Air Handlers Final
Air Handlers Final
Air Handlers Final
(September 2019)
Juan Sebastian Gonzalez, Paula Daniela Gonzalez, Heber Andres Marin Duran, David Santiago
Alvarado Monroy
I. AIR HANDLER
Definition:
The purpose of air conditioning is to control the temperature, humidity, filtration, and air movement of
the indoor environment. The atmospheric air always contains moisture in the form of water vapor, but
the maximum amount of water vapor that may be contained in the air depends on its temperature and so
the higher the temperature, the more water vapor that can be contained in it.
In air conditioning, the humidification of air to increase the moisture content is achieved by the use of
a humidifier, and in reverse, the moisture content of the air is reduced by a dehumidification process.
[ CITATION Nar17 \l 3082 ]
Components:
Filters
Its main function is to provide a clean dust-free air to the system. The Filtration is generally located in
the first air entrance in order to protect and keep all the intern components clean
Heating and cooling elements
These elements are the responsible to change the air temperature and therefore the humidity level. It can be used
heat exchangers.
Humidifier
Humidifiers are used to maintain a specific humidity level. The humidity is essential in the AHU
because it ensures the high air quality, prevents the static electricity and preserve material properties.
Mixing Chamber
It is used to get the desired air temperature mixing the right amount of cool outside air and warm inside return
air. A mixing chamber is therefore used which has dampers controlling the ratio between the return, outside, and
exhaust air.
Blower
The blower moves the air around the air handler, and it can change the air flow rates depending of its operation
speed.
Heat Recovery Device
The main function is to recovery the residual energy resultant after the gas exhaustion, take that gases and use
them to pre-heat the fresh air before it enters to the room.
Vibration Isolators
These are the responsible to not transmit the vibrations generated by the blowers inside the air handlers. The
isolators are placed before and after de AHU and between the fan compartment.
II. FUNCTIONING
An Air Handling Unit (AHU) is used to re-condition and circulate air as part of a heating, ventilating and air-
conditioning system.
The basic function of the AHU is taking in outside air, re-condition it and supply it as fresh air to a building. All
exhaust air is removed, which creates an acceptable indoor air quality. Depending on the required temperature of
the re-conditioned air, the fresh air is either heated by a recovery unit or heating coil or cooled by a cooling coil.
In buildings, where the hygienic requirements for air quality are lower, some of the air from the rooms can be re-
circulated via a mixing chamber and this can result in significant energy savings. A mixing chamber has
dampers for controlling the ratio between the return, outside and exhaust air.
The AHU is a large metal box containing separate ventilators for supply and exhaust, heating coil, cooling coil,
heating/cooling recovery system, air filter racks or chambers, sound attenuators, mixing chamber, and dampers.
AHUs connect to ductwork that distributes the conditioned air through the building and returns it to the AHU.
A heat/cooling recovery exchanger is normally fitted to the AHU for energy savings and increasing capacity.
An AHU designed for outdoor use, typically on roofs, is also known as a rooftop unit (RTU). [ CITATION Gru \l
9226 ]
AIR COOLED SYSTEMS: Air cooled computer room air conditioners are widely used in IT environments of
all sizes and have established themselves as the “staple” for small and medium rooms. This type of system is
often referred to as a DX system or split system. The “DX” designation stands for direct expansion and although
this term often refers to an air-cooled system, in fact any system that uses refrigerant and an evaporator coil can
be called a DX system. In an air-cooled system half the components of the refrigeration cycle are in the
computer room air conditioner (also known as a CRAC unit) and the rest are outdoors in the air cooled
condenser as shown in Figure 1. Refrigerant circulates between the indoor and outdoor components in pipes
called refrigerant lines. Heat from the IT environment is “pumped” to the outdoor environment using this
circulating flow of refrigerant. [ CITATION The \l 9226 ]
AIR COOLED SELF-CONTAINED SYSTEMS: Self-contained systems locate all the components of the
refrigeration cycle in one enclosure that is usually found in the IT environment. Heat exits the self-contained
system as a stream of hot (about 120°F [49°C]) air called exhaust air. This stream of hot air must be routed away
from the IT room to the outdoors or into an unconditioned space to ensure proper cooling of computer
equipment as illustrated in Figure 2. If mounted above a drop ceiling and not using condenser air inlet or outlet
ducts, the hot exhaust air from the condensing coil can be rejected directly into the drop ceiling area. [ CITATION
The \l 9226 ]
GLYCOL COOLED SYSTEMS: This type of system locates all refrigeration cycle components in one
enclosure (like a self-contained system) but replaces the bulky condensing coil with a much smaller heat
exchanger shown in Figure 3. The heat exchanger uses flowing glycol (a mixture of water and ethylene glycol,
similar to automobile anti-freeze) to collect heat from the refrigerant and transport it away from the IT
environment. Heat exchangers and glycol pipes are always smaller than condensing coils (2-piece air cooled
systems) and condenser air ducts (selfcontained air cooled systems) because the glycol mixture has the capability
to collect and transport much more heat than air does. The glycol flows via pipes to an outdoor-mounted device
called a fluid cooler.[ CITATION The \l 9226 ]
WATER COOLED SYSTEMS: Water cooled systems are like glycol cooled systems in that all refrigeration
cycle components are located inside the computer room air conditioner. However, there are two important
differences between a glycol cooled system and a water-cooled system:
• A water (also called condenser water) loop is used instead of glycol to collect and transport heat away from the
IT environment
• Heat is rejected to the outside atmosphere via a cooling tower instead of a fluid cooler.
As seen in Figure 4, a cooling tower rejects heat from the IT room to the outdoor environment by spraying
warm condenser water onto sponge-like material (called fill) at the top of the tower. [CITATION The \l 9226 ]
IV. APPLICATIONS IN THE INDUSTRY
In Thermal loads calculation there are some generalities that cannot be avoided like:
Variety of materials each one with its thermophysical properties.
Complexity of geometries.
Heat Storage in the building components makes the heat transference more transient than stationary.
Relations between thermal phenomena.
Heat gain by conduction and radiation solar through doors and windows.
In the calculation of heat gain through doors and windows it becomes necessary to select the type of construction, the
number of arrangements, description of the window or door, description of the type of silo glass there is, guidance,
determine if it is with shadow or without shadow and calculate the area of the door or window. The equation used in the
calculation is as follows:[ CITATION AGU06 \l 9226 ]
VI. BIBLIOGRAPHY
[3] T. Evans, «The Different Types of Air Conditioning Equipment for IT enviroments,» APC, 2004.