Low Energy Building: The Importance Of Ventilation

by Brian Flax | Apr 17, 2020

Typically in Ireland, many older homes experience ventilation via undesired air leakages, open windows, and wall vents such hit and miss vents. The natural air ventilation from wall vents has not been tolerated by many homeowners. Over time, building occupants may have closed these vent types, resulting in a build up of stale, polluted and often toxic indoor air.

Thankfully, with the introduction of stricter building regulations (Part F 2019), the rise in low energy builds and passive homes, alongside increased awareness of the benefits of efficient home ventilation, we have seen huge improvements in both the new build and retrofit market.

Why is ventilation so important?

In simple terms: To breath fresh air!

Our indoor environment can become polluted by breathing, cooking, dust, dander, chemicals from cleaning products, drying clothes and more. During colder months of the year, the air inside your home is warm and carries more vapour than the outside air, causing vapour pressure, resulting in high levels of humidity.

Another culprit of excess moisture comes from human breathing and perspiration, where a household of 4 occupants can create 24 pints of airborne moisture a day. Particles in the air, alongside high humidity levels from the kitchen and bathrooms, can directly affect the occupants’ health, especially those suffering with allergies and respiratory conditions such as asthma. Mould, mildew, and mites thrive in humid environments, and prolonged exposure to these can lead to serious health conditions.


Black mould is often the result of poor building ventilation, as pictured above

Low energy building & ventilation

When constructing a low energy or passive house, you must look at insulation, renewable energy sources, airtightness and ventilation working as as a designed system. Most new builds now aim for an A-Rating, complete with superior insulation U-values, at least one renewable energy source (solar PV, heat pump), airtightness performance level of 5m3/(h.m2) or less, and an effective ventilation system to guarantee a safe, comfortable and healthy indoor environment.

As each home is different, each system will have to be designed effectively to achieve low energy consumption or passive house standards. The unique design will include a ventilation system that suits the buildings needs, and supports an airtight home by extracting polluted air, humidity, CO2, and volatile organic compounds (VOCs), replacing it with fresh filtered air.

The most efficient and smart ventilation systems on the market are Demand Control Ventilation, and Mechanical Heat Recovery Ventilation Systems.

Demand Control Ventilation

Demand Control Ventilation is a fully ducted unit that monitors humidity and carbon monoxide via sensors. This smart system detects high levels of humidity and CO2, and relies on sensors placed in the inlets and exhausts of rooms to respond to the needs of the room and its occupants. The sensors consist of polyamide strips that expand and contract, in essence opening and closing the vents until the room reaches a desired air quality. The speed of air change depends on the levels in the house, the number of occupants and their activities, such as someone taking a shower, boiling a kettle or drying clothes in a room. When the house is empty and the air quality is near perfect, the vents will remain closed and will limit heat loss.

This system achieves the main aim of ventilation: indoor air quality, and secondly, saves energy because it does not use electricity as the nylon-like membranes expand and contract to push the valves open and close. More importantly, it is only in use when necessary, reducing energy consumption.


Whole-home demand control ventilation system installed in the attic of a home

Mechanical Heat Recovery Ventilation

Mechanical Heat Recovery Ventilation (MHRV) is a more energy efficient system that has ventilation valves present in each room, where humid, stale, polluted air is extracted and replaced with fresh air from the outside. Heat is also recovered from the extracted air, and passed onto the fresh filtered air via a heat recovery unit, which is usually housed in the attic of a home. The extract and supply air are in two separate air streams that never mix, and the heat recovery unit is connected to all room valves by a series of ducting throughout the home.

Mechanical Heat Recovery Ventilation is mandatory for passive house standards, but also suitable for low energy builds. It is important to note that MHRV is only effective when used in an airtight home, with an airtightness performance level of 3m3/(h.m2). Heat exchangers in MVHR systems should work to a minimum efficiency of 75%, where the maximum amount of heat is extracted from the air.

According to ventilation experts, MHRV system provides maximum energy efficiency by using no more than 45 watts of electrical energy, an average of €60 per year to run with a medium-sized unit. The level of heat recovery from the unit results in a reduction of the usage of your home heating system, thus saving more energy.

It is important to note that both systems require maintenance, and frequent filter changes (which can be done by the occupant).

This diagram shows a typical mechanical heat recovery ventilation system installed in the attic of a home. The system ensures fresh air is supplied to the indoor environment, while extracting the heat from stale indoor air as it exits the home.


Main takeaways

  • Ventilation is extremely important for indoor air quality, and occupants’ health and comfort
  • When building a new home, you must adhere to the ventilation guidelines as set out in Part F 2019. Your ventilation system must provide 0.3l/s/m2 or 5l/s per person, which correlates to the rate of supply of fresh air per person
  • There are two smart types of ventilation systems available – Demand Control Ventilation, and Mechanical Heat Recovery Ventilation
  • Demand Control Ventilation is used in homes that are not completely air tight. This system uses a system of sensors that detect excessive levels of humidity and CO2 and opens the vents to extract this air, while allowing the supply of fresh air in
  • Mechanical Heat Recovery Ventilation is only effective in airtight homes. The system extracts air using one air stream, while a heat recovery unit recovers heat from the air leaving the home and passes it to the fresh air supply incoming
  • Both units work to create a healthy indoor environment.
  • Mechanical Heat Recovery Ventilation is a mandatory component of a passive house
  • Each home needs to be designed for ventilation effectiveness – not every unit will suit every home
  • Both systems save energy, but the Mechanical Heat Recovery Ventilation system saves more as it recovers heat energy

Passive House plus magazine have some insightful articles on ventilation and specifically Mechanical Heat Recovery Ventilation.

Are you in the process of planning or designing a low energy home or Passive House? Speak with our technical department today and see how KORE can help you achieve your low energy goals. Consultations are free of charge and can be scheduled remotely for your convenience.

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