browse

| Overview

As the name suggests, a 2-pipe fan coil unit comprises 2 pipes, allowing water supply with a fan that runs air over it. The air is further conditioned by the running water. The thermostat only has control over whether to turn on the fan and at what speed. The building's central plant determines whether the pipes are getting hot or cold water. As such, turning on the fan when the building is providing hot water and the current temp is above the desired temp is counterproductive.

A coil fed by 1 pair of supply pipes provides heating or cooling. The correct mode is based on sensing supply water temperature.

| How it Works

The 75F SmartStat 2 Pipe Fan Coil unit is a unique profile, that provides both heating and cooling conditioning.

Based on the conditioning and fan modes the system is in, and the temperature of the supply water from the chiller, the heating, and cooling operations are triggered, and the corresponding actions and conditioning are achieved. 

The reheat capability is enabled with the auxiliary heating stage, which is only triggered during the Auto and Heat Only mode (where additional heat is required).

  • 3 Stage Fan Speed Control
  • Single Stage auxiliary heating equipment control
  • Single-stage water valve control
  • 2 Thermistor inputs connecting to Airflow Temperature Sensor & Supply Water Temperature
  • Occupancy Sensing Control

Additionally, it also supports the Auto Force Occupied and Auto-Away occupancy-based controls. 

| Application of Deadband and Hysteresis

The diagrams below show the application of the Deadband and Hysteresis Band and their role:

12.png

13.png

| Wiring Diagram

mceclip0.png

| Configuration

  • Select the SmartStat option from the device screen.

4.jpg

  • Select 2 Pipe FCU from the module type.

17.jpg

The pairing options are displayed on the screen which provides the steps to successfully pair the device.

  • Click Pair to start the pairing.

7.JPG

  • Select the displayed Bluetooth address.

8.JPG

  • Enter the PIN displayed on the device and press Pair.

9.JPG

You can see the configuration screen for the 2 PIPE FCU with the following options available for configuration.

10.jpg

Note: The water valve control option and the supply water temperature are enabled by default, since they are the major actors in influencing the algorithm.

| Configuration Parameters

Once the SmartStat is paired as a 2 Pipe Fan Coil profile, you will need to enable the required configuration parameters as below, which define the physical characteristics of the device.

Parameters Usage/Purpose/Trigger
Fan Medium Speed Activated when space temp is 2 degrees less or 2 degrees more from the heating or cooling desired setpoint respectively
Fan High Speed Activated when space temp is 3 degrees less or 3 degrees more from the heating or cooling desired setpoint respectively
Fan Low Speed Activated when space temp is 1 degree less or 1 degree more from the heating or cooling desired setpoint respectively
Aux Heating Stage 1 Activated when the central plant is in cooling, but this particular zone is below the setpoint. 
Water Valve Controls the water valve to keep the zone close to the setpoint. 
Airflow Temperature Sensor Only select if using an airflow sensor. These are helpful for troubleshooting. 
Supply Water Sensor Required for gauging the supply water temperature. 
Enable Occupancy Setting Select if you would like to use the Occupancy Setting for setpoint control.   
  • Enable the required parameters as below.

11.jpg

  • Click Set to confirm the parameters configured.

| Post Configuration

The zones paired with 2PIPE FCU profile is displayed in the CCU as below.

21.jpg

 

Below are widgets configured in the heatmap pages in the portals.

 

22.jpg

23.jpg

The user is also provided with profile reconfiguration options from the Internal portal as shown below, with all the features and capabilities that were available in CCU as explained in the above sections. 

24.JPG

 

| Fan Modes

 2 Pipe FCU profile supports the following fan and conditioning modes.

  • Off
  • Auto
  • Fan Low Current Occupied Period [From hardware changed]
  • Fan Low Occupied Period
  • Fan Low All Times
  • Fan Medium Current Occupied Period [From hardware changed]
  • Fan Medium Occupied Period
  • Fan Medium All Times
  • Fan High Current Occupied Period [From hardware changed]
  • Fan High Occupied Period
  • Fan High All Times

mceclip0.png

Note: The SmartStat hardware supports only the following fan modes at its end.

And when a change is made, it would translate to the following in the CCU.

  • Auto------ Auto
  • Low------Fan Low Current Occupied Period
  • Medium-------Fan Medium Current Occupied Period
  • High-------Fan High Current Occupied Period 

| Conditioning Modes

  • Off
  • Auto
  • Cool Only 
  • Heat Only

mceclip1.png

| Thermistor Inputs for 2 Pipe FCU Profile

The Th2 or the supply water temperature sensing for chilled/hot temperature is used to determine the mode the system needs to operate.

A predefined set of values are set for the cooling and heating threshold using the relevant tuners for the 2 Pipe FCU profile, and the sensed Th2 value is compared with the threshold values set earlier. Based on whether the sensed Th2 value is less than or greater than the threshold values, the modes of operation are triggered.

The Th2 input (Supply Water Temperature) plays a crucial role in determining the functionality of the profile for further initiating several modes for the 2 Pipe FCU profile. 

| Modes of Operation Based on Th2 Input and User Intents

Let us consider the multiple working modes of operation available under the 2 Pipe FCU Profile.

Mode Operations
Off Mode All relays associated with multiple inputs will be non-functional and set OFF
Heat Only Operation
  • Auxillary heating control is deactivated.
  • Water control is deactivated (Fan mode is off) 

If

Then

Th2 is more than the '2-pipe Fancoil Heating Threshold'(85) 

(Central plant provides   hot water)       

  • Fan stages activate when the current temperature is less than the desired temperature.
  • The Fan low, medium, and high activate when the current temperature is 1F, 2F, and 3F, less than the heating desired temperature respectively.
  • Fan stages (Low, medium, and High) deactivate when the current temperature is 0.5F, 1F, and 2F, less than the desired temperature.
  • Water valve activates when the current temperature is 1F less than the heating desired temperature.

Th2 is less than the '2-pipe Fancoil Cooling Threshold'(65)

(Central plant provides   cold water) 

  • Fan stages deactivate if the fan mode is Auto. Else the fan stages activate as per the user-specified fan speeds.
  • Water valve control is deactivated. 

Th2 is => '2-pipe Fancoil Cooling Threshold'(65) and <=  '2-pipe Fancoil Heating Threshold'(85) 

 

  • Water valve control activates and periodically cycles water for a predefined time period.
  • Fan stages deactivate if the fan mode is Auto. Else the fan stages activate as per the user-specified fan speeds.
Cool Only Operation
  • Auxillary heating control is deactivated (if fan mode is off).
  • Water control is deactivated (if fan mode is off)

If

Then

Th2 is more than the '2-pipe Fancoil Heating Threshold'(85) 

(Central plant provides   hot water)       

  • Water valve control is deactivated.
  • Auxillary heating control is deactivated.
  • Fan stages activate as per the user-specified fan speeds (If fan mode is not auto)

Th2 is less than the '2-pipe Fancoil Cooling Threshold'(65)

(Central plant provides   cold water) 

  • Fan stages activate when the current temperature is more than the cooling desired temperature.
  • The Fan low, medium, and high activate when the current temperature is 1F, 2F, and 3F, more than the cooling desired temperature.
  • Fan stages (Low, medium, and High) deactivate when the current temperature is 0.5F, 1F, and 2F, more than the desired temperature.
  • Water valve control activates when the current temperature is at least 1F more than the desired temperature. and deactivates when the current temperature is 0.5F more than the desired temperature.
  • Auxiliary heating control is deactivated.

Th2 is => '2-pipe Fancoil Cooling Threshold'(65) and <=  '2-pipe Fancoil Heating Threshold'(85) 

 

  • Water valve control activates and periodically cycles water for a predefined time period.
  • Auxillary heating control deactivates.
  • Fan stages deactivate if the fan mode is Auto. Else the fan stages activate as per the user-specified fan speeds.
Auto Mode

 

If

Then

Th2 is more than the '2-pipe Fancoil Heating Threshold'(85) 

(Central plant provides   hotheat-only     

 Operates as in heat-only mode.

 

Th2 is less than the '2-pipe Fancoil Cooling Threshold'(65)

(Central plant provides   cold water) 

Operates the relays as in cool-only mode.

 

Th2 is => '2-pipe Fancoil Cooling Threshold'(65) and <=  '2-pipe Fancoil Heating Threshold'(85) 

 

 

  • Water valve control activates and periodically cycles water for a predefined time period.
  • Fan stages and Auxillary heating controls deactivate.

 

| Equip Graphics for Smartstat 2Pipe

Equipment graphics is available for all the terminal profiles. It provides a graphical representation of system-level equipment and enables monitoring of key point parameters associated with terminal profiles.

Smartstat 2 Pipe.png

The highlighted list of points is predefined for visualization alongside the graphic for the respective profile.

 

Previous
Next

Comments

0 comments

Please sign in to leave a comment.

Was this article helpful?

0 out of 0 found this helpful
Powered by Zendesk