Retired air tightness technician Trevor Clark talks about ventilation, its history and how to improve air flow in a building.

It is important to understand that here: When we refer to ventilation we are talking about wanted air flow inside a building, and not the medical ventilation term that refers to organic breathing by biological animals and other life forms, note also; Unwanted air flow within a building is not ventilation.

Ventilating a space with fresh air aims to avoid ‘bad air’. The poisonous component of air was later identified as carbon dioxide (CO 2 ), in the very late 1700s, starting a debate as to the nature of ‘bad air’ which humans perceive to be stuffy or unpleasant.

It was noted in 1872 that CO 2 concentration closely correlates to perceived air quality.

By 1935, research suggested the primary component of ‘bad air’ was odour, perceived by the human olfactory nerves.

At lower, more comfortable temperatures, lower ventilation rates were satisfactory.

However while it is preferable to minimize ventilation with outdoor air to conserve energy, cost, or filtration, the reduced ventilation rates were found to be a contributing factor to sick building syndrome.

ASHRAE continues to publish space-by-space ventilation rate recommendations, which are decided by a consensus committee of industry experts. The modern descendants of ASHRAE standard 62-1975 are ASHRAE 62.2 for dwellings.

The regulations for new dwellings seem to be ever-changing but the Passive Haus build system appears to provide a good basis for ventilating a dwelling. There is not a simple one size fits all answer.

Designing a balanced energy recovery/reclaim system can be complicated when considering an existing building that is undergoing a retrofit for energy.

Improved insulation, air tightness and ventilation in order to reduce heating costs. When upgrading an existing dwelling per the above the risk of black mould can triple!

Often it is overlooked to apply an appropriate ventilation strategy and this can be a grave error.

Living in a draughty dwelling, there is no need to think about fresh air as the problem is being removed by excess air infiltration.

If most of the draughts have been blocked off and new air tight windows have been installed, the air infiltration rate is greatly reduced, it is then the potential condensation problem becomes a reality. Especially in older properties, as there will be more cold bridges in the external shell which don’t have as much insulation. These areas attract condensation because of colder inner surface temperature, which helps mould growth.

Therefore it is important to think about a suitable ventilation strategy when older dwellings are being upgraded. If you are reading this information, then you are already considering the improvements as outlined above.

We would strongly recommend seeking guidance from a specialist company who will provide you with a ventilation system designed specifically for your home.

A ventilation solution should be considered to provide a bespoke solution that removes excess moisture and pollution to provide enough fresh air for the occupants.

It is important to say that the use of extract fans alone, are not good for energy conservation. The fan reduces the air pressure within the building immediately.

The air out is warm, moist and dirty (losing the dirt is OK) – this air now needs replacing, outside air, at a higher pressure will find a way inside via gaps, cracks and holes in the building. The pressure difference does not need to be high; at 1 Pascal unwanted air will enter or leave a building. A higher the pressure difference means more unwanted air flow.

Not only has energy gone out of the dwelling but the cold air entering now needs heating, all due to the extract fan!

As a very general guide any room (bath, shower) should have 10-15 Air Changes per Hour (ACH), a toilet six ACH, while a kitchen hob hood should provide a ACH of 15 times the volume of the kitchen while the fans are switched on. Modern balanced ventilation systems are designed to run continuously and provide a whole house ACH rate of between 0.5 and 1 24 hours/day for 7days per week per year (365 days), but these tend to have energy exchange.