How to Use CO2 Readings to Evaluate Indoor Ventilation Malaysia

How to Use CO2 Readings to Evaluate Indoor Ventilation Malaysia

CO₂ measurement is widely used when investigating ventilation conditions in occupied indoor spaces.

But simply seeing a CO₂ number on a meter is not enough.

The more useful question is:

How does the CO₂ reading change with occupancy, time and ventilation conditions?

For offices, meeting rooms, classrooms and commercial buildings in Malaysia, monitoring CO₂ trends can provide useful information during ventilation investigations.

The TENMARS TM-380 Multi IAQ Monitor uses an NDIR sensor for CO₂ measurement and simultaneously measures:

CO₂

PM2.5

PM10

Temperature

Relative humidity

This allows users to investigate ventilation-related conditions while also observing particulate matter and general indoor environmental conditions.

Why Is CO₂ Useful for Ventilation Investigation?

People continuously generate carbon dioxide through respiration.

When a room becomes occupied, indoor CO₂ can increase.

How quickly it changes depends on factors including:

Number of occupants

Room size

Duration of occupancy

Outdoor-air ventilation

Building operation

This makes CO₂ a useful parameter when investigating how an occupied room behaves.

Don't Look at Only One CO₂ Reading

A common mistake is taking one reading and immediately trying to classify the entire room.

A more informative approach is to observe the trend.

For example:

Before Occupancy → During Occupancy → After Occupancy

This shows how the room responds as people enter and leave.

Step 1: Establish a Baseline

Take a measurement before the room becomes heavily occupied.

For example, measure a meeting room before employees arrive.

Record:

CO₂

Time

Occupancy

Room condition

This creates a baseline for comparison.

Step 2: Monitor During Occupancy

Once people enter the room, continue observing CO₂.

For example:

9:00 AM — Empty room

9:15 AM — 10 occupants enter

9:30 AM — Measure

10:00 AM — Measure

10:30 AM — Measure

The trend can provide more useful information than one isolated reading.

Step 3: Observe What Happens After Occupancy

When the meeting ends, continue monitoring.

Does CO₂ begin to decrease?

How quickly?

This can provide additional information about the behaviour of the room and its ventilation.

Example: Meeting Room

Imagine an office meeting room with twelve occupants.

The air-conditioning is operating.

The temperature remains comfortable.

But CO₂ gradually increases throughout the meeting.

This demonstrates an important principle:

Cooling performance and ventilation conditions are not necessarily the same thing.

A room can feel cool while ventilation relative to occupancy still requires investigation.

Air-Conditioning Does Not Automatically Mean Fresh-Air Ventilation

Many people associate air-conditioning with fresh air.

However, cooling and ventilation perform different functions.

Depending on the building system, air may be cooled or recirculated while outdoor-air ventilation is handled separately.

Therefore, CO₂ measurement can provide additional information that temperature alone cannot provide.

Compare Similar Rooms

Another useful technique is to compare different rooms.

For example:

Open Office

versus

Small Meeting Room

versus

Large Conference Room

versus

Training Room

If one room consistently shows a different CO₂ pattern under similar occupancy conditions, facility teams have a clearer area for further investigation.

Occupancy Matters

CO₂ readings should always be considered together with occupancy.

A room containing two people and the same room containing twenty people represent very different conditions.

When recording measurements, note:

Number of occupants

Time

Door/window condition

HVAC operation

This makes the results more meaningful.

Room Size Matters Too

A small meeting room may experience different CO₂ changes from a large open office.

Therefore, avoid comparing numbers without considering the physical space and occupancy.

The objective is not simply to find the “highest number”.

The objective is to understand how the room behaves under actual use.

Why Data Recording Is Useful

Some ventilation-related problems occur only at particular times.

For example:

Morning training sessions

Afternoon meetings

Full classrooms

Peak office occupancy

A quick five-minute inspection may miss the issue.

The TENMARS TM-380 supports manual and automatic recording, allowing measurements to be observed over a longer period.

Don't Use CO₂ as the Only IAQ Measurement

CO₂ is useful for ventilation investigation, but it does not measure particulate pollution.

A room can have relatively low CO₂ while PM2.5 is elevated.

This becomes particularly relevant during Malaysia haze periods.

For this reason, a broader IAQ investigation may also include:

PM2.5

PM10

Temperature

Relative humidity

Malaysia Haze Creates a Ventilation Challenge

During haze, building operators may close windows and doors to reduce outdoor particulate entry.

Air purifiers may also be used.

These measures can help manage indoor particulate conditions.

However, heavily occupied enclosed spaces still require appropriate ventilation.

Therefore, it can be useful to observe:

PM2.5 / PM10 → Particulate conditions

and

CO₂ → Ventilation-related conditions

together.

Example: Closed Meeting Room During Haze

Suppose a meeting room contains ten people.

The windows are closed.

An air purifier is operating.

After one hour:

PM2.5 has decreased

but

CO₂ has increased.

This tells the facility team that particulate control and ventilation are two separate issues.

A PM2.5 reading alone would not show the complete situation.

Can Opening Windows Reduce CO₂?

Opening windows may increase air exchange in some situations.

However, whether this is appropriate depends on:

Outdoor conditions

Building design

Weather

Haze

Traffic pollution

Safety

HVAC operation

During poor outdoor air quality, simply opening windows may introduce particulate pollution.

Professional building management therefore requires consideration of both ventilation and outdoor conditions.

Compare Before and After HVAC Changes

CO₂ measurements can also be useful when comparing conditions before and after a ventilation-related adjustment.

A basic comparison could be:

Before Adjustment

Record CO₂ under representative occupancy.

Adjustment

The HVAC professional makes the appropriate system change.

After Adjustment

Repeat measurements under comparable conditions.

This provides objective measurement data for comparison.

Measure at Appropriate Locations

Portable CO₂ measurements can be taken in different occupied areas such as:

Meeting rooms

Open offices

Conference rooms

Classrooms

Training rooms

Enclosed workspaces

Avoid assuming that one measurement location represents an entire building.

Different zones may behave differently.

CO₂ Is an Indicator, Not a Complete Diagnosis

An elevated CO₂ reading does not automatically tell you exactly which component of the HVAC system requires adjustment.

It indicates that ventilation relative to occupancy may warrant investigation.

The next step may involve qualified HVAC, facility or environmental professionals reviewing:

Ventilation operation

Outdoor-air supply

Occupancy

Room usage

System schedules

Building conditions

Measurement supports troubleshooting; it does not replace technical diagnosis.

Who Can Use CO₂ Monitoring?

CO₂ measurement can be useful for:

HVAC contractors

Facility managers

Building maintenance teams

M&E contractors

Schools

Universities

Office managers

Environmental consultants

Safety personnel

Commercial building operators

Why Use a Multi-Parameter Instrument?

If ventilation is the only issue being investigated, a dedicated CO₂ meter may be sufficient.

However, building problems often involve more than one environmental factor.

The TENMARS TM-380 allows users to simultaneously investigate:

CO₂ + PM2.5 + PM10 + Temperature + Relative Humidity

This provides greater flexibility for general IAQ troubleshooting.

TENMARS TM-380 for Ventilation Checking Malaysia

For Malaysian HVAC contractors, facility managers and building maintenance professionals, CO₂ monitoring can provide valuable information when investigating occupied indoor spaces.

Rather than looking at one number, observe how CO₂ changes:

Before occupancy → During occupancy → After occupancy

Compare different rooms.

Record occupancy.

Observe changes over time.

And when outdoor pollution or haze is relevant, consider particulate measurements alongside CO₂.

The TENMARS TM-380 provides these measurements in one portable IAQ instrument.

Contact MTM Precision

MTM Precision Sdn. Bhd.

Showroom & Service Centre

No. 29-1 & 29-2, Jalan Bandar 18,

Pusat Bandar Puchong,