The proper exchange of air in a residential building takes place in a way that is not noticeable to the occupants, and results in their well-being and no signs of moisture in the rooms. Although there are many ventilation systems, in single-family homes we most often encounter two – gravitational and mechanical. Let’s learn more about them to find out how to effectively get rid of stale air and supply the interiors with fresh air.
Foggy windows, walls with visible signs of mold and mildew, poor well-being of residents, their tendency to allergies and respiratory illnesses, a noxious, foul odor in the interiors – all this is avoided when ventilation is working properly. Along with the fresh air entering the apartment, at the same time escapes the used air, which contains water vapor, carbon dioxide, and pollutants. If an emergency situation requires it, we use the simplest type of air exchange – we create a draft. This one, however, has the property that it cools the rooms too much to benefit from its efficiency except in occasional cases.
In residential construction, we encounter two types of ventilation: gravity and mechanical. Here are the principles of their operation.
We also recommend an interesting article – https://myintelligenthouse.com/best-air-purifier-for-500-square-feet/.
Table of Contents
1. Gravity system
Involves the free exchange of air between rooms and the outside space by taking advantage of the pressure difference prevailing between the refreshed interiors of the building and the outlet of the ventilation duct. A properly functioning system pulls stale air out of the rooms and replaces it with fresh air, which flows in both through leaks in windows and other parts of the building and through effectively functioning supply grilles and micro-gaps in window sashes.
This system is effective in operation and is often used in our latitude since for most of the year the sustained temperatures serve their proper function. Only when the temperature drops below zero and then when it is very high does the operation of the gravitational system need to be assisted. In the first case, air exchange is too intensive and leads to the escape of heat prevailing in the rooms, while in the second case, the intensity of ventilation needs to be intensified, for example, by opening a window or balcony door.
The pros of using a gravity system:
- it is inexpensive, noiseless, and works on its own;
- one properly designed and constructed chimney containing ventilation ducts provides air exchange to many rooms.
Disadvantages of a gravity system:
- causes heat escape in winter;
- does not perform sufficiently in summer at high temperatures;
- since it requires an adequate distance (at least 3 m) between the outlet grille and the end of the ventilation duct, it does not perform sufficiently in attics;
- causes thermal discomfort in places where the vents are located;
- its effectiveness is negatively affected by strong winds.
2. Mechanical systems
A mechanical system involves the exchange of air forced by electrically powered devices, which are fans. Since a mechanical exhaust system means the mechanical removal of air from the premises, it does not work well when using open-chamber gas appliances for indoor and domestic water heating. The use of fans facilitates air exchange in rooms such as kitchens, bathrooms, and toilets, and we can use the machine itself in any of these interiors, as well as on top of the exhaust duct.
In turn, the use of a supply and exhaust system makes it possible to recover heat from the extracted air or accumulated inside the ground and heat with it the fresh air supplied to the rooms, which happens through the use of a heat exchanger – this type of solution is worth considering at the stage of designing the house.
Advantages of mechanical ventilation systems:
- the supply and exhaust system can be used for heat recovery, which saves heating costs;
- the use of a recuperator and air handling unit will allow not only to increase but also to reduce the temperature in the premises;
- does not require support by the additional opening of windows;
- allows you to preheat the air, enrich it with additional water vapor or clean it with filters;
- operate effectively regardless of the season and prevailing outdoor temperatures.
Disadvantages of mechanical systems:
- the work of the fans is audible,
- their installation is more expensive, and the cost is increased by the energy consumption of running fans,
- their components may fail.
Combination of both types of ventilation – hybrid system
Taking into account the significant advantages and disadvantages of the two systems mentioned above, manufacturers have developed their functional combination – a single system that incorporates elements of gravity and mechanical ventilation. In practice, it works in such a way that whenever the operation of the former is sufficient, the mechanical parts are not activated. Only when the sensors detect the inefficiency of the factors responsible for the gravitational operation, the supporting devices are switched on – they are low-pressure fans in the form of hybrid caps installed on the tops of the exhaust ducts.
Their task is to create negative pressure in the duct with force the same or similar to that obtained naturally in the case of gravitational ventilation. Thanks to this solution inside the exhaust duct there will be no reverse draft and, therefore, no reversal of the direction of the flowing air. The operation of hybrid caps is not affected by gusty winds, including the runoff that reverses the draft in typical gravity systems. Thus, hybrid ventilation is a modified mechanical exhaust system. The operation of devices placed on top of the roof chimney does not require the consumption of large amounts of electricity, especially since the hybrid hoods do not operate continuously, but are activated by sensors that control the strength of the draft.
How about an air conditioner?
Air conditioning, familiar to us from public transportation or workplaces, is primarily a way to cool interiors during the prevailing high temperatures, but individual devices for this purpose also have the opposite effect. Air conditioners can heat rooms, but their efficiency in this regard is lower than in the case of cooling, and they also operate in this mode within the temperature range specified by the manufacturer. Some models also have the ability not only to cause forced air movement inside the room, but also to draw air from outside the building to supply the interior, with which they support ventilation – these are the so-called ducted air conditioners. However, the perceptible movement of air produced by the device and its audible operation are not conducive to its use as a room fan.