Important terms covering ventilation

Key indicators for annual electricity consumption: Key indicators stating the annual electricity consumption in relation to the ventilated area (kWh/m2/year: kWh per m2 per year). The key indicators make it easy to compare the electricity consumption of buildings of similar sizes.

Key indicators for electricity consumption per m2: The expected annual amount of electricity consumption per m2 based on the readings, and how much this will be, if the ventilation is either increased or decreased, in relation to the requirements.

Key indicators for electrical power: Key indicators stating the electrical power of motors in relation to the ventilated area (W/m2: watts per m2), and indicating the system’s capacity, e.g. how much power is required to ventilate a given area.

Key indicators for energy efficiency: The measured energy efficiency and how much this should be, if the ventilation is either increased or decreased, in relation to the requirements. The better the energy efficiency, the lower the electricity consumption.

Key indicators for extraction: The measured air volume that is extracted in relation to how much fresh air there should be. Too little ventilation provides a poor indoor environment and too much ventilation produces draughts and results in excessive consumption of electricity and heat.

Key indicators for operating time: How many hours the system is operational throughout a year, and the amount of time the system runs during the day, in the evening and at night.

Operation and maintenance strategies

• CO2 control: CO2 control is used in locations with variable footfall loadings. If the occupancy of a space is high, the CO2 concentration will rise, and this causes the system to increase the ventilation and supply more fresh air. The CO2 concentration is measured with a CO2 sensor.
  
• Continuous operation: Continuous operation is used in situations where spaces are in use around the clock, for example in residential units.
  
• Time control: Time control is typically used for locations which are used in a fixed pattern. The ventilation system can be controlled by a clock timer, a building management system or similar.

SFP (Specific Fan Power)
SFP states what the electrical power of a motor needs to be in order to transport a given volume of air. The higher the number, the more efficient the system.

A new high efficiency ventilation system today can use as little as 1,000-1,500 W/m3/s (watts per m3 extracted per second). SFP does not indicate whether the system is running for longer than necessary.

System types

• Comfort dual-duct system: Same as ‘Comfort single duct system’, where ‘dual duct’ means that some of the air supply is heated and cooled separately in the air handling unit. The 2 air volumes are then ducted to a mixing chamber which mixes the air to the required supply temperature before ducting it to the required spaces.
  
• Comfort single-duct system: A comfort system is designed both to maintain the required temperature in a space and to provide fresh air. The term ‘single duct’ means that the air supply is heated or cooled in the air handling unit and thereafter distributed to the space in 1 primary duct.
  
• Ventilation – supply and extraction: Same as ‘Ventilation – extraction’ above, where ‘supply and extraction’ means that the system both supplies air to and extracts air from the spaces.

Temperature efficiency
If the ventilation system has heat recovery, the temperature efficiency stated indicates how efficient the heat recovery device is. The minimum temperature efficiency should be at least 65%. The closer the temperature efficiency is to 100% the better.

Typically, it is possible to come up to 70% for a cross-flow heat exchanger, which is the most common type. The best heat exchangers can come up to 87%.

Ventilation principles

• Displacement: Displacement allows for cooled air to be introduced in the space at or near the floor level. The air warms up, rises, and is extracted at ceiling level of the space. Most of the contaminated air will therefore be at the upper level in the space.
  
• Mixing: Mixing allows for fresh air to be supplied to the space via fittings that can be installed in the space as required. The air supply is mixed with the air in the space.

Ventilation systems

• CAV (Constant Air Volume) system: The supply and extraction air volumes are constant regardless of the load. A system where the air regulation is carried out by means of flow control or mixer damper falls under the CAV category, although this rarely produces a significant saving of electricity consumed by the fan.
  
• VAV (Variable Air Volume) system: The supply and extraction air volumes are constantly adjusted to suit the actual needs, based on the heating and occupancy requirements, in such a way that ensures significant reductions in electricity consumption. Systems under this heading include those with fan motors with stepped and stepless speed regulation (e.g. 2-speed units), and/or where the fan has adjustable fan blades. The system is more efficient than CAV in circumstances where demand varies considerably.