Choosing between CO2, NH3 and GLYCOL circulation

[Renaud]

Having to build a new 12.000 m² fresh warehouse (2°C for meat and dairy) I have contacted three refrigeration companies.

One company tells me to go for NH3
The second one tells me to go for CO2
And the third, you guessed it, suggests Glycol

They all have valid points. Can you point me to some documentation that could help me choose between the alternatives?

Thak you very much

[US Iceman]

Hi Renaud,

Welcome to the RE forums.

This will be a thread I will follow closely. I do not have any documentation on the subject, but do think this will be an interesting discussion.

A point I can raise now is; have the contractors provided any estimated operating costs to you? I would consider asking them to furnish this information for summer and winter periods. This will supply you with some basic information that you can use in your evaluation of the proposals.

If the average operating cost is "x" Euros per month, then you can compare this to 12.000 m² and then also your initial costs too.

Therefore you will find; "x" Euros/m² for operating and initial costs.

I would also ask them how they are controlling your system too. Do they have control systems they will provide and how will the control system save you operating costs.

[Renato RR]

Find someone who will design system for you and than ask offer, that way you get best result.If you pay consultant he will calculate all you want:electric consumption,spare part availybility,competence of instolers etc.and you can go on tenis during that period.

Best regards,
Renato

[Renaud]

As of now we have only had preliminary discussions with the three companies, where we talked over the project and gave them the plans. We have asked them to give us a preliminary study and budget in order to decide with which company to go further into the full study (for which we will pay of course).

Some "figures" I have received for operating costs:
Ammonia : 100%
CO2 : 108%
Glycol : 130%

investment is the highest for glycol

We have asked the companies to hand in some figures and first sketches for the end of the week but I doubt I will be able to choose with which company we would want to work with solely based on what they will hand in.

[NoNickName]

I can't see how glycol system TCO can cost 30% more than nh3.

[Samarjit Sen]

I would like know that for the Glycol System, how do they propose to chill Glycol. Either it would be with a NH3 or a CO2 refrigeration system. Am I correct or if I am wrong please do correct me.

With whatever I have learnt from this Forum, I feel using NH# would be the best way.

[NoNickName]

Glycol brine is chilled with a standard chiller, probably using a HFC refrigerant.

[US Iceman]

We have asked them to give us a preliminary study and budget...

That I think is a good business practice. You really need to understand what you are buying and how much it will cost to operate.

Is the CO2 system also using ammonia, or only CO2?

If you are anticipating using the CO2 or glycol options I suggest you ask them how they plan to defrost the evaporator coils. If they use electric defrost for either of these two options, have they included the electricity for defrost in their operating costs.

Or, if they suggest water defrost have they included water usage and associated charges?

Some "figures" I have received for operating costs:
Ammonia : 100%
CO2 : 108%
Glycol : 130%

Are these operating costs or investment costs?

[US Iceman]

Here are some links I found that may be useful to you. These are both related to the same project, but it closely mirrors your requirements I believe.

http://www.mmrefrigeration.com/mmsit...%20Systems.pdf
(0.7 MB)

http://www.ra.danfoss.com/TechnicalI...oldstorage.pdf
(2.9 MB)

[Renaud]

Thank you for your links I will read this for sure.

To answer some of the questions above:
The refrigeration will be done through NH3, this is certain. Only the circulation is problematic.
The figures that were given to me are for operating costs only. I don't know how they were reached exactly but was promised some literature on the matter so I will get back to you once I get it.
The three companies we contacted all design and install alls sorts of systems but they are not manufacturers and are not tied to a particular technology. They are all speaking from experience.

[Lowrider]

A thing to keep in mind is maintenace costs and reliability!

Also look at the pro's and con's of all systems. For instance failure.

One could imagine CO2 or NH3 system, when a component fails, the whole system could be down! The glycol system is more reliable, especially if combined with multiple chillers, either on NH3 or HFC's. The downside could be larger installation costs.

My money is on the glycol system! I've built and serviced a lot off these without big problems and on failure of one chiller, the system can keep running!

[US Iceman]

My money is on the glycol system! I've built and serviced a lot off these without big problems and on failure of one Chiller, the system can keep running!

I'm going to paraphrase your comment slightly...

My money is on the NH3 or CO2 system! I have also been involved in both of these with no major problems. You can still keep running if one compressor fails, etc. provided you have some redundancy (similar to multiple chillers).

[Dan]

Quote:

Originally Posted by: Renaud

Some "figures" I have received for operating costs:
Ammonia : 100%
CO2 : 108%
Glycol : 130%

I wonder if the person quoting this was referring to operational costs and not installation costs.

1. Ammonia is used as a base figure using Ammonia as a primary refrigerant circulating through the evaporators.

2. CO2 is used as a secondary circulating refrigerant utilizing both latent and sensible cooling effects, with a small loss due to the necessary heat exchange inefficiencies.

3. Glycol has only sensible heat transfer and therefore is less efficient by far.

Nah... Never mind. I am not sure what the fellow is thinking. Two stage Ammonia and CO2? This doesn't make sense for meat and dairy unless you have a large frozen component. Co2 is probably not the way to go unless there are other considerations.

I am puzzled as to what 3 systems are being suggested.

[Renaud]

All cooling will be done through Ammonia. So the three systems are:
Ammonia cooling + Ammonia circulation
Ammonia cooling + CO2 circulation
Ammonia cooling + Glycol circulation

The % are OPERATING COSTS only

[BESC5240]

Hi Renaud,

I don't know in which part of the country your plant will be but in Flanders the end user will get a compensation (subsidy) from the Flemish gouvernment when using CO2/NH3 cascade.
Take a look at :
http://www.vlaanderen.be/ecologiepremie
(The code for this technology is 1309).
I'm not sure this kind of subsidy also exsist in the Walloon part of the country, but presummably it does.

Technically I would also go for CO2/NH3.

Best regards

[Renaud]

The project would be located in Flanders so this is very interesting news for us. I can not access the ecologiepremie website before they send me a login and password by post. Do you have any idea of the importance of the premie ? % of investment or tax refund ?

[BESC5240]

Hi Renaud,

I went to check and to my surprise the 'ecologiepremie' (EP) system has been ended.
look at : http://ewbl-publicatie.vlaanderen.be...=1155714193818
But it seems that there is a 'light' version of this EP.
I propose you contact de 'Vlaamse Overheid - Agentschap economie -Afdeling Economisch Ondersteuningsbeleid - Cel Ecologiepremie' :
http://ewbl-publicatie.vlaanderen.be...=1155714193988
Best regards
BESC5240

[Gonzalo Arias]

Dear Friend:
1)
Using NH3 in the evaporator is the most efficient about energy; I will use reciprocating compressors, if I believe the room cooling demand is very changing most off the time.

If you can define some substantial minimum load use a combination screw-piston compressor system. A screw compressor with variable Vi as a base compressor to carry with the base load working from 70% to 100% of its capacity (at these capacities screw compressors have an efficiency quite as they were piston compressors). And to deal with the picks use a reciprocating compressor with discharge capacity cylinders (pistons) to carry with loads above the capacity of the screw compressor up to the maximum load
If this is the case, I suggest to investigate the cooling load demand during a representative period of time to define time Vs load curves in order to find (or estimate) a base and maximum capacities of the compressors., and to do a detailed energy cost analysis, taking into account the load demand, the BHP, the efficiency of the compressor at the various point of the load demand curves, the energy cost, etc.
Remember that a low initial investment could drive you to a high energy cost for the rest of the life time of the project.

2)
If you are very much concerned about safety or NH3 contamination risks inside the cool rooms you should use glycol (brine) in the evaporators and NH3 in the power room.
But remember that to use a secondary refrigerant (in this case, glycol) the SST (saturated suction temperature) of the primary refrigerant (NH3) should be keep about 10F below the SST used in the case of the use off NH3 alone. This mean more energy cost. But is not that bad in the case of rooms above freezing.

3)
Try to do the load calculations, the load curves, the integrated time during the chosen period of time (week, month, year), define your base and pick load, the TD at your evaporators in the different rooms (the recommended TD depends on the stored goods), and give to the bidders your energy cost, the numbers of year for energy evaluation cost and as much spec as you can in order to get equivalent quotations for comparing apples with apples (not include in the bidding documentation, the installations cost, only: equipment, control panels, main valves, tanks, costly hardware). It is also important to ask for energy consumption of the system at various loads. Drive the vendors to your best system selection instead to let them impose what is best for their business
Best Regards
GAR&Ing.

[Plank!]

I'm surprised the CO2 system is 8% less efficient than the pumped NH3.

We use NH3/CO2 systems in many applications and in all cases i believe it was more efficient (plus there is the tax incentive...)

For the 2°C rooms we use hot gas defrost at around 43BAR

also CO2 can be used as a "volotile" secondary, giving much more duty for the refrigerant volume, and therefor much smaller/lighter pipework.

hot gas defrost is still possible with CO2 as a secondary "volatile" fluid, plenty of heat available on the NH3 oil coolers

[Plank!]

Quote:

Originally Posted by: Renaud

Nah... Never mind. I am not sure what the fellow is thinking. Two stage Ammonia and CO2? This doesn't make sense for meat and dairy unless you have a large frozen component. Co2 is probably not the way to go unless there are other considerations.

It can still be a single stage system with pumped CO2 as a volatile secondary fluid.

The chiller/heat exchanger just has the added duty of CO2 condenser

[PaulZ]

Hi All
I have read all the above and the company I work for have refrigerated 4 supermarket distribution warehouses using Glycol as the refrigerant in the 2, 7 and 13 degree rooms.
The main plant is NH3 with plate heat exchangers using a closed loop Glycol circuit.
The defrosting is done by shutting a 3 way valve and having a secondary pump and heater element and thermostat. The brine is heated during defrost and circulated through the coil.
This system works fairly well only problem is if heaters fail or trip the coil can ice up.
Pumped liquid NH3 is probably the best but the amount of refrigerant in the plant can large and the leak factor has to be considered.
Hope this has helped.
Paul

[Pud]

G'Day Renaud,
Renaud, how concerned are you about the environment?
It seems that a cascade system using Carbon Dioxide as the primary and Ammonia as the secondary would be the most efficient and environmentally friendlly.

Cheers Pud