fort continuously. Mixing air quality is very likely to occur
and ought to be tolerated in such a case.
A mixing ventilation system can provide uniform pollutant
distribution at best. If the favorable characteristics of a
radiant cooled ceiling with respect to thermal comfort are
most important, an air-conditioning concept can be realized
with mixing ventilation and a cooled ceiling. Usually
such a system will not involve any problems with thermal
comfort when the cooling load does not exceed 100 Wrm2
w4x. But one has to make sure that the supply air diffusers
are properly designed, situated and adjusted to avoid any
draft problems. To obtain the best possible mixing airflow
pattern, the entire ceiling ought to be covered by cooled
areas. If this cannot be done, the mixing of fresh air and
supply air might not be the best at all times and places and
the air quality in the occupied zone can be varying.
Appendix A
To illustrate the possible combinations of ventilation
system and cooled ceiling the following Fig. 17 and Table
3 were created. For this purpose, some assumptions had to
be made: The cooling capacity of a radiant cooling ceiling
usually does not significantly exceed 70 Wrm2. Thus, this
value and results from Eq. 8. as well as a temperature
differential between exhaust air and supply air of 6 K
displacement flow.or 12 K mixing flow. were used to
draw the lines and areas in Fig. 17. Cooling loads beyond
100 Wrm2 are not considered, as it is not possible to
exclude problems with thermal comfort totally. In conjunction
with Table 3, Fig. 17 allows one to estimate the air
quality when a cooled ceiling is combined with a mechanical
ventilation system.
A.1. Example for using Fig. 17 and Table 3
An open plan office provides 8 m2 for each working
place and the outdoor air requirement shall be 60 m3rh
per person. This results in a supply airflow of 7.5 m3rh
m2 ..
The cooling load may consist of heat released by people
10 Wrm2., computers25 Wrm2., lighting10 Wrm2 .
and an exterior heat gain 20 Wrm2 . and amounts to 55
Wrm2.
For this data, a cooled ceiling combined with either
mixing flow or displacement flow would be able to ther-
mally condition the spacearea in Fig. 17.. Displacement
flow could provide a slightly better air quality in the
occupied zone than a mixing flow systemTable 3..
A.2. For comparison
If an all-air-system was supposed to remove the loads
from the space, the supply airflow would have to be
increased to about 14 m3rh m2. with mixing ventilation.
or even up to 28 m3rh m2 . when displacement ventilation
ought to be used