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VAV-PRC011M-EN 149
Application Considerations
Electric Reheat
Electric heating coils are applied on VAV terminal units as terminal reheat devices. Electric heat coil
capacity is rated in kilowatts (kW). Coils are available with the total capacity divided into one, two,
or three stages.
Electric heat coils are available in single-phase or three-phase models. This refers to the type of
power source connected to the coil. Single-phase models have resistance elements internally
connected in parallel. Three- phase models have resistance elements internally connected in a
delta or a wye configuration.
The current draw for the electric coil will depend upon whether it is a single-phase coil or a three-
phase coil. The current draw is necessary for determining what size wire should be used to power
the electric coils and how big the primary power fusing should be.
The equations for current draw for these coils are:
VariTrane three-phase electric heat is available in balanced configurations. For example, a 9 kW
three-phase coil, each stage would carry 1/3 or 3 kW of the load.
It is important to note that these coils have certain minimum airflow rates for each amount of kW
heat the coil can supply to operate safely. See Figure 29, p. 40 for minimum air flow rates by unit
inlet size and electric heat kW.
The equation that relates the airflow across an electric coil to the temperature rise and the coil
change in temperature is:
Where
CFM=Minimum airflow rate across the coil
kW=The heating capacity of the electric coil
3145=A constant
DP=The maximum rise in air temperature across the coil (usually 50 degrees F (28 degrees C))
Electric heat coils are available with magnetic or mercury contactors. Magnetic contactors are less
expensive than mercury contactors. However, mercury contactors can be cycled at a more rapid
rate without failing. Mercury contactors are rated for heavier duty use and should be used in as
many applications as possible. For pneumatic applications the electric coils are available with
factory-installed pressure-electric switches.
1φamps
kW 1000×
PrimaryVoltage
--------------------------------------------------
=
3φamps
kW 1000×
PrimaryVoltage 3
-----------------------------------------------------------
=
CFM
kW 3145×
ΔT
-------------------------------
=
- Product Catalog 1
- Introduction 2
- Table of Contents 3
- UC210 BACnet Controller 8
- UC400 BACnet Controller 8
- Air-Fi Wireless System 9
- Wireless Zone Sensor Set 9
- Pneumatic Controller 10
- Binary Input Controller 10
- Features and Benefits 11
- Agency Certifications 12
- Model Number Descriptions 14
- Selection Procedure 17
- General Data 19
- 20 VAV-PRC011M-EN 20
- Performance Data 21
- 22 VAV-PRC011M-EN 22
- VAV-PRC011M-EN 23 23
- 24 VAV-PRC011M-EN 24
- VAV-PRC011M-EN 25 25
- 26 VAV-PRC011M-EN 26
- VAV-PRC011M-EN 27 27
- 28 VAV-PRC011M-EN 28
- VAV-PRC011M-EN 29 29
- 30 VAV-PRC011M-EN 30
- VAV-PRC011M-EN 31 31
- 32 VAV-PRC011M-EN 32
- VAV-PRC011M-EN 33 33
- 34 VAV-PRC011M-EN 34
- VAV-PRC011M-EN 35 35
- 36 VAV-PRC011M-EN 36
- VAV-PRC011M-EN 37 37
- 38 VAV-PRC011M-EN 38
- Electrical Data 39
- 40 VAV-PRC011M-EN 40
- VAV-PRC011M-EN 41 41
- 42 VAV-PRC011M-EN 42
- VAV-PRC011M-EN 43 43
- 44 VAV-PRC011M-EN 44
- VAV-PRC011M-EN 45 45
- 46 VAV-PRC011M-EN 46
- VAV-PRC011M-EN 47 47
- 48 VAV-PRC011M-EN 48
- VAV-PRC011M-EN 49 49
- 50 VAV-PRC011M-EN 50
- Dimensional Data 51
- 52 VAV-PRC011M-EN 52
- VAV-PRC011M-EN 53 53
- 54 VAV-PRC011M-EN 54
- VAV-PRC011M-EN 55 55
- LEFT HAND RIGHT HAND 56
- VAV-PRC011M-EN 59 59
- Mechanical Specifications 60
- Outlet Conection 61
- Hot Water Coils 61
- Electric Heat Coils 61
- Electric Heat Options 61
- Direct Digitals Controls 62
- Control Options 63
- Hot Water Valves 63
- 64 VAV-PRC011M-EN 64
- Dual-Duct VAV Terminal Units 66
- Octave Band 234567NC 67
- Outlet Connection 77
- Direct Digital Controls 77
- Reliable Operation 80
- Safe Operation 80
- System-Level Optimization 80
- Simplified Installation 80
- Controller Flexibility 81
- Control Logic 81
- Space Temperature Control 82
- General Operation-Cooling 82
- Ventilation Control 84
- Flow Tracking Control 85
- General Features and Benefits 88
- ONMARK open protocol 94
- DDC Controls 100
- Air-Fi™ Wireless System 101
- Dimensions 102
- Specifications 102
- DDC Zone Sensor 104
- Wall Sensor and Duct CO 105
- DDC Zone Sensor with LCD 106
- Zone Occupancy Sensor 107
- Two-Position Water Valve 109
- Proportional Water Valve 110
- VAV Piping Package 111
- Transformers 113
- Trane Spring Return Actuator 115
- VariTrane™ DDC Retrofit Kit 116
- Retrofit Kit Actuator 116
- Static Pressure Controller 117
- Pneumatic Controls 121
- Pneumatic Damper Actuator 123
- Reversing Relay 123
- Signal Limiter 125
- VAV-PRC011M-EN 133 133
- Controls Specifications 134
- DDC Retrofit Kit (VRTO) 136
- Retrofit Kit Options 136
- Other Options Available 137
- Application Considerations 138
- Terminal Heat 139
- Dual-Duct Systems 139
- VariTrane VAV Terminal Units 140
- VAV Terminal Unit Types 140
- Fan-Pressure Optimization 141
- Ventilation Reset 141
- Control Types 142
- Pneumatic Control Systems 143
- Room Thermostats 144
- Pneumatic Volume Regulators 144
- Flow Measurement and Control 146
- Accuracy 147
- Air Density Effects 147
- Reheat Options 148
- Electric Reheat 149
- Insulation 150
- Acoustics 150
- Insulation types 151
- Placement of units 151
- Unit Attenuation 151
- Certification and Testing 152
- Duct Design 153
- Best Practices 154
- Unit Conversions 155
- VariTrac™ catalog 157
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