2025-07-03 HVAC/R, Wiki
Delta p (Δp) – two small characters with big impact. In industrial systems, building automation, and refrigeration or HVAC technology, differential pressure is a key measurement. It helps keep systems efficient, detect faults early, and plan maintenance instead of reacting to failures.
But what exactly does Delta p mean? How is it calculated, and what can it reveal about system performance? This article answers the most important questions and shows how monitoring Delta p can help companies save money and prevent downtime.
Delta p (Δp) stands for the pressure difference between two points within a system.
Δp = p₁ – p₂
The term originates from physics: the Greek letter Delta (Δ) represents change, and “p” stands for pressure. The value is typically measured in Pascal (Pa), millibar (mbar), or bar.
Example:
If you measure 2.1 bar before a filter in a pipeline and 1.6 bar after, then
→ Δp = 0.5 bar
Too high or too low a differential pressure is often an early warning sign: blockages, leaks, misadjustments, or decreasing efficiency frequently appear first as a shift in Δp. The right sensor can detect these changes reliably and in time – often before they lead to costly breakdowns or failures.
Filters in ventilation systems, hydraulic loops, or cooling circuits gradually clog over time. This increases the pressure drop across the filter – visible as rising Δp. If the threshold is exceeded, it’s time to change the filter.
Advantage: Condition-based maintenance instead of rigid service intervals.
A stable differential pressure is critical for flow performance and energy efficiency. If Δp increases, this can indicate blockages, narrowing pipes, or mechanical issues.
As Δp increases, heat transfer typically decreases – caused by fouling, scaling, or air in the system. Monitoring the pressure drop helps detect issues early and maintain optimal thermal efficiency.
In refrigeration systems, oil differential pressure (Δp across the oil pump) is a key safety factor. If this value drops too low, it means the compressor might no longer be sufficiently lubricated – which can lead to catastrophic failure within seconds.
Differential pressure sensors measure pressure at two points simultaneously and calculate the difference. There are various sensor types:
| Sensor Type | Measuring Principle | Advantages |
|---|---|---|
| Mechanical | Spring, diaphragm, piston | Robust, cost-effective, simple |
| Electronic | Piezoelectric, Hall effect | High accuracy, digital output possible |
| MEMS | Microchip-based | Compact, IoT-capable, very precise |
Tip: Advanced models like the KRIWAN DPM1 sensor offers diagnostics and remote monitoring via IO-Link or Modbus – perfect for smart industrial setups.
| Unit | Conversion |
|---|---|
| 1 bar | = 100,000 Pascal (Pa) |
| 1 mbar | = 100 Pascal (Pa) |
| 1 psi | ≈ 68.95 mbar |
A food manufacturer notices an unusual rise in Δp across a heat exchanger. The cause? Gradual scaling inside the pipes. Without monitoring, flow would have dropped, the coolant overheated, and the batch quality suffered.
Thanks to a simple sensor, a costly shutdown was avoided.
That depends on the application.
In air filters, 50–300 Pa is common. Always follow manufacturer specs.
Ideally in real-time via sensor, otherwise at regular intervals (daily/weekly), depending on how critical the system is.
Cold air is denser → higher resistance → Δp rises.
Also, moisture and ice can block filters more quickly in winter.
Not usually. Most industrial Δp sensors have fixed factory-set thresholds tailored to specific equipment. Programmable versions are available for flexible systems.
No. The switching thresholds (e.g., 0.65 bar or 0.95 bar) are factory-set to match the specific compressor types – post-installation adjustment is not intended.
The system uses a two-part design:
A solid metal screw-in component measures the pressure on the high- and low-pressure sides of the oil pump.
The electronic module (such as the Delta‑P II or INT250) evaluates the movement of an internal piston (acting like a diaphragm) – without direct contact. This separation ensures that mechanics and electronics operate independently and reliably.
Advantages:
Replacement without system downtime – the electronic module can be removed without opening the oil circuit.
Minimized leakage risk – fewer auxiliary lines and seals are required, reducing potential failure points.
The screw-in component is made of stainless steel and designed to withstand temperatures from –30 °C to +90 °C, depending on the model.
Special versions for CO₂ systems can handle temperatures up to +140 °C reliably.
Whether in industry, buildings, or refrigeration systems – Delta p is one of the most valuable and cost-effective early warning indicators available.
Smart monitoring of differential pressure improves system reliability, reduces energy use, and prevents unplanned failures.
Discover our sensor solutions for Delta p or contact our team for expert advice on how to integrate reliable Δp monitoring into your system.
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