What is a Metering Device – Refrigeration Components 4.67/5 (3)

What is a Metering Device – Refrigeration Components

What you will learn from What is a Metering Device:
1) We will answer the question, “What is a metering device” by defining the various types of HVAC equipment that use different types of metering devices and why.
2) How the metering device is involved in the refrigeration cycle
3) A comprehensive list of metering devices defining the metering devices commonly used in HVAC
4) Lots of resource and related links to help you learn more about metering devices.

What is a Metering Device - TXV- Thermostatic Expansion Valve
TXV Metering Device for a Heat Pump

Depending on the type of HVAC air conditioning or heat pump system it is and the efficiency range of the system will depend on the type of metering device the system has installed by the HVAC manufacturer of the air conditioner or heat pump system. Lower efficiency HVAC air conditioner and heat pump models have fixed orifice types while higher efficiency systems have thermostatic expansion valves installed in the HVAC air conditioner or heat pump system. The thermostatic expansion valve is far more complex than the fixed orifice metering device as the thermostatic expansion valve metering device modulates the refrigerant flow based on the temperature of the refrigerant temperature in the evaporator coil. This allows a specific amount of refrigerant, based on demand, to be metered into the evaporator coil while the fixed orifice metering device allows the same amount of refrigerant to enter the enter the coil no matter the conditions or the demand. As the liquid refrigerant enters the metering device it changes temperature and pressure. A partial amount of the liquid refrigerant flashes into a refrigerant gas or vapor as it leaves the metering device and enters the evaporator coil.

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Evaporator Coil for Heat Pumps & Air Conditioners | HVAC Refrigeration 5/5 (2)

Evaporator Coil for Heat Pumps & Air Conditioners

Old Evaporator Coil in a Rooftop Air ConditionerEvaporator Coil for Heat Pumps & Air Conditioners – the evaporator is responsible for absorbing heat into the coils and the refrigerant. The evaporator is an essential component of vapor compression refrigeration. This is usually done as result of passing air or water over the evaporator coil where a heat exchange process takes place. Heat leaves the air or water (whatever medium is used) and is absorbed into the coil and the liquid refrigerant. As more and more heat is absorbed by the evaporator coil and the refrigerant again changes state from a liquid to a refrigerant vapor. By the time the refrigerant leaves the evaporator coil the refrigerant should be all vapor and ready to be received again by the refrigeration compressor.

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The Condenser for Air Conditioners and Heat Pumps| HVAC Refrigeration 5/5 (2)

The Condenser for Air Conditioners and Heat Pumps - Trane Heat Pump Condenser
Trane Heat Pump Condenser

The Condenser for Air Conditioners and Heat Pumps

The condenser coil receives the high pressure high temperature refrigerant vapor from the compressor and immediately begins to remove heat from the refrigerant vapor. As the refrigerant vapor makes its way through the condenser coil more and more heat is removed and the refrigerant vapor changes state from a refrigerant vapor to a refrigerant liquid. While the liquid refrigerant changes temperatures from a higher temperature to a slightly lower temperature the pressure remains constant. As the refrigerant vapor leaves the condenser coil it makes it way to the metering device.

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The Compressor | HVAC Refrigeration 5/5 (1)

The Compressor | HVAC Refrigeration

The Compressor in an HVAC refrigeration system
Compressor in an HVAC refrigeration system

In a typical HVAC air conditioner or heat pump there are four major components that make the process of refrigeration work. Basically, this is how air conditioners work. And how heat pumps work. The first component in the process is a compressor or the heart of any air conditioner or heat pump system.

The Compressor | HVAC Refrigeration – How it Works

HVAC Refrigeration Compressor – A compressor receives the refrigerant vapor from the evaporator coil and compresses the refrigerant vapor. The vapor enters the refrigeration compressor at a low pressure and a low temperature and leaves the refrigeration compressor at a higher temperature and a higher pressure. The lower temperature refrigerant vapor is responsible for providing cooling for the refrigeration compressor and it also carries with it a small amount of oil which migrates from the compressor throughout the system. After the refrigerant vapor is compressed it is discharged to the condenser coil. A compressor is an essential component in the vapor compression process of refrigeration.

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Fixing a Refrigerant Leak | Air Conditioner & Heat Pump Diagnosis & Repair 5/5 (2)

Fixing a Refrigerant Leak

Fixing a Refrigerant Leak – The Basics

Fixing a refrigerant leak on an evaporator coil
A new evaporator coil

Fixing a Refrigerant Leak – You had the new air conditioner or heat pump system installed some years ago and suddenly it stopped heating or cooling properly so you call the HVAC contractor to check it out. The HVAC technician arrives and spends about thirty minutes HVAC troubleshooting and then he comes to you with the news. The unit needs a charge of refrigerant. It is low on refrigerant (R-22) or R-410A. You ask the HVAC technician if it is normal for this to occur and he informs that, no, it is not normal for the HVAC system to lose refrigerant that you have a refrigerant leak.

So you advance to the next question and ask, “can you find and fix the refrigerant leak”. The HVAC technician says yes he can. Here are the options for you and depending on which option you choose will depend on the cost.

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Compressor Rebuild | HVAC Heating and Cooling Refrigeration 5/5 (1)

Refrigeration - HVAC Compressor Rebuild
Rebuilt Reciprocating Compressor

Compressor Rebuild – This freshly rebuilt reciprocating compressor is destined for a large commercial chiller. Chillers chill water for air conditioning. Compressors compress refrigerant vapor and pump the compressed refrigerant to the condenser to be condensed into a liquid. The compressor provides compression which is an integral part of the refrigeration process. The old compressor was condemned for electrical burn out. The windings in the old one burned up and caused the circuit breaker to trip.

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HVAC Centrifugal Compressors | HVAC Refrigeration 5/5 (1)

HVAC Centrifugal Compressors
McQuay Chiller Uses HVAC Centrifugal Compressors

HVAC Centrifugal Compressors – Centrifugal compressors are used in many applications including pipeline transport of natural gas along with many other related applications including vapor compression refrigeration. These compressors have different operating limitations than the reciprocating compressor, the scroll compressor, and the rotary compressor. They an operating range where it operates efficiently however outside of this range, either the over or under that operating range, is basically useless. Other issues make them not ideal for use in certain applications because of the operating range issues.

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Refrigerant Alarm Control for Chiller Room 5/5 (1)

Refrigerant Alarm Control for Chiller Room
Refrigerant Alarm Control for Chiller Room

This refrigerant alarm serves two chiller rooms and alerts operators and other staff that refrigerant has been released into the mechanical room. Chillers have a built in pressure relief valve that will release the refrigerant in the event too much pressure builds up in the system. This prevents a possible explosion from too much pressure and also protects the equipment from a catastrophic failure that would make the chiller unusable. Other failure scenarios that set off the refrigerant alarm includes a refrigerant leak from the chiller so the alarm would alert the maintenance staff of a chiller refrigeration leak condition. Refrigerant will asphyxiate humans and the alarm is required by code for obvious safety reasons. The refrigerant alarm control automatically sets off audible horns, sirens, and automatically activates exhaust fans to evacuate the refrigerant from the mechanical room.

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R-410A versus R-22 Refrigerants | HVAC Refrigeration 5/5 (1)

R-410A versus R-22 Refrigerants

R-410A versus R-22 Refrigerants

R-22 is a refrigerant that has been widely used in air conditioners and heat pumps for many years. It has been deemed hazardous to the environment and it will begin phase-out by law in the year 2010. The replacement refrigerant for R-22, R-410A, is being produced to meet the rising demand for new air conditioner and heat pumps systems. Why do consumers need to understand the impact this law is having on the HVAC market? Because it will determine what HVAC consumers pat for future repairs made to their equipment. Everything boils down to the new law, refrigerant and HVAC equipment manufacturers retrofitting factories for the new HVAC equipment, and supply and demand. The changeover has already begun and there is some apprehension about this changeover.

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Old Leaking Condenser Coils 5/5 (1)

Old Leaking Condenser Coils
Old coil with HVAC Refrigerant Leaks

Old Leaking Condenser Coils

Old Leaking Condenser Coils (also referred to as freon leaks) can cause serious issues with HVAC heat pump equipment. HVAC refrigeration circuits are designed and built to hold the refrigerant. It is a sealed hermetic system. The HVAC refrigeration circuit should never need refrigerant. An HVAC refrigeration system does not burn refrigerant. The refrigerant is used over and over again to move heat from one place to another. Aside from a leak, once the refrigeration system is properly charged, the system should never need refrigerant for the life of the equipment.

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