HVAC Valve Functions

Valve Functions in HVAC Systems

• Play a critical role in regulating, controlling, and directing fluid flow (water, refrigerants, air).
• Valves help maintain desired operational parameters and system balance.

Flow Control

• Regulate the amount of fluid flowing through a system.
• Helps balance system performance across various zones.

Shut-Off (Isolation)

• Completely stop fluid flow when maintenance or repair is necessary.
• Isolates specific system parts without disrupting the entire HVAC operation.

Pressure Regulation

• Designed to maintain or reduce pressure within the system.
• Ensures safe and efficient operation.
• Pressure relief valves prevent overpressure situations.

Temperature Control

• Modulate the flow of heated or cooled fluid.
• Maintains desired temperatures for chilled or hot water systems.

Directional Control

• Ensure fluid flows in the desired direction.
• Check valves allow fluid flow in one direction.
• Prevents backflow to protect equipment.

Balancing

• Ensure even fluid distribution across the HVAC system.
• Optimizes energy efficiency and comfort, especially in multi-zone systems.

Mixing and Diverting

• Mixing valves combine fluids at different temperatures to achieve a desired temperature.
• Diverting valves direct flow to different circuits or zones.

Safety and Protection

• Safety valves, like pressure relief valves, prevent system damage by releasing excess pressure or fluid.
• Safety valves activate automatically when limits are exceeded.

Service and Access Valves

• Used for system pressure readings, service procedures, and component isolation.

Types of Flow Control Valves - Globe Valves

• Purpose: Precise flow regulation.
• Feature: Linear motion design.
• Feature: Good for throttling applications.
• Feature: High pressure drop because of the design.
• Application: Chilled or hot water systems with precise flow adjustment needs.

Types of Flow Control Valves - Ball Valves

• Purpose: On/off flow control.
• Feature: Quarter-turn operation.
• Feature: Low pressure drop when fully open.
• Feature: Not ideal for throttling.
• Application: Isolating sections of HVAC systems, including coils and heat exchangers.

Types of Flow Control Valves - Butterfly Valves

• Purpose: Flow control for larger pipes.
• Feature: Quarter-turn operation.
• Feature: Compact design.
• Feature: Suitable for throttling and shut-off.
• Feature: Minimal pressure drop.
• Application: Chilled water and water cooled systems.

Types of Flow Control Valves - Gate Valves

• Purpose: On/off flow control in a fully open/closed position.
• Feature: Not suitable for throttling.
• Feature: Linear motion operation.
• Feature: Minimal flow restriction when open.
• Application: Isolation of sections in larger systems.

Types of Flow Control Valves - Check Valves

• Purpose: Prevent backflow in the system.
• Feature: One-way flow.
• Feature: No manual control.
• Application: Pump discharge lines and refrigerant lines.

Types of Flow Control Valves - Three-Way Valves

• Purpose: Mix or divert flow between two circuits.
• Feature: Available in mixing or diverting configurations.
• Feature: Modulate to maintain the desired temperature or flow rate.
• Application: Cooling tower loops and chilled water systems.

Types of Flow Control Valves - Solenoid Valves

• Purpose: Automated on/off control using an electric signal.
• Feature: Quick actuation.
• Feature: Can integrate with Building Management Systems(BMS).
• Application: Refrigeration circuits, chilled water system, and reversing valves.

Types of Flow Control Valves - Flow Balancing Valves

• Purpose: Ensure even distribution of flow in multi-zone systems.
• Feature: Manually adjustable or automatic.
• Feature: It may include flow measurement capabilities.
• Application: Hydronic systems, fan coils, and terminal units.

Types of Water Regulating Valves

• Two main types: one controls system pressure, the other manages head pressure in water-cooled refrigeration.
• Water pressure regulating valves are used for two main purposes.
• Air-cooled systems have become more common because they are easier to maintain.

Reducing Supply Water Pressure in Hot Water Systems

• These valves reduce incoming water pressure to the desired pressure for hot water heating systems.
• They have an adjustment screw on top to tighten the spring and regulate pressure.
• Installed on the supply water makeup line.
• Many have a manual bypass for servicing without shutting down.
• Systems may include a manual feedline for filling the system directly, bypassing the valve.

Regulating Water Flow to Condensers in Water-Cooled Equipment

• These valves manage the flow of water to the condenser.
• Maintains steady head pressure.
• The valve senses refrigerant pressure on the high side.
• Adjusts water flow to maintain a preset head pressure.
• Located typically on the outlet of the condenser.

How Pressure Is Balanced

• The valve is controlled by refrigerant pressure on the high side and spring pressure inside.
• High refrigerant pressure opens the valve to allow more water through.
• If the head pressure drops too low, spring pressure closes the valve to reduce water flow.

Types of Safety Valves - Pressure Relief Valves (PRVs)

• Purpose: Prevent excessive pressure build-up in HVAC equipment.
• Used in boilers, compressors, and refrigeration systems.
• Operation: Opens automatically when internal pressure exceeds a set limit.
• Returns normal when pressure is restored.
• Application: Boiler systems to prevent pressure-related failures.
• Application: Chillers and refrigeration systems protect against overpressure by refrigerant expansion.

Types of Safety Valves - Vacuum Relief Valves

• Purpose: Prevent negative pressure (vacuum conditions) in systems.
• Prevents equipment damage or tank collapse.
• Operation: Opens to allow air or fluid into the system when vacuum is detected.
• Application: Chilled water systems and storage tanks.

Types of Safety Valves - Temperature and Pressure Relief Valves (T&P Valves)

• Protect against high temperature and high pressure in water heaters or storage tanks.
• Activates if water temperature exceeds 210°F.
• Activates if pressure surpasses 150 psi.

Types of Safety Valves - Fusible Plug Safety Valves

• Purpose: Provides thermal protection by melting at a specific temperature for pressure release.
• Operation: Contains a metal alloy plug that melts when surrounding temperature exceeds a preset value.
• Safety valve releases refrigerant or fluid.
• Application: Refrigeration systems and equipment with high-temperature risks.

Expansion Valves and Metering Devices

• It divides the system's high side from the low side via the compressor.
• Installed on the liquid line just before the evaporator.
• Expansion valves have a full column of liquid for them to operate correctly with measurable subcooling.

Type of Metering Devices - Thermostatic Expansion Valve (TXV or TEV)

• Function: Maintains a constant superheat, not pressure.
• The bulb that is filled refrigerants causes the evaporator to open more or less.
• Better control of liquid flow under varying load conditions.
• Apply commonly to refrigeration and air-conditioning units.

Type of Metering Devices - Capillary Tube

• Function: A fixed metering device that uses a long, narrow tube for pressure drop to regulate refridgerant.
• A tube's length and diameter determins how the water flows by the refridgerant properties.
• Simple, low cost and reliable for small systems.
• Limitation: Limited adaptability to load changes, so systems work best with stable conditions.
• Commonly used for refridgerators, freezers and small AC.

Type of Metering Devices - Automatic Expansion Valve (AXV)

• Function: The Evaporator maintains constant pressure, no matter the changes in load.
• The valve shuts off in response to high pressure.
• Simple, effective, steady load condition
• Limitation: Poor performance under varibale loads and does not respond to superheat change.
• Apications: Older refrigerations systems and small systems like ice cream machines.

Type of Metering Devices - Electronic Expansion Valve (EEV)

• Precisely controls refridgerant flow with electronic sensors or a stepper motor.
• Functions: Snesors track things like superheat, temp, and pressure, then the valve coil turns causing screws to let more or less liquid through.
• High efficiency, precise control and adaptability and load fulctuationa.
• Variable refridgerant flow systems, systems with interver tech, and advanced AC units.

Accessory Devices - Filter Driers

• Purpose: Remove moisture, dirt, and other contaminants from the refrigerant.
• Protect the system from damage.
• Liquid Line Filter Drier: Installed in the liquid line to protect metering devices.
• Suction Line Filter Drier: Installed in the suction line to protect the compressor.
• Application: Most refrigeration and air-conditioning systems.

Accessory Devices - Sight Glass (Moisture Indicator)

• Visual indication of refrigerant flow and moisture content.
• Color indicator changes based on moisture levels.
• Helps detect refrigerant undercharging or overcharging.
• Location: Installed in the liquid line before the metering device.

Accessory Devices - Accumulators

• Prevent liquid refrigerant from entering the compressor (liquid slugging or flood back).
• Orifice on the outlet meters refrigerant and oil back to the compressor.
• Low-temperature systems, heat pump systems, and wide-load systems.

Accessory Devices - Oil Seperators

• Prevent the oil, helps lubricates compresors, from circulating in the entrie system.
• Separates oil from the refrigerant using centrifugal force or mechanical baffles.
• The refrigerant-oil mix then enters the oil seperator.
• The oil is seperated from the refridgerant which exits through the seperator, then passes through the system.
• The collected oil goes back to the compressor to continues lubrication.

Accessory Devices - Liquid Recievers

• Liquid Receivers: Acts like a fridge for excessive liquid from the condenser which cools and turns the fridge back into a fluid.
• Helps mange fluids, store it until its needed. Enough fridge to keep a consistent cooling.
• Allows fridge to change: Large systems often need an adjusted fridge in the system based on seasonal differences.
• The reciever has enough space to add or remove fridge.
• How it works: Regrigerant enters as high pressur liquide, with spacing for some Vapor above the liquid.
• The coolant is directer to an expansion valve before entering an evaportater to absrob heat.

Valves and Accessory Common Failures Exercise

• What are the most common failures of various devices and how do they affect the system?
• Devices include filter driers, service/access valves, TXVs, EEVs, check valves, capillary tubes, and solenoid valves.