Air Changes per Hour Monitor with Touch Screen

Product Overview

The AI-CRS1-TFT is a touchscreen Air Changes per Hour (ACH) monitor for occupied buildings and ventilation-controlled spaces. Typical sites include offices, classrooms, laboratories, healthcare rooms and enclosed car parks.

It measures the room's air change rate and shows it continuously, so facility teams can check that the ventilation system is delivering the air replacement it was designed for.

The system has two parts: a full colour 3.5" TFT touchscreen display unit and a separate ACH transmitter. The transmitter measures ventilation air velocity, and the system uses that reading to calculate the room's actual ACH value.

How It Works

The ACH transmitter measures ventilation air velocity. Using the configured duct and room dimensions, it calculates Air Changes per Hour, which is the number of times the room's air volume is theoretically replaced in one hour. In simple terms, ACH equals airflow per hour divided by room volume.

The 3.5" touchscreen shows the result with its engineering unit, so facility staff get a continuous readout instead of relying on periodic manual airflow testing. The measuring range can be programmed between 0 and 500 ACH to suit the room and duct dimensions of each installation.
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The ACH transmitter measures ventilation air velocity. Using the configured duct and room dimensions, it calculates Air Changes per Hour, which is the number of times the room's air volume is theoretically replaced in one hour. In simple terms, ACH equals airflow per hour divided by room volume.

The 3.5" touchscreen shows the result with its engineering unit, so facility staff get a continuous readout instead of relying on periodic manual airflow testing. The measuring range can be programmed between 0 and 500 ACH to suit the room and duct dimensions of each installation.
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Understanding the ACH Calculation

ACH is a calculated value, not a direct sensor reading. That is why correct configuration matters as much as the sensor itself. The ACH transmitter measures air velocity in the ventilation duct. The system combines that reading with two configured inputs, the duct cross-sectional dimensions and the room volume, to calculate the final ACH figure.

The underlying relationship is simple:

ACH = Airflow per Hour ÷ Room Volume

Multiplying the measured air velocity by the duct's cross-sectional area gives a volumetric flow rate, which is the airflow per hour. Dividing that flow rate by the room's total volume shows how many times the room's air is theoretically replaced in an hour.

Duct dimensions and room volume are entered during configuration. They are not measured automatically, so accuracy depends on these figures matching the actual installation. Suppose the room volume is wrong, for example because it ignores fixed equipment or changes in ceiling height.

The ACH reading will then not reflect true ventilation performance, even though the air velocity measurement itself is correct. For this reason, confirm the room and duct dimensions carefully at installation, and check them again if the room's layout changes later. Our engineering team can help review these details during system configuration.

Why ACH Matters for Indoor Air Quality and Building Efficiency

The air change rate is one of the clearest indicators of whether a space is being ventilated properly. If ACH is too low, CO₂, odours, moisture and airborne contaminants build up, which affects occupant comfort, alertness and health. If ACH is higher than the space needs, the HVAC system spends energy conditioning and moving air that brings no added benefit. Continuous ACH monitoring gives building managers the data to balance good indoor air quality against energy use, instead of guessing from design figures alone.

Features

• 3.5" High-Resolution TFT Touchscreen:
  
  Clear local display of the ACH value with engineering unit.
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• Programmable 0 to 500 ACH Range:
  
  Configurable to match specific room and duct dimensions.
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• High & Low Limit Alarms:
  
  Built-in audible buzzer alerts when ACH moves outside configured limits.
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• Alarm Acknowledgement Key:
  
  Front-plate flush key for acknowledging alerts after corrective action.
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• RS-485 Modbus RTU Communication:
  
  Supports integration with BMS, EMS, SCADA, or PLC systems.
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• Optional 4-20mA Retransmission Output:
  
  Analog output for compatible building automation and monitoring systems.
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• Two-Part System Design:
  
  Separate touchscreen display unit and ACH transmitter for flexible installation.
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• Modular Wall/Brick Wall Mountable Enclosure:
  
  Mild-steel back box with stainless steel front flush plate.

Applications

• Offices and Commercial Buildings:
  
  Confirms that occupied floors, meeting rooms and shared spaces receive enough fresh or clean air, and helps facility teams avoid over-ventilating and wasting HVAC energy.
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• Schools and Classrooms:
  
  Gives a continuous view of ventilation in densely occupied rooms, where air exchange affects concentration, comfort and the spread of airborne illness.
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• Healthcare Rooms:
  
  Tracks ventilation in operating rooms, isolation areas and treatment rooms, where the required air change rate is defined by the room design criteria.
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• Laboratories:
  
  Tracks ventilation rate in lab spaces where air exchange affects both safety and process conditions.
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• Enclosed Car Parks:
  
  Checks that the ventilation system keeps exhaust fumes from building up in underground or covered parking structures.
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• Battery Rooms:
  
  Verifies that ventilation is running as designed in rooms where charging batteries may release gases that must be diluted and removed.
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• Paint Booths and Hazardous Areas:
  
  Gives continuous ACH visibility where ventilation rate is part of the design basis for keeping solvent vapours and flammable gases below hazardous levels.
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• Data Centers:
  
  Ensures that freshly ventilated, filtered air is circulated in mission critical environments resulting in low particulate matter, VOC & corrosive gas concentrations .

Why Continuous ACH Monitoring Matters

Periodic testing confirms ventilation performance only at the moment of the test. Afterwards, HVAC conditions can change because of filter loading, fan performance issues, damper adjustments, duct obstruction or airflow sensor problems. All of these reduce ACH, often without setting off any other visible alarm. A permanently installed monitor gives facility teams ongoing visibility between scheduled HVAC inspections, so reduced ventilation can be caught and corrected before it turns into an air quality, comfort or safety problem.

Specifications

Ventilation Standards and Guidelines

ACH is now widely used as a practical benchmark for ventilation in ordinary occupied buildings, not only in specialist facilities. The AI-CRS1-TFT gives building owners a continuous way to check performance against the targets below:

• US EPA Clean Air in Buildings Challenge (2022):
  
  Recommends delivering more than 5 ACH of clean air in occupied spaces. The monitor lets facility teams see whether a room is meeting that benchmark day to day.
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• Lancet COVID-19 Commission (2022):
  
  Proposed graded targets of roughly 4, 5 and 6 ACH, described as good, better and best, for non-healthcare spaces such as offices and schools. Configurable alarm limits can be set to match whichever tier a building is aiming for.
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• WHO Roadmap to Improve and Ensure Good Indoor Ventilation (2021):
  
  Mainly expresses ventilation in litres per second per person, but recommends active monitoring of ventilation performance. A permanently installed ACH monitor is a direct way to put that into practice.
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• Ventilation Design for Specialist Spaces (NFPA and IEC 60079-10-1):
  
  Enclosed car parks, battery rooms, paint booths and hazardous areas use ventilation rate as part of their design basis under the relevant NFPA standards. Under IEC 60079-10-1, ventilation also affects how hazardous area zones are classified.
  
  Where the monitor serves a classified area, install the display unit outside the hazardous zone unless suitably certified equipment is specified. ACE Instruments can advise on flameproof options for these applications.

Always confirm the exact ACH target for a space against the applicable building code, design standard and project specification before configuration. RS-485 Modbus RTU communication lets the ACH data be logged in a facility's BMS, EMS or SCADA system, giving a continuous record of ventilation performance.

Frequently Asked Questions

1. What is the AI-CRS1-TFT Air Changes per Hour Monitor?
The AI-CRS1-TFT is a touchscreen ACH monitor for occupied buildings and ventilation-controlled spaces. It measures and displays the room's air change rate continuously, so facility teams can check that the ventilation system is delivering the intended air replacement. The system consists of a touchscreen display unit and an ACH transmitter.

2. What does ACH mean?
ACH stands for Air Changes per Hour. It shows how many times the ventilation system theoretically replaces the volume of air in a room in one hour. For example, 12 ACH means the airflow supplied to or exhausted from the room equals about 12 times the room's volume every hour.

3. Why is ACH monitoring important in buildings?
ACH is a key indicator of ventilation performance and therefore of indoor air quality. Monitoring it shows facility teams whether rooms are getting the intended ventilation rate. It also helps them spot drops caused by HVAC problems, airflow imbalance, filter loading, damper issues or fan performance changes, and avoid over-ventilation that wastes energy.

4. What ACH level is recommended for offices and classrooms?
Guidance varies. The US EPA Clean Air in Buildings Challenge recommends more than 5 ACH of clean air in occupied spaces. The Lancet COVID-19 Commission proposed roughly 4, 5 and 6 ACH as good, better and best targets for non-healthcare spaces. Some commonly followed guidelines include: 

• Residences: 0.35 to 1 ACH (minimum 0.35 per ASHRAE 62.2, or not less than 15 CFM per person)

• General Offices: 4 to 6 ACH (per ASHRAE 62.1 commercial guidelines based on size and occupancy)

• Hospitals (Patient Rooms): 6 to 12 total ACH per ASHRAE Standard 170

The right target for a building should be confirmed against local codes and the project design.

5. How does the AI-CRS1-TFT measure Air Changes per Hour?
The ACH transmitter measures ventilation air velocity and uses the configured duct and room dimensions to work out the Air Changes per Hour. The touchscreen monitor then displays that ACH value. The measuring range can be programmed from 0 to 500 ACH depending on the room and duct size.

6. What information is needed to calculate ACH correctly?
ACH depends mainly on the airflow rate and the room volume, so correct room and duct dimensions are essential when configuring the system. In simple terms, ACH equals airflow per hour divided by room volume. ACE Instruments can help select and configure the system for the room and ventilation arrangement.

7. What type of display does the AI-CRS1-TFT use?
The monitor has a 3.5-inch high-resolution TFT touchscreen that clearly shows the ACH value and its engineering unit. Facility engineers and building staff can check ventilation performance at the display itself.

8. Can the AI-CRS1-TFT alarm when ACH becomes too low?
Yes. The monitor has an in-built buzzer with configurable high and low limit alarms. If the ACH value moves outside those limits, it sounds a local alarm so facility personnel can investigate the ventilation system.

9. Can staff acknowledge the alarm?
Yes. The AI-CRS1-TFT has an alarm acknowledgement key. Personnel can use it to silence the audible alarm once they have recognised the abnormal ventilation condition and started corrective action.

10. What could cause the ACH reading in a room to decrease?
A reduction in ACH can point to several ventilation issues, such as:

• Reduced supply or exhaust airflow
• Fan performance problems
• Dirty or loaded filters
• Incorrect damper position
• Duct obstruction
• Changes in HVAC balancing
• Airflow sensor problems

Continuous ACH monitoring helps maintenance teams find these changes earlier than periodic manual airflow checks would.

11. Can the AI-CRS1-TFT be used in car parks, battery rooms or paint booths?
Yes. ACH monitoring is useful in any space where ventilation rate is part of the design basis, including enclosed car parks, battery rooms and paint booths. In classified hazardous areas, install the display unit outside the hazardous zone unless suitably certified equipment is specified. ACE Instruments can advise on the right arrangement.

12. Can the AI-CRS1-TFT be connected to a Building Management System?
Yes. The monitor supports RS-485 Modbus RTU communication for integration with BMS, EMS, SCADA and other compatible monitoring systems. The ACH value can then be monitored centrally as well as on the local display.

13. Is a 4-20 mA output available?
Yes. An optional 4-20 mA analogue retransmission output is available. It provides another way to send the measured ACH value to compatible building automation, data acquisition or monitoring systems.

14. What is the advantage of real-time ACH monitoring over periodic testing?
Periodic testing confirms ventilation performance only at the time of the test. HVAC conditions can change afterwards because of filter loading, fan problems, damper adjustments or system modifications. A permanently installed ACH monitor provides ongoing visibility, so engineering teams can spot changes between scheduled inspections.

15. Can the ACH range be configured for different room sizes?
Yes. The measuring range can be programmed between 0 and 500 ACH depending on room size and duct size. This lets the system be configured for many different ventilation applications.

16. Can the monitor be installed in a modular wall?
Yes. The device features a mild-steel back box with a stainless steel front flush plate that can be mounted in a modular wall or a brick wall. This gives a neat installation in commercial, institutional and controlled-environment interiors.

17. What power supply does the AI-CRS1-TFT require?
The AI-CRS1-TFT runs on a 24 VDC power supply. This makes it easy to integrate into typical low-voltage building monitoring and control installations.

18. What are the main advantages of the AI-CRS1-TFT?
The key benefits include:

• Real-time Air Changes per Hour monitoring
• Programmable 0 to 500 ACH measurement range
• 3.5-inch TFT touchscreen display
• High and low ACH alarms with built-in buzzer
• Alarm acknowledgement facility
• RS-485 Modbus RTU communication
• Optional 4-20 mA retransmission
• BMS, EMS and SCADA integration
• Flush-mounted installation
• Data to balance indoor air quality against HVAC energy use

19. How do I choose the right ACH monitoring configuration for my building?
Selection depends on room volume, duct dimensions, ventilation airflow, expected ACH range, installation location, alarm requirements, and whether the monitor must integrate with a BMS or EMS. Our engineering team can review these application details and configure the AI-CRS1-TFT for your space.