Evaporator Coil – the evaporator coil is responsible for absorbing heat into the coils and the refrigerant. The evaporator coil 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.
A new evaporator coil replacing an old leaking coil
The evaporator coil is typically inside the air handling unit or it can be installed in the duct work near the air handling unit. When the air handler blower turns on and the condenser is running refrigerant flows from the compressor through the condenser coils and then through the metering device. and into the evaporator coil. The refrigerant changes state in the evaporator coil and again in the condensing unit. In the evaporator coil the change of state is from a liquid to a vapor while in the condenser the change of state is from a vapor to a liquid. This is all necessary for the process of refrigeration to work properly. The typical evaporator coil is constructed of copper with aluminum fins surrounding the copper coils. The aluminum adds surface area to the copper coils and enhances the heat exchange rate making the coils more efficient.
Components of Vapor Compression Refrigeration – The 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.
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.
It is possible that you may have to run a new thermostat wire from the air handler or furnace to the location where the existing thermostat is located. Running new thermostat wire can challenging even for professionals. If you must the follow will hopefully help you in this endeavor. Pulling new thermostat wire should only be done as a last resort. The purpose of running new thermostat wire is necessary for certain reasons such as:
The most obvious reason is that the new thermostat requires an additional wire and there are no other wires available in the thermostat wire bundle to use for the new thermostat. This is common so do not fret.
The existing thermostat wire is very old and brittle which you do not trust.
The existing thermostat wire was damaged.
The existing thermostat wire is not long enough for the new thermostat terminations. Here is a tip that may solve the problem.
As my late Uncle used to tell me, “Here’s an old Indian trick we can use that may solve our problem.” The keyword there is “may” solve our problem. If the wire is not long enough for a proper termination at the new thermostat then take a small piece of thermostat wire about 6 inches long and use a small wire appropriate for #18 solid wire and wire nut the short piece to the 6 inch wire. The six inch wire should be long enough to make the proper termination and when finished you can push the wire nut back into the wall.
Be Careful when you take the thermostat off the wall especially with the wires to make sure the existing thermostat wire does not fall into the void of the wall. If that happens then you will be pulling wire whether you need to pull the new wire or not as you need the thermostat wire but it fell into the void of the wall. Just remember to be careful when you take the old thermostat loose from the wall.
Another Indian trick for you. Before you take the old thermostat from the wall have a pencil or pen nearby. As soon as you get the wires loose and the old sub-base of the old thermostat out of the way take the pencil or pen and wrap one of the wires around it. This will prevent the thermostat wire bundle from falling back into the void of the wall and will save you lots of time and headaches of pulling a new wire or trying to get the wire that fell back out of the void.
By now you should have figured out if you have the proper amount of wires or if any of the above conditions will necessitate you pulling a new thermostat wire. It is still not too late to call a professional and let them take care of the head ache.
If you are still here and reading this then you are a true DIYer and you are determined to complete this installation by yourself. Now it is time to get things right 100% because you are going to have to make a trip to the local hardware or big box store for some materials. Here is a list of some basics you will possibly need to finish the job of pulling new thermostat wire.
Thermostat Wire – Read below for the correct type and number of conductors you will need.
A long auger bit.
A stud finder
A fish tape – preferably the flexible nylon type
A flash light
& lots of patience.
First you need to read the manual and determine for the type of HVAC system you have and the thermostat you are installing to determine the number if thermostat wires you will need for the bundle.
There may be someone out there thinking they will move the thermostat to another location and HighPerformanceHVAC.com wants to discourage you from doing that as your thermostat location was most likely selected by an engineer, architect, or an HVAC Master designer and the current location of the existing thermostat is the best place in the house for the thermostat. There is no reason to second guess the experts. Some people may think that, “because I need to pull a new thermostat wire I may as well go ahead and move the thermostat to a better location”? This is not a good idea as the thermostat needs to be located in an area close to the return (or where you may change your filter), on an inner wall versus a wall that experiences a heat load (outer wall), and out of direct sunlight. Another place where thermostats should not be installed are near sources of heat or sources of something that cools or blows cool air. All these things will cause problems with the thermostat and you will find yourself either too hot or too cold because the thermostat will never work properly if it is not installed in the proper location inside the house.
The thermostat senses temperature and the temperature of the air near the thermostat should be the temperature of the air going into the return or close to the temperature of the air going into the return. Avoid moving the thermostat as it can and often times will cause serious problems and prevent you from being comfortable. It can also increase your utility bills rather than decrease them.
After you get the new wire and all the tools listed above then you need to fish the wire through the wall and to the either the crawl space, basement, and in some cases the attic. The key is that you must get the new wire from where the thermostat is located to where the gas furnace or air handler is located. If you are lucky then you can use the old thermostat wire and attach it to the new thermostat wire securely and use the old thermostat wire to pull the new thermostat wire however experience tells me that in most situations this will not be possible because usually when someone was installing the original thermostat they put a couple of staples into it to hold in place most likely before the drywall or plaster was put on the walls and the wall was simply studs.
Remember it is key that you have the number of conductors needed before you pull the new wire in the wall. This is extremely important that you get it right because if you are just one wire short this will not work. For example, if you have a gas furnace with two stages of heat and an air conditioner with two stages of cooling and you are installing a digital thermostat you need to makes sure of two things before pulling the wire:
That you have the correct thermostat. The thermostat needed in this case will require two stages of heating and two stages of cooling. That is the thermostat will have a W-1 and a W-2 terminals plus a Y1 and a Y2 terminals on the thermostat to properly control the equipment. The two W terminals will control the two stages of heating and the Y terminals will control the two stages of cooling.
You have the number of conductors in the thermostat wire bundle to properly control the equipment and feed the thermostat with power. All thermostats whether powered or not have the R wire or a red wire (if your thermostat wiring follows the proper protocol) and this red wire is the 24 volts of power needed to control the air conditioner, air handler, or furnace plus it can feed the thermostat power if the 24 volt circuit is completed at the thermostat. In this case, in addition to the 24 volt red wire, and 24 volt common wire from the transformer or terminal strip board in the air handler or furnace also needs to be ran to the thermostat simply to power the digital thermostat. That termination should be done at the C terminal in the thermostat and originate at the C terminal on the control circuit board in the furnace or air handler.
Exception for RC and RH Terminals
The only exception to this is if you have split transformers for the heating and cooling systems. For example, a boiler can have its very own transformer while the air conditioning system will its very own thermostat located inside the air handler of the air conditioner. In this case then the thermostat should only be fed by one power source. A choice needs to be made to use either the air conditioner or the boiler transformer and the wires identified and separated. The thermostat also needs to have two R terminals – RC and RH – where the boiler red wire is terminated at RH and the air conditioner red wire is terminate at RC. This also means if you are going to pull new thermostat wire you are going to have to pull separate wire for the boiler and a separate wire for the air conditioner. The boiler is likely a two wire bundle with a red and white wire inside the bundle with the red wire terminated at the RH terminal and the white wire terminate at the W terminal.
10 SEER units cannot be purchased in the US any longer. The new standard as mandated by the Department of Energy as of January 2006 is 13 SEER. This 30 percent increase in efficiency from 10 SEER requires a change out of the inside coil. In 2011 the Senate is proposing a new SEER and AFUE standard that will be based on where you reside in the USA. The country will be split up into three regions. Northern, Southern, and the Southwestern regions with each region having different efficiency standards. The proposed efficiency standards for each region are as follows: Continue reading “2011 Proposed Increase in SEER – EER – AFUE – HSPF” »
I did not see any reference to my question and would appreciate a response as soon as possible, as due to medical situation, have to make a decision soon. We own an OLD house with 13′ ceilings in a large part of the home and 11″ ceilings in the LV/DR and BR. We are oscillating on where to place the ducts….Floor or ceiling. It appears to be counterproductive to me to put the duct work in the ceiling since it will have so far to go. We are looking for the most cost effective, not upfront cost but operating cost, solution. In addition, we are considering DF heat pumps. The house will need 2 or 3 to be zoned correctly. Please let me know about the duct placement and thank you for your help? Continue reading “Duct Work and High Ceilings” »
The variable air volume box or VAV box is a commercial solution to adding multiple zones to large buildings. VAV boxes offer zoning solutions so that separate zoning demands or temperature selections can be maintained in different areas of the building. If the president of the company wants the temperature in their office to be 70 degrees Fahrenheit but the vice president wants their office to be 74 degrees Fahrenheit then it is possible with the VAV zoning system as long as their VAV boxes are on different zones. This particular VAV box in the picture is not fan powered. It relies on the main VAV air handling unit to provide all the air. Generally, when a fan powered VAV box is calling for heat the damper inside the VAV box closes down so that minimal CFM’s are coming through the primary duct from the air handler. The fan turns on an pulls air from the plenum space above the ceiling. This plenum air is normally warmer than the air inside the occupied space. The heating system kicks in and adds heat to the air until a setpoint is attained. The heat for a VAV box can typically be a hot water coil or electric heat strips. The VAV box in the picture has hot water reheat. Continue reading “Variable Air Volume Box VAV Box Hot Water Reheat” »
These controllers will control an air handler once the wiring is completed. The panel is freshly mounted and waiting for the technician to run the piping and pull the wire from the control points. Other points, such as outside air, temperature sensors in piping or ductwork, flow meters, actuators, or other control points can be terminated to these controllers and the data collected from those input points can be networked over the entire building automation system through the communication trunks. Included in this panel are: a terminal strip connection point for line voltage and control voltage, a transformer to step-down line voltage to the required control voltage of 24 volts which powers the controllers and a surge arrestor which is a requirement on many government jobs.
This is a current switch sometimes referred to as a CT switch. This switch has an adjustable range from 1 to 200 Amperes. This switch also has a trip setting so it will trip if an adjusted set amount of amperes is exceeded.
The basics of DDC include learning about the status of a fan or a compressor or pump. How does a DDC controller read the status of the device it is monitoring? There are several ways to prove a device is running and some pros and cons of each type of device used to monitor on or off status. This is a basic DDC guide or reference to help a person understand the basics of DDC status and how it works. When one learns how DDC status works they can improve their troubleshooting skills. Too many maintenance technicians and others including HVAC technicians don’t understand DDC systems or building automation systems and are therefore crippled when it comes to troubleshooting DDC systems. High Performance HVAC hopes to change that and help HVAC techs and HVAC maintenance staff learn the basics of DDC systems including how DDC status works. Once someone understands the basics about DDC a light will turn on and they will see that DDC is not really rocket science.
The (Field) Technical Aspects of Direct Digital Control
A HVAC technician who knows nothing about HVAC control systems would wonder how these hvac control systems work. To understand hvac controls, one must understand basic electricity and circuits. Starting with a large commercial VAV air handling unit with three stages of DX cooling and add all the necessary hvac ddc control points. We have variable frequency drives (VFD’s) on the return and supply blower fans. There is a mixed air damper which closes off the return and opens up to outside air for economizing and CO2 control. Static pressure control will be achieved with a duct pressure transducer and the HVAC control program through the frequency drives and blower motors. Direct Digital Control needs to monitor supply air temperature, mixed air temperature, and return air temperature along with outside air and outside humidity. We will also monitor the duct smoke detectors and a freezestat for safety reasons. This is the set-up and we need to make it work. We need to get a point count and set-up our inputs and outputs.