Professional Member
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.
Professional Member*
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.
Professional Member*
Its actually simple physics not the sizes of your units.
If I want to remove 110°F heat from a condenser coil I have to have a temperature lower then 110°F.
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.
Professional Member*
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.
Professional Member*
Hallways getting hot, how are the offices?... are there windows in these hallways? If your unit is not sized for such hot temperatures then you might try ways to lower the cooling load... like blinds on windows, turning off some lights, etc...
Lowering your OSA might help, but your employees might start complaining about air quality.
You can call me Sam
It should be a crime to be a mechanical engineer in San Diego
Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)
AOP Committee/Professional Member*
It's design temp meeting capacity.Originally Posted by abcando
I would see if the hallways are primary served by a unit or two that you can identify, and upsize those units. Adding a couple of multi stage larger units allows for good humidity control when operating near setpoint, and increased capacity during the hottest days.
Yes, a larger curb, some ductwork, and possible electrical service to the new units needs to be considered.
[Avatar photo from a Florida training accident. Everyone walked away.]
2 Tim 3:16-17
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Professional Member
Just a guess, Have these condensers been split to clean? Awhile back one of our accounts was not keeping up. You could run water through it. split and clean little seeds and strands from plant life.
Professional Member
Do you turn the units off at night? Timeclock or control system? I agree with the other guys, just trying to throw something else out there.
Professional Member*
Everything been tested & balanced? ..
This is not the ARP forum
Last edited by beenthere; 07-06-2012 at 04:40 PM. Reason: removed negative political comment
Professional Member
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.
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.
Professional Member
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.
Professional Member*
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
Professional Member
Record setting temperatures and equipment not designed for those temperatures are causing problems all over.
Professional Member
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.
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Rideway Precision Mechanical, Inc
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Just give us a call and we can help you out!!! We will let you know what you need, and what you should do. Here to help! We are a commercial and residential HVAC company located in Villa Park!
Last edited by Chris_Worthington; 07-06-2012 at 01:52 PM. Reason: Email Addresses Removed
Professional Member*
Excessive use of city water to cool the coils will RUIN your condenser coils.
Professional Member*
You guys going to go out and charge them to tell him what they already know ?
That their equipment isnt rated for ambients in excess of 95 degrees ?
Last edited by Chris_Worthington; 07-06-2012 at 01:52 PM. Reason: Email Addresses Removed
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Email addresses belong in your profile and NOT posted in the forum. Thank you in advance for reading the sites rules and complying with them
Regular Guest
Actually no, Sixer. The point was that he wondered if he needed to units and that he was unsure if the contractor did a proper load measurement. Sorry, was trying to help out, knowing he is in the area.
And thanks for sarcasm. Must be the heat.
Professional Member
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.
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