Air source heat pumps: 6 myths busted!

Decarbonising a large building estate is rarely as simple as replacing one technology with another. Doug Johnson, Founding Director of energy and building performance specialists Mesh, looks at the importance of data-led decision-making. For Estates Directors responsible for large property portfolios, the pressure to decarbonise is coming from multiple directions. Organisations need to reduce operational carbon, transition away from fossil fuels, improve energy efficiency, control escalating running costs and maintain occupier comfort, particularly when climate change is leading to more buildings overheating in summer. At the same time, buildings still need to perform their primary function, capital budgets are constrained and major interventions have to be costed and planned. Against that background, it can be tempting to start with the technology – such as heat pumps, solar PV, insulation and new heating systems. However, whilst all of these technologies may form part of the solution, they are rarely the right starting point. Why Assessing Building Performance Matters For a large and diverse estate, the first question should be much simpler – how are our buildings actually performing? This distinction matters because two apparently similar buildings can have very different energy performance profiles depending on age, fabric, heating and hot water systems, controls, condition and patterns of occupation. Understanding these variables will make the difference between a credible long-term decarbonisation strategy, and a costly and disruptive programme of interventions that could fail to deliver the optimum results. Estates directors and strategic property leads are under growing pressure to reduce operational costs, cut carbon emissions and prepare building estates for the transition away from fossil fuels. Yet most estates were never designed as a single asset. They are often a portfolio of buildings from different decades, built to different standards, used in different ways and, in many cases, still running on fossil fuels. Decarbonisation such an estate should not be viewed as a single project. It needs a strategic, evidence-led programme, rather than an individual renewable technology specification. Understanding Actual Buildings Not Assumptions Mesh recently completed a detailed building performance assessment and energy strategy for Hampshire & Isle of Wight Fire & Rescue Service, examining its headquarters in Eastleigh and six fire stations selected to represent the age, scale and typology found across its wider 62-building estate. Occupancy patterns varied enormously, from office-based staff working regular hours in fire stations to facilities that stand largely empty until a crew returns from a call-out and needs the building to become comfortable within minutes. Building fabric, heating controls and hot water demand all varied widely. This is true of most large estates, whether in emergency services, local authorities, education, healthcare or the commercial sector. Treating a diverse portfolio as if it were one building type, or applying a single technology across the board, consistently produces less value and, in some cases, worse outcomes for occupants. Building the Evidence Base The starting point for any credible decarbonisation strategy should be data. For the Hampshire & Isle of Wight project, that meant analysing three years of energy billing data for each of the seven buildings assessed to understand how consumption varied through the year and how each heating system responded to changes in external temperature. This produced a benchmark energy use intensity figure for each building typology, allowing direct comparison against national emergency services benchmarks and establishing a clear baseline against which future improvements can be measured. Alongside this, detailed building fabric assessments quantified heat loss through U-value calculations for roofs and walls, and tested the impact of a range of insulation interventions and materials against both capital cost and payback period. Occupancy patterns, heating and hot water systems, and controls were also assessed. Once this evidence base was in place, solutions could be identified for improvement and a strategy for implementation developed. An Evidence-led Energy Strategy A genuinely evidence-led strategy will rarely point towards a single solution. For some buildings in this estate, relatively low-cost measures made the most sense: Centralising heating controls. Aligning heating schedules with actual occupancy levels rather than fixed assumptions. Replacing stored hot water cylinders with instant systems where demand was variable and unpredictable. In several buildings, radiators needed resizing to improve both energy efficiency and occupier comfort where rooms had previously been reconfigured. The analysis supported a move towards air source heat pumps (ASHPs) to reduce space heating energy consumption by around 50 per cent. However, a full transition to ASHPs raised a significant challenge – heat pumps operate at lower flow rates than gas boilers. This means existing radiator and pipework systems are not always compatible without significant capital investment and operational disruption. Disruption is a key issue for emergency services, as it is for many organisations. The solution was a hybrid approach – heat pumps for handling the majority of annual heating demand, with gas heating retained as back-up during the coldest periods. For an emergency services estate where continuity of service is non-negotiable, this delivered a substantial reduction in carbon and running costs without the capital cost or disruption of complete system replacement. Why This Approach Matters for Estates Directors For facilities or estates manager responsible for a complex property portfolio, this project illustrates a broader principle. Understanding how buildings are actually used and perform through evidence-based analysis – energy data, fabric performance, occupancy patterns and modelling – allows capital investment to be targeted at the remediation work which will deliver the greatest benefit in terms of cost and carbon reduction. According to Carrie Dickson, Energy and Sustainability Officer for Property and Facilities at Hampshire & Isle of Wight Fire & Rescue: “ Our aim with this project was to optimise the energy performance of each building and to apply those learnings to our wider estate across Hampshire and the Isle of Wight. We now have the evidence-based analysis needed to understand which buildings perform well and where improvements and technical adjustments are best targeted to reduce energy consumption. The project data and feasibility studies will also be helpful to inform larger capital projects, both new build and refurbishment.” A Practical Starting Point The Hampshire Fire & Rescue estate project reinforces that the decarbonisation of any building should always be evidence-led. When you understand energy consumption, building fabric, services, controls, occupancy patterns and operational requirements for different building types, solutions can be modelled and optimised, and investment prioritised against energy, carbon and cost reductions and practical deliverability. For Hampshire & Isle of Wight Fire & Rescue Service, this approach has created a clearer route towards improving the performance of its existing buildings and progressively reducing the reliance on fossil fuels. For other organisations facing the same challenge, the principle is equally applicable. About Mesh Mesh offers a range of building performance engineering and M&E design services to help organisations in the public and private sectors to improve the energy efficiency of new and existing buildings, housing and estates. This includes support for architectural design, the planning process, thermal modelling and overheating analyses; carbon reduction strategies; feasibility studies for renewable technologies; MEP design and engineering, and regulatory compliance.

Sustainability, impact and integrity form the basis of Mesh's culture where creativity and fun are still very present. As part of this ethos, each year we hold a series of volunteering days for our team. 11 of our colleagues from as far afield as Portugal, Exeter and Bristol recently joined the Surrey Society to work with rangers at West Horsley Place – a 400-acre estate near Guildford – and help maintain some of their ancient woodland. The team lent a hand with ‘coppicing’. This practice involves felling a tree to create a living stump called a ‘stool’ which supports regrowth into new, fast-growing poles or rods. Regular cutting of the stools can extend the life of a tree for centuries, provide sustainable materials for a range of uses, and encourages biodiversity. Doug Johnson, Founding Director of Mesh: "We had a fantastic day in the fresh air which was followed by our monthly team meeting in the beautiful grounds and a social dinner afterwards. Thank you to the Surrey Society for giving us the opportunity to volunteer on another of their projects. This independent charity does some great work to encourage people to explore the outstanding landscape in Surrey. This fits so well with Mesh's sustainability values." 

Mesh has been announced as a runner up for Energy Consultancy of the Year at the National Energy Efficiency Awards. This latest accolade follows our success in winning Regional Energy Efficiency Consultancy of the Year at the South East Energy Efficiency Awards. According to Doug Johnson, Founding Director of Mesh: "As one of the smaller, specialist consultancies, this was a significant achievement for such a prestigious award and in a highly competitive category. The awards event was a fantastic celebration of innovation and achievement in improving energy efficiency across the built environment. Our teams are committed to excellence in both building performance analysis and building services design – delivering practical solutions and strategies for our clients to accelerate decarbonisation and improve the energy efficiency of new and existing homes and buildings. It is wonderful to have our team's talent and hard work recognised with this national accolade from the industry." 

Adapting heritage buildings for modern use creates a particular engineering challenge – how do you deliver comfort and energy performance, within the constraints of a historic building? Doug Johnson, Mesh Founding Director of building performance specialists Mesh, shares his insight from a recent project. When we talk about successful heritage transformations, the conversation usually focuses on the architectural design and the restoration process. Less visible but equally important, is the role of building services engineering. Change of use breathes new life into historic buildings. However, achieving year-round comfort for visitors and occupiers of galleries, offices, hospitality or retail can be challenging, not least when occupancy levels fluctuate. Historic buildings are expected to deliver the same standards of comfort, environmental control and operational performance as modern buildings, yet they were never designed to accommodate contemporary MEP systems. Getting that balance right requires different thinking. A Grade II listed Georgian townhouse in London's Mayfair was recently transformed into a space for contemporary art. This provides a useful illustration of the principles involved and how the challenges were addressed. Dating back to the 1730s, the six-storey building in Mayfair was once home to the Burlington Fine Arts Club. It has now been sensitively converted into a suite of contemporary art galleries for Sadie Coles HQ. The objective was not simply to install heating and cooling. It was to create a comfortable, flexible, efficient and futureproof internal environment whilst ensuring that the engineering services remained almost entirely invisible. The Importance of Designing Around Occupancy A key consideration for intelligent building services design is looking at the predicted occupancy levels and whether these will vary. Museums, galleries, visitor attractions, civic buildings and cultural venues can all move rapidly from quiet periods of low occupancy to large events with significant increases in heat gain and ventilation requirements. Rather than designing for a single occupancy assumption, modelling multiple use scenarios provides a much clearer understanding of how a building needs to perform throughout the year. By analysing different occupancy patterns, environmental conditions and operational requirements, MEP systems can be sized more accurately to avoid both underperforming and over-engineered solutions which increase energy consumption. In heritage projects, this approach is particularly valuable because space for plant and services is often limited. Every piece of equipment needs to justify its inclusion. Early Co-ordination and Integration with the Architectural Design Heritage and listed buildings rarely offer generous service routes. Unlike new-build projects, where risers, ceiling voids and plant spaces can be designed in from the outset, historic buildings often require services to be threaded through a series of constrained voids. This challenge becomes even greater in tall, narrow buildings such as townhouses, where plant may need to serve multiple floors through restricted vertical routes. The lesson is clear – building services engineering has to be designed in from the outset. Early collaboration between architects, engineers and conservation specialists is essential to establish whether the proposed systems are feasible, where equipment can be located and how services can be integrated within the building fabric. The earlier this co-ordination takes place, the greater the opportunity to avoid compromise, reduce project risk and optimise energy efficiency. Increasing Capacity for Heating and Cooling in a Heritage Setting A common response to increasing heating or cooling demands is simply to add more equipment. In many heritage settings, that option is not possible. Planning restrictions, minimising visual impact and noise levels, and conservation requirements often limit the number and location of external plant units. Roofs, courtyards and rear elevations frequently offer little flexibility which demands a more intelligent approach to system design. On the Sadie Coles gallery project, instead of increasing the number of external units, a zoned strategy was developed which matched available plant capacity to individual rooms based on anticipated occupancy patterns and the predicted demand for heating and cooling. This allowed the available capacity to be used with greater energy efficiency whilst maintaining compliance with planning constraints. The broader lesson is that building performance is not solely determined by the quantity of equipment installed. Understanding how spaces are used often unlocks opportunities to achieve enhanced performance within the available infrastructure. Maintaining a Clean Aesthetic The most effective building services design is often the least visible whilst meeting performance requirements. This is particularly true in heritage settings where restored architectural features, historic detailing and carefully considered interiors should remain the focus. Achieving this requires close collaboration with the wider design team. Diffusers, grilles, fan coil units, controls and service routes must be carefully integrated into the architecture rather than be imposed upon it. In gallery environments, there is an additional consideration – the services engineering must not distract from the exhibits themselves, either visually or acoustically. This demands a level of co-ordination and design discipline that goes beyond compliance. Passive Design Matters Any building should be as energy efficient as possible and passive measures often provide some of the most effective opportunities to improve comfort whilst minimising energy consumption. In the Mayfair gallery, a glazed roof lantern was both a beautiful architectural feature and a potential source of overheating. Rather than relying solely on active cooling, actuated roof lights were incorporated into the glazing above to allow warm air to be purged naturally from the space below. Combined with natural ventilation through restored sash windows, this approach reduced cooling demand whilst improving thermal comfort. These principles are not new, but remain highly relevant. Understanding airflow, solar gain and natural ventilation can often deliver significant benefits alongside the design of mechanical systems. Futureproofing Heritage Assets Buildings that have survived for centuries have often done so because they have adapted over time. The services strategy should support that continued evolution. Futureproofing does not necessarily require major additional investment. Sometimes it simply means incorporating connection points, spare capacity or flexible infrastructure that allows future adaptations to be made more easily. In the case of the gallery project, provision was included for supplementary low-level electric heating should the building use change. Such measures may never be required, but they provide resilience and flexibility that can extend the useful life of the building with the least disruption possible. Services Engineering to Support Heritage Buildings Successful heritage refurbishment is not about choosing between conservation and performance. It is about achieving both. The most effective building services solutions are those that support the architectural and client vision, improve comfort, reduce energy consumption and remain largely unseen by the people using the building. When done well, engineering becomes part of the fabric of the building rather than an addition to it. That is ultimately what intelligent building services design should achieve – modern performance delivered in a way that respects the past whilst preparing buildings for the future. The Project Team: Client: Sadie Coles HQ Lead contractor (design and delivery): Work Ltd Architectural partner: Giles Reid Architects MEP design / building performance: Mesh About Mesh Mesh offers a range of design and engineering services to help organisations in the public and private sectors to improve the energy efficiency of new and existing buildings, housing and estates. This includes support for architects; planning; thermal modelling and overheating analyses; carbon reduction strategies; feasibility studies for renewable technologies; MEP design, and regulatory compliance.

Building performance specialist Mesh is providing a range of multi-disciplinary services for a new build scheme and estate rejuvenation programme at Waterperry House and Gardens, including building performance and embodied carbon analysis, BREEAM assessments and MEP services design and engineering.

Mesh has been appointed to work on three new care home projects – in Cambridge, Barnstaple and in the Exmoor National Park – providing assistance with regulatory compliance, analysis to mitigate overheating, energy strategy development, and low-carbon services design, engineering, and specification. There has been a significant increase in demand for Mesh's building performance services for care home projects this year. There are a number of drivers: Running costs - there is a clear need to reduce operational costs in care homes given global uncertainty around energy prices. Comfort - It is vitally important to maintain the comfort of residents and vulnerable people, and particularly to reduce the risk of overheating in light of climate change and rising temperatures in the summer months. Performance - New build care homes and extensions have to perform over time rather than simply meet minimum requirements for statutory compliance. Sustainable living - In a competitive care home market, more sustainable living accommodation means lower bills for residents and enhanced wellbeing.  Dylan Ross of Mesh: “Care homes are occupied 24/7 so building performance and energy efficiency really matters. We are seeing more care home developers and operators look beyond regulatory compliance and at how their buildings will actually perform over time – in terms of energy use, thermal comfort and maintenance implications. Our role is to bring building performance and services design together using evidence-led solutions to help inform decision making and deliver buildings for social care that maximise comfort for residents and minimise energy consumption, carbon emissions and running costs for care home operators.” Mesh specialises in improving the energy efficiency of both new and existing buildings, and works with care home operators, developers and architects.

Building performance specialist Mesh has worked with Hampshire Fire & Rescue Service to improve the energy efficiency of its building estate and support decarbonisation.

Building performance and M&E engineering specialist Mesh has appointed Jen Wallace as Managing Director

Building performance specialists Mesh have been announced as a finalist for National Consultancy of the Year at the Energy Efficiency Awards