Sizing Condenser to Evaporators for different Applications

[PHENERGY]

Hello there,
How does one go about deciding on the best size Condensing Unit to match an Evaporator for a specific purpose?
for eg. I have a 15 ton Larkin Evap. (three Fans four bladed 27 degree pitch, 26inch diameter) that I intend to use in a 24x12x8ft insulated Box, I would like to ceate a "Blast Freezer" running R404A to operate at -30 F or lower, so what size Condenser do I use???

If I wanted on the other hand to create a maintaining Freezer whereby Frozen product is inserted and is maintained frozen, how can I go about deciding what size compressor/condenser to use?

Peter

[Peter_1]

Because you're a energy consultant, you perhaps have to take another approach then a customer or a tech.
You specific needs to select a condenser which will make that the whole set-up will run with the less energy as possible.

What will you use? Open or hermetic compressors.
In theory you need a condenser equal to the evaporating capacity + absorbed capacity by the compressor and selected with a DT of 10K compared to the hottest expected outside temperature. If outside temperatures can swing between large margins, you also need some sort of HP control on the fans (HP pressostat, VFD...) to maintain HP for your TEV.

[PHENERGY]

Proper operation of the Blast Freezer is ALL that is needed to Save Energy in the Application for which it is to be utilised. I simply need to have as much BTU's above 95,000 as posible at a Temperature at or lower than -30 F with more than 1800 CFM of air circulation. I intend to use Semi Hermetic Compressor, and the hotest days in our area can reach 35 C while nights are lowest at 21 C. From my limited understanding of what you have outlined, I can see that a 15 Ton Condensing Unit cannot deliver, therefore should I go with a 20 Ton???

Incidentally what is the defination for the abbreviation "DT"??

Peter

[Peter_1]

Proper operation of the Blast Freezer is ALL that is needed to Save Energy in the Application for which it is to be utilised. Peter

This is not ALL what is needed to save energy. It's a wrong statement. It starts and depends almost solely with a proper design.

You can have more BTU's if you lower the HP (and even rise the LP), so a lower DT over the condenser and also designed that way. Because once designed and installed, you can't change it afterwards.

The air circulation doesn't say anything: the design of the whole concept, especially the room itselves is much more important.

You need a condensing unit who can give at 95,000 BTU at the desired evaporating and condensing pressures. That's all.
If the 95,00 is correct of course.
I'm not familiar wit IP units but did a conversion from your 95.000 BTU to tons which gave me completely different figures.
You need something around a 30 Hp unit, given that 95,000 is correct.

Do you need capacity control, partial load, is room stacked always full, is it a FIFO freezer, ....

DT: if outside conditions are 35°C then you're compressor must be able to condense at max 45°C or ....psi (you didn't gave the gas you will use)

Without having the intention to be rude....designing a blast-freezer is not that easy as it looks on the first sight.
I strongly recommend that you try to find someone experienced to figure out, eventually together with you what your client needs.

[PHENERGY]

Well, you did initially state that my outlook is gonna differ because I an an energy consultant, the fact of the matter is that the system that the blast Freezer is to REPLACE uses quite alot more energy. The Gas Iwill Use is R-404A. I do not use a blast Freezer simply to blast freeze but as part of a totally different concept, so from my perspective ALL I have to do is to get a proper operation at
-30 F and the minimum air circulation and presto I will have saved lots of energy ( will post results after completion of this design) the fact of the matter too is that I am in consultation with a Very experienced Contractor but I like to cross reference and have an idea of things before he makes his recomendations he is to give me his design tomorrow. For a previous blast freezer he designed and used two 15 HP condensing Units, but I did not know the evap size, this time arround I know the Evap size, so I guess he may design at or arround 30 HP as you have suggested.

Peter

[TXiceman]

Peter_1 is right. It is not hard to balance a unit cooler with a condensing unit. You simply plot the unit cooler at a couple of capacities and TD's (temperature diferences) and then cross plot the condensing unit against the unit cooler. Where ther cross is the balance point with no line losses. You need to offset the unit cooler by 2 dF to allow for suciton losses and that is you actual real world balance.

Also, designing a blast freezer is not all that hard, but does require some knowledge of air flow and product spacing/packing. Does your Larkin unit cooler have cast air foril fans or are they the stamped flat sheet metal baldes? You generally want to rate a unit cooler fan for 1/2" W.C. (water column) static pressure (SP) because you will have some static loss in a blast cell getting the air through and around. A flat sheet metal blade can not produce the static pressure and will not produce sufficient CFM (air flow).

If you want to balance a separate condenser with a compressor and them a unit cooler, you have a whole new ball game. It ican be balanced by hand, but takes a bit more work. Both of these are something that I do on a daily basis, bit not something to expalin over the net. If you post some model numbers, I can see if I have the literature on the equipment and could do a balance. If it is used equipment andyou are changing refrigerants, you need to watch out on the unit cooler. The distributor and nozzle may not work for te new application.

Sounds as though you need to hire a refrigeration engineer to keep you out of trouble.

Ken