How to Measure Differential Pressure in Data Centre Hot and Cold Aisles Malaysia
How to Measure Differential Pressure in Data Centre Hot and Cold Aisles Malaysia
Content
Correct airflow is essential for maintaining stable server-inlet temperatures in a data centre.
Room temperature alone cannot show whether sufficient cooling air is reaching each rack. A data hall may appear cold while air is bypassing the servers, escaping through openings or recirculating from the hot aisle into the cold aisle.
Differential-pressure measurement helps facility teams evaluate airflow direction and pressure differences between areas such as raised floors, cold aisles, hot aisles and surrounding rooms.
What Is Differential Pressure?
Differential pressure is the difference in air pressure between two locations.
It is commonly expressed in:
Pa
hPa
mbar
mmH2O
inH2O
A differential-pressure meter normally has two pressure ports:
High-pressure port
Low-pressure port
The instrument calculates the pressure difference between the two connected locations.
Why Differential Pressure Matters in a Data Centre
Pressure differences influence how cooling air moves through the facility.
Differential-pressure testing can help identify:
Insufficient raised-floor pressure
Excessive air leakage
Uneven cold-aisle supply
Hot-air recirculation
Bypass airflow
Restricted filters
Containment leakage
Incorrect room pressurisation
Cooling-unit airflow imbalance
Pressure measurement should be combined with temperature and airflow checks because pressure alone does not confirm cooling performance.
Raised-Floor Pressure
In a raised-floor data centre, the underfloor space may act as a supply-air plenum.
Cooling air must travel through:
Raised-floor cavity
Perforated tiles or grilles
Cold aisle
Server inlet
Rack equipment
Hot aisle
Return-air path
If underfloor pressure is too low, racks located further from the cooling unit may receive insufficient airflow.
If pressure is excessively high, the system may be using unnecessary fan energy or supplying more air than required.
Cold-Aisle and Hot-Aisle Pressure
A suitable pressure relationship helps maintain the intended airflow direction.
Problems can occur when:
Hot air enters the cold aisle
Cold air bypasses the server racks
Containment doors remain open
Cable openings are unsealed
Empty rack spaces lack blanking panels
Floor tiles are installed in the wrong locations
Cooling-unit fans are not balanced
Differential-pressure measurements can help locate these problems, but the exact target depends on the facility design.
Room Pressurisation
Data-centre rooms may be maintained at a pressure different from adjacent corridors or outdoor areas.
Positive room pressure may help reduce the entry of:
Dust
Humid outdoor air
Smoke
Unfiltered contaminants
Excessive positive pressure can create:
Difficulty opening or closing doors
Uncontrolled air loss
Increased cooling demand
Air leakage into neighbouring areas
Negative pressure may draw warm, humid or contaminated air into the data hall.
Equipment Needed
A basic differential-pressure survey may require:
Differential-pressure meter or manometer
Flexible pressure tubing
Static-pressure probes where appropriate
Temperature and humidity meter
Airflow meter or anemometer
Data-recording sheet
Floor or rack layout
Labels for test points
The tubing and probe configuration must match the measurement objective.
Before Starting the Measurement
Record the facility operating condition:
Number of cooling units running
Fan speed
IT load
Rack occupancy
Containment status
Doors open or closed
Floor-tile arrangement
Filter condition
Recent maintenance
Alarm status
Measurements taken under different operating conditions should not be compared without documenting the difference.
How to Connect a Differential-Pressure Meter
For a typical comparison:
Connect the high-pressure port to the location expected to have higher pressure.
Connect the low-pressure port to the location expected to have lower pressure.
If the connections are reversed, the instrument may display a negative value.
A negative reading is not automatically an error. It may show that the actual pressure direction is opposite to the expected direction.
Measuring Raised-Floor Pressure
To compare the underfloor plenum with the data hall:
Confirm that cooling equipment is operating normally.
Zero the differential-pressure meter according to its instructions.
Place one pressure tube or probe in the raised-floor plenum.
Keep the reference port in the room.
Allow the reading to stabilise.
Record the pressure difference.
Repeat at several locations.
Useful positions include:
Near the cooling unit
Middle of the room
Furthest rack row
High-density rack area
Known hot spot
End of the cold aisle
One underfloor measurement cannot represent the entire plenum.
Measuring Cold-Aisle Containment
To assess a cold aisle:
Keep doors and containment panels in their normal operating position.
Place one pressure point inside the contained aisle.
Place the reference point outside the aisle.
Record the differential pressure.
Repeat at both ends and near the middle.
Compare pressure with rack-inlet temperature and airflow.
A positive pressure inside the cold aisle may support outward airflow, but the correct target must be determined by the facility design.
Excessive pressure does not necessarily improve cooling if air is escaping through gaps instead of passing through servers.
Measuring Hot-Aisle Containment
For a contained hot aisle:
Place one pressure point inside the hot aisle.
Place the second point in the surrounding room.
Observe the pressure direction.
Check containment doors and ceiling return paths.
Compare with hot-aisle temperature and cooling-unit return conditions.
Leakage can cause hot exhaust air to re-enter server inlets.
Measuring Across Filters
Differential pressure can indicate filter restriction.
Measure pressure:
Upstream of the filter
Downstream of the filter
As a filter accumulates dust, the pressure drop may increase.
The result should be compared with:
Equipment manufacturer’s limit
Clean-filter baseline
Fan operating condition
Airflow requirement
Changing a filter solely because of time may be wasteful, but operating with an excessively restricted filter may reduce airflow and increase fan energy.
Measuring Across Cooling Coils
Pressure drop across a coil may change because of:
Dust buildup
Moisture
Blocked fins
Damaged coil
Incorrect airflow
Filter problems
Differential pressure is one diagnostic indicator. Visual inspection, airflow and temperature measurements should also be performed.
Using a Measurement Grid
For a larger facility, divide the data hall into a measurement grid.
Record:
Test-point number
Location
Pressure difference
Rack-inlet temperature
Air velocity
Cooling-unit status
Remarks
A grid can reveal whether pressure decreases with distance or changes between rack rows.
Interpreting a Low Reading
A lower-than-expected differential pressure may be caused by:
Insufficient fan speed
Cooling-unit failure
Open floor panels
Unsealed cable openings
Excessive number of perforated tiles
Containment leakage
Open doors
Blocked airflow path
Incorrect measurement method
Damaged tubing
Confirm the instrument setup before changing fan speed.
Interpreting a High Reading
A higher-than-expected pressure may indicate:
Excessive fan speed
Too few open floor tiles
Restricted server airflow
Closed dampers
Blocked filters
Poor return path
Control-system error
Incorrect reference location
High pressure may increase fan energy without improving rack cooling.
Why Pressure Alone Is Not Enough
The same pressure difference can produce different airflow depending on:
Opening size
Grille design
Tile type
Rack resistance
Server fan behaviour
Leakage
Air density
Containment geometry
Combine pressure measurement with:
Rack-inlet temperature
Return-air temperature
Air velocity
IT load
Fan speed
Visual inspection
Thermal imaging
This provides a more complete understanding of airflow performance.
Common Measurement Mistakes
Failing to Zero the Meter
The instrument should be zeroed according to the manufacturer’s instructions before critical measurements.
Pinched or Leaking Tubing
Damaged tubing can cause unstable or incorrect results.
Holding the Tube in Moving Air
A bare tube facing directly into airflow may measure velocity pressure rather than the intended static pressure.
Use the appropriate probe and orientation.
Comparing Different Operating Conditions
Pressure may change when cooling units, doors or server loads change.
Measuring Only One Location
Raised floors and contained aisles may have uneven pressure.
Ignoring Units
Confirm that all results use the same unit before comparison.
Adjusting Fan Speed Too Quickly
A pressure change may alter airflow throughout the data hall. Make controlled adjustments and recheck temperatures.
Recommended Survey Sequence
Review alarms and layout.
Record active cooling equipment.
Verify the meter and tubing.
Measure room-to-corridor pressure.
Measure raised-floor pressure at several points.
Measure cold- or hot-aisle pressure.
Check filter or coil pressure drop where applicable.
Measure rack-inlet temperature.
Check airflow at representative outlets.
Inspect containment and openings.
Make one adjustment at a time.
Repeat the survey and document the result.
When to Repeat the Test
Repeat differential-pressure testing after:
Installing new racks
Increasing IT load
Moving floor tiles
Changing fan speed
Modifying containment
Replacing filters
Servicing cooling equipment
Opening new data-hall capacity
Investigating hot spots
Detecting increased PUE
Receiving repeated temperature alarms
The measurement should also form part of planned preventive maintenance.
Instruments for Data Centre Airflow Inspection
Useful instrument categories include:
Differential-pressure meters
Digital manometers
Airflow meters
Hot-wire anemometers
Temperature and humidity meters
Data loggers
Thermal imaging cameras
Electrical testers
Sound-level meters
Each instrument addresses a different part of the cooling and airflow system.
Data Centre Testing Instruments from MTM Precision
MTM Precision supplies testing instruments for data-centre inspection and preventive maintenance in Malaysia.
Relevant products include:
Differential-pressure meters
Airflow and anemometer instruments
Temperature and humidity meters
Temperature and humidity data loggers
NOYAFA NF-522 thermal imaging camera
Wintact thermal imaging cameras
Clamp meters and electrical testers
Vibration meters for pumps and fans
NOYAFA NF-8209 Pro and NF-8506 network cable testers
NOYAFA NF-IPC728HSO CCTV and network tester
Product selection should be based on the expected pressure range, required resolution, logging requirement and application.
Contact MTM Precision
MTM Precision Sdn. Bhd. (744811-A)
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com / enquiry@mtmpre.com.my
Website: www.mtmpre.com.my
Visit our Puchong Showroom & Service Centre for differential-pressure meter and data-centre testing instrument selection.
Operating hours: Monday to Friday, 9:00 AM–6:00 PM.
20 Sep 2026
