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Energy-efficient ventilation systems: what are the options?

Energy-efficient ventilation systems: what are the options?

Julie, Interior Designer, Manchester

Guide written by:

Julie, Interior Designer, Manchester

40 guides

Installing whole-house ventilation can be a great way to improve energy efficiency in the home. A well-designed mechanical extract ventilation system, especially one with heat recovery, can minimise heat loss and make indoor air healthier by removing pollutants. Read on to learn more about energy-efficient ventilation.

While ventilation may not be your first port of call when setting out to make your home more energy efficient, it can play an important complementary role alongside other measures. In addition to eliminating excess humidity in the home, a well-designed ventilation system will remove stale indoor air that has been polluted by sources such as moisture, pet hair, VOCs, fine particles from cooking or fuel-burning combustion appliances. Essential for a healthy home, ventilation also works to improve energy performance and limit heat loss.

It is imperative to ventilate your home adequately. While airing out the house on a daily basis is essential, it won't always suffice, especially in cold weather or if you have any windowless rooms.

Advantages of whole-house ventilation

Whole-house mechanical ventilation replaces stale indoor air with fresh air from the outdoors which limits the presence of indoor pollutants produced by day-to-day activities as outlined above. It also helps to remove humidity which, in turn, prevents mould growth and removes odours. These controlled systems do all that without lowering the temperature of the home.

It is highly recommended to install whole-house ventilation in new builds but it can also be retrofitted in older homes as part of energy-efficient renovation work.

There are two main types of whole-house mechanical ventilation: mechanical extract ventilation (MEV) and mechanical ventilation with heat recovery (MVHR). Let's took a quick look at how each system works before we delve any further into their characteristics and differences.

Mechanical Extract Ventilation (MEV)

MEV systems represent the most basic type of continuous mechanical ventilation. There are two different types of MEV systems:

  • basic: these units do not have humidity sensors and run continuously which uses up energy and can generate heat loss;
  • demand-controlled: these humidity-controlled units switch on automatically when humidity reaches a certain level meaning they use less energy.

Mechanical Ventilation with Heat Recovery (MVHR)

MVHR systems are much more efficient than MEV systems and come in three main types:

  • basic: these units extract stale air and release heated air continuously. This system is the most energy-intensive of the various options but is also the least expensive;
  • humidity-controlled: these units extract stale air and release heated air according to the level of humidity detected. They are more expensive but less energy intensive than basic units;
  • active thermodynamic heat recovery: these units extract stale air and release heated air to over 25°C thanks to a high-performing heat pump. They are the most expensive but also the most efficient units.
We recommend installing a demand-controlled MEV system as a bare minimum.

MEV systems renew air continuously by creating one-way air flow: that is to say, they take indoor air and release it outdoors. An impeller or centrifugal vane fan is used to extract stale air from 'wet rooms' of the home (such as the kitchen, bathroom, toilet and utility room) through vents before sending it outdoors via ducting. Fresh air is released passively into the home by trickle air inlets which are usually installed over windows and doors.

To work out the minimum air flow rate of your MEV unit, you simply need to calculate the total volume of your home and divide this number by 24 (since the air in your home should be fully replaced every 24 hours at least).

Basic MEV systems

Basic MEV systems are used to provide continuous low level extraction to replace indoor air with fresh air. This is the most basic form of whole-house ventilation available and a good option if you are working with a tight budget. These systems have excellent lifespans and require little maintenance. However, since they are designed to work constantly – without taking into account outdoor conditions or indoor humidity levels – they do use more energy.

You may experience cool draughts with this type of system.

Demand-controlled whole-house ventilation

Demand-controlled MEV systems work in the same way as basic models but are humidity-controlled. This means that they turn on and off automatically and are regulated by a humidity sensor which adjusts ventilation rates to match indoor conditions. These systems prevent unnecessary electricity usage and, in turn, lower energy consumption. There are a couple of different types of demand-controlled whole-house ventilation systems.

Basic demand-controlled MEV systems

A demand-controlled MEV system is fitted with humidity-controlled extract vents, but the air supply system is passive. This type of system tends to be fitted in shared buildings that are in the process of being renovated or in commercial buildings, rather than individual houses.

Positive Input Ventilation

More expensive than a basic MEV unit, this type of system is fitted with humidity-controlled extract vents but it also features air inlets which actively push in fresh air from the outdoors when necessary. This type of system can help to limit heat loss, reduce energy consumption and maximise savings.

As the name suggests, mechanical ventilation with heat recovery comprises two circuits: one works to extract stale air while the other releases fresh heated air indoors. The two air circuits (interior and exterior) cross paths in a central heat exchanger. Any available heat is extracted from the outgoing air and is fed back into the supply air. The result is that the supply air is heated which considerably improves thermal comfort in the home and helps to reduce energy bills, even though this system does consume more electricity than a basic MEV system.

Continuous or demand-controlled MVHR

Just like with MEV systems, MVHR can either provide a constant flow of air or can be demand-controlled depending on the level of humidity indoors where the extract vents are installed. A demand-controlled system offers the same advantages and disadvantages as outlined above: lower energy consumption and enhanced comfort but a higher purchase cost.

MVHR systems with heat pumps

Some MVHR systems can be used alongside a heat pump. Instead of capturing heat from the outside air like a traditional heat pump, a heat pump used with a MVHR system takes heat from the stale air extracted by the ventilation system to release it back indoors. These thermodynamic systems can be used for ventilation and heating, and most models also work as air conditioning in the summer. While these systems are state of the art when it comes to ventilation, they are also expensive and can only be used in highly energy efficient (or passive) buildings.

Efficient and economical, MVHR systems with heat pumps have long been used in homes across Northern Europe.

Guide written by:

Julie, Interior Designer, Manchester, 40 guides

Julie, Interior Designer, Manchester

After years of DIY, renovation and designing, I decided to turn my passion into a career. Starting in 2006, in the South-West, I helped people with renovation or construction projects. My expertise and curiosity led me to look further into innovative ideas for myself and my clients. Indeed, to live your passion is also to transform the space you live in and the objects you use daily. My family love my creations and ideas that I bring into their lives! My favourite thing to do: use colour to brighten up interior space. But also tips to hide away clutter. Your home is just never big enough, is it? It is therefore a great pleasure to share my tips with you, so that you also can take as much pleasure as I do when starting up your next project!  

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