What is a mechanical ventilation with heat recovery (MVHR) system?

What if your property had a system capable of recycling the hot air it produced? Discover how MVHR systems work and whether it’s suitable for your premises.

At Mid-Tech Services, we’ve applied our experience and knowledge to designing, creating, and installing high-quality ventilation systems.

Considering the current energy crisis, for our clients to save big chunks on their energy bills, Mechanical Ventilation with Heat Recovery (MVHR) has become a desired sustainable solution especially in large scale commercial buildings. But what are these ventilation systems?

What is an MVHR?

Ventilation with heat recovery is a mechanical ventilation system that ensures minimal heat loss when ventilating a room. MVHR is a common term for these systems/units. They can also be called HRV (Heat Recovery Systems).

How do these systems work?

The MVHR system/units work by extracting the stale air inside the building and feeding it through filters. Extracting the heat energy so that it’s not exhausted to the outside, energy is subsequently transferred back into the building through a filtration system.

The main components of MVHR systems are:

• A heat recovery cell (where the indoor heat/air is extracted and supplied into the outside air coming into the building).
• Fans (pull in the air and blow out the air).
• Filters (filtering outside air from dust and particles inside the unit, protecting the longevity, system efficiency and improving indoor air quality (IAQ)).

Alongside these features, MVHR systems also come with a summer bypass, meaning they can control the amount of energy recovered and controlled manually or through an electronic sensor.

What are the benefits of an MVHR system?

Some benefits of a heat recovery ventilation system include the following points:

• Fresh filtered air.
• Minimises heating loss – which will help you save on your heating and energy bills.
• Reduces overheating problems.
• Eliminates excess moisture from the building and furnishings – which increases the longevity of building structures.
• Improves your physical and mental health.
• Retains heat.

Combining an Air Source Heat Pump for maximum performance.

An Air Source Heat Pump is a system that takes air from outside, heats it and provides it indoors as space heating (through radiators and/or underfloor heating as well as hot water).

Combining an MVHR system with an air source heat pump is an super effective energy-efficient solution to heating and ventilation. When used in conjunction with each other, the heat pump will heat incoming air first, and then the MVHR unit kicks in and functions as normal.

Installing an air source heat pump (ASHP) can lower your energy bills by up to 75%, especially if you are replacing an LPG (liquefied petroleum gas), oil, or coal-fuelled boiler system.

The MVHR system can recover over 90% of the heat from the outgoing stale air before feeding it back into the building as warm, fresh, filtered air. Reusing this heat rather than losing it to the outside air through passive ventilation ensures that the heat pump can efficiently maintain the property at a comfortable temperature all year round.

During the winter, MVHR systems can increase their efficiency by up to 10%. They are also silent and can improve the standard of living in a home by up to 40%.

What is the best system for me?

There are various factors to consider when comparing MVHR systems.

Firstly, you should understand the technology used to determine whether MVHR is ideal for your property. For example, the structure of your building may not be suitable for installing an MVHR system. You’ll find that MVHR suits properties with a high degree of airtightness (new builds) so indoor air doesn’t just escape through cracks and poor insulated rooms. This is a massive waste of energy and money!

You’ll also need to consider your property location, as noise and air pollution offer different levels in different areas. (A UK pollution map will give you an idea of the pollution level in your area.) Determining your location and pollution levels will distinguish what type of filtration you need.

Another aspect to consider is which unit complies with the government building standards for the size of the property. This includes the size of the building, the number of rooms, wet rooms, and occupants.

Ducting is also critical. Ducting that is too small for the airflow rate will result in high resistance and velocity of air, creating noise issues. Semi-Rigid radial duct systems create less system pressure than traditional branch systems.

Other things to consider are accessibility to the unit for maintenance, how you want to control the system (apps or wall monitors) and any extras like CO₂ monitors.

However, we’re only scratching the surface. We recommend you contact the team at Mid-Tech Services, and discover our other ventilation blogs for more information, as it’s paramount that an MVHR system is designed by a specialist and installed correctly by competent professionals.

How much does an MVHR system cost?

MVHR systems range in cost depending on the features, functions and ducting.

A semi-rigid ducting system costs more than a traditional branch ducting system but offers lower audibility and other benefits that branch ducting doesn’t have.

And although semi-rigid ducting costs more, it’s cheaper to install as it takes less time to install compared to branch ducting.

There are five types of costs to consider with MVHR:

1. Design and consulting costs.
2. MVHR unit.
3. Ducting.
4. Installation and commissioning.
5. Ongoing costs (filters).

You may want to add the life-cycle costs based on durability and if parts can be fixed or switched. The question is what level of quality, functionality, durability, and service you want.

Where do you install an MVHR Unit?

MVHR units can be large, especially high-performing systems. Air requires space to move efficiently and quietly.

For optimal results, you should consider the following points when situating your MVHR unit:

• Ease of access for filter changes and maintenance. When accessing your MVHR unit, you probably don’t want to balance across ceiling joists whilst trying not to stick your foot through something.
• Allow maintenance space around the MVHR unit (typically 500mm in front).
• Ideally, the unit is placed in a central location to minimise duct runs.
• Often the system is placed within a thermal envelope, such as a utility room, plant room, warm loft, or storeroom. In this case, place the system close to an external wall to keep the intake and exhaust ducts as short as possible.
• Insulated systems can remain outside the thermal envelope, like a garage. Place the system close to the partition wall of the house to keep the supply and extract ducting as short as possible.
• Smaller MVHR systems can be ceiling mounted with a maintenance hatch. Therefore, the unit should be close to the external wall with the intake and exhaust penetrations.
• If all this is not possible, MVHR systems can stay in a cold loft. However, pay particular attention to the supply and extract ducting. Ideally, these are placed underneath the loft insulation. The UK standard is 25 mm of quilt insulation (or equivalent), but we recommend 50mm to 100mm of quilt insulation with an aluminium foil coating.

Get in touch with the MVHR system specialists.

If you’re looking for a company that offers full and bespoke MVHR maintenance, design and installation services across the West Midlands, London, and surrounding areas, contact Mid-Tech Services today.

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