Home TechTime July 2015 Whats the Difference
Download

Description: Description: NEP's iMac:Users:frederick:Desktop:TechTime July 2015 Banner.png

TechTime is a Neptronic publication aiming to inform you of common issues highlighted by our technical support team and the best way to deal with them. Each edition will contain three new topics and will be posted on neptronic.com.

Description: NEP's iMac:Users:frederick:Desktop:Suggest Topic.png

Description: Description: commun:Frédéric:Frédéric:Communications:TechTime:May 2015:Images:HVAC Controls Divider.png

What's the Difference?

2 Pipe vs 4 Pipe Fan Coil

There are many questions that arise when setting up a fan coil controller. Most of these interrogations come when setting up a TFC series controllers. While in the configuration of the TFC, one of the first settings asks if it is a 2 pipe or 4 pipe system.

 

In order to clarify the differences, we will expose these two concepts.

 

2 Pipe Fan Coil

 

 

Description: NEP's iMac:Users:frederick:Desktop:2 Pipe Fan Coil.png

 

 

The 2 pipe system consists of a single water coil connected to two pipes (supply and return) and one valvle that can serve as either chill water coil or hot water coil depending on the mode of the system. This type of fan coil cannot cool and heat at the same time and is dependent of the actual mode of the building.

 

The 2 pipe fan coil requires a changeover sensor, usually a strap-on temperature sensor installed on the water supply, to determine the mode of the system.

 

These units can be equiped with an auxiliary electric heater to compensate the limitations of the system.

 

 

4 Pipe Fan Coil

 

 

Description: NEP's iMac:Users:frederick:Desktop:4 Pipe Fan Coil.png

 

 

The 4 pipe system consists of two separate cooling and heating water coils. Each coil has its own dedicated set of pipes (supply and return) and valve. This type of fan coil can cool and heat at the same time and is not dependant of the actual mode of the building.

 

Contrarely to the 2 pipe system, the 4 pipe fan coil does not require a changeover sensor since both hot and chill water is available.

 

These units can be equiped with an auxiliary electric heater to boost the heating capacity (if required).

 

The 4 pipe fan coil can also use a chill water coil and an electric or gas heater. As long as the cooling and heating are independent of each other, the system will be a 4 pipe configuration.

 

 

Not all fan coils are equipped in this manner but the concept remains. The important thing to remember is that for a two pipe fan coil, a changeover sensor is required to determine the system mode (cooling or heating). In other words, the fan coil is dependent of the system mode. If cooling is available and no electric reheat coil is present, then the fan coil can only cool. If heating is available, no cooling is possible.

 

If no changeover sensor is required, this means that system falls automatically on the 4 pipe system. The 4 pipe system has two available sources (heating and cooling) which makes the fan coil independent of the system mode. Unlike to the 2 pipe system, it can cool and heat at the same time allowing for dehumidification to occur.

 

TFC/TFH series controller options

 

 

 

This is the configuration required when setting up an analog valve in a 2 pipe fan coil.

 

- AO1: Modulating valve

- AI2: Changeover sensor or switch

- TO1 & TO2 are not used

- AO2 is not used

This is the configuration required when setting up an On/Off valve in a 2 pipe fan coil.

 

- TO1: On/Off valve

- AI2: Changeover sensor or switch

- TO2 is not used

- AO1 & AO2 are not used

This is the configuration required when setting up an Floating valve in a 2 pipe fan coil.

 

- TO1 & TO2: Floating valve

- AI2: Changeover sensor or switch

- AO1 & AO2 are not used

 

2 Pipe

Analog

On/Off

Floating

Terminals

Fan option

analog

1 spd

2spd

3spd

analog

1 spd

2spd

3spd

analog

1 spd

2spd

3spd

TB1

1

Common

Common

Common

Common

2

24 VAC

24 Vac

24 Vac

24 Vac

3

Common Triac

Common Triac

Common Triac

Common Triac

4

Triac output 1 (TO1)

Floating output 1

-

2 Pipe on/off

2 Pipe floating (close)

5

Triac output 2 (TO2)

-

-                             

2 Pipe floating (open)

6

Triac output 3 (TO3) Reheat

Local reheat (optional) (on/off or pulse)

Local reheat (optional) (on/off or pulse)

Local reheat (optional) (on/off or pulse)

7

Common Relay

-

Common Relay

-

Common Relay

-

Common Relay

8

Digital output 1 (DO1)

-

-

-

High

-

-

-

High

-

-

-

High

9

Digital output 2 (DO2)

-

-

High

Med

-

-

High

Med

-

-

High

Med

10

Digital output 3 (DO3) /
Analog Fan Speed (AO4)

Fan analog

1 spd

Low

Low

Fan analog

1 spd

Low

Low

Fan analog

1 spd

Low

Low

11

Occupancy Sensor (DI1)

Occupancy Sensor (optional)

Occupancy Sensor (optional)

Occupancy Sensor (optional)

12

External Temp. Sensor (AI1)

External Temp. Sensor (optional)

External Temp. Sensor (optional)

External Temp. Sensor (optional)

13

External Changeover (AI2)

External Changeover

External Changeover

External Changeover

14

Analog output 1 (AO1)

2 Pipe analog

-

-

15

Analog output 2 (AO2)

-

-

-

16

Analog output 3 (AO3) Reheat

Local reheat analog (optional)

Local reheat analog (optional)

Local reheat analog (optional)

 

 

 

 

Since the cooling and heating are independent from each other, the 4 pipe fan coil allow the signals to be different as well. While in the configuration process, you are required to identify what signal is used for cooling and heating (Analog, On/Off or Pulse).

 

4 Pipe

Cool & Heat Analog

Cool & Heat On/Off

Cool Analog-Heat On/Off or pulse

Cool On/Off - Heat Analog

Terminals

Fan option

analog

1 spd

2 spd

3 spd

analog

1 spd

2 spd

3 spd

analog

1 spd

2 spd

3 spd

analog

1 spd

2 spd

3 spd

TB1

1

Common

Common

Common

Common

Common

2

24 Vac

24 Vac

24 Vac

24 Vac

24 Vac

3

Common Triac

Common Triac

Common Triac

Common Triac

Common Triac

4

Triac output 1 (TO1)

Floating output 1

-

4 Pipe on/off cool

-

4 Pipe on/off cool

5

Triac output 2 (TO2)

-

4 Pipe (on/off or pulse) heat

4 Pipe (on/off or pulse) heat

-

6

Triac output 3 (TO3) Reheat

Local reheat (optional) (on/off or pulse)

Local reheat (optional) (on/off or pulse)

Local reheat (optional) (on/off or pulse)

Local reheat (optional) (on/off or pulse)

7

Common Relay

-

Common Relay

-

Common Relay

-

Common Relay

-

Common Relay

8

Digital output 1 (DO1)

-

-

-

High

-

-

-

High

-

-

-

High

-

-

-

High

9

Digital output 2 (DO2)

-

-

High

Med

-

-

High

Med

-

-

High

Med

-

-

High

Med

10

Digital output 3 (DO3) / Analog Fan Speed (AO4)

Fan analog

1 spd

Low

Low

Fan analog

1 spd

Low

Low

Fan analog

1 spd

Low

Low

Fan analog

1 spd

Low

Low

11

Occupancy Sensor (DI1)

Occupancy Sensor (optional)

Occupancy Sensor (optional)

Occupancy Sensor (optional)

Occupancy Sensor (optional)

12

Ext. Temp Sensor (AI1)

External Temp. Sensor (optional)

External Temp. Sensor (optional)

External Temp. Sensor (optional)

External Temp. Sensor (optional)

13

External Changeover (AI2)

-

-

-

-

14

Analog output 1 (AO1)

4 Pipe analog cool

-

4 Pipe analog cool

-

15

Analog output 2 (AO2)

4 Pipe analog heat

-

-                                                    

4 Pipe analog heat

16

Analog output 3 (AO3) Reheat

Local reheat analog (optional)

Local reheat analog (optional)

Local reheat analog (optional)

Local reheat analog (optional)

 

You can look at the original instruction document here:

http://neptronic.com/Controls/PDF/TFC24F3XYZ1-121112.pdf

 

The EFC series controllers do not have this type of settings. To setup a 2 pipe fan coil, the Changeover Ramp (COR) must be used and a changeover sensor or switch must be installed and configured.

 

In conclusion;

2 pipe fan coil uses 1 water coil to heat or cool and is dependent of the system mode. It requires a changeover sensor or switch.

 

4 pipe fan coil have two distinct cooling and heating coils. It does not require a changeover sensor or switch. It is also independent from the system mode.

 

Description: Description: commun:Frédéric:Frédéric:Communications:TechTime:April 2015:Images:Faces:Patrick Lafrance Tech Bulletin Pic.png

Patrick Lafrance

Technical Support – HVAC Controls

Contact him at this email address patrick.lafrance@neptronic.com