This technical report discusses the mechanical design aspects of HVAC systems, focusing on various components such as cooling systems, chillers, and air handling units, particularly in the context of Bahrain Airport's Central Utility Complex. It compares air-cooled and water-cooled chiller systems, highlighting the advantages of air-cooled systems in terms of initial and operating costs, as well as space requirements. The report serves as a reference for the author while completing their graduate training program at ETEC in Beirut, Lebanon.

1. TAHLEEQ: GRADUATE TRAINING PROGRAM
TECHNICAL REPORT 1
“HVAC SYSTEMS”
WORK PLACEMENT 1
PLACEMENT DEPARTMENT (OR CONTRACTOR): ETEC (MECHANICAL)
PLACEMENT CITY/LOCATION: BEIRUT, LEBANON
PREPARED BY: HUSAIN ALAWI S SHUBBER BAQER
7th
NOV 2014

2. PAGE 2 OF 11
Table of Contents
1. Summary...................................................................................................................................................................................................3
2. Scope of Work .......................................................................................................................................................................................... 3
3. HVAC Systems.......................................................................................................................................................................................... 3
3.1 Cooling System .................................................................................................................................................................................. 4
3.1.1 Chiller.......................................................................................................................................................................................... 4
3.1.2 Cooling Tower............................................................................................................................................................................. 4
3.1.2.1 Cooling Tower Construction................................................................................................................................................ 5
3.1.2.2 Cooling Tower Process....................................................................................................................................................... 5
3.1.3 Condenser Pump........................................................................................................................................................................6
3.1.3.1 Traditional Water Pumping System.....................................................................................................................................6
3.1.4 Primary Pump............................................................................................................................................................................ 7
3.1.5 Secondary Pump........................................................................................................................................................................9
3.1.5.1 Traditional Secondary Pumping System ............................................................................................................................. 9
3.2 Air Handling Unit (AHU) For Clean Room System.............................................................................................................................10
3.2.1 Filters........................................................................................................................................................................................10
3.2.2 Air Intake Fan...........................................................................................................................................................................10
3.2.3 Cooling and Heating Coil...........................................................................................................................................................10
3.3.4 Exhaust Fan............................................................................................................................................................................... 11

3. PAGE 3 OF 11
1. Summary
The purpose of this technical report is to discuss some of the technical aspects involved in the
mechanical design of the HVAC systems. Figures are illustrated in order show the key aspects in each
HVAC system and how it works in conjunction with other related systems. This report was prepared for
my own reference and as part of my learning process during the work placement.
2. Scope of Work
All the technical aspects discussed will be limited to the design, application, methods for operating and
control, and services of HVAC systems in the Central Utility Complex (CUC). The HVAC systems at
Bahrain Airport are limited to Cooling and Air Handling Unit (AHU).
3. HVAC Systems
Is the technology of indoor and vehicular environmental comfort. The main goal of this system is to
provide thermal comfort and acceptable air quality. However, there three main sections involved in this
system, one is the cooling system, two is the heating system (which is not required for The Passenger
Terminal Building PTB at Bahrain Airport), and three is the air handling unit (AHU). All the three systems
are illustrated in the figure below (See Figure 1) showing how they are connected in conjunction with
each other.
Figure 1: Shows the three sections of HVAC system and how they are connected together
Air Handling Unit (AHU)
Heating System
Cooling System

4. PAGE 4 OF 11
3.1 Cooling System
The cooling system uses the temperature of the environment that the HVAC is controlling. There are five
main parts in this system that are:
1. Chiller
2. Cooling Tower
3. Condenser Pump
4. Primary Pump
5. Secondary Pump
3.1.1 Chiller
As far as Bahrain Airport’s PTB is concerned, it has been decided to use the Air-Cooled Chiller System.
ETEC has provided as study comparing two main chiller systems (Water-Cooled Chiller & Air-Cooled
Chiller Systems). Conventional thinking promotes water-cooled chillers as a better choice in terms of
efficiency. Looking only at the compressor costs, this may be true. However, using state-of-the-art
technology with centrifugal compressor and variable control, air-cooled chillers are often the better
choice.
It’s important to look at the total operating costs involved, not only the compressor cost. In water-
cooled chiller system, cooling tower’s operating cost should be added to the total operating cost of the
water cooled chiller system. Cooling tower cost include the tower fan, water and sewer costs, chemical
costs (as the water should be chemically treated), and pumping cost.
Listed below, are the three main points concluded from the comparison study that was performed by
ETEC:
 Initial cost: air cooled system (B.D. 3,310,000.00) less than water cooled
(B.D. 4,405,000.00).
 Total yearly operating cost: air cooled system (B.D. 734,815.00) less than water cooled (B.D.
823,610.00).
 Space Allocation: air cooled system (3012 m2
) less than water cooled (4834 m2
).
Hence, ETEC has recommended using Air-Cooled Chillers for the production of chilled water.
(Note: This information is taken from the Comparison Report which has been performed by ETEC)
3.1.2 Cooling Tower
Cooling towers are used to cool warm condenser water in Water Cooled Chiller System (The use of
cooling tower for the chiller system recommended for PTB is not applicable, as Air Cooled Chiller will be
used). The warm water absorbs heat from the chiller’s condenser section and releases it into the
atmosphere in the cooling tower. The tower fans provide moving air to cool the warm water primarily

5. PAGE 5 OF 11
be evaporation (i.e. evaporative cooling). The concept of this process is to return a constant condenser
water temperature to the chiller.
3.1.2.1 Cooling Tower Construction
The three cell cooling tower shown in figure 2 has axial fans mounted on the top of the tower. These
fans draw cooling air through the sides of the tower and exhaust through the top of the tower.
The shafts of the motors are horizontal while the fan shafts are vertical – See Figure 2 below. A right
angle gearbox is mounted at the base of each fan and along drive shaft connects the drive motor to the
gearbox.
Figure 2: Shows the construction of the cooling tower
3.1.2.2 Cooling Tower Process
Now after explaining the construction of the cooling tower, let’s have look at how the cooling process
works. The warm water is sent through a water inlet pipe to the cooling tower. After that, it’s
distributed across the top of the cooling tower and gravity causes the water to cascade down the sides
across fill material – See Figure 3.
The fill material causes the water drops to break into smaller water droplets, which results in creating a
larger area for heat transfer. The cooling tower draws air across the water droplets, cooling by an
exchange of latent heat resulting from evaporation of a small amount of water. After passing through
the cooling tower, the water collects in the tower basin and is pumped back to the chiller condenser
section by the condenser water pump – See Figure 3. It should be noted that in cold weather operation,
the cooling tower will have a heater in the tower basin to keep the water from freezing.
Cooling tower fans need to be controlled because cooling towers are designed for maximum load
conditions. However, in most of the applications, maximum load occurs for only less than 10% of the

6. PAGE 6 OF 11
time. Therefore, if controlling flow becomes important, the speed of the motor driving the cooling tower
fan can be controlled.
Controlling the motor:
 Saves energy
 Reduces wear and tear
 Reduces audible noise
 Reduces water use
Figure 3: Shows the process used to cool warm condenser water “Evaporative Cooling” in cooling tower
3.1.3 Condenser Pump
Condenser water pumps are primarily used to circulate water through the condenser section of the
water cooled chillers and their associated cooling tower. The condenser water absorbs the heat from
the chillers condenser section and releases it into the atmosphere in the cooling tower by evaporation.
The cooled water collects in the tower basin where it is then pumped back to the chiller condenser.
3.1.3.1 Traditional Water Pumping System
Traditionally, a condenser water pump continuously circulates the water at full flow. The temperature if
the condenser water is determined by the cooling tower fans operation:
The lower the condenser water temperature the lower the energy consumption by the chiller .
WATER INLET PIPEWATER INLET PIPE

7. PAGE 7 OF 11
However, the decrease in energy consumption is small and reducing the speed of the cooling tower fans
can save more energy. The condenser water pump continuously circulates the cooling tower water at a
constant flow. The chiller manufacturer recommends the flow through the condenser section for best
heat rejection. Often the condenser pump is oversized for a safety margin and requires field balancing
with a balancing valve to increase the system resistance and to prevent too high flow rate, as excess
flow can erode the chiller tubes which results in increasing maintenance.
3.1.4 Primary Pump
Boilers and chillers (only boilers will be used for Bahrain Airport HVAC system) are constant flow devices
in which constant flow of water is necessary for efficient and safe operation. In order to provide
constant flow, HVAC systems are designed with two independent water loops that are:
1) Primary Loop
2) Secondary Loop
Primary Loop primary loop provides constant flow through the boiler or chiller, and the Secondary Loop
provides variable water flow throughout the buildings to air handling units or other devices with heating
or cooling coil.
Primary pumps in primary/secondary systems have the task of supplying a constant flow of water
through the boiler or chiller. These devices have an ideal flow rate (flow rates that are too high or too
low can reduce the system efficiency and possibly damage the equipment). A common pipe connects
the primary loop with the secondary loop to “decouple” the loops, because it hydraulically separates the
primary from secondary loops as seen in the Figure below. In general, the connection is kept as short as
possible to minimize the pressure drop.
Figure 4: Shows the arrangement of the primary and secondary pumps with the heating and cooling systems
See Figure 4 below

8. PAGE 8 OF 11
Primary pumps can be a part of primary only or primary/secondary system. In primary only system, the
pumps typically provide a constant design flow through the chiller, set by a balancing valve during
balancing or commissioning. Moreover, three-way valves are often used on cooling or heating coils of
the air handling unit (AHU) to maintain this constant flow through the primary circuit – See Figure 5
below.
Figure 5: Shows the configuration of the three-way valves within the heating and cooling coils
Primary or secondary chilled water systems are generally used in commercial buildings to improve the
efficiency in large central chilled water systems. The primary or secondary pumping system separates
the primary production loop from the secondary distribution loop, which as a result allows the pump in
chillers primary production loop to maintain constant design flow, while the secondary distribution
pumps provide a variable flow as the two-way valves on the chilled water coil varies based on cooling
load demand. Moreover, the primary pump needs to be balances to produce the correct flow. Further to
add, the balancing valve on the
pump discharge is adjusted to
provide correct flow by adding
restriction (pressure drop) to the
circuit
Figure 5: Show the arrangement of
the balancing valve within the
chillers and boilers in the heating
and cooling system

9. PAGE 9 OF 11
3.1.5 Secondary Pump
In secondary pumping application the pump draws a variable flow from the primary loop. The flow
through the secondary pump can be less than, equal or greater than the flow in the primary loop. When
the secondary flow is greater than the primary flow some of the returned water in the secondary loop is
pumped back through the decouple pipe without going through the chiller.
3.1.5.1 Traditional Secondary Pumping System
Primary pumps are sized to manage flow requirement and drop in pressure in the production loop only
whereas the larger secondary pumps are sized to circulate the water throughout the system. Decoupled
from the primary pumps,
secondary pumps no longer have
flow constrains and as a result the
system can utilize two way valves
in the cooling or heating coils, and
other energy saving methods
without any problems for the
boiler or chiller.
In a traditional system with two-
way valves as the valves close
when the building loads are
satisfied, the discharge pressure
increases. As the pressure
increases the system resistance
increases and the system curve
rides up the pump curve to a
newer operating point at higher pressure and a lower flow – See Figure 7. Riding the pump curve results
in a slight reduction in pump energy as it
can be seen by comparing the two areas
in Figure 7. As more two-ways valves
close, the discharge pressure continues to
increase. At some point, the system
pressure may be so great that it forces
the two-ways valves to remain open,
even though flow may be further
reduced. As a result, a loss of
temperature control in the building
occurs hence waste of energy.
Figure 6: Shows the two-way valve arrangement with in the cooling and
heating coil
Figure 7: Shows graphically the increase in pressure as the
resistance increases (resistance of flow due to closing of valve)

10. PAGE 10 OF 11
3.2 Air Handling Unit (AHU) For Clean Room System
The air handling unit (AHU) controls the temperature and the relative humidity in the room. Depending
upon the design requirements, some AHU’s provide 100% fresh outside air while other use recirculation
method.
3.2.1 Filters
Constant air volume is usually supplied and high efficiency filters are added to provide proper room
cleanliness. Two types of efficiency filters may be provided:
1) High-efficiency particulate air (HEPA), which filters with efficiency in excess of 99.97% of 3 micro
particles – See Figure 8a.
2) Ultra low penetration air (ULPA), which filters with a minimum efficiency of 99.999% for 0.12
micro particles – See Figure 8b.
Figure 8: Shows the types of efficiency filter (HEPA & ULPA)
3.2.2 Air Intake Fan
Conventional systems have constant speed fresh air fan, this fan simply pulls the fresh outside air into
the system and through a pre-filter to eliminate much of normal debris and dirt or dust found in the
outside air. In the traditional fresh air intake system the speed remains constant in spite of an increase
or decrease in pressure. As the filter becomes dirty the pressure drop across it increases.
3.2.3 Cooling and Heating Coil
Air handling unit may require providing heating or cooling, or both of them to change the temperature
of air supplied by the intake fan. Temperature is not the only parameter that needs to be controlled in
order to provide a suitable thermal environment. The level of humidity is another important parameter
that affects the people’s definition of suitable thermal environment. Such conditioning (i.e. cooling and
heating) is provided by the installation of heat exchanger coil (s) within the air handling unit’s air stream.
Moreover, these coils may direct or indirect to the medium providing the heating or cooling effect.
Coils are typically manufactured from copper for the tubes, and copper or aluminum for the fin in order
to air heat transfer. In the case of cooling coil, eliminator plates are usually installed to remove and drain
a) b)

11. PAGE 11 OF 11
condensate. The hot water or steam is provided by a central boiler, and chilled water is provided by a
central chiller – See Figure 1. Typically, downstream temperature sensors are used to monitor and
control “on/off coil” temperatures, in conjunction with a motorized control valve that is installed prior
to the coil.
If dehumidification is required, then the cooling coil is commanded to over-cool so that the dew point is
reached and condensation occurs. In order to reheat the air to the desired supply temperature, a heater
coil is placed after the cooling coil. This has the effect of reducing the relative humidity level of the
supplied air.
3.3.4 Exhaust Fan
Exhaust fan is used to exhaust air from the clean room to the outside, as this is done for a specific air
change requirements or for a minimum fresh air requirements. Normal flow modulation technique are
used on this fan such as Inlet Guide Vane (IGV) or Discharge Damper Control – See Figure 9a&9b, as the
air is exhausted from the facility and does not have an impact on maintaining the correct class rating of
the clean room.
Figure 9: Shows a) Inlet Guidance Vane flow modulation positions b) Discharge Damper flow modulation positions
a) b)