One of the major challenges on the path to Net Zero by 2050 is insufficient energy storage. The focus often centres on electricity storage, but with the electrification of heat and the growing reliance on heat networks, the demand on renewables is intensifying. Unfortunately, during the evenings and nights – when electricity is most needed for heating – solar power, one of our primary renewable energy sources, is unavailable. Currently, when the grid isn’t green, we still resort to burning gas to make up the shortfall. At this point, heat pumps offer only marginal efficiency gains over gas boilers. To optimise the use of renewable electricity and heat pump technology, we must decouple heat demand from supply.
Following the energy efficiency hierarchy, reducing energy consumption is the first step. In schools, where most energy is used for heating, reducing heat demand should be the priority. However, in England and Wales, high heat loss hybrid ventilation (NVHR) is often prioritised over mechanical ventilation with heat recovery (MVHR), which minimises heat loss. This approach, endorsed by the Department for Education due to its low CAPEX, compromises comfort and air quality. To achieve Net Zero, Scottish Passivhaus schools offer a better model: MVHR.
Using heat pumps, some of the additional losses provided by NVHR can be made up for. However, MVHR consistently delivers better comfort and indoor air quality than natural-oriented solutions.
Next, it’s essential to ensure that the systems in use are energy efficient. For ventilation, this can be achieved by implementing decentralised MVHR systems with low specific fan powers, thereby minimising the energy required to deliver air to the space. Balancing the heating system is crucial for energy centre efficiency. Pressure-independent thermostatic radiator valves (PI-TRVs) automatically balance radiators to a pre-set flow rate, regardless of changes elsewhere in the system.
If these steps are implemented correctly, the building’s heat demand will be significantly reduced, leading to a smaller heating plant requirement and less reliance on renewable energy sources – a substantial CAPEX saving.
In the energy centre, heat pumps have become ubiquitous. Most heat pump systems typically have separate circuits for heating and domestic hot water (DHW), necessitating either separate heat pumps or the use of calorifiers to boost DHW temperatures.
Calorifiers have long created challenges in achieving efficient plant rooms, primarily due to their role in preventing the growth of Legionella bacteria. A straightforward solution is to eliminate stored hot water altogether. By using heat interface units (HIUs) with plate heat exchangers near tapping points, stored hot water can be eliminated, allowing for a lower system flow temperature and improving the seasonal coefficient of performance (SCOP) of heat pumps. This approach enables a single heat pump circuit, delivering further CAPEX savings.
However, it is crucial to maintain peak efficiency when employing heat pumps; the cost of not doing so can be high. Often, heat pumps are sized to meet the peak heat demand of buildings, even though extreme cold scenarios (-5°C) may only occur for a few hours each year. A more effective strategy is to employ hybrid plant systems, which use heat pumps in conjunction with considerable thermal storage and electric boilers for peak load conditions. Thermal storage acts as a heat battery, storing energy when green electricity is abundant and releasing it when demand is high – known as peak shaving, and the electric boiler deals with the few peak cold days of the year. This significantly reduces the size of energy centres. This strategy can reduce energy centre costs by up to 70% and lower embodied carbon.
Decoupling heat supply from demand allows the heat source to operate during the greenest periods, significantly reducing energy costs and carbon emissions.
Not only are the costs or the plant reduced, but the size of the electricity supply is also reduced, the upgrading of which can make some projects prohibitively expensive.
To ensure consistent performance, these systems should be monitored by an appropriate energy management system (EMS), with alarms set to alert facilities managers to issues such as a drop in the delta T across the heating system. This allows for quick resolution of problems that might otherwise go unnoticed as long as occupants remain comfortable, maintaining the system’s design conditions.
By moving away from traditional heat delivery methods and embracing holistic design in school heating and ventilation, we can not only reduce capital costs but also create superior environments aligned with the future of decarbonised, all-electric energy centre design. These techniques, which have been wildly successful in the UK residential market, hold great promise for the commercial sector. Adopting Danish heat network-style approaches in classrooms and energy centres is a strategic move that can propel the UK towards achieving its Net Zero ambitions by 2050.
Read the latest issue of School Building Magazine here: https://schoolbuilding.org.uk/mmc-publications/
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