Summary
Designing DHW. Adveco highlights existing and new hurdles impeding sustainability strategies which target water heating, a business-critical service with potentially high energy demands and one of the notable contributors to carbon emissions from the non-domestic built environment…
Adveco highlights existing and new hurdles impeding sustainability strategies which target water heating, a business-critical service with potentially high energy demands and one of the notable contributors to carbon emissions from the non-domestic built environment. We start with designing DHW…
Designing a successful domestic hot water (DHW) system for a commercial building today necessitates a holistic understanding of system design. One which demands a nuanced approach, carefully balancing adherence to stringent building legislation, paramount safety considerations, economic viability, and the growing imperative of environmental sustainability.
One of the foundational approaches lies in a thorough understanding and implementation of the UK Building Regulations, specifically Part G (Sanitation, hot water safety and water efficiency) and Part L (Conservation of fuel and power). Part G sets clear guidelines on the provision of hot water at safe temperatures to prevent scalding, mandates measures to limit water wastage, and specifies requirements for the design and installation of hot water systems. Part L focuses on energy efficiency, requiring systems to be designed to minimise heat losses (through effective insulation of pipes and storage vessels), efficient heat generation, and appropriate controls. Compliance with these regulations is not merely a legal obligation but a crucial step towards ensuring safety and energy efficiency.
Safety remains a non-negotiable aspect of hot water system optimisation. Beyond regulatory compliance, a proactive approach to safety involves meticulous risk assessments during the design and installation phases. This includes identifying potential hazards such as legionella growth, which thrives in stagnant warm water. Implementing strategies like maintaining hot water storage temperatures above 60°C, ensuring regular flushing of the system, and preventative design of pipework to avoid dead legs. Furthermore, regular maintenance and inspection schedules are essential to identify and rectify any potential safety issues before they escalate.
Cost optimisation requires a comprehensive lifecycle perspective, encompassing initial capital expenditure, ongoing operational costs (primarily energy), and maintenance expenses. While the allure of lower upfront costs might be tempting, a more strategic approach considers the long-term energy consumption and potential for savings through efficient technologies. Investing in high-efficiency boilers or heat pumps, properly sized storage tanks to minimise reheating losses, and sophisticated control systems can significantly reduce energy bills over the system’s lifespan. That said, good design will also help significantly lower capital investment, as it helps avoid system oversizing, which inherently leads to excess investment in unnecessary or duplicated appliances. Furthermore, designing for durability, especially when considering local water quality (hard or soft), can minimise long-term maintenance, repair and replacement costs. Recognising the total cost of ownership is therefore crucial for making informed decisions.
Finally, there is sustainability, which involves minimising the system’s environmental footprint through reduced energy consumption and the adoption of renewable energy sources. Heat pumps, for example, offer a significantly lower carbon footprint compared to traditional fossil fuel boilers, but are best deployed extracting heat from the air to preheat a hot water system. Solar thermal systems, a true and well-proven renewable, can directly harness solar energy to preheat or fully heat water, further reducing reliance on conventional energy sources. Integrating smart controls and monitoring systems can further optimise energy usage by adjusting heating schedules based on occupancy and demand, preventing unnecessary energy waste.
As a result, sustainability has not only emerged as a key driver in the optimisation of commercial hot water systems, but has started to supersede both cost optimisation and, of some concern, safety. This is notably the case with the latest generation of high-temperature heat pumps dependent upon poorly regulated propane-based R290 refrigerants, and electrical systems, such as photovoltaics (PV), which have a known potential for causing electrical fires on rooftops. Both technologies are fêted by the government as critical to the roll-out of sustainability strategies, but, in the wake of the Grenfell Enquiry, are increasingly problematic in their current iterations.
With an unprecedented acceleration in technology, many are now racing to keep up with innovation in this field, further compounding errors typically arising from poor design or installation.
Gas to Electric – Recognising Common Errors
Without a doubt, one of the great challenges that faces the UK is the retrofit of HVAC systems across the commercial built environment. According to the Department for Business, Energy, & Industry Strategy (BEIS), there were 1,755,000 recognised non-domestic buildings in England and Wales at the end of March 2024. The UK Green Building Council (UKGBC) estimates that 80% of these buildings will still be here in 2050, meaning the large majority, which still rely on gas water heating, will require retrofit over the next 25 years if improved performance for sustainable operation is to be achieved. Transitioning commercial water heating from gas to electric presents unique design challenges, and several common errors can arise if these differences aren’t carefully considered.
To enable change requires accurate load assessment. Underestimation leads to an insufficient hot water supply during peak times, causing user dissatisfaction. Conversely, overestimation results in oversized systems with higher capital costs and increased energy losses due to heating and storing excessive water. Accurate load calculations, considering occupancy patterns and usage habits, are crucial for optimal system sizing and can be easily secured by monitoring live flow through the system via low-cost, non-invasive water metering. The latest generation of water heaters may even incorporate water metering as a feature.
Without credible data, one frequent mistake is to plan for a direct capacity swap without accounting for energy characteristics. Simply replacing a gas boiler with an electric heater of the same kilowatt rating can lead to undersized systems. Electric heating elements, or systems using heat pumps for low-carbon preheat, will have a slower recovery rate compared to gas-based systems, meaning they take longer to reheat water. A design must factor in this slower recovery and increase the storage volume or the kW rating of the electric heater to meet peak demands.
Another pitfall of transitioning from gas to electric is neglecting the electrical infrastructure. Existing commercial buildings might have sufficient gas supply but lack the necessary electrical capacity for a high-demand electric water heating system. The resultant upgrades to the building’s electrical supply are not only extremely costly, but can also seriously impact project timeframes, either of which can stall or lead to cancellation of sustainability projects. A thorough assessment of the existing electrical infrastructure and DHW demands can help deliver systems that require less electrical capacity, accelerating project timeframes as well as reducing capital investment and ongoing operational costs, which are another major consideration.
While electric systems eliminate gas usage for greater carbon savings, electricity costs per unit of energy are much higher, by a factor of four at the time of writing. This is not simply a case of choosing better value electricity tariffs; it also requires balancing a DHW application design to optimise running costs. This is best achieved by taking advantage of low-carbon technology, such as heat pumps and solar thermal, to preheat water and offset the demands of the more expensive primary electrical heating. Failing to design the system to effectively utilise self-generated heat during daylight hours is a key missed opportunity. Electric water heating is an ideal partner for on-site renewable energy generation, of which solar thermal is by far the most efficient, proven and safe option, offsetting at least 30% of annual electrical demand throughout the UK. With smart controls and appropriately sized storage, applications can maximise the benefits of renewable and low-carbon integration.
An integrated perspective for future water heating
A holistic approach to optimising DHW integrates legislation, safety, cost, and sustainability throughout the entire lifecycle of the hot water system, from initial design to ongoing operation and maintenance. This requires a thorough understanding of building regulations, load assessment, appropriate component selection, optimised system layout, robust safety measures, and consideration for future needs and maintenance. Engaging experienced and qualified professionals is crucial to ensure a commercial hot water system is safe, efficient, cost-effective, and compliant, especially when transitioning from existing gas to electric hot water provision.
Commercial building operators that embrace an integrated perspective that considers the interconnectedness of these critical factors will advance building sustainability faster, while prioritising safety and minimising costs now and in the future.
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