Carryover in heat wheels

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The carryover can be prevented using a purge sector under certain conditions, depending on the arrangement of the fans. You must take account of this condition during the design Phase.
For functional reasons, air is "rotated" from one air stream to the other as it flows through the rotor. This is called carryover and has many effects:

  • The mass flows have to be corrected
  • This causes an increase of the air flow rate of at least one fan
  • The supply air quality is impaired by the exhaust air (see VDI 6022)
  • The technical data can change

The carryover can be calculated in a simplified manner as follows:

Carryover M = f.n.T / 30    [m3/s]   [01]
with rotor Depth T
speed of Rotation n 
and half of rotor area f = d2.π / 8

Relative carryover Mr = M/V = 10.n.T / 3.v  [%]  [02] 
with Speed v = V/f 
und volumentric current V

Under normal framework conditions, there was a carryover of about 3 – 13% of the nominal air stream; this is a variable which has to be considered.

Carryover occurs on both sides

It is important that the carryover occurs twice in the rotor:

  • Once from the extract air to the supply air
  • Once from the outside air to the exhaust air

The volumentric current balance is therefore correct at first glance: The missing outside air is replaced by the corresponding extract air. But it is exactly this that must be avoided, or at least compensated for by higher air flow rates.

Caution: The calculation above is idealised for visualisation purposes: The filling of the rotor - the rotor structure created from micro channels through winding - is ignored!
(The rotor filling is usually defined by fill level FG = fF / f, whereby fF is the area covered by filling. This reduces the free section and the carryover while the flow speed is increased by about 5 - 10%.)

Do you want to know more?

Thomas Richter