Unit Selection - Modine Manufacturing DBP Installation And Service Manual

unit selection

selection Procedure
In order to properly select an indirect-fired heating, ventilating,
cooling or make-up air unit, it is necessary to have the following
basic information.
1. required air handling capacity (cfm).
The air capacity of the unit is usually determined by the
ventilation air requirements, exhaust load of the building,
infiltration losses, or the air turns/changes of the space.
2. outdoor and indoor design temperature.
The outdoor design temperature is determined by using
the ASHRAE Guide design temperatures for the city where
the equipment is to be installed. For heating and ventilating
units, the desired room temperature would be used as the
indoor design temperature. In the case of 100% make-up
air units, the discharge air temperature should be at least
equal to the temperature of the air being exhausted.
3. required heating output capacity (Btu/Hr).
The heating output capacity of the unit is determined by
using the formula:
BTU/HR = CFM x Temp. Rise (°F) x 1.08
4. external static pressure to unit.
The external static pressure (E.S.P.) is determined using
the ASHRAE Guide for duct losses, or may be provided by
the design engineer.
5. unit configuration with options and accessories
(filters or dampers).
The unit configuration is determined by the location
where the unit is to be installed. The critical options and
accessories are those that add internal static pressure
(I.S.P.) to the unit. Once these items are determined, the
pressure drop curves would be used to calculate the total
pressure drop (T.S.P.)
Total Static Pressure = Internal + External Static Pressure
6. 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 unit is installed downstream of a
cooling coil or evaporative cooler, and when the combined
entering/return air to the unit is below 40°F.
7. type of fuel.
Either natural or propane gas determined by the design
engineer.
8. gas control staging method.
Either single stage, two stage, mechanical modulation, or
electronic modulation determined by the design engineer.
9. main power supply voltage to unit.
10. altitude at which unit is to be installed.
With this information a basic unit can be selected as shown in
the following example.
28
selection example conditions
Select an indirect-fired, 100% make-up air unit to meet the
following conditions:
1. CFM at sea level = 5,000 cfm
2. Outdoor design temp. = 10°F
Indoor design temp. = 70°F
3. Heating output capacity =
5000 cfm x (70°F -10°F) x 1.08 = 324,000 Btu/Hr
4. External Static Pressure = 0.65
5. The unit with the controls on the Right Hand Side is to be
provided with the following:
2" Permanent Filters, and Fresh Air Damper.
6. Heat exchanger and burner = 409 Stainless Steel.
7. Gas Type = Natural
8. Gas Controls = Electronic Modulating with Duct Sensing.
9. Supply Voltage: 460V/60Hz/3Ph
10. Altitude: 1000 feet
With the information listed above, the basic model, using the
Model Nomenclature shown on page 55, can be selected as
shown in the following example:
1. determine the model configuration and venting:
The Model Configuration is determined by the required
sections of the unit (Blower only) and the venting style
(power vented) that are obtained from item #5. Using the
Model Nomenclature on page 55, the Model Configuration
and Venting = DBP.
2. determine the furnace input rating (mBH):
Using the Heating output capacity, the Furnace Input
Rating is determined from Table 26.1. The closest model
to 324,000 Btu/Hr output has an Btu/Hr Input rating of
400,000 Btu/Hr so the Furnace Input Rating = 400.
3. determine the Heat exchanger/Burner/drip Pan
material:
From item #2 in Selection Example Conditions, the Heat
Exchanger and Burner required are 409 Stainless Steel.
Because the Drip Pan material is not specified, the standard
Aluminized Steel drip pan will be used. Thus, the Heat
Exchanger/Burner/Drip Pan Material = S.
4. determine the development sequence:
From item #8 in Selection Example Conditions, the
modulating gas controls result in the Development
Sequence = M.
5. determine the access side:
From item #5 in Selection Example Conditions, the Right
Hand Gas controls result in the Access Side = R.
6. determine the air temperature rise:
From item #2 in Selection Example Conditions, the Air
Temperature Rise is 60°F (70°F - 10°F). However, using the
output capacity of the DBP400 @ 5000 cfm, the resulting
temperature rise is 59.3°F (320,000/(5000 x 1.08)). Since
the rise is less than 60°F, the air baffle must remain in place.
7. determine the gas type:
From item #7 in Selection Example Conditions, the Natural
Gas results in the Gas Type = N.
8. determine the gas valve:
From item #8 in Selection Example Conditions, the
Electronic Modulating with Duct Sensing results in the Gas
Valve = 4.
9. determine the additional safety switches:
Since no additional safety switches were specified, the
Additional Safety Switches = 0.
5-565.1