Project Spotlight: Bespoke Free-Cooling Controls for Mission-Critical Data Centres

What This Project Covered

This project demonstrates how iACS delivered:

• Bespoke data centre cooling controls
• Custom control-panel design and manufacture
• Free-cooling optimisation
• Application-specific software development
• Master-and-slave control architecture
• EC fan management
• Intelligent fresh-air and recirculation control
• External and internal temperature and humidity monitoring
• Dew-point and enthalpy-based free-cooling logic
• Belimo MP-Bus actuator integration
• BACnet/IP Building Management System integration
• VESDA fire-alarm shutdown sequencing
• Electrical isolation between interconnected panels
• Factory simulation and on-site commissioning
• A scalable solution deployed across several UK locations

Table of Contents

1. Project Overview
2. Why Data Centres Need Intelligent Cooling Controls
3. How Data Centre Free Cooling Works
4. The Cooling Units and Control Requirements
5. The Multi-Panel Control Architecture
6. The Bespoke iACS Solution
7. Environmental Monitoring and Free-Cooling Logic
8. EC Fan and MP-Bus Damper Control
9. BACnet/IP BMS Integration
10. The Fire-Alarm Integration Challenge
11. Preventing Uncontrolled Restarts
12. Protecting Controllers Through Signal Isolation
13. Factory Testing and On-Site Commissioning
14. On-Site Commissioning
15. The Multi-Site Rollout
16. The Project Outcome
17. Why This Project Matters
18. Key Capabilities Demonstrated
19. The Value of Bespoke Data Centre Controls
20. Looking for Data Centre Controls Support?

1. Project Overview

Sector

Data Centres and Telecommunications

Application

Data hall free-cooling systems.

Direct Customer

4Energy Ltd

End User

A leading UK telecommunications provider.

Locations

Multiple UK data halls, including sites in:

• Derby
• Glasgow
• Oswestry
  
  

Project Period

Multiple phases delivered between 2013 and 2017.

iACS Scope

• Bespoke control-panel engineering
• Panel manufacture
• Custom software development
• Master-and-slave system coordination
• Environmental control strategy
• MP-Bus actuator integration
• BACnet/IP integration
• Fire-alarm sequence programming
• Factory testing
• On-site commissioning
• Multi-site rollout support
  
  

Cooling Application

Multiple 4Energy COOLair free-cooling units.

Project Status

Successfully commissioned and deployed across multiple sites

The project developed over several phases, with repeat orders following the successful commissioning of the initial installation.

2. Why Data Centres Need Intelligent Cooling Controls

Data halls generate large quantities of heat continuously.

Servers, networking equipment and power infrastructure operate around the clock, creating a cooling requirement that does not disappear overnight or during colder seasons.

A successful data centre environmental-control strategy must therefore provide:

• Continuous heat removal
• Stable room temperatures
• Controlled humidity
• Reliable airflow
• Rapid alarm response
• Safe operation during fire conditions
• Integration with central monitoring systems
• Energy-efficient operation whenever outdoor conditions permit

Traditional mechanical cooling can maintain these conditions, but it consumes significant energy.

Free-cooling systems reduce that demand by using favourable outdoor air to cool the data hall. However, introducing outside air directly into a mission-critical environment requires sophisticated control.

The system must know not only whether the outdoor air is cooler, but whether its moisture content and overall thermal condition make it safe and beneficial to use.

3. How Data Centre Free Cooling Works

Free cooling uses lower-temperature outdoor air to reduce or replace mechanical cooling when external conditions are suitable.

A simplified operating sequence is:

1. External temperature and humidity are measured.
2. Internal data hall conditions are monitored.
3. The controller compares internal and external air conditions.
4. The control strategy determines whether outdoor air can provide useful cooling.
5. Fresh-air and recirculation dampers modulate to achieve the required mixture.
6. EC fans adjust airflow to maintain the data hall setpoint.
7. Mechanical cooling demand is reduced whenever free cooling can meet the load.

This can lower energy consumption and extend the periods during which compressor-based cooling is not required.

However, outdoor temperature alone is not enough to make a safe decision.

Air that appears cool may contain excessive moisture. Introducing it into the data hall could create humidity problems or increase the risk of condensation.

The control strategy must therefore consider several variables together, including:

• External temperature
• External relative humidity
• Internal temperature
• Internal relative humidity
• Dew point
• Enthalpy
• Temperature differential
• Data hall operating limits

4. The Cooling Units and Control Requirements

The physical system consisted of multiple independent COOLair units installed across the data halls.

Each cooling unit included:

• EC fans
• Modulating fresh-air dampers
• Recirculation dampers
• Belimo actuators
• Internal environmental sensors
• External temperature and humidity sensors
• Filter monitoring
• A local programmable controller
• A local operator display

The dampers blended outdoor and recirculated air to maintain the required environmental conditions while maximising free-cooling availability.

The controls had to prevent unsuitable outdoor air from entering the space when it was:

• Too warm
• Too cold
• Too humid
• Outside the acceptable dew-point range
• Unable to provide a useful cooling benefit

At the same time, the system needed to react smoothly rather than repeatedly switching between operating states.

This required carefully tuned P.I.D. control and coordinated modulation of fans and dampers.

5. The Multi-Panel Control Architecture

The project required more than a collection of independent cooling-unit panels.

Multiple units operated within each data hall and needed to respond as one coordinated cooling system.

iACS developed a two-level control architecture.

Local COOLair Control Panels

Each free-cooling unit had its own controller.

The local panel managed:

• EC fan operation
• Fresh-air damper position
• Recirculation damper position
• Local temperature control
• Local humidity monitoring
• P.I.D. control loops
• Filter alarms
• Unit status
• Local safety functions

This allowed each unit to respond to its own sensors and operating conditions.

Central Marshalling Panel

A central marshalling panel coordinated the individual cooling units within the data hall.

Its responsibilities included:

• System-wide commands
• Coordination of multiple units
• Fire-alarm distribution
• Common shutdown control
• BMS communication
• Global alarm management
• Controlled restart logic

This master-and-slave arrangement provided local resilience while maintaining central supervision.

It also created a scalable architecture that could be repeated as additional halls and sites were added.

6. The Bespoke iACS Solution

iACS designed, manufactured and programmed a complete control package based on CAREL programmable-controller technology.

The recorded project scope included 14 custom control panels housed in IP55 metal enclosures.

The panels incorporated:

• CAREL pCO5 programmable controllers
• Custom 1TOOL application software
• PGD operator displays
• MP-Bus communication cards
• BACnet/IP communication cards
• Appropriately sized transformers
• Protection and isolation devices
• Field terminals for sensors, fans and actuators

The solution was not based on generic software.

iACS developed the application around the specific operating requirements of the free-cooling equipment, the data halls and the fire-safety interfaces.

Effective free cooling depends on accurate environmental data.

The system used internal and external temperature and humidity sensors, with suitable environmental protection for external locations.

The software continuously evaluated whether outdoor air could be introduced safely and beneficially.

Temperature Comparison

The controller compared external and internal temperatures to determine whether outdoor air could provide useful cooling.

Humidity Monitoring

External humidity was checked to prevent unsuitable moisture levels from being introduced into the data hall.

Dew-Point Protection

Dew point provided a more meaningful measure of moisture content than relative humidity alone.

This helped the controller reject outdoor air that could increase condensation risk.

Enthalpy Comparison

Enthalpy considers both the sensible and latent energy contained in the air.

Using this comparison allowed the software to determine whether outdoor air genuinely offered a lower-energy cooling opportunity.

Modulating Control

Rather than simply opening or closing the outside-air dampers, the control strategy modulated them between 0% and 100%.

This allowed the system to blend outside and recirculated air progressively, reducing abrupt environmental changes and supporting stable data hall conditions.

8. EC Fan and MP-Bus Damper Control

The cooling units used EC fans, giving the control system the ability to regulate airflow electronically.

EC fan control provides several advantages:

• Variable-speed operation
• Reduced fan energy at part load
• Improved airflow control
• Lower noise
• Simplified modulation
• Better response to changing cooling demand

The project also used Belimo MP-Bus actuators for the modulating dampers.

Direct MP-Bus communication allowed the controllers to:

• Command damper position
• Receive actuator feedback
• Verify movement
• Monitor actuator status
• Reduce conventional field wiring
• Improve fault diagnostics

The actuators included fail-safe or spring-return functionality where required so the dampers could move to their safe position during a shutdown.

The integration enabled precise 0–100% damper modulation with position feedback to the controller.

9. BACnet/IP BMS Integration

The control system had to communicate with the telecommunications provider’s wider Building Management System.

BACnet/IP communication was incorporated through dedicated Ethernet cards within the marshalling panels.

This enabled central visibility of information such as:

• Unit status
• Temperature values
• Humidity values
• Fan operation
• Damper positions
• Filter alarms
• Fire-alarm status
• General faults
• System operating mode

BMS integration allowed facilities teams to monitor the free-cooling installation alongside other critical building services.

It also reduced the need for large numbers of individually hardwired status points.

10. The Fire-Alarm Integration Challenge

The most safety-critical aspect of the project was the integration with the data halls’ VESDA system.

VESDA stands for Very Early Smoke Detection Apparatus. It continuously samples the air and can detect very small concentrations of smoke before conventional detectors respond.

When the VESDA system generated an alarm, the controls needed to:

1. Stop all relevant COOLair units immediately.
2. Remove fan-enable signals.
3. Command the outside-air dampers to close.
4. Allow spring-return actuators to move to their safe position.
5. Prevent the ventilation system from supplying additional oxygen to the affected environment.
6. Communicate the shutdown state to the wider system.

The shutdown had to operate consistently across every local panel, making central coordination through the marshalling panel essential.

11. Preventing Uncontrolled Restarts

Stopping the units was only part of the challenge.

The project team also had to consider what would happen when the VESDA alarm cleared.

An automatic alarm reset could remove the shutdown input before the cause of the smoke condition had been fully investigated. Without carefully designed logic, the cooling units could restart unexpectedly.

iACS developed a bespoke fire-shutdown sequence so the equipment would not return to normal operation without the intended reset process.

The sequence ensured:

• Immediate response to the fire input
• Coordinated shutdown of every connected unit
• Closure of fresh-air dampers
• Retention of a safe stopped condition
• Prevention of uncontrolled restart
• Deliberate reset before normal operation resumed

This is an important example of why life-safety integration cannot be treated as a simple run-permit input.

The complete behaviour of the system, during activation, while the alarm is present and after it clears, must be considered.

12. Protecting Controllers Through Signal Isolation

Another challenge arose from the electrical relationship between the central marshalling panel and the individual COOLair panels.

The system needed to exchange 24V signals between several panels. However, separate panel power supplies may not share identical electrical references.

Directly connecting these circuits can introduce:

• Potential differences
• Circulating currents
• Stray voltages
• Unreliable digital-input states
• Damage to controller electronics

iACS identified this risk during the design process and introduced opto-isolator relays.

What Does an Opto-Isolator Do?

An opto-isolator transfers a control signal while maintaining electrical separation between the two circuits.

In this application, it allowed the marshalling panel to exchange commands and status signals with the local panels without directly joining their voltage references.

This protected the controller circuit boards and improved the reliability of the multi-panel system.

The change demonstrates the value of reviewing the complete electrical architecture rather than treating each control panel in isolation.

13. Factory Testing and Software Simulation

Before attending site, the bespoke control software underwent simulation and functional testing at iACS.

Factory testing allowed engineers to verify:

• Sensor-response logic
• Free-cooling enable conditions
• P.I.D. sequences
• Damper commands
• Fan control
• BMS communication
• Fire-alarm behaviour
• Inter-panel signalling
• Manual-reset requirements

Testing complex sequences before site attendance reduces commissioning risk and allows engineers to identify logic issues in a controlled environment.

It is especially valuable where multiple panels must respond together to a common event.

14. On-Site Commissioning

Following factory testing, iACS engineers attended the initial data centre site to commission the system alongside 4Energy.

Commissioning included:

• Sensor verification
• Fan testing
• Damper modulation
• MP-Bus communication checks
• Free-cooling sequence testing
• Environmental threshold verification
• Inter-panel communication
• BACnet/IP checks
• Simulated VESDA alarms
• Full shutdown testing
• Restart and reset verification

The commissioning team deliberately simulated emergency conditions to prove that all affected units shut down as required.

The client subsequently confirmed that the shutdown tests had passed and that the units operated as expected.

15. The Multi-Site Rollout

The initial successful deployment created a repeatable control architecture.

The same core approach was subsequently used across additional data halls and locations, including Derby, Glasgow and Oswestry.

The rollout extended over several phases between 2013 and 2017.

This repeat business is significant because it demonstrated that the solution was:

• Reliable in operation
• Scalable across different halls
• Repeatable in production
• Flexible enough for site-specific requirements
• Suitable for mission-critical environments
• Supported by consistent software and documentation

Rather than designing each site entirely from the beginning, iACS could reuse the proven architecture while adapting configuration details to each application.

16. The Project Outcome

The completed system provided a coordinated free-cooling platform across multiple data halls.

The solution successfully delivered:

• Controlled use of outdoor air
• Reduced reliance on mechanical cooling when conditions permitted
• Stable internal temperature and humidity control
• Coordinated operation of multiple free-cooling units
• EC fan modulation
• Accurate MP-Bus damper control
• Central BACnet/IP monitoring
• Safe response to VESDA alarms
• Protection against unintended restart
• Electrically isolated inter-panel signalling
• A repeatable architecture for further sites

The successful shutdown testing was a particularly important milestone.

Following commissioning, the client reported that the system had passed the shutdown tests, the units operated as expected and the installation could be placed into continuous service.

The solution was then adopted across additional locations, validating both the control strategy and the underlying panel architecture.

17. Why This Project Matters

This project demonstrates that energy efficiency and operational resilience do not need to conflict.

Free cooling can significantly reduce the energy associated with data hall temperature control, but only when the environmental logic, actuator control and safety sequences are engineered correctly.

The system needed to answer several critical questions continuously:

• Is outdoor air cool enough to be useful?
• Is it dry enough to introduce safely?
• What damper position will maintain stable conditions?
• How should several independent units operate together?
• How should the BMS monitor the system?
• What must happen during a fire alarm?
• How can an unsafe automatic restart be prevented?
• How should signals be shared safely between separately powered panels?

iACS resolved these requirements through a combination of bespoke hardware, programmable software, open communications and detailed commissioning.

18. Key Capabilities Demonstrated

Bespoke Control-Panel Engineering

Fourteen custom panels were designed and manufactured around the cooling application and site requirements.

Custom Software Development

Application-specific software was created using CAREL 1TOOL rather than relying on generic control logic.

Free-Cooling Optimisation

Temperature, humidity, dew-point and enthalpy conditions were evaluated before outdoor air was introduced.

Master-and-Slave System Coordination

Central marshalling panels orchestrated multiple local cooling-unit controllers.

EC Fan Management

Variable-speed fan control supported energy-efficient response to changing cooling demand.

MP-Bus Actuator Integration

Belimo actuators were controlled digitally with positioning and operational feedback.

BACnet/IP Integration

The control system communicated with the wider BMS over an open building-automation protocol.

Life-Safety Sequence Programming

Custom logic coordinated safe shutdown and controlled reset following a VESDA alarm.

Electrical Risk Management

Opto-isolation protected controllers where signals crossed between separately powered panels.

Multi-Site Delivery

The proven design was successfully deployed across several data halls over multiple project phases.

19. The Value of Bespoke Data Centre Controls

Standard HVAC logic may not be suitable for mission-critical cooling.

Data centre controls must account for:

• Continuous operation
• High internal heat loads
• Tight environmental limits
• Redundancy
• Energy efficiency
• Multiple interacting units
• Life-safety integration
• Central monitoring
• Controlled failure behaviour
• Safe restart procedures

A bespoke controls approach allows the system to respond to the exact operating philosophy of the facility rather than forcing the equipment into a generic sequence.

20. Supporting Modern Data Centre Applications

The same engineering principles can support a range of critical environments, including: Telecommunications facilities Colocation data centres Enterprise data centres Edge computing sites Network-operation centres Server rooms Critical communications infrastructure Industrial control rooms Battery and energy-storage facilities As data centres continue to prioritise energy performance, free-cooling optimisation and intelligent controls will become increasingly important.

Looking for a Controls Partner for a Mission-Critical Environment?

Data centre controls require more than basic fan and damper automation.

They require a complete operating strategy that balances environmental stability, energy efficiency, system coordination, fire safety and long-term reliability.

At iACS, our engineering services include:

• Bespoke control-panel design
• Control-panel manufacture
• Programmable HVAC software
• Free-cooling strategies
• P.I.D. loop development
• EC fan control
• Damper and actuator integration
• BACnet and Modbus communication
• Fire-alarm interfaces
• Master-and-slave control architectures
• Factory simulation
• Installation support
• On-site commissioning
• Retrofit and optimisation services

Whether you are developing a new data centre cooling system or improving existing infrastructure, our engineering team can create a solution tailored to your operational requirements.

 Speak with iACS today to discuss how our bespoke controls, software and commissioning expertise can help protect critical infrastructure while maximising cooling efficiency.