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  1. #1
    Join Date
    Mar 2012
    Location
    west burb IL
    Posts
    95

    RTU's not cooling the building enough

    Today and the past few ones have been scorching hot outside and the temperatures inside our facility have been suffering badly.

    We have several 7.5 ton units each serving one wing of the building. On days with outside temps of up to about 95F, the building seems comfortable enough and the units seem able to cope up. But when it gets to about 100F out, the hallway temps begin to rise to about 78 to 81 and everyone will of course start complaining about it.

    We clean the coils regularly and we have the HVAC contractor doing regular PM's on the units. I know that these units were not designed based on these very high temperatures but I would think they should also be able to keep the building comfortable at all times.

    We have replaced older units with new ones, and the contractor have just changed them with the same sizes. With these new ones being used, we're always still having this issue of not enough cooling inside on really hot weather and we would at times end up renting portable ones to supplement the cooling.

    Do you guys think we should get bigger units? I don't remember our contractor having done any load calculations inside our facility, and we'll soon need to replace another one. Would appreciate any suggestions.

  2. #2
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    A larger unit will most likely require a curb adapter if not a curb change. Also you have to take into account the higher electrical load and the existing duct work if adding more capacity.

    Given your location it my be more practical to struggle through the few days a year you have to deal with excessive ambient.

  3. #3
    Join Date
    Mar 2012
    Location
    west burb IL
    Posts
    95
    Today's forecast for the Chicago area - 103F, geez! Thanks guys for the advices. We are actually a nursing home facility with about 200 bed capacity. A 7.5 ton RTU serves a wing with an average of 15 resident rooms (mostly 2 beds) and 1 or 2 offices.

    There is one thermostat per wing located in each hallway. When the stats read high in the hallways, you can expect the resident rooms and offices to be warmer.

    Larger curbs, some ductwork and electrical service changes seem like a lot of work, costly too, but good to be informed about it.

    We have 3 units with double coils on them and I make sure we split them when cleaning including this stupidly setup smaller unit in the picture for our laundry. It makes me mad whenever we clean this one.

    We also have covered most of our outside air intakes. Not good I know, but no complaints about air quality somehow. We also advised the residents to keep the blinds closed for now.

    Quote Originally Posted by Six View Post

    Given your location it my be more practical to struggle through the few days a year you have to deal with excessive ambient.
    I think this is what we'll end up doing for this season again. But summer has just started a few days ago. I dread of thinking how much more hot weather we're going to have.
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  4. #4
    Join Date
    Mar 2008
    Location
    NC
    Posts
    1,461
    I know this is going to elicit a number of negative comments, buy I've seen water sprinklers wetting the coils to get thru extreme conditions.

  5. #5
    Join Date
    Oct 2001
    Posts
    6,966
    is the returns ducted from the space back up to the rooftop or egg crated tiles pulling the ceiling heat back?
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  6. #6
    Join Date
    Mar 2012
    Location
    west burb IL
    Posts
    95
    Quote Originally Posted by ncboston View Post
    I know this is going to elicit a number of negative comments, buy I've seen water sprinklers wetting the coils to get thru extreme conditions.
    We actually have sprinklers set up in 3 of our units right now. We try everything to reduce heat inside.

    Quote Originally Posted by maxster
    is the returns ducted from the space back up to the rooftop or egg crated tiles pulling the ceiling heat back?
    Yeah, the returns are ducted back to the roof toop.

  7. #7
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    Quote Originally Posted by abcando View Post
    We actually have sprinklers set up in 3 of our units right now. We try everything to reduce heat inside.



    Yeah, the returns are ducted back to the roof toop.
    Excessive use of city water to cool the coils will RUIN your condenser coils.

  8. #8
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    973
    Run those units 24/7. catch the load early and you should help slide by the 3pm heat hump.

    And close the OA dampers. completely.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    Quote Originally Posted by ncboston View Post
    I know this is going to elicit a number of negative comments, buy I've seen water sprinklers wetting the coils to get thru extreme conditions.
    Yep, I know of a couple buildings with sprinklers set up for extreme temp days.
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  10. #10
    Join Date
    Jun 2012
    Posts
    529
    Quote Originally Posted by beenthere View Post
    Yep, I know of a couple buildings with sprinklers set up for extreme temp days.
    Went to a school that had a Trane chiller with a real nice sprinkler system. All PVC with fire suppression style sprinkler heads over each coil section. It was even controlled by a pressure switch hooked up to a water solenoid valve.

  11. #11
    Join Date
    Feb 2010
    Location
    Cal
    Posts
    1,596
    Quote Originally Posted by abcando View Post
    We are actually a nursing home facility ...
    Be careful what you post about your situation in an open forum. If someone expires due to heat or dehydration, you might make the news, or worse.

  12. #12
    Join Date
    Oct 2010
    Location
    Baton Rouge, LA
    Posts
    1,113
    Its actually simple physics not the sizes of your units.

    If I want to remove 110F heat from a condenser coil I have to have a temperature lower then 110F.

    We know this cause of the Second law of Thermodynamics, heat moves to cold.

    Hence, the closer outside temperatures come to the temperature of your refrigerant in the condenser coils the less amount of heat you will remove. Since the point of an AC system is to take heat from where we don't want it and move it to where we don't care if the system can't remove the heat...........
    If you're too "open" minded, your brains will fall out.
    Artificial intelligence is no match for natural stupidity.

  13. #13
    Join Date
    Feb 2010
    Location
    Cal
    Posts
    1,596
    Outside air intake puts a big hit on capacity during extreme periods. You might consider making a temporary adjustment to the osa volume. Can't adjust equipment efficiency or insulation .

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