Hot water storage for commercial properties as part of a net zero strategy,

Hot Water Storage As Part Of A Net Zero Strategy

UK commercial properties planning to invest in reducing carbon emissions should be considering hot water storage as a core part of their strategy.  With the aim of driving down 78% of carbon emissions by 2035 the government’s focus for net zero has leant heavily on the introduction of heat pumps and a transition to grid electricity, with particular stress and support placed on domestic installations. Many will argue that this is leading to a critical oversight of the commercial sector, and a rush to embrace new technology rather than considering existing options that support high temperature, intensive and/or long peaks, plus the multi-outlet demands typically found in commercial hot water applications. Hot water cylinders are a case in point, with proven, untapped potential to be used for smarter thermal storage.

Indirect-fired water heaters (also known as calorifiers) and buffer tanks are a requirement on commercial build projects where large volume storage of water at high temperatures is specified. In essence, these act as the batteries of a domestic hot water (DHW) system within a commercial property and can be more cost-effective and less environmentally damaging.

To introduce thermal energy into the hot water cylinder an additional heat source is required. Typically, the water will be heated directly by a gas or more preferably now an electric boiler, passing it through the cylinder and using heat exchange to transfer energy to the cold water in a separate system of pipework. This does mean that an indirect water heater cannot react as quickly to demand as a direct-fired water heater, however, with the cylinder working as a buffer and storing the hot water reduces the operational demands placed on the boiler. With the boiler no longer required to work as hard to meet the DHW needs of a building, energy is saved, costs are reduced and emissions fall.

Due to the transfer of heat through the walls of the heat exchanger element, the two fluids do not mix. Important for carbon-lowering strategies, this allows for more options in terms of the external heat supply and introduces a range of renewable technologies that use other fluids for heat transfer including solar thermal collectors and Air Source Heat Pumps (ASHP). Using heat pumps or solar as an energy source to preheat water within an indirect cylinder then enables a reduction in work from the direct top-up heat source. This is what enables DHW systems to reduce energy costs and emissions to varying degrees depending on whether this additional heating is provided by electricity or gas.

This is why hot water storage systems need to be seen as an essential part of any renewable strategy where energy input needs to be stored or deployed as and when required. One other key advantage of separating the supplies is that the risks of external contamination such as a build-up of scale in hard water areas or the corrosive effects of soft water are curtailed. Limescale is proving especially damaging in new high-intensity, all-electric systems installed in hard water areas.

Some will argue that since hot water storage is short term it lacks the versatility of local electric production and battery storage. But as with any hot water application, understanding the relationship between storage and recovery, and correct sizing is extremely important for efficient and cost-effective operation by ensuring thermal demands are optimised and not wasted.

According to the Hot Water Association a 300-litre tank, similar in size to that employed in smaller commercial projects, will store approximately 14kWh of energy. That is directly comparable to the storage capacities exhibited by current generation battery systems, but without the environmental footprint of Cobalt, and Lithium, used in their manufacture. Considerations of the harmful manufacturing processes and embedded carbon are rightly being incorporated as part of a well-thought-through sustainability strategy, so again hot water cylinders, typically manufactured with recycled copper and stainless steel, are a more environmentally friendly, well-understood, easy-to-install and much lower cost alternative for comparable gains.

At the heart of a successful low-carbon hot water system is a well-informed application design. Patterns of hot water usage and recognition of periods of peak demands often make sizing a complicated process. Poorly designed systems will therefore often overcompensate and, by being oversized become more costly and less efficient.

At its simplest, a commercial system should hold an hour of hot water output in storage, but the function of the building, its population and activities will adjust requirements, for example, where hospitals will typically exhibit a 24/7 demand for hot water, schools and offices may be limited to just 7½ hours per day. In some refurbishment scenarios, we will also see a physical limitation of space available for DHW storage, in which case a system will put more demand on the boiler or renewable to increase the output for preheating, reducing the required size of the cylinder.

Integrating an indirect water heater within a hot water system gives you a number of design options, as a larger cylinder means the boiler can be smaller, or the reverse if the existing system has a large efficient boiler. Understanding the hot water demand is critical. If demand is not so great, then using a larger cylinder can lead to unnecessary capital and ongoing operational expenditure. Go too small and the storage could prove inadequate and the system will not achieve its operational requirements. Attaining the correct balance of demand and efficient, cost-effective supply is what ultimately defines a successful system.

At Adveco, these factors are supported by a wide variety of cylinders.  The Stainless Steel Indirect (SSI) range, for example, is supplied with a single high-output internal heat exchange coil at a low level to serve as an indirect water heater.

The ATSx range provides water heaters designed to be used with indirect heat sources across a range of DHW installations exhibiting smaller demands but requiring more than six bar pressure. For more complex and renewable-based systems, the Stainless Steel Twin-Coil (SST) or ATSR ranges offer a pair of independent internal heat exchange coils to serve DHW systems. Each high-output coil can be used with a separate heat source, enabling effective integration of renewable technologies or multiple heat sources, or alternatively can be combined to increase the heat transfer capacity from a single high-output source.

The GL range of hot water cylinders provides a lower cost choice, with the GLC serving as indirect water heaters or preheat vessels, GLE serving as an electric water heater or buffer, and the GLT range offering twin coils for two separate heat sources.

These hot water cylinder ranges come with multiple connectivity options and offer from 200 to 5000 litres of storage, giving specifiers a wealth of choices when designing bespoke DHW systems with Adveco.

Care Home Sustainability

Care Home Sustainability

Care home sustainability is growing on the radar of operations & building managers. It is becoming a facet of the decision-making for families and an indicator of the personal comfort the residential client can expect from a facility.  Refurbishing existing facilities has a number of implications, not least cost, but also disturbance of residents, so where can quick, easier wins be made as part of a decarbonisation strategy?

Every care home needs hot water. From basins to baths and showers, catering and wash down. Most facilities will run successfully on a system based around gas-fired water heaters unless a new build in which case the preference is to move to electric water heating to take advantage of the increasingly less ‘dirty’ grid. This does have implications for running costs, with electricity on average costing as much as 3.8 times that of gas. So why change things? The simple answer is net zero, and the need to be more sustainable. Because of the ubiquitous need for hot water, which can account for as much as 30% of a building’s daily energy demands, addressing how it is secured is one of the best ways of making active carbon savings today to begin delivering care home sustainability.

Deploying either heat pumps or solar thermal as a renewable to provision the initial preheat, is the most logical approach. Where problems and unnecessary costs can quickly arise is when existing gas-fired ‘top up’ water heating is replaced with like-for-like electric which can lead to gross system oversizing. Domestic hot water (DHW) systems that deliver care home sustainability should still be designed to accurately meet a business’ needs. At Adveco, our application design team has a thorough knowledge of residential care, understanding the peak hour and length of the peak, which are the starting point for determining demand and ensuring the hot water system is correctly sized.

This demands a bespoke approach as every facility is different. The number of rooms, facilities such as basins, showers, deeper baths and guest mobility, all impact on the sizing. The physical constraints of the property, from plant room and roof space to noise levels all impact technology choices.  Adveco can advise on this sizing and provide accurate monitoring to ensure applications are fit for purpose and future proof. As a result, decisions to move to more sustainable operations are optimised and do not leave properties facing unwarranted capital or unexpected new operational costs.

Visit Adveco’s healthcare resource page

Healthcare Sustainability

Healthcare Sustainability

Recent research by the University of Exeter sets out the scale of the challenge the NHS faces if it is to achieve healthcare sustainability targets set under the government’s net zero plan by 2040, a full decade ahead of the wider commercial sector.

With a calculated carbon footprint equivalent to 31 million tonnes of CO2, 62% of which can be attributed to its wider supply chain, the NHS must reduce emissions by 8% each year through until 2036.

This means stakeholders across government, NHS and industry need to be working together in order to provide new standards for procurement and innovation to ensure sustainable practices.  One area that accounts for a consistent and definitive need within the NHS is the provision of hot water. A core facet of hygienic working practices and the provision of healthy spaces for treatment and care, heating water can be an energy-intensive process, accounting for as much as 30% of daily energy demands. It is also a provision that can immediately deliver a reduction in carbon emissions and operational costs once implemented, whether a building is new construction, or more likely a refurbishment of existing property within the NHS estates,

For more sustainable domestic hot water (DHW) systems, we expect healthcare facilities will look for hot water to be generated at a commercial scale via multiple localised systems that each provide hot water to wash hand basins and showers for a dedicated area. This has been the most common use case seen across recent pandemic-driven refurbishments for example. This typically will see systems arranged on a ward-by-ward basis, but appliances may also supply hot water to local shared spaces where appropriate. Such systems will demand hot water be stored and distributed at a minimum temperature of 60°C. Working flows could be required up to 75°C with minimum return temperatures not below 50°C.

The overriding issue is that NHS health technical memoranda (HTM) 04-01* states that, preheat vessels cannot be used unless they can be guaranteed to preheat to a minimum of 45°C. This could immediately preclude for instance the use of solar thermal as a lone source for preheat. However, it matches well to the minimum working flow temperature for preheat that we would design into a system utilising the current generation of air source heat pump. Solar thermal would be more effective for the provision of top-up heating. Awareness of this facet of the HTM has historically been either ignored or missed, so solar thermal has been deployed in a number of health facilities, often successfully, and Adveco has been servicing hospital solar systems for more than a decade in such locations as Merseyside and Greater Manchester. That said, we are aware of systems that have not met the requirements of the HTM leading to costly decommissioning.

To achieve net zero and meet NHS mandates for DHW a typical sustainable application would see hot water generated via a pair of parallel-arranged hot water cylinders to ensure redundancy. These would be sized to provide 60% of the hot water demand for the area served based on a peak 15-minute duration loading. The heat into the cylinder would come from a combination of solar thermal collectors and an air source heat pump working in conjunction to guarantee the preheat temperature

The design of the system allows for the heat pump to contribute to the incoming cold water.  That ensures 45°C while taking full advantage of the COP of the heat pump.  The solar thermal is employed after the heat pump to heat the water from 45°to 50 or 60°C depending on the time of year. We calculate the solar contribution over the year, with a system able to provide about 10% of the peak output when conditions are at their worst – short days with low sun and heavy cloud cover – rising to 30% under optimal conditions.

Should temperatures of up to 75°C be required, a high-temperature electric heat source would be used. Whilst typically an immersion, we would suggest specifying an electric boiler to avoid issues of scale in hard water areas, also well as delivering further system redundancy since the boiler will incorporate multiple immersions within its chassis. The electric boiler tops up what the solar could not manage. Still, by delivering preheat through both the ASHP and solar thermal system, demands on more costly electric heating are considerably reduced, if not avoided entirely. While higher temperatures will reduce solar efficiency, it is still useful to offset the high-grade heat than the low-grade/high COP heat pump heat and help to deliver on healthcare sustainability targets.

Example three-cylinder arrangement to meet healthcare sustainability and NHS HTM.  The heat pump and solar use a dual coil cylinder with the heat pump on the bottom and the solar on top. With this arrangement, there is no thermal conflict between the heat pump and solar adds what it can. 

The entire tank is heated to 45C by the heat pump and then receives solar top-up. A purge pump would run once per day to use the after heater to heat up the preheater for sterilisation to prevent legionella.

*Reference link

Read The Adveco February 2023 Newsletter

Read The Adveco February 2023 Newsletter

Welcome to the Adveco February 2023 newsletter covering Net Zero in review, healthcare hot water, and more award wins for our work with heat pumps for hot water applications designed for commercial properties…

Click here to read the Adveco February 2023 Newsletter