RTU's not cooling the building enough

[John Markl]

Actually its not. Not on the commercial side anyway.

People realize that its short term and will eventually damage the coils. Of course I speak for Houston but working on roofs and in mechanical rooms for 20 years Ive seen it only a few times.

That doesn't qualify as common.

We've had water hooked up with a pressure control to the rooftop condensers on 150 tons of AC on a five-story office building for years without damage to fins.

It's a matter of maintaing enough flow for the water to carry the minerals off with it, as opposed to "misting" or soaker hoses.

Most of the water evaporates on the flat roof, but some runs down the gutters....In fact, the building owner will call us (A CPA who offices there) if he doesn't see water coming out of the gutter during hot weather.

Conversely, We service a retirement home with 200+ units....we replaced about 30 of them last year under a capital expenditure, because the facility irrigation system sprays a fine mist which DOES eat the coils out over time.

I used to listen to Mark Davis on WBAP in the mornings, and would cringe when he would advertise those misting systems for home AC units. I even sent him an email about it, which of course, he never answered.

[Six]

You're in North Texas ? We provided water for a old Carrier Chiller used the perforated garden hoses.

We told the customer it would ruin what was left of those coils and in about 5 months and sure enough it did.

They're not designed to have city water run through them but I wonder if the environmemt plays a factor too.

We have to deal with serious humidity down here so there is not much evaporation going on at all.

[John Markl]

Might want to consider going to 2 stage 10 ton units, with the blower slowed to 320 CFM per ton. If your 7.5 ton units are moving 400 CFM per ton, that comes out to 3,000CFM. A 10 ton at 320 CFM per ton comes out to 3,200 CFM. Not a big increase in CFM.

We have been recommending that a lot on replacement quotes....Go two-stage....get good, even cooling and humidity removal during moderate weather, with the capacity to "pour it on" when things get tough.

Automobile manufacturers are offering the same thing.

[abcando]

if at 95 degrees and below your equipment does the job they are sized correctly and working properly. most equipment is designed to maintain 20 degree between outside and inside temp sounds like they are doing all they can do close outside air dampers if you can in a nursing home i would watch it. use water as needed and when the heat is over put everything back to proper settings. Good luck and take care in the heat

Its not the equipment that is designed to only maintain a 20 degree difference. It the system may have only been sized to maintain a 20 degree difference.

Grocery stores have no problem maintaining 30 or more degrees below outdoor temp. The systems are sized to be able to do it. The equipment doesn't care.

This is actually the point of my inquiry here. There are a lot of areas where higher than 95F temps are common (including ours) during summer time, then these equipment or systems that are mostly designed to maintain 20 degree temp difference are not ideal to use in a lot of situations.

I go to other larger buildings and it still feels comfortable inside even cooler than normal despite the extremely hot condition outside. It would be nice to be able to have something that can do 30 or more degree temp. difference in our place.

The pictures show our temporary sprinkler setup on the roof. To be honest, I don't really feel any better inside the building by doing this, but I know it's because of the extreme heat outside. I'm sure the units are getting relieved somehow and I just imagine it would feel worse inside without doing this.

I'm considering doing the pvc setup soon, it sucks to have to pull hoses on top of the roof whenever we need to do it.

I appreciate the discussion about the good and bad of it.

[John Markl]

Well, your equipment looks plenty "new enough"....but from the pics, it looks like you have some serious ductwork issues.

[abcando]

I agree with you John, we have some ridiculous ductwork setup above the roof.

[Six]

Well, your equipment looks plenty "new enough"....but from the pics, it looks like you have some serious ductwork issues.

As long as they're insulated well enough to withstand the extreme roof temps I don't see a problem with them.

It's a sloppy application of foam type insulation. He should take a split at the unit and then take a split at the entering and leaving ductwork inside the building and compare the numbers.

I wonder how much heat he's picking up through that ductwork ??

Maybe he needs to run a sprinkler set up for the duct work ?

[John Markl]

As long as they're insulated well enough to withstand the extreme roof temps I don't see a problem with them.

It's a sloppy application of foam type insulation. He should take a split at the unit and then take a split at the entering and leaving ductwork inside the building and compare the numbers.

I wonder how much heat he's picking up through that ductwork ??

Maybe he needs to run a sprinkler set up for the duct work ?

I'm more concerned about the size and configuration. By the time you allow for all that foam and cool-seal, and presumably some internal insulation, the actual air space for 7.5 tons looks pretty shaky.

[abcando]

As long as they're insulated well enough to withstand the extreme roof temps I don't see a problem with them.

It's a sloppy application of foam type insulation. He should take a split at the unit and then take a split at the entering and leaving ductwork inside the building and compare the numbers.

I wonder how much heat he's picking up through that ductwork ??

Maybe he needs to run a sprinkler set up for the duct work ?

The foam insulation was done just last year. Prior to that, the insulation was either bad or there was none. I had actually used the sprinkler on some exposed metal ducts .

The guys scraped the old one to the metal and sprayed the new one about 1" to 2" thick. I was hoping this could have done the trick until this heat wave happened.

I had taken splits at the units and inside but on different days. I'll try to do it again and compare.

[gwoner]

My money is on closed dampers,boxes, check the design specs for CFM.Sounds like someone needs some test and balance report to remedy this situation.