Basic human needs are independent of the building type, but the way ventilation is used to meet those needs can depend on the building type. This is discussed in the following sections.
2.6.1 Renovation of residential buildings
Renovation of existing residential buildings can be performed at different levels.
- Renovation of one room at a time, which can include replacement of windows in the particular room, improved airtightness of building envelope and interior upgrade
- More extensive renovation, which can include additional insulation, replacement of all windows in the house, improved airtightness and more.
Many house owners are interested in improving energy performance as part of the renovation. This can have consequences for the ventilation of the house and, therefore, on the indoor air quality. By improving airtightness and replacing old windows with new windows, the unintended infiltration is reduced. This requires that other measures be taken to ensure adequate ventilation. The right ventilation depends on the type of room. Most existing residential buildings use natural ventilation, and the following is based on that assumption.
Bedrooms are characterised by being a relatively small rooms where people spend a long time, typically 6 to 8 hours per 24-hour period. The bedroom is the room where we spend the most time during our lives. It is very important for our health to ensure adequate ventilation of bedrooms. Many residential buildings have insufficient ventilation of bedrooms even before they are renovated. To ensure adequate ventilation by natural ventilation, at least two windows should be installed. The windows should have ventilation flaps or grilles that can be opened during the night for as much of the year as possible. Windows at two different heights in the room will perform much better than two windows at the same height; they enable the stack effect to work. However, ventilation flaps alone will not always be sufficient to ensure adequate air quality in a bedroom. Electrically operated windows (VELUX INTEGRA®) provide much better opportunities than manually operated windows, as they can be programmed to make one or two airings during the night. Decentralised, mechanical ventilation can be considered.
The ventilation rate of the bedroom during the night is higher when the bedroom door is open. A study of ventilation rates in typical houses showed the following ventilation rates for different door positions. Closed door: 0.3 ACH; Door ajar: 0.4 ACH; Door open: 0.5 ACH (Bekö et al., 2011).
The use of a children’s room depends greatly on the age of the child, and whether it is used for sleeping only or also for homework, play or entertainment during the day. There are often many toys and electronic appliances in this room, which increases the need for ventilation due to emissions. But children are often unaware of the importance of ventilation. The considerations that are given for bedrooms also apply to children’s rooms, but with the additional emphasis on high airings discipline – which many families with children do not have time for. So electrically operated products are particularly relevant in this room.
Living and dining rooms
Living and dining rooms typically have more floor area per person than bedrooms, and we spend less time in living rooms than in bedrooms. This makes it easier to provide adequate ventilation of living rooms. The ventilation must often meet comfort requirements (feeling of fresh air) rather than health requirements. The need for ventilation in a living room can change from low to very high (with guests in the house), and the ventilation design must reflect that. A flexible ventilation design includes two to three operable facade windows and a similar number of roof windows to allow efficient airings when the need is high. Manually operated windows may be sufficient if ventilation flaps are used in combination with a reasonable use of airings. Electrically operated windows can provide additional peace of mind.
Activities in the kitchen generate humidity, smell and fine particles, all of which are most effectively removed by efficient ventilation at the time of the activity. Cooking hoods are important, but their performance is reduced as they get dirty from grease, and airings while cooking is a good habit and an efficient supplement. The airings are most efficient when windows located at two different heights can be opened, e.g. facade windows and roof windows. Due to the heat generated by ovens and stoves, cold draughts are rarely a problem in kitchens. As the need for ventilation is usually easy to sense and smell, it is simple for occupants to make airings at the right time. Humidity-controlled electrically operated windows can be an additional benefit.
Bathroom activities produce humidity and smells. umidity generation is high during baths, but bathrooms are not used much during a 24-hour cycle. An efficient ventilation design, therefore, allows high ventilation rates for short periods. Bathrooms are often equipped with mechanical extract ventilation, but good possibilities for airings are an advantage. The most efficient airings are achieved with windows at two different heights. As the need for ventilation is usually easy to sense and smell, it is simple for occupants to make airings at the right time. Humidity-controlled electrically operated windows can be an additional benefit.
Natural ventilation exhaust path
In houses with natural ventilation, it is important to consider the flow path of the air in the house when it is renovated. The flow path depends greatly on wind direction, wind speed and external temperature conditions, and a specific window can function both as inlet and extract. However, high-placed windows (and stack ducts) will function mainly as extracts.
In one-storey houses, roof windows in kitchens and bathrooms will often function as extracts and will ensure that air is generally taken into the house through bedrooms and living rooms and extracted through wet rooms.
In two-storey houses, windows at the upper level will often function as extracts. If bedrooms are located on the upper floor, it is important that bedroom windows are not used as extracts, as this may cause overheating and will increase the risk that the air entering the bedroom is from other rooms in the house and therefore less fresh. An efficient solution is to place a roof window above the staircase on the upper floor, as this window will often function as an extract for the lower level.
2.6.2 New residential buildings
The choice of ventilation system in new residential buildings is often heavily influenced by energy legislation and by the energy performance ambitions of the future houseowner. In Northern European countries, mechanical ventilation with heat recovery is becoming a de facto standard, thanks to its ability to reduce heating demand during winter.
Natural ventilation remains the most energy-efficient ventilation system during summer in all European countries, as there is no heat loss and no demand for electricity to drive fans.
In new residential buildings, both mechanical and natural ventilation can meet legislative and performance requirements. Natural ventilation can be the primary mode of ventilation or a supplement to mechanical ventilation.
In situations where mechanical ventilation is selected as the primary ventilation system, it is important to emphasise that natural ventilation is an important addition. Including natural ventilation in the ventilation design of a new building provides these particular benefits:
- No use of electricity in warm part of year (energy-neutral ventilation)
- Increased indoor air quality in warm part of year, as the air change rate can be increased during summer at no additional energy cost
- Allows efficient airings when activities create a specific need for ventilation (e.g. bathing, cooking)
- Provides contact to the outdoor environment and a sense of fresh air (see section 2.2.4)
- Efficiently prevents overheating through ventilative cooling
(see the Thermal Comfort chapter)
Many of the considerations on renovation of existing buildings discussed in the previous section 2.6.1 also apply to new buildings.