quency vector. Using this function, design conditions for a given
percentage of time are determined.
3. Calculation methods
Based on ASHRAE report 1273, DBTs are grouped by equal bins
(0.5 ◦C) [11]. Each value Fk
DB of the frequency vector counts all DBTs
where DBTk is the center of bin k and DBT is the bin interval. The
cumulative distribution function (CDF) is obtained by summing all
hours below a certain level:CDFk
DB shows the probability (P) that DBT is less than the upper
limit of the bin:In addition, the climate change impacts directly on the cool-
ing device performance in buildings. Statistical investigations have
been shown thatDEC,VC package cooling, and centralVC or absorp-
tion systems are used 79.9%, 2.6% and 17.5% of cooling devices in
Tehran respectively [12]. Current statistics show that the investi-
gation of outdoor design conditions on the performance of these
systems plays an important role for the future decision making in
selecting proper cooling devices.
With DEC, outside air is blown through a water-saturated
medium (usually cellulose pad) and cooled by evaporation. DEC
adds moisture to the air stream until the air stream is close to
saturation. The DBT is reduced, while the WBT stays the same.
Based onDEC process, the cooling potential of the systemis directly
affected by the difference between DBT and WBT, which is called
wet-bulb depression (WBD). With IEC, a secondary air stream is
cooled by water. The cooled secondary air stream goes through a
heat exchanger, where it cools the primary air stream. The cooled
primary air stream is circulated by a blower. Indirect evaporative
cooling does not add moisture to the primary air stream. Both the
DBT and WBT are reduced. With IDEC, the primary air stream is
cooled first with IEC and then cooled further DEC.
Several research aboutDEC and IDEC systems in Iran are adopted
by Heidarinejad et al. [13,14]. These studies showed the advantage
of DEC and IDEC in Tehran to prepare the thermal comfort condi-
tion but the effects of climate change were not considered in their
studies. The saturation effectiveness of DEC system is defined by
Eq. (4):
εDEC = DBTout − DBTout,DEC
DBTout −WBTout
(4)
Also, the performance of IDEC is calculated by using Eq. (5):
εIEC = DBTout − DBTout,IEC
DBTout −WBTout
(5)
where DBTout and WBTout are outdoor DBT and WBT respectively
and DBTout,DEC and DBTout,IEC are the outlet air DBT,which obtained
byDEC and indirect evaporative cooling (IEC) devices. Eq. (4) clearly
illustrates that the performance of DEC system is affected by out-
door design condition. For further investigation, it is assumed
that εDEC and εIEC are 0.85 and 0.8 respectively [14]. For different
decades DBTout,DEC is calculated using Eq. (4) and shown in Table 2.
The results illustrate that DEC systems can put the building into
the proper thermal comfort condition during 1967–1996while this
systemis not capable of preparing comfort condition after 1997. In
addition, outlet air DBT achieved by DEC is increased in the recent
decades so the cooling effect of the systemreduced obviously (com-
pareTcooling in Table 2). It can be concluded thatDEC should not be
selected as cooling device for future in residential buildings.More-
over, DBTout,IDEC has risen about 26% in the last decade of study
compared to 1967–1976. While IDEC can prepare thermal com-
fort in all decades of research, the cooling effect of the system has
decreased at about 19 percent. These reductions in cooling effect
need more consideration about selecting appropriate IDEC system
with higher capacity within these days compared to 1967–1976 能源和建筑英文文献和中文翻译(3):http://www.youerw.com/fanyi/lunwen_8028.html