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Performance

Compact unit including ventilation heat recovery and air to water heat pump is a cost-efficient system for ventilation heating (www.passiv.de)
Proper size of a ventilation unit serves for better heat recovery efficiency and lower specific power consumption. Unit B is for lower air flows than unit A. Certified ventilation machines offer information on heat recovery efficiency and specific power demand according to air flow.

Simple systems
The aim of a passive House is to gain high energy-efficiency and comfort by high quality building envelope and simple building service’s system. The extra investment into building envelope can be mostly gained back by simplifying the system. Solutions that serve for multiple purposes are thus advantageous.

Ventilation heating system is an efficient heat distribution system that serves for both ventilation and space heating. If an exhaust air heat pump is included into the scheme, the whole system serves for heating of hot water as well. Ventilation heating system is by far the most economical heating system for an energy-efficient house. A Passive House requires heat recovery from ventilation, and as such ventilation system serves both for air exchange and space heating.

The efficiency of the heat recovery unit should be as high as possible. Mechanical exhaust ventilation, natural ventilation, or hybrid ventilation systems are not an alternative. The heat recovery unit needs to have a by-pass possibility due to the risk of over-heating. De-frosting is needed at least in cold climates. De-frosting by heat or cyclic use of heat recovery for de-frosting reduces the efficiency of heat recovery. Thus other ways and means should be applied as far as possible. Ground duct pre-heating of supply air may reduce or eliminate the de-frosting demand.

Ventilation
The yearly energy efficiency depends also on the size of the unit and diameters of the ductwork. Over-sized machines have lower specific power demand over the whole range of required air flow rates. Rotating (regenerative) wheel heat recovery units have in general higher efficiency rates than flat plate (recuperative) heat exchangers. In some countries rotating wheel heat recovery units are not recommended.

In Passive House ventilation heating systems are preferred. Since the ventilation rate and air volumes are most of the time similar to conventional housing the noise control is not different to standard residential buildings. However, according to recent research results, noise from ventilation devices is usually experienced disturbing even though it does not exceed the building code requirements (28 dB(A)).

People prefer noise levels of 22-25 dB(A) in bedrooms. They also tend to control ventilation according to disturbing noise level especially if the background noise level is low, e.g., in the single family housing areas. In addition to conventional system’s damper an extra damper may be required for the supply air duct. The sound dampers should be designed in a way that the ventilation can be near the maximum and still on acceptable noise level.