Systems with balanced or positive Pressure in the room

Ventilation systems based on neutral pressure was previously popular. It was easy to fit the circular air intake at the chimney in the roof alternate with the air outlets.

The energy consumption is however three to four times higher, because you must have fans in both air intake and air outlet to get neutral pressure. In the air intake unit the air must change direction twice and at elevated speed, which put extra load at the fan and consequently higher power consumption.

In an attempt to reduce power consumption you may leave fans in the air outlets out. Then the system will have positive pressure in the room. The air intake still changes the air direction twice, so the savings leaving the fan out is modest.

An issue is, however, that the positive pressure forces stale air through cracks in the building to the outdoor. In wintertime the air cools down and forms condense water, which makes the insulation wet and less effective. The water might even freeze with the risk of damaging walls. Positive pressure system may only be installed where the building can stand this phenomenon.

 

Strengths

Weaknesses

Low sensibility to wind pressure

Very high energy consumption

Independent of geometry of building

Many rotating parts

 

Rather expensive

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