View Full Version : Hi Ya'll, I have another head-scratcher. Sorry, it's a long read.
08-02-2004, 09:11 PM
Went to a hair salon today where my employer changed out an old 5-ton gas pack for a new one back in mid-April. The tenant in the space is complaining of high humidity in her space since the new unit was installed. She had PERGO type wood flooring installed at some point in the past and the floor boards are now buckling severly and paper products are becoming limp, curling and wrinkling all throughout the space.
They're also complaining that the cookies they leave out for snacking are getting very soggy. They are very NOT HAPPY about this!
In the space today I found that the floor is indeed buckling way too much.
We put some data-loggers in the space from last Wednesday afternoon until about noon today.
The graphs from the loggers show some severe swings in humidity and temperature throughout the period. Values are as follows.
Front of space/reception area:
Temp Min 69.20 deg. F Temp Max 78.68 deg F
RH% Min 54.8 %RH RH% Max 80.06 %RH
Rear of space/Wash Station-Hair drying area
Temp Min 69.59 deg F Temp Max 79.36 deg F
RH% Min 52.31 %RH RH% Max 78.18 %RH
Above Drop Ceiling next to Front Return Grille
Temp Min 69.79 deg F Temp Max 79.95 deg F
RH% Min 52.72 %RH RH% Max 76.38 %RH
If you can imagine the graphs as a saw toothed wave, the Temperature and Humidity readings are moving in opposite directions during the 24 hr periods of the days. When the temp decreases, the humidity rises. And, when the temp rises, the humidity decreases.
I took our balometer and checked airflow volumes between supplies and returns and found one problem. There are 859 cfm's of air coming from all the supply grilles and only 596 cfm's of air through the return grilles. The supplies are all 6" round runs with a 6' flex run to the lay-in grilles. They average about 72 cfm each.
There are two 24x24 lay-in return filter grilles for 20x20x1 filters with a 14" flex run each to the return plenum under the unit. There were 1" pleated filters in the grilles with 2" pleated filters in the RTU. I removed the 1" filters from the grilles. I still don't have enough return airflow.
I checked on my Ductulator and found that the return plenum needs to be 15" x 20" and that is what it is into the unit. With two 14" return runs to the plenum, there should be plenty of return air.
I have opened the sheave on the blower motor as far as I dare to slow the blower and give the evap coil a bit more ability to collect the latent heat from the air. I helped another tech a few days ago and we found the set-screw on the adjustable sheave had worked loose and spun itself shut running the blower too fast and drawing moisture off of the evap. coil. We do not have a tachometer so I can't reference the fan curve to see what is happening with the blower.
I checked the ductwork and did not find any leakage anywhere I could look. Unfortunately, it's a bit higher off the floor than I can reach even with a ladder, it was a visual inspection mostly.
Where the plenums joins the bottom of the RTU, both are well sealed. I probed around with a small wire and met resistance all around the perimeter, no openings.
There is a fresh-air intake on the return panel of the unit, it has been completely closed.
I do not find any problems with the refrigeration circuit of this unit. It's a CARRIER 48TFD006A511, Serial# 1604G20288. My ODA was 92 deg. F and my pressures were 265 psig high and 82 psig low. My return temp was 77 deg F and the supply was 58 deg F. These were taken at the unit, across the coil. On the grilles inside I only got an 11 deg F Delta-T. All the ductwork is insulated. I didn't take SH and SC as I felt they were not necessary for this problem. The unit is removing as much moisture from the air as it can, good pee-stream from the condensate drain and, it is removing a fair amount of heat from the space as the air from the condenser coil was rather warm. Hands-on measurement, didn't use the thermometer. I am concerned about the 82 psig suction pressure with the 77 deg F return air temp. The pressure seems a bit high for that temp. This unit has a metered header leading into the evap coil, no restrictions there. There were no leaks of outside air into the unit that I could find except for the screw slots on the fresh-air damper on the return panel. Those slots are 1/4" wide and about 3-4" long, with a gasket behind them. Shouldn't be enough infiltration to be a concern.
The tenant is past becoming upset about this and has told me that she is going to call her landlord and tell them she is leaving the space if the problem is not corrected. According to the tenant, there have been 8 seperate service techs out there to work on this problem and I'm No. 9. She's very unhappy with the service she is getting and the fact that her expensive new floor is coming apart and also causing people to trip from the pressure ridges.
My biggest concern is, where is all this extra latent heat coming from and how can I get rid of it? And, why were there no problems with the old unit and this one is nothing but a problem? The old one was replaced due to a lightning strike and the new one has been hit twice since install, I've been told. The old one was a CARRIER also so, keep the derogatory comments to yourself please. I've only been on this one twice and I thought I had it the last time. I was wrong!
I apologize for the length of this read. I figured giving all the info I had would be helpful to those who can help me. I appreciate all attempts to help me solve this problem. THANK YOU!!
with balometers you will hardly find two the same. I would not worry to much about your return being slightly lower due to infiltration of outside air @ your outdoor air intake. even fully shut you are pulling outside air.I am more worried about your 800+ cfm. you should be up around 2000cfm and you will have to be more specific on your temp/hum charting.
what is the weather like?
[Edited by svc on 08-02-2004 at 10:07 PM]
08-02-2004, 09:33 PM
4 TON? If so, the cfms top limit should be 1600 cfm and the bottom should be 1280 cfm.
[Edited by rob10 on 08-02-2004 at 09:35 PM]
08-02-2004, 09:39 PM
Hey maybe i can help here, you are on the right track about the blower I have had that same problem adjusted airflow and humidity problem went away (adjusted sheaves). Is this unit short cycling at all on temp? Is the space temp dropping to fast? Do you know how long it takes the space to pull down say from 78f to 70f . Also I wonder about those 2- 14 inch return grills sounds like you have enough return air did you make sure the flex is not kinked going back to unit. Where are you pulling the return air from I'm concerned about the 77 deg return, also i see this unit is going off at night is this causing floor to buckle?? and one more thing why the hell would you put wood floors in a hair salon that with all the water and crap in the salon should have went with tile.. JMO
08-02-2004, 10:07 PM
What kind of metering device does this unit have? If it's a piston, I'm thinking maybe it's just slightly not seated properly? I actually had this problem once. Just slapping the gauges on, everything looked normal (this is before I really understood the value of superheat/subcooling), but in the heat of the day the tenant complained of sub-par cooling. Sure, the unit still cooled, but not like it should, and when I'd visit the apartment in the hot afternoon, the air was somewhat cool, but sticky.
I took apart piston after pumpdown and found it ever so slightly not seating correctly due to just a minute amount of trash. Cleaned it up, reassembled, restored charge, got great cooling and a really happy tenant.
I'm a bit surprised as thoroughly as you've gone over this system and ductwork that you skipped superheat and subcooling. Had I done that on the apartment unit I would've found the problem in a heartbeat. As it was I made a good stab and got lucky. Since I've learned the value of these readings, just feeling things isn't good enough for me anymore. I still do it, but go by the line, "trust, but verify" when it comes to my senses.
08-02-2004, 11:17 PM
svc, I have opened the sheave on the blower motor in an effort to reduce the amount of latent heat in the space. I knew this would cause a corresponding decrease in overall cfm of airflow but, my main concern is removing the excess latent heat. Weather here in Columbia, SC has been mostly rainy for much of the last several weeks/months. This is the only unit of ours, that I know about, that is having such difficulty keeping the RH at a reasonable level in the space.
I did consider posting the graphs in this thread but decided it wouldn't show very well as the lines on the graphs are rather thin and light and they would, most likely, have gotten lost through the process of scanning and posting.
rob10, this is a 5 ton RTU so I am aware that my airflow should be about 2000 cfm with a minimum of no less than maybe 1600 cfm. When I came to this job last week, we found the sheave had closed itself from a loose setscrew on the adjusting half and caused the blower to run so fast that it pulled condensate off of the evap coil. I thought this was the problem the tenant was complaining about when we were told her printer paper was curling instead of laying flat as paper should.
service guy, as near as I can tell, the unit is not short cycling. The thermostat is set at about 73 deg F for cooling and seems to maintain that temp, at the thermostat that is. Space temp does not seem to be dropping too fast but, the scale on the data-loggers I used were set for hourly measurements. The trend seems to be about 12 hours between lowest and highest temp readings. Lowest for one was about 69 deg F and highest was 74 deg F.
I did look at the return flex runs and they are not kinked and are resonably supported from the grille to the plenum. The grille in the front of the space, however, is pulling about twice the cfm's as the grille in the rear of the space. I can't get to the flex easily enough to see if the liner has fallen in the rear flex.
All of the return is pulled through two return filter grilles in the drop ceiling in the space with no filters in them. I removed them earlier, there are filters in the RTU already.
As for wood floors in a hair salon, I am very aware of the latent heat load in these type establishments. I, too, would have used VCT for the floor. I think the tenant may have been trying to "put on airs" as I have heard situations like this described, know what I mean?
Most of the heat load will be staff, customers, hair dryers, hair wash stations, pedicure and manicure station, some electronic equipment, picture windows at the front of the space, tinted, and some incandescent lights in the ceiling. Not many of those though, mostly flourescent lighting.
shophound, this unit is one of those CARRIERS where the metering orifices are in the liquid line header at the evaporator. 7 or 8 circuits each with their own fixed orifice. No seating problem there, it can't move.
I agree about the importance of SH and SC measurements but, as I said, I felt they weren't necessary here. I'm more than confident the charge is correct and that there are no restrictions or bypassing in the refrigerant circuit. I will be honest, the majority of the time I do use SH and SC measurements. I'll be going back to this unit probably in the near future so I'll get them just to be absolutely sure. I also just remembered, I lost my clamp thermometer just recently so I couldn't get an SC or SH reading to save my life, I had to do it the old schooler's way today. I'll have a replacement soon though.
I know it is removing the latent heat but, it isn't removing enough. I'm wondering if this unit is being subjected to an increasing latent heat load throughout the day or is it something else?
Again, I appreciate your responses. Thank You!!
08-02-2004, 11:17 PM
5 tons with under 1000 cfm and what looks like a slightly higher than normal suction pressure doesn't add up. The combination of multiple techs and 2 sets of pleated filters would really get me thinking someone had screwed with the charge.
Does the humidity drop at night ? and the temp remain stable all day long ? If they have a gas fired water heater might want to check the venting on it.
08-02-2004, 11:39 PM
you need to find why cfm is so low.
static pressure profile of the unit would help.
or have test and balance stop by and check out the cfm problem.
08-03-2004, 12:01 AM
I think I would start over.Speed the blower back up to 2000 cfm & take your sh/sc readings.
08-03-2004, 07:08 AM
If you are starting at the unit with a 20 degree split but only ending up with 11 degrees at the vents, you have some severe duct loss/gains. Since you are short on the return air measurements, start with checking the return for duct leaks. Is this unit a downflow? The horizontal access panels can be removed for you to look down the duct from the roof and you can check the seal at the roof and make sure that it is sealed OK. I had a customer complain of high humidity after a remodel and found the HVAC contractor the general hired set these same units on curbs with 3" hanging open on the return end. The same curb is used on multiple tonnages and you must shove the unit all the way forward at the return end. If you have this, both the supply and return will be leaking at the roof. If there is a dent in the middle of the unit, supply can go back into return but that would make your suction pressure and temperature lower. I don't know how you are maintaining that suction pressure at those CFM's! You're at half of the minimum you should be at, that is if you are catching it all.
08-03-2004, 09:29 AM
I agree with the others get the air flow as close to 2000 cfm also can you trend the data in 5 min intervals. you need to know what the humidity in the space is, the supply air temperature, and the space temperature. then compare the space temperature and humidity on a psychrometric chart and see if your supply air temperature is getting below the dew point on the chart. If not you have equipment problems if it is getting below the dew point check for outside infiltration. also tell them to shut the door.
08-03-2004, 12:46 PM
Get the airflow back up and recheck system SH. Also, is the fan cycling with temp or is fan running continuously? Could be putting removed moisture right back into area after mechanical shuts down, causes spikes in RH as system cycles.
08-03-2004, 01:32 PM
To me, it's all in the basics. Get back on the roof and set the system up the way it is designed to be, airflow, temp drop, RA ari temps, SA temps, pressures, amp draw, etc, etc. Once that is established go into the space and measure for the same airflow and, especially, compare the supply temps and the return air temp to what you had on the roof. If they are different, there is your problem.
BTW, do your installers install a new thermostat and, if so, have they configured it correctly? Is there a hole in the wall behind it setting off the thermostat too soon or too late?
Record all the normal basics and tell us what they are. That will point to what your problem is.
08-03-2004, 06:37 PM
I'd expect 100-110 cfm through a 6" w/flex. I like what seaboard says about the curb. Your suction is way up there and should mean almost too much air for the space temp but your reading too low total cfm. If you were sucking outside air and loosing supply air on the curb this would give similar results.
08-03-2004, 11:05 PM
I spoke with our other two, more seasoned, techs about this problem this morning. I know that we have done PM's on this unit at least twice since it was installed. Our PM techs are our apprentices and I'm wondering, like cynic mentioned, if one of our PM techs found a low suction pressure because the filters indoors were seriously stopped up and added refrigerant to get the pressures right.
I have been after all of them to take temperature measurements whenever they are working with any system and I don't think it's quite sunk in yet. I'm keeping after them about this, it's too important. But then again, I did shrug off SC and SH on this unit so I can't rag them too hard. Man, did I goof or what?
I told our service dispatcher, who runs the show anyway contrary to the service mgr's beliefs, that I want to go back and recover the refrigerant and get it weighed in properly, reset the airflow and see what happens. One of my bosses, who set up this changeout spoke with me today about this unit and I told him the same thing. He thought that the charge should be correct since the unit was charged at the factory. I stated my concern about the PM techs so he knows where I stand. I think he's going to bring CARRIER in on this one. BTW, I have had a TRANE RTU that lost a compressor and when I recovered the refrigerant, it had THREE TIMES the listed charge weight in it. No wonder the compressor failed, it was trying to pump straight liquid. And, I know that the factory can make mistakes also so, I want to recover and recharge to be certain.
I checked the curb most thoroughly and found that the unit and the curb are tightly sealed together, I can't find any outside air infiltration anywhere, except for the screw slots on the fresh air damper. That is one of the main reasons I'm suspecting an overcharge at this point. The suction pressure was too high for the return air temp and it's all return air. And, of course, I feel like an idiot for not taking SC and SH. These would have shown the problem immediately.
Well, if you don't screwup once in awhile, you're doing something wrong. Right?
DeltaT, for whatever reason unknown to me, this one of my bosses has yet to install a new thermosat when he sells a changeout. Invariably, one of us techs gets to go back and install a new T'stat because the old one failed. This is the same Honeywell T-87 style T'stat that was installed with the previous unit maybe 8 years ago. I did check the calibration and found it is within one degree of what my thermometer showed the temp at that point on the wall to be. It is mounted on an interior wall so I don't believe there is any surplus or lack of heat there to affect it's operation.
I'm having to deal with two messed up hydronic systems at other jobsites and numerous service calls so I'm not real sure if I'll be back on this job any time soon. I may know something tomorrow or Friday but, I'm not holding my breath. I'll keep up with the updates anyway, I want this thing fixed, more than the customer does.
08-04-2004, 01:14 AM
Originally posted by william antley
DeltaT, for whatever reason unknown to me, this one of my bosses has yet to install a new thermosat when he sells a changeout.
This is the same Honeywell T-87 style T'stat that was installed with the previous unit maybe 8 years ago.
So, here's what you do. Make any kind of excuse to get that boss to go look at that roof top unit and get him up on that roof....and push him off!
Can't believe he is so cheap and short sighted. I bet when he gets new tires for your vans he only buys 3 new tires.
08-04-2004, 07:04 AM
Doing that sounds like a good idea but, he's the one who signs the paychecks. The other guys may not be too happy with me if I did that. LOL
As far as tires go, he doesn't have much say about that. The owner makes sure we take care of the trucks.
But, I'm gonna keep nosing around to find out what is going on. The tenant there is only slightly more bothered by this than I am so, I'm not gonna let it lay. If I have any say, it's gonna get fixed and fixed right.
08-04-2004, 08:47 PM
You're going to have to get the suction pressure down to remove the humidity.
With a pressure of 82psi, no part of of your evaporator is going to be below 49F. If you perfectly sealed the building and ducts, you could theoretically pull the dew point down to 49F, which at 72F room yields about 45% relative humidity. Given the reality of imperfect systems, real life doors and leaks, and a heck of a moisture load from the operations, you will never even get close.
At this point the airflow issue is irrelevant, excepting that it marginally effects evap pressure. You have another problem somewhere.
Obviously, as others have said, SH/SC numbers would be very helpful for diagnosis.
08-04-2004, 09:36 PM
I spoke with the boss this morning and told him my concerns and the results of the discussion with the other two techs.
I went back to the site this morning and recovered the refrigerant and, lo and behold, it WAS overcharged. I pulled out 11 lbs 9 oz. The plate rate was for 7 lbs 14 ozs. It must have been a "friday" unit.
I recycled the refrigerant to the plate rating, may have been short by .015 lbs-no problem, and checked it against the mfr's charging chart. The readings were dead-on with the chart after a suitable run time from restart.
I also sped up the blower to the original sheave setting and let it roll.
I'm going to put the data-loggers back into the space for a weekend of readings and download them on Monday and see how it's doing now.
My biggest concern now, aside from the unit still messing up, is how soon we'll have to replace the compressor. Near the end of the recovery the bottom 4" of the compressor was covered in ice. After some more recovery the recovery machine would get into a vacuum, about 6-8" hg and rise back up to 0-.5 psig. Freon under the oil so I'm wondering when the bearings will fail.
I left the machine going until it held about 10" hg vacuum and put a vacuum pump on after that for awhile. I let it run to maybe 27-28" hg for about thirty minutes. Hopefully I got any remaining refrigerant from under the oil.
I'll know more Monday when I download the loggers.
08-04-2004, 10:12 PM
I notice from a lot of posts on this web-site that overcharge is a common diagnosis. Are there really that many guys out there dumping refrigerant in units based solely on a low suction pressure? The pressures you stated in your original post do not look like an overcharge. If those pressures and your airflow measurements are correct, you very well could have bad compressor valves. That would definately cause the unit to cool perhaps OK but not have a cold enough evaporator to take the humidity out well. I would start by measuring those temps again at the unit and at the registers. See if that temp gain/loss you had is on the return or supply side or both. Sounds like your losing half your effective cooling above the ceiling. Check the door and see if the building is under positive or negative pressure. We recently wrapped up a project installing 269 new Carriers and I am getting similar complaints of high humidity. The weather here has been freaky here lately however. We are experiencing rain everyday but the temps have generally stayed below 90 so the load is not high enough to dry the air out great. Tenants are complaining everywhere. The old units of course suffered from low air flow due to banged up coils and dirty blowers but I guess they dehumidified great when we could keep them running!
08-04-2004, 11:15 PM
Seabord....... when I saw multiple techs and 2 sets of pleated filters two names of people I work with (and several more that I can't remember their names but have long since been fired) popped right into my mind. I deal with overcharged stuff far too often.
08-04-2004, 11:44 PM
Sounds like the apartment maintenance guys I saw today on a job. They were driving a golf cart around all the buildings. Their only supplies were a box of light bulbs and a jug of R-22 that was continuosly attatched to a set of guages. "Doesn't work huh? Must need freon."
08-05-2004, 09:42 PM
Just one more thing to think about.....I know it was mentioned earlier but try setting the fan to auto if that is not already the case, this can be really helpful. And find a way to get to those ducts if correcting the charge and blower speed does not help. I am changing a 6 year old copeland 5 ton can tomorrow due to weak valves that manifested itself in a high humidity problem.............High suction = Less latent heat removal capacity as I'm sure you are aware.
08-05-2004, 11:45 PM
I've been keeping up with our seniorest tech about this unit. He called me today with a similar problem. He had 18 units to start-up at a local high school and the ones he had checked up to calling me were exhibiting similar pressures and temperatures as the one I've been fussing with. I asked him to get some superheats on a few of them to see what is happening. I'll see him Friday morn and I'll ask him about it. We're now thinking that whatever device the tech at the manufacturing plant is using to weigh in the charge may be seriously out of calibration.
If this is so, we're gonna take it up with Carrier, this may be a BIG problem for them.
The fan was set for "auto" and the setpoint is at 72 deg. F. I'll get the data-loggers Monday and get the info to see what is happening now. When I went in the shop this morning I checked the floor where there were pressure ridges. The ones I checked seemed to be less high than they had been. I'll know more sometime Monday.
08-06-2004, 07:53 AM
[Edited by spiderkiller on 08-06-2004 at 08:08 AM]
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