commercial DHW applications
Simon Bennett, senior applications engineer, Adveco, examines the scale of an increasingly complex challenge facing the commercial sector when it comes to addressing fossil-fuel use within buildings
S Adveco’s Simon Bennett
tatistics from the Department for Business, Energy, & Industry Strategy (BEIS) Non-Domestic National Energy Efficiency Data-Framework (ND-NEED) defined more than 1,656,000 non-domestic buildings in England and Wales at the end of March 2020 and that number continues to grow. This puts into perspective the decarbonisation challenge for the commercial sector. Meanwhile, air source heat pumps (ASHP) have become the poster child technology for the government’s Net Zero strategy. The advantage of ASHPs is that, with a performance greater than 100%, they can extract additional energy from outside of the building’s metered systems delivering significant carbon savings. The problem starts when the efficiency of an ASHP is based on working flow water temperatures of 35°C. It needs to be recognised that this temperature is insufficient to safely provide DHW for commercial applications, where achieving 60°C in a calorifier is a basic requirement. Additionally, the lower system temperatures required for truly efficient ASHP operation are likely to increase the size of a system and, at 35°C working flow, it will also struggle to support underfloor heating in the UK’s cooler months. In short, using ASHP for commercial projects is currently going to be complex and,
compared to traditional gas-fired alternatives, is going to have higher up-front costs. This is especially so for DHW applications, so designing an ASHP-based system for peak efficiency and delivering reductions in CO₂ emissions to meet sustainability goals is, therefore, a must to help offset the additional capital investment. For a commercial DHW system, it is
recommended that a working water temperature from the ASHP must be at least 55°C. This is certainly attainable from current generation ASHPs when deployed in a hybrid approach. This uses the ASHP as preheat and combines it with either gas-fired or more preferably an electric top-up to achieve the required hot water temperature. This is where the additional system complexity and cost can creep in. This is why correctly balancing a system so that it doesn’t fight itself becomes a critical issue. That is best served by a mix of physical spacing in the vessel and system monitoring with dedicated controls to ensure the ASHP preheat and immersion work seamlessly to deliver the highest operational efficiencies. With a clear sight of energy and water usage, facility managers also then gain more comprehensive control over day-to- day operations which translates into energy reduction and real carbon savings. Technical improvement of ASHPs is also a critical need, and in the past year, there have been significant inroads made in the alteration of hydrofluorocarbon (HFC) refrigerant usage. R-32 (Difluoromethane HFC32) has begun to replace R410A and while all HFCs remain greenhouse gasses, R-32 has a much lower Global Warming Potential (GWP). GWP is a measure of the impact on the atmosphere of one kilo of released HFC compared to a single kilo of carbon thus indicating its greenhouse potential. A kilo of R410A, which has been typically used as the refrigerant of choice in ASHPs, if leaked would do 2,090 times the damage of a kilo of carbon. As an example, using R-32 in Adveco’s FPi ASHP’s has reduced their GWP by 80%. More importantly, new refrigerants are not only environmentally friendly, but they also enable higher performance which means units can be more compact and lower cost moving forward. This April, the European Commission
proposed for a tightening of F-Gas regulations, accelerating phasedown schedule beyond 2030 to remove 97.6 per cent of HFCs in the market by 2050. It also sought to tighten ozone depleting substances proposals. In practice, this would require a further redesign of heat pump systems from manufacturers to support R290 as the default refrigerant. More commonly known as propane, R290, is often referred to as a ‘natural refrigerant’ with a long history of use in the refrigeration industry. In terms of application in heat pumps propane stands out as it combines an extremely low GWP, where 1 kg of propane is equivalent to only 3 kg of CO2, with excellent thermodynamic properties. These
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properties translate into good coefficient of performance (COP) in a heat pump even at commercial working temperatures up to 75°C and potentially much higher. This means future commercial systems can be less complex, without the need for additional electric immersion for high-temperature flushing for legionella protection. That said, immersions will almost certainly still be specified to provide system redundancy ensuring business-critical DHW demands are met. Very high-temperature propane heat pumps, delivering flows of up to 90°C are attainable but become increasingly limited in terms of application as temperature increases, so will not be applicable to every commercial site. Propane also demands specialist installation, with training required to handle flammables, although future generations of propane heat pumps should use increasingly smaller amounts of the refrigerant increasing installation and maintenance safety. With an envisaged minimum of 600,000 heat pump installations per year by 2028 set to climb to 1.9 million per year from 2035, specialist installers will be in considerable demand, so there are fears that already complex project timeframes could well be negatively impacted by the new proposals. In the meantime, with R32 heat pumps becoming more widely available, the expectation is for a mixed offering to the commercial sector well into the later 2030s that will rely heavily on R32 systems with R290 eventually taking the lead as high- temperature ASHP technology matures and becomes more widely applicable. This is especially the case for existing commercial buildings that will struggle to cost-effectively achieve insulation levels needed for lower temperature systems that are better suited to new build projects.
What is very clear at this stage is that commercial organisations face a complex technical and regulatory challenge in the coming decades if they are to successfully navigate to a future with decarbonised buildings across their estates. It’s good to know that more benign ASHP refrigerants that do not add to global warming are coming to market and the potential for necessary higher temperature heat pumps for DHW is a development that we will see in the market sooner rather than later. Consulting with expert providers at the earliest planning stages though will pay dividends in the longer term, helping to balance the use of cost- effective and familiar technology now with new developments in the mid-to-longer term.
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