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Don't even know where to start on this one.
S Ebels
Member Posts: 2,322
I'll see if I can resize the pics.
Compressors are Trane
If you're refering to the hot gas solenoid, it appears to be just a normal refrig type unit to me.
Single circuit evap and condenser
I have no idea on anything to do with the control side of things. The cabinet was locked and there was no schematic left on the premisis. I think they wanted to be sure their company was the only one that was called back.
Now the pics
On the picture of the compressors you can see the hot gas solenoid in the upper left corner.
The face damper covers better than half of the evap coil and as you can see it's wired into the DDC system
The copper tube running across the air blender appears to be a home made cap tube of some kind. It's also connected to the DDC
In the evap piping picture,you can see the hot gas bypass tee'd into the liquid line right next to the cabinet and after the lower TXV. Both the 10T and the 15T are pumping through the uninsulated 1 1/8" copper line.
On the pic of the accumulator you can see two pressure sensing devices near the top. One is tapped into the high side and one is in the low side. Both are wired to the DDC. I know they are using them to sense pressure but I can't tell what exactly they would affect if they see pressure outside of their limits. What would they be controlling with these?
There are three areas on the condenser that are leaking just like the one in the pic. Anyone ever try a product called Super Seal 3 Phase on a leak like this?
Compressors are Trane
If you're refering to the hot gas solenoid, it appears to be just a normal refrig type unit to me.
Single circuit evap and condenser
I have no idea on anything to do with the control side of things. The cabinet was locked and there was no schematic left on the premisis. I think they wanted to be sure their company was the only one that was called back.
Now the pics
On the picture of the compressors you can see the hot gas solenoid in the upper left corner.
The face damper covers better than half of the evap coil and as you can see it's wired into the DDC system
The copper tube running across the air blender appears to be a home made cap tube of some kind. It's also connected to the DDC
In the evap piping picture,you can see the hot gas bypass tee'd into the liquid line right next to the cabinet and after the lower TXV. Both the 10T and the 15T are pumping through the uninsulated 1 1/8" copper line.
On the pic of the accumulator you can see two pressure sensing devices near the top. One is tapped into the high side and one is in the low side. Both are wired to the DDC. I know they are using them to sense pressure but I can't tell what exactly they would affect if they see pressure outside of their limits. What would they be controlling with these?
There are three areas on the condenser that are leaking just like the one in the pic. Anyone ever try a product called Super Seal 3 Phase on a leak like this?
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Comments
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So oversized it's just stupid
We recently signed on the dotted line to do service, maintenance and equipment changeouts for a chain of banks here in Northern Michigan so I've been going around documenting all the equipment. I came across this system at one of the branches which is basically a house type structure with a full basement and 2 floors above ground. When I looked at it, I couldn't believe what I was seeing. It's so over sized, over engineered, over built that it should never have been installed in a building of this size.
As brief as I can be, there's a Trane 25 Ton split system airhandler serving the basement and first floor. The system uses a 400K Bryan flex tube boiler for heat with coils in the ducts as near as I can figure out. The velocity noise in the duct system sounds like you're driving down the road at 60mph with the windows down. They put up with that all day long because it's constant fan. I can't see as anything can be changed regarding that problem.
The condenser coil appears to have developed a few leaks as there is evidence of attempted repairs in three spots. The 15 Ton compressor was manually disabled and the whole thing is running on the 10 ton which is in reality about all the building needs for the 6,500 sq ft it's cooling for the first floor and the basement. (The basement was about 55* when I was there.)
The second floor has its own separate system which consists of 3, 80K Lennox Pulse furnaces each with a 3T A/C condenser. So we have 240,000 input for heating and 9 Tons of cooling in an area of roughly 5,500 sq ft.on the second floor.
I did a rough heat loss figuring WaaaaaY bad infiltration (1 AC/H)
to account for outside air ducted into the system and still only came up with 11 Tons cooling and 129,000 heating load for the first floor and the basement which the 25T system serves.
So my question is, can you think of any solutions to the constant short cycling of the A/C compressors. When both are running they cycle about every 5-10 minutes. Service life is poor obviously because I was told they've burned out 2 of the 10T's and 3 of the 15T's since 1998 when the system was installed. Any options you can think of for taming the air flow without messing up the A/C side?
I'll attach a couple pics of the building and some of the equipment to give you an idea of what I have to deal with here. The whole thing looks like some mechanical engineers wet dream.0 -
see it alot
Steve like your self i also do see alot of commerical jobs that are way over sized with roof tops and big splits .On the few that we where given card blanch we just threw all the junk away and started over ,in one instance we removed 2 15 ton units and re did the whole job duct work and all and installed 2 5 ton roof tops the what i call jet fan noises where a thing of the past we did seperate supply and retruns for each office and lobby ,not a return pleum or pulling from above the cieling .We ducted each return back to a main trunck ,i a;lso sized my ducts and runs properly so now the system is so quite that you barely can here the unit running ,i also enourage a constance fan it combined with seperate supply and returns will give you a excellent overall temp in my experences done this way my room temps will not vary more then 1.5 to 2 degrees another plus of constance fan is when couplered with a ecomizer or outside air will keep the building from feeling like it's full of stale air .I know that just about all the commerical building i run into are way oversized and most where not the installation companies fault it was a design engeener who speced it all and gets a percentage of final cost for using his design and spec and nobody with out a few letter at the end of there names will challenge them you know that .There's are real golden rule that states you have to know what you can and whatr you can and the smrts to know what you can,t change .peace and good luck clammyR.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating0 -
11 tons ?
Few thoughts..... Why are both stages trying to run if not needed would be the first thing I would look at. rawal valve(s) might be an option haven't installed one yet but have seen a couple. Hot gas bypass if 2 more pipes could be run from condensing unit.... actually combine hot gas bypass with a bypass between the supply and return to slow the airflow may solve both problems.
How much outdoor air is actually called for and more importantly is it actually coming in ? I have had to eat my words about stuff being oversized it is 98% of the time but they sized it for a design day with no consideration of reality.0 -
I have to study this thing more..........
It appears that there is some type of an air bypass in the AHU. There is junk hung all over this thing including several pressure sensors attached to the supply duct which look like they "talk" to the bypass damper. Jim Bergman brought up the possibility of the scroll type compressors rotating backwards as pressures equalize when they shut off. Sounds plausible because of the number of compressors they have gone through in only 8 years of operation, There are no check valves in the piping which would prevent this.
Tell me what Hot gas bypass would do for this system. I'm familiar with the process but only in the context of using it to defrost coils in commercial freezers. I'm all ears!0 -
Classic DX issue, Steve
As anothermarty suggested, hot gas bypass is a way to cheat the system and get it to behave. I have to think that it will be pretty muggy in such a building with all of that tonnage. What is the CFM of the Trane unit? And how much outside air?
If the OD design is 90 with a 74 degree wetbulb and the unit takes in 20% outside air, such a unit would require a total cooling load of 35.74 BTUH per CFM. Expressed another way, the unit would have a per-ton airflow rate of 336 CFM per Ton. Just a check figure anyway. And that is on a peak day, 1 to 5 percent of the time if that.
The only way I know to rectify this is to install smaller compressor increments to better respond to the loading, but the piping and controls would be a mess.
VAV is out if you stay with DX cooling. The DX controls would not likely respond fast enough and you would freeze your evaporator.
My solution? Take out the DX refrigerant coil and condenser. Install a small air cooled chiller and a VFD on the AHU supply fan responding to return air temperature. You did not mention what if any terminal control they have. I like the self-contained thermostatic diffusers, sort of the lowest denominator of VAV control. But at least with chilled water the coil will respond to VAV control and not frost over.
A block of thoughts, not the final word by any means.0 -
Hot Gas Bypass
takes hot gas from the compressor (before the condenser) and meters it into the evaporator, imposing a load on the system. Energy hog and is outlawed by many energy codes (and ignored sometimes out of necessity). But your commercial freezer experience is essentially the same principle.
The bypass duct you mention could be "face and bypass" as a means of discharge air control. This is a tough thing for you could drop your air volume below the freeze-point of the coil. What the bypass duct may be is air volume control. You may have VAV boxes out in the space- might this be the case? When such boxes throttle down as their spaces become satisifed, the air has to go somewhere and this may be what your bypass duct is about. Poor Man's VAV I would call it. Downside (is there an upside here?
is that the cold air bypassed to the return can cause short cycling because the temperature is satisfied almost immediately. And with 25 tons if it was running as such, that is a fast event. 0 -
I have a feeling
It looks like someone may have tried a bypass system somewhat like you describe. Not really a bypass from the cursory look that I gave the thing, more like just a throttling damper on the intake side of the blower. I noticed a damper control/actuator on the side of the air handler and I can't imagine what else a damper in that location would be used for. I'm no commercial A/C expert but if that's what the damper is there for, it seems like it would cause a lot more problems than it would solve.
If you look at picture 159, you can see the actuator mounted on the side of the AHU. From right to left you are looking at the blower cabinet, then the evap coil cabinet and the next cabinet is called an air blending unit. The conduit contains a what looks like a sensor that goes into the fan side and into the air blender. The damper is on the inlet side of the evap coil and I have no idea what is in the air blender.
If they want to pursue "fixing" the system, I'll have to start taking things apart until I understand what is trying to be accomplished. From what I was told, they just had a controls company come in and add a bunch of stuff, to the tune of $7,800 (the facilities coordinator didn't know exactly what) that was supposed to relieve the air noise and solve the on going self destruction of the compressors. Obviously didn't work.
It's always fun getting into a malfunctioning system after several other companies have tried their hand at "fixing" a problem(s). You have to find the original problem and start working from there to understand what all the other repairs were supposed to do.0 -
good luck
There are a pile of clues that at some point in time that basement air handler did the whole building. If it did all the money spent to get things working right( enough parts, time and money anything can be made to work) may be better spent on a correct sized replacement.0 -
Air Blenders and other devices
Steve- An air blender is a type of diffuser which imparts a vortex on incoming airstreams. I am always pleased to see them for they mix better than opposed dampers and afford less sensor error downstream. The damper actuator if it is upstream of the evaporator? My first inclination is that it is a face and bypass damper with an internal bypass path over or under the cooling coil. I use them in Florida, not in Michigan... so my second guess is that it is strictly a volume damper. But regardless, without precise metering of refrigerant and modulating of capacity, you are asking for problems. Frosted coil would be the first symptom.
I agree with you, you have to "get into the head" of the original designer. In the meantime, if you have to adjust to keep capacity and AC in operation versus cycling, outside air would be your ace. Increase the amount of OA to increase the load until the system gets into a stable operating range consistent with however much functional tonnage you have left.
Another observation: The AHU is mounted right on grade. How is the cooling coil condensate removed? Is the coil trap in a pit on the opposite side? You would need some height to maintain a seal and keep drainage flow going.
Any air balancing reports to get a handle on airside performance? That is where I would start.
Keep me posted-
Brad0 -
How else will they keep the supply of cold cash?
The bank should add on a wing to its building, just large enough to match the excess mechanical room capacity. Easy.
Along those same lines, could it be possible to have the whole building cooled with the giant cooler? I am assuming the giant condenser is ok, now, you could increase the total evaporator size for your giant unit by piping the refrigerant lines for the three upstairs evaporators into this one system rather than each into their own compressor/condenser unit. This should better match the giant compressor operation and increase efficiency. With thermostatic expansion valves, oversized evaporators shouldn't be complicating your life, and then you could reduce airflow.
The hot gas bypass is an energy taboo, but it will save the compressor. In a weird way, it provides the superheat I think your system badly needs right now.
Am I making sense so far? I am just thinking of ideas for the fun of it. Here's another one.
What about installing a variable frequency drive on the compressor itself? Now, instead of the motor turning itself on and off every five minutes, it will simply run at half the power. Variable frequency drives have gotten cheap nowadays, it might be worth a try. Some new AC machines have them built in, why shouldn't your bank have one too?
I am not sure my thinking cap is on straight tonight, but I thought I'd jump in anyways.
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Mr. Ebels:
Reading over the post it does sound like you have a constance air volume system. Or something like a carrie's VVT system. More likely the frist.
With the boilers in the system and coils thoughtout the systems they could be or are reheat coils. As told to you before in an eariler post their could be VAV boxes out in the system which is more probabale becuse it is a bank and has a commerical system in it.
What kind of control system does it have? pneumatics, metasys, andover or maybe automatic logic? Look at the dampers at the air handler. Does it have two damper to the out side? one before other? In these type of systems you have a discharge air damper and a freah air intake that is before the mixing chamber. Many of the new systems we put in have VFD drive on them now.
Another thing to look at is this a single duct system or a duel duct?
Thier is more than one way to control these systems and tearing out the system and puting in a lite commerical RTU system is not really the answer.
were are you located?
Larry0 -
OMG! 34 tons of cooling?? In northern Michigan???
That's not a wet dream--it's a 24-7 beat-off... No wonder that it's self-destructing.
As to taming those beasts?
LOTS of fresh air intake? While possibly beyond the abilities of the device, check out www.rawal.com for proportional unloading of the condensing unit. Call/write/fax the inventor--he's quite helpful and won't steer you wrong. Multiple evaps served by a single condensing unit are possible.
As to velocity noise? High-quality VS controllers for the blower motors??? With LOTS of unloading that's almost certain to be constant, surely you can significantly reduce velocity with little concern for a freeze-up.
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Anothermarty
The AHU in the basement just serves the basement and the first floor, always has. The facilities coordinator told me that the second floor has always been served by the 3 lennox furnaces w A/C's that are there now. I'm going up there tomorrow to check some pressures and take a few panels off and see wht's going on. I'm curious as to what configuration the damper in the evap coil is and I also want to find out what an "air blending cabinet" is.0 -
Air blenders, dampers and drains, OH MY!
"Steve- An air blender is a type of diffuser which imparts a vortex on incoming airstreams."
OK, so why do I want a vortex in the first place?
"But regardless, without precise metering of refrigerant and modulating of capacity, you are asking for problems."
I've been thinking about the damper, where it is placed etc. and I think it must have intended it to serve as a restrictor in the airflow. A couple people in the building told me that the noise wasn't as bad as it used to be since that was installed last year. (It's still bad, must have been horrible before) Now, we have excess condensing power for the load in the first place, what happens when we remove more of the load by reducing airflow? One guess I have is that the TXV's can't compensate that much and liquid refrigerant is slugging back to the compressors. Could be a cause, maybe not the only cause, of all the failures.
The drain trap is indeed sub surface. Good eye for the Brad guy.
Going back there tomorrow in order to get some measurements on duct pressure, refrigerant pressure, temps and dimensions of the fresh air intake duct along with damper operation. Also going to try and figure out what exactly controls this whole mess. It ain't no T-87, that much is for sure.0 -
Dat's right
25 tons + 9 tons = 34tons or 408,000 btu's of cooling power for about 20,000 sq ft. Approximately 7,000 of which is underground.........must have been for dehumidification down there. The system designer must have used the old rule of thumb that said you need 1 ton of cooling for every 600 sq ft.
The only thing I can figure is the system was designed for "blow through" ventilation in the summer. As in 100% outside air.
I'll check out the Rawal thing.
The blower motor is singular, not plural, as in one. Probably in the 7.5 HP range.
A really neat, helpful thing is that I am about the 6th contractor to look at and suggest a remedy for this system. All the others have been "let go" along with the original designer and installation company from what I understand.
What this thing needs would be the A/C equivalent of outdoor reset with variable speed pumps. There has to be something like that available for this type of use. We have a 100HP rack system in the store for the frozen cases and it has a control the stages and rotates the compressors as the load requires. Maybe I'll start with those guys.0 -
Vortices...
Everyone ought to have a vortex, Steve- Get yours today!
The blender, take a look at it. By swirling the air, breaking the upstream air into separate streams and forcing them on the downstream side against each other, they do a fantastic job of mixing airstreams of disparate temperatures. Downstream the hot and cold spots are minimized so sensors do not "hunt" on you or save you from tripping a freeze-stat.
As Larry suggests, I agree it is likely a constant volume system that maybe wants to be VAV... Yes, get the airflow data I am very curious as to how this system maps out. I wish you were closer to me, I'd come by to take a look.0 -
Definitely
Constant air volume, along with constant noise, constant cycling of the compressors etc, etc.
Controls are electrical made by Reliable Control company. Ever hear of them?
Single duct and damper on the outside air.
This system is crying out for VFD.
Single duct, Dual duct??
Tearing it all out would be the last resort and I would never advise them to do so. You would have to shut down the building and I doubt they are interested in that.
I'm in Northern Lower Michigan between Cadillac and Houghton Lake. The job is in Charlevoix.
To prove I'm from Michigan.......... turn your right hand over and look at your palm. I live at the web of your middle and ring finger, the job is at the tip of your ring finger. 
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Rawal variable expansion valve + variable speed drive for the blower = your solution. That is IF the Rawal valve can unload as much as seems to be required...
Inventor himself corresponds and he seems honest enough to say if his device will perform properly AND reliably with the system in question.0 -
Out in the sticks huh?
Then I take it you do not have a return air fan? They can be coaxil fans that looks kind of like a beer keg on it's side.
I haven't seen releiable control systems myself. I have seen a lot of old system and new one and it seem that every couple of months I run across something I have never seen. I do see a lot of releible transformer in control panel with control relays that is tried into a main panel. Likewise, some of these systems take a lot time to trace out when your not familular with them. Then again even when you are it still takes a lot of time to trace everything out and the locations of all the panels. A lot of time when you find the main panel you will find a print with orginal sequence of opperation in them. That is why this trade is so challaging sometimes. That and everyone thinks you should know everything as soon as you walk in the door. But if they will give some time you can figue it out.
Single duct comes out of the Air handler and supplies the VAV system with a mixed air tempature. It is related to the return air temp, room tempature and outside tempature. For, example if the return air is 78 and the room temp is 72 and the out side tempature is 85 you could have a mixed air temp of 65 to try and maintain room tempature output of the discharge of the duct single duct. Then out in the space if the discharge air become to cool you would have a reheat coil in the duct work by a VAV box. This system could have a heating coil in the air handler too. And this also is what was talked about in an earlier post with the face and by-pass damper one way it supplies heat and the other cooling. To give a mixed discharge air tempature.
A Duel duct system has the heating coil and cooling coil right at the Air handler and usally does not have reheats by the VAV boxes. But you will notice that it has two duct right off the discharge of the air handler. One duct is coming form the heating coil and the other form the cooling coil, then at the VAV boxes there are two round ducts one from the heat duct and one from the cooling duct these are attached to VAV Box to mix to a room supply tempature needed for that location.
What kind of thermostats are being used to make sure the room is satisfied?
Larry
P.S. what kind of damper motors are they using?0 -
I just notice your pictures. The trane air handler look and see if that reurn duct is tied into the outside aie grill it might be hard to tell until you open up the return air door and look up.
I have seen when you put in a commerical system and the local guy don't know how it work because they only do residenial that they willcome in later and rip some of it out and put in furnas. But I have also seem it done as a back up system too.
Larry0 -
Larry
Yep! I'm in the sticks and I love it. I live, play and work where most folks want to retire. I can look out my door across about a mile and a half of fields and see the farm where my mom was born and raised. If I want to go hunting or fishing, I just have to grab my gear and walk out the door.
Are you in Michigan?
Back to the topic at hand. All the hot water boiler piping goes up into the ceiling and it looks as though there may be multiple heating coils located throughout the duct system. There are no boiler pipes anywhere around the AHU. I want to track those coils down tomorrow and see how they are controlled. There doesn't seem to be any logic to the system as far as warm weather shutdown goes. When I was there last week the outdoor temp was 82-84* and the boiler temp was standing at 180* with the circulator running.
I'll have some more pics tomorrow night along with some details.0 -
Found out today
A: The Reliable control system is made in house by the HVAC contractor that installed it. There's a 30"x30" cabinet on the wall behind the AHU that controls everything in the building HVAC wise. It is locked and no-one in the bank has a key. The bank manager said "They told us that no one else could service the system but them so there was no reason to leave a key". Nice!
B: It is piped for hot gas bypass. I kept looking at this one line that t'd into the liquid line after the TXV and before the "header?" where the liquid line branches out into the evap coil. Wondered what the heck are they dumping liquid into the low pressure side of the system for. So I traced it back into the outdoor unit and found that it t's directly off the compressor discharge BEFORE reaching the condenser. There's a solenoid on the hot gas side that is wired into the afore mentioned control box. Interestingly, The schematic furnished by Trane also shows provision for hot gas bypass but it doesn't wire in to where Trane shows it.
C: Brad, I see what you mean about the vortex in the air blender. Those diffusers would definitely rototill the air flow.
There is a damper that covers half the face of the evap coil. It too, is wired into the nonobtainium accesseum control box.
E: There are three condenser fans on top of the outdoor unit. The first one on is in a raised steel cabinet with motorized louvres on it.The other two are mounted on ring type fan gaurds. With just the 10T compressor running, the fan with the louvres is the only one blowing. Being that the other two are off, air is pulled into the cabinet on the downstream side of the condenser coil instead of being pulled through it. I noticed that the air temp coming from the operating discharge fan was nearly ambient and the condenser coil was hot. So being the experimentative type, I threw a couple big garbage bags over the non running fan openings. In a matter of about 2 minutes I had nice hot air (95* @ 64* ambient) coming from the operating fan. Went inside and checked discharge air temp from the AHU and it had dropped from 66* to 54* BINGO!!
So........
Any suggestions as far as dealing with the fan situation? Obviously, being that everything else looks OK, except the holes in the condenser coil, this seems to resolve the lack of cooling complaint.0 -
Found out today
A: The Reliable control system is made in house by the HVAC contractor that installed it. There's a 30"x30" cabinet on the wall behind the AHU that controls everything in the building HVAC wise. It is locked and no-one in the bank has a key. The bank manager said "They told us that no one else could service the system but them so there was no reason to leave a key". Nice!
B: It is piped for hot gas bypass. I kept looking at this one line that t'd into the liquid line after the TXV and before the "header?" where the liquid line branches out into the evap coil. Wondered what the heck are they dumping liquid into the low pressure side of the system for. So I traced it back into the outdoor unit and found that it t's directly off the compressor discharge BEFORE reaching the condenser. There's a solenoid on the hot gas side that is wired into the afore mentioned control box. Interestingly, The schematic furnished by Trane also shows provision for hot gas bypass but it doesn't wire in to where Trane shows it.
C: Brad, I see what you mean about the vortex in the air blender. Those diffusers would definitely rototill the air flow. There is a damper that covers half the face of the evap coil. It too, is wired into the nonobtainium accesseum control box.
E: There are three condenser fans on top of the outdoor unit. The first one on is in a raised steel cabinet with motorized louvres on it.The other two are mounted on ring type fan gaurds. With just the 10T compressor running, the fan with the louvres is the only one blowing. Being that the other two are off, air is pulled into the cabinet on the downstream side of the condenser coil instead of being pulled through it. I noticed that the air temp coming from the operating discharge fan was nearly ambient and the condenser coil was hot. So being the experimentative type, I threw a couple big garbage bags over the non running fan openings. In a matter of about 2 minutes I had nice hot air (95* @ 64* ambient) coming from the operating fan. Went inside and checked discharge air temp from the AHU and it had dropped from 66* to 54* BINGO!!
So........
Any suggestions as far as dealing with the fan situation? Obviously, being that everything else looks OK, except the holes in the condenser coil, this seems to resolve the lack of cooling complaint.0 -
Check
Check the rotation of the fan? Is it a three phase fan? Second check the location of the fan, being a frist stage it should draw air through the coil as you have figued out all ready. Is it riding in the shout correctly? To high or low I find this one all the time. Thrid is it missing a metal sperater between cells of fan?
Larry0 -
> A: The Reliable control system is made in house
> by the HVAC contractor that installed it. There's
> a 30"x30" cabinet on the wall behind the AHU that
> controls everything in the building HVAC wise. It
> is locked and no-one in the bank has a key. The
> bank manager said "They told us that no one else
> could service the system but them so there was no
> reason to leave a key". Nice!
>
> B: It is piped
> for hot gas bypass. I kept looking at this one
> line that t'd into the liquid line after the TXV
> and before the "header?" where the liquid line
> branches out into the evap coil. Wondered what
> the heck are they dumping liquid into the low
> pressure side of the system for. So I traced it
> back into the outdoor unit and found that it t's
> directly off the compressor discharge BEFORE
> reaching the condenser. There's a solenoid on the
> hot gas side that is wired into the afore
> mentioned control box. Interestingly, The
> schematic furnished by Trane also shows provision
> for hot gas bypass but it doesn't wire in to
> where Trane shows it.
>
> C: Brad, I see what you
> mean about the vortex in the air blender. Those
> diffusers would definitely rototill the air
> flow.
>
> There is a damper that covers half
> the face of the evap coil. It too, is wired into
> the nonobtainium accesseum control box.
>
> E:
> There are three condenser fans on top of the
> outdoor unit. The first one on is in a raised
> steel cabinet with motorized louvres on it.The
> other two are mounted on ring type fan gaurds.
> With just the 10T compressor running, the fan
> with the louvres is the only one blowing. Being
> that the other two are off, air is pulled into
> the cabinet on the downstream side of the
> condenser coil instead of being pulled through
> it. I noticed that the air temp coming from the
> operating discharge fan was nearly ambient and
> the condenser coil was hot. So being the
> experimentative type, I threw a couple big
> garbage bags over the non running fan openings.
> In a matter of about 2 minutes I had nice hot air
> (95* @ 64* ambient) coming from the operating
> fan. Went inside and checked discharge air temp
> from the AHU and it had dropped from 66* to 54*
> BINGO!!
>
> So........
>
> Any suggestions as far
> as dealing with the fan situation? Obviously,
> being that everything else looks OK, except the
> holes in the condenser coil, this seems to
> resolve the lack of cooling complaint.
0 -
> A: The Reliable control system is made in house
> by the HVAC contractor that installed it. There's
> a 30"x30" cabinet on the wall behind the AHU that
> controls everything in the building HVAC wise. It
> is locked and no-one in the bank has a key. The
> bank manager said "They told us that no one else
> could service the system but them so there was no
> reason to leave a key". Nice!
>
> B: It is piped
> for hot gas bypass. I kept looking at this one
> line that t'd into the liquid line after the TXV
> and before the "header?" where the liquid line
> branches out into the evap coil. Wondered what
> the heck are they dumping liquid into the low
> pressure side of the system for. So I traced it
> back into the outdoor unit and found that it t's
> directly off the compressor discharge BEFORE
> reaching the condenser. There's a solenoid on the
> hot gas side that is wired into the afore
> mentioned control box. Interestingly, The
> schematic furnished by Trane also shows provision
> for hot gas bypass but it doesn't wire in to
> where Trane shows it.
>
> C: Brad, I see what you
> mean about the vortex in the air blender. Those
> diffusers would definitely rototill the air
> flow.
>
> There is a damper that covers half
> the face of the evap coil. It too, is wired into
> the nonobtainium accesseum control box.
>
> E:
> There are three condenser fans on top of the
> outdoor unit. The first one on is in a raised
> steel cabinet with motorized louvres on it.The
> other two are mounted on ring type fan gaurds.
> With just the 10T compressor running, the fan
> with the louvres is the only one blowing. Being
> that the other two are off, air is pulled into
> the cabinet on the downstream side of the
> condenser coil instead of being pulled through
> it. I noticed that the air temp coming from the
> operating discharge fan was nearly ambient and
> the condenser coil was hot. So being the
> experimentative type, I threw a couple big
> garbage bags over the non running fan openings.
> In a matter of about 2 minutes I had nice hot air
> (95* @ 64* ambient) coming from the operating
> fan. Went inside and checked discharge air temp
> from the AHU and it had dropped from 66* to 54*
> BINGO!!
>
> So........
>
> Any suggestions as far
> as dealing with the fan situation? Obviously,
> being that everything else looks OK, except the
> holes in the condenser coil, this seems to
> resolve the lack of cooling complaint.
0 -
Mr. Ebels
That control panel is a DDC board that send the signel out or receives one and then send it down to the computer. You really don't need to get in to it unless the whole board has fryed.
Thinking about it you will still need to find out what type of program system they use and if you need to cordinate with the control company to meet you out there.
Hot gas by pass is used on a system like this to simulate a load on the compressors when there is a low demand load from the space.
The system still comes back to a VAV Constance volumn system and we still don't know the type of T-stats? Sometimes they don't have a name on them but it could help if we had a picture.
Larry0 -
Point By Point
A. "Reliable". What good marketing that it has to be said.
B. Hot Gas Bypass is normally piped as you stated, hot gas to evaporator. Not an expert on the wiring side frankly.
C. Rototill. I like that! Handy suckers when you need them. They thought to use them but lost sight of load versus capacity given all that tonnage.
D. Use of a face and bypass damper to obscure the coil. That is really odd. Wondering why it does not frost. Suspect if conventional F/BP that it responds to discharge temperature.
E. The condenser fan with the damper arrangement sounds like conventional head pressure control. The damper modulates toward closed to prevent over-condensing especially during low ambient weather and low load conditions. Seems with all that capacity there was enough condensing going on by convection as your plastic bag experiement made clear.
Seems you might consider head pressure control dampers on the other two fans? Granted this is a band-aid or jury-rig compared to proper size and matching of condenser to evaporator to actual load...0 -
The more I look at this system
The more I realize that every company before me, that has looked at it must have reached the same conclusion that I have. That being, it's way too big!
You need to know that in all the times I have observed this system, the 10T compressor was the only one running. The facilities manager for the bank told me that one of the previous HVAC companies has disabled the 15T so it will not run. This explains why the evap is not frosting. It also bring up a number of ?? as to what the heck is happening in a 25T evap coil with only 10T of compressor driving it. Maybe the face damper was an attempt to "downsize" the evap coil?0 -
THAT makes sense, Steve
Sort of a diffuser plate or artificial restriction as a way to downsize the coil. Good call. If the evaporator is fully face circuited (minimal bypass; all air goes through the coil sees a cold surface) then the humidity control should be fairly decent.
Makes the point that designing and installng it right the first time is a tad less expensive.
BTW: I turned over my mitten-hand to see where in Michigan you are. No where near me here in MA. And just so you know, lift your left arm and curl it like you are flexing your bicep. Like Popeye. There. You have God's provided map of Cape Cod.
Enjoy!
Brad0 -
Doing it right the first time...............
The facilities manager told me that they have "invested" over $54,000 in the A/C side of the system since it was installed. This is for upgrades and "fixes" to make the system work and does not include any maintenance, repair or replacement of failed components. That's just crazy!0 -
more info ?
How about a picture of the evap from the tx valve side and the condensing unit piping connections? What kind of compressors are in the condensing unit ? does the solonoid look like a discharge bypass one or a regular solonoid ? Single circut evap ? is it a single circut condensing unit ? And most importantly I have seen controls companies do some of the strangest things imaginable like basing hot gas on outdoor air temp not whats going on in the space.0 -
> I'll see if I can resize the pics.
>
> Compressors
> are Trane
>
> If you're refering to the hot gas
> solenoid, it appears to be just a normal refrig
> type unit to me.
>
> Single circuit evap and
> condenser
>
> I have no idea on anything to do
> with the control side of things. The cabinet was
> locked and there was no schematic left on the
> premisis. I think they wanted to be sure their
> company was the only one that was called
> back.
>
> Now the pics
>
> On the picture of the
> compressors you can see the hot gas solenoid in
> the upper left corner.
>
> The face damper covers
> better than half of the evap coil and as you can
> see it's wired into the DDC system
>
> The copper
> tube running across the air blender appears to be
> a home made cap tube of some kind. It's also
> connected to the DDC
>
> In the evap piping
> picture,you can see the hot gas bypass tee'd into
> the liquid line right next to the cabinet and
> after the lower TXV. Both the 10T and the 15T are
> pumping through the uninsulated 1 1/8" copper
> line.
>
> On the pic of the accumulator you can
> see two pressure sensing devices near the top.
> One is tapped into the high side and one is in
> the low side. Both are wired to the DDC
>
> There
> are three areas on the condenser that are
> leaking.
0 -
Good luck!!
Hey Steve,
Good Luck on the cond coils-you are gonna need it!! I know of a Trane cond unit on it's 4th coil change out! There is another exact size unit next to it and no leaks ever! Factory said had a run of bad coils, but how do you explain that over 4 years. Are they savin em for just this job!!
That accumalator is a suction line drier canistor. At least they used Sporlan.
Don, soon to be from Mo0 -
Suction line drier?
There's a liquid line filter/drier down in the mechanical room. Heavy duty cast aluminum piece with a bolted end cap and iso valves before and after. Why would they put a filter/drier on both the liquid and suction lines?0 -
Frist the suction accumulator is a suction filer dryer they use them when there has been a burn out in the compressors to clean up the acid in the system. They usally take out the cores after a while? you can pump it down and check to see if any cores are left it. you usally can tell to if you have a pressure drop across the dryer
the pressue switches are just to tell the DDC system that what the pressure are so you don't have to hook up gauges.
The cap tube is a mixed air senor maybe? it could be used as a freeze stat? I don't know I would have to see if you have a haeting coil in the air handler if only a cooling coil it is probalily you return air tempature.
Like I said before you may need to call the control company to meet yo there the customer should know what kind of DDC system they are using.
Larry
0 -
Larry
There are no heating coils in the AHU. There are a number of them out in the duct system.0 -
ewwwwwwwwwww
A locked box never stopped me If you dont want to get into the controls and I don't think there is any way to really cure it with whats there, seeing the condensor coil and how someone did that suction line drier I have a suggestion.
Run a full blown load if its over 10 tons but less than 15 (or real close) rip out condensing unit, put in one with a semi hermetic compressor carrier still makes them, order it with or install pressure activated unloaders. That coil is a 2 circuit evap probably could be used with a 10 or a 15 ton condensing unit alone if needed.Hot gas may still be needed but the pipe is there and thats the toughest part worst case it would have to be moved to other circut.
Now that you have dealt with the gross oversizing and short cycling odds are pretty good you could get away with changing the pulleys on the air handler to reduce noise actually disable the solonoid and existing damper and you could do that now.0 -
Detail Photos Steve
Steve-
Thanks for the detail photos. A couple of things jump out at me:
The face dampers have no safing. Air can go around as much as through the damper. If they wanted an orifice or diffuser plate that is sort of what they have. An adjustable diffuser plate.
The air blender looks like it has the temperature capillary across it. No good. Not sure what it is sensing but being so close to the airstreams it will pick up whatever comes out of the blender ports. Capillary wants to be downstream of filters if that is possible. (Pleated filters are a secondary blender but at least the primary blender swirls have a chance to mix.)
$54,000? This is a BANK??? They manage OPM?? I dunno...
That is a lot of money for band-aids.0 -
That's right you said that before
That's right you said there was no heating coil in the auh. Sometimes I forget to read over the posts again to refresh my mind.
Anyway Brad is giving you good information on the system I am in agreemant with what he is saying. I work on a lot of stuff, like I'm sure you do, and sometimes it takes a little time to figure it out.
The DDC controls are not the real problem it is the location of the sensors and the dampers I can not think of why they would want so much air blowing by like that. It defeets the purpose of the dampers.
Do they just have sensors on the wall? They have to control the room temp some way. Have you looked into the ceilings to see if they have VAV controlers? Are they working or are they shut down? Which is what it kind of sounds like because you have foliesity noises.
Larry0
This discussion has been closed.
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