暖通空调系统英文文献和中文翻译(4)
systems have been utilized since the 1960s. Energy saving is one
of primary reasons that VAV systems are very popular design
choices today for some commercial buildings and many industrial
applications.
In this study, both CAV and VAV air distribution systems were
investigated. In the VAV system, the mixing air supplied to con-
ditioned space is constant at a temperature of 15 C, but the mix-
ing air flow rate is varied by the combined action of the closing
of the zonal VAV box dampers and the fan speed controller to
meet the building cooling load. In the CAV system, supply air
flow rate is constant, but supply air temperature (minimum
15 C) is varied to remove the heat gain from inside of condi-
tioned space. Outdoor air requirement of the sample building
was obtained to be 1596 m3
/h for minimum ventilation level in
accordance with ASHRAE Standard 62 ventilation rate procedure
[25].Building cooling load was calculated according to the Radiant
Time Series (RTS) method suggested by ASHRAE [26,27]. Hourly
distribution of the design-cooling load calculated for all types of
buildings considered are shown in Fig. 3. In the calculation, out-
door design conditions for Adana were taken to be 38 C dry bulb
temperature and 26 C wet bulb temperature. As shown in Fig. 3,
design-cooling load of the no insulation building is 145.14 kWand sensible heat ratio (SHR) is 0.98. Design cooling loads of Build-
ings A, B and C are 92.15 kW, 94.19 kWand 97.11 kW, respectively,
and their SHRs are all 0.97. Design cooling load of the sample
building is decreased maximum 33% due to thermal insulation. In-
crease of the thickness of the insulation material does not reduce
significantly cooling load of the building. Design cooling load of
Building A, which has the best insulation, is only 2% and 5% less
than that of Building B and Building C, respectively. Hourly distri-
butions of parts of the design-cooling load for building without
insulation are presented in Fig. 4. As it can be seen in Fig. 4, the
cooling load due to opaque external components (external wall,
roof, and floor) surface areas of the building without insulation is
about 40% of the maximumtotal cooling load. For this reason, ther-
mal insulation was applied to the building’s opaque surfaces for
reducing of heat gain in buildings through the envelope. Moreover,
space-cooling load can be reduced because of the low solar heat
gains, when fenestration surface area (openings) is decreased. Sim-
ilarly, cooling load is influenced by thermal mass of opaque ele-
ments [1,2,7]. In this study, the ratio of the building’s openings
to the opaque areas is 0.45. Constructionmaterials of sample build-
ing were the same for all calculations.
Variation of the ratio of cooling load due to insulation applied
opaque external components to the total cooling load of the build-ing during occupation period is shown in Fig. 5. The ratio obtained
for the no insulation building is also shown in the figure. As can be
seen from the figure, the opaque external components of the no
insulation building constitute approximately 50% of the total load,
while this percentage is between 2% and 20% for the insulated
buildings (Buildings A, B and C).
Using the design conditions given above (design-cooling load,
sensible heat ratio, minimum fresh air ventilation requirement
and supply air temperature), the maximum (design) cooling coil
capacity and the maximum(design) total mass flow rates of supply
and return fans were determined with an iterative approach (Table
6). Therefore, a computer programwas written for the calculations.
Capacities of the supply and return fans for CAV and VAV systems
are the same.
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