Ian Rogers, Gilberts’ Sales Director, offers some timely advice to help estate managers be star performers

For many building managers in the education sector, there is a feeling of having changed vocation without realising. Now, they are jugglers, struggling to keep all the balls (budgets, carbon reduction, rising energy bills, Regulatory compliance, pupil health & wellbeing- Covid, flu, Strep A- and air quality) in the air.

Revisiting one strategy could tip the balance in your favour- HVAC. It helps that the Government has announced a further £500m funding for energy efficiency upgrades, in addition to the £1.8b for improving the condition of school buildings and the £1.4b for the Public Sector Decarbonisation Scheme(1).

Department of Education (BB 101) preference is for ventilation strategies that are sustainable. Natural ventilation has for years been the strategy of choice, and the recommendation of the DfE. It also ticks the sustainability box, being natural (as the name implies) and requiring little (if any) energy to function, making a significant contribution towards a school’s carbon footprint.

That has evolved in more recent times towards hybrid ventilation- indeed, this is now the option of choice for the Education Funding Agency. This leads with natural ventilation (which uses no energy and therefore low running costs) providing air changes only as and when required via a low energy fan.

The latest evolution is hybrid ventilation with heat recovery (MFS-HR). One unit provides up to 75% heat recovery whilst still delivering an airflow rate of up to 470l/s to meet requirements.



How it works

Installed through the external façade or window, hybrid ventilation rejects ‘used’ internal and removes the heat to be re-used when supplying pre-tempered fresh external air to ventilate the internal space, providing free cooling or heat recovery with no risk of cross contamination- and therefore completely Covid safe.

A mixing damper within modulates airflow to allow by-pass of air whilst collecting the energy whn required. The integrated low energy fan ensures an even distribution of airflow, controlling CO2 levels and maintaining good indoor air quality (IAQ). The smart Mistrale Control Unit gives individual, automatic room control, requiring no occupier input to maintain the comfort levels within. It does though have a simple override function to allow local adjustment by the teacher/ occupier for any required local control.


Cutting costs

More importantly in the current climate, more importantly for managers trying to balance budgets, MFS-HR does more than deliver Covid-compliant indoor air quality (IAQ). As a stand-alone system there is no ductwork in each zone/classroom, so hybrid ventilation with heat recovery is fast and cost-efficient to install- be it new build or as a refit/refurbishment/upgrade scheme. This also helps future-proof the system as the school estate grows, the system can correspondingly expand with ease.

Having the benefit of heat recovery means there is a reduced requirement for additional, stand-alone heating. When combined with a heat source pump system in place of conventional boilers, the market leading 75% heat recovery reduces the building energy requirements and subsequently the size and cost of any renewable installation.

With an optional water to air heat exchanger integrated into the MFS-HR, typically up to 4kW of heating or 2kW of cooling (depending on flow and return ai temperature) can be obtained, thereby eliminating the capital, material and installation and carbon costs (embodied and emissive) inherent with separate central heating, with all its associated pipework, radiators etc.

Each unit is installed at high level, optimising- and liberating- precious floor space. This also minimises the need for more expensive low surface temperature (LST) emitters.

With schools facing a 100%+ increase on energy bills(2), it is worth noting that MFS-HR can cost as little as £10/annum/zone to operate (depending on fuel tariff). Costs are even less when, as already suggested, installed with PV, wind turbines or other renewables.

In hot weather, the system provides free night cooling, providing internal air ready for the new school day. In winter a morning warm-up can be. Utilised if installed with an I nternal coil option, bringing the classroom temperature up to the preset before automatically switching off prior to occupancy.



MFS-HR can achieve up to 75% heat recovery- almost twice that of any other similar systems on the market.

It can be integrated with heat source pumps with low energy and high efficiency. The whole MFS range makes optimal use of recyclable materials making it low on embodied carbon. It attains air leakage better than legislative requirements – 3m3/HR/m2, and a U value of less than 1W/m2/°C, all combining to further enhance the green credentials with minimal leakage and thermal loss.

Computer modelling of hybrid systems has shown in a typical primary school, all the ventilation performance criteria are met, and an improvement in the Target Emission Rate (TER).

Hybrid ventilation with heat recovery can achieve BREEAM credits, under energy and health & wellbeing, whether in new build, or refurbishment.

With energy bills reportedly quadrupling in the past year, and the Government’s objective of reducing emissions in the public sector by 75% by 2037, MFS-HR must surely be the strategy for low energy, low carbon, healthy educational buildings?







Jonathon Hunter Hill

Product Manager – AirMaster SMVs


In most Romance languages, the word for insulation translates directly as isolation. On the road to Net Zero, one of the UK’s primary challenges is to cut heat loss from buildings by isolating the inside from the outside. Increases in air tightness, and reductions in U-values and thermal bridging, will continue to reduce heat loss from buildings. But the increased air tightness creates a particular problem: we are aiming to eliminate natural air exchange between indoors and outdoors to reduce heat loss, cutting the primary method of ventilation that the UK has long relied upon.

Ventilation is required to maintain good indoor air quality in buildings, whether it be reducing the humidity to prevent damp and mould, or to minimise CO2 levels to prevent inhibition of brain function. This creates a different problem: by extracting air from buildings, we also extract heat, which must then be made up from other sources. This is a vicious circle in that we have reduced heat loss through natural air exchange, but may incur heat loss through mechanical ventilation. In buildings with relatively low occupancy densities, such as domestic environments, a low rate of air change per hour (ACH-1) is required, for example 2-4 ACH-1 for living rooms. But in buildings with relatively high occupancy densities, such as offices and schools, the ventilation rate required to maintain good indoor air quality is 4-6 ACH-1, so a great deal of heat can be lost.

The UK has long been in the habit of using natural ventilation for buildings, but Net Zero put paid to that. The solution is to recover the heat from the air using mechanical ventilation with heat recovery (MVHR). In Europe, this is the de facto ventilation solution for new buildings. Indeed, in European deep refurbishments and new builds this is typically a legal requirement. MVHR extracts stale air from rooms, passing it through a heat exchanger. At the same, fresh air is drawn in from outside and is passed through the heat exchanger, the two pathways being separated by a hydraulic break. Heat flows from hot to cold, so the stale air deposits its heat into the heat exchanger, which is picked up by the colder fresh air, warming it before it enters the room. This can reduce heat demand by up to 90%.

When it comes to the UK’s new build schools, in the School Output Specification (Technical Annex 2H: Energy) the Department for Education has set minimum energy intensity targets of 52 / 67 kWh/m2 (primary and special educational needs / secondary schools respectively). The Output Specification indicates that heating should comprise 8 kWh/m2 of this target. Heat load (heat loss), therefore, must be absolutely minimal in order to meet this criterion. Using natural, hybrid, or mixed mode ventilation solutions, this target simply will not be met. It can only be achieved using MVHR, and MVHR with a low specific fan power (SFP) at that.

Factoring in both electrical consumption, heat demand associated with ventilation, fabric losses, and internal gains, a classroom with decentralized MVHR will have a heat load of approximately 600 kWh/year. Comparatively, a classroom with the best hybrid solution would have a heat load of approximately 3,500 kWh/year. This is a factor of six different, entirely due to heat recovery, which in this case will recover approximately 84% of the classroom’s heat. (

In many cases, schools are being designed to use air source heat pumps combined with solar PV panels for generation. If we assume that the heat pump has an SCOP of 3.2 and that PV covers and average of 50% of the building’s electricity demand, the performance gap narrows. However, the outstanding heat load is still approximately a factor of five times higher when using hybrid ventilation as opposed to decentralized MVHR. The result of a reduced heat load is a reduced requirement for both heat plant and renewable energy generation, resulting in net lower lifecycle carbon emissions and may result in lower capital costs.

In specifying ventilation units of any type, I strongly encourage designers to consider not only the electrical energy, but also the heat loss associated with the type of ventilation considered; to take a holistic approach to ventilation. MVHR inevitably has a higher electrical demand, but will slash the building’s heat demand.

When we consider the building fabric to meet our Net Zero goals, it is essential that we consider minimising heat loss through ventilation as a core element of said fabric. This will only be achieved with good quality MVHR if we are to satisfy the requirements for energy intensity and the indoor air quality. With the rise in energy prices, we must reconsider CAPEX vs OPEX. We can learn a great deal from the more mature energy markets of Europe.