Welcome to our comprehensive overview of HVAC systems, where we explore the fundamental

components and design principles that form the backbone of climate control in various facilities.

Starting with the high-side equipment—the heart of HVAC systems—chillers operate using
mechanisms such as absorption, centrifugal, or reciprocating methods to play a crucial role in
heat absorption and rejection. These are paired with cooling towers to ensure optimal efficiency
by dissipating heat from the system. Cooling towers, categorized as natural draft, forced draft, or
induced draft, contribute significantly to this heat dissipation process. Understanding the
classifications of chillers and their interaction with cooling towers is essential for achieving
overall system efficiency.

On the low side, air handling units (AHUs) are responsible for air distribution and regulation.
Classified as single-zone, dual-zone, or multi-zone, AHUs ensure proper circulation and
conditioning of air within controlled environments. Fan coil units (FCUs) further refine
temperature control and offer flexibility in mounting configurations. AHUs act as the workhorses
of indoor air regulation, and understanding their key components—such as filters, coils,
humidifiers, fans, dampers, and controls—is vital for effective design and operation.

The chilled water pumping system plays a critical role in the circulation of chilled water through
chillers, pumps, piping, and terminal units. Different distribution schemes, such as constant
primary flow or primary variable flow, govern how water moves throughout the system. Key
concepts like static head, dynamic head, and Net Positive Suction Head (NPSH) are crucial
for ensuring the pumping system operates efficiently and reliably.

Efficient transport of fluids and air relies heavily on well-designed piping and ductwork. A
proper understanding of chilled water pipe sizing, duct sizing methods, and the selection of
fittings and accessories is necessary for optimal system performance. The choice of duct
construction materials, insulation methods, and support systems plays a key role in minimizing
energy loss and ensuring long-term durability. External static pressure and insulation principles
are especially important in maintaining the system's efficiency and effectiveness.

In conclusion, a comprehensive understanding of HVAC components and systems—from high-

side and low-side equipment to air handling units, pumping systems, and piping/duct design—is
imperative for professionals in the field. A holistic approach is essential for the successful
design, installation, and maintenance of efficient HVAC systems tailored to diverse
environmental needs. As technology evolves, staying current with industry standards and
innovations is critical.

1. What is HVAC?

HVAC stands for Heating, Ventilation, and Air Conditioning. It is a system used in buildings
to control the temperature, humidity, and air quality to ensure comfort and safety.

🔹 2. High-Side Equipment
These are the components of the HVAC system responsible for cooling and heat rejection.

✅ Chillers

A chiller is a machine that removes heat from a liquid (usually water), which is then used to cool
a building.

 Types of chillers:
o Absorption Chiller: Uses heat instead of electricity (more common where waste
heat is available).
o Centrifugal Chiller: Uses a rotating impeller to compress refrigerant (used in
large buildings).
o Reciprocating Chiller: Uses a piston-cylinder arrangement within a compressor
to compress refrigerant, facilitating the refrigeration cycle. It's a common type of
chiller, particularly for smaller to medium cooling loads, and is known for its
relatively simple design and lower initial cost compared to some other chiller
types

✅ Cooling Towers

A cooling tower is used to release the unwanted heat from the chiller into the atmosphere using
water and air.

 Types:
o Natural Draft: Uses natural airflow.
o Forced Draft: Uses fans to blow air through.
o Induced Draft: Uses fans to pull air through (most common type).

🔹 3. Low-Side Equipment

These components distribute and regulate air inside buildings.

✅ Air Handling Unit (AHU)

An AHU is a large metal box containing components that condition and circulate air.

 Types:
o Single-zone: Serves one large area.
o Dual-zone: Serves two areas independently.
o Multi-zone: Serves multiple areas with separate controls.

✅ Fan Coil Unit (FCU)

A FCU is a small device with a fan and coil that provides heating or cooling to a room.
  Mounting Types: Can be wall-mounted, ceiling-mounted, or floor-mounted depending
on room layout.

🔹 4. Chilled Water System

This system carries chilled water from the chiller to the building and back.

✅ Chilled Water Pumping System

Circulates cold water using pumps. It transfers chilled water to air handlers and fan coils.

 Distribution Schemes:
o Constant Primary Flow: Pump runs at a constant speed (old method).
o Primary Variable Flow: Pump adjusts speed to demand (energy efficient).

✅ Important Terms

 Static Head: The pressure needed to lift water to a certain height.

 Dynamic Head: Pressure needed to overcome friction in pipes.
 NPSH (Net Positive Suction Head): Ensures the pump doesn’t suck in air or vapor
(which causes damage).

🔹 5. Piping and Duct Systems

They transport water and air to different parts of the building.

✅ Pipe Sizing

The process of choosing the right pipe diameter for water flow. Too small = high pressure loss;
too big = unnecessary cost.

✅ Duct Sizing

Choosing the correct size for air ducts to ensure proper airflow and low noise.

✅ Duct Construction Materials

Usually made of galvanized steel or aluminum. Important to choose good materials for energy
efficiency.

✅ Insulation
Used to cover pipes and ducts to prevent heat gain or loss and reduce condensation.

🔹 6. External Static Pressure (ESP)

It’s the resistance to airflow in ducts and filters.

 Higher ESP = harder the fan has to work.

 Lower ESP = more efficient system.

🔹 7. Major AHU Components

 Filters – Clean the air by removing dust and particles.

 Coils – Heat or cool the air using water or refrigerant.
 Humidifiers – Add moisture to the air.
 Fans – Move air through the system.
 Dampers – Control airflow direction and volume.
 Controls – Thermostats, sensors, and actuators to automate operation.

🔹 8. Conclusion

To design, install, and maintain an efficient HVAC system, you need to understand both high-
side and low-side components. You must also learn how air and water move through the system,
how pressure and insulation affect efficiency, and how to size pipes and ducts correctly.

uses a piston-cylinder arrangement within a compressor to compress

refrigerant, facilitating the refrigeration cycle. It's a common type of chiller,
particularly for smaller to medium cooling loads, and is known for its relatively
simple design and lower initial cost compared to some other chiller types

📊 Comparison of R134a vs R22 vs R1234yf

Property R134a R22 R1234yf

HCFC
Chemical Type HFC (Hydrofluorocarbon) HFO (Hydrofluoroolefin)
(Hydrochlorofluorocarbon)
 Property R134a R22 R1234yf

Ozone Depletion
0 0.05 0
Potential (ODP)

Global Warming
1430 1810 <1
Potential (GWP)

Slightly flammable
Flammability Non-flammable Non-flammable
(mild)

Toxicity Non-toxic Non-toxic Non-toxic

Cars, refrigerators, New cars, eco-friendly

Used In Older HVAC systems, A/C units
chillers HVAC units

MO/AB (Mineral or
Refrigerant Oil POE (Polyester) POE
Alkylbenzene)

Still common but being Replacing R134a in new

Availability Being phased out globally
phased out systems

Pressure Range
Low to Medium Medium Similar to R134a
(Typical)

Environmental High concern (banned in many

Moderate concern Eco-friendly (preferred)
Status areas)

✅ Why is R134a Used?

R134a is a hydrofluorocarbon (HFC) refrigerant commonly used in automotive AC systems,

refrigerators, and some HVAC systems. It's preferred in many applications because of the
following reasons:

🔹 1. Non-Ozone Depleting

Unlike older refrigerants like R-12 or R-22, R134a does not contain chlorine, so it does not
damage the ozone layer.

🔹 2. Good Thermodynamic Properties

🔹 3. Safe to Use

 Non-flammable, Non-toxic

🔹 4. Widely Available and Cost-Effective

🔹 6. Used in Automotive AC Systems

R134a replaced R-12 in cars after the 1990s due to environmental regulations. It's still used in
many cars today (although newer vehicles now use R1234yf for lower global warming impact).

⚠️Limitations / Environmental Concerns

 Although it doesn’t deplete the ozone layer, R134a has a high Global Warming
Potential (GWP) (~1430 times more than CO₂).
 more environmentally friendly refrigerants are R1234yf, R290 (Propane), or CO₂
(R744).