Measuring airflow for residential forced-air systems for HVAC professionals

[ Music ] >> hi, i’m Scott Pigg. >> and i’m John Viner. We’re each from Seventhwave. As a heating and coolingprofessional, you’re employed difficult at what you do and take pridein getting the job done correct. That’s why we’re here to talktoday about measuring air waft for residential airconditioners and warmth pumps. We’re no longer selling whatever and we don’t represent anyone’s merchandise or services.However as independent energyefficiency researchers, we have now had the opportunity tomake measurements on enormous quantities of residential systems. And we might prefer to sharethat expertise with you. >> in this video, we’ll talk about why proper airflow is important, the way it influences method efficiencyhere, within the upper Midwest, and we will go throughthe pros and cons of different waysto measure air drift. >> All right. Let’s get started. >> best. >> k. Right here we’re looking at a high-quality new excessive efficiencygas furnace that additionally serves at the air handler for a two-and-a-half of-toncentral air conditioner.The question is, in the summeris this furnace producing the right amount of air flowfor the cooling process? We will discover in a minute,once we honestly experiment it. But first, let’s talk about howmuch air drift we’re looking for and the consequences of nothaving the right quantity. So, you traditionally already comprehend that producers aregenerally looking for somewhere in the variety of 300 to 400cubic feet per minute per ton of cooling capacity, interms of cooling air float. So, right here, we would belooking for whatever within the 800 to 1,000 CFM range. And i’m definite you alreadyknow the consequences of getting air flowthat’s too low. You’re watching at very coldevaporator coil temperatures, and potentially a frozencoil and all the issues that go together with that. However after we test systemshere, in the upper Midwest, what we clearly to find isthat we’re more likely to seek out air flowthat’s too excessive.And that is in general becausehere, where it is bloodless, we have a tendency to put in bigfurnaces with massive blower motors. And we pair them up withsmall air conditioners. And that’s dangerous, too, becausehigh air float creates its possess set of problems. Quantity one, it hurts theability of the process to dehumidify the air. And it also approach so much moreblower electricity going through the procedure. And it simply makes for anoisier overall experience and no more comfortable overallexperience for the house owner.So, we by and large find that abouthalf of methods that we experiment in our study on this a part of the nation haveair drift that is larger than four hundred CFM per ton. But most effective about one in ten haveair go with the flow that is under 300 CFM per ton. After we right thoseair waft issues, we in general see an improvementin effectivity efficiency of about 5 percentage. However we’ve got seen increasesas a lot as 30% when air flow wasreally a long methods off. All proper. So, we’ll take a appear and see how good this systemis doing, in phrases of air waft, by means of measuring it with anumber of special methods. There are tons of different waysto go about measuring air flow. Here, we’re going toconcentrate on just a few. We’ll talk about usinga calibrated float plate. We will appear at air float bymeasuring pace in the ducts.We can look at staticpressure and how we will use that with manufacturer’sliterature, to estimate air flow. We are going to speak about including upair flow by using measuring go with the flow from individual registers. And finally, we are going to appear atthe temperature cut up system for measuring air flow. Let’s get began. >> Let’s start with this gadget,which is a calibrated float plate that takes the placeof the filter.Truly, air drift isvery predictably correlated with the stress dropacross this plate. So, simply via measuringthe pressure drop, we will get a good size of the whole air flowgoing by way of the method. We rather like this device. And we use it oftenin our research. It is correct andrelatively effortless to use. Within the kit, you get truly,two glide plates, exclusive sizes with a bunch of spacersthat allow you to adapt the precise plateto any filter slot dimension. The predominant downside isthe up-entrance cost. Which is set $800, now not including a gooddigital manometer. Which might be adigital, or an additional strategy to say it, is a pressure gauge. The one we’ve got is made by using the same manufactureras the drift plate. It’s correct right here,that we are going to be utilising. So, it may do the stress toair waft translation for us and give us a directreading of air float. We mix the waft platewith a stress gauge. We are able to read CFM, cubicfeet per minute, instantly. So, let’s take alook at it in motion.Okay, i go todrill the hole for the supply pressurereference tap for the TrueFlow plate. This permits me to comprehend thesupply strain at this point with the filter in place, and with the TrueFlowplate in situation. Which. [ Drilling Sound ] by using measuring that strain,i can see the difference in resistance between thefilter and the pressure plate. Helps me calibratethe air go with the flow and CFM. I’ll stick the staticpressure probe in, factor it in the direction of the air move. So, now that thepressure faucet is in place in my give trunk line. I’ve turned the air handler on. We’ve turned it in the coolingmode to get cooling velocity. My digital manometer isreading static pressure within the deliver trunk withthe filter in situation.I’m going to hit enter so thatmy digital manometer documents that stress. Subsequent, i go toremove the filter and insert the TrueFlowpressure plate. So, now that i have theTrueFlow plate established, then I’ve blanketed up thefilter slot opening simply to eliminate any leakagethat could occur there. Now, I hook the TrueFlow plateup to my digital manometer. My digital manometer is ready toread the exact drift plate. It’s been programmed withthe suitable flow plate. We hook up the pressurehoses on both aspect of the pressure plate tothe digital manometer. And the manometer goes toread out cubic toes per minute, CFM, of air flow acrossthat pressure go with the flow plate.Right now, we are readingseven ninety, 700 and ninety-eighthundred CFM, i have right here. So, that’s right on the lowend that we’re asking for, for this two and a half tonair conditioning system. That is it. It is very simple, handy to make use of. And as we statedearlier, very correct. >> okay. So, our second way of measuring air flowinvolves measuring the velocity of the air in the ductwork. If we all know the velocityof the air that’s going by means of a element of duct,in say, ft per minute. And we all know its crosssectional discipline in square toes, we are able to put those two piecesof information collectively and calculate cubicfeet per minute. Now, there’s a couple ofdifferent ways which you could go about getting at this velocity. One is to make use of a pitottube, like this one, where you’ve a shorttube with a gap ultimately that you simply face intothe air movement.And the better the pace, the greater the pressureon that gap. And by means of measuring that pressure, that you would be able to translatepressure into pace. But at present, we’re going touse yet another gadget. And that is thishot wire anemometer. Now, this thing works byhaving an awfully tiny little wire in its tip that’s heated. And because the air goes acrossthat heated wire, it can be cooled. And through measuringthat cooling effect, we can translateinto air speed. Now, it could be greatwith both the pitot tube or this anemometer, ifwe would simply stick this into the ductworkin any given spot, take one studying,and be executed with it.But the trouble is that airvelocity varies on the inside of the duct from one part to theother and from front to back. And mostly, if varies quite a bit. So, if we rather care aboutgetting a good measurement of air float, we’re reallygonna have got to make a quantity of measurements to get theaverage speed of the air through that section of duct. So, ok. So, here we’re onthe bottom of the furnace. And i’ve marked the locationof 5 holes that i am going to drill in this best longstraight component to return duct. And those holes are notexactly within the same place. We is not going to go in today, whythey are the place they’re. But which you can look that up,on-line for more detail.But we’re simply going to goahead and drill five holes. And we will run ourhotwire anemometer by means of each and every one among them. [ Drilling Sound ] okay. So, I’ve drilledmy 5 holes. And now, what i’ll do istake this probe, and i’ll prolong it all the wayinto each one of the most holes. And then, slowly withdrawit even as we’re using our anemometer, right here, toaverage the pace throughout each one of those holes. Alright, last gap. So, we have achieved ourfive traverses by way of the five holes. And now we have got ouroverall common pace of 540 feet per minute. And when you multiply thatby the sides of the ductwork, which is ten inchesby 23 inches, that works out tojust about 860 CFM. However i will be able to inform youthat we saw the whole lot from one hundred ninety ft per minute,with the speed, there, to over 800 ft per minute. And one factor we can exhibit you, is considering the fact that this littleunit can data log and we recorded these traverses,we will show you a graph of what these five velocitytraverses appear like.So, another way tomeasure air flow is to take some staticpressure measurements at exclusive placesin the approach. After which, take that informationto the brand literature the place we are able to appear up air go with the flow asa perform of static pressure. And we’ve got particularly gottwo alternative, here. One is this static pressure riseacross the air handler, itself. And the opposite one would bethe static pressure drop across the evaporator coil. On this case, we’regoing to make use of the upward push across this furnace unit, the place we have now theliterature to be had. And you can see that we’ve put astatic pressure probe down here in the blower return cupboard. And then, we haveanother one up right here in between the furnaceoutlet and the backside of the evaporator coil. And we have the process running. And you can see that we’remeasuring just a bit below half of an inch of watercolumn throughout this method. So, with the manufacturerliterature in hand, we can seem up, basedon the pace faucet, the model of the furnace, and the static pressurerise that we’re seeing.And we read off of the chart that we’re seeingabout 975 CFM. Which is just a little bithigher than we measured with the float plate, butin the equal ballpark. Now, this procedure will work well if you have the manufacturer’sliterature. It won’t work at all, if youdon’t have that available. And quite often, it can be probablypreferable you probably have a choice, to make the measurement usingthe whole external static of the furnace, rather than thepressure drop across the coil.On the grounds that with the coil,that you may have problems with, is the coil wet,is the coil dry? And if that coil has beenin place for a even as, it is going to have somedirt buildup on it. And that could influence thereadings that you just get. >> ok. Yet another manner tomeasure air drift is at each and every of the registers usingour hot wire anemometer. The hot wire anemometermeasures feet per minute, if we know the register dimension and its net free areain square inches. So, it’ll require going to the brand’sspecification sheet to be certain we know the openarea of the face of this grille. The hotwire anemometermeasures toes per minute. And we have got to do atraverse throughout that register to get an averagefeet per minute. Then, we multiply that bythe square toes opening of the register. And we then are equipped tocalculate cubic feet per minute. So, i will start our traverseacross this register. And we are going to take a couple of passes.Now, measuring airflow like this is first-class for diagnosing comfort problemsand distribution disorders. But we do not generallyrecommend it for getting at approach air float backat the air handler. It simply takes too long tomeasure all the registers in the residence, and there’s toomuch uncertainty from including up all these individualregister measurements. Might be you are questioning howaccurate these approaches are. And we had been, too. So, we made one extrameasurement on this method, making use of a calibrated fan tomatch the approach strain and provides us an awfully accuratemeasurement of system flow. In comparison with that gold common,the opposite measurements are in reasonable contract. The go with the flow plate measurementwas slightly lower. And the size founded on static pressurewas slightly greater. But they have been allwithin ten percentage. We didn’t try to measure systemflow from register measurements, seeing that if wouldhave taken too long. And the temperature break up methodis just a hallmark of glide, no longer a right away measurement. Plus, we couldn’t do that experiment in view that the indoorconditions weren’t right. As a rule, we favorthe waft plate test.Considering it takes a fast andreasonable accurate value. The hotwire anemometerapproach will also be accurate, but it takes more time. The static pressureapproach is the quickest. But we’ve observed that thereadings can fluctuate some, depending on the place youmeasure the static strain. And you have to havean air glide chart for that equipmentyou’re measuring. But our checks on thisparticular system show that if you happen to take yourtime to do it proper, that you would be able to get good air flowmeasurements making use of a quantity of extraordinary tactics. One different notice; if you’re wayabove sea degree, you would have got to make changes forair density at altitude. >> One final approach for assessing cooling air flowis a relatively easy one to do, but which you can handiest do itunder distinctive conditions.And it can be called thetemperature split procedure. And it can be quite a bit likemeasuring temperature rise when you are assessingair float for heating. In that we’re lookingat the change between the warm returnair that’s coming back to the procedure, and the coolsupply air that is popping out the backside ofthe evaporator coil. That temperaturedifference it known as the ”temperature cut up”. So, if we have a method that’srunning quite high air flow, that air is going over thatevaporator coil very swiftly and it is no longer gettingcooled down very so much.So, this temperature difference,or this temperature split, will be on the low facet. On the other hand, if we now have asystem with very low air drift, that air is residing on thatevaporator coil for a very long time, it can be getting cooled down a lot. So, we will see alarge difference between the return air and thesupply air that’s popping out. And via gauging the magnitudeof that temperature break up, we are able to get a sense ofwhether our air glide is in the correct ball park. But there is a rub. Simplest a part of theenergy that’s going into this cooling coil goes to truely cool thetemperature of the air. The relaxation of it’s going toremoving humidity from the air and it would not reducethe temperature.So, depending on how humidthe air is, that is coming into the system, it’s going to affectthe target temperature break up that we’re looking for. If we’ve got very dry air that’scoming in, we are going to be watching for an extraordinarily excessive temperaturesplit for our goal. Alternatively, if we havereally humid air that’s coming again on the returnside, we’ll be looking for a fairly lowtemperature break up. So, to make thismeasurement, all we quite have got to do is measure thetemperature on the deliver side.Do not forget, measurethe temperature, the dry bulb temperature, and the moist bulb temperatureon the return facet. After which, use our targettemperature break up desk to appear up, established onreturn dry bulb temperature and return wet bulb temperature,what our target quantity is. After which, compare that towhat we genuinely measure. But there may be one different thingthat we have to fear about. If we see a low temperaturesplit, it could be thatair flow is excessive, however it might also besomething else that is unsuitable with the procedure. For illustration, if refrigerantcharge is low, our procedure may not be puttingout its full quantity of cooling, that in and of itself will leadto a low temperature cut up. And if we’re no longer careful,we could misdiagnose that as an air drift problem, as a substitute of what’s reallya refrigerant challenge. However, if we seea high temperature split, then that is a prettygood indication that we’ve got low airflow on our approach.Now, the final consideration is that our temperature splittarget table handiest works for a distinctive variety of dry bulb and wet bulb returntemperatures. And if we’re outside ofthat range, we’re now not going to be capable to makethat size. And that’s the cases,here today. We’re off the chartsas far as being equipped to get a target temperaturesplit. So, we is not going to be ableto measure it, today. Well, there you may have it. One of the vital bits and bobs of more than a few ways tomeasure air float. I hope this conjures up youto start measuring air float on the methods thatyou set up or provider. >> when you observed thisvideo priceless, please watch our othervideos related to details of our study findingsand pointers for householders. Thanks, for staring at. [ Music ].

Leave a Reply

Your email address will not be published. Required fields are marked *