RTU

[killeentech]

How long does a evp blower belt normaly last and how often should very be replaced?how tight shouldthe belt be ? Also how to check pulley alignment?

[Jpaulsmith]

Belts usually need to be replaced every year. Tightness depends on the unit, it should tell you in the owners/service manual. If you can't find it then I would go 5/16" of play. To check pulley alignment take a straight edge and put it on the motor sheave. It should stay flat against the motor sheave and the blower pulley if alignment is correct.

[zw17]

Too many variables to say how often and how it should be adjusted.

This is why you hire a trained tech, to solve these issues.

[killeentech]

This is why you hire a trained tech, to solve these issues.

isnt this a forum for questions.
Thanks jpaulsmith . I know very simple question just was never explained to me

[JEF1980]

Talk to your local rep where you buy belts and they will sell you a tension pen with a book with the belt sizes and correct tensions. Wear all depends on alignment if its across line start or on a VFD. Are they fixed sheaves or did someone leave varible pitch sheaves on after start up.

[Six]

Check them on quarterly PMs. Adjust or replace as needed.

[coolerinfrederick]

i'm actually in a debate now with a co worker on whether or not to cycle the blower (belt driven) on & off during occupied modes. for years and at all my accts. i keep the fan on when unit is in occupied mode. he just can't see my points

[dlove]

Check them on quarterly PMs. Adjust or replace as needed.

Hummm so every fan belt in all equipment in the world has the same PM...all you have to do is check it every quarter....

I think i like zw17's advice

[dlove]

i'm actually in a debate now with a co worker on whether or not to cycle the blower (belt driven) on & off during occupied modes. for years and at all my accts. i keep the fan on when unit is in occupied mode. he just can't see my points

i agree with with you. I most cases and depending on the system and the space its supplying, running Fan during occupancy times is the way to go for a few reasons.

You don't have the start and stop belt jerking, amp spikes, you maintain a better temp over the course of the day. Anyone that trends temps will tell you, you don't have the spikes and valleys in temps when the fans goes off/on for a call for heat or cool. Starting and stopping cost more to operate and wears the motor and belts out faster. IMO

[techreptdh]

How long does a evp blower belt normaly last and how often should very be replaced?how tight shouldthe belt be ? Also how to check pulley alignment?

It's hard to say how long belts should last, mainly because of conditions as some have mentioned. But if the alignment is true and the sheave and pulley is not worn you should be able to get a year or longer out of the better belts.If money isn't an issue, it is a better policy to just change it after a year or so. And by all means don't use fractional hp belts on anything over 3 hp or better. You're asking for trouble. Also do yourself a favor and only buy quality belts and a belt tension checker. You'll save yourself a lot of grief and it's a nice tool to have in your tool bag.Ok, I'm off my soapbox now.
Good Luck!

[valdelocc]

All belts are not equal, cogged belts last longer, some brands are better than others, I prefer Gates over Browning, Dayton etc. good sheaves make belts last longer, just tension it enough to where it wont slip.

[19characterusername]

i agree with with you. I most cases and depending on the system and the space its supplying, running Fan during occupancy times is the way to go for a few reasons.

You don't have the start and stop belt jerking, amp spikes, you maintain a better temp over the course of the day. Anyone that trends temps will tell you, you don't have the spikes and valleys in temps when the fans goes off/on for a call for heat or cool. Starting and stopping cost more to operate and wears the motor and belts out faster. IMO

And you can't ventilate continuously during occupancy times without the fan running. That is a code requirement in all NYC 1968 code, NYC new code, IMC based jurisdictions, CA and probably everywhere. Sorry for continuing the hijack...

Closer to the topic, is it generally recommended to put non adjustable sheaves on after TAB has determined the final required fan RPM? I had not heard that before.

[valdelocc]

I dont like the idea of running the blower all the time in RTU's, there are huge temperature differences between the roof and the living space, most RTU's are poorly insulated, meaning the air being circulated is gaining or loosing BTU's through the RTU walls and gaps, the problems become more noticeable in hot humid weather and cycling the blowers with demand helps a lot.

[jpsmith1cm]

I dont like the idea of running the blower all the time in RTU's, there are huge temperature differences between the roof and the living space, most RTU's are poorly insulated, meaning the air being circulated is gaining or loosing BTU's through the RTU walls and gaps, the problems become more noticeable in hot humid weather and cycling the blowers with demand helps a lot.

Then how do you meet fresh air requirements?

How do you maintain building pressurization?

[valdelocc]

Then how do you meet fresh air requirements?

How do you maintain building pressurization?

in some cases all must be reverted back to basics, the number one function of a RTU is to maintain a comfortable space temperature and my number one goal is to keep the customer comfortable.
Years ago there were no such requirements and we all survive.

[hvac wiz 79]

Many of the accounts i service don't run continuous fan in occupied. once the area reaches set point, if the space temp rises a few tenths of a degree the fan kicks on for a few minutes. If the temp drops the fan cuts off. Can't say i like this method as the majority of stores have comfort complaints it's all EMS controlled. The other thing that irks me is techs with no knowledge or understanding of fresh air requirements shut down dampers fully closed. I set up a building back to what the TAB folks initially had it at as they left the info printed on each unit. A month or so later dampers were shut, building under severe negative pressure & the manager said a tech in my company told him the building can't cool bringing in unconditioned OD air so he closed them down . :banghead::banghead: ... but i guess the surge of hot air that rushed through the store as the automatic doors slid open, truly not being conditioned was fine

[Six]

Hummm so every fan belt in all equipment in the world has the same PM...all you have to do is check it every quarter....

I think i like zw17's advice

No, you make a special trip at a 2 hour minimum charge to your customer because you suspect a belt issue.

Seriously ?

I didnt think I had to be so descriptive. Consult the manufacturer for recomended belt tension if your not sure, check for shiv and pulley wear and alignmemt and buy a aftermarket tool to check for tension.

Can you venture a guess on what would be a good time to do those things ? Service calls and quarterly inspections.

[2sac]

If it needs changing, change it. If you believe the belts are wearing too quickly, check pulleys, alignment, and tension. A and B belts are heavier duty than 4L and 5L belts. Cogged belts run cooler and may last longer, but tend to wear pulleys prematurely.

[techreptdh]

And you can't ventilate continuously during occupancy times without the fan running. That is a code requirement in all NYC 1968 code, NYC new code, IMC based jurisdictions, CA and probably everywhere. Sorry for continuing the hijack...

Closer to the topic, is it generally recommended to put non adjustable sheaves on after TAB has determined the final required fan RPM? I had not heard that before.

Yes its true that the sheaves should be replaced, but it's not always done. I guess due to cost. I will put the fixed sheaves on after the v/p sheaves wear out, especially where multi-groove sheaves are involved.

[19characterusername]

Yes its true that the sheaves should be replaced, but it's not always done. I guess due to cost. I will put the fixed sheaves on after the v/p sheaves wear out, especially where multi-groove sheaves are involved.

Thanks again. Never heard that before. I'll start putting that in my TAB specs. There also appears to be a distinct operational advantage to removing adjustability after TAB so that someone silly doesn't monkey around with properly commisioned RPMs because "there's not enough airflow". I'd probably put it in for after engineer and CxA approval of the TAB report.



...



This is getting soooo off topic but, @valdelocc what you're advocating is probably ok for average resi construction or particularly leaky commercial buildings with lots of old operable windows where infiltration can take care of ventilation. But it's not allowed and hasn't been allowed for a very long time for everything else. It's also a terrible idea for everything else. Ventilation is a comfort issue just as much as temp and humidity control. I'll grant that the code rates aren't perfect and certainly don't represent the best and state of the art engineering vis a vis IAQ, but they generally do the job and are easy to design to.

My thinking is if a RTU has SA temp issues or humidity control issues due to varying or extreme OA temps, then the controls aren't sufficiently sophisticated, the unit is lacking a feature it needs for the design like hot gas reheat or modulating heat, the unit was improperly selected without accounting for the OA load, or the OA flow hasn't been balanced to design. Throwing an enthalpy wheel, even a RTU manufacturer's bolt-on, cheapo wheel option on most RTUs will reduce control and capacity issues because it will significantly moderate the mixed air temp. You just have to watch for frosting in the winter in cold climates. DCV will also help out since most of the time it will reduce the ventilation airflow below design.