Energy Saving v Legionella Risk

Going green’ is not just a focus on using de-carbonised energy to generate hot water. It’s a combination of efficient generation and reducing waste.

How is this achieved?

Good housekeeping, rational designs/installations, and working practices can be effective in saving energy safely and is an addition to a disproportionate focus on decarbonised generation in the quest to ‘going green’. The more complex the solution to decarbonisation is, the greater the cost and potential for mechanical and human error.

Can you make the call between ‘just in case’ as guidance, such as ACOP L8 and HSG274, advises or being rational with your design and Legionella risk assessment reflecting actual use?

Part 1 – Hot Water Generation

Heat Pumps

Two main types of heat pump are used to heat domestic hot water. Ground source heat pumps circulate water through pipework installed in the ground, extracting warmth from the ground. Air source heat pumps use fans to pass air across coils to extract the energy from the air.

Net-zero incentives direct us to heat pumps, and manufacturers share that the energy output from air source heat pumps is circa 3kW for each 1kW input. This, however, is under optimum conditions, which vary with the UK climate. Note that for this ‘free’ energy, the heat pump requires 1kWe (electrical energy) to generate 3kWt (thermal energy), meaning your electricity demand will significantly increase if your primary energy is currently gas. Additionally, associated plant and equipment, combined with the required plant space, is costly and sizeable.

Heat pump technology continues to improve to overcome the challenge of generating hot water at the required operational temperature. Manufacturers advise that low-grade heat is a thing of the past. However, it still needs to be checked that temperatures are achievable through the UK seasons and that achieving 70^oC for the pasteurisation of the hot water system is also possible. It may be that you will need supplementary heating.

Solar Thermal Energy

Solar water heating starts with solar collectors, panels, or tubes that circulate a mixture of water and anti-freeze to and from the hot water cylinder. Due to the UK climate, hot water cannot be guaranteed all year round; therefore, a supplementary heat source, e.g., an immersion heater, is needed to achieve 60^oC, and therefore the least suitable for the UK climate.

Solar / Photovoltaic (PV) Panels.

PV panels are the most common domestic renewable energy source in the UK. They capture the sun’s energy and convert it into electricity and are a supplementary source to the mains electricity installed; therefore, there is no need for a supplementary heat source for generating hot water.

Part 2 – Energy Saving

Water Boilers vs. Kettles

Are you conscious of this situation at home, filling a kettle just for one hot drink? The same logic applies in the workplace; hence, since the 1980s, wall-hung water boilers have brought efficiency as they only heat the replenished water following someone making a cuppa. Yes, there are standing losses, but the water boiler insulation slows down the rate of heat loss.

Water Coolers

Water coolers are often the expected source of drinking water in many large facilities. Some find that the refreshment of chilled drinking water is better than the water from a tap, but if you are serious about ‘going green’, have you ever thought about avoiding their installation?

Avoiding water coolers: -

• Removes the bacteria risk and maintenance requirements.
• Removes purchase and installation costs.
• Removes the electricity usage (between 0.5 and 1.2kWh/day).
• Increases usage from dedicated welfare kitchenettes.

If water coolers are to be installed be rational in their number and install only in centralised high-use areas to improve use.

Domestic water outlets

Habits of ‘future-proofing’ facilities bring excess, and outlets should only be installed if needed. Avoid outlets you 'Believe' will be used or those ‘just in case’ as this will bring ‘by design’ infrequently used outlets that require dedicated flushing regimes using resources, water, and energy (hot water generation/booster pumps). For example, have you included dedicated outlets installed for the window cleaning contractor who attends maybe twice a year, giving you the need to flush weekly for 50 weeks, and then find that the contractor uses their own distilled water?

Healthcare standards are adopting this approach, primarily for improved patient care, by omitting wash-hand basins in patient rooms (removing the hazard) if en-suite bathrooms are present.

Thermal Insulation – keeping the hot water hot and cold water cold

Piped services and plant and equipment should be adequately insulated. Often, hot and cold water pipes are routed side by side in service risers and ceiling/floor voids. Ensuring pipework is insulated keeps the energy within the hot water pipes, reducing heat gain in the space and reducing the warming impact on insulated cold pipes. Maintaining hot water above 50^oC (or 55^oC in healthcare premises) and cold water below 20^oC is key to lowering legionella risk.

Pipe Distribution Losses

Insulated pipes still bring distribution losses, so removing hot water centralised pipework removes the associated distribution losses. Approaches can include using localised mini-plate heat exchangers (heat interface units) served from a centralised heating network or point-of-use electric water heaters can be used. Each approach does, however, come with its varied characteristics and components; consequently, it should be selected on an informed basis via the Water Safety Project Design Review. Either way, reducing hot water centralised pipework and plant reduces the system volume, energy losses and risk from components like calorifiers.

‘Value’ Engineering

True value engineering is where the justification for keeping or adding quality to minimise risk, and Op Ex occurs, i.e. remote monitoring that can provide data to inform if outlets are infrequently used. Or if we are talking omissions, it’s removing thermostatic mixing valves (TMVs) / taps where the scalding risk assessment has identified this opportunity.

‘Gloves off’ approach

Disposable gloves bring increased bacteria risk. They create moisture and warmth on the hands, an ideal environment for bacteria to grow, as well as cross-contamination from contact with various surfaces. Avoiding unnecessary use of gloves removes the environmental impact from both the disposal aspect and the manufacturing and transportation costs (embodied carbon). Gloves should not be a substitute for hand washing; therefore, the ‘Gloves Off’ approach could, but should not, bring greater water/energy consumption.

Embodied Carbon

All items of a water system should factor in ‘Embodied Carbon, ’ the total CO₂ from the energy used to create any item from its origin as raw material through to the end of the disposal / recycle process.

Water systems' design, installation, and operation need to be looked at from a holistic perspective. Identifying the user risk and their specific needs through design risk assessment will help keep decisions rational, minimising the environmental impact.

Summary

Ensuring the design risk assessment is a true reflection of actual use minimises waste. Avoiding the unnecessary installation of outlets, including those with thermostatic control, removes

• the hazard reducing the risk,
  
  
• the flushing requirement and associated water consumption / minimise energy costs
  
  
• ppm requirements
  
  

Cap Ex and Op Ex benefits are also brought whilst eliminating associated embodied carbon.

Over-designing for future-proofing adds margins, bringing exaggerated demand, which leads to oversized plant and equipment and inefficiencies. Rational designs allow the hot water generating infrastructure to be sized accurately.

Editors Note: The information provided in this blog is correct at the original publication date – March 2025.

© Water Hygiene Centre 2025