Rel Hum. Control

How do you all control humidity in cold rooms, especially in fresh meat rooms?

We install a heater in front of the evaporator (+/- 1/3 of the capacity of the cooling) and give priority to the cooling. As soon we have reached temperature (or with a 2 zone thermostat, 1°C before reaching desired temperature) we engage heating via the humidistat.

Saw/serviced a Stulz computerroom cooler (downflow) an evaporator with 2 circuits (2/3 - 1/3) with 2 TEV and 2 SV. They shutted off 1/3 of the evap when they needed drying. Seemeda good idea.

Any other systems?

check www.munters.com

one of the best.

chemi

Peter,
What is your desired humidity in the cold room?

It was just a hypothetical question.
Fresh meat rooms +/- 80%

Hi Chemi,

I know Munters but they are to expensive for such an application.
We installed already some big machines (for the Belgium army)of them but i actually don't like this kind of installations. It's just installing the machine, some ductwork, plug in the power and that's it.

hello peter:)
Ive seen humidification units on fresh meat refrigerated cases .One is the smeva unit which works on ultrasonic principle.With the assistance of electronics ,a ceramic vibrating plate or (transducer).
By means of vibration ,water above the transducer is also set into vibraton and microscopically small amounts of water are swung upwards well over the water surface .The form and dimension of resevoir and piping is such that only droplets of usable size are taken along by passing air .Transport air is guided past these droplets by means of a fan.
water levels are controlled integrally by the electronics.
Usually the RH on storage of fresh meat in the uk is not that imperative.
when the meat is sold across the counter the RH is controlled for aesthetic reasons .
regards mark:)

Hi Mark:)
we control the humidity in post slaughter chills. This is to reduce weight loss, weight loss = loss in money. I worked it out once that in a 200 carcase cattle chill an improvement or reduction in weight loss of 1/2% would save £80K per year. Control is simple, you just measure the humidity in the room and constantly adjust the evaporation to suit.:D
Kind Regards. Andy

Peter,
The Stulz computerroom ac reduce evaporator surface to achieve lower evaporating temp thus more dehumidification.
But for meat storage room, they prefer higher humidity(90%+?) to reduce weigh loss. so semms it needn't further dehumidification.
for such a dehumidification case, i think fan speed modulation is more energy efficient than electric reheat.

http://www.humidity.com/ this is the site for Nortec. We have used them in photlabs, comp. rooms, ect. I'm sure they make a jet like humidifier for meat applications. It's called the OCTO SELF-CONTAINED SYSTEM. it's in the nossle section i belive.

Quote:

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Originally posted by Peter_1

How do you all control humidity in cold rooms, especially in fresh meat rooms?

We install a heater in front of the evaporator (+/- 1/3 of the capacity of the cooling) and give priority to the cooling. As soon we have reached temperature (or with a 2 zone thermostat, 1°C before reaching desired temperature) we engage heating via the humidistat.

Saw/serviced a Stulz computerroom cooler (downflow) an evaporator with 2 circuits (2/3 - 1/3) with 2 TEV and 2 SV. They shutted off 1/3 of the evap when they needed drying. Seemeda good idea.

Any other systems?

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It sounds as though you're trying to dehumidify. This seems strange since we usually design a meat room with extra evaporator surface (coil surface temp determines the dew point of the discharge air. Low air-to-coil TD gives better (ie, higher) relative humidity) and low speed fans to slow dessication.

Just as in a flower box, you don't want to disturb the air layer next to the surface of the product, since vapor exchange first occurs in that layer.

If you are trying to dehumidify, what is the source of the humidity? If you exceed certain air velocities across coils you will throw moisture off. Is there a spray-washing process or some humidity producing source in the same space?

Even if the access to the room is from a warm, humid space, the evap coils should be pulling it right out again. If the system couldn't handle the latent load, you ought to see it in failure to maintain sensible level as well, but you are able actually to install heaters. I'm confused. .......But that's okay, I'm used to it!

hi peter,

the units Mark Fiddy refers to are widely used to increase humidity. the best thing about them, are no moving parts.

I have installd a few of them in a big hatchery to keep 95% for little chicks. controlled by a humidistat.

chemi

I was surprised you knew the Dutch company Smeva.
I serviced some time Smeva counters and know the product very well.

Terefore, I have a lot of (older) manuals which are very difficult to get (it seems) If you ever need something, give me a call. Mostly from the Showmasters.

They used the ultrasonic plates (i think they came from another Dutch company, Contronics)

They're not longer allowed in Belgium unless you use a reversed osmose system. This is because all the dirt which is normally in the untreated water gets sprayed on the food (sand particles, lime, clorine...)

And if you don't use this, the plates become covered with lime and they function not so well.

Did you know that the cost for one plate is only +/- 10 Euro's? But the total cost for a unit is far more expensive.

Quote:

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Originally posted by RogGoetsch
It sounds as though you're trying to dehumidify. This seems strange since we usually design a meat room with extra evaporator surface (coil surface temp determines the dew point of the discharge air. Low air-to-coil TD gives better (ie, higher) relative humidity) and low speed fans to slow dessication.

Just as in a flower box, you don't want to disturb the air layer next to the surface of the product, since vapor exchange first occurs in that layer.

If you are trying to dehumidify, what is the source of the humidity? If you exceed certain air velocities across coils you will throw moisture off. Is there a spray-washing process or some humidity producing source in the same space?

Even if the access to the room is from a warm, humid space, the evap coils should be pulling it right out again. If the system couldn't handle the latent load, you ought to see it in failure to maintain sensible level as well, but you are able actually to install heaters. I'm confused. .......But that's okay, I'm used to it!

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Also strange for me because we see it everywhere the way I described.

There also another phenomena which happens (I'm far from a
food specialist) but if the RH doesn't stay around 80 %, then there is a special bacteria growing on the skin of the meat, it's like sort of slime.
Be aware that animals in Belgium may not be injected with hormones or any other growing medication.

Also, when they enter the hot carcasses in the cold rooms, it's almost like steam you seeing. Then we need to dry the room.

Problems becomes always worser in the winter:
1st doors are more open and cold air from outside is entering the rooms
2nd lower condensing pressures makes that refr. plant has more capacity.
These two affects the total effective cooling time - in a positive way - to cool down the meat.
But if the evaporators don't cool long enough, there is not enough dehumidification. Then it becomes all soaking wet on the floors and the meat becomes sticky and even gray to black.

Even the vets in the slaughtery know this phenomena.

It goes even that far that I had a client (he died 2 years ago), he went in his cold rooms and the first thing he did was looking to the ground, smelling the air tasting the meat and then said "there is something wrong with the cooling system" (without even looking at it). He called me then always" Peter you have to come, I have a problem". " Is the temperature OK?". "Yes, but I know there is something".
In the beginning I taught (didn't say) "What do you know butcher of a cooling system". But I learned in the years I worked for him that he always pinpointed the problem without seeing his compressors.


Story of lowering condensing pressure and conservation of the meat (more then 10 years ago):
We had a client where we installed a very small rack with heat reclaim for hot water. There was also a second smaller storage boiler with entering water from the heat reclaim and electrical reheat. Clients son should install later during his holidays all the water connections. COldrooms where satisfying for 3 months. The son installs the whole hydraulic water-system and from that day, the meat became sticky, wet, gray...in one word no conservation at all.
Client called me and said that this happened from one day to another since the modification.
I went there and measured the head pressure: we had something of 10 bar (140 Psig) (can't remember that so well anymore) There was a HP switch on the condenser which we forgot to set on 15 bar (220 Psig) I adjusted it and since then , the conservation was back as usual.

Peter,
Interesting info.
From what i read, Fresh meat storage condition is around -2C to 0C, 85-95%¡£

Ah, carcass chilling! I knew I was missing part of the picture! My only experience is with commercial meat storage, not on the slaughterhouse end. I had no idea excess humidity could be a problem.

I, too, have found that the customer often can tell right away when something is not quite right, especially butchers and florists. Even if temps are okay, I will keep looking when one of them is worried.

Lin,
Indeed, we set RH on 85%.
There is a rule we follow - one i find in different books - that we have to run with a DT of 7K and the machines has to run appr. 14 to 16 hours/day.

Found somethin on the net
http://www.fao.org/DOCREP/004/T0279E/T0279E03.htm justbelow figure 9 (some sort of thermometer) "Water is required by micro-organisms so reducing the water available below the optimum level will prolong shelf-life.

If meat is stored at a relative humidity (RH) below 95 percent, moisture will be lost from the surface. Since most spoilage bacteria, being aerobic, can grow only on the surface, this surface drying will extend the shelf-life. Moulds (fungi) are able to grow in drier conditions than bacteria so that desiccation has a selective effect on microbial growth"

Hi:)
meat has a number of differing requirements, dependant on what stage of storage it is at.
Post slaughter, most beef goes through a pull down cycle, this would be typically, holding at 10 deg for 10 hours at maximum humidity 9low weight loss), then a pulldown with coolers selected at a 6K to 8K td, lots of capacity, down to a temperature of -2deg C. After which the beef is stored at 2 deg C, with reduced fan speed.
More often than not beef is stored in a ripening room, where the humidity is controlled, and reduced from the post slaughter stage by dehumidification units (Munters), this excelerates the maturing of the meat, giving a quicker turn around time.
Regards. Andy. :D

Looking at a psychrometric chart, where 35F intersects with 80% RH, we show a wet bulb/dewpoint temperature of 30F.

When the air entering the coil is at 35F, if the coil temperature is such that the coil leaving air wetbulb temperature is 30F, then the coil will stop removing humidity. If the coil is not allowed to drop below this temperature, then the humidity cannot drop below 80% @ 35F.

A common way to maintain a lower limit for the coil temperature is with an evaporator pressure regulating (EPR) valve.

Quote:

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Originally posted by Gary
Looking at a psychrometric chart, where 35F intersects with 80% RH, we show a wet bulb/dewpoint temperature of 30F.

When the air entering the coil is at 35F, if the coil temperature is such that the coil leaving air wetbulb temperature is 30F, then the coil will stop removing humidity. If the coil is not allowed to drop below this temperature, then the humidity cannot drop below 80% @ 35F.

A common way to maintain a lower limit for the coil temperature is with an evaporator pressure regulating (EPR) valve.

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Unless I understood it wrong but installing a EPR can only rise the evaporating pressure and also reduce dehumidification due to the increased coil temperature.

We lowered in the past the evpaorating pressure on the racks to increase dehumidification.

Hi:)
on the low weight loss chill we employ an evaporator pressure regulator, a motorised valve controlled by a PLC, the motorised valve allows for very close control of the evaporation temperature, and thus the room humidity.:)
Regards. Andy.

Big ass coils!!! Low coil td (2 - 4K). Thats how pretty much all meat rooms are done in oz. Giving a physically bigger coil running at a higher sst to achieve temp (usually running around -3 SST to achieve a 0 to 1 deg celcius room temp).
Forced draft Deli cases use the same principles, run as higher sst as you can to achieve temp.

in independent cold room system(not shareing condensing part with other humidity modulating rooms), I think evap. surface reduction is more energy efficient than electric reheat. air flow rate reduction is most efficient but may issue cold air distribution problem result in uneven temp inside room while dehumidifing.

in multi-rooms system, the suction pressure is controlled within a dead-band,and is independent to individual room's load, so the dehumidification capacity of surface and air flow reduction methods are limited(in fact. evap. partial surface do nothing better than full evap. surface). maybe in here, 2 speeds fan with electric reheat is the solution.

evap. pressure regulation require a lower actual suction pressure due to the pressure loss through regulating valve. and there may need a more smart control system, when any of room call for more dehumidification(the regulating valve open widely), more comprossor load up to achieve lower suction pressure, then enhance dehumidification capacity in the room. when all regulating valves is partial opened, mean that the suction pressure is low enough, so some compressors could be shut down.