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  1. #14
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    Quote Originally Posted by 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.
    Then how do you meet fresh air requirements?

    How do you maintain building pressurization?

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    Quote Originally Posted by jpsmith1cm View Post
    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.

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    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

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    Quote Originally Posted by dlove View Post
    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.

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    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.
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    Quote Originally Posted by 19characterusername View Post
    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.

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    thanks techreptdh

    Quote Originally Posted by techreptdh View Post
    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.


  8. #21
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    Quote Originally Posted by valdelocc View Post
    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.
    But there ARE these requirements today and we MUST live up to them.


    In my experience, cycling the fan on a RTU is not a great idea.

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    Quote Originally Posted by jpsmith1cm View Post
    But there ARE these requirements today and we MUST live up to them.


    In my experience, cycling the fan on a RTU is not a great idea.
    In my neck of the woods there are not general mandates or laws pertaining minimum fresh air, IAQ etc.
    ASHRAE put out the "standards" which amount to a set of recommendations. in rare cases the engineer designs the hvac system by the book, the installers puts the puzzle together in similar fashion and everything works in perfect harmony, fan run all the time,units handle latent and sensible loads as it should, space runs at 40 RH/74F and tenants are happy.
    In some other cases everything is out of whack and we are called in to "make it work".
    Besides building pressurization and fresh air requirements why would you recommend running the blower all the time?

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    In an office with lots of rooms and one stat it will help keep the air turned over and reduce hot rooms when rooms have loads out of balance. But if the RTU is not intended to provide ventilation fan cycling is acceptable. Also if the design was meant to be intermittently ventilated and average out to the correct rate (very very rare). That being said, western NY has the same IMC vent rates from the state code that we see here in the city from the 2008 nyc code. Check chapter 4 of the NY state mechanical code.

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    Quote Originally Posted by 19characterusername View Post
    In an office with lots of rooms and one stat it will help keep the air turned over and reduce hot rooms when rooms have loads out of balance. But if the RTU is not intended to provide ventilation fan cycling is acceptable. Also if the design was meant to be intermittently ventilated and average out to the correct rate (very very rare). That being said, western NY has the same IMC vent rates from the state code that we see here in the city from the 2008 nyc code. Check chapter 4 of the NY state mechanical code.
    I must be way behind times, I have to admit I didn't know NYS has a mechanical code. For the longest time HVAC work was pretty much unregulated throughout NYS with exception of the big apple.
    Pretty much all the small accounts I service dont comply with codes and wont pay us to bring them there either on the other hand Hotels, Hospitals,schools and government buildings are up to snuff .

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    Typically existing only needs to comply with the code in force at the time of building permit for the work being done. Certain activities will trigger a need to comply with current code. Basic service calls arent typically it. But you should put bringing things up to code on your clients radar so they can budget for upgrades down the road.

  13. #26
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    Quote Originally Posted by valdelocc


    Besides building pressurization and fresh air requirements why would you recommend running the blower all the time?
    Comfort.

    Running a fan all the time keeps the air circulating.

    This prevents warm spots/cold spots. Also prevents air stratification.

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