalog and the Model Nomenclature shown
on page 23, can be selected as shown:
1. Determine the Model and Input Rating (MBH):
Using the Heating output capacity, the Furnace Input Rating
is determined from Table 6.1. 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, separated combustion unit heater is
PTS. The model and size are a PTS200.
2. Determination of Heat Exchanger Material:
From item #4 in the example, the Heat Exchanger required is
409 Stainless Steel. Thus, the Heat Exchanger Material = S
from the Model Nomenclature on page 23.
3. Determine the Ignition Type:
The Ignition Type = S from the Model Nomenclature on page 23.
4. Determine Power Code Required:
Referring to Table 6.2, it can be seen that the supply
voltage from the example conditions is not available (460V).
A transformer kit selected later in this example must be used.
In this instance, from Table 6.2 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. From Table
12.2, we are directed to use Control Code (CC) of 11.
6. Determine the fan guard type:
No specific type of fan guard was specified, so select Fan
Guard = S from the Model Nomenclature on page 23.
At this point we have a full model number of:
PTS200SS0111SBAN
7. 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 12.1 we see that a 460V to 115V step down
transformer is required. As noted in the footnote for Table 12.1,
the size can be determined to be 0.75kVA from Table 6.2.
Selection Example (Propeller Unit)