The term “thermal expansion valve” (TXV) may sound like obscure technical jargon only HVAC professionals need to understand, but the TXV is an important feature you’ll want to know about if you’re shopping for a high-efficiency air conditioner. This little device helps your system operate more efficiently during the warm, humid summers we get in the Baltimore area. That translates to lower electric bills for you.
A thermal expansion valve is a refrigerant metering device. All air conditioners and heat pumps have a refrigerant metering device that modulates the flow of refrigerant from the condenser into the evaporator coil.
Older and less efficient air conditioners typically contain fixed orifice devices, either capillary tubes or piston types. A capillary tube is simply a narrow length of copper tubing. This design has long been the standard in cheaper air conditioners. In both types of devices, the opening through which the refrigerant flows is fixed in size. Because of this, neither device can precisely control the amount of refrigerant that’s fed into the evaporator. The amount the evaporator receives is usually either too much or too little for the cooling load.
That’s a problem because the evaporator’s efficiency and performance depend on how much refrigerant it receives. When indoor temperatures are high, the evaporator requires more refrigerant to absorb that heat. In cooler temperatures, however, the evaporator needs less refrigerant. Your whole A/C system’s energy efficiency is reduced when the evaporator doesn’t get the precise amount of refrigerant it needs.
The thermal expansion valve solves this problem. This advanced metering device detects how much refrigerant is needed for the cooling load at any given moment and adjusts the flow to supply that amount. This type of device has two main advantages.
- It maximizes evaporator efficiency by providing the optimal amount of refrigerant at all times.
- It protects the compressor by preventing “slugging,” a damaging processes that occurs when liquid refrigerant passes through the compressor’s suction line and discharge valves.
A thermal expansion valve contains a valve needle that allows it to open and close to let through varying amounts of refrigerant. It also uses a sensing bulb attached to the refrigerant line exiting the evaporator (evaporator outlet). This bulb senses the temperature of the refrigerant leaving the evaporator.
In the top of the TXV is a flexible diaphragm that moves the valve needle in response to the current cooling load. As the evaporator outlet temperature rises, indicating a higher cooling load, the bulb pressure increases. This causes the diaphragm to press down and open the valve needle to allow more refrigerant through. When evaporator and/or spring pressure increase, indicating a lower cooling load, this pushes the diaphragm up, closing the valve and decreasing the refrigerant flow.
To operate the valve needle, evaporator pressure plus spring pressure balance out against bulb pressure. This means the valve is never fully open or closed except under extreme conditions. Instead, it opens just enough to let through the precise amount of refrigerant that’s necessary to manage the cooling load at the moment.
While a thermal expansion valve improves an A/C system’s efficiency somewhat, there are a few other features to look for to ensure you’re getting a truly efficient air conditioner. These are features such as:
- An Energy Efficiency Ratio (EER) above 11.6. The EER is also known as a high-temperature rating because it indicates how well the system performs in very hot weather.
- An electronically commutated motor (ECM) to run the fan. Frequently referred to as a variable-speed motor, the ECM is more energy efficient than the older permanent split capacitor (PSC) motors in large part because it can adjust its speed to meet your cooling demands.
- A scroll compressor, which is more energy efficient, quieter, and more durable than the reciprocating compressors used in less efficient A/C systems.
- An automatic-delay fan switch that runs your fan for a few minutes after your compressor shuts off to push any remaining conditioned air out into your rooms.
- A “check filter” indicator light that shows you when it’s time to inspect your filter. A dirty air conditioner filter reduces your system’s efficiency, so replacing the filter on time helps control your energy expenses.
Choosing the air conditioner that’s right for your needs and installing it for optimal performance requires an experienced professional. If you’re looking to upgrade your cooling system, contact us at Griffith Energy Services. We provide reliable services for homeowners in Maryland (Baltimore, Frederick, Hagerstown, Manassas, Westminster and Easton), as well as in Dover, Delaware and Martinsburg, West Virginia.
Written by Kevin Spain
