refrigeration warehouse questions

[bnuncc07]

hello. im a student and we are trying to design a refrigeration warehouse for a class. It includes having 3 freezers at around 20 degrees F, and 1 deep freezer around -40 degrees F.

From what ive seen, using ammonia in a liquid overfeed system seems to be the best route, but i was wondering if anyone recommends anything else.

Also is there a particular place that I can goto to get prices or estimates for the systems parts. any companies that are better or worse then others? thanks

[nh3wizard]

You might want to look into a 2 stage system since you want the -40, but there are other things you need to know prior, what size are your rooms going to be; what is the temp of your product coming in, what temp do you want to store it at...You have a company in NC called General Refrigeration, they just opened a shop there, plus The Stellar Group has a office in NC

[US Iceman]

Along with the idea of using a two-stage system, you might also consider looking at two temperatures on the low-stage (booster) side of the system. One overfeed system and booster(s) for -20F, and another overfeed system and booster(s) for the -40F loads.

Whether or not this is cost effective depends on the cost of electricity and the relevant cooling loads for each of those two areas.

You will also probably have some dock cooling loads, so these could be performed by the high-stage compressor(s). I would seriously investigate the possibility of setting the intermediate pressure at the required evaporating pressures for the dock air units, instead of using something like 25 psig suction pressure (which it seems everyone likes to do).

Just about any manufacturer should be OK. It's not so much the equipment name you use, as it is the manner in which the system is designed.

[Josip]

Hi, Bnucc07

welcome to RE

hello. im a student and we are trying to design a refrigeration warehouse for a class. It includes having 3 freezers at around 20 degrees F, and 1 deep freezer around -40 degrees F.

Can you tell us what you plan to keep in 3 freezers at 20*F (-6,6*C)? Pretty high temp for freezer room very unusual for me, but never too late to learn something new
Is that maybe evaporating temp?

Along with this:

....are other things you need to know prior, what size are your rooms going to be; what is the temp of your product coming in, what temp do you want to store it at...

Of course you need a most important

-quantity/mass of goods you want to store

to calculate needed cooling/freezing capacity:

Then you can try to decide about system:

You might want to look into a 2 stage system since you want the -40,

or

Along with the idea of using a two-stage system, you might also consider looking at two temperatures on the low-stage (booster) side of the system. One overfeed system and booster(s) for -20F, and another overfeed system and booster(s) for the -40F loads.

Best regards, Josip

[bnuncc07]

thanks for the input guys. to try and answer some of your questions.

The Deep Freezer:
-floor area: 25000 sq ft
-required temp: -35 degrees F
-Thermal load: 98.4 Tons
-sensible to total ratio: 0.85

Freezers 1,2.3:
-floor area: 25000 sq ft
-required temp: 28 degrees F
-Thermal load: 69.2 Tons
-sensible to total ratio: 0.85

Warehouse roof height: 40 ft

Loading Dock:
-floor area: 13500 sq ft
-required temp: 40 degrees F
-Thermal load: 72.1 Tons

The system also has to be able to be doubled in size for future expansion without being shutdown.

Mainly i am looking in to the design and cost of the evaporator coils, but any useful info is appreciated. thanks again.

[US Iceman]

OK, I have a question... What type of school are you going to and why this example? Just curious.

Freezers 1,2.3:
-floor area: 25000 sq ft
-required temp: 28 degrees F
-Thermal load: 69.2 Tons
-sensible to total ratio: 0.85

Is the 25,000 sq. ft. for each freezer or the total for three rooms?

28F is not a freezer, more of a cooler. I have to agree with Josip on this point. Where did the freezer terminology come from? I used -20F in my earlier post, since you said freezer, so now I'm a little confused.

Who provided a sensible heat ratio of 0.85? All of the cooling coils for industrial refrigeration are rated on 100% sensible heat, no latent.

Any/most of the dehumidification is done by the dock units. Since their evaporator temperature will be about 27F (or so) they will remove a lot of the water from the air entering the "freezers".

Using my quick rules of thumb, the dock loads should be about 90 tons or slightly higher. 72 Tons sounds a little light....

The system also has to be able to be doubled in size for future expansion without being shutdown.

That should not be a problem. Size the pumps, vessels and the main headers for the future capacity and add valves for the future tie-ins. The expansion should be able to tie-in without any shutdowns.

[bnuncc07]

well this is a mechanical engineering class, and the teacher is a retired PE from the industry. I agree with the temps that its not really a freezer, its a refrigerated warehouse i guess.

The 25000 sq ft and all specs are per room, sry.

All of these specs were provided by him, and frankly im rather lost because this is the first class where we have actually dealt much with heat exchangers, and deff the first time they shown us HVAC, so i am really lost as far as all of this goes. But either way we have to design this warehouse's cooling system.

Mainly just looking for any help or suggestions that i can get. thanks.

[US Iceman]

Without mentioning names, the only time I have ever seen the sensible heat ratio used is for air conditioning problems. Never on refrigeration, so I question that first.

Do I understand you that this is a class for HVAC, and they expect you to design a liquid overfeed system for a multi-temperature warehouse?

Did he spend any time talking about this, or just give you a problem to work on with no supporting information/dicussion?

This seems a little backward to me....

[nh3wizard]

[
Did he spend any time talking about this, or just give you a problem to work on with no supporting information/dicussion?

This seems a little backward to me....[/QUOTE]

Thats what I was thinking... didnt know if he was trying to get them to ask more questions because he didnt give them enough information or just getting them to think And I didnt see that the instructor was a PE, that explains alot

[US Iceman]

Usually you talk about the process first, then explain the details, then work the problem.

I'm almost wondering if the instructor is sure.

[frank]

What's a PE??

Iceman - you are correct about the sensible heat ratio, it is only used in the Psychrometric Chart and not the Mollier Chart.

[nh3wizard]

In the US it referred to a Professional Engineer

[frank]

Thanks NH3 -

[nh3wizard]

I hope I didnt offend any Professional Engineer's out there; just trying to throw out some humor

[Josip]

Hi, bnuncc07

well this is a mechanical engineering class, and the teacher is a retired PE from the industry.

or fired

Very strange way of teaching and learning, but definitely hard.

Excuse me, which year of study are you?

Best regards, Josip

[bnuncc07]

i am a senoir, and this class is a thermal fluids design class. It not nessecarily suppsoed to be HVAC but its what he likes to do... We have had no formal HVAC studies, and he really hasnt covered anything besides basic HXs and piping systems...

This warehouse is our project for the semester, it doesnt have to be liquid overfeed or NH3, but ive read that those are hte most efficient ones to use for this type of situation....

He is a retired PE who was head over engineers for Maytag and other companies for yrs, then went back to get his PhD, and now is teaching... seems to really know his stuff, but does have a bassackwards way of teaching.... basically you do the work on your own, and do it wrong... then he tells you this is how you should have done it..

[bnuncc07]

mainly i haveto figure out a ballpark cost estimate for the Evaporator system by the end of the week, and i cant find any general prices or costs anywhere online....

is there anywhere i should look, or what ballpark could someone give me.... thanks

[NH3LVR]

bnuncc07;
I think that the problem you are facing is that (at least in the US) manufacturers rarely sell directly to end users. They almost never advertise list prices, as you have discovered.
Although component information on valves etc. is now widely available on the net, pricing is not open to the public.
You might try looking at the Thomas register. If you called a manufacturer and explained you were a student, they might be willing to give you some ballpark figures. But they will need to know exactly what you want.
Good luck.

[bnuncc07]

so is $800k sounds like a resonable ballpark for just the evaporative system (coils, reciever, pump for liquid overfeed).... or is that too high or low? thanks

[US Iceman]

For a budget number you could just about double that to include the compressors, insulation system, installation, and maybe have something left over for a control system.

It might be high, but that's why they call them estimates.

[TXiceman]

I can see that having worked at Maytag as a refrigeration expert will really put him in the forefront fro industrial ammonia refrigeration.

To get to a price solution, you will need to do a design for the system and then select equipment. Now you will need to get some support from vendors for compressors, vessels and evaporators.

Your instructor should know that this type equipment is bid only to contractors and very rarely end users. In addition, he is expecting the vendors to go to a lot of work to teach his course to his students and price allof the equipment.

There are plenty of ways to budget estimate the design with minimal details, but you will not have the support design work.

I had one senior level course in college on refrigeration and HVAC. I had already been working in the industry and decided the course was a joke and dropped the class as I did not need it to graduate.

It sounds like the instructor may have a project he is supposed to be working on and trying to get his students to do the work for him.

Sorry to be so senical, but I get a bit upset at some of the instructors and especially some of the ones that call themselves PE's since I am one.

This is the sort of problem that I could bang out a budget in a matter of a few hours, but it also has 37 years of experience to help fine turn it. It would be a +/- 20% type number.

Ken