Presentation on theme: "Performance measurement"— Presentation transcript:
1Performance measurement SERVICE PROCEDUREAirflow measurementSystem chargingPerformance measurementLIVE: INTRODUCTIONTHANKS LAURA AND GOOD MORNING !! I’M GLEN MCDOWELL AND WELCOME TO OUR BROADCAST. I’m excitied about the oportunity to discuss how to perform some of the most important service prodedures of the heating and air conditioning trade. anyone that services heating and air conditioning equipment must know how to perform these procedures if they are to be successful.BEGIN POWERPOINT:I’ll be discussing airflow measurement first, then James Jarman will talk about system charging and I’ll be back to finish up with performance measurement.Proper airflow should be considered the most important factor in delivering comfort to the space being conditioned.Lack of airflow causes the lose of sensible capacity, poor system performance and increases the risk of compressor failure.Excessive airflow reduces latent capacity, humidity removal and the overall comfort level in the space.THERFORE:
2Airflow measurementAn accurate airflow measurement must be performed before the system can be properly charged with refrigerant or before any attempt is made to measure performance.READ SLIDE FIRST: THEN LIVEFor normal residential cooling and heat pump applications, proper airflow quanities range from cubic feet per minute per ton of system capacity.All the performance curves for charging and calculating superheat that we’ll be using in the show today are based on a nominal 400 cfm per ton.Knowing how to accurately measure the amount of airflow being delivered to the space is the first step in properly charging a sysyem with refrigerant or evaluating systems performance.Let’s look at the equation for calculating cfm.
3BTUH (OUTPUT) CFM = TEMP DIFFERENCE X 1.08 Airflow measurementBTUH (OUTPUT)CFM = TEMP DIFFERENCE X 1.08POWERPOINT:The equation says that Cfm (cubic feet per minute) of air is equal to the btu per hour output divided by the temperature difference or delta “t” times 1.08.1.08 Is the specific heat of one pound of standard air at 70 degrees at a barametric pressure at sea level of Inches of mercury.Btu per hour output is calculated by multiplying the input times the fuel effeciency.LIVE:We’ll come back to the CFM equation a little later but let’s first look at some of the methods of calculating btu per hour input.
4Measurement Methods power measurement - watt-hour meter electric resistance heat and heat pumpspower measurement - volt-ampereelectric resistance heatclocking a gas meternatural gas furnacescalculating input by orifice capicitypropane gas furnacestotal static pressurePOWERPOINT:The first method is a power input measurement using a residential watt-hour meter. This method is used to measure the instantaneous power consumption of an alternating current load. We’ll look at how to use this method to determine the kw input where electric resistance heaters are installed and later to calculate the heating capacity of a heat pump.The next method (volt ampere) is the easiest to use but slightly less accurate. We will use this method to determine the kw input where electric resistance heaters are installed by measuring the applied volts and amperes and convert the result into btuh input.For natural gas furnaces, we’ll discuss how to clock the gas meter outside the structure to determine the input rate in cubic feet per hour of a natural gas appliance and convert the input rate to btu per hour.Next, we’ll learn how to calculate CFM for furnaces that have been converted to propane fuel.And last, how to measure total external static pressure and determine airflow using published performance data.O.K.... Let’s get started with a look at the watt hour meter.
5POWERPOINT:We’ve all seen electrical watt-hour meters mounted on the outside of homes, apartments and businesses, but let’s take a closer look. Notice that the meter disc has a black mark on it. It rotates at a rate that’s slow enough to count the revolutions and record the time with the second hand on our wrist watch. Note the kh factor on the lower right portion of the meter face. It will normally be 7.2 Or 3.6 Depending to the type of meter.LIVE:Clocking the watt-hour meter is a quick and accurate way of calculating watt consumption. However, before you use this procedure be sure you take the following precautions first. Check with the homeowner or building manager before proceding:
6WATT-HOUR METERPower input measurements, by the watt-hour meter require power interruption to all appliances in the structure except the indoor fan motor and electric heaters.Do not turn off power to:Life support devisesAppliances subject to damage from power interruptionPOWERPOINT:This procedure requires that power be interupted to all appliances in the structure except the indoor fan motor and the electric resistance heaters.Be sure YOU DO NOT turn power off to life support devices such as kidney dyolisis machines, heart monitors, ect.Or appliances that are subject to damage from power interruption.
7WATT-HOUR METERSet the thermostat to heat or emergency heat and adjust the setpoint to 90 degrees.Locate the watt-hour meter serving the structure.Clock the black mark on the meter disc for 20 revolutions using a stop watch or the second hand on your wrist watch.POWERPOINT:Once you have the customers approval: set the thermostat so that the heating cycle will stay on during the test Locate the watt-hour meter and record the kh factor on the meter face. Then record how many seconds it takes for the meter disc to make 20 revolutions. Always use a minimum of 20 revolutions for an accurate calculation.Once you record the kh factor and the time required for 20 revolutions you are ready to use the equation to determine the kw input for the electric resistance heaters. Let’s look at the equation.
8Power Input Formula Revolutions x KH factor x 3.6 20 revolutions KW (KILOWATT) INPUT =Seconds20 revolutionskh = 7.265 secondsKw or kilowatt hours is equal to the number of disc revolutions times the kh factor stamped on the meter face times a constant of 3.6. This is divided by the time in seconds required for 20 revolutions of the meter disc. The constant of 3.6 In the equation converts watt seconds into kilowatt hours.As an example let’s use 20 as the number of revolutions and a kh factor of The time recorded for 20 revolutions is 65 seconds......Let’s use the equation to calculate the kw input for our example.
9Power Input Formula 20 rev x 7.2 kh x 3.6 518.4 KW = = = 7.97 kw 65 65 20 revolutions times 7.2 kh times 3.6 is equal to divided by 65 seconds or 7.97 Kw. The next step is to convert 7.97 Kw to btu per hour input and then multiply that times the fuel effeciency to get the output we need for our CFM equation.
10electric resistance heat is 100% effecient 1 KW = 3413 BTU PER HOUR7.97 kw x 3413 = 27,202 btuh (input)electric resistance heat is 100% effecientinput = outputPOWERPOINT:One kw is equal to 3413 btu per hour......So multiply 7.97 Kw times That gives us 27,202 btu per hour input electric resistance heat is 100% effecient so input is equal to output.LIVE:All right that’s the top part of our CFM equation.... Let’s finish our example before we go on to the next method. Our next step in our airflow equation is to find out what the temperature difference is accross the heat source so let’s take a look at a drawing of a typical air handler installation.
11POWERPOINT:Always take the return air temperature measurement as close to the equipment as possible.This eliminates any temperature error due to heat lose or gain in return air duct work between the return air opening and the equipment.Take Return Air Temperature Measurement as Close to Equipment as Possible
12Do not take measurement while in radiant heat area (line of sight). Radiant heat will bias your temperature measurement and cause error in your calculation. Measure the supply air temperature in the trunk and branch ducts and stay within 6 feet of the heat source.Do NOT Take Temperature Measurement in the Line of Sight of Heat Source.
13Take an Average of ALL Supply Duct Temperatures Take an average of all supply duct temperatures within 6 feet of the heat source. Take as many readings as necessary. add the readings together and divide by the number of measurements to get an average.Take an Average of ALL Supply Duct Temperatures
14Use a Calibrated Thermometer to Measure Temperature. Pocket thermometers are ok for this procedure as long as they are calibrated but are not as reliable as an electronic temperature analysizer.The more care you take with your measurements, the more accurate your CFM calculation is going to be.Use a Calibrated Thermometer to Measure Temperature.
15Use the Same Thermometer for ALL Temperature Measurements Using the same thermometer eliminates error between instruments.LIVE: SHOW THERMOMETERSNow...Let’s go back to our formula for calculating cfm and finish our example.Use the Same Thermometer for ALL Temperature Measurements
16Airflow measurement BTUH (OUTPUT) CFM = TEMP DIFFERENCE X 1.08 EXAMPLE:27,202 BTUH (output)27 degrees delta “T”Cfm is equal to the btu per hour output divided by the temperature difference times 1.08.We calculated 27,202 btuh output earlier so we can plug that in on the top of our equation. And let’s say that we measured a 27 degree delta T or temperature difference . Let’s see what the calculated CFM comes out to be.
17Airflow measurement 27,202 BTUH 27,202 BTUH CFM = = = 933 CFM X27,202 btu per hour output divided by 27 times 1.08 is equal to 27,202 divided by or 933 CFM.
18Measurement Methods power measurement - volt-ampere POWERPOINT:The next method of calculating btu per hour input is one of the most practical ways for the service technician to measure airflow for air handlers with strip heat. The tools required are a volt meter, an accurate thermometer and a clamp on ampere meter.LIVE:When using this method, it’s not necessary to interrupt power to other appliances in the home. The volt-ampere method measures the instantaneous power consumption for electric resistance heaters like the last method. Only this time, we will need to have access to the high voltage circuit wiring connected to the electric resistance heaters in the air handler.Let’s look at the steps required to get the data we need for our equation.power measurement - volt-ampereelectric resistance heat
19POWER MEASUREMENT VOLT-AMPERE set the thermostat to the heat or emergency heat mode, in the case of a heat pump, so that only the resistance heaters and the fan motor are activiated.measure the applied voltage to the resistance heaters while they are operating.measure the current draw for each circuit if more than one and add them together.measure the temperature difference entering and leaving the air handler.POWERPOINT:First, set the thermostat so the heating cycle will stay on during the test. Make sure that only the strip heaters and the fan motor are operating.Next measure the applied voltage at the resistance heaters high voltage connections. Do not use voltage rating information on the nameplate.Using your clamp-on ampere meter, measure and record the current draw for each circuit and add them together.And finally, measure and record the temperature difference accross the heat source.
20POWER MEASUREMENT VOLT-AMPERE multiply the applied volts times the total current draw (amperes)VOLTS X AMPERES = WATTSBTUH (OUTPUT) = WATTS X 3.413Next convert the applied voltage and amperage to btu per hour by multiplying volts times amperes to get watts. One watt is equal to Btu per hour. Remember that electric resistance heat is 100% effecient so input will be equal to output. Plug your btuh output calculation into the CFM equation and divide by the temperature difference times 1.08 to find CFM.O.K Are ready to move on to gas furnaces and clocking the gas meter?
21Measurement Methods Clocking a gas meter Natural gas furnaces .For natural gas furnaces, we will discuss how to clock the gas meter outside the home to determine the input rate in cubic feet per hour for a natural gas furnace and convert the input rate to btu per hour.let’s look at the gas meter.
222 cubic feet per revolution The gas meter, like the watt-hour meter is an instrument that can be used to accurately measure fuel consumption. With this method, time the two cubic foot dial on the meter for one revolution and calculate the btu per hour input. Before we use this method, we need to do several things first.2 cubic feetper revolution
23GAS FURNACE INPUTmake sure no other appliances are on during the test.set the thermostat to heat mode and 90 degrees.record the seconds required for one revolution of the 2 cubic foot dial on the gas meter.determine the gas flow rate in cubic feet per hour from the following equation or use a gas flow table.The first thing we want to do is to turn all other gas consuming appliance in the structure to the pilot position. Pilot gas consumption will be insignificant for this test.Activate the heating cycle so the furnace will stay on.Locate the 2 cubic foot dial on the gas meter serving the structure and record the seconds it takes for one complete revolution.now we can use the recorded data to calculate the gas flow rate.
24GAS FURNACE INPUT 2 cu. feet per revolution x 3600 cu. ft per hour = Cubic feet per hour is equal to the cubic feet consumption per revolution times 3600 (3600 converts hours into seconds) divided by the time in seconds per revolution.As an example, let’s say that we recorded 60 seconds for one revolution of the gas meters 2 cubic foot dial.
25GAS FURNACE INPUT 2 cu. feet per revolution x 3600 cu. ft per hour = time (in seconds) per revolutionCubic feet per hour is equal to the cubic feet consumption per revolution times 3600 (3600 converts hours into seconds) divided by the time in seconds per revolution.As an example, let’s say that we recorded 60 seconds for one revolution of the gas meters 2 cubic foot dial.
26GAS FURNACE INPUT example: 1 rev. (2cu.ft. dial) = 60 seconds 2 cu. feet per revolution x 3600cu. ft per hour =time (in seconds) per revolutionexample: 1 rev. (2cu.ft. dial) = 60 secondsCubic feet per hour is equal to the cubic feet consumption per revolution times 3600 (3600 converts hours into seconds) divided by the time in seconds per revolution.As an example, let’s say that we recorded 60 seconds for one revolution of the gas meters 2 cubic foot dial.
27GAS FURNACE INPUT 2 cu. ft. per revolution x 3600 cu. feet per hour = cu. feet per hour = = = 120 CFHCubic feet per hour is equal to 2 cubic feet times 3600 divided by 60 seconds. That’s equal to 7200 divided by 60 or 120 cubic feet per hour input.Now let’s look at the easy way to determine cubic feet per hour.
28Using the chart in your handout, find the 60 seconds we recorded for one revolution of the 2 cubic foot dial and read the cubic foot per hour input in the column to the right.Once we have calculated the input rate in cubic feet per hour, we need to convert the cubic feet per hour to btu per hour input.LIVE:BTU content per cubic foot of natural gas may vary from one day to the next due to demand load usually caused by severe winter weather conditions. Gas utility companies mix inert gases with the natural gas to maintain supply line pressure during periods of heavy demand on the gas well. It’s a good idea to check with the gas utility company first for the correct btu content per cubic foot for better accuracy. An alternate is to use an average of 1000 btu per cubic foot for your calculation when the actual heat content cannot be obtained.O.K. Let’s do some more math....60 SECONDS120 CFH
29GAS FURNACE INPUT BTUH = HEAT CONTENT X CUBIC FOOT/HOUR BTUH = 1000 BTU X 120 CFH = 120,000 BTUH (INPUT)BTUH (OUTPUT) = BTUH (INPUT) X EFFECIENCYUSE A MIN. OF 80% EFFICIENCY FOR NAT. GASUSE FURNACE AFUE EFFECIENCY IF HIGHER THAN 80%The btu per hour input is equal to the heat content per cubic foot times the calculated cubic foot per hour. Using the average of 1000 btu per cubic foot times 120 cubic feet per hour we calculated an input rate of 120,000 btu per hour. LIVE:At this point, it is important to check the input rating on the nameplate of the furnace. The calculated input should be within 2% of the input rating stamped on the nameplate. If it’s not, the furnace gas outlet manifold pressure should be adjusted to the correct pressure. If the calculated input rate is more than 7% of the nameplate, the furnace probably has the wrong orifices installed.Natural gas has a minimum effeciency of 80 %. Don’t confuse this with the furnace AFUE effeciency. Furnaces will have higher or lower AFUE effeciency ratings due to design differences such as cabinet insulation, blower motor effeciency, ignition controls, heat exchanger designs, etc. However, we use the furnace AFUE effeciency when it is higher than 80%.Ok let’s work an example. Using the 120,000 btuh (input) we calculated previously. What would be the CFM for a 92% effecient natural gas furnace with a temperature rise of 55 degrees?
30GAS FURNACE INPUT 120,000 BTUH X 92% CFM = 55 X 1.08 110,400 BTUH (OUTPUT)CFM = = 1858 CFM59.4POWERPOINT:120,000 Btu per hour input times the furnace effeciency of 92% divided by the temperature rise of 55 degrees times 1.08 Is equal to 110,400 btu per hour (output) divided by 59.4 Which is equal to HEATING CFM.O.K...here is an important point to remember!!!...if we are trying to calculate HEAT PUMP OR COOLING airflow, change the blower speed tap to the correct fan speed BEFORE YOU CONDUCT THIS TEST.What do we do if the furnace is coverted to propane?
31Measurement Methods calculating input by orifice capacity propane gas furnacesPOWERPOINT:LET’S look at how to calculate btuh output for furnaces that have been converted to propane fuel.LIVE:Since there won’t be a gas meter to clock, we have to calculate the input by input pressure and burner orifice capacity.Let’s look at the steps required to do that.
32CALCULATING CFM AND INPUT BY ORIFICE CAPACITY determine the burners orifice size.count the number of orifices in the furnace.set the gas valves outlet manifold pressure to 11 inches of water column.set the thermostat to heat mode and 90 degrees.measure the temperature difference entering and leaving the furnace.POWERPOINT:First we need to record the burner orifice size. That’s the brass spud connected to the gas manifold. It will have the drill size stamped on it.Next count the total number of orifices in the furnace.Then, make sure that the gas valve outlet manifold pressure is set to 11 inches of water column.Next, set the thermostat so that the furnace will stay on during the test. Be sure you are using the blower speed tap that you want to measure for CFM.And finally, record the temperature rise accross the furnace heat exchanger.
33CALCULATING CFM AND INPUT BY ORIFICE CAPACITY determine the btu per hour input for the selected orifice size using table f-2 in apendix f of the national fuel gas code.multiply the btu per hour input times the number of orifices counted in the furnace.multiply the btu per hour input times the furnace effeciency (minimum 80%).Once you have collected the data, you can use table f-2 in your handout to determine the btuh input for the selected orifice size. The complete table can be found in appendix F in the national fuel gas code.Next, multiply the btuh input times the number of orifices in the furnaceAnd finally, multiply the caluclated input times the furnace AFUE efficiency. Remember to use a minimum of 80%.As an example, let’s say that our furnace using LP gas has a # 55 orifice size and we counted 5 orifices in the furnace.
34table F-2Table f-2 says that a # 55 orfice using propane fuel with a gas valve outlet manifold pressure of 11 inches of water column has an input of 21,939 BTUH.5 Orifices times 21,939 is equal to 109,695 BTU per hour input.To find CFM plug 109,695 BTUH into the top of the CFM equation and multiply times 80% or the furnace AFUE effeciency, whichever is higher and divide by the measured temperature rise times 1.08.
35Measurement Methods total external static pressure Our final method for calculating CFM of airflow is the Total external static pressure method. The static pressure method is the least reliable of all field methods of measuring airflow.What is static pressure?
36STATIC PRESSURE Definition: The pressure measured above or below atmospheric pressure created by the blower independant of air velocity. It is exerted in all direction to the inside walls of the ductwork and is measured at a 90 degree angle to the airflow.think of a baloon. static pressure inside a baloon pushes the inside walls outward at an equal pressure in all directions. likewise, air being pushed or sucked down a duct by a blower causes the ductwork to expand or contract. Let’s look at how to measure total external static pressure.
37Total external static pressure is measured by connecting an instrument like an incline manometer or magnahelic to a sensor tip in the return duct and one in the supply duct at the same time. When connected in this manner, the fluid in the instrument is pulled down the scale by the return pressure and pushed down the scale by the supply pressure. The results is a total of both pressures added together.Show instruments
38Measure return static pressure close to air handler or furnace cabinet. messure return static pressure as close to air handler or furnace cabinet as possibleMeasure the return air static pressure away from duct work fittings but within several inches of the air handler or furnace cabinet. There are a variety of sensor tips. It can be as simplea as a short 1/4 inch diameter tube that is square and bur free on the end and connected to the instrument by a flexible hose. The sensor tip must inserted at a 90 degree angle to the airflow. A variety of sensor tips are available from dwyer instruments that will accomplish this task and improve accuracy.Show trail tails and sensor tips
39Measure supply static pressure downstream of all pressure drops Measure supply static pressure downstream of all pressure drops. Average readings where turbulant airrflow is presentthe supply static pressure will be turbulant and erratic in the supply plenum. measure suppy static within several inches of the outlet of the air handler or furnace coil. it will be necessary to take several individual measurements accross the plenum area as illustrated in the drawing and average the readings together to improve accuracy. once the total external static pressure measurement is recorded, we can compare the result to the manufacturer’s published airflow performance data to determine CFM of airflow.
40PRODUCT DATA TWEO48C140B - BAY96X1415 PUB # 22-1298-03 PAGE # 8 EXAMPLE:Measured external static pressure = .5 In. W.C.Blower set on high speed tapAs an example let’s say that we measured an average total external static pressure of .5 Inches of water column.Our air handler is a TWE048C140B0.It has a BAY96X1415 accessory heater installed.Let’s look at the performance data to get our airflow.SHOW PRODUCT DATA:
41Product Data TWE048C140B - BAY96X1415 EXAMPLE:Measured external static pressure = .5 In. W.C.Pressure drop accross heater = .13 In. W.C.Final static pressure = .63Airflow = approx CFMPRODUCT DATA SHOWS BETWEEN 1600 AND INCHES W.C.NOW LOOK ON PAGE 10 TO GET THE PRESSURE DROP FOR THE CFM. THATS ABOUT .13ADD .5 PLUS THE .13 FOR THE HEATERS FOR A FINAL STATIC PRESSURE AND GO BACK TO PAGE 8..63 WILL GIVE US A CFM OF APPROX 1550 CFM.
42TUD100C948H - TXC049C4HPB EXAMPLE: Measured external static pressure = .30 In. W.C.Blower set on black - high speed tap
43Product Data TUD100C948H - TXC049C4HPB EXAMPLE:Measured external static pressure = .30 In. W.C.Pressure drop accross coil = .30 In. W.C.Final total external static pressure = .60 In. W.C.Blower set on black - high speed tapAirflow = 1595 CFM
44Product Data TUD100C948H Airflow = 1550 CFM EXAMPLE: Temperature rise = 47 degreesAirflow = 1550 CFM