compressor sizing

hi everyone

I've just bought a freezer room

9m x 5.6m m 3m high

panels are 5 inches thick

(I'm not sure if this helps or not but I did some of the maths for you to help)

87.6sq meters of wall space
50.4 ceiling
50.4 floor

or 188.4sq meters total

approx 1000kg of "cool" meat to (hopefully) be frozen in 24 hours

can anyone give me a rough idea of how much cooling capacity I need to run at -20'C ?

quite a lot of door openings, but will be fitted with those plastic hang down things (plan to make a "porch" just inside with them too)

I know a GOOD refrigeration engineer (hard to find around here) who will be sorting it all out for me... but I like to know what I'll talking about before I start talking about it to him... and he's really busy guy so I don't want to waste his time !

installed outside (with a roof over) in north east england

if you can give me a rough idea of the min I need and what you would recommend ?

thanks

Alan.

I had a play with cool tools (if only to help me understand the system better)

I came out with an average cooling demand of 8.3kw

and a max of 11.8kw

but to be fair... I don't really know what I'm doing there.... so would be grateful of some experienced input ;)

thanks

Alan

Glad to see the business is still growing Alan.

I'm sure someone will be along soon to help you out.

thanks Brian
(I always have to double take your name because the refrigeration engineer I use is called Brian too!)

things are going pretty well production wise... lots of work to do / being done... tho tbh prices are a little low right now.... they'll be going up soon which will probably cut back on production a bit... just want to push on for a bit longer until we have a few more customers / until we've nicked a few more from the competition ;)

I made a simple calculation using your data hope this help.

assuming your entering temp of product is at 0 C:

your cooling capacity would be 39,473 btuh, for me using 5 inches for as panel thickness is a waste of money i think you can set up a cold room for 4 inches ( if the Polyurethane ).

cool... google tells me that is 11.6kw... so thats about the same my play with cooltools brought up :-)

I bought the room 2nd hand it was only £720 but has no cooling gear with it - it's just the bare room.... I'm thinking it's a bargin... (hope it is)

hopefully should be getting some good second hand compressors etc.. too soon (fridge guy sorting them out for me)

going to install seperate systems along side each other... probably 3 or 4 depending what comes up.... will I be ok to just have them all runing away next to each other ? maybe set different temps on some of them ? so say set two of them to -17'c and the other two of them to -20'C to stop them cutting in and out all the time?

yes, that was based on heatcraft. if you really want to be in safe side i made a computation using a software we used and the outcome is 20 kw. around 15 hp at - 26 C evap temp (sst)

cool.... if the 2nd hand compressors do work out then I was going to aim well into overkill land anyway.... will give a bit more room for summer heat / busy times / maintenance etc...

next question....

as the room will be running (approx) 4 separate systems, all controlled seperatly... what is the best way to run them ?

run them all set to the same temp (with shorter defrosts I presume?)

run maybe 2 at the desired temp (-20'C) and 2 at a slightly higher temp (-17'C?) - to help prevent short cycling - could create defrost problems? higher temp system's wouldn't require as much defrosting

run all to the same temp - but turn some of them off when they're not needed (low load times / weekends etc..)

I don't really want to have them defrosting when it's not needed... - at a guess 4 system's defrosting for 20min 3 times a day could put 12kw of heat into the room??

maybe only have the defrost timers spinning when the compressor is running ? (might have to add extra defrost times to compensate?)

might be better to have one system running colder than the others... so they all pull the room down to temp and then one keeps running longer... so the rest won't be running at all ? (or much)

or any other ideas ?


p.s. thanks for all your help so far guys... as you can tell I like to know exactly what's going on with my machines etc.. and I'm not used to having to ask for advice... I've grown accustomed to being the one everyone else is asking for advice !

Alan :-)

Quote:

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Originally Posted by knighty

I don't really want to have them defrosting when it's not needed... - at a guess 4 system's defrosting for 20min 3 times a day could put 12kw of heat into the room??

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How did you came up with this number?
When you defrosting ice, heat is consumed by ice melting and it is localized because fans are not working.

ahh... I didn't really think about that

it was kind of a guess... I rmemeber seeing an old freezer we scrapped having a total of 3kw of heating elements in it for defrosting...

so went with 3kw x 1hour(3x20min) x 4 systems = 12kw

Most of that heat went down the drain...Literally.

Maybe not a huge concern, but how well this works out, and to some degree how it needs to be controlled, depends on how you are going to introduce and presumably remove that 1000 Kg per day. Thats about 20% of what your freezer would hold stacked out, and you will need some serious air movement to freeze it out if it goes in and lives the whole 24-hours as a 1.2-meter cube....

A kilo at a time, spread through the day, distributed around, is a whole different picture.

Quote:

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Originally Posted by knighty

approx 1000kg of "cool" meat to (hopefully) be frozen in 24 hours

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Rough estimate:

(((1000 x 2 x 1) + (1000 x 85) + (1000 x 0.9 x 20))x1.16)/22 = 5.5 kW or +/- 5.5 HP at -30°C/40°C

= sensible heat before freezing + latent heat of freezing + sensible heat of freezing for water (meat is +/- 100% water)

So a 7.5 HP will do the job but this is just the beginning of the job, storage and air circulation is as much important as the cooling load.

22 hours because unit must also have time available to defrost.
16 hours/day is more realistic, so 7.5 kW (+/- 7.5 HP)