الفهرس 
HIGHLY COOLED AIR SYSTEMOnly 14 pages are availabe for public view
 |  | from | 114 |  |  |
| | | from | 114 | | |
Abstract
This chapter introduce a conclusion of the present research and the main
conclusions that can be useful for other future studies will also presented in this
field. Highly cooled air system confirmed its performance versus the customary
conventional air system on the side of uniform temperature distribution attaining
in some different tested cases with different supply air angles and also with the
ceiling shape change.
That is with the advantages of using the highly cooled air system, which was
explained before such as lower airflow rates are required for attaining the human
comfort inside the conditioned space and what arranged on this advantage like
energy saving, small duct sizing and other more economical installation and
running requirements. Computational Fluid Dynamics (CFD) technique and the
governing equations of Naiver Stokes were mentioned including the sequence of
the numerical solution with selecting the proper turbulence model. Case validation
was introduced as an adiabatic similar case with forced convection flow supplied
to the room. Results from numerical simulations were compared to the
experimental results given by the referenced literature and a good correspondence
was observed. Based on case validation, CFD numerical technique was used to
evaluate the human comfort in different cases.
The cold air supplied to for spaces with different supply/return arrangements at
different four supply air angles. A mixed convection was occurring inside the space
between the cold air and the room air caused a large eddy in the middle of the room,
and other small eddied at the corners.
A simplified flow pattern is deduced from the flow field describing the flow as a
main stream travelling from the inlet to the next adhered to walls along the bath,
thus collecting load directly from these walls. This main stream induces an eddy
that collects the load from the rest of the boundaries and transfers this load to the
pg. 86
main stream. When this main stream passes directly through the occupied zone, the
large velocity disturbs comfort. The larger the portion of load carried directly by
the main stream, the lesser the energy use. When the inlet and the exit are on the
same wall, the main stream might follow a short cut beyond certain supply angles.
Curving the ceiling is seen to retard the onset of the short cut.
Air temperature and velocity distribution were tested for each case and at each
supply air angle to evaluate the performance of the highly cooled air system and
how the effectiveness of the supply and return air places changing on comfort
inside the space.
The results of the conventional air system are displayed side by side to the cold air
system for all cases. the cold air system was more comfortable than the
conventional air system in the majority of cases and always requires lower flow
rate.
5.2. Conclusions
Upon the numerical results obtained from simulating the highly cooled air system
in the different introduced cases, the following conclusions can be considered:
While the conventional air conditioning system offered an acceptable
performance, the highly cooled air system also introduces a successful
environmental conditions.
By air temperature and velocity distribution analysis in the four cases, there
is much similarity of attaining comfort with using the highly cooled air
system as the conventional air system even in the cases, where the
occupied zone had fallen out the comfort, the main reason was not the
lower supply airflow rate or the lower supply air temperature. The proof of
that was repeat this with the conventional air system.
Comfort achieving inside the space is related to some factors like the air
movement not only the temperature inside the room.
Many factors influence on achieving comfort in the space other than the
supply airflow rate and even the supply air temperature such the supply air
angle and also the place of air inlet and outlet.
pg. 87
Temperature and velocity distribution in the space were accepted and no
cold spots were formed because of the good mixing of the air in the entire
space.
Air circulation inside the room enhanced the performance of highly cooled
air system.
Supply air at low side position is relatively energy saving in comparison
with the high side location to achieve the desired temperature and velocity
in the breathing zone, where the area near the floor is usually represented
the large share of the total heat load of the space. This arrangement allow
an earlier mixing with room air removing the load at θ = 0º and 22.5º.
Highly cooled air system affirms its efficiency even with the room ceiling
shape change in the case of vault ceiling.
When the supply and the return are located on the same wall, the main flow
is seen to make a shortcut at high supply angles, and so deteriorating
comfort and increasing the required flow rate. The angle where the flow
pattern switches to make the shortcut is retarded by the ceiling curvature.
5.3. Recommendations for later work
Consider different air outlets as square and round ceiling diffuser with the
swirl effect and check for the ability of attaining comfort with each type.
Study the highly cooled air system in other more room geometries.
Study the performance of highly cooled air system with air supplied to the
space by forced convection with different Reynold’s number values
Check and held a comparison for other different turbulence models with
CFD numerical technique.
Study the performance of the highly cooled air system with the effect of air
humidity changing.
Study the performance of the highly cooled air system and the conventional
system at other different supply air angles and make a comparison between
the results.
Use the CFD technique to get the inlet air angle between 22.5° and 45° at
pg. 88
which the mixing flow changes its direction.
Use the CFD technique for the work of an experimental study focusing on
the effect of solar radiation on the walls and windows and how it influences
the air flow and the temperature distribution