Introduction to the different types of ventilation
– Create a comfortable environment in terms of CO2 & humidity.
– Purge pollutants such as VOC and NOX.
– Combat condensation.
Our home is an important part of our everyday life, and good air quality contributes to a healthy living environment.
Good air quality is achieved through effective ventilation . An effective ventilation strategy incorporates extract ventilation from “wet rooms” (such as a kitchen or utility) to remove stale air, supply ventilation to habitable spaces (living rooms or bedrooms) to provide fresh air, as well as purge ventilation (achieved by opening a window e.g.) to rapidly remove stale air and odours.
Until recently, the structure of the house itself would allow enough air to infiltrate through gaps in windows and wall, in addition to passive wall vents. However, as building methods and materials improved, and energy efficiency standards became tighter, this infiltration was reduced to a minimum.
Excessive ventilation greatly reduces the energy efficiency of a building by increasing the load on the heating system.
Fresh air drawn in from the outside must be heated to a comfortable temperature by the building’s heating system. Stale air, exhausted to the outside, carries heat energy away from the building. Excess ventilation therefore, can reduce the energy efficiency of a building.
New methods of air supply are required. These methods of ventilation must balance competing for the demands of comfort and hygiene, with the requirement to reduce energy consumption.
Intermittent Extract Fans & Background Ventilation.
How does it work?
This system comprises of background ventilators such as trickle ventilators fitted to windows, or standard hole-in-the-wall ventilators, with extract fans fitted in wet rooms. The background ventilators act to supply air to habitable spaces, while intermittently operated extract fans provide the extract ventilation removing odors and excessive humidity from wet rooms.
|The simplicity of the system||Does not benefit from “intelligent” sensors, unlike system 3 (DCV).|
|Effortlessness installation||Single façade dwellings require additional background ventilators fitted at low level|
|Extraction fans are often connected to lights switches, which means the occupants remain in control||Extract fans may cause noise nuisance|
Passive Stack Ventilation and background ventilators.
How does it work?
A passive stack is a non-mechanical approach to ventilation, where air vents are located in various locations around the dwelling. Using the principle of convection, currents allow the movement of air through the ducts.
With passive stack system, airflow rates are very much weather dependant. Strong gusts can cause over ventilation and surges in ventilation rates; little or no wind may result in inadequate ventilation.
The system is completely uncontrolled. Large amounts of cold air can be drawn into the building, increasing the heat load.
|No running costs (unless mechanical backup is required)||Difficult to replicate system design for standard dwelling design formats|
|Quiet operation||May not be effective in all conditions and may need mechanical back up at times, particularly during warm periods|
|Ductwork may be difficult to conceal|
|Maximises heat loss|
|Efficiency may vary depending on the weather|
Demand Control Ventilation.
Demand-controlled ventilation (DCV) automatically regulates ventilation based on actual demand using a suitable sensor. DCV can be triggered by occupancy sensors, moisture sensors or air-quality sensors detecting carbon dioxide or other pollutants, or a combination of these.
The difference between DCV and basic intermittent ventilation is that DCV operates automatically, without requiring any manual user intervention.
How does it work?
A central fan provides a continuous background extraction rate. A controller in the fan maintains a constant air pressure in the system, increasing or decreasing the fan speed as required. Humidity sensitive extracts located in wet rooms open and close depending on room humidity. If a particular room has high humidity, the extract opens.
When the extract opens, this causes a pressure drop in the system. The fan automatically increases speed to return to the target pressure. The more extracts open, the higher the extract rate is.
Other models of extractor can be triggered by occupancy, carbon dioxide or other air contaminants.
Coupled with the boosted fan speed, this combination means that stale air is extracted only from areas where air quality is below the required standard.
The system ventilation rate is always matched to the actual demand, reducing energy consumption by fans and reducing overventilation and heat energy consumption.
|Continuous ventilation at predetermined rates||Perceived high running cost|
|Single penetration to external building fabric (central extract)||Potentially noisy, requires considered design|
|Controlled ventilation system independent of outside wind and pressure||Duct work requires qualified installer (labour intensive, adds to the final cost)|
Continuous Mechanical Supply & Extract with Heat Recovery.
Mechanical Ventilation with Heat Recovery (MVHR) continually removes stale moist air from wet rooms, while supplying a balanced amount of outside air directly to habitable rooms.
The difference between MVHR and other ventilation systems is that with MVHR, the heat energy carried by the stale air is used to partially heat the fresh intake air through a heat exchanger.
This reduces the demand on the building’s heating system and minimises the loss of heat to the outside atmosphere while maintaining fresh clean air.
How does it work?
Stale, humid air is extracted from wet rooms at a continuous rate. This air is carried through ductwork to a central ventilation machine where it is passed through a heat exchanger element before being exhausted through the
Fresh cold air is drawn in from the outside through an intake grille. It is then passed through the heat exchanger where it is heated by the stale exhaust air. The fresh, warmed air is then supplied through sealed ductwork to the habited rooms of the house.
The supply rate and extract rate are balanced to maintain comfortable air pressure and reduce draughts.
It is important to note that the intake and exhaust air streams never mix.
|Controlled airflows||Duct work requires qualified installer|
|Pre-heated incoming fresh air||Can’t use open fire must use room sealed stove|
|Heat exchange reduces heat demand||Must be commissioned using an anemometer|
|Limits outside noise pollution||Filter needs to be cleaned/replaced at set intervals|
|Improves BER asset rating if combined with airtightness below 3 ach@50pa|
|Easy to demonstrate building regulations compliance.|
|Controlled ventilation system independent of outside wind and pressure|
|Filters particulates of incoming air|