Heating systems


hybrid future B


y now, professionals throughout the industry are aware of the target of Net Zero carbon set for 2050. In order to achieve this, the UK’s Climate Change Committee (CCC) recommends a carbon reduction of 68% by 2030 and 78% by 2035 when compared to 1990 levels. Such ambitious targets are one of the key drivers behind embracing greener alternatives – especially in terms of improving the energy efficiency of commercial buildings. A key factor in reducing emissions is the


decarbonisation of the electricity grid. Statistically speaking, there have already been significant advances in this area; for example, according to the National Grid, in 2012, 43% of the UK’s electricity was generated by coal power stations, but by 2022, this figure had shrunk to 1.5% to be overtaken by renewable sources – which accounted for 38% of the electricity produced. With the UK government having committed to


fully decarbonising electricity generation by 2035, emissions from this process are continuing to fall. Indeed, government data shows that in 2012, the emission factor was measured at 0.537kg CO2e/ kWh, whereas in 2021 this figure had decreased to 0.198kg CO2e/kWh, due to the phasing out of fossil fuels (particularly coal) in the process of generating electricity. Given the green benefits of decarbonised electricity,


it makes environmental and economic sense to embrace air source heat pump (ASHP) technology. However, many commercial buildings, whether libraries, hospitals, offices or schools, have large heating (and hot water) peak loads that can sometimes be challenging to meet. As a result, heat pumps alone may not suffice – especially in existing applications. A heat pump with a good coefficient of performance (COP) – such as the AEROTOP® M and AEROTOP® L from ELCO – connected to a low temperature heating circuit will always produce less carbon per useful kWh


22 June 2023


Commercial heat pumps are an integral part of a


Considering global sustainability targets, utilising heat pumps alongside high efficiency condensing boilers is the next logical step towards a Net Zero future, explains Silviu Catana, specification manager at ELCO Heating Solutions


Left: Silviu Catana, specification manager at ELCO Heating Solutions


compared to a gas boiler. However, issues can arise when outside air temperatures fall and a building’s heating system requires a higher output – coupled with a reduction in heat energy available from the ambient air, which impacts the COP. Fortunately, these issues are easily overcome


by employing a bivalent approach – often referred to as a hybrid system. This sees an ASHP used in conjunction with a gas condensing boiler (or multiple boilers), with the latter ‘topping up’ the system to ensure the entire heating load is met, whatever the temperature may be outdoors. In this set-up, the ASHP is sized to meet the majority of a building’s required energy, with any additional boilers switching on when a low threshold arises. Put practically, the bivalent switching point is set at the design stage, with the boilers firing up when an outdoor sensor connected to a Building Management System (BMS) detects the pre-set temperature. Be aware, however, careful design work needs to be undertaken to ensure such a system operates effectively and efficiently. In fact, the boilers will only function as intended if weather-compensation is included. This functionality ensures the required flow temperatures drop as it gets warmer outside the building. Importantly, each of the system’s two distinct heat sources must avoid high return temperatures in the weather compensated circuits – otherwise the heat pump runs the risk of being bypassed, which would result in the boiler having to take on the entire heating load. One example of an effective bivalent system would


be designing a heat pump to carry the entire (100%) heating load for mild conditions above 4°C. Doing so creates maximum efficiencies for over six months of the year, ensuring an excellent seasonal performance factor (SPF) – even when flow temperatures reach 50°C. Subsequently, should temperatures drop between -2°C and 4°C, bivalent operation can be deployed, with the system using both the heat pump and boiler together; doing so allows a heat pump to deliver the same COP, provided its flow temperature is also reduced. Lastly, in the event of temperatures dropping under -2°C (causing a significant fall in COP), a condensing boiler can still provide the entire heating energy, thereby optimising system efficiency. Of course, when designing a hybrid system of this nature, it can be complex including both heat pumps and boilers together. As a result, it is wise to incorporate products from the same manufacturer, as the technologies used will share the same digital protocols, enabling them to successfully communicate with each other as part of a complete system. This also provides consultants with a single point of contact, capable of advising on how best to utilise the different products to meet the design requirements of a specific application, whether it is a school, public office or historic building. Indeed, consultants will need manufacturers to


supply the COPs for their products across a range of ambient temperatures and load conditions in order to obtain an accurate SPF – i.e. the average efficiency of an ASHP. This data provides essential information on the performance of the unit supplying heating energy to a system throughout a season or for a specific period, where the parameters required in the system vary based on factors such as external temperature, a building’s fabric and/or thermal inertia. Having this data available from the manufacturer ensures an effective approach to calculating the heating energy produced – and consumed – by the heat pump in all conditions during the allocated time. So, as the UK electricity grid continues to


decarbonise and we move towards a greener future, sustainable products – such as heat pumps – are already becoming more prominent in commercial projects. And, by incorporating them into existing buildings as part of a hybrid strategy and utilising the appropriate controls, the goal of achieving net zero by 2050 moves ever closer.


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