INDUSTRIAL & COMMERCIAL HEATING Why solid design practice matters A


Using heat pumps where possible to decarbonise heating and hot water in buildings should be the aim, but not at the expense of best practice design, says Baxi’s technical director Andy Green


ccording to the latest government statistics, the built environment accounts for 30% of total UK emissions. As businesses and organisations increasingly require their


buildings to be more operationally efficient, and with heat currently responsible for just over three quarters of this figure, the heating and hot water service is a natural target for improvement. Ultimately, where possible, an all-electric


approach based around heat pumps should be the favoured approach. We see air source heat pumps (ASHP) as the most popular and cost-effective choice of heat pump and are pleased to be expanding our existing Remeha heat pump range to include both high and low temperature ASHPs. With the potential efficiency of today’s air


source heat pumps as high as 400% in many cases, the merits of this technology are well established, particularly in buildings designed from the ground up to use low temperature heating effectively.


In existing buildings, however, the transition to fully electric low carbon heating and hot water provision can be a more complex task. On every refurbishment project, there will be a number of constraints, including time, budget, available power and physical space. As a result, these buildings will likely need a series of adaptations, typically carried out in phases, to make them heat-pump ready.


Admittedly, technological developments


are providing more flexible solutions to existing technical hurdles. High temperature ASHPs, which can be more easily retrofitted on a traditional heating system that requires high water temperature, are a case in point. But just because high temperature ASHPs are able to reach the required temperatures, they won’t necessarily achieve the most efficient system. And as a poorly performing heat pump will result in high running costs, an inadequately heated building, and unreliable heating and hot water, this should be avoided at all costs.


Best practice guidance


Instead, when retrofitting heat pumps into existing buildings, it’s likely that the following series of adaptations will need to be made to ensure high performance.


1. Reduce energy usage – reduce building energy consumption and heat losses by carrying out passive energy-efficiency measures such as draught proofing and roof and wall insulation


2. Energy consumption profile – understand the building profile. Energy usage patterns will show the peaks in heating and domestic hot water usage which will help us understand where heat pumps can be used most effectively


3. Energy-efficient system – take steps to allow the system to operate more efficiently at a maximum flow temperature of 55°C or lower, in line with Building Regulations. This will also prepare the heating system for the successful integration of heat pumps which operate most efficiently at low temperature outputs


4. Plan ahead – ensure that there is sufficient space for the heat pumps and adequate electrical load capacity


Low carbon domestic hot water generation


When it comes to moving to a low carbon hot water system, additional factors must be taken into account. In healthcare premises, for example, the Health and Safety Executive (HSE) advises that domestic hot water (DHW) should be stored at least at 60ºC and distributed so that it reaches 55ºC in healthcare premises to reduce the risk of legionella.


So while the focus should be on reducing operational energy usage and increasing renewable energy supply where possible, prioritising safe water is critical.


Let’s consider possible ASHPs design strategies for domestic hot water generation.


All-electric approach


Low temperature ASHPs can be used with direct electric or direct gas-fired solutions to raise the DHW to safe temperatures. As previously stated, the direct electric approach is more likely to be the option of choice, but it is important to note that this would involve higher volumes of stored DHW – certainly compared with low-storage direct gas-fired water heaters which the building may previously have relied on. [See Fig 1] If considering this solution, it is therefore important to consider potential issues relating to available space and weight for the larger cylinders – particularly when dealing with rooftop or non-basement plant rooms. Controlling


24 BUILDING SERVICES & ENVIRONMENTAL ENGINEER OCTOBER 2023


legionella within the larger volumes of stored water will also need to be carefully monitored and managed. High temperature ASHPs 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). This makes it a truly low-to-zero carbon solution. This option also offers greater design flexibility and requires less space, for a much simpler design and easier installation. The caveat is that the coefficiency of performance of heat pumps falls off at higher temperatures, affecting the real-world efficiency and subsequently operating costs.


Hybrid solutions


As with space heating, on projects where an all-electric solution is not considered suitable, a hybrid approach to hot water generation using two energy sources should not be overlooked as an important step forward on the net-zero path. With refurbishment projects, for example, where the natural gas supply might be maintained, there is the opportunity to use ASHPs to preheat direct gas-fired water heaters (DGFWH). [See Fig 2] Integrating ASHPs and DGFWHs in a hybrid system can provide a practical solution to the project limitations previously described while meeting hot water demand more sustainably and making significant progress towards decarbonisation.


Early engagement


While there is no silver bullet to heat decarbonisation, there are many opportunities and multiple options to reduce the carbon intensity of heat in buildings. Your chosen manufacturer should be able to supply all the equipment as well as providing expert product and technical advice at every stage of the project. With early engagement, we can help you identify and deliver the best value performance for budget for optimal outcomes. Working together, and following best practice guidance, we can identify the most appropriate solution for each project at every stage of the decarbonisation process.


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