Final Exam for next year

[Peter_1]

This will be the final work/exams for next year classes I'm giving.
What do you guys think of it?
I appreciate your comments.
They start in September 2008 and they must give this 'project' to me in June 2009 where they will then have to defend it before a jury.


GIVEN.
A client wants a cooling/freezing chamber for the quick chilling of hot prepared foods.
The company starts at 06:00
The first chariot with 100 kg hot meals enters in the cooler at 90°C at 07:30.
Then, each hour another chariot enters the room till we have 5 chariots and a total of 500 kg food.
The goods must be cooled according HACCP.
After the quick cooling process, the room must be maintained at 2°C.
As soon night rates starts, client must have the choice to start a freezing cycle to freeze all the goods to -20°C.
At 06:00 the next morning, the room is emptied completely and cleaned before the unit is switched on again at 07:30.
So the room can function as a freezer and as a cooler.
Client wants also heat reclaim on this system to preheat water.

DEMANDS.
1 Determine Total cooling load in cooling and freezing cycle. Don’t forget the chariots, opening of the doors.
2 Re-do your calculations with Coolpack and compare results.
3 Select all components (main components and all regulating devices)with the catalogs. You clearly state how you came to the result and add a marked copy of the catalog page.
Add also pages with correction factors
4 Re- do all the calculations with the software and compare your results.
5 The compressors are located in a machineroom 6 m (18 ft) above the cooling room. Condenser and receiver are on the roof 14 m height above floor level.
6 Calculate manually suction, discharge and liquid Lines.
7 Re-do your calculations with Coolpack and Danven and compare the results.
8 Calculate line isolation.
9 Draw a equilibrium diagram in cooling and freezing phase and determine working points with an ambient of 30°C and -10°C.
10 Draw both cycles in a lop-P, each on a separate page (Coolpack and manual) Determine all the relevant pressures and temperatures.
11 With which COP will the plant run in summer and winter?
12 Draw a complete electrical layout
13 Draw the complete refrigerant circuit.
14 Determine refrigerant volume and clearly give how you came to the result.
15 Determine room, panel thickness, door , Floor and pressure valves on the room.
16 Make a complete material list and give a price for each. Give also an estimate how long you will work on this project.
17 Make a complete offer to your client like you should sell this, selling conditions included.


Following combinations are allowed
• Bock compressor + Roller evaporator + Searle condensors.
• Bitzer compressor + Goedhart evaporator+ Guntner condensors
• DWM compressor + Friga Bohn/Heatcraft evaporator+ Searle condensers

Danfoss, Alco, Honeywell

Eliwell, Dixell, Carel,..

[chillin out]

Consider me already failed.

Looks good though, well done Peter.

Chillin

[chemi-cool]

Very impresive Peter.

A good choice. I'm glad its not some useless freezer, these things have high demend.

Can I order a copy of the winnig design?

[US Iceman]

Very nice Peter.

I have one comment: You should list the location of the facility (I'm sure it is in Belgium someplace), but ask them how they might take advantage of the cold weather to increase the COP. Then they might ask questions about why this matters and how you design for the cold weather benefits.

[Peter_1]

Thanks Chemi, I will make you receive a copy but it will be in Dutch of course

USIceman, I thought for a while giving an extra difficulty saying that this machine must be installed on a height of 6000 ft with ambient ranging from very cold to very hot.

But, to be honest, this seemed not relevant for our country.

But a very good add-on could be that client asks to develop a machine which runs as efficient as possible (low condensing with low ambients, small DT's, VFD on the compressor perhaps, hot gas defrost, heat reclaim, ... )
I also thought on the hot gas-defrost because the heaters can't be removed not that easy out of the coils.

Thanks for the tip USIceman in Brussels.

[nike123]

Nice one! If I found some free time, I will try to make this exam for myself and try to see what good am I! Maybe than (if it is not too embarrassing for me) I will send result to you by mail to get grade.

What HACCP standard you are referring here?

[Peter_1]

Nike, you have a whole year to make it

I hope I covered the most, line selection, evaporator installed underneath the compressor (oil syphons), receiver high ( DP increase in the liquid line), heat reclaim, different capacities, ....

[frank]

Peter

Good questions, and towards the end it adds the pressure on them.

A couple of questions though.

Surely you need to give them an indication of the SHC of the goods?

Without it, how can they calculate the refrigeration duty? Also, what time scale is allowed for chilling and freezing?

Do they have to calculate the individual chariot cooling times (at 1 hour intervals) or await until all chariots are in place?

[Peter_1]

Surely you need to give them an indication of the SHC of the goods?
Without it, how can they calculate the refrigeration duty? Also, what time scale is allowed for chilling and freezing?
Do they have to calculate the individual chariot cooling times (at 1 hour intervals) or await until all chariots are in place?

Well, the prepared foods are meat and vegetables,...They must consider a worst case scenario.
What I do in such an occasion is considering the whole meal as a mass of water which approaches very close reality: most consists of water.

I mention HACCP so that they search how fast it must go. Out of my head: to 10°C in 120 minutes, to 7°C within 5 hours and within 24 hours to 2°C.

So the biggest load will be - I think, I haven't measured yet - after the last chariot is entered the cold room.
The first one is entered in the room and it's cooled 1 hour before a second one enters. So, the first one isn't fully cooled yet.

I realize that these things must approached theoretically as good as possible. In real life, I should do a test in a cold room of a client and looking how fast we can cool it down.
But I know that 120 minutes is long enough to cool it down to 10°C.

How I see it: the compressors must start as soon the first chariot enters the room.They have to calculate theoretically how far the temperature will descend (assuming a linear descend which isn't the case) after one hour and add this decreased heat load to the new heat load entered in the room. Both chariots cool further down and after another hour the 3th is entered in the room, second cooled down already more, second half and half and so on.

So they must use a little iteration at the start I suppose.

Hope I don't make it to difficult but this is a real life situation anyhow.

Freezing times is easier because everything is already at the same temperature when starting. Freezing time is during night rate 10PM till 6 AM here in Belgium and during weekends

[US Iceman]

What I do in such an occasion is considering the whole meal as a mass of water which approaches very close reality: most consists of water.

Very good. I do the samething myself. Then you do not have to be concerned about what the product actually is. This also allows you to change the prodcut without changing anything else.

BTW, you are welcome on the tip. I thought you might be interested and thought you might have done something similar in the past, since you are so creative.

Did anything ever happen with the old brewery compressor Peter?

[Peter_1]

.... I do the samething myself. Then you do not have to be concerned about what the product actually is. This also allows you to change the product without changing anything else.

BTW, you are welcome on the tip. I thought you might be interested and thought you might have done something similar in the past, since you are so creative.

Did anything ever happen with the old brewery compressor Peter?

If you take water, then you're sure you calculation will fit for every product.

I will add certainly something about energy saving techniques so that the students at least thinks what they can do do lower energy consumption.

As you've seen, I've done something similar but this is at least 10 years ago. I've seen the pyramid for the last time 5 to 6 years ago in Brussels at Batibouw.
http://www.batibouw.com/en/Batibouw_2008.htm

Well the old compressor,... glad you reminded me to it, I forgot it and will take contact once again .Let you know something.

[US Iceman]

I will add certainly something about energy saving techniques so that the students at least thinks what they can do do lower energy consumption.

I think that is a good idea. If you talk about using a balanced port TXV and that it might be useful for lowering energy costs in cold weather operation, then you could ask them on the test to consider cold weather climates for reducing energy.

Then when the students look at you funny you can say we talked about this before...