ventilation for refrigeration room

[Nedal Iben Ali]

im working on designing refrigeration rooms for storage of several types of fruits and vegetables.

as known, the percentage of oxygen and carbon dioxide and ethylene should be controlled. this can be done by ventilating the refrigeration room by a flow rate of fresh air depending on room size and product quantity.

please help me with the amount of this flow rate required for long term storage.

best wishes

Eng. Nedal Iben Ali

[Peter_1]

You must do this with feedback of the proper sensors, too risky for your product trying to maintain a preset value or a rule of thumb.
There are special controllers for this task.
http://www.vdhproducts.nl/ is one possible supplier we see here many times.

[salil sampson]

hi can i ask a question related to refrigeration?What should be the pressure on discharge line of R404 gas for blast frezeer freezing to -40*c

[salil sampson]

i meant the correct discharge pressure so that the system does not suffer at low temp

[taz24]

i meant the correct discharge pressure so that the system does not suffer at low temp

Thats sort of like asking

How long is a piece of string.

The discharge pressure is dependant on ambient air temp.
The pressure could be as low as 8 bar or up as high as 22 bar.

Pressure in refrigeration is not important it just corrisponds to the actual temp.
Temp is important.

taz.

[Peter_1]

Spot on Taz, discharge pressure has nothing to do with the evaporating temperature

[Sledge]

Thats sort of like asking

How long is a piece of string.

The discharge pressure is dependant on ambient air temp.
The pressure could be as low as 8 bar or up as high as 22 bar.

Pressure in refrigeration is not important it just corrisponds to the actual temp.
Temp is important.

taz.

I had always attempted to make things work, based on 95 degree F condensing. That is our design conditions for Toronto. When it is colder than that we artifically raise the head pressure, through the use of head master/head pressure controls.

I agree that the evap and condensor temps are not related, but the design should be to meet highest ambients that the condensor will see. Then one would add additional controls to maintain the head pressure.

We do however allow the head pressure to drop in cold weather, but we limit that drop to the point where we maintain the pressure differential between high and low pressure required by the refrigerant, rule of thumb is 100psi.

When we dont do it this way, the evap ends up being starved in low ambients, and freezing up.

Have I been approaching this incorrectly? Is there another way?

[lana]

Basically you are correct.

We have to maintain the pressure differential for the TEV to operate correctly. This also depends on the selection of the TEV nozzle. If the nozzle is selected for a given pressure drop, then this must be maintained otherwise the capacity of the TEV drops therefore, starved evaporator is the result.
The opposite is also valid. If the nozzle is selected for low pressure difference, and now there is large pressure differential then TEV gives more capacity. We have this problem with the imported second hand units from Europe where the nozzle is selected for low ambient. Here we have higher ambient in summer which results ....in the other hand air cooled condenser is selected for 15°C TD (for Europe) but here we need 8-10°C TD. So you can see the problem.

Cheers

[setrad7791]

dicharge temp has a direct relation to evap temp your statement is totally incorrect! if the head pressure drops the suction pressure drops.. i.e evap temp

[lana]

dicharge temp has a direct relation to evap temp your statement is totally incorrect! if the head pressure drops the suction pressure drops.. i.e evap temp

To whose statement are you referring to ?

[taz24]

To whose statement are you referring to ?

I think he must of been refering to my statement lana.
I stated earlier that cond pressure did not affect suction pressure.

Cheers taz.

[lana]

Hi everybody,

I would like to discuss something here.

Actually suction and discharge pressures are inter connected and effect each other.

If suction pressure rises say for any fault or condition change then discharge pressure rises too. BUT the amount of increase is not the same as the suction pressure.

The opposite situation is also valid.
If any HP fault makes the discharge pressure to rise then suction pressure would rise but not with the same amount as the discharge pressure.

The increase or decrease of pressures depends on the fault.

Clear example is the excess refrigerant charge fault. If there is excess refrigerant then both pressures would rise BUT the discharge pressure would rise more than the suction, this is why this fault is categorized as High Pressure Fault.

The only fault which makes the suction pressure rise but the discharge pressure to drop is the compressor fault. That's why this fault is the easiest to diagnose.


So I should say that setrad7791 is right. Pressures do effect each other and so would the saturation temperatures.

Cheers

[Josip]

Hi, Nedal Iben Ali

Welcome to RE forums.

im working on designing refrigeration rooms for storage of several types of fruits and vegetables.
as known, the percentage of oxygen and carbon dioxide and ethylene should be controlled. this can be done by ventilating the refrigeration room by a flow rate of fresh air depending on room size and product quantity.
please help me with the amount of this flow rate required for long term storage.
best wishes
Eng. Nedal Iben Ali

You can use air ventilation/cooling if outside air temperature is lower than you need/have in your cold room at least after harvesting...

But for long terms storage of fruits/vegetables I think this suggestion is much better

You must do this with feedback of the proper sensors, too risky for your product trying to maintain a preset value or a rule of thumb. There are special controllers for this task.

Only rooms with controlled atmosphere (CA) can preserve your goods well.

Best regards, Josip