Pressure Sensor Installation Methods in HVAC System

Pressure Sensor Installation Methods | Air, Room, Outdoor, Liquid, and Flow Measurement Guidelines

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Introduction to Pressure Sensor Installation and Best Practices

Pressure sensors are essential components in HVAC, building automation, and industrial stems.
Their performance depends heavily on proper installation, orientation, and placement. Incorrect installation can lead to measurement errors, system inefficiency, and equipment damage.

Pressure Sensor Installation Methods in HVAC system

This article provides a detailed guide on general pressure sensor installation principles and specific methods for air ducts, rooms, outdoor environments, liquids, and flow applications.
Technicians, engineers, and automation professionals can use this reference to ensure accurate and reliable pressure measurement across various systems.

🧰 General Pressure Sensor Installation Guidelines

Method of Installation

1. Pressure sensors are sensitive to mounting orientation and must follow the manufacturer’s recommended instructions.

Proper installation ensures accurate readings and protects sensors from environmental damage.

2. Pressure tubes must be provided with an isolatable T-fitting near the device head for test purposes.

3. To prevent overload on one side when making adjustments, the connection must always be fitted with an isolating bypass.

4. Where there is a risk of condensation, the differential pressure tube must be installed at a gradient of 1:30 and fitted with a drain mechanism. The drainage point must be lower than the device head and sensing point. Protect from frost and avoid U-shapes.

5. Pressure tubes containing circulating air must not be introduced into the open air or routed through cold rooms or ducts. This prevents the risk of condensate freezing in the tubes (e.g. with pneumatic venting sensors).

6. Mount on a vibration-free surface.

7. The pressure-tapping point must not be located in turbulent air. Ensure sufficiently long settling zones upstream and downstream of the tapping point. A settling-zone consists of a straight section of pipe or duct, with no obstructions.

🌬️ Pressure Sensors for Air Applications

Method of Installation

1. The measuring tip is screwed or glued to the duct wall.

Seal to protect from external air.
Remove any swarf from the inside of the duct.

Method of Installation

2. Protruding fixing screws will impair correct measurement.

3. Correct installation.

4. Avoid using tips which protrude into the duct for static pressure measurements.

5. Probes are used to measure static pressure in the duct. Must be installed parallel to the flow and either with the flow or against it.

Sizing the pressure tubes (measuring tubes) for air and gases:

Keep the tube as short as possible. An internal diameter of 4 mm is sufficient for pressure tubes of up to two meters in length.
For longer pressure tubes, the internal diameter should be as indicated in the diagram.

👉Example: A pressure tube of 6 m requires an internal diameter of 6 mm.

6. Connect the sensor and measuring instrument to the same point.

7. The tapping point must not be located where it will be affected by obstructions to the flow.

8. Where more than one sensor is used, the sensors should be installed on the same plane in the flow, and not in a position where one device will obstruct the air flow to the other.

9. Leave sufficient clearance downstream of any obstacles (dg = Equivalent diameter).

🏠 Pressure Sensors for Room Applications:

The end of the pressure tube leading into the room should be protected by an air-permeable cover.
Seal gaps between cable/plastic tubing and conduit. Otherwise measurements will be falsified by incorrect circulation of the air.

🌤️ Pressure Sensors for Outdoor Applications:

Measure the outdoor pressure in an area sheltered from wind. Individual façades are not suitable measurement locations, as the pressure varies according to the wind direction.

The correct location for measurement is a place where the air can circulate freely, such as a flat roof.
Note: however, that the sensing point must be fitted with a wind shield.

Options:

Calculate average based on pressure measurements taken on several façades.
Measure pressure in an open space (min 1.5 m above ground level). Multiple sensing point on flat roof.

💧 Pressure Sensors for Liquids

Method of Installation:

Pressure tapping point:

Sensing hole: diameter 5 mm, drilled and deburred.
Smooth interior (no burrs).
Use a damping coil to avoid transferring vibrations. Bend a 1 m long copper pipe, 4…6 mm in diameter, into a spiral with loops with a diameter of 15 cm.
Wrong: Air bubbles and condensate remain trapped.
Wrong: Condensate cannot be drained.

🧩Installation in conjunction with liquids:

Always install the pressure sensor in a location which is lower than the sensing point.

🧩Installation in conjunction with vapours/gases:

Always install the pressure sensor in a location which is higher than the sensing point.

Pressure measurement in conjunction with liquids:

Do not measure at the top of the pipe (trapped air or air bubbles) or at the bottom (dirt).
The correct location for a sensing point is at the side.
Condensing gases: Measure at the top to prevent condensate from entering the pressure tube.

💨Flow Velocity Measurement Air

The pressure-tapping point must not be located in turbulent air. Ensure sufficiently long sett ling-zones upstream and downstream of the tapping point.
A settling-zone consists of a straight section of pipe or duct, with no obstructions.

💡 Formula:

dg = 2a × b a + b

❓dg = Equivalent diameter

Fan-belt monitoring:

The differential pressure across the fan is only suitable for fan-belt monitoring.

❌ Negative connection (–) on suction side use copper tube

✔️ Positive connection (+) on discharge side: use Pitot tube.

Flow detectors (electrothermal):

Electrothermal flow detectors must be installed in a zone with a high flow velocity, e.g. where pipes narrow.

Differential pressure:

Do not monitor flow or differential pressure where flow resistance is variable, e.g. at filters, cooling coils, fans etc. Suitable locations: heating coils, silencers, baffles, attenuators.

💦 Flow Monitoring in Water Systems

If differential pressure is used to monitor the flow, it is important to ensure that there are no stop valves or balancing valves between the sensing points.

🏭 Air Quality Sensors (Room Applications)

There are two types of air quality sensors:

Mixed gas (or VOC) sensors:

The accumulation of up to 24 different gases is measured in the ambient air (total concentration measured).

Selective gas sensors:

These measure only one gas (e.g. CO₂ ) in the ambient air (selective measurement).
Do not locate temperature or humidity sensors above or below the AQ sensor.
The heated sensor element produces significant intrinsic heat in the device. Owing to this characteristic, the room temperature or room humidity must not be measured in the immediate vicinity. Maintain a clearance of minimum 60 mm on each side of the AQ sensor.

CO₂ sensors:

Selective gas sensors may require maintenance at regular intervals. Please consult the manufacturer’s instructions. The sensor must be installed in an accessible location.

1. Avoid recesses (e.g. shelving) and alcoves.

2. Do not install directly adjacent to doors.

3. Do not install behind curtains.

4. Seal gaps between cable/plastic tubing and conduit. Otherwise measurements will be falsified by incorrect circulation of the air.

🏁 Conclusion

Proper installation of pressure sensors is critical for achieving accurate measurements in HVAC, building automation, and industrial systems.

By following the manufacturer guidelines and applying the best practices outlined in this article, technicians and engineers can ensure reliable pressure monitoring in air ducts, rooms, outdoor environments, water systems, and flow applications.

This guide serves as a valuable reference for professionals seeking to improve sensor accuracy, system reliability, and overall operational efficiency.