hey thanks for watching this video this is one class from the 2022 hvacr symposium in claremont florida we have the symposium every year and so to find out more information kind of upcoming go to hvacrschool.com symposium big thanks to our sponsors for this event which was accutools and truetech tools they're the two title sponsors that made the event possible in this great session rick streaker talks about the impact of static pressure on fan and blower motors appreciate everybody being here i want to thank brian and his team for uh for doing this i know a lot of you guys have come a little bit of a distance to participate in this but i think it's a great event for all of us so again my name is rick streaker i'm out of georgia and i started out in the motor shop in 1969 in dayton ohio and i worked for fasco and also ao smith before going to work for packard so uh the impact of static pressure on fan and blowers well that's easy that's easy stuff i think first of all let's take a look at the refrigeration cycle because when we look at the refrigeration cycle we can see where the fans and blowers come into play when we look at this cycle what what those fans and blowers are doing are helping us move air over our coils in order to make that refrigerant more effective in our heat transfer so we use fans on the condensing units how about on the evaporator side do we use fans or do we use blowers in refrigeration fans or blowers in refrigeration fans but don't we use blowers in hvac so we use fans on the condenser side for both the refrigeration and hvac applications with condensers but we use fans in refrigeration and blowers and hvac why is that why don't we use fans for everything wouldn't that make things a little bit easier why don't we use fans in heating and air because we're moving that air much greater distance aren't we so we're taking that air from maybe an area over here in our living area and moving it way across the house and how do we get that there we go through ducks you know now what do those ducks do what does that do to our airflow it helps restrict the air flow doesn't it so the air doesn't want to move through those things the ducts don't don't want the air to move through there and so in order to get the air all the way over there we have to pressurize it and that's what a blower does a pressure that blower is going to pressurize that air it'll squeeze it down and move it help us to move that air greater distances than we can with the fan blade the fan blade isn't able to effectively move it through those ducts because of the static pressure so we use axial fans has anybody heard that term before axial what is an axial fan chris you know what an axial fan is propeller blade so it looks like this now we call it an axial fan because that fan blade it's turning around an axis and it's moving the air around an axis and it pulls fan uh pulls air from one side of that fan blade and pushes it through the other side of that fan blade and provides more force more pressure through that as it's moving that's an axial fan so when we look at a fan blade this is on a refrigeration application it's taking the air bringing the air in from one side pushing it through the other side now when we look at an axial fan an axial fan is affected by static pressure its performance is affected by static pressure so free air with the static pressure on the fan blade results in the least loading on that motor does that make sense if it's free air what would be free air if i were running operating a motor with a fan blade on it and if i'm running it on this table here this is considered free air that would be the least load on that motor but now as i add static pressure how would i add static pressure to that put it in my condensing unit so i put that in the condensing unit what if i put it in the condensing unit but don't put the guard on top of it have i had added static pressure to that yeah what if i put the guard on it now does that change the amount of static pressure i've applied to that and it does so as i add static pressure to that what does that do to the load it increases the load and if i have a psc motor what might that do to the speed of that motor as i add static it would slow it down as i add static as i add load to it it would slow it down what would happen to the amps on a psc as i add load as i add static what would the amps on the motor do they would go up that makes sense doesn't it does anybody disagree with that no that makes sense if we were to look at a fan catalog page if we look at that particular catalog page we can see certain performance characteristics of that now one thing that's not shown on that is the effect of static pressure as i move from the left to the right that's an increase of static pressure and that would result in changes of my air it would change the impact on the performance of that fan as well but as i add static pressure to that it's going to increase the load on the fan blade now if i have a residential condensing unit typically i might see about .3 inches of static maybe a little more static on a commercial unit who checks the static pressure on the condensing unit is there anybody who does not you eric you check everything eric but probably you don't check that but but you can visibly look at that condensing unit if you see the amps are high on the condensing unit and you see that the coil is dirty or if you've just mown the lawn and you have grass clippings all over that you can probably associate that there's probably more load on the motor that your amps on the motor are going to be a little bit higher that's pretty intuitive that kind of makes sense so if i look at this that unit is there anything that might impact the static pressure no problems with that right is there anything that would impact the static pressure on that yeah yeah and if it's pretty close to the wall that could impact my static pressure as well and i like how we have those uh connections right up there that's nice and convenient for the kids to play with so but that as we add static to that that's going to put more load on this it's going to result in less air too how about that and look how close those units are and that's going to affect my static it's going to affect the amount of air that i have on that and i could see an increase in my amps as a result and again a reduction of air and these are things that you typically run across that stuff happens if somebody has a deck built over their condensing unit and if they have a trap door on that deck if you were to measure the amps of the motor with the trapdoor on with the trapdoor off that's going to affect that static pressure which is going to affect the load which is going to affect the amps on that motor so those things all affect static pressure and the load that i see on that how about that anybody ever run into anything like that so what's that going to do to the amps on the motor cause them to go up what would that do to the operating temperature of the motor it would increase it what would that do to the speed of the motor slow it down a little bit so when we think about load it's going to impact the performance of that motor and if i increase the load the motor is probably going to slow down a little bit if it slows down a little bit i could probably see that i've increased the load just by looking at my amps on that and my amps would go up what about centrifugal fans what are centrifugal fan eric be quiet what are centrifugal fans don't say anything about don't answer this what are centrifugal fans blowers they're called centrifugal fans but we call them blowers centrifugal blowers squirrel cage blowers they look like this if we look at these blowers most of the blowers that we work with are that a what we call a forward curve blower that's the majority we see some others we see some backward curved or radial blowers but most of the blowers that we see in our residential applications are going to be those forward curved blowers now with a forward curve blower something a little bit different about them than with a fan an axial fan so with a forward curved blower we bring air into the inlet of the blower so that would be the inlet that's the outlet of the blower but we bring air into the inlet and we do something different with that air than what we do with a fan with an axial fan now with that air coming into the inlet we change the direction of the air typically we change it by 90 degrees so we bring the air into the inlet we change the direction of it by 90 degrees and we pressurize that air in the housing of the blower and then we discharge that air a little bit different function with that blower than with a fan so does that have an impact on anything would that result in any different impact with static pressure does static pressure affect a blower the same way that it affects an axial fan a fan blade does it so let's say that i take the blower out of my furnace and i put it on the table is this considered free air low static or would this be considered high static low static free air low static now when i run that blower on the table with no static on it would i expect that that blower is going to operate at a lower amp range or a higher amp range than maybe it's nameplate amps higher well when i ran that fan blade in free air weren't my amps low the least load on it so i'm trying to do more work now what that blower is doing it's taking the air that is available to it and if i'm running it in here it has all this air that is available to it and it's trying to take all of this air into its little inlet change the direction of it and pressurize that air that thing's going to work as hard as it can what would i expect to happen to that blower operating in that condition what would the motor react reaction be may go out on the overload protector and that motor is probably going to run a little bit slower than what its operating speed is designed for and what would the amps look like really high really high amps now i take that blower and i put it back in the furnace i don't put the doors on there and the furnace doesn't have a filter in it when i put the blower back in that furnace and operate it have i changed the static pressure what have i done to the static pressure have i increased it or have i decreased it i've increased it because it was free air here zero static so now i've increased the static pressure i've increased static pressure does that increase the load on the blower it decreases well why is that why would it decrease so now what i've done is i've restricted the amount of work that that blower is going to do you know a wise man i heard a guy talk about this one time i thought it was a great description of what was going on if we look at that blower that blower's designed for a certain amount of work how the how do they identify the amount of work that the blowers supposed to be doing there's a measurement that we use for that cfm cubic feet per minute now i like to think of the load on that blower as boxes of air boxes of air one foot by one foot by one foot a cubic foot now if my motor i'm looking at this from the perspective of an air over motor right now and we want to keep this in mind but that motor let's say that it's a half horsepower motor it's designed to move a half horsepower of these boxes of air how many boxes of air is that i'm not smart enough to know that i don't know how many boxes of air it is but i do know that if i have restriction to my air on my system and if my system is designed for that half horsepower motor i'm supposed to have half horsepower of these but if i put restrictions on it it's going to reduce the amount of air that it sees so the number of boxes of air that it was doing on this table is going to be greater than the number of boxes of air it's going to do in my furnace with the door off now remember i've got the filter off of there right now if i put the door back on the furnace does that change my static pressure if it changes the static pressure does it increase it or decrease it it increases the static pressure so if it increases the static pressure what will that do to the load less lived now wait does this stuff make any sense that's not what we saw with the fan blade as i increased the static pressure with a fan blade it had increased it increased the load on that but as i increase the static pressure on a blower remember what i'm doing i'm restricting the amount of air so i have less of those boxes of air and if i have less boxes of air i have less load so now i put the door on the furnace i'm restricting more or my increase in static pressure is affecting that my motor will speed up a little bit if that's a psc motor what will the amps do well if it speeds up it's working harder right no it's speeding up not because that motor is designed to go faster but as i put load on it or i take load away that's going to affect the speed of that so now as i as i take load away because i'm restricting the air the motor goes a little bit faster and i may be able to hear that what will the amps do they drop okay let's look at something else here i didn't have the filter in there when i put the filter in will that affect my static pressure what will it do to the static pressure it'll increase it so if it increases the static pressure what does that do to the load of the motor it decreases it i'm restricting air so the motor may go a little faster what will the amp still good job okay now let's assume that my filter is dirty dirty's bad isn't it a dirty filter is bad does that affect the static pressure what will it do to the static pressure increase it so what does that do to the load on the motor dirty filters does that make the motor work harder not on a blower it's restricting more air so there's even less load on that motor will go a little faster what will the amps do drop we love low amps right are low amps good not necessarily so on these motors the motors that are designed for our air moving equipment they are designed for really a specific load now load there's a narrow operating window in there and if i'm trying to operate a motor on my air over motors outside of that range might have a little bit of a problem and the motor could be too strong it can also be too weak and we recognize if a motor is too weak real high amps but if the motor is too strong my amps are going to be real low now if i've got a motor that is too strong for the application or if i don't have enough load on it because of static pressure that changes my airflow doesn't it restricts air flow so now if that motor is operating with too little load on it what's going to happen the motor is going to operate and efficiently and if it operates inefficiently what will that do to the winding temperature of the motor it'll increase it even if my amps are low yeah so now i've got real low amps but the motor is operating inefficiently that means the winding temperature increases but i have less load than what the motor is designed for when it's operating efficiently so what will happen to the life of the motor you're going to shorten the life of the motor and as a rule of thumb if you change the winding temperature of a motor by 10 degrees c 18 degrees f you affect the life of the motor by what percentage would you guess 50 50 now let's say that i do have dirty filters and that motor doesn't have as much load on it will it affect anything else in my system besides the motor i think it could affect the capacitor what might it do to the capacitor if that motor is operating at a higher speed than what it's designed for my capacitor volts increase so if my capacitor volts increase and if they exceed the rating of the capacitor what do you think it does the life of the capacitor shortens the life of the capacitor there's a whole effect with that thing so now when we look at blowers versus fans the static pressure affects it differently and just the opposite manner so with blowers free air is the maximum loading and my amps are going to be high at that point but as i add static it restricts air it restricts the number of those boxes of air that that blower is working and less air then takes load off of that and my amps will drop the speed will increase with that does it make a difference if i check the amps with the door off of the furnace and why does it affect that yeah it changes my static which impacts the load the number of those boxes of air and so as i measure that outside of the conditions that it's designed for i could be seeing numbers that don't really reflect what's going on with that particular product so i always have to make sure everything is in place when i check the amps make sure all the doors panels filters guards if that condensing unit is under the deck and there's a trap door to access it you've got to make sure all of those things are in place when you're checking the amps of that motor to make sure whether it's operating properly or not so those are important characteristics to consider now this happens to be a blower chart it's a complete blower but you guys change a lot of blower wheels don't you so you you'll go out and just buy a replacement for the blower wheel and keep the housing that's in there have you ever asked the guy at the counter what cfm is that blower wheel anybody ever ask the counter guy that if you do he's going to give you the same answer i give you i don't know i don't know what the cfm of that is until i match that with the housing so until it's matched with the housing i really can't tell you what the performance of that's going to be but when we select those replacement wheels we select them so they have the same physical characteristics as the blower that was in there and then when we put that in the housing of that blower we expect that it's going to be similar in performance now if we look at this chart and if we look at this blower the very bottom row and look all the way at the right and this catalog we identified that blower as a thousand cfm so if you go into the wholesaler and you want a thousand cfm blower that may be what they give you but more than likely if you need a thousand cfm in your application and if you put that blower in there you're not gonna get a thousand cfm why not because when you install that blower into an application now you're going to introduce static pressure and when you introduce static pressure you're going to restrict air and let's say that i have an application requiring 0.4 inches of water column well now all of a sudden i'm only getting 850. that happens to be a two-speed blower that's why we see two different numbers in there but if i'm operating this on high with 0.4 inches of static the air i'm going to get is 850 cfm so if you need a thousand cfm at .4 inches you need to let the wholesaler know that that's what you need in order to get the right one so we have to look at the performance we need at specific static pressures typically on a furnace we might see about .8 inches of static but that will have static pressures from 0.4 up to about 0.8 generally with our static now these motors that we have in these applications they're called air over motors what does that imply air over yeah it's the air it's the load that it's applied to that's going to keep that motor from overheating now when we look at belt drive motors for example those motors cool themselves and so they may react to static pressure in terms of their ability to to handle it a little bit differently than what i might see with an air over motor but it's important to remember that in these applications they're air over motors so with that what does that do to my static and what does that do to the amps on my psc motor what and one of the most difficult things and this is difficult for me too is to make sure that i'm telling you properly this stuff when we talk about blowers to me it's not intuitive when i talk about fan blades that all makes sense and i can see it and it looks sensible to me but when i see that i see trouble and my natural tendency is to think now my motor is going to be higher in amps but it's not it's still bad but my amps are going to be real low and what makes it so bad is now the motor is operating so inefficiently that i'm putting so much heat in there but i'm not getting the airflow because i'm restricting air that's where the problem comes in so those low amps are a problem as well as high amps so these are air over motors so the condenser totally enclosed the blower an open motor now what's going to be important to make sure i had mentioned to you that we select these motors and they're designed to operate within a narrow window because they have to have the right load on them if we don't have the right load on them then that motor is going to overheat and so we use a rule of thumb when we replace these and the rule of thumb is that if this is the bad motor my replacement motor should be equal to the amps of that motor the nameplate amps the fla to that motor but not more than 25 percent stronger so that's identifying this window now as a technician what's critical for you is that once you select a replacement and you install it that you check the amps of the motor and that you check the amps with everything in place and then when you check the amps this comes as a little bit of a surprise to folks it's okay if the amps are a little bit higher than name plate but not more than 10 percent higher as long as those amps aren't more than 10 percent higher than what the name plate on that motor says i've got the proper amount of load the motor is operating in the right efficiency i'm getting the right amount of heat in there and i've got the proper amount of air which is the load helping to cool that motor but then also the amps should never be more than 25 below name plate if it's more than 25 below the name plate amps that's an indication it's too inefficient i don't have enough load on there i put more heat in the winding of the motor and remember the load is the air so if i don't have the proper load on it then that motor is not going to get the right amount of air to keep it from overheating now chris chris is really good at these products here so when we look at electronically commutated motors what do we call those do we call them variable speed if you went to chris's class they're not all variable speed are they there are some that are but they're not all variable speed but what they are is air over motors so these motors also are dependent upon having the proper load on them for them to operate for the longevity they're designed for so on these motors one thing about them one thing i love about these things that we can't do with pscs as effectively is design them for the appropriate static pressure so now my psc design is essentially used for both condensers and for blowers but on ecs i can design it more specifically if it's being used with a fan blade or if it's being used with a blower well why is that because they react differently to the static pressure so now we can design them and take into account what's going to happen to them as we put them in a load whether they're used in a fan or in a blower so when they're used with fan typically we design them as what we call a constant speed but when we use them with blowers we can even get more refined on them and we can design them when my furnace has a bunch of bells and whistles and gives me a lot of capability a lot of high efficiency ratings in that equipment or something that is more basic so we can design them as a constant airflow or the constant torque did anybody uh attend chris's class on ecs yeah and i'll bet you he talked about these motors being designed for these different applications that's why they're designed like that now when i have a constant speed motor the fan blade's going to react the same way to my load it's going to react the same way to the static pressure so that fan as i increase static i have more load but that motor now will increase its torque so that my speed remains the same on that that doesn't happen with a psc but the load on the fan reacts the same to the static pressure whether i've got an ec or a psc on there but the motor can react a little bit differently now with the blower remember that blower operates a little bit differently it reacts differently to the static pressure but that blower doesn't matter whether it's equipped with an ec or psc the load on that blower reacts the same way to the static pressure and as i increase my static and i i restrict the amount of air that i have it removes load but if i reduce my static pressure i have more load i don't have as much restriction of air so the devices themselves the fans of the blowers are going to react the same way but the motors are going to react a little bit differently now when we look at this this is showing on that red line and you probably saw in chris's presentation a constant air flow and it's comparing the air of an a constant airflow equipped blower so in this case if it's designed for 1200 cfm we'll see that as my static changes even though the load on that motor is going to change by the static the motor reacts in order to maintain the same amount of air by increasing its speed as i have the restriction in that air where as with a psc we can see that that will decline comparing the psc to a constant torque in x13 they look a little more similar to what we see on that curve of the constant airflow but they do a better job in terms of maintaining air than what a psc does how many have heard that if i have a bad static condition put an ec in there who's who's heard that yeah so you guys who attended chris's class yesterday what did chris say about that that's hogwash isn't it no that's not going to happen so i have the same restrictions one of the reasons for the same restrictions that static pressure is the load on that these motors are air over motors they're designed to have a certain amount of air on them so we can't correct a bad static condition by putting an ec in there what do you have to do to correct it ductwork yeah or have eric come in eric can eric can fix anything so you have to correct that static condition you can't put a different motor in there you can't put a larger horsepower motor in there if you have a static condition a bad static condition so if you think that a larger horsepower is going to give you more air that motor's going to fail prematurely so i think that we what i want everybody to leave with is just a better understanding that there is a difference between the reaction of a fan blade and the reaction of a blower when it comes to changes in static pressure but it's easy to overlook that and as a technician if you see dirty filters your first thought is that your amps are going to be high and that's not the case the motor is going to fail and your capacitor is going to fail but it's not because it's overloaded it's actually under loaded and not getting the proper amount of air so with all of these motors whether they be ecs whether they be psc's whether they be shaded pole motors we want these motors to be operated in the load situation they're designed for and that load is air and the static pressure that we see well we've got a website you guys can go to uh we've got some training videos on there if uh if you're interested in those uh feel free to access access that uh for us so that's our our website questions yes yes and when we look at static pressure that static pressure is on both sides of that blower so we have static pressure on the inlet side we have static pressure on the outlet side the total static is taking my inlet side which is a negative static pressure changing the sign of that and adding it to the positive static pressure on the outlet side that would be the total static that's a good question thanks for bringing that up it depends upon the ec so with my constant speed i would see that as i add static more load on it but i'm providing more torque my amps go up on my constant air flow as that motor becomes unloaded that motor is going to produce a higher speed i'm going to increase speed my amps will go up on that so it depends on what we look at that's a wrap okay appreciate you guys thanks for watching this video again to find out everything we have going on you can download the free hvac school app on android or on iphone or go to hvacrschool.com and then specifically up in the top you'll see events to find out more about upcoming symposiums hope to see you there thanks for watching our video if you enjoyed it and got something out of it if you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel and click the notifications bell to be notified when new videos come out hvac school is far more than a youtube channel you can find out more by going to hvacrschool.com which is our website and hub for all of our content including tech tips videos podcasts and so much more you can also subscribe to the podcast on any podcast app of your choosing you can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching you.