The Tubeless Differential Pressure Measurement (TDPM) system replaces the physical tubes used in the industry with wireless communicating platforms to measure and derive differential pressure for building pressurization measurement and control. Designed to work with economizers, air handlers and exhaust/intake fans, the TDPM controls pressurization within the building to a pressure set point. Easy to install, this solution eliminates the physical tubes used with standard differential pressure sensors. The integrated PID controls the fan and dampers. The TDPM represents the next generation technology for Smart Building Environmental controls. The Tubeless features significantly lowers installation cost, time and risk.

HIGH RESOLUTION & RELIABILITY AND SELF CALIBRATION

The Tubeless system replaces the use of electro-mechanical analog Pressure transducers, which are required to be specified to the pressure required, with MicroElectro-Mechanical (MEMs) based sensors like those used in Drones or on a smart watch. Use of the TDPM eliminates the requirement for transducers calibrated to various pressure sizes – One system will meet all pressure differential ranges. The XCSpec system self-calibrates during unoccupied times or times when new air is not being introduced into the system (economizer is Off or Outside Air Damper actuator is closed). Reliability of the MEMs sensors is significantly improved from that of a pressure transducer.

An Installer selects the buildings target pressure. The system is designed to maintain the specified pressure within +/-3 pascals (.008” wc).

INTEGRATED PI FUNCTION

The 0-10V output is derived from the differential pres¬sure value and then processed through a PID function to control external equipment. The PID parameters are set up by the installer with support from the mobile application:

• Auto Loads default PI Values
• In-Building Pressure Set Point configurable by installer
• Default values can be over ridden
• Auto Calibrates the Maximum and Minimum FAN Speeds.

MULTIPLE PRESSURE POINTS Can be measured and added to the Control Output

Using multiple transmitters, each transmittter pressure value is added proportionally to calculate a resultant differential for the output control. The system periodically runs self-calibration throughout operation.

Pressure Watch Pro Application Note:

Calibration and Operational periods of the AQ Extender

This app note is to provide an understand of the calibration and operation of the XCSpec Pressure measurement and control system. For configuration of the PI functions and running the Space Calibration please reference the Application Note - Space Calibration and PI Settings of the AQ Extender

Outputs: There are two outputs from the Pressure Watch Pro:

White Wire: This is a 0-10V output under PI control for a VFD based on derived pressure differential.

You can manually enter many of the PI control parameters on the PWPR- DCV Web Server System Commissioning Page. Please reference the Space Calibration and PI settings app note:

Manual Test of Wiring between the VFD and PWPR-DCV: Wiring between the PWPR-DCV and VFD input can be tested using the Manual Test Tab on the Fan Commissioning page on the PWPR-DCV. This function controls the 0-10V PI output voltage directly. A 50% input test value results in a 5-volt signal.

Green with yellow striped Wire:  This is a 0-10V output under the rate of change control to connect to the actuator on an Input air damper for Demand Controlled Ventilation based on CO2 PPM. On the PWPR-DCV Web Server, CO2 Commissioning Page, the PPM range that the 0-10V output is linearized across can be manually entered. The CO2 commissioning page has an input to configure the DCV output for 0-10V or 2-10V output voltage – depending on the Economizer configuration.

The Rate of Change between output steps for the actuator can be configured at installation time. On the Advanced page of the device, the rate of change allows setting this up from 0.1 to 1 – where a one does not limit the shift at the output damper while a 0.1 will move the output damper 1/10 of the range – effectively taking 10 steps to get to the complete output based on ppm.

Manual Test of Wiring between the Economizer or Outside Air Actuator and PWPR-DCV: Wiring between the PWPR-DCV and Economizer DCV input can be tested using the Manual Test Tab on the CO2 commissioning page on the PWPR-DCV web server. The DCV output voltage is directly set based on the input test value—a 50% input value results in a 5-volt output.

Inputs: The Pressure Watch Pro has two sense inputs: one is used to tell the PWPR-DCV unit start/stop calibration, and the second is used to start/stop pressure-based PI Control.

Blue Wire: This is an input to the unit to Activate the PI Controls based on derived pressure. This is a cycle that is controlling the attached VFD.

Green Wire: This is input for the unit to start a calibration cycle. This zeroing cycle allows the PWPR-DCV to zeroize out the effects of altitude differences between sensors, production differences between sensors, and changes to outside barometric pressure. Note: A calibration cycle can not be initiated while the unit controls the VFD.

The purpose of the zeroizing cycle is to correct for the effects on the sensors due to automatically

1. Manufacturing differences between sensors.
2. Altitude difference between sensors
3. Sensor Drift

The diagram below is a live depiction of an operating unit from 14:40 through 15:20.This unit reports a new set of data parameters to the cloud approximately every 30 seconds. The dots on the graph line up all the parameters with a specific time marker, in this case, 14:59:52 PDT. The values at that time marker are shown next to their associated parameter. For example, the differential pressure at this time is .5409 pascals.

Different colors identify these data parameters. The colors are as follows:

• Green – The desired building set point is the designed building set point for installation. This is on the commissioning setup page.
• Red – PI Duty – this is % that the fan is being controlled to run. 100% is the max fan setting.
• Dark Blue - Receiver Pressure – The absolute pressure is measured at the PWPR-DCV. It is most often in the outside air and subject to barometric changes.
• Black – Derived differential pressure – Calculated pressure difference in pascals between the Receiver pressure and the absolute pressure being measured in the space.
• Gray – Transmitter pressure is the absolute pressure most typically measured in the tenant space. The Transmitter pressure is sent to the Receiver, which then derives the differential pressure.
• Orange SHADE - Economizer On – This is the input signal to the PWPR-DCV that tells it to start PI Control. The economizer is on the graph below whenever the graph has orange shading. When there is no shading, the unit is in a zeroizing or calibrating mode.
• Light Blue – Tx Offsets – this term is calculated while the units are in zeroizing mode. This is the term it takes to set the pressure difference between the transmitter and the receiver to zero. By calculating this term, we are zeroizing out the pressure difference between sensors, the pressure difference due to altitude and the pressure differences due to barometric changes on the outside that have not yet impacted the inside of the building (pressure envelope).

First, note the area that does not have any shading. This is a calibration or zeroizing period. During this time, you will see the Tx Offset continually updating to determine the term that would bring the measured difference between the Rx Pressure minus the Tx Pressure to zero. Compare the graph above Tx offset term with the graph below.

Use Case 1: ECON ON & Calibration ON (blue and green) are wired together.

When the Econ On signal Goes active High, the PWPR-DCV stops the zeroizing functions and determines the TX Offset based on the average of the last 10 terms. This TX Offset is used in the ongoing derived pressure calculations, resulting in a pressure value adjusted for altitude, drift, and manufacturing differences.

The Calibration signal starts and stops the zeroizing cycle, which will set the TX Offset Value. The Econ On signal starts and stops the PI control of the VFD. The Econ On signal can be tied directly to the Outside Air Damper control – creating a direct relationship between introducing new air and activating the exhaust fan. This works particularly well for Demand Controlled Ventilation, which drives the Outside Air damper based on PPM readings from the tenant space. When tied to the outside air damper, the PI function operates based on both economizing and DCV periods to exhaust the additional air.

The diagram below depicts that the PWPR-DCV changes state from calibration (zeroizing) to Operational. Note – the Tx Offset line, from this point forward, stays at the same value, and the PWPR-DCV is no longer updating the Tx offset value.

KEY POINT TO UNDERSTANDING THE VALUE OF PRESSURE BEING MAINTAIN:

A key element to understanding the Pressure Watch Pro system is the transition point from zeroizing to controlling. The PWPR-DCV assumes the pressure at this transition point is the “ZERO” pressure value. The system design is based on the ECON ON being the point at which new air is introduced into the system. Hence, the PWPR-DCV assumes that the pressure BEFORE the new air is introduced is the proper or desired ambient pressure to maintain.

The above shows that the Desired Pressure Set Point (green line) is 0.00 pascals. In this setup, the PI controls the exhaust fan to maintain the entry pressure (of 0.00 pascals) + Desired Pressure Set Point (0.00) = pressure at the start of the Economizing Cycle.

In the above, if the Desired Pressure Set Point is 100 pascals, the PWPR-DCV will control the exhaust fan to maintain the entry pressure (0.00) + Desired pressure set point (100 pascals) = pressure at the start of the economizer cycle + 100 pascals.

When the Econ On signal Goes active High, the PWPR-DCV stops the zeroizing functions and begins PI Operation. The Red Line below is the output of the PI. The Black Line below is the Derived Pressure being measured between the transmitter and the PWPR-DCV Unit. The right legend is in pascals and should be used for referencing the derived differential pressure value while the left legend is the absolute pressure readings coming from the pressure sensors in the transmitter and receiver – all in pascals.

In the Diagram, you can see the PI (RED) slowly ramp up – from 15:01 to 15:06. The control of this ramp can be set through the web page on the PWPR-DCV. Changing the P and/or I or slo[e will change the reaction time of the PWPR-DCV to pressure changes. Default values are recommended and pre-programmed into the unit

The PI Output is update with new control values based on the Loop Time value. Please note: all of these values can be adjusted on the PWPR-DCV web server.

The objective of the PI is to control the exhaust fan to maintain the Set Point. In the above, you can see the reaction of the PI to slight changes in the outside or inside pressures. The PI continues to run while the Economizer On signal is active.

The PI is running during the time ECON is ON – this is depicted as the shaded orange area. The graph below depicts the PI start-up, control duty cycles, and then Econ OFF, resulting in the PI turning off and the unit transitioning to Calibration mode.

The Calibration signal starts and stops the zeroizing cycle, which will set the TX Offset Value. The Econ On signal starts and stops the PI control of the VFD—the example above tied these two signals together. The Econ On signal can be tied directly to the Outside Air Damper control – creating a direct relationship between introducing new air and activating the exhaust fan. This works particularly well for Demand Controlled Ventilation, which drives the Outside Air damper based on PPM readings from the tenant space. The PI function operates based on economizing and DCV cycles when tied to the outside air damper.

However, the calibration (zeroing) on / off can be separated from the start of introducing new air. If calibration is performed while the building is not running a supply fan, for example, and the building is allowed to pressure equalize with the outside air through building leakage, running the calibration cycle at this time provides the PWPR-DCV determines the building quiet non-active base pressure. (This assumes doors and windows are not being opened/closed by tenants.) If zeroization is done now, the offset value represents a non-pressurized or close to zero pressurization between the inside and outside air. The PWPR-DCV determines “good” tx offset values based on achieving inside/outside pressure equilibrium within a given Pascal noise ratio.

If the above algorithm is used, then the PI will maintain the true Setpoint of 100 pascals as opposed to the entry+Set Point pressure.

In the graph below, calibration occurs up until 16:27, at which time we stop. During this time, during the calibration cycle, we are NOT running any supply fans or performing other activities that impact the building pressure. The building is at a quiescent state.

At 16:27, we start the supply fan but NOT the exhaust PI (as you see, the duty cycle is inactive. So, the inside space