Traditional cooling tower control will either rely upon thermostatic control through variable speed drives (VSDs) to modulate fan speed by water temperature. It’s simple, reliable but…. limited. EWK Smart control integrates multiple sensors, a PLC, and HMI interface to optimise performance across the whole system, not just fan speed, which leads to a whole host of benefits…..
This article compares VSD-only and Smart Control configurations in industrial cooling systems, outlining what each delivers in energy efficiency, reliability, and compliance, and what to consider when specifying or upgrading your system.
1. VSD Control – The Established Baseline
Variable Speed Drives (VSDs) remain the standard method of fan control in most cooling towers. A temperature sensor in the cold-water circuit modulates fan speed to maintain a target temperature. It’s simple, proven, and relatively inexpensive.
For a typical 500 – 1000 kW duty tower, a VSD can trim fan energy use by a significant amount versus fixed-speed operation. However, its logic is narrow it only “sees” temperature. It doesn’t assess water flow, ambient conditions, or mechanical strain, and so can’t optimise the system holistically.
VSD control works best where – (See our latest article on this)
- Loads are steady,
- Water quality and mechanical condition are well-managed,
- Operator oversight is regular.
But in variable or compliance-driven environments, that simplicity becomes a constraint. See our calculator below to understand what savings YOUR COMPANY could make through adopting this simple cost-effective technology:
2. Smart Control – Integrated Optimisation
Smart-controlled towers such as EWK-A Smart models combine a PLC, HMI, and a network of sensors monitoring temperature, pressure, vibration, oil condition, sump level, and ambient climate.
Each device serves a distinct function:
| Device | Function | Benefit |
|---|---|---|
| Vibration sensor | Monitors gearbox/motor condition | Predicts bearing or drive issues before failure |
| Load cell | Detects packing fouling or blockage | Triggers maintenance before performance loss |
| Inlet pressure sensor | Verifies water flow | Protects circulation pumps |
| Ambient temp & humidity sensor | Monitors conditions | Adjusts fan and spray setpoints dynamically |
| Scheduling control | Restricts fan speed by time | Supports night-time noise compliance |
| PLC + HMI | System logic and interface | Enables remote monitoring and operator tuning |
This network transforms control philosophy from reactive to predictive, using data to anticipate, not just respond.
3. Control Philosophy: Reactive vs Predictive
A VSD-only tower reacts to a single variable cold-water temperature. A Smart system weighs multiple data inputs to optimise across performance, compliance, and asset life.
For example:
- Vibration trend: rising amplitude signals can indicate bearing wear. This allows for predictive maintenance to be planned before failure, potentially saving 10,000's in production losses.
- Pack weight increase: alarms due to increased fouling, highlighting to maintenance teams, triggering cleaning procedures before pressure drop escalates and thermal performance drops.
- High sump level: alerts to make-up valve failure, avoiding overflow or uncontrollable water levels.
- Ambient feedback: enables fan modulation based on humidity as well as temperature. Reducing energy and water usage.
Vistech and EWK's use of this technology is not about complexity for complexity sake or due to engineers' need to overcomplicate things.... it’s about resilience and quantifiable financial, water and energy savings. Predictive control avoids downtime and improves duty stability across the year.
4. Performance and ROI
Payback periods typically range 12–24 months once Smart Control algorithms are tuned, depending on duty, water quality, and site energy tariffs. For large industrial sites running year-round, Smart Control can yield five-figure annual savings with fewer unplanned stoppages. VSD-only operation are typical particularly in systems with variable load or multi-tower setups.
5. Implementation Considerations
Retrofitting Smart Control onto existing towers is something we've been able to complete for many systems around the UK. VSDs, sensors, and PLCs can be integrated into older units during scheduled shutdowns. The key is accurate data calibration as the setpoints must reflect verified flow, temperature, and pressure readings for your specific system.
New builds benefit from full integration during design. This allows for optimal routing of sensor wiring, weatherproof control enclosures, and factory-tested logic.
A Functional Design Specification (FDS) or FEED study should precede implementation, defining:
- Sensor locations and I/O mapping,
- Data validation method,
- Alarm limits and operator access hierarchy.
6. When a Simple VSD Still Makes Sense
Not every site needs Smart Control. For smaller or intermittent duties, a well-calibrated VSD may still be optimal.
Typical scenarios:
- Single-cell towers below 200 kW duty.
- Non-critical or seasonal operations (e.g. HVAC condenser water)
The rule of thumb: if downtime cost is high, Smart Control pays back quickly; if not, simplicity may win.
7. Summary Comparison
| Aspect | VSD Control | Smart Control |
|---|---|---|
| Fan Energy Optimisation | ✔ Basic temperature-based | ✔✔ Multi-variable, humidity & schedule-based |
| Mechanical Protection | ✖ None | ✔ Vibration, oil, level alarms |
| Maintenance Insight | ✖ Manual | ✔ Predictive alerts (pack fouling, flow deviation) |
| Water Management | ✖ Manual | ✔ Sump-level and make-up monitoring |
| Compliance Support | ✖ None | ✔ Noise/time scheduling, HSG 274 traceability |
| ROI Potential | 12–18 months (energy only) | 12–24 months (energy + asset life) |
Practical Checklist – Before You Specify Control Upgrades
- Verify cooling duty (kW) and load variation.
- Confirm target cold-water temperature range.
- Check whether inlet/outlet pressure data is available.
- Assess noise limits and scheduling restrictions.
- Identify existing sensors and signal types (analogue/digital).
- Review water treatment and fouling frequency.
- Evaluate downtime risk and redundancy needs.
- Ensure operator training or HMI support capacity.
- Compare energy tariffs to model potential ROI.
- Commission a Technical Survey to verify parameters.
Whats Next?
- Book a technical survey to assess upgrade viability.
- Compare Smart Cooling Towers.
- Review control retrofit options.
- Discuss funding routes.
- Contact Vistech Engineering for a quotation.