Danish farmers that wish to establish or expand animal production facilities have to document that the expected odour
nuisances at the neighbours are kept below certain thresholds. To do so the expected odour emission must be calculated
from norm figures for expected odour emission from the wished production, and a certain atmospheric dispersion model
(OLM) must be used to calculate whether the requirements are fulfilled. The farmers can choose to use the dispersion
model for a calculation that takes into account individual preconditions as locations and design of ventilations chimneys.
Alternatively they can use standard curves that gives the required distance to neighbours calculated at standardized
preconditions. If the thresholds are not met, the farmer can include environmental technologies mentioned on a special
list maintained by the environmental authorities. Currently biological air cleaners are the sole technology mentioned on
the list that significantly can reduces the odour emission and the consequent required distance to the neighbours. An
alternative to the relative expensive biological air cleaners is to release the air at a larger height which increases the
dilution of odour before it reaches the neighbours. Low potentials found in elder analyses in relatively small herds might
explain why the method is not already frequently used. Larger herds improve the possibilities to use larger chimneys and
generate a larger vertical momentum which increases the effective release height.
The aim of this work is to enlighten the potential of merging and elevation of ventilation chimneys in order to reduce
odour concentration around large pig production facilities. The analyses are based on an assumed facility with an
installed ventilation capacity of 720000 m3
h
-1, which, in the reference case, is assumed to be released from 60 chimneys
0.7 m above the roof. Merging these chimneys to four or fewer 10 m high chimneys reduces the odour nuisance distance
to the neighbours by 59-67 %.