Making progress towards net zero by tackling heat decarbonisation

Secondary School, fabric first, boiler replacement
Secondary School fabric first (modern pre-mix boiler, modulating operation)

What are the challenges and opportunities for organisations as they tackle heat decarbonisation amid the continued energy crisis? Rob Erwood of Baxi Commercial solutions has answers.

Energy has arguably never been a hotter topic. As we head into autumn, organisations will be seeking every available opportunity to mitigate rocketing energy costs to protect their operations. But as the summer heatwaves reminded us, even in these difficult times, the drive for greater sustainability cannot be allowed to wane.

Heat is one of the prime sectors to target. It accounts for around a third of the UK’s annual carbon footprint, making near full decarbonisation in existing buildings necessary if we are to achieve our 2050 net zero ambition. Put simply, how we heat our buildings must change.

Ultimately, the aim is to transition to low carbon heating technology such as heat pumps. Reflecting this, government funding is mostly limited to full electrification of heat – helping scale up the heat pump market and meet its ambitious target of 600,000 units a year by 2028.

The merits of heat pumps like our Remeha E-HP AW Air Source Heat Pump (ASHP) range are well established in new and well-insulated buildings. But, realistically, not all projects and budgets can be engineered fully with just heat pumps at present.

In existing buildings, the transition to low carbon heating and hot water provision is more complex. On every refurbishment project, there will be a number of constraints, including time, budget, available power and physical space, to name but a few.

If a solution is simply tailored around the heat pump rather than the retrofit challenges in the building, the anticipated result will not be achieved. And what no one wants is a poorly performing heat pump that will result in high running costs, an inadequately heated building, and unreliable heating and hot water.

With this in mind, how can building services engineers and heat experts help organisations improve the efficiency of their heating service, protect their operations during the energy crisis and continue to make progress towards net zero?

Plotting pathways

The reality is that most existing buildings will not achieve full heat decarbonisation overnight. Instead, they will need a series of adaptations before they are heat-pump ready. A good starting point is to encourage customers to identify their immediate, medium and long-term goals. Having a clear understanding of their targets, the available time to complete the work, the budget and any funding opportunities, will make it possible to plan out and design the various stages of work. 

Defining a phased approach to decarbonisation has the advantage of enabling organisations to budget ahead while ensuring good practice design for maximum energy, carbon and cost reductions at each stage.

Step one - maximise energy efficiency

In the UK’s notoriously poorly insulated buildings, the initial focus should be on increasing energy efficiency. Energy efficiency is absolutely critical to reducing emissions and will have an immediate impact on a building’s energy consumption and heating bills.

Implementing passive measures such as roof and wall insulation, draught-proofing and improving the thermal performance of windows and doors will reduce heat losses and energy demand, helping mitigate rising energy prices.

Investing in energy efficiency measures will also help prepare the building fabric for the transition to low carbon heating.

 Step two – more efficient system

In buildings where heat pumps are not currently an option, it’s important to seize any achievable opportunities within the project parameters to use the energy source more efficiently and lower energy consumption. One example is to install a more efficient system.

Upgrading inefficient or ageing heating plant with more energy-efficient equipment should not be overlooked as an achievable means of improving heating reliability and efficiency. Replacing old non-condensing gas boilers with modern condensing models that are up to 20% more efficient, for example, will result in immediate and ongoing energy and carbon savings.

To enhance the sustainability of the installation, look for future-ready boilers that are certified to operate on the proposed 20% hydrogen blend and can achieve ultra-low NOx emission levels.

 Low temperature heating system

In most projects, it should be possible to address the system’s distribution pipework and heat emitters to operate at lower temperatures than the traditional 82°C/71°C or 80°C/60°C flow and return system designs. This will allow the condensing boilers to operate in condensing mode, where they achieve their maximum efficiencies. It will also future proof the building and prepare the heating system for the integration of low carbon technologies at a later stage, as these operate most efficiently at low temperature outputs.

Secondary School (fabric first, multivalent system)
Secondary School (fabric first, multivalent system)

Comparing energy usage and emissions

To understand the savings that could be made from improving the building fabric and carrying out a boiler replacement, we have carried out comparisons of two energy systems using smart simulation software.

For the purpose of the comparison, we have focused on schools, which are, at the time of writing, struggling to absorb a 200% increase in heating bills and remain open without additional funding.

We have assumed a secondary school that currently relies on an old 500 kW non-condensing gas boiler, running at 80% efficiency for heat, with a 1,200 litre indirect hot water cylinder. The school has 40 classrooms, an assembly/sports hall, a shower block with 10 showers and 10 changing rooms, a kitchen, dining area, offices and corridors. The school has 1,000 children on roll.

The simulation software calculates the total annual fuel and/or electricity consumption of the old system to be 1,081,994 kWh.

Complex retrofit challenges combined with budget constraints mean that the project cannot be engineered fully with just ASHPs at present. The recommendation is to carry out a stepwise refurbishment programme, with each stage designed to be able to be completed during the school shutdown period.

The first phase involves carrying out fabric improvements and a boiler replacement to improve the efficiency of the system.

Following the implementation of this first phase, the simulation software calculates a fall in the system’s total annual fuel and/or electricity consumption to 682,380 kWh.

That’s a reduction in annual energy consumption of almost 37%.

Using SAP 10.2 carbon intensity figures of 0.21 for gas and 0.136 for electric, we calculate that the annual carbon savings from this approach are 83,918 kg.

Step three – multivalent solutions

Multivalent methods of heat generation cannot be ignored as an important step in the heat decarbonisation process.

Returning to our secondary school simulation, the recommendation for the second phase of the heating refurbishment programme is to integrate a ASHP into the system.

The simulation reveals that the total annual energy consumption after this phase falls by 134,000 kWh – nearly half the total of the original system. The annual carbon reduction from this latest phase amounts to an impressive 235,006 kg.

Clearly, a fully served ASHP building will achieve one of the lowest carbon footprints in new and well-insulated non-domestic buildings.

But where an all-electric approach is not feasible due to affordability, budget constraints or technical limitations, these simulations illustrate how a phased approach can achieve important energy and carbon savings at every stage.

The heat decarbonisation challenge is far from new. But against a backdrop of surging energy prices, unsustainable running costs, rising inflation, higher wages and squeezed budgets, the energy trilemma is more complex than ever.

By working together, we can achieve the most appropriate solutions for organisations, balancing best performance for budget value with best practice for heat decarbonisation. In so doing, we can do our bit to help them navigate a course through the energy crisis and continue their journey to net zero.

These simulations have been taken from our new guide Schools and the heat decarbonisation challenge. To read the full report, visit:

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