0C Coldroom Evaporator operating at 20C

Hi all,

I need to pick some brains.

I have to create a large coldroom (to be operated at 0C) and have selected the evaporator with the following:

• 3 off evaporators
• 25 kW duty
• Propylene glycol (35%) Supply/Return at -10C / -6C
• Air on / Air off at 2C / 0C
• 2off 800 diameter fans (100 Pa) per unit

From the above evaporators can be selected.

Here comes my Story/Question: During the early project lifespan, the Coldroom shall be used for other purpose and operate at 20C (air off). However, the 3 evaporators must not change when changing from a 20C room to 0C room.

From my calculations - when operating at 20C, the evaporators are physically oversized as the LMTD differ greatly.

Any tips?
Does this mean that my valve station will be modulating alot?
Has anyone done this before.
Whats the dehumidification effect?

Regards,

Hi, samiam :)

.... what is your cold room for... onion .... potato... something else ...

Best regards,Josip

Hi Josip,

Its a general coldroom - no product spec yet.

Regards,

First of all that is a diverse range of temperatures you have. One main issue I see initially is the need to provide uniform air flow of the area to be maintained by temperature.

Is this area constant during the operation at 20°C? And, is this the same area that will be maintained at 0°C? If so, then you need to maintain a uniform air flow throughout the space, which eliminates the possibility of of only using one or two coils at 20°C as opposed to three coils at 0°C.

When the space temperature is 0°C the coil will probably operate with frost on them. During the operation with 20°C the coils will be operating wet. Therefore, you either need to ensure the face velocity of air off of the coils is low enough to prevent water being pulled off of the coils. This could be done with VFD's or by carefully selecting the coils so that operate with low face velocity in either condition.

Then...you can evaluate the need for control valve modulation, floating set points for temperature control, etc.

And, just as important is the need to have the refrigeration system designed so that it can operate at both conditions (20­C or 0°C) with the most efficient mode to deliver the lowest operating cost.

It's not impossible...it just takes some work and careful review.

Keep the fans running on all evaporators, but let just one actually working. The total air flow will allow uniform air mixing, but the cooling capacity will just be 1/3.
Please note that the compressors or condensing unit that is, must be capable of working at 1/3 of design load.

Hi - thanks for the feedback thus far.

A point that I forgot to mention. The room is a 0C Coldroom but until they build the reminder of the warehouse (in 3 years time). Until then it needs to operate at 20C.
(I do have VSD fans)

any more tips

Look at using water cooling through evaps and a dry cooler, you know the wet buld condition, if necessary add a high temp water chiller to suppliment cooling capacity, later on design a chilled glycol system for total duty once at 0'C, don't forget partial defrost on evaps.
magoo