VRF Systems Explained - Variable refrigerant flow basics HVAC

Introduction

In this video, we will learn how air conditioning units can provide both heating and cooling at the same time using the low boiling point of the refrigerant and some clever valves. We will also see how Variable Refrigerant Flow (VRF) units work.

Air Conditioning Units

• Air conditioning units can provide cooling by using the low boiling point of the refrigerant.

• Clever valves can be used to provide both heating and cooling at the same time.

VRF Units

• VRF stands for Variable Refrigerant Flow.

• A VRF unit can provide cooling, heating, or a mixture of both at the same time.

• VRF units are often used in offices, hotels, retail, education, and healthcare facilities because they have different heating and cooling demands within these types of buildings.

Basic Refrigeration System

In this section, we will learn about the four main parts of a basic refrigeration system - compressor, condenser, expansion valve, and evaporator - and how they are connected via a pipe with a special fluid called refrigerant flowing through it.

Four Main Parts

• The four main parts of a basic refrigeration system are compressor, condenser, expansion valve, and evaporator.

• The compressor squeezes the refrigerant into a small volume and pushes it around the entire system.

• The condenser and the evaporator are both heat exchangers that allow thermal energy to transfer between the air and the refrigerant without them coming into direct contact with each other.

• The expansion valve is either a thermostatic or electronic expansion valve.

Refrigeration System Process

• The refrigerant leaves the compressor as a high pressure, high temperature superheated vapor.

• The refrigerant passes through the tube of the condenser where it is cooled by removing heat from it and then flows to the expansion valve.

• As thermal energy is removed from the refrigerant, it will condense into a liquid similar to how steam condenses into a liquid on a window on a cold day.

• The refrigerant then flows through either a thermostatic or electronic expansion valve.

Conclusion

In this video, we learned about how air conditioning units can provide both heating and cooling at the same time using clever valves and VRF units. We also learned about the four main parts of a basic refrigeration system - compressor, condenser, expansion valve, and evaporator - and how they work together to cool or heat an area.

Key Takeaways

• Air conditioning units can provide both heating and cooling at the same time using clever valves.

• VRF units are often used in buildings with different heating and cooling demands.

• A basic refrigeration system has four main parts - compressor, condenser, expansion valve, and evaporator - that work together to cool or heat an area.

How VRF Units Work

This section explains how Variable Refrigerant Flow (VRF) units work and the advantages they offer.

VRF Unit Components

• VRF valves use a sensor and controller to measure superheat at the exit of the evaporator. The valve will then open or close to restrict the flow of refrigerant into the evaporator in order to try and maintain a constant superheat value.

• The refrigerant drops in pressure and temperature because it is expanding in volume, much like when you spray a pressurized liquid through a nozzle.

• The heat of the room is enough to boil the refrigerant, which turns into a gas that carries unwanted heat away.

• Under low load conditions, less refrigerant can pass through the expansion valve so pressure increases as refrigerant backs up in the system.

Unloading Methods

• One method known as unloading opens a solenoid valve to recirculate refrigerant back into the compressor until pressure decreases enough. This is very inefficient because it does not provide any cooling.

• Another method is to simply turn off the compressor when pressure is too high and then turn it on again when this drops. However, this causes surges in pressure resulting in poor thermal control.

Advantages of VRF Units

• A VRF unit uses an inverter to change the speed of the compressor so that the volume of refrigerant flowing around the system changes to match current cooling demand.

• The energy consumption of this system is far lower and we get optimal thermal control.

• We can connect multiple indoor units to a single external condenser. Each indoor unit has an expansion valve. The compressor changes its speed to suit the system requirements as these open and close.

Heating with VRF Units

This section explains how heating with VRF units works.

Heat Pump Operation

• Heating-only VRF systems are essentially just an air conditioning system running in reverse, absorbing heat from the outside air and transferring this indoors.

• As long as the air is above the boiling point temperature, it will cause the refrigerant to boil and so we can absorb thermal energy from the air.

• The refrigerant has an extremely low boiling point, which allows us to absorb thermal energy even when the air is cold.

Introduction to HVAC Systems

This section provides an introduction to HVAC systems and how they work.

Heating and Cooling in HVAC Systems

• Thermal energy is collected from the air and released into the room.

• A reversing valve is used to provide both heating and cooling.

• Hot gas discharged from the compressor is sent into the reversing valve.

• In cooling mode, hot refrigerant is sent straight to the outdoor unit where thermal energy is removed. In heating mode, hot gas is sent straight to indoor heat exchanger.

Multiple Units in Commercial Buildings

• Multiple units can provide heating or cooling at the same time.

• Each indoor unit is connected to a branch controller that contains valves for directing refrigerant flow.

Variable Speed Compressor

• A variable speed compressor located outside sends hot refrigerant around the building.

• In mixed mode, hot discharge of compressor is sent to both indoor and outdoor units.

Full Cooling Mode, Full Heating Mode, Mixed Mode

• In full cooling mode, all indoor units are collecting heat while all outdoor units are rejecting heat.

• In full heating mode, all outdoor units are collecting heat while all indoor units are rejecting heat.

• In mixed mode, thermal energy is transferred between units based on their requirements for heating or cooling.

Heating and Cooling Loads

In this section, the speaker discusses how to manage heating and cooling loads when they are not equal.

Managing Unequal Heating and Cooling Loads

• If the heating and cooling loads are not equal, we will need to run some outdoor units to collect more thermal energy.

• When there is only one indoor unit in cooling mode, it will not be able to collect sufficient thermal energy.

• Therefore, we need to provide other units with heating by running additional outdoor units.

Further Learning

In this section, the speaker recommends additional resources for learning about refrigeration engineering.

Additional Resources

• Check out these videos for further learning about refrigeration engineering.