What is a Metering Device – Refrigeration Components

Posted on June 11, 2012 by Richard Ashworth

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.

Specific Types of Metering Devices used in HVAC Refrigeration:

Thermostatic Expansion Valve – Also referred to as the TEV or TXV for short the thermostatic expansion is used in many air conditioning and heat pump applications including use in chillers for chilled water systems. TXVs respond to the temperature of the refrigerant leaving the evaporator coil or evaporator barrel. The TXV has a sensing bulb that holds a slight refrigerant charge inside the bulb. The TXV bulb is remote from the TXV and is attached to the TXV via a capillary tube or cap tube. As the temperature increases and decreases the refrigerant inside the bulb responds by expanding and contracting based on the temperature pressure relationship of refrigerants. As the refrigerant expands and contracts causes a bellows to move in and out which causes a piston to open and close precisely based on the leaving temperature of the refrigerant in the evaporator coil. This allows the TXV metering device to feed the evaporator coil the precise amount of refrigerant it needs to maintain a specific superheat. Because the TXV precisely meters the refrigerant the TXV is used in many air conditioner and heat pump systems that need a higher efficiency. A properly engineered and installed system that uses a TXV will only give the evaporator coil what it demands and nothing more or nothing less.
The other type of expansion valve used in HVAC is the fixed orifice. The fixed orifice is simple and can be either a piston type or utilize a distributor that feeds capillary tubes which terminate in the evaporator coil. The piston type comes in various sizes and is interchangeable with the capacity or tonnage of the condensing unit. Always follow the manufacturers instructions for piston size if using the fixed orifice for HVAC refrigeration.
Capillary tubes (cap tubes) are also used to meter refrigerant to the evaporator coil. These are considered fixed orifice since they hole in the tube(s) is a fixed size.
There are other non-conventional types of metering devices used for HVAC refrigeration including the float type and the electronic type however these are not commonly used in standard HVAC equipment.

There are other types of metering devices used in HVAC vapor compression refrigeration but these are the most common types are used in HVACR in both the commercial market and residential markets. As systems grow more sophisticated and complex that is likely to change. Electronic types are the next big step in refrigeration used for air conditioning and heat pump systems.

High Performance HVAC

Metering Device

Refrigeration HVAC – Components of Vapor Compression Refrigeration – The Condenser

Posted on June 11, 2012 by Richard Ashworth

The Condenser

Trane Heat Pump Condenser

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.

Most condensing units utilized in HVAC whether it is the commercial HVAC field or the residential HVAC field are constructed of copper with aluminum fins. The aluminum fins are mechanically attach to the copper tubes that make up the condenser coils or the piping that channels the refrigerant from the beginning of the condenser coils all the way to the end or exit of the condensing unit where the refrigerant makes its way to the metering device. The aluminum fins attached to the copper pipe enhance the heat exchange process in the air source condensing units. A few manufacturers use only aluminum coils in their condensing units to take advantage of the efficient heat exchange properties of aluminum. The aluminum coils also have fins on them and these are usually referred to as spine fin coils. The spine fins extend the surface area of the aluminum coil enhancing the heat exchange process for efficiency purposes.

Many condensing units also house the compressor and condensing unit controls. The condensing typically utilizes its own dedicated circuit from the main circuit breaker panel. In a split system the condensing unit will have a line set or refrigeration lines that run from the condensing unit to the evaporator coil inside the building. The condenser is an essential component of vapor compression refrigeration.

High Performance HVAC

Components of Vapor Compression Refrigeration – The Condenser

Refrigeration HVAC – Components of Vapor Compression Refrigeration – The Compressor

Posted on June 11, 2012 by Richard Ashworth

The Compressor

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 the compressor or the heart of any air conditioner or heat pump system.

HVAC Refrigeration Compressor – The HVAC refrigeration 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. The compressor is an essential component in the vapor compression process of refrigeration.

It is necessary for the evaporator to supply the compressor with vapor refrigerant as it is impossible to compress a liquid. Compressors that receive liquid refrigerant can fail mechanically. In heat pump applications the system is equipped with a refrigerant accumulator. The accumulator allows liquid to boil into a vapor before entering the compressor thereby preventing any liquid refrigerant from entering the compressor. The term liquid slugging is used for compressors that receive liquid refrigerant. A properly installed, maintained, and engineered air conditioner or heat pump system will never experience liquid slugging so it is especially important that qualified personnel install and service air conditioning and heat pump systems.

High Performance HVAC

Components of Vapor Compression Refrigeration – The Compressor

Refrigeration Pressure Switches

Posted on June 11, 2012 by Richard Ashworth

Refrigeration Cycle Component Diagram for air conditioners and heat pumps

Refrigeration Pressure Switches

Richard – What are refrigeration pressure switches used for in refrigeration circuits and how do refrigeration pressure switches protect the system from further damage?

Thanks for the question and for being a reader of High Performance HVAC! First there two types of basic refrigeration switches in the typical high grade residential system. I say high grade because not every refrigeration system in air conditioners and heat pumps have refrigeration switches to protect the refrigeration system.

High Pressure Refrigeration Switch – The high pressure switch will kill the compressor circuit if the pressure exceeds the rating on the pressure switch. These pressures will vary depending on the type of refrigerant the air conditioner or heat pump uses in the system. On some air conditioners or heat pumps this switch is manually reset only simply because if it trips there is definitely a problem that needs to be resolved before the system should run again. On Rheem and Ruud heat pumps and air conditioners the reset button is usually red on located near the control panel. A simple push of the switch will reset the switch and the operation of the air conditioner should return to normal until the pressure exceeds the rating of the switch. Things that can cause the pressure switch to trip include:

Bad condenser fan motor
Coils plugged up with dirt and debris
Fins on the coils bent
Blockage in the refrigeration system

These issues, if they exist, should be taken care of before before the switch is reset. The high pressure switch prevents the system from operating at extremely high pressures.

Low Pressure Switch – The low pressure switch is typically an automatically reset switch that will reset itself when the pressure on the low pressure side of the refrigeration systems returns to normal or above the setting on the switch. When a refrigeration system operates at lower than normal pressures the system can freeze up with the freezing beginning at the evaporator coil and working its way back to the compressor via the suction line. Freezing of the refrigeration system is bad and lead to liquid refrigerant slugging in the compressor which can lead to compressor failure. Things that can cause the low pressure switch to trip include:

Low refrigerant charge from a refrigerant leak
Blower motor failure in the air handler
Plugged evaporator coils or a blockage of air flow
Failure of a refrigeration component in the refrigeration system

Again, if these issues exist in the refrigeration system they need to be addressed to prevent the low pressure refrigeration switch from tripping.

High Performance HVAC

Variable Speed ECM Condenser Fan Motors

Posted on June 11, 2012 by Richard Ashworth

High SEER Trane Condenser Variable Speed ECM Condenser Fan Motor

This high SEER Trane condenser uses an ECM variable speed fan motor to modulate the speed of the fan

Variable Speed ECM Condenser Fan Motors are use in condensers for the high efficient models so that the fan speed for the condenser fan motor can be modulate according to the load of the system. The variable speed ECM condenser fan motors are used in condensers that either have a modulating compressor or condensers that have two compressors where one compressor is small and one compressor is large. The variable speed ECM condenser fan motor adds to the efficiency of the system by modulating the condenser fan motor to match the compressor use needed to satisfy the load.

On very hot days you need more air conditioning capacity to satisfy the heating load demand put on your home in the summer. In milder weather you do not need to run the air conditioner at 100% to satisfy the higher demand. HVAC equipment manufacturers have introduced systems that have the ability to run in two-stages so that on the hotter days you can satisfy the demand and on the cooler days you can run the system at a lower setting thereby using less energy.

Using less energy is the objective so how do we do this? The solution is two-fold for having an efficient running system. One is to reduce the heat gain by insulating the home and adding things to the home such as attic fans. These things help reduce heat gain to the living areas that you want to condition with cool less humid air. The second thing you can do is to purchase a higher efficient system that can modulate or offers staging from a high level for higher demand to lower level for lower demand.

HVAC Manufacturers introduced two-stage compressors and in the future (offered currently in commercial systems) modulating compressors that will run according to the demand based on exactly what you need to condition your space. Since the compressor would stage based on demand they needed a condenser fan motor that would also stage based on demand. Some manufacturers use a standard multi-speed condenser fan motor while others use a variable speed ECM condenser fan motor to facilitate a higher speed for the increased demand when the system is calling for higher demand and a lower speed when the system is calling for a lower demand. So when the compressor is running at a higher speed the condenser fan motor will also run at a high speed and when the compressor is running at a lower speed the condenser fan motor will run at a lower speed.

High Performance HVAC

Variable Speed ECM Condenser Fan Motors

Fixing a Refrigerant Leak – Air Conditioner Diagnosis & Repair

Posted on June 11, 2012 by Richard Ashworth

Fixing a refrigerant leak on an evaporator coil

A new evaporator coil replacing an old leaking coil

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 troubleshooting and then he comes to you with the news. The unit needs a charge of refrigerant. It is low on freon (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 leak. So you advance to the next question and ask, “can you find the 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.

Continue reading “Fixing a Refrigerant Leak – Air Conditioner Diagnosis & Repair” »

ECM Blower Motors

Posted on June 10, 2012 by Richard Ashworth

ECM Variable Speed Blowers

An ECM Variable Speed Blower Motor in a squirrel cage blower

Variable speed blower motors have become increasingly popular in residential air conditioning and heating systems and for good reason; these motors increase efficiency of the systems and offer a whole range of other benefits that help the system and the consumer.

Variable Speed Blower Motors first offer a higher efficiency for air conditioning systems based on the manufacturers set up of the control with the ECM Variable Speed Motor. Each manufacturer calls it a different thing such as Trane calling it the Comfort R and Carrier calling it Infinity Control. Despite what the manufacturer calls it helps efficiency with air conditioning by starting the blower slowly and letting it run at a 50% speed for the first few minutes (up to 7 minutes) to remove more humidity. This increases comfort and efficiency by removing more moisture from the air. The lower the humidity in the cooler you will feel so the variable speed blower with this type of control will enhance comfort.

ECM variable speed motor manufacturers include General Electric and Emerson with Emerson offering their very own packaged control and control program to meet various control sequences to meet efficiency and comfort for any manufacturer that uses the Emerson ECM variable speed motors for their equipment.

Other benefits include:

Soft start capabilities which reduces high inrush current like conventional blower motors.
Precision control to deliver a set amount of CFM’s for whatever the HVAC equipment manufacturers need for their equipment for airflow control.
High efficiency which reduces energy bills.
Very quiet operation
Better comfort as described above

One of the disadvantages include a high replacement cost if something happens to the motor or controls. ECM variable speed motors need the attention of a qualified HVAC technician if something goes wrong as special diagnostic tools are needed to diagnose any problems which may arise with the motor or controls.

These motors are typically offered in the medium to higher end models of air handlers and furnaces so you will have to pay a little more for the initial cost but the benefits will give you a pay back in the future with increased comfort and higher efficiency. Here at High Performance HVAC we always recommend going for higher efficiency models because the cost of energy is not going to go down in the future and the high efficiency models will help reduce the cost of energy so your utility bills will be reasonable in the future. The bonus this air handler or furnace component also adds comfort while increasing efficiency.

Troubleshooting ECM Blower Motors Basics

Never assume the blower motor is bad. Always perform a cursory look at other components and inputs before condemning the ECM blower motor. Check the air filters and duct work integrity before beginning component checks outlined below. The system needs good air flow to function properly.

Check the main control board in the air handler. Wiring connections including the thermostat wire coming from the thermostat. Always perform these checks with the power turned off. Check for loose connections, corrosion, and burned spots on the board. Some HVAC equipment has an additional control board for control of the ECM blower motor in the air handler. Also check all the connections going to the motor including pins inside the molex plug connection. A bent or loose pin will cause problems.. A plastic molex plug should make the connection between the motor and the control board.
Next check the input voltage for the board. Restore power and use a volt meter to check both the main line voltage and the control voltage. The control board should use 24 volt for the control voltage and all voltage ranges should be plus or minus 10%. Make sure that the safety circuit is good. Switches in the safety circuit will keep the system from running.
Using the manufacturers instructions, check additional settings on the control board. Many have dip switches that will control RPM’s for the proper air flow for the sizing requirements of the system. Ensure these are set properly.
Ensure when you start the system that you wait for the programmed delays. An ECM blower motor, properly programmed, will start off very slow and then ramp up to a low speed according to what the program calls for. After a specific period of time, usually around 7 minutes, the blower will ramp up to 100% of the program according to where the dip switch settings is set for RPM’s or CFM’s.

If this doesn’t work then and you still have problems check with the manufacturer for a ECM blower motor troubleshooting flow chart or guide. Some manufacturers have a diagnostic tool that will confirm specific problems and can indicate if the motor or the controls are bad. If the motor is turning too many RPM’s or not enough RPM’s and is causing issues with the air conditioning or heating system because of improper air flow then it is a good idea to check the dip switch settings on the board. Good luck.

Air Handler Information

ECM Blower Motors

Troubleshooting Electronic Ignition Gas Furnace – Repair Basics

Posted on June 9, 2012 by Richard Ashworth

Gas Furnace Electronic Ignition Troubleshooting

Electronic Control Board for an Electronic Ignition Gas Furnace

Electronic ignition for gas furnaces is the modern way for furnaces to light the main burners on modern gas furnaces. Electronic ignition gas furnace technology has evolved from the standing pilot gas furnace ignition systems that continue to be used today however there are less and less standing pilot gas furnaces used today. If your furnace is not working and you want to troubleshoot an electronic ignition gas furnace system it is important to make sure you know which type of ignition system you have for your furnace. Additionally there are different types of electronic ignition gas furnace systems and it is important to differentiate between the types of electronic ignition systems before troubleshooting a gas furnace electronic ignition. We will break it all down for you in this series article: “Troubleshooting an Electronic Ignition Gas Furnace“.

More on gas furnaces and electronic ignition here.

High Performance HVAC

Proper Humidity Levels and Factors for Home Comfort and Health

Posted on June 9, 2012 by Richard Ashworth

The Contents and Make Up of Air and Humidity

Proper Levels of humidity Factors for Home Comfort and Health Humidity is important to our home and health and it is important to maintain the correct humidity in our homes and workplaces for our health. What is humidity? Humidity is simply little water droplets in the air. Cold air is nearly saturated with these little water droplets because the contents of cold air allow the air to hold more water droplets or humidity. As air is heated it expands and holds less humidity. When you heat the air in your home using a furnace, boiler, or heat pump this air expands and becomes drier. It is air with less humidity relatively speaking before it was heated and compared to the outside air. Air that is 30° F with 80% humidity will only be 15% humidity at 75° F. That is a big difference in humidity levels in the home after the air is heated. Granted, you are not heating air from 30° F to 75° F with your furnace. Depending on the set up of your thermostat and heating system you are most likely heating air that is 68° F to around 70° F to 75° F depending on the thermostat setting. The point is unless you have a source providing humidity to the air stream you are simply reheating dry air from inside the structure. There will be minimal infiltration humidity but the infiltration humidity will never be enough to bring the humidity levels up to healthy levels inside the structure for the inhabitants, plants, and furniture.

The Study of Psycrometrics

Psychrometric Chart content and make up of air

Psycrometric Chart

Yes, that is psycrometrics and it has nothing to do with psychology. It is the study of air and its properties. It is used in HVAC by HVAC technicians and HVAC engineers to determine the contents and make up of air. The HVAC industry uses Psychrometric Charts to plot the contents and make up of air. Using the Psychrometric Chart a technician or engineer can determine the relative humidity, enthalpy value, dry-bulb temperature, wet-bulb temperature, dew point and vapor pressure if they have a few of the listed values. With this data engineers and technicians can solve problems or assign values and set points. For example, an economizer system that is controlled by the building automation system can be controlled by an enthalpy value. This value associated with an And Gate will only allow the economizer to open under certain conditions that will allow the mechanical cooling systems to shut down and take in free cooling from outside the structure. The temperature, humidity, and all the contents and make up of the air will be optimum for free cooling using the economizer. By knowing the contents and make up of air one can set up HVAC systems to work better and one can also use the data provided by knowing the contents and make up of air to troubleshoot problems with HVAC and building systems.

Indoor Air Quality and Humidity

It is important to maintain correct levels of humidity in the home for many reasons. Comfort is on factor, indoor air quality is another factor, and saving energy is another factor. All three are related in one way or another but each are separate factors. If you reside in the northern climate regions where the average temperatures are less than 20° F you want the indoor humidity to be relative to outside air humidity. Temperatures about 20° F the recommended relative humidity inside the home or business is 35% to 45%. The construction of the home or business will also determine the amount of humidity. If you have vapor barriers and good tight windows and doors you need a good mechanical ventilation system. Humidity levels can rise above 60% causing excessive moisture inside the structure which will lead to mold, mildew, and possible water damage. Make sure you have a good mechanical ventilation system inside your structure to avoid moisture issues. Bathroom ventilation fans, hood fans over stoves, and other type of exhaust fans inside the structure pull out excessive moisture when cooking or showering. If you have this problem it most likely shows up in the form of mold growth inside closets, kitchens, bathrooms, and ceilings. Additionally, if you have excessive moisture problems your windows will frequently fog or have a lot of moisture on the windows.

Low Humidity

Low humidity levels cause problems also. Static electricity, dry skin, dry sinuses, and other health problems including increased flu illness can occur. Additionally, low humidity levels cause problems with wood inside the home. To test for low humidity levels in the home make a glass of ice water and set it somewhere away from the kitchen or bathroom. If after five minutes water droplets do not form on the outside of the glass then you have a problem with low humidity levels in your house and you need to get a humidifier. If your structure is suffering from low humidity levels you will also feel cooler resulting in a desire to turn the thermostat up. Therefore adding a humidifier to the HVAC system will cause you to turn the thermostat down. The correct levels of humidity in your home can increase comfort, save you money on your utility bills, and make you healthier.

Warm Air Expands

Remember that your furnace or heat pump DOES NOT remove the moisture from the air. The furnace or heat pump simply makes the air warmer and warmer air expands making the percentage of moisture in the air less than when it was cold. Relative Humidity is the amount of water vapor percentage that is in a given amount of air at a given temperature. Air is considered to be saturated with moisture when it reaches 100% relative humidity however you can quickly change the 100% relative humidity in air by increasing its temperature. Decrease the temperature and the moisture condenses from the air or it can be considered rain. When you heat the air you increase its volume and without a humidifier adding moisture to the air you are decreasing relative humidity. Adding a whole house humidifier to your home will always help maintain higher levels of moisture in the house and that will counter all the problems associated with low humidity levels.

High Performance HVAC

Humidity Levels and Factors for Proper Home Comfort and Health

Home Humidity Problems Maintaining Proper Home Humidity

Posted on June 9, 2012 by Richard Ashworth

Is 60% Humidity in the Home Too High?

HIGH HUMIDITY 60 % +. Within the last month, I moved into a new house. It has dry walls and not plaster walls. The furnace and hot water tank were installed a week or so before we moved in to the house. Last week we determined that there is a humidity issue when the windows were sweating. We are trying to determine the source of the humidity. The contractor feels it may be the high efficiency furnace. I have a Lennox g61mp. The combustion air is pulled from within the un finished basement. Should the air be pulled from the outside? The gases are vented via PVC pipe which slopes back to the furnace.

Could the furnace be causing the humidity problem? If yes, what could be causing the humidity problem? The installer said it is not the furnace.

Answer…….

Maintaining the proper humidity levels in the home is important not only for health (as indicated on High Performance HVAC Humidifiers Page) but also for the wood products in the home including doors and windows. The quick answer to your question about the furnace causing the humidity problems is no. Gas furnaces and other heating appliances tend to dehumidify the air and do not create any more humidification. I wonder where your supply vents are located and are they directed to blow hot air towards the windows? Condensation is created when the temperature of air is colder than the dew point. A prime place for this to occur is windows and doors. This is part of the reason why many supply vents for forced air systems, and radiators for hot water systems, are placed near windows and doors. It keeps the windows warmer and above the dew point and also makes the air warm from your heat loss near these locations.

Lennox G61MP Gas Furnace

The furnace you describe, the Lennox G61MP, is a condensing furnace and having the combustion air intake in the basement actually contributes to removing humidity from the basement. It sucks the air from the basement for use in the combustion process and the humidity in this air is condensed during the combustion process in the heat exchanger. This condensation is gotten rid of down a condensation drain near the furnace or blown out the exhaust where the combustion gases are expelled. If your supply vents are located near the doors and windows and you still have this problem then it may be time for new doors and windows as you have too much heat loss at these places and all the humidity is being condensed around the windows in your home.

Proper Humidity Levels