subzero refrigeration

[EAJ82]

hey all..
what's the difference in designing a refrigeration cycle for air conditioning and for refrigerating?
For example: u design an air conditioning cycle to have 80/67 entry conditions with like 45F for evaporating temp, and on the condenser u may try 95F outdoor air, to 125F condensing temperature...
but what about the refrigeration when u have a room way below 0 Celsius (32F)..0F lets say..
how do u do that?

Thank you
Elie

 

[willard3]

I'm not sure I understand your question.

Really, the only thing that changes is evap EAT and LAT and, depending upon the refrigerant, the condensing temperature may change.

 

[EAJ82]

well if u need to design the condenser and evaporator, where do u start? do u design them to work at 80F then see what it will give u at 0F ?

 

[IRstuff]

Why wouldn't you design it for the operational temperatures?

TTFN

FAQ731-376

 

[EAJ82]

if u design it for the operational temperatures this is what happens:
at startup the freezer temperature is high, the compressor is stronger and needs more cooling. Since u made ur design on the operational temperature your condenser will be very small compared to the maximum power of the compressor. Ur system will heat up and shut down.
But when evp temperatures reach very low levels, the compressor power is more than halved so it needs only half the condenser.
What my question is, at what temp. should i design it so i don't face problems like overheating and stuff. Standards say that in HVAC u need to measure the capacity of ur machine at 80/67 entering conditions and design it accordingly.. what about subzero refrigeration.

 

[IRstuff]

You're an engineer; please refrain from using IM speak.

Again, you're designing for the whole system, hence the plural on "operation temperatures." You have to design for a particular lifetime, reliability, maintainability, energy consumption, cooling capacity, ambient conditions, region of the world where it's used, installation constraints, etc. It's not just about temperatures.

What about subzero refrigeration? It's a different problem with different requirements. There are no humans being cooled in this problem, hence many of the constraints used in A/C don't apply.

TTFN

FAQ731-376

 

[ChrisConley]

If find it annoying and distracting, but I'm not going to tell anyone how to type. That's a different forum.

http://www.eng-tips.com/threadminder.cfm?pid=1010

I'm my opinion it does look horribly unprofessional.

Back to the question: the unit has to be sized large enough to pull the space down from ambient to the design condition in a reasonable time. The unit also has to be sized to meet the heat gains occuring at static design.

The original equipment sizing will be the largest load that the unit has to produce at the worst expected combination of design temperatures. Part-load can be met with a number of strategies, the simplest being cycling. If a really tight temperature control is required then VFD and other tight capacity control concepts can be introduced.

 

[CorBlimeyLimey]

"If find it annoying and distracting, but I'm not going to tell anyone how to type. That's a different forum."
Anyone who communicates (types) that way in a site created for "Engineering Professionals" will not be bothered to seek out and frequent forum1010 . So if it is not pointed out that the chosen quality of communication is sadly lacking in professionalism, how will the OP come become cognisant of this shortfall?

 

[ChrisConley]

My complaint was the tone or IRStuff's response, and tone in writing is another whole issue.

I'll tell someone if I find their writing style annoying and that I find it 'horribly unprofessional'. I'll even start a new thread in another forum to discuss it. I won't tell them how to type though.

You're an engineer; please refrain from using IM speak.

Feels very authoritarian for a peer forum.

 

[CorBlimeyLimey]

"To each his own" ... but please note the "please" in IRstuff's comment. That made it a polite request, not an order or instruction on how to type.

In my opinion IRstuff's post had the perfect combination of constructive criticism with constructive help.

4 wot 1ts wurf, IRs p0st was purfik, no wot 1 m33n

 

[IRstuff]

IM speak is generally a turn-off for engineers, therefore, writing in IM speak tends to prevent getting cogent and helpful responses. The fact that the OP is getting relatively few responses speaks volumes.

TTFN

FAQ731-376

 

[imok2]

Unless IRstuff is a site administrater and /or is getting paid to tell people how they should write and he finds it annoying then maybe he shoulden't respond to the question. For me the most important thing to do is to give the best answer one can . (see rule seven) Having said that, I agree with IRstuff that we should always strive the improve our writing.

" The fact that the OP is getting relatively few responses speaks volumes" Forgive me but what is "OP" I find it a turn-off when I don't see a word spelled out

 

[ChrisConley]

OP is original post(er).

That one took me a long time.

 

[imok2]

Thanks Cris, I had no clue.

 

[CorBlimeyLimey]

imok2 ... Touché. However, OP (and IM) are generally accepted abbreviations; not some mangled english letters and numbers masquerading as a language.

"... and that's all I have to say about that!"

 

[willard3]

I will say that the IM speak prevented me from understanding the original question.....how is that a benefit, professional or otherwise?

Engineers already get a bad enough rap for poor English skills.

 

[imok2]

"However, OP (and IM) are generally accepted abbreviations; not some mangled english letters and numbers masquerading as a language" OK but not necesserly known by all, However I do get your point and I agree. Think: (smily face)

 

[IRstuff]

"Annoying" was NOT from me. We're all professionals and need to keep this place reasonably efficient on our own, since there are no designated moderators here.

My objective is to always give the best possible answer, but sometimes, the best answer is not an engineering answer. Getting the OP to communicate and elucidate is quite often required to even come close to getting any answer to a question.

TTFN

FAQ731-376