BOILERS & HOT WATER The low-carbon hot water challenge T
Hospital and healthcare premises face unique challenges when it comes to decarbonising hot water to ensure a safe, reliable and efficient service. Andy Green, technical director at Baxi, discusses the challenges and opportunities
he NHS is committed to reaching net zero from its directly controlled emissions by 2040, with a target of an 80% reduction in emissions between 2028 and 2032. This target places duties on NHS England, and all trusts, foundation trusts, and integrated care boards, to contribute towards statutory emissions and environmental targets. The high hot water demand frequently associated with hospitals makes it a clear target for efficiency improvement and emissions reduction. But it’s one that comes with certain challenges – from the huge variety of building types and hot water systems to the specific considerations relating to domestic hot water (DHW) provision in these hygiene-critical environments. First and foremost is the need to prioritise patient safety and wellbeing. Delivering an adequate hot water supply quickly ensures that healthcare professionals have the water they need to keep patients safe and comfortable. However, hospital hot water distribution systems are highly complex. Consequently, measures need to be implemented to prevent the build-up of waterborne pathogens, mostly related to the control of legionella bacteria, in the hot water system. To reduce the risk of legionella, the Health and Safety Executive advises that DHW should be stored at least at 60ºC and distributed so that it reaches 55ºC at point of use in healthcare premises. As the risk of patient scalding or burning
increases when water temperatures are too high, a further consideration is temperature control which needs to be provided at hot water outlets to protect patient safety. With a huge variety of building types and heating systems across the one estate, there will be any number of possible solutions and the chosen route will depend on multiple factors. With that in mind, let’s consider some of the available opportunities to drive down emissions related to the hot water system while continuing to prioritise patient safety.
Dedicated plant
The first step should always be to understand how and where energy is being used. In buildings where a central boiler plant and calorifier provide both heating and DHW, separating out the hot water is advisable to avoid unnecessary energy use. The chosen technology can then be sized more closely to meet the specific requirements for each building more efficiently. This also opens up the ability to site direct electric or direct gas-fired
hot water equipment at – or very close to – point of use.
Depending on the building, the existing hot water system and where the hospital is in its sustainability plan, another option might be to replace any non-condensing direct-fired water heaters with more energy-efficient condensing models to improve performance and reduce associated emissions.
Low and high temperature heat pumps
For the larger task of replacing the heating system, installing heat pumps will likely be the favoured approach. There are a number of ways in which air source heat pumps (ASHPs) can be used for DHW generation. Low temperature ASHPs can be used with
direct electric water heaters in an all-electric approach or direct gas-fired solutions in a hybrid approach to raise the DHW to safe temperatures.
The all-electric approach is more likely to be the option of choice but would involve higher volumes of stored DHW. It is therefore important to consider available space and weight for the larger cylinders – particularly when dealing with rooftop or non-basement plant rooms. Additional forms of legionella control legionella within the larger volumes of stored water will also need to be carefully monitored and managed. Another option is high temperature ASHPs which are capable of delivering the high flow temperature required to meet the design temperature for sanitary hot water. The
advantage of using HT heat pumps is that it avoids the need for an alternative form of technology to store the DHW above legionella temperatures (60ºC or higher), bringing greater design flexibility. This option also requires less space, for a much simpler design and easier installation. However, it should be noted that the coefficiency of performance of heat pumps drops off at higher temperatures, affecting the real-world efficiency and subsequently operating costs.
Hybrid solutions
In older NHS buildings, where the natural gas supply might be maintained, there is the opportunity to use ASHPs to preheat direct gas-fired water heaters (DGFWH) in a hybrid approach. From a design perspective, DGFWHs have
greatly reduced storage compared with other systems, which means less weight and fewer issues within roof top plant rooms. Importantly, energy usage is also reduced, along with associated emissions, as there is less water to maintain at temperature. Some DGFWHs such as the Andrews MAXXflo Evo also come with in-built anti-legionella functions as standard which make legionella control far more straightforward, reducing maintenance time for facilities managers. With smart return temperature sensor technology, they have the ability to provide further energy and emission savings by reducing the time required to complete the pasteurisation process.
Point-of-use
Point-of-use electric water heaters should also be considered as an efficient solution to an immediate supply of sanitary hot water in hospitals and GP surgeries, as they only generate energy when required. Installing a point-of-use water heater such as the Heatrae Sadia Multipoint that incorporates anti- legionella functionality, water pasteurisation and anti-tamper design, will ensure that water is adequately stored, cycled and distributed.
Specialist support
As each project and building type will have its own particular requirements, estates managers will benefit from support from specialists when planning their pathway to the energy transition. Your manufacturer of choice should be able to advise not just on their specific products but also on the legislation and guidance relating to hot water delivery. For a balanced resource on the options available to reduce the carbon intensity of domestic hot water generation in hospitals and healthcare facilities, download the free guide, Hospitals, healthcare facilities and the low- carbon hot water challenge. Visit: https://www.
baxi.co.uk/landing-pages/knowledge-centre/ hospitals-healthcare-buildings-and-the-low- carbon-hot-water-challenge.
12 BUILDING SERVICES & ENVIRONMENTAL ENGINEER FEBRUARY 2024 Read the latest at:
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