Singapore’s climate is hot and humid. Air conditioning (HVAC) systems run long and hard to create comfortable conditions in workplaces, hotels and homes. That consumes a lot of energy, which in turn takes its toll on the environment. 

If there’s any way to produce like-for-like conditions – cool, odourless and clean air – while meaningfully reducing HVAC energy consumption, it’s going to produce a lifetime of benefits. From lower energy costs, to lower carbon emissions, to an overall strengthening of the HVAC operator’s Environmental, Social and Governance ( ESG ) strategy and credentials.

If you’re a luxurious 5 star venue, every one of those points resonates all the louder. That’s how BSG and one of Singapore’s best known venues came together. One smart hotelier aiming to reduce its energy and maintenance bills, improve the experience of guests through cool, odourless and clean air, and shrink its carbon footprint too. One smart hygiene business with the ability to retrofit its technology to sophisticated HVAC systems.

By delivering clinical doses of UV to air handling units (AHUs) and their cooling coils, BSG’s technology keeps them clean and so produces significant reductions in power consumption, C0² and cleaning costs.

Under the hood: a worst case scenario

Drawing hot and humid air onto an AHU coil creates perfect conditions for the growth of bacteria and fungi that – in community – create biofilms. Biofilms are very robust, sticky, and they are resistant to water and detergents (…think organic polymer). They have serious impacts on the efficiency of HVAC systems, not to mention the quality of air breathed by humans. 

Even very thin biofilms can significantly reduce heat transfer between a cooling (or heating) coil and the airflow, requiring chiller units (or heaters) to work proportionally harder to maintain desirable temperatures.

Biofilms cause supply fans in an AHU to work harder too. The reduced heat transfer at the cooling coil means the off-coil air is less cool. The HVAC’s flow control will attempt to make up for that by increasing the airflow to the downstream spaces. 

And the biofilms directly impede airflow through the coil, which causes another increase in fan speed to compensate. 

Not how, but how much

But the ‘how’ is only part of the story, and probably the bit that you already knew pretty well. The better question is ‘how much?’ One unwelcome fact is that a fan’s power consumption operates on a cube law – a fan spinning 2x as fast uses 8x the energy, for example. So even small changes in fan speed create big differences in energy consumption. 

That said, we can’t figure this out with maths alone. HVAC systems have lots of active components, and there are multiple feedback loops engineered into systems for control and efficiency. Shortfalls or surpluses in performance here are compensated for, smoothed out, there.

That means there’s a teaspoonful of unpredictability in every HVAC control system that makes it essential to test and measure, rather than predict. That way we can accurately characterise performance across different operating conditions. 

In Singapore, that’s exactly what we’ve done.  We created a controlled experiment within a live HVAC system, to discover just how much difference BSG’s COILCARE^TM can deliver. In real world conditions and in real time.

From those results, we’ve been able to calculate how much net energy the solution has saved over the measurement period. And from there it’s possible to make a good estimate of total cost savings over a year. 

Proof of concept

BSGs COILCARE solution uses clinical doses of UV radiation to prevent the growth of biofilms, by effectively eliminating the microorganisms that cause them – at the AHU coils and in circulating airflows. The solution is precisely engineered, from the composition of the lamps upwards, to:

• perform effectively in the high humidity, low temperature environment created close to the cooling coils. 
• dose a very high percentage of the coil area
• penetrate the depth of the coil
• Minimise its own disturbance to airflow

As proof of concept, the key outcome was that the solution should recover its own startup and operational costs, and produce a net cost saving from HVAC energy reduction, as well as through the elimination of alternative coil cleaning costs.

The Blueprint

To establish baselines, airside instrumentation monitored temperature and humidity trends from mid January. Chilled water temperature sensors and airflow sensors went live in mid March.

BSG COILCARE was installed in the AHU of Floor 26 (of 35) and became operational on 3rd April – Day Zero.

The range of measurements captured by our instrumentation is shown below. Measurements were logged every 30 seconds. That’s nearly 3000 measurements every day, for 84 consecutive days, taking the proof of concept from early April to the last week of June.

Outcomes and key results

Bottom line energy savings – extrapolated for all 35 AHUs at the venue. Centre column reflects energy savings in USD in 2023, with the right hand column reflecting energy savings in EUR.

Other savings – eliminating the alternative maintenance regime of stripping AHUs and manually cleaning coils:

Other benefits and savings include: 

• Extended AHU life
• Further heat transfer improvements 
• Fine tuning of control systems

The breakdown – key contributing measurements and statistics

29% increase in heat transmission

U-value (measured as W/m²K) at the coil showed a rising trend, steepest at Day Zero, but still positive at day 84. This rise – by nearly one third – corresponds well with measurements taken on comparable COILCARE-protected systems elsewhere. On well maintained systems, COILCARE still typically improves coil U-values by 20 to 40%.

Lower supply fan speeds

Airflow (in ms^-1) reduced from a daily mean of 15.1ms^-1 to 14.1ms^-1 over the period – a result of reduced AHU fan speed. The increased U-value delivered cooler supply air at the same ‘water-in’ temperature (7℃). To maintain the target zone temperature, the variable air volume (VAV) box restricts air flow, in a feedback loop causing the AHU’s variable frequency drive (VFR) to slow the fan. 

35% reduction in chilled water energy demand

Or Q-value (measured in MJ). The second feedback loop centres on the chilled water valve. Cooler supply air – from that increasing U-value again – means cooler return air to the AHU (ie a larger ΔT). That’s the signal for the chilled water valve to reduce flow, so the chiller has less work to do. 

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