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Samarjit Sen
20-06-2007, 03:19 PM
I was called today by a refrigeration firm who had supplied an air chiller to a polythene sheet manufacturer for supply of air at 9 Deg. C. The party has designed the system based on the system of Euro Chiller.

The air intake is at 40 Deg. C. It is total fresh air and are supposed to cool the air down to 9 Deg. C and supply the same to the blowing mold.

The quantity of air supply is 3000 cfm.

The refrigeration compressor installed is MT 125 of Maneurop with R 22. The refrigeration capacity is 22.50 kw at - 5 Deg. C Te and 40 Deg. C Tc. The plant has a water cooled condenser. The cooling coil has a dimension of 24" x 30 " x 8 row deep.
with 10 fpi.

The machine is mounted on a rotary table with the blowing machine. There is a water well below the rotary platform. Water in the well is being supplied by a cooling tower. From the well water is being pumped into the condenser and the outlet is being supplied to the same well. This is one thing I failed to understand as the temperature of the well water shall gradually rise and the water inlet temperature shall be more.

Now when the refrigeration unit is started the air temperature initially is about 18 Deg. C and gradually rises. The discharge pressure too starts to rise as the well water temperature rises.

The entire plant is something which I failed to understand. Since the refrigeration firm is well known to me and are now helpless, I thought of how to help them out. The only remedy left to me is to refer to the forum.

Could some one give me some views as to what could be wrong and how to rectify the same.

Somehow I have a feeling that DX Coil size is not corect.

lana
20-06-2007, 03:36 PM
Hi Samarjit Sen,

What is the entering wet bulb temperature?

I can check the coil for you.

You mentioned that the well water is supplied by a cooling tower. What do you mean?

Cheers

Samarjit Sen
20-06-2007, 05:40 PM
Hi Lana,

The Wet Bulb temperature entering the air chiller is about 32 Deg. C.

There is a very big pit on the centre of this rotating platform has been installed. The diameter of the pit and the platform should be about 10 to 12 ft. At the bottom of the pit there is weel. Not the natural well but an artificial well. In this well they are supplying water through the Cooling Tower. The Cooling tower is not connected to the shell & tube condenser. From this well water is pumped to the condenser and the water outlet is being poured back into the well. This system is absurd as over time the temperature of the well water shall rise and this water shall be fed to the condenser.

The reason adopted for such a system was that as the chiller is mounted on the rotating platform, it is not possible for connecting the shell & tube condenser to the cooling tower.

I hope I have been able to state the facts properly, if not please post the informations required.

lana
20-06-2007, 05:52 PM
Hi Samarjit Sen,

First of all I checked the coil and it can give you around 13.5C outlet temperature with te = 5C.

Secondly, about the cooling tower. This is my question again.
There is a big water tank made in the ground and the cooling tower packings are on top of it. Water goes through the packings into the tank.
Is this right?

Regards
LANA

Samarjit Sen
20-06-2007, 06:01 PM
Lana the cooling tower is installed on the terrace of the factory. By a separate pump the water is being recirculated from the cooling tower to the well located in the pit . The machines are all locatedf above the pit and is in constant circular motion. The condenser is in no way connected to the cooling tower. It is the water in the well which is being passed through the condenser and back to the well. A separate pump is taking the well water to the cooling tower and returning the same to the well.

Could you give me an idea as to the size of the coil which can maintain a temperature of 9 Deg. C air out let temperature.

Thank you Lana.

Samarjit Sen
20-06-2007, 06:03 PM
The Cooling tower is a normal FRP bottle shape.

US Iceman
20-06-2007, 06:29 PM
The water sumps should be separate. One for supply water to the condensers (from the cooling tower), and the other sump should be used for the return water from the condensers (and back to the cooling tower).

A single sump used as you describe is not very good at all. You will have mixing problems and loss of cooling tower capacity and refrigeration system capacity.

lana
20-06-2007, 06:30 PM
In order to get 9C outlet temperature, the face velocity must be reduced. So the coil dimension must be bigger.
110 x 65 cm , 8 rows , 10 FPI

On the other hand in order to cool 3000 CFM of 40C/32C air to 9C/8.9C you have to have around 142 kW of capacity.
It is a simple psychrometric calculation which gives you this capacity.
Q = m x Dh
Q = capacity needed (kW)
m = air mass flow rate (kg/s)
Dh = air enthalpy difference (kJ/kg)

Q = 1.69 [kg/s] x (111.26 - 27.11) [kJ/kg] = 142 kW
But you said that the compressor has 22 kW of capacity. :confused:

Because there is no return air so the capacity is huge. This needs something like a 60HP of compressor.:eek:

Please verify the info.

About the well water, because the cooling tower is cooling the water then there must be no problem about the pit water getting hot.
I suggest you check the cooling cycle first. Maybe there are some commissioning problems like refrigerant charge or ....
The problem you mentioned about the high pressure needs careful investigation to find the cause. First thing I would look at is the suction pressure. If suction pressure starts to go up because of high load the discharge pressure will go up as well.

Good luck .
Keep us posted.
Regards
LANA

nevgee
20-06-2007, 10:16 PM
Hi guys

Just reading your problem here and without going into any detail, I see there would be a problem as US Iceman states with mixing water in the well. If the well is necessary, then it needs to be split into halve with a wier plate. This would allow cooled water from tower flow into one halve and from this same half the pick up water to the condenser. Likewise. in the other halve the return from condenser would collect and be taken to the tower. If flow from the condesnser stops, then the tower water would just pump over the wier plate.
flow rates of each pump need to be established and I guess an ideal would be for the tower pump to have a greater flow than the condeser pump.

Hope this adds to the debate.

Samarjit Sen
21-06-2007, 03:02 AM
I have been thinking the same as US Iceman and Nevgee. The condenser water system has to be modified or else use an air cooled condenser with R 134a or R 124 refrigerant.

Regarding the capacity, I too had worked out the load and the same comes to what Lana has suggested. Now this party insists that there are a number of units of EuroChillers. Italy installed here for similar production. They had taken the physical dimensions and used the same compressor as they had used. But as per the heat load it just not matches.

Is it possible that if two Cooling Coils are used with a single compressor. The Coils are located in front of each other. One expansion valve operates both the coils. It just an idea. Lana you being the expert do you thing it is possible.

lana
21-06-2007, 03:11 AM
If two coils are used then the problem for capacity still stands. One compressor gives 22 kW.
Using two coils would not solve the problem.

If similar units have been used check if the design parameters are the same and they are operating at the same conditions as your unit. I mean inlet dry/wet bulb temperatures.

Cheers

US Iceman
21-06-2007, 03:18 AM
One relatively simple way to correct the water problem is to use a separate water pump to pump the water to the condensers. Allow the water to flow out of the condensers back into the sump, and then use a separate pump to return the water to the cooling tower.

I'm not quite sure on the installation as you described it but if there is some kind of rotation involved you can get rotary couplings for the water line feeding the refrigeration condensers.

Sledge
21-06-2007, 07:07 AM
In order to get 9C outlet temperature, the face velocity must be reduced. So the coil dimension must be bigger.
110 x 65 cm , 8 rows , 10 FPI

On the other hand in order to cool 3000 CFM of 40C/32C air to 9C/8.9C you have to have around 142 kW of capacity.
It is a simple psychrometric calculation which gives you this capacity.
Q = m x Dh
Q = capacity needed (kW)
m = air mass flow rate (kg/s)
Dh = air enthalpy difference (kJ/kg)

Q = 1.69 [kg/s] x (111.26 - 27.11) [kJ/kg] = 142 kW
But you said that the compressor has 22 kW of capacity. :confused:

Because there is no return air so the capacity is huge. This needs something like a 60HP of compressor.:eek:

Please verify the info.

About the well water, because the cooling tower is cooling the water then there must be no problem about the pit water getting hot.
I suggest you check the cooling cycle first. Maybe there are some commissioning problems like refrigerant charge or ....
The problem you mentioned about the high pressure needs careful investigation to find the cause. First thing I would look at is the suction pressure. If suction pressure starts to go up because of high load the discharge pressure will go up as well.

Good luck .
Keep us posted.
Regards
LANA

Cheers Lana

dont want to hijack thread, but can you tell me where you get these facts and figures, I am accumulating as much refernce material as I can find, to start my own self education program.

Sledge
21-06-2007, 07:12 AM
A thought about the sump, cooling tower, condensor arrangement.

I am thinking that the inlet to the condensor should be from the well, and the water leaving the condensor should feed directly to the cooling tower. The cooling tower would then drain into the well. I am viewing this as a circuit, that would make the well an extension of the cooling tower sump.

Ravi
21-06-2007, 10:32 AM
Lana is on the money. You are pushing more air than your system can take care of. Even if you maintain the system lowest temperature above the ADP (i.e if you only cool sensibly), your system requirement is not enough.

For 3000cfm and with a dT of 31C or 55.8F, the cooling load is 1.1x3000x55.8 = 184140btu/hr or 53.93 kW.

Alternately, for 22kW, trim down the flowrate to 22x3414.42/(1.1x55.8) = 1224cfm. You have to further reduce the flowrate (not to levels that cause icing on the coil) if the moisture condenses at 9C or above.

Samarjit Sen
21-06-2007, 11:00 AM
Hi Lana,

Let me tell you first, is that it is not my unit. I would have preferred to install an air cooled unit based on the system as adopted for steel plants. There I have also done air chilling at an ambient of 60 Deg. C using R 124.

The person who has supplied this unit says he has seen such chillers of Euro Chillers, Italy being used under the same condition. The only difference is that the water from the cooling tower is being directly pumped into the condensers. The platform on that is not circulating but is ocillating . I feel that there is some basic fault. Maybe the air supplied is less. I may have to visit the site once again.

US Iceman, Since the platform on which all the equipments are fixed is rotating 360 Deg continuously, it is not possible to have the water directly pumped in from the Cooling Tower. But they can have two circular water sumps. One to which the cooling tower shall be supplying the water and from where by means of a pump ( they had an undersized pump) supply the water to the condenser. The out let shall fall into the outer circular sump from where the water can be pumped to the cooling tower.

Sledge, the inlet to the pump is from the well by means of a pump which was half the capacity. I have asked them to change the pump and put a larger capacity one. It is not possible to have the outlet of the condenser directly connected to the cooling tower, as the platform on which this is fixed is constantly rotating clockwise. So what they have done is that they are pouring the water outlet into the same sump. a seperate pump is pumping the water from this sump tothe cooling tower and the same is being returned to the sump. This way gradually the temperature of water shall rise.

Not attaining the desired conditions as I feel is due to higher volume of air, inefficient condensation due to water circulation.

Will appreciate your advice, suggestions and opinions.

US Iceman
21-06-2007, 01:50 PM
Hi Samarjit Sen,

One thing I just remembered from a similar facility I did some work in years ago concerns the water sumps.

The system I worked on was for a rubber extrusion process where they used chilled water to cool rubber strips coming from an extrusion machine. The chilled water was pumped into long slender tank and then the water fell into a sump. The water was collected from this sump and pumped back to the water chiller.

The problem I found was over a period of time the little rubber pellets (they poured into the hoppers on the extrusion machines) found their way into the water sump. They eventually plugged up the chiller!

If you have an opportunity, it may be worthwhile to check one condenser for fouling/debris that can find it's way into the sump.

US Iceman
21-06-2007, 01:53 PM
Here is a link to those rotary joints/couplings. Please notice where they are made.;)

http://www.aiplen.com/rotary1.htm#

Samarjit Sen
21-06-2007, 02:54 PM
Dear US Iceman,

Thank you for the link for the coupling.

As I am unable to draw the system, I shall try to describe the same as much as possible.

There is a large pit on the floor about 12 ft. in diameter. This pit is filled with water from the cooling tower and acts as the water sump. At the centre of the floor of the pit a vertical pillar of 18" is fitted. To this pillar a hexagonal platform of say 10 ft. dia is fitted and which keeps moving round and round. This platform is at about 2.5 ft. ht from the pit floor and the same level as factory floor. All machineries including the air chiller is fitted on to the platform and every thing moves round . If a flexible hose is fitted to the condenser, then the same shall wound round the pillar and break off.

The only alternative is to have two cicular water sumps. One will be inner and the other outer. One shall have the water from the condenser- pumped to the Cooling Tower and back to the outer ring sump from where the water could be pumped in to the condenser. This can take care of the condenser water temperature.

US Iceman
21-06-2007, 03:23 PM
My thought was to have the piping overhead and then feed the water directly down to the equipment as the platform rotates. That is where the rotary coupling is needed.

I have seen these used before in similar processes and they seem to work quite well.

The vertical pipe (supply water) above the coupling is fixed. Under the coupling, the pipe simple rotates with the platform. Then the water falls into the sump.

I do agree you should probably use two pumps. I might also suggest the use of a large basket strainer in the discharge of the pump supplying water to the condensers to help keep them free of any debris.

Samarjit Sen
21-06-2007, 04:08 PM
It is not possible to fix the water line at the top. The polythene film is being ejected from the top and same goes through a number of horizontal cylinders. If the water line is fixed, it will be obstructed by the polythen film line.

I have asked the refrigeration firm who had done this job to meet me tomorrow morning at my office so that I can describe him the water sump and get it done. This will improve the performance to some extent. Further I have been informed that the owners are changing the air blower so as to reduce the air discharge.

I shall let you know the progress and the result.

lana
21-06-2007, 04:37 PM
Hi Samarjit Sen,

Would you please check the attached drawing and confirm if this is the system.

BTW when I say "your system" I mean your described system, I don't mean that you designed it or anything. It is a manner of speaking. Hope you are not offended by this.

Cheers

lana
21-06-2007, 04:43 PM
Hi Sledge,


dont want to hijack thread, but can you tell me where you get these facts and figures, I am accumulating as much refernce material as I can find, to start my own self education program.

This is a basic psychromeric fact and everybody would know this if studied this section of science. Nothing difficult to it.

Psychrometric calculations are all mathematical relationships which are easily converted to computer programmes. I have developed my own but you can get that for free from Internet.

Cheers

US Iceman
21-06-2007, 04:45 PM
lana,

Your drawing is the way I have visualized this also. But I did not think about an overhead transfer for the process. :(

Samarjit Sen
21-06-2007, 05:48 PM
Lana,

It is just as per your drawing. The only thing is that the extruder is at the centre and polythene sheets are blown up from the centre in a cylidrical form and then they are turned horizontal by going over a number of rotating cylinders.

Thank you for the drawing. Please do not feel that I was offended bacause you said my plant, I was just joking.

lana
21-06-2007, 05:58 PM
Hi there,

I think if the water sump is big enough and also the cooling tower water inlet and outlet are directed to different side of the sump then it should not be a big problem. Considering that the cooling tower flow is more than the condenser water flow.
This is just my thought.

I would first investigate the chiller and this would lead to the condenser problem, if there was.

Cheers

Samarjit Sen
21-06-2007, 06:15 PM
Lana,

Will the continuous flow of out let condenser water to the sump, don't you think that at some stage the temperature of the sump water shall start to rise, which in turn will effect the condensing temperature.

Further the cooling tower pump in this case is smaller. Maybe if a larger Cooling tower is provided with a pump with a higher flow this problem might be solved. It is all guess work. In my 44 years of being in this field I have never seen a refrigeration plant like this.

lana
21-06-2007, 06:23 PM
Yes it is unusual.

Think that this system is a big thermal storage. In this system the tank of a thermal storage is the water sump. The chiller which chills the water here is the cooling tower. And the consumer is the condenser.
If cooling tower water flow is enough (must be way more than the condenser water flow), then water in the sump will be stabilized to a certain temperature.
BTW a water agitator in the sump could be helpful.:cool:

Cheers

US Iceman
21-06-2007, 06:48 PM
If you can divide the sump into two sections and seal the divider adequately you should be in a better position than you are now.

Use one section as a hot sump for the outlet water from the condensers. The other section is the cold sump for the cool water from the tower.

I may have still missed some details, but I hope this provides some useful information.

nevgee
22-06-2007, 12:18 AM
Hi guys,

Assuming the conser heat rejection is equal or less than the tower output, then there will be a flow of energy outward thru the tower. The sump will settle at a mean temperature.

To gain benefit from the weir plate arrangement in this case you would need to install a dividing plate or wall (weir) that is concentric to the outer wall of the sump. Thus spliting the sump into two halves. Choose which to be the colder and warmer. Say the middle is cold, then this would be the supply to the condenser and receive the cooled water from the tower. likewise, the outer would be the collector from the condeser and be the supply to the tower.

hope this helps

nevgee
22-06-2007, 12:27 AM
Post for Sledge

Have you got a copy of Roy Dossat's "Principles of Refrigeration" You might find it a very useful reference book.

Samarjit Sen
22-06-2007, 05:06 AM
You are correct US Iceman. I am going to ask them to devide the sump in two separate parts and to have a higher volume of water flow pump for the Cooling Tower,

Could you please tell me how do you upload the sketch on the forum.

nevgee
22-06-2007, 08:41 AM
You must remember to allow for a high level over flow into the corresponding section. So that in the event of any imbalance of flow between the two pumps, then the overspill will be into the corresponding section.
For instance, If one pump stops then the other will continue to transfer water from one section to the other. An over flow will occur. If the top of the dividing wall is set at an adequate level then the overspill will flow over the wall top into the adjoining section, this is the weir principle. Electrical interlocks on the pumps will help. However, the tower should have more capacity than the condenser therfore more water flow. The weir then allows for the warmer section to eventually achieve cooling during low load conditions thus increasing further thermal storage during low load conditions.

Hope this helps

US Iceman
22-06-2007, 03:30 PM
Could you please tell me how do you upload the sketch on the forum.


When you are posting a reply or new thread look directly below the box where you type your messages. There is a button labeled "Manage Attachment".

When you click on this button, another screen appears where you can browse your computer for the file location you wish to attach.

After you locate the file for attachment, then click the upload button. When this is completed you close that screen and return to the editing screen again.

You will see the file listed in the Attach Files section below. Then you simply sumbit your reply, or post your thread.

The file size limit is 100 kb.

The file I attached was done in PowerPoint and then printed to a PDF using Adobe Acrobat.

Samarjit Sen
25-06-2007, 06:52 PM
The owners have reduced the air volume through the fan and the temperature attained is 19 Deg. C from 40 Deg. C. The temperature of water in the sump keeps increasing. Both the owners and the refrigeration contractors are happy, so I thought it is better to keep my mouth shut.

Thank you all for the various informations and the guide lines given. At least with the discussions I have definately come to know a lot of facts and I am sure other members have also learnt a lot.

US Iceman
25-06-2007, 07:31 PM
At least you know what to do about the sump temperatures the next time the issue comes up in a conversation.:D

suny
29-07-2007, 04:00 PM
Hi Samarjit Sen

Ambient temp in Italy is very much lower than 40 deg C. As Lanas views cooling load should be more than Italys. This is a common problem we are facing in our countries buying & copying refrigeration equipments that are not compatible for tropicalized countries due to lack of knowledge. I also feel that you should isolate the cooling tower and circulate with higher flow rate water pump.

Further I have posted a new post on your request with regard to the ice plant. Please give your advise on that.

Suny

suny
29-07-2007, 05:26 PM
Hi Lana/Ravi

Please explain how you arrived at 142 kw cooling load. Ravis calculation is correct on British system. I feel that there is a mistake on conversation you have done from Cubic Foot/Minute to Kilo Liters/Second &
Please give us in detail.

Suny