Fin spacing

[Rio69]

Hi,
We have to convert an old apple cold store +1degC, to ice cream cold store, with temp. -28degC.
There are 8 rooms, with 4pcs. R404a multisets.
The customer wants to keep existing evaporators which are in very good condition.
We will build new multisets appropriate for new working condition.
The surface of the evaporators is huge due to heavy load required to cool down apples during first 24 hours.
My only consideration is fin spacing, which is 6mm. Normaly I would use 10mm at least.
To prevent excess ice formation, we will have ante room before main entry in corridor, where I can install some dehumidifying, or "frost trap".
Can anyone share similar expiriance, or any advice...

Thanks.

Rio

[chemi-cool]

It will not work.


Maximum fin spacing is 4 per inch.
What about defrost?
Can you get a picture of the pipes arrangement in the coil?

[Sandro Baptista]

I would say that there is very chances to work correctly. It also depends of the air moist inlet to the ice store, but with a dehumidifier, I agree it really will help a lot.

Because the aircoolers are for a DX system (needs more surface than for a pumped system, and the inlet air transfer heat with the superheated part) and because you told that the aircoolers are huge, which is good because it can accomodate more ice witout blocking...so I would say there is very good chances of working well.

[US Iceman]

I agree with Chemi. I don't care how big the coils are, if the fin spacing is too close together the frost will bridge the fins very quickly and then you loose air flow!

3 fins per inch would be better, but it should not be more than 4.

Even though the apple cooler worked at 1°C, the evaporating temperature would be lower than 0°C so frost would form on those coils too. The difference being the much lower evaporating temperature for the ice cream storage. In that application, the coils will generate a lot more frost (due to the colder temperatures).

I understand someone is trying to save money by not buying new equipment, but if they use the existing equipment they will probably face a lot of issues to make it work!

[Sandro Baptista]

I agree with Chemi. I don't care how big the coils are, if the fin spacing is too close together the frost will bridge the fins very quickly and then you loose air flow!

ICEMAN I agree about you say of save money on new equipment but if the refrigeration needs for the ice cream cold stores are much lower than for the apple stores I think that with the existing aircoolers that have a lot of heat transfer surface.

Supposing you have:

- Evaporator nº1 you have selected with 8 mm fin space with for instance 150 m2 heat transfer surface;

- Evaporator nº2 (existing) you have selected with 6 mm fin space with for instance 300 m2 heat transfer surface

I think the evaporator nº2 would do it with the same defrost intervals. The same quantity of ice spread in surface of evaporators nº1 and nº2 will allow the evaporator nº2 to have a small fin spacing for the same blockage surface.

Don't you agree?

[US Iceman]

The same quantity of ice spread in surface of evaporators nº1 and nº2 will allow the evaporator nº2 to have a small fin spacing for the same blockage surface.

There is some truth to that. However, this assumes the same amount of frost would form over a larger area, than the same amount of frost over a smaller area.

My guess is... both will generate the same amount of frost since the cooling capacity of both coils should be the same.

The problem I believe with the ice cream application is that the temperatures are a lot lower than that required for apple storage. Therefore, the coils will have more frost since more moisture is being pulled from the air in the freezer (rather than the cooler).

You mentioned DX and pumped liquid, but the original poster did not. So... we have to be careful of what we assume and not interject something new into the discussion which might not apply at all.

[Sandro Baptista]

You mentioned DX and pumped liquid, but the original poster did not. So... we have to be careful of what we assume and not interject something new into the discussion which might not apply at all.

I'm sorry...you are right I guess I gave a big "step". I assume that because Rio69 has talk about R404A. Of course that it could be pumped but normally for those freóns we use DX sytems...at least in Portugal.

[Yuri B.]

If for +1C they used DX what could it be anything else if they want a transfer to - 28C? What about the eficiency?

[lowcool]

gday rio fin spacing should be no issue,buffalo low temp coils use 236 fins/metre for up to 13.4 kw,heavy duty coils up to 34 kw use 197 fins/metre,if defrosting is a problem you can always use water,dont worry about excess frosting and extra defrost or two wont hurt especially if water is used its pretty quick.good luck
ps might pay to enquire about distributor orifice,but its probably my imagination

[Rio69]

Thank you all for your valuable opinions.
We will try to use the old coolers..

Rio