AIR SOURCE & GROUND SOURCE HEAT PUMPS
Setting the standard for energy efficiency in schools
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UK schools are estimated to account for more than half of a typical local authority’s carbon emissions. Andreea Maniou, senior manager at ELCO Heating Solutions (part of the Ariston Group), explains how air source heat pumps can play a pivotal role in improving energy efficiency in schools and futureproofing them in line with green legislation
chools are estimated to attribute for around 2% of UK greenhouse gas emissions, which is equivalent to 15% of the UK’s public sector emissions. In fact, according to the ‘Let’s Go
Zero’ campaign, schools can contribute to significantly reducing national carbon emissions, with data showing 625,000 tonnes of CO2 could be prevented from entering the atmosphere.
Now, although the key date associated with achieving net zero is 2050, back in 2021, the UK Government committed to investing a further £1.425 billion in the Public Sector Decarbonisation Scheme, with the aim of reducing direct emissions from public sector buildings by 75% by 2037. Many commercial heating technologies available to specifiers already comply with the legislative requirements of using low carbon heat sources. Air source heat pumps (or ASHPs) are certainly no exception, as they consistently deliver extremely high COPs (coefficients of performance), significantly reducing emissions when compared to traditional gas boiler systems. But how well can these technologies be integrated into educational applications?
Air source benefits
Fitting ASHPs in schools and universities not only contributes to sustainability goals, they also offer high levels of reliability, provided they are regularly maintained. Now, there are some challenges when adopting heat pump technologies, especially in terms of hot water (DHW) preparation. The high efficiencies of ASHPs have already been widely demonstrated, especially at low flow temperatures, such as when used with underfloor heating, for example. However, be aware that using an ASHP in schools and universities can have some limitations, especially in terms of hot water production. As a result, considering whether an ASHP should be designed as the lead appliance should be part of a project’s concept phase. Furthermore, if you choose to separate the
production of heating from the production of DHW, heat pump water heaters could also be used in a cascade arrangement. If you choose to preheat the domestic hot water from the average 10°C to 55°C, for example, and use a second heating source (e.g. an electric immersion heater) to raise it to 60°C to prevent legionella from forming in the system, this is another viable option for schools.
A hybrid approach
Now, variations in the outside temperatures mean that an additional condensing gas boiler may still be required when integrating heat pumps into a school’s heating system – especially when the temperatures required by the system are higher than what an ASHP alone can deliver. Creating a hybrid (or bivalent) system of this nature is common in refurbishment and retrofit projects, with the heat pump doing the heavy lifting and the second heating source handling a maximum 15% of the required energy demand in the whole year. The percentage of the input of the second heating source depends heavily of the flow temperature of the heating system. The lower the design (or redesign) of the flow temperature of the heating system, the less the second heating source will be called upon. At ELCO, we can do all these calculations by using our Hybrid System Wizard (HSW), which is free of charge to all consultants wanting to provide the best solution for their customers and for the planet. So, what are the driving forces behind implementing heat pumps in an educational project such as a school? The main factors are economical – primarily the running costs involved – and CO2 reductions, in line with reducing public sector building emissions as referenced earlier. Perhaps the take up of heart pump technologies in schools (and other public buildings) could be encouraged by having a different tariff for the electricity used by the heat pumps, separate from the energy used for lighting and other amenities.
This would then influence the decision makers that only look at the annual cost of electricity, encouraging investment in new heat pumps as opposed to repairing a 20-year old boiler that runs on natural gas, oil, LPG – or even coal! In a hybrid system, the bivalent principle (i.e. how long an ASHP will be allowed to run) ensures a heat pump is sized to meet a building’s heat load for over 85% of the time it is required, and allows it to operate at favourable COPs. So, when the outside air temperature reaches a low threshold (and heat pump output becomes insufficient), or if the system needs to remain free from fossil fuels, the ‘top-up’ can be carried out by an electric immersion heater. (By using the HSW referenced earlier, all these options can be compared, allowing the best one to be chosen for each project.) However, hybrid systems using two different heat
sources must be carefully designed if we want to get the most out of the air source heat pumps. In fact, bivalent systems utilising heat pumps will only be successful when weather-compensated. This ensures the required system flow temperatures drop accordingly when the outdoor temperature increases. Avoiding high return water temperatures in the weather compensated circuits in each heat source is critical, otherwise there is a risk of the heat pump being bypassed and the entire heating load taken on solely by the boiler or the secondary heat source.
Ask the experts
Given there are two different technologies involved, designing a hybrid system consisting of heat pumps and boilers can be more complex compared to a project using a single heat source. The best means of ensuring success is to employ heat pump and boiler products from the same manufacturer. After all, this enables each technology to communicate efficiently with the other by utilising a common language protocol, while allowing consultants to seek advice from one supplier regarding how best to match products to the respective design requirements – whatever the size of school, college or university. So, there are many benefits to utilising air
source heat pump technology throughout UK schools and universities. As we have found out first hand from working on distinguished academy projects in Derbyshire and Staffordshire, ASHPs offer greater levels of energy efficiency and even some cost savings when compared with older boilers running on oil or LPG. Whether used alone or as part of a hybrid system, the education sector should be looking towards heat pump technology to ensure emissions are reduced in line with UK government targets.
16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER SEPTEMBER 2023 Read the latest at:
www.bsee.co.uk
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