Author: Dale T. Rossi Online Editor: Zachary Williams SERVICE ASSISTANT OVERVIEW FDSI Online Training May 5, 2009 Table Service Assistant Description... 2 Installing the Main Unit... 3 Ambient Temperature... 4 Suction Pressure... 5 Suction Pressure... 6 Suction Pressure... 6 Liquid Pressure... 7 Liquid Pressure... 8 Air Side Sensors... 9 Using the Tool... 10 PVS Software Screen Description... 11 PVS software screen description... 12 PVS Software Screen Description... 13 PVS Software Screen Description... 15 Fundamentals for a Valid Test... 17 Fundamentals for a Valid Test... 19 Service Assistant Specifics... 21 Service Assistant Specifics... 22 Range of Equipment... 24 Service Assistant Overview... 25
Service Assistant Description SERVICE ASSISTANT DESCRIPTION The Service Assistant measures: Suction pressure Liquid pressure Suction temperature Liquid temperature Ambient temperature Return air dry-bulb and wet-bulb temperature Supply air dry-bulb and wet-bulb temperature The ACRx PVS software operates on the Palm platform or on Windows Mobile devices using a Palm emulator. All the device-specific instructions assume that a Palm TX, the PDA generally supplied with the Service Assistant is used. The Service Assistant measures a variety of pressures and temperatures. 2
Installing the Main Unit INSTALLING THE MAIN UNIT The tool may lay on the roof or hang from a secure place. Avoid dropping the tool. Falls are a common cause of sensor connection breakage. The Service Assistant, in use, is usually hung from a gas line or placed on the roof. 3
Ambient Temperature AMBIENT TEMPERATURE Ambient temperature is the temperature of the air entering the condenser. Place the sensor in the air stream, worrying less about radiation from the Sun. The ambient temperature is the temperature of the air entering the condenser. It is important to get an accurate ambient temperature measurement. It is easy to overestimate the ambient temperature by careless placement of the sensor. The sensor should be in the air stream being pulled through the condenser coil by the condenser fan. The best place to sense the ambient temperature is near the top of the condenser where the airflow is the greatest. It is more important that the sensor is in the airflow than in the shade, but if shade is available near the top of the condenser that will yield even better results. 4
Suction Pressure SUCTION PRESSURE The suction pressure hose is installed on the suction service access fitting. The suction pressure hose is connected as it normally would be. 5
Suction Pressure Suction Pressure SUCTION TEMPERATURE The suction temperature sensor is installed on the suction line, near the compressor. Install outside the unit on split systems. The suction temperature sensor is a clamp-on thermocouple. It can be placed on the suction line near the compressor. If you are working on a split system, the suction temperature sensor can be clamped to the suction line outside the unit as you normally would. The temperature sensor clamp will accommodate pipe sizes up to one and one eighth inches. If the suction line you are working on is larger than that, the clamping probe may be replaced with any standard K-type thermocouple bead probe that you can tape to the pipe and insolate. 6
Liquid Pressure LIQUID PRESSURE The liquid pressure hose is installed on the high-side service access fitting. Use the discharge line as a second option when a liquid connection is not available. The high side hose should be connected to the liquid line access fitting whenever possible. Discharge pressure may be used whenever a convenient liquid access port isn t available. 7
Liquid Pressure LIQUID TEMPERATURE The liquid temperature sensor is installed on the liquid line, even when measuring discharge pressure. The liquid temperature sensor must be put on the liquid line, near the outlet of the condenser regardless of whether or not liquid or discharge pressure is used. 8
Air Side Sensors AIR SIDE SENSORS The return air sensor measures the temperature and humidity of the air entering the evaporator. The supply air sensor measures the temperature and humidity of the air leaving the evaporator. The return air sensor measures the temperature and the humidity of the air entering the evaporator. It is important that the sensor be placed so it will sense air that is representative of the average condition of the air entering the evaporator. The supply air sensor is usually placed between the evaporator and the fan. It is important to place it so it can measure the temperature and the humidity of the cold air off the evaporator. Be careful to not place the sensor where it can get pulled into the fan. When working on split systems, it can be inconvenient to run wires from the condensing unit, where you will be using the Service Assistant, to the air handler, where the return and supply air measurements are made. When this is a problem, the air side measurements can be measured using the Service Assistant or another tool and hand entered into the Palm Pilot when the air side sensors are not plugged into the tool. This same tactic can be used to enter the ambient temperature in potentially inconvenient situations, like working on computer room units. 9
Using the Tool USING THE TOOL Install all sensors and read the sensor values. Make sure everything looks like it makes sense before thinking about diagnostics or saving data. Before moving on to diagnostics, it is important to make sure all the sensors are properly installed and collecting sensible data. 10
PVS Software Screen Description PVS SOFTWARE SCREEN DESCRIPTION The Service Assistant measures: Suction pressure Liquid pressure Suction temperature Liquid temperature Ambient temperature This is the Sensor Input screen in the PVS software on the Palm Pilot. It displays several values. You will see: Suction pressure; Liquid pressure; Suction temperature; Liquid temperature; and Ambient temperature. 11
PVS software screen description PVS SOFTWARE SCREEN DESCRIPTION The Service Assistant measures: Suction pressure Liquid pressure Suction temperature Liquid temperature Ambient temperature Return air dry-bulb and wetbulb temperature Supply air dry-bulb and wetbulb temperature Also displayed are the dry- and wet- bulb temperatures for both the return air and supply air. Carefully review the data being collected to be sure it is complete and it looks correct. Check to see if the return air is warmer than the supply air to be sure the air side sensors are installed correctly. The suction temperature should be cooler than the liquid temperature and the liquid temperature probably shouldn t be above 150 F as it might be if the liquid sensor were on the discharge line. You will tap the Next button in the lower-right corner of the Palm s screen when you are satisfied with the data. 12
PVS Software Screen Description PVS SOFTWARE SCREEN DESCRIPTION Evaporator Temperature Superheat Condensing Temperature Over Ambient Subcooling The Refrigerant Test screen is key when diagnosing a refrigeration cycle. Notice that there are four bar graphs. The top bar represents evaporating temperature. Notice the abbreviation ET to the left of the graph, as well as the temperature just underneath it: 36 F. The second graph represents superheat and is labeled SH. The third graph labeled COA represents condensing temperature over ambient. The final graph, labeled SC, represents subcooling. 13
In later training, you will find out more about those four values. For the moment we are simply interested in how the graphs are read. Notice that each bar graph is divided into four sections. The line in the middle of a graph is the goal value for that quantity. In this case the evaporating temperature goal value is 45 F. You can see that evaporating temperature may be above the goal or below the goal. In this example our evaporating temperature is 36 F and our goal is 45 F, so we are below the goal. Notice that there is a number to the left of the evaporating temperature goal value. In this case it is 35. Thirty-five is the minimum acceptable value for evaporating temperature. With a minimum acceptable value of 35, a goal value of 45 and a reading of 36, we are above the acceptable value but below the goal. The name for this evaluation is OK-. As you can see, the SH reading is also OK minus. COA and SC are OK+ because the readings are between the goal value and the highest acceptable value. Since all of the graphed values are between the minimum and maximum acceptable values for each quantity, we have a diagnosis of Acceptable. If any of the graphed quantities were below the minimum or LO or above the maximum or HI, a diagnosis other than Acceptable may be given. When you are ready to leave this screen press the Next button in the lower-right. Depending on the application assigned to you, there may or may not be other screens such as a charge test screen or an airflow test screen. However, the final screen in the series will always be the Efficiency and Capacity screen. 14
PVS Software Screen Description PVS SOFTWARE SCREEN DESCRIPTION Efficiency Index Capacity Index Power Used Adjusted Runtime $ Savings Potential This screen shows the impact of running with faults. In the upper left, there is the EI or the efficiency index. The efficiency index is the ratio of how efficient the unit is currently running as compared to how efficient it would be if all the graphed values were at their goals under current driving conditions. The driving conditions are both the ambient temperature and the return air wet-bulb temperature0. These are the conditions that materially affect the expected operation of the air conditioner. In the upper left, under the EI is the CI or the capacity index. The capacity index is the ratio of how much capacity the unit is currently delivering as compared to how much capacity it would deliver if all the graphed values were at their goals under current driving conditions. As you can imagine, if all the graphed values were at their goals the EI and CI would be at or near 100. 15
On the bottom of the screen are the four variables that must be entered in order to convert the EI and CI to savings potential in dollars. The four variables are the stage capacity, the design efficiency, expressed as SEER or EER, the estimated full load equivalent runtime and the cost of energy which is a blended rate in cents per kilowatt hour. The software calculates the dollar value for bringing the EI and CI to 100. In this case a 10 SEER, 7½ ton unit, running 1500 hours per year, on 15 cent kilowatts would cost an additional $681 to run per year in its current condition. If the four graphed values were at their goals, this unit would cost almost $700 less per year to operate and would have fewer service calls. Some of the saved energy comes from raising the efficiency of the unit, lowering the power usage when the unit is running. Some of the savings comes from increasing the capacity, having the unit satisfy its load more quickly and shutting off sooner. The runtime number in this example, 1772 hours, is equal to the estimated equivalent full load runtime divided by the capacity index. So, that s 1500 divided by.84 which equals 1772 hours, the time the unit would have to run to transfer its heat load with its diminished capacity. The last calculated value on this screen shows the power that the unit is currently consuming in three phase kw. 16
Fundamentals for a Valid Test FUNDAMENTALS FOR A VALID TEST Steady state operation Fully loaded units All compressors running Not related to building load Acceptable testing conditions Minimum 55 ambient, 50 return air wet bulb Maximum 115 ambient, 76 return air wet bulb There are several criteria that must be met before a technician diagnosis a refrigeration cycle, regardless of the tools in use. The unit must be operating in steady state, which means there must be no condenser fans cycling and no TXV hunting and the compressor should be running continuously for 10 to 15 minutes prior to testing. A good indication of steady state operation is when the liquid temperature stops changing. The air conditioning unit should be running for some reasonable time before tests begin. If there are several units at a facility to test, they may be started and running prior to testing so that they are already in steady state operation when the technician starts to work on them. This is called the production method, jumping out the next few units, testing-in a unit, and then moving quickly to the next. It is the best way to get many units done quickly. 17
It is always best if tests are run with fully loaded units. A fully loaded unit is one in which all compressors are running, and if there are cylinder head unloaders, that they are loaded. This suggestion is not related to the load in the building. 18
Fundamentals for a Valid Test FUNDAMENTALS FOR A VALID TEST Correct understanding of the unit: Correct refrigerant Correct EER or SEER Fixed orifice or TxV High side pressure measurement: Discharge or Hot Gas line (condenser pressure drop) Liquid line (no condenser pressure drop) There are some other things to be aware of when testing units, again regardless of the tools you are using. These include being careful that the equipment setup is correct. Be sure that you know which refrigerant you are using. You will need to select the correct refrigerant in the Palm. Be sure that you know what metering device is used and that the correct metering device is selected in the software. Be sure that the choice of where the high side pressure information is coming from, discharge or liquid pressure, is correctly defined. We will go through this in more detail later when we set up the unit in the software. There must be a minimum amount of refrigerant flow though the system. This means that there must be at least a 100 pound pressure difference between the high side and the low side of a system for an r22 TxV unit. This is usually only a problem in cold weather. 19
We control head pressure using low ambient accessories. Low ambient accessories control the condenser fans to maintain a minimum head pressure. Since the condenser fans are not operating in a steady way when this happens, the low ambient accessories must be disabled and the refrigeration cycle must achieve steady state operation before testing. 20
Service Assistant Specifics SERVICE ASSISTANT SPECIFICS The Service Assistant measures the ambient temperature and the return air wet bulb temperature. The Service Assistant adjusts the performance expectations based on the driving conditions. Notice the Superheat and condensing temperature over ambient goals Lastly, there is a range of driving conditions under which the unit is testable. The minimum temperature condition is a 55 F ambient temperature and a 50 F minimum return air wet bulb temperature. The maximum temperature condition is a 115 F ambient temperature and a 76 F maximum return air wet bulb temperature. These are the conditions under which the manufacturers publish performance data. Even within this range of acceptable conditions, there will be times where the efficiency and capacity of the machine will not be calculable when working with fixed orifice units. 21
Service Assistant Specifics SERVICE ASSISTANT SPECIFICS The Service Assistant assumes you are working on a fully loaded, constant volume unit. Working on multi-zone equipment or with unloaders complicates the analysis. The Service Assistant is designed to work with constant volume units. These are units that always have the same amount of air passing through them. Multi-zone equipment provides special challenges for the person doing the testing and the person doing the reporting. When working on multi-zone equipment, testing becomes more complicated. When a VFD is controlling the indoor fan motor, the practical solution is to allow the static pressure to be controlled as it normally would be, and then to diagnose each refrigeration cycle one at a time. This is because multi-zone units are sometimes oversized, running all compressors fully loaded and running the fan to its maximum capacity which may be unnatural for that unit. In order to report energy savings in a consistent way, record the setting of the VFD as it was when the test-in data was saved, and then test-out with the same airflow setting. Also record the percent loading of the compressors and estimate the part load capacity. Again, test-out at the same part-load condition. This strategy will cancel out changes to the refrigeration cycle caused by actions of the control system, leaving only the e ffects of the service work that was performed. 22
For example, if there are two, 20-ton compressors in the circuit and only one of them is running, consider it a 20-ton stage for testing purposes. When making the test-out record, set the VFD and the part load condition to be the same as was the case for the test-in record. Put all this information into the comment screen and let the back office figure out the savings estimate. 23
Range of Equipment RANGE OF EQUIPMENT Constant volume units with no size limitation. Rooftop package units Commercial and residential split systems. Air-source heat pumps in cooling mode. Water cooled units with accessory sensors and special palm application. The Service Assistant is tested and approved to work on virtually any size equipment with the following configuration. It must have an air-cooled condenser. It must have direct expansion evaporators (no chillers for now). It must have a positive displacement compressor; that is a reciprocating, scroll, or screw compressor. The Service Assistant will work with all the refrigerants commonly used in comfort cooling including both R22 and R410A. Additionally, it will accept R134A, R12, and some others. Be sure to vent any residual refrigerant from the hoses when changing refrigerants. Don t worry about residual oil. The Service Assistant is tested and approved for air-to-air space cooling applications. That is, DX air cooled commercial rooftop package units, commercial and residential split systems and heat pumps in cooling mode. Additionally, there is a software application available for working on water cooled units that require accessory entering and leaving condenser water temperature sensors. The Service Assistant is not approved for use with ductless split systems. 24
Service Assistant Overview SERVICE ASSISTANT OVERVIEW On average, half of all units would have at least a 20% potential energy savings. The units at a facility are often all in about the same condition, the same age, maintained in about the same way and have about the same runtime. So, expect the units at a facility to be operating similarly. There may be an individual unit here and there that is different, but if the first few units you work on are running pretty well, it is probable that they are all mostly running well. Conversely, if there are lots of problems with the first few, there is a good chance there will be problems all over the roof. There is great value in ranking facilities based on the average energy efficiency of all the units at each facility. By doing this, the units and buildings that are having problems are known and maintenance resources can be deployed where they will produce the greatest return on investment. 25
Doing refrigeration cycle tune-ups can make a lot of sense. A tune-up is a job that is sold with the expectation that each unit will be left running well, or that a repair quote will follow. That job would start with a survey of all the units with the make, model and serial numbers entered into the Palm Pilot along with all the unit set-up information. The test-in is then performed and followed by cleaning both coils. When that is complete, the Service Assistant is used to analyze the unit; then, charge and airflow adjustments are made. The test-out data record is saved and comments are added to explain remaining service issues. The reporting will show the customer a more complete picture of the state of their units and estimate the energy that will be saved because of the tune-up. In doing that, the remaining repairs are often approved and the rate of service calls for comfort issues is noticeably reduced. 26