Bigger Pulley?

[madcitysw]

Anyway I asked my teacher how should I increase the airflow coming inside the BK Store because it always hot inside in the kitchen, one of my classmate and I cleaned both unit's coils since we found that it was dirty. This helps a little, but then it seems lacking of airflow coming inside the store. So we talked to our teacher and he said that we should change the pulley since it is belt drive. My questions is, do we change the pulley to a bigger size or smaller? I taken that we will also need to change the belt as well. Any tips would be usefel.

Thanks
Shane

[Tech Rob]

You really should be consulting with a test/balance firm about this. Every part of a refrigeration system is designed with a specific capacity, temperature, and airflow in mind. If you alter any one of these factors, the others must be altered accordingly. If you increase air volume or velocity across an evaporator coil, you're decreasing the dehumidifying abilities of the machine, as well as heat transfer across the coil.

Is your ductwork able to carry any more air than it already is? If not, you'd be spinning your wheels (and burning out blower motors). Increasing sheave sizes even one inch can dramatically increase the current draw of a motor.

This is just my opinion, so take it for what it is... I think you should leave this one for the professionals, before you bite off more than you can chew.

[jayguy]

a bigger sheave on the drive will increase the driven speed.

a smaller sheave on the driven will increase the driven speed.

i would always recommend increasing sheave sizes. it gives more surface area for the belts to grip which allows less tension on the belts before slippage occurs. less tension on the belts means less tension on the bearings. everybody wins. :p

belt sizing depends on sheave sizes and how much motor movement you have.

Fan Laws:
all else being the same (duct sizing, driven fan size, etc.), if you double the driven fan speed, you will need 8 times the motor horsepower.

i would be more inclined to double check all of the ducts, clean the coils real good, etc. this will obviously pay more (in energy effeciency) than just speeding up the fan. you may still have to speed the fan up...just use caution.

good luck

[heatingman]

If you change the pulley sizes too much, you will run over the fan curve for the motor and over amp. Also the existing belt will not likely fit anymore.

[chiller mekanik]

The only thing I would add to ALL of the GOOD advice you've been given so far is:

Look closely at the drive pulley, if its variable pitch & you can see that the belt use to ride in a higher groove, you can turn it in to get the belt back to its original position. If the pulley is grooved you may have to replace the pulley, so, when you install the new pulley you will want to have it out from the center position the same amount of turns as the old one. The new one will move more air than the old one because its not grooved. ALL of this has to be done while monitoring the amps closely to make sure you don't overload a starter heater assy or the motor itself.

The ideal thing to do in this case is to install a fixed pulley in place of the variable pulley, but thats another story for another time.

If you already have a fixed pulley, none of what I've typed here will apply.

[dirtyboy103us]

if you are going to try to increase speed you have to re-adjust belt also
where the tension is not going to hurt your sheaves or belts

you will need a little info on the proper way to do this along with the info on how its going to affect the motors amp draw and air velocity

you could have your teacher call Browning and talked to tech support
and he will send him all kinds of literature for you guys

the first thing you are going to be coming out of school is a maintenance guy so the more information on changing and replacements is up to you.......... learn it while you can



V-Belt Maintenance


Everyone who has spent any time at all in the Power Transmission business, has gotten this call more than once: "The V-Belts you sold me three weeks ago are failing. They are no good!" It has always amazed me that people that install V-belts sometimes are the ones that seem to know the least about V-belt maintenance.

WHAT TO LOOK FOR

Belt Tensioning

Belt tensioning is a frequently overlooked factor in proper drive maintenance. V-belts will continue to transmit torque even if they are slipping slightly. A properly tensioned drive should have an efficiency of slightly over 96%. If improper tensioning allows a 4% slip, efficiency drops off to approximately 92%. As the slip drops to the 6% range, an excess amount of heat is generated. The condition becomes even more serious as the belt approaches 8% slip. At 8% slip, drive efficiency has dropped off to 80%. At this point the drive will not function. Belt tension can only be properly checked with a Belt Tension Checker. It is important that all the belts on the drive have the same tension. DO NOT OVER TENSION! Be sure to recheck frequently during the first 24-48 hours. It is also a good practice to check tension on a periodic basis.

Worn Sheaves

Before installing a new set of belts, the sheave walls should always be checked for wear. Through continued use, the sheave walls become "dished" out which reduces the ability of the belt to wedge in the groove. Sheave wear is much less apparent than belt wear – yet equally critical. Generally, when sheave sidewall wear exceeds .025" when measured with a feeler gauge and a straightedge, the sheave should be replaced.

Misalignment

Misalignment is another V-belt maintenance condition that can cause a loss of efficiency. Misalignment can cause belt slip resulting in belt heat buildup. These conditions dramatically decrease belt drive efficiency. Drives should be checked to assure the parallel position of the sheave shafts and correct alignment of the sheave grooves. A simple and effective means of checking drive alignment is to use a straightedge or a tight cord across the sheave faces to assure four point contact.

In summary, a properly installed and maintained drive will transmit full rated power for the life of the belt.
Source: Goodyear Laboratories

http://www.mptdrives.com/techtips.htm

[tolmn61]

Mad
One other thought is to check the max speed for your blower wheel it is possible to over turn it and in time it will self destruct.

[markwolf]

You can't just turn the air up without looking at the whole building as one integrated system.
you have exhaust & makeup fans for the hood.are the filters clean in them?are the ducts clear?dampers opening or opened?Is it air balanced to manufacturers specs?
If you speed up the air are you going to exceede the temp drop across the evaporator?You cleaned the coils did you clean the blower wheel?-even the slightest buildup in the fan decreases the ammount of air it will move dramatically.
some kitchen makeup airs have cooling too,does the one for the store?
The kitchen hoods are often neglected you will find dampers so greased up hardly any air will pass through them.I have found them with failed fire dampers partially closed.
Also exhaust fans can be just caked with goo from the cooktop.If part of your pm is not the fans you should at least look so they can have them pulled & cleaned if need be.
same for the make up air.
In other words the whole kitchen system must be addressed before making any changes to airflow.If you do not you could cause more problems than you had in the first place.IMO

[madcitysw]

You can't just turn the air up without looking at the whole building as one integrated system.
you have exhaust & makeup fans for the hood.are the filters clean in them?are the ducts clear?dampers opening or opened?Is it air balanced to manufacturers specs?
If you speed up the air are you going to exceede the temp drop across the evaporator?You cleaned the coils did you clean the blower wheel?-even the slightest buildup in the fan decreases the ammount of air it will move dramatically.
some kitchen makeup airs have cooling too,does the one for the store?
The kitchen hoods are often neglected you will find dampers so greased up hardly any air will pass through them.I have found them with failed fire dampers partially closed.
Also exhaust fans can be just caked with goo from the cooktop.If part of your pm is not the fans you should at least look so they can have them pulled & cleaned if need be.
same for the make up air.
In other words the whole kitchen system must be addressed before making any changes to airflow.If you do not you could cause more problems than you had in the first place.IMO

Well, I worked in the Sparta BK yesterday because they were having the same problem as Dobson. I really cleaned out both unit's coils that goes to the kitchen like I did in Dobson and cleaned out the fan as much as I could. I came back about two hours later and found that it really helped alot and was alot cooler than normally. However dobson is not in that case, it didn't even help at all, it seems that it made it worse LOL and they are still complaining about how hot it is in there and yes it at least 90F, so I going to check into the pressure/temp on the units and see what's up with both of theirs.

Um.. The makeup air is really the A/C units that makes the air that is lost by the exhaust hoods. That why the blower is always on even when the A/C is not running. However, we do have a make up fans in the bathrooms since it has it own exhaust ducts.

[Tech Rob]

Well, I worked in the Sparta BK yesterday because they were having the same problem as Dobson. I really cleaned out both unit's coils that goes to the kitchen like I did in Dobson and cleaned out the fan as much as I could. I came back about two hours later and found that it really helped alot and was alot cooler than normally. However dobson is not in that case, it didn't even help at all, it seems that it made it worse LOL and they are still complaining about how hot it is in there and yes it at least 90F, so I going to check into the pressure/temp on the units and see what's up with both of theirs.

Um.. The makeup air is really the A/C units that makes the air that is lost by the exhaust hoods. That why the blower is always on even when the A/C is not running. However, we do have a make up fans in the bathrooms since it has it own exhaust ducts.

Are you sure the blowers don't run continuously because of remote temp sensors in the return airstream?

[51fitter]

You need a starting point to go from. Just don't start changing things. If you can get how things were first set up as far as airflow that is what you use. (old prints). Get a flow hood to know exactly what is being put out cfm wise. Get the amps on the motor also, and check them with name plate amps. All things being the same I would be looking on the ac side more then airflow if they were fine all this time now this year they are hot. What changed? If you change anything make the changes small and see what happens.

[skorepeo]

with out much more info just guessing my advice is check the return are the dampers set right?

i had a situation awhile back where the economizers were closed and the store was always hot it turned out that the indoor return was not big enough and so the economizers had to be open about 20%. even with 105 degree outdoor temps this configuration gave 73 degree indoor temps.

the store owner said that for about 3 years all anyone ever did was clean the coil change filters and then tell him that the unit was undersized

this was a small 25 ton chilled water coil and yes the first thing that i did was clean the coil and change filters

another situation that i came across was the wrong size belts an A belt was being used on a system that required B belts the B belt sat farther to the outside of the drive sheave and with proper tension and alignment it gave just the right amount of air.

if you can get to the blower wheel and take it outside use a good degreaser on it those get nasty clogged in a kitchen even the draw through ones

how are the shaft bearings are they properly greased are they worn out both motor and blower shaft bearings

are the exhaust hoods clean what about the motor bearings and belts on the exhaust fans

these are just a few things to check before trying to redesign the system

if this is a chilled water coil check the water temp what is your delta T what is the unit designed for if you are getting a 8 degree delta T and it is designed for 12 then check the motor amps and if they are low then it should be ok to run the sheaves in and then check the delta T and amps again if they are within parameters then you are ok

if your delta T is high then you have a water flow issue check the valve and strainers is there a balancing valve

I hate it when someone says just change the sheave or pulley for more air flow the system was designed and ran good until something happened that changed the parameters and unless someone changed the pulley or sheave then there should be no reason to change it unless a worn one with one that has the same specs

if it is a dx coil then speeding up the airflow will have a negative effect the air moving across the coil to fast wont give up the heat you will have hotter air and may freeze the coil what are your pressures

if you want to be a good tech then troubleshoot and know what the problem is first then fix it right the first time to many just change parts until they get lucky and get the one that is broke

If it isn't broke don't fix it!!! and if there is not enough time to do it right the first time how will you ever find the time to go back and do it again!!!

good luck comes with knowledge patience skill and the ability to use them at
just the right time :)

[smitty1968]

The 1st thing you have to do is look at the whole picture.

This being a Restraunt im sure it has more than 1 RTU.
It has to have Exhaust fans. and some sort of Make up air.

heres the deal....

example..

When you open the back door do you feel a breeze coming in?

If the answer is yes, then heres your situation.

lets say your BK's total exhausted air is 2500 cfm.
In order to maintain a desent temp. you must have just as much new air coming into the store as you are pulling out through your exhaust.

* 80% (2000 cfm) coming into the kitchen as make up air.
* 20% (500 cfm) coming from your Roof Top Units (Economizer or manual
damper.
This is known as "Neutral Air" perfect conditions
More exhaust than make up air = "Negative Air"
More Make up air than exhaust = "Posative Air"

Being in a Negative is Horrible. If your 40% negative it will pull the 40 % needed from somwhere. be it through your economizers or from a door being opened and closed.
The system will literaly pull all of the conditioned air out of the space and dump it out through the exhaust fans.

Everytime the doors are opened you pull in huge amounts of humidity.
If this is happening the store will never recover.

I would 1st look at the whole picture, check out the Duct also you may have some flex lines off in the ceiling.

[madcitysw]

The 1st thing you have to do is look at the whole picture.

This being a Restraunt im sure it has more than 1 RTU.
It has to have Exhaust fans. and some sort of Make up air.

heres the deal....

example..

When you open the back door do you feel a breeze coming in?

If the answer is yes, then heres your situation.

lets say your BK's total exhausted air is 2500 cfm.
In order to maintain a desent temp. you must have just as much new air coming into the store as you are pulling out through your exhaust.

* 80% (2000 cfm) coming into the kitchen as make up air.
* 20% (500 cfm) coming from your Roof Top Units (Economizer or manual
damper.
This is known as "Neutral Air" perfect conditions
More exhaust than make up air = "Negative Air"
More Make up air than exhaust = "Posative Air"

Being in a Negative is Horrible. If your 40% negative it will pull the 40 % needed from somwhere. be it through your economizers or from a door being opened and closed.
The system will literaly pull all of the conditioned air out of the space and dump it out through the exhaust fans.

Everytime the doors are opened you pull in huge amounts of humidity.
If this is happening the store will never recover.

I would 1st look at the whole picture, check out the Duct also you may have some flex lines off in the ceiling.

Well I worked at Dobson today to solve their problem. I got down and got dirty with a bandage on my finger :( I had the whole top cover off one of the unit, so that I could really tight one of the blower fans since it was squalling like a pig when you turn on the unit, well... my hand slip and my finger went into the evaporator coil and now have like three cuts from it. Jeez that felt like a razor blade. Well, I noticed both pulley was very shining (taken that it because it been slipping) the blower problem was fixed and I cleaned out all the coils for sure and installed all new filters. I cleaned out the intake vent which goes into the blower since that was cogged up, but I not too sure what a damper is??? Well, I came back a little later and found that it was alot cooler than I started, so I hope that fixes the problem for now. I don't think the store is in negative pressure, at least it don't feel like it. I don't have any device to check the pressure in the store yet. :(

[smitty1968]

[QUOTE= I don't think the store is in negative pressure, at least it don't feel like it. I don't have any device to check the pressure in the store yet. :([/QUOTE]

Easy way to check if your store is in a Negative-

Open the back door.. if you feel a breeze coming in from the outside then your in a negative

[dirtyboy103us]

Easy way to check if your store is in a Negative-

Open the back door.. if you feel a breeze coming in from the outside then your in a negative


if you smoke use a cigg or your lighter