Uneven Temperature Distribution in Cold Room

[Ray123]

Hi all,
We have a 40ft x 90ft coldroom, due to the requirement under standard, temperature everywhere in the coldroom needs to be maintain between 3 to 7 deg c. However, in the recent weeks, cold spots and hot spots seem to be present everywhere in the coldroom, triggering the temperature mapping alarm. Especially during mid night or weekend, when the operation stops.

Does anyone has any experience dealing with hotspot or coldspot? We tried a couple of methods, such as switching on the light during the weekend, reposition of sensor etc, but it doesn't seem to help much.

[dogma]

I'd suggest a perforated ducting system to evenly distribute air flow across the ceiling and returns up the wall.

Basically use perforated sheet metal and line the ceiling and return walls, If that makes sence.

Air supply and return distribution is the only thing I can think of that will provide long term resolution to the problem.

patent Pending.

regards

DOGMA

[US Iceman]

One of the most common problems with cold storage units is this: designers use a maximum calculated cooling load and then pick the quantity of evaporators that will cost the least. What can happen is exactly what you describe.

With a small number of coils the total cooling capacity is installed, but the air flow provided by the fans and the location of the evaporator coils creates uneven temperature distributions (i.e., hot and cold spots).

The common method used to correct this to install additional air circulating fans close to the hot spots to provide more air flow to the required location.

This happens all too often...

[RANGER1]

Could racking also be interfering with air flow . If air coolers blow down isle it would be better .
Some of the places we look after have air con type ducting .
Boning rooms also have long socks to distribute air and avoid drafts .
Like iceman says also , no airflow pockets of air at differant temps .
Extra fans also mean extra heat load .
Possibly differant fans/motors in air coolers could help with air throw distance and circulation .
Each air cooler could also be checked for performance air on/off temps + air flow, maybe 1 is not working correctly .

[nike123]

Hi all,
We have a 40ft x 90ft coldroom,

How many and what make and model# of evaporators are in that room? Are they mounted at longer side of room?

However, in the recent weeks, cold spots and hot spots seem to be present everywhere in the coldroom, triggering the temperature mapping alarm. Especially during mid night or weekend, when the operation stops.

Why the operation stops during midnight or weekend?
It is not clear if somebody switch off cooling during that time or alarm condition triggers switching off of equipment.

We tried a couple of methods, such as switching on the light during the weekend, reposition of sensor etc, but it doesn't seem to help much.

I don't see how switching on of light could help. It could only add to heat load.

[Electrocoolman]

However, in the recent weeks, cold spots and hot spots seem to be present everywhere in the coldroom, triggering the temperature mapping alarm.

This suggests that it was OK. So what has changed in the coldroom?

As suggested, has the racking been moved? Coldroom over full with goods?

Is the air throw sufficient to reach the length of room, or if more than one evaporator are their operating conditions comparable?

Have you checked fans all blowing, or is one (or more) freewheeling. Is there anything obstructing evaporator fins - polythene, build up of dirt, ICE etc.

What is 'air off' temperature - correct or higher than normal. Have you checked refrigerant level? How about condensers - all fans running?, clean?

What are system P&Ts? Higher than normal?

Have you checked the defrost controller? Do defrosts coincide with alarms - having trouble recovering after defrost? If multi evaporators do both defrost independantly or at the same time?

You need to investigate further, and post more info.

[Segei]

Hi all,
We have a 40ft x 90ft coldroom, due to the requirement under standard, temperature everywhere in the coldroom needs to be maintain between 3 to 7 deg c. However, in the recent weeks, cold spots and hot spots seem to be present everywhere in the coldroom, triggering the temperature mapping alarm. Especially during mid night or weekend, when the operation stops.

Does anyone has any experience dealing with hotspot or coldspot? We tried a couple of methods, such as switching on the light during the weekend, reposition of sensor etc, but it doesn't seem to help much.

What is the height of this room?
Cold stops can happen only if the fans blowing cool air to the sensors. Location the sensors is very important. Hot stops can happen due to poor air circulation. Several reasons of poor circulation can be.

[Ray123]

How many and what make and model# of evaporators are in that room? Are they mounted at longer side of room?

Sorry for the late reply, these few days were at the site to find out more information on this problem. I wasn't really sure about the model, but these evaporators are manufactured by Guetner. There are 3 evaporators installed along the long edge.

Why the operation stops during midnight or weekend?
It is not clear if somebody switch off cooling during that time or alarm condition triggers switching off of equipment.

The picking process only operates during the weekday working hours. After that, the ante room and cold room doors will be shut and lights off, but the cooling system remains operating

I don't see how switching on of light could help. It could only add to heat load.

Both high temperature and low temperature alarms presence in the cold room. Switching on the lights help to reduce the tendency of low temperature alarm. But it doesn't seem to be a good solution, sometimes the lights are accidentally off

[Ray123]

This suggests that it was OK. So what has changed in the coldroom?

I can't really see what’s different between the past and now. About 2 months ago, we started to receive high temperature alarm from the system. As we adjust the sensor location, the other sensor in the room started to send out high and low temperature alarm.

As suggested, has the racking been moved? Coldroom over full with goods?

The racking remains as it is since its first operation. The goods are stored randomly across the cold room. No obvious imbalance of goods storage in the cold room is observed.

Is the air throw sufficient to reach the length of room, or if more than one evaporator are their operating conditions comparable?

The width of the cold room is 40ft, the fan throw distance of the evaporator is 80ft. The setting for all three evaporators are the same. While the each evaporator air return sensor senses different temperature, the refrigeration timing of each blowers is slightly different.

Have you checked fans all blowing, or is one (or more) freewheeling. Is there anything obstructing evaporator fins - polythene, build up of dirt, ICE etc.

Just went up to see the evaporators. No abnormal condition is seen. I was carrying with me a thermocouple, the temperature reading directly opposite the blower is 4.0 deg C at the time.

What is 'air off' temperature - correct or higher than normal. Have you checked refrigerant level? How about condensers - all fans running?, clean?

The evaporator fans are set to operate all time (fan off temperature of 50 deg C). Previously there was some minor gas leak and we charged in about 14 kg of refrigerant after we fixed the leak, the refrigerant level is between the bottom and top sight glass. Condenser fans are operating as usual. Previously the air cooled condensers are found dirty, so we conducted some chemical cleaning to it.

What are system P&Ts? Higher than normal?

If I am correct, P&T refers to pressure and temperature. The refrigerant is R404, room design temperature 4 deg C. The high side and low side pressure at compressor is 250psi and 35psi respectively.

Have you checked the defrost controller? Do defrosts coincide with alarms - having trouble recovering after defrost? If multi evaporators do both defrost independantly or at the same time?

Yes, high temperature alarm coincide with defrost timing. There are multiple sensors and evaporators in the room, when an evaporator defrost, the sensor directly opposite it will tent to sense higher temperature. Once in a while, the sensor besides the opposite sensor will sense the heat also.
Low temperature alarm is much more unpredictable. Still couldn't see any fix pattern for low temperature alarm.

[Ray123]

What is the height of this room?
Cold stops can happen only if the fans blowing cool air to the sensors. Location the sensors is very important. Hot stops can happen due to poor air circulation. Several reasons of poor circulation can be.

The height of the cold room is 35 ft. Temperature mapping sensors are located around the cold room. For those sensors placed directly opposite the coldroom, it is placed opposite but at the center between 2 evaporators to avoid direct fan blow.

[Segei]

Sometimes you have illusion of cold and hot spots if temperature of incoming product is higher or lower than temperature in the cooler.
In your case probably the reason of cold and hot spots is high temperature difference on the suction side. Your air is 4C, but coil is -16C(35psig). This is 20C TD. Usually, TD should be 5-10C. Your evap. coil solenoids cycle wildly on and off, especially during the nights or weekends when ref. load is lower. Increase suction pressure to 40psig and than to 45psig. Higher suction pressure will reduce temperature fluctuation and improve efficiency of your plant.

[nike123]

If I am correct, P&T refers to pressure and temperature. The refrigerant is R404, room design temperature 4 deg C. The high side and low side pressure at compressor is 250psi and 35psi respectively.

If that pressures are at design temperatures, you probanbly have problem with evaporator air flow. Also, height of 35 ft could pose problem with distribution of air.
Could you give details of Guntner evaporators. It looks like we should check their air flow distribution.
At what height are they mounted and could you describe or make photo of load and evaporator position.

[Sandro Baptista]

Also send us a "hand drawing" for instead indicating where are: the hot spots, cold spots, location of the temperature sensores and the distribution of the aircoolers on the refrigerated room. Also how is the electrical command of the fans (when they stop and start) and electric command of electric valves?

Regards

[750 Valve]

Do the compressor(s) have capacity control?? that evap temp is VERY low for its application. Perhaps an unloader is not functioning correctly or poor compressor staging if multiple comps, that TD will lead to some pretty cold air off temps which may be triggering the low temp alarms, then depending on what is cycling the room temp control (perhaps its being affected by such cold air off temps) it may exaggerate any airflow patterns providing cold and warm spots.

[samlee12]

One of the systems i work on is set so if a coil is on defrost the temperature sensor will increase for that zone and could cause a high temp alarm, there is a time delay that will ignore the high temp. reading for 99 minutes during defrost which is appr. 30 minutes so i have a additional 66 min. after to allow zone to recouperate. temp sensors are also located behind and below coils five feet up from floor in the return air flow.

[abet_meneses]

Is the evaporators controlled by a single compressor?If that is the case, and all the
blowers and refrigerant operates normally there might be a some problem on the selection of evaporators as causing an maldistributon of cold air pointed by US ICEMAN.

We have some installation before with equally same volume of coldroom for chocolate and doesn't encountered that problem.

[Magoo]

Too much traffic, doors open, lack of fan power, poor circulation, add fans, add slat curtains on doors, hassle people that leave doors open. Perhaps spend a day on site and monitor what actually happens, and get the the real picture of what is happening and different from start-up date.
magoo

[danpitcher]

Did the alarms begin after you had the refrigerant leaks? If so did you re-use any of the R404a that was in the system when the leak was present? If you did the blend of refrigerants could be out slightly. This could give you higher pressures and it also can effect the glide of the refrigerant. Good luck.

[S.M.Gokhale]

Hot pockets could also be due to poor cold air distribution in the cold room or any conditioned area.

One solution is to instal supply air ductwork for which the fans of the unit cooler should develop sufficient static pressure. You can check this with the supplier of unit coolers. The air should be distributed evenly throughout the store.

There is no need to instal a return air duct.

[Ke-Fibertec UK]

Its a fairly large room being served by 3 coolers 20+ feet apart, it sounds like a distribution issue. I would agree with S.M.Gokhale, install some supply air ductwork!

[US Iceman]

I would NOT install duct work!

Duct work collects dirt, bacteria, etc. It is a dark location that can be moist which will allow some bacteria to grow in the dirt that eventually accumulates in the duct. Dirt and debris provide the nutrients for the bacteria and mold to grow in.

[Segei]

Duck work requires more fan power to move air. Efficiency of the system will decrease.

[Sridhar1312]

As long as the evaporator fan is high static to throw air upto 40 feet and if you equal number of evaporators there should not be problem.Ideally for cold rooms standby power ais must as mostly perishable materials are stored.

[Sridhar1312]

Agree with you for cold rooms and frozen sores ducting is not at all done for obvious reason.
At the same time the eveporator front portion shall be left free without at any storage otherwise it may hith the storage rack and short cycle.

[Ke-Fibertec UK]

I agree that normal ductwork should not be installed in a cold room, but textile ducting can be as it does not need insulating, does not absorb water and can be taken down and washed in a washing machine to remove any dirt build up inside.
http://80.165.29.186/uk/files/referebcer/I~000016.jpg

[Segei]

I agree that normal ductwork should not be installed in a cold room, but textile ducting can be as it does not need insulating, does not absorb water and can be taken down and washed in a washing machine to remove any dirt build up inside.
http://80.165.29.186/uk/files/referebcer/I~000016.jpg

It will be headache to wash this ducting.
I found that people very often forget about natural convection. They think that cool air should be delivered in every corner of the room.
As far as I understand on this picture they try to deliver cool air into the space with low ceiling. However, cool air will go there by natural convection.

[DeB]

Gidday Ray 123,What model and quantity are the Guntner evaporators? what is the condensing unit that is running these evaporators? I would suggest running at that low pressure would indicate insufficient liquid at the TX valves. This will cause the distributors to give uneven refrigerant distribution through the coil circuits.In turn the room will develop uneven temperature spots. I prefer to have liquid line sight glasses on large multiple evap systems installed just before each valve. This gives you a quick check to make sure you have full liquid to each valve. If the system has worked satisfactorily in the past there is no reason to expect a common design fault. I have designed many systems with Guntner evaps and have not had this problem. Do the Evaps have Guntner air streamers fitted?

[Segei]

Ray 123.
Did you try to increase the suction pressure? How it is going?

[cvsaraf]

Ray 123.
Did you try to increase the suction pressure? How it is going?

Dear Ray,
pl. send me details Like Evaporator Models, Condensing Unit Models- compressor,condenser coil details, Hand sketch showing installations , Racks, Hot& cold pockets, Senser Location , Defrost system @ cvsaraf@yahoo.com definately I can help you.

[Ray123]

Gidday Ray 123,What model and quantity are the Guntner evaporators? what is the condensing unit that is running these evaporators? I would suggest running at that low pressure would indicate insufficient liquid at the TX valves. This will cause the distributors to give uneven refrigerant distribution through the coil circuits.In turn the room will develop uneven temperature spots. I prefer to have liquid line sight glasses on large multiple evap systems installed just before each valve. This gives you a quick check to make sure you have full liquid to each valve. If the system has worked satisfactorily in the past there is no reason to expect a common design fault. I have designed many systems with Guntner evaps and have not had this problem. Do the Evaps have Guntner air streamers fitted?

Couldn't really recall which model is the evaporator, but there are 3 evaporators in the coldroom along the long edge side. Had a check on the sight glass of the system, the refrigerant in the system is still sufficient, no sign of bubble on the sight glass.

We had traced the alarm for the past few weeks, there are quite a few low temperature alarm happened when the return air sensor of the two evaporators away from the cold room door achieved temperature set point, while the one nears to the door still operating. I was thinking of calibrating the evaporator return air sensor of the evaporator nears to cold room door to be equivalent with the other two, but was a bit concern over the high temperature alarm. Since when the door is open, warmer air from ante room could penetrate into the room.

[Ray123]

Ray 123.
Did you try to increase the suction pressure? How it is going?

Didn't really have a chance to reduce the suction pressure yet. The cold room is fully loaded at the moment, since it has been operated for quite a while, and though occasionally with hot or cold spot, the temperature is generally stable. I am a bit concern if the change of the parameter could affect the system condition.

[Ray123]

One of the systems i work on is set so if a coil is on defrost the temperature sensor will increase for that zone and could cause a high temp alarm, there is a time delay that will ignore the high temp. reading for 99 minutes during defrost which is appr. 30 minutes so i have a additional 66 min. after to allow zone to recouperate. temp sensors are also located behind and below coils five feet up from floor in the return air flow.

But in the case where the evaporator controllers and temperature monitoring system are of different system, and evaporators are staggered to defrost, is there any way which we can link up the two system to create the alarm delay after defrost?

[Segei]

Didn't really have a chance to reduce the suction pressure yet. The cold room is fully loaded at the moment, since it has been operated for quite a while, and though occasionally with hot or cold spot, the temperature is generally stable. I am a bit concern if the change of the parameter could affect the system condition.

You should increase suction pressure not reduce. If you have concerns, do small step at a time. Increase suction pressure by 3 psig(0.2 bars) and monitor for week or 2 weeks. If everything is fine, do next step. Small steps won't hurt the system. If you do nothing, nothing will improve.

[Yuri B.]

Sorry, not exactly the answer to your last qw.
First of all, as it was advised by many posters, make sure air circulation in the cold room is adequate (by that, the additional fans' heat introduced will be insignificant). Then, maybe, add an independant (from regulation) alarm controller, commutate alarm sensors at different points in the room together so that an average temperature accross the room was being measured - not a (fleeting rising) sample here, a (momentary falling) sample there, etc.
Otherwise you seems to be doomed to hunt the ghosts of the "coldspots" - "hotspots" till the end of the lifetime of the room.

[Peter_1]

Switching on the lights help to reduce the tendency of low temperature alarm. But it doesn't seem to be a good solution, sometimes the lights are accidentally off

I don't see the relation with the lights in the room?

[Yuri B.]

It seems to be a very exceptional cold room.

[Segei]

I don't see the relation with the lights in the room?

Light create additional(parasitic) load and evaporators run longer in cooling mode instead of cycling wildly. Higher suction pressure or higher ref.load will improve temperature fluctuation. Certainly, it isn't efficient step.

[Yuri B.]

That room is not lightened however by searchlights - just fluorescent tubes, I assume.

[Ray123]

That room is not lightened however by searchlights - just fluorescent tubes, I assume.

Two rows of 300 W light bulbs were installed in the cold room, if I remember correctly, there should be 5 to 6 light bulbs per row, which should generate between 3.0 to 3.6 kW.

Segei has a point, receiving relatively more heat load from light bulbs and cooling directly from evaporators, stabilizing the temperature of the top layer sensors has become even more challenging.

[Yuri B.]

20 fluorescent 58W tubes would have lightened up that coldroom like a readingroom.

[Ray123]

20 fluorescent 58W tubes would have lightened up that coldroom like a readingroom.

But the cold room height is 35ft..

[Yuri B.]

11 m is not very exceptional height, and a coldroom need not be lightened up like a readingroom.
Temperatures difference is very substantional between near to floor and near the ceiling during defrost times. In one thread here someone mentioned having seen louvers on evap-s - I bet they were in like yours high-ceiling room.
I abide to my advice - arange it so that the alarm controller receive an average temp across the room.

[Yuri B.]

Ray, how long durate those deviations in temp-s? If they are only transient, maybe filter for them too short (alarm time delays)? Are they so harmful to the product?

[Yuri B.]

Do you maybe have indeed (I did not get it correct) computer /some registering device's "trends" - and by that for each sensor - evincing intolerably long term alarming temp deviations here and there in the room? In such case, only improved air movement could help.

[Ray123]

Ray, how long durate those deviations in temp-s? If they are only transient, maybe filter for them too short (alarm time delays)? Are they so harmful to the product?

The maximum defrost time is about 20 to 30 minutes, if I remembered correctly. There are instances where alarm happened consistently right after one of the 3 evaporators defrosted. I wanted to cross link the evaporator controllers with the temperature mapping sensor to eliminate the alarm, but there are multiple evaporator defrost in sequence, still couldn't find any way to hook up these 2 systems.

[Yuri B.]

Clear, DX on/off cooling is far from being precise. One is helpless here.

I am sure the spots are short term only. How many "mapping" sensors are there ? No matter how simplistic it sounds - as there may be a better solution - you could commutate 4 sensors as one (according to Mod. Argus). Then the controller will register average temp across (the points of) the room (where sensors are positioned).