Chiller Systems

The chiller industry encompasses both commercial and industrial applications, often in large structures like office buildings, hospitals, universities, and factories. Though chillers in these settings are more extensive than residential systems, they share similar fundamental components. Chiller technicians are HVAC and refrigeration specialists skilled in operating and maintaining these complex systems in larger commercial environments.

A chiller is an essential system component designed to produce chilled water to cool various spaces or processes. Chillers are categorized into two main types based on operating pressure: high-pressure and low-pressure systems. High-pressure systems use compressors operating above atmospheric pressure, while low-pressure systems use centrifugal compressors, which operate in a vacuum or below atmospheric pressure.

Types of Chiller Systems

1. Water-Cooled Chillers: These are the most common and efficient chiller systems, utilizing a water-pool condenser connected to a cooling tower. They maintain stable refrigerant pressure, promoting lower energy consumption year-round. In these systems, the chilled water circulates from the evaporator to the air handling unit (AHU) for cooling and returns to the chiller for reconditioning.

2. Air-Cooled Chillers: These chillers use an outdoor condenser that condenses the hot refrigerant gas back into a liquid. They are smaller and less common in commercial settings but are frequently used in heat recovery systems, especially in locations without access to adequate water supplies.

3. Heat Recovery Units: These systems utilize both evaporators and condensers to reclaim and repurpose heat energy within the building. They are flexible, as they can be either water- or air-cooled, depending on system requirements.

Refrigerants in Chiller Systems

Chiller systems employ two types of refrigerants:

• Primary refrigerants undergo phase changes from liquid to gas and back, facilitating heat exchange.
• Secondary refrigerants are chemically treated water solutions that remain in a liquid state, aiding in transferring heat without changing states, albeit being non-potable.

Chiller Components and Metering Devices

1. Evaporator: The chiller's evaporator barrel circulates water through tubes surrounded by low-pressure refrigerant. Heat is absorbed from the water, and multiple passes through the evaporator increase system efficiency. The number of passes can often be determined by the configuration of the pipes on the barrel.

2. Condenser: Similar to other water-cooled systems but larger, the condenser unit cools the refrigerant after it absorbs heat. Condensers typically have a separate water circuit that sends heat to the cooling tower.

3. Metering Devices: The electronic expansion valve is the primary metering device in chiller systems, controlling refrigerant flow with both temperature and pressure sensors for optimal evaporator efficiency.

4. Compressors: Compressors in chillers include scroll, screw, and centrifugal compressors, with newer systems avoiding reciprocating compressors. Centrifugal and magnetic levitation compressors are specialized for chillers, offering enhanced efficiency.

Pumps in Chiller Systems

Chillers require specialized pumps not found in residential systems:

1. Evaporator Loop Pump: This pump circulates chilled water from the evaporator to the AHU, where it absorbs heat and then returns to the chiller.

2. Condenser Loop Pump: This pump helps remove heat from the chiller and directs it to the cooling tower or dissipates it within the building as needed.

3. Heat Rejection System Pumps: These pumps support a secondary refrigerant or water loop, connecting the cooling tower and chiller condenser to discharge excess heat from the system.

Heat Rejection Systems

The primary function of heat rejection systems is to release the condenser’s absorbed heat into the atmosphere. Chiller systems use three main heat rejection methods:

1. Cooling Towers: An open system, cooling towers allow water to flow through the condenser, evaporating to remove heat. Though effective, they are gradually being phased out due to the high maintenance required and the potential for dirt buildup.

2. Fluid Coolers (Closed-Circuit Towers): These closed systems use an internal coil for water circulation, preventing the condenser water from contacting the external spray water. They rely on fans for evaporative cooling and heat transfer.

3. Dry Coolers (Direct Exchange): In this closed system, heat energy directly transfers from the condenser to ambient air. With no spray pumps, dry coolers use a pressure-operated valve for temperature regulation, making them simpler and more maintenance-friendly.

Air Handling Units (AHUs)

Air Handling Units are vital components of chiller systems, especially in large buildings. They filter incoming air through smaller filters arranged in rows before passing it across a chilled water coil to absorb heat. This method is safer and more economical than refrigerant-based systems, making it ideal for hospitals and offices. AHUs also include freeze stats that protect the coils from freezing by halting operation when the incoming air temperature drops below 36°F.

These elements collectively form the core operations of a chiller system, showcasing the detailed functioning and efficiency required in commercial refrigeration and air conditioning applications.