The most consistent issue we see in when replacing school hot water systems is oversizing, whether through a lack of understanding of application design or concerns over providing suitable backup to ensure system continuity. The result of oversizing is however always the same, unnecessary capital costs for system supply and installation.
As schools plan to adopt greener building operations, replacing old gas-fired systems with like-for-like electric is another guaranteed way to gain an oversized system, but can also lead to undersizing if storage is not large enough to account for low, slow heating associated with heat pump based electric systems. Getting that balance right is critical as per kW price of electricity remains much higher than that of gas. Plus, if not optimised, the system will generate excess capital costs in terms of size and number of water heating appliances and complexity of installation. That in turn can also become more time-consuming and disruptive, a cause for concern if refurbishment work is scheduled into the narrow window afforded by the school holidays. More importantly, if the new electric system is oversized the required amperage could exceed a building’s available electrical supply. Bringing new supply in means excavating, possibly as far as the substation, which will see costs soar, or even stall the project.
This can best be avoided by collecting live onsite data. A valuable, non-invasive, and low-cost exercise, it should be undertaken to assess actual usage, including time and duration of peak demands which is critical for correct sizing. When assessing a school’s domestic hot water (DHW) usage, it is important to also establish basic information on energy sources, be they gas or electric, planned use of renewables such as heat pumps or solar thermal and the level of system redundancy and backup. This helps steer the design of the replacement system.
This approach has already been applied to several public sector sites in the UK where there is a strong impetus from the government for properties to be rapidly decarbonised in line with net zero strategies. Data collected by Adveco has enabled our application design team to provide recommended alternatives that avoid common issues that arise from replacing school hot water systems.
Replacing school hot water systems that are gas-fired with an electric system still has several cost implications. Correct sizing with metered data can reduce the costs of purchasing and installing new hardware, potentially saving tens of thousands of pounds depending on the scale and complexity of the DHW application. Excavation works to bring in increased electric supply though can quickly raise project costs to anything as high as £500,000 if in a city location! So optimising designs to avoid this is critical.
Operational costs do however climb and will continue to do so while grid electric prices remain much higher than those of gas grid supplies. The application of renewables including heat pumps and solar thermal can reduce, but not completely offset those direct electric costs.
The advantage is clearly defined in the reduction of carbon emissions, and, as work continues to decarbonise the electricity grid, the emission reduction figures supplied in the new system design should improve considerably, adding further environmental value to the system over the course of its operational lifespan. Decarbonisation of hot water still comes with implicit operational costs, but when replacing a school hot water system metering helps to clarify costs and puts a realistic number on the ledger that can be factored into a school’s decarbonisation strategy.