HVAC Investigation

Heating Ventilation and Air Conditioning are the primary properties of thermal comfort. Commonly
known as HVAC in industry, it is the technology of indoor, vehicular and other enclosed spaces
environmental comfort. The overall purpose of a HVAC system is to provide thermal comfort and
acceptable indoor air quality to the space it is installed to.

HVAC is a key design consideration in medium to large industrial buildings, office buildings and
speciality buildings such as aquariums where safe and healthy building conditions must be
monitored and regulated specifically in relation to temperature and humidity. This is typically
achieved by injecting and manipulating fresh air from the outdoors. The way this air is injected and
manipulated varies based on the type of HVAC system in use which is determined based on the
building requirements. However ventilation is often considered the most important aspect of HVAC
technology.

Ventilation is the process of replacing air in any space with fresh air. This is done to achieve a higher
air quality (based on the buildings requirements) indoors than that of the air outside of the building.
This is to ensure temperature control, oxygen replenishment as well as the removal of unwanted air
characteristics such as; pollution, smoke, odours, dust, heat, airborne bacteria, etc. This constant
replacement of interior air also works to keep the internal air within the building circulating which in
turn prevents stagnation of the air which may cause health risks. The way in which the air is
circulated and ventilated fall into 2 primary methods; forced/ mechanical and natural. The method
used varies based on the building requirements and the surrounding environment.

Forced or mechanical ventilation is generally done by using an air handler. This is a unit which
regulates and circulates the air for the HVAC system. It is most commonly a large metal box on the
exterior of a building which contains a blower, filters, sounds dampeners and sometimes heating or
cooling elements to pre-treat the air for the HVAC system.

Figure 1, Air Handler[ CITATION SOS09 \l 3081 ]

Kitchens and washrooms generally have forced exhaust vents to control odour primarily but can also
help control humidity. Design considerations are typically flow rate, fan speed, fan size and
acceptable noise level. Desk fans as well as ceiling fans can also be considered in a HVAC system
despite not directly effecting temperature or humidity. This is due to their primary use being to
circulate air around the immediate vicinity which can lower the perceived temperature by increasing
the evaporation of perspiration from the occupants. Due to the properties of hot air, ceiling fans are
often used to circulate the hotter air back down to the occupants in winter.

Natural ventilation utilises environmental factors to adequately circulate the air within a building
without the use of fans or other mechanical systems. Generally this is done with strategic placement
of louvers, windows and when applicable, trickle vents. In larger buildings, the building layout is
designed so that hot air is permitted to rise and exit the building through high level openings which
in turn causes cool air to be drawn into the building through low level openings, this is referred to as
the "stack effect" [ CITATION ASH05 \l 3081 ]. This type of ventilation when done correctly uses very
little energy however specific care needs to be taken to ensure thermal comfort is consistent.
Generally it has been shown that in humid and warm climates, the use of only natural ventilation is
not sufficient. In these cases air conditioning systems are used as supplements or backups.

Figure 2, Trickle Vent [ CITATION Hel16 \l 3081 ]

An air conditioning system or standalone air conditioning unit supplies cooling and humidity control
within a HVAC system. This may be done a number of ways which will be investigated into greater
detail in the next section of this literature review. Air conditioned buildings generally have sealed
windows and openings as large open airways severely negatively affect the system as a whole.
Outside, fresh air is drawn into the air conditioning system by a dedicated vent to the heat
exchanger sector which creates a positive pressure. The percentage of fresh air that is introduced
into the building is primarily regulated by adjusting this vent and is commonly set to allow 10% fresh
air to enter the HVAC system [ CITATION ASH05 \l 3081 ].

Air conditioning and refrigeration techniques used to lower the air temperature rely on removing
heat from the entering fresh air. This is done through radiation, convection or conduction,
depending on the type of air conditioning system being used. The media used in refrigeration
systems such as air, water, ice and other chemicals are known as refrigerants. A refrigerant is utilised
in either a heat pump system where a compressor drives a thermodynamic refrigeration cycle, or in
a free cooling system which relies on pumps to circulate a cool refrigerant such as a glycol mix
[ CITATION Don95 \l 3081 ].

The refrigeration cycle consists of 4 stages which allows heat from the interior building air to transfer
through the refrigerant to the outside air. For this investigation it is said stage 1 will be at the
compressor. Here refrigerant in a gaseous state is compressed by the compressor to a high pressure
and temperature. Once in this state, the refrigerant is moved through a heat exchanger where
energy is transferred to the outside air in the form of heat. This causes the refrigerant to cool and
condense into a liquid state. To ensure proper flow rate, an expansion valve is used which also
lowers the pressure. Once the cooled liquid refrigerant is flowing at the correct rate, it enters
another heat exchanger where it is able to evaporate. This evaporation causes the refrigerant to
absorb heat energy from the internal air and then returns to the compressor to begin the cycle
again. The heat energy absorbed from the internal air lowers the air temperature resulting in being
able to regulate internal building temperature. This cycle can also be reversed to allow heating of
the internal air during cooler months of the year.

Figure 3, Heating Cycle Diagram[ CITATION Pet06 \l 3081 ]

Due to the underlying principles, free cooling systems can have very high efficiencies. These systems
are often used in conjunction with seasonal thermal energy storage systems so that the cool of
winter may be used for air conditioning in the summer. These thermal energy storage mediums are
often a natural underground rock mass which is accessed by the use of small bore heat exchangers,
or deep aquifers. When restrictions are in place which only allow in small storage solutions, a hybrid
is commonly implemented which use free cooling early in the cooling season but when efficiency
drops off, moves to a heat pump to cool the refrigerant. This is made possible by the storage being
used as a heat sink when the system is in cooling mode. This causes the temperature to gradually
increase throughout the cooling season.
Possible Alternative A

As this report is an investigation into the improvement of the HVAC system used within building 30
on the CQU Rockhampton campus, other forms of HVAC not currently in use will be analysed. This
analysis will consist of exploring the advantages and disadvantages along with common installations
to determine if the technology would be appropriate for this project.

Firstly, a look at a type of air conditioning unit that is not currently in use within building 30 on CQU
Rockhampton campus, a window air conditioner. This type of air conditioner is also known as a box
air conditioner and is installed either within a window space or a slot in the wall.

Advantages of the window air conditioner mainly stem from its small independent size. As the unit is
a heat pump which drives a full thermodynamic cycle, it relies little on exterior input or bulky
attachments. Since the unit is fully self contained and designer to cool a single room, the occupant of
the room can set the temperature to a level which is more comfortable personally for them. Due to
this, the unit can also be disabled when the occupant is vacant without negatively impacting
surrounding rooms. Based on these reasons, the popularity of window air conditioners has risen in
the early century, which has lead to an increase into research to improve their efficiencies while also
lowering the overall cost of the unit initially. With greater efficiencies and design, units emit less
noise and are now relatively quiet. As the hot air is immediately exhausted to the outside of the
building along with water from the cooling process, there is no need for extra exhaust vents or
drainage systems.

Figure 4, Window Air Conditioner [ CITATION Gee08 \l 3081 ]

The design of the window air conditioner itself presents disadvantages which generally cannot be
overcome. This may cause this type of HVAC system to not be compatible with the environment
where it will be installed. As it has been established, the window air conditioner is installed in either
a window or a wall slot. This requires either a slot be cut into an existing wall if this air conditioner
was not originally planned to be installed. Or if installed in a window, removes the option for that
window to be used to create natural ventilation. If the air conditioner is removed in the future, a
vacant gap will be left which will require repair, adding to the cost of the removal. Security is also a
factor as if the air conditioner was not initially installed correctly, it may provide an easy entry point
for unauthorised personnel. Further complications of an incorrect install is hot air seeping back into
the room from the outside due to improperly fitted enclosure, effecting the efficiency of the unit.
Generally in the modern fashion of today's buildings, window air conditioners are not seen as the
ultimate in decorating or class [ CITATION Geo12 \l 3081 ]. Drainage may also be an issue if not
properly managed, it may cause rust if falling on a metal roof or create a hazard if near a walkway.

Most commonly window air conditioners are used in private domiciles. Due to the advantages listed
earlier, window air conditions generally are used for private used where a cheap and efficient
cooling system is needed for a single room. In these cases, consistent cooling of a whole building are
not commonly a requirement.