Ammonia / Glycol vs Ammonia / CO2

Hi Everyone,

We are currently in the concept design stage of a food storage and processing facility with the majority of the spaces being operated around 4 degC (around 8,000-10,000sqm). Only around 400 sqm of the facility is freezer store operated around -25degC. Various 4degC spaces are occupied permanently and hence outside air treatment air handling units are required to provide conditioned air into the space.

The facility is still in concept design stage, but we are throwing around some ideas regarding servicing the various areas.

For the freezer stores, we are most likely going down the route of sub-critical DX R-744 cascaded against some sort of high stage loop. This plants may be local to the freezer stores, which would help with the provision of warm glycol defrost to the freezer store evaporators.

For the 4degC spaces, we would like to work towards a high stage ammonia system (in plant room only) with low pressure receiver and flooded heat exchanger arrangement (noting that the site is in close proximity of residential and commercial areas). With regards to MT reticulation, we are considering a secondary propylene glycol loop vs a pumped CO2 system. I understand the CO2 system will be operating quite a bit more efficiently, but I'd be keen to hear some thoughts/feedback on these options, especially around the following topics:

1. Cost
Pipework and evaporators smaller for CO2, however more cost involved with regards to valve sets, heat exchangers, controls?

2. Risk of Ammonium Carbamate
In order to keep the ammonia charge to a bear minimum, a flooded cascade (plate or shell and plate) heat exchanger with low pressure receiver/separation vessel appears to be the way forward. Double sheet shell in tube appears to result in significantly larger ammonia charges. How can we mitigate the risk? What is the latest in terms of detection? I read that ammonium carbamate detectors can be used, but where do you locate these in a flooded HX arrangement? Is the intent to detect the substance in the ammonia wet return line and isolate the HX if detection occurs?

3. Ammonia Wet Scrubber
Given we are in a densely populated area, we are looking at providing wet scrubbers in the exhaust ventilation system for the ammonia plant room. Has anyone ever used one of these? How big/costly are these? How efficient are they? Who makes them?

4. Room Temperature and Air Handling Unit Supply Air Temperature Control
Some of the rooms may be required to operate under variable operating conditions. In addition, the outside air treatment air handling unit would also require to be fitted with a glycol/CO2 coil. Has anyone every used CO2 to control the supply air temperature of an AHU via using a motorised evaporator pressure regulator on the CO2 outlet of the coil (vary the CO2 pressure/temperature in the coil to maintain supply air temperature at set-point? Any ideas on how it can be done otherwise? This would be no issue with a glycol system, but keen to see how it can be done with CO2?

5. Thermal Energy Metering
It appears some of the cool rooms are to be leased by tenants and consideration should be given to providing thermal energy metering. Thermal energy metering with glycol (flow meter plus differential temperature sensor) is not an issue. Does anyone know of an accurate way to measure liquid CO2 flow rate? Any suitable products out there that are reliable and have been used for such applications?

Apologies for the multitude of questions. Hopefully some of you have had experience with the above! Any responses would be much appreciated.

Thanks and kind regards,
M

Hi, Miehadtje ...
please, find below within your questions some of my thoughts (in blue) regarding your project ...

Quote:

---

Originally Posted by Miehadtje

Hi Everyone,

We are currently in the concept design stage of a food storage and processing facility with the majority of the spaces being operated around 4 degC (around 8,000-10,000sqm). Only around 400 sqm of the facility is freezer store operated around -25degC. Various 4degC spaces are occupied permanently and hence outside air treatment air handling units are required to provide conditioned air into the space.

For complete food storage working around 4*C you can use ammonia glycol indirect cooling ....

For freezer store working around -25*C you can very easy use one stage ammonia system (-32*C/30*C)

Attached are some links to get an idea ... with CO2 we can have some benefits only with evaporating pressure below -45*C where ammonia is with very poor COP ... all pressures above -33*C are perfect for ammonia refrigeration units with critical ammonia charge ... means very small amount
(such unit I can keep in my sleeping room without to be afraid to hurt me in case of some small leak ;))



The facility is still in concept design stage, but we are throwing around some ideas regarding servicing the various areas.

For the freezer stores, we are most likely going down the route of sub-critical DX R-744 cascaded against some sort of high stage loop. This plants may be local to the freezer stores, which would help with the provision of warm glycol defrost to the freezer store evaporators.

For the 4degC spaces, we would like to work towards a high stage ammonia system (in plant room only) with low pressure receiver and flooded heat exchanger arrangement (noting that the site is in close proximity of residential and commercial areas). With regards to MT reticulation, we are considering a secondary propylene glycol loop vs a pumped CO2 system. I understand the CO2 system will be operating quite a bit more efficiently, but I'd be keen to hear some thoughts/feedback on these options, especially around the following topics:

1. Cost
Pipework and evaporators smaller for CO2, however more cost involved with regards to valve sets, heat exchangers, controls?

Installing one stage ammonia units with glycol has some benefits ... this calculation must be on long runs and I believe ammonia-glycol is the winner...

http://www.sabroe.com/fileadmin/user..._ENG120dpi.pdf

http://www.sabroe.com/fileadmin/user...7_GB120dpi.pdf



2. Risk of Ammonium Carbamate
In order to keep the ammonia charge to a bear minimum, a flooded cascade (plate or shell and plate) heat exchanger with low pressure receiver/separation vessel appears to be the way forward. Double sheet shell in tube appears to result in significantly larger ammonia charges. How can we mitigate the risk? What is the latest in terms of detection? I read that ammonium carbamate detectors can be used, but where do you locate these in a flooded HX arrangement? Is the intent to detect the substance in the ammonia wet return line and isolate the HX if detection occurs?

No CO2 no carbamate - one stage ammonia is very simple and very reliable system ...



3. Ammonia Wet Scrubber
Given we are in a densely populated area, we are looking at providing wet scrubbers in the exhaust ventilation system for the ammonia plant room. Has anyone ever used one of these? How big/costly are these? How efficient are they? Who makes them?

Ammonia refrigeration units with critical ammonia charge are not of big danger even in very populated areas ... of course you need to check safety rules and requests for your area ...



4. Room Temperature and Air Handling Unit Supply Air Temperature Control
Some of the rooms may be required to operate under variable operating conditions. In addition, the outside air treatment air handling unit would also require to be fitted with a glycol/CO2 coil. Has anyone every used CO2 to control the supply air temperature of an AHU via using a motorised evaporator pressure regulator on the CO2 outlet of the coil (vary the CO2 pressure/temperature in the coil to maintain supply air temperature at set-point? Any ideas on how it can be done otherwise? This would be no issue with a glycol system, but keen to see how it can be done with CO2?

Using warm glycol for defrosting you can use it also within AHU for supply air temperature control of course mixing it with cold glycol ... why to use CO2 at all ...




5. Thermal Energy Metering
It appears some of the cool rooms are to be leased by tenants and consideration should be given to providing thermal energy metering. Thermal energy metering with glycol (flow meter plus differential temperature sensor) is not an issue. Does anyone know of an accurate way to measure liquid CO2 flow rate? Any suitable products out there that are reliable and have been used for such applications?

Using glycol your thermal energy metering will be very simple agree with you ....
for CO2 I do not have any idea ... sorry ...
maybe you can check it within Danfoss ...
http://products.danfoss.com/productr...uction-line/#/

In my opinion ammonia and glycol are the best and the most safe in your temperature regimes ... of course some other people will not agree with me ...
above answers are only my opinion and please do not feel bad

anyhow, maybe is not bad idea to reconsider your concept design again ..


Apologies for the multitude of questions. Hopefully some of you have had experience with the above! Any responses would be much appreciated.

Thanks and kind regards,
M

---

I do hope that some of valuable RE members will come with some other suggestion/s ...

Best regards, Josip

Hi Josip,

Your responses are much appreciated.

With regards to your freezer store comments: I would have thought that at those temperatures, a single stage economised ammonia system would be required (rather than single stage with economiser). That would add another vessel and increase ammonia charge. Also, given it is quite important we keep the ammonia charge limited and confined to a plant room, we would require a secondary refrigerant to be recirculated to the coils. I would think that CO2 would be the way to go then as a propylene glycol solution would become too viscous.

Also, iff you have to have a high stage plant operating anyway for the 4degC spaces, it makes sense to just cascade the sub-critical CO2 against this system and providing cooling for the freezer stores.

Thoughts?

Hello,
I saw the cooling of glycol flooded NH3 from the cascade evaporator and worked.

Josef.

Hi Miehadtje,

we equiped two facility like your project.
200 kw at -36/-7°C CO2 for a small freezing tunnel and a storage electric defrost. 4 x small bitzer compressors, direct expansion from -7°C CO2 vessel.
375 kw glycol +5.5/+1°C / NH3 -10°C used for rooms at +10°C
pumped C02 at -7°C for +2/+4 storage. direct NH3/CO2 exchanger.
1000 Kw ammonia compressors (4)
720 kg ammonia / 2900 kg C02
so it works well but the technology was customer design specifications, glycol defrost on CO2 should be better in a dual coil evaporator. we still use direct exchange NH3/CO2 but.....
ammonia / CO2 direct exange is perfect if no accident occur....in case of leak or break it's the worst situation you can expect in a life. I had to face to this kind of damage; 5000kg of C02 in 480 kg of ammonia. at the end you have to face to a court! plant stopped during 7 days, 4 month to repair (court investigations, at least 2 month without)
better to use a glycol loop!
metering C02 is not a problem with a mass flow meter, you have still to calculate enthalpy at different points (pressure sensors, temp sensors); this is an other story
no recent experience in air scrubbers; one in the past in an hospital.
everything is possible!

Hi, Miehadtje ...

Quote:

---

Originally Posted by Miehadtje

Hi Josip,

Your responses are much appreciated.

With regards to your freezer store comments: I would have thought that at those temperatures, a single stage economised ammonia system would be required (rather than single stage with economiser). That would add another vessel and increase ammonia charge. Also, given it is quite important we keep the ammonia charge limited and confined to a plant room, we would require a secondary refrigerant to be recirculated to the coils. I would think that CO2 would be the way to go then as a propylene glycol solution would become too viscous.

Also, iff you have to have a high stage plant operating anyway for the 4degC spaces, it makes sense to just cascade the sub-critical CO2 against this system and providing cooling for the freezer stores.

Thoughts?

---

You should go with economizer to save as much as possible energy .... your temperature difference is almost 65K ... what means or two stage plant or one stage plant with economizer ...

of course you need to use few smaller compressors to be able to run them at 100% capacity to get some benefits from your economizer ... this is matter of plant capacity control ... you will have many small or smaller rooms rent by tenants and they will move goods in and out all the time and your compressors have to cover those small capacity changes by day time efficiently ... the best to cover this type of capacity change are piston compressors in parallel with screws ... but again within your temperature range I do not see any need for CO2 at all...


Then, if you use one of available vessels http://www.vahterus.com/en/applications

for condenser and another one for economizer and another one for evaporator ... (you can discuss your needs with manufacturer and maybe they have some good solutions or proposals for your plant) ... your ammonia charge will be very very small ...

Speaking about viscosity of secondary coolant, please, check this
http://www.temper.se/page/temper/


So, in my opinion ammonia&glycol are winners ... also ammonia is more green than CO2 ...

but, I must be honest ...

reading your posts I got a feeling that you already made decision for CO2 plant .. what I respect, but not approve ...


Best regards, Josip

Any reason why freezer store cannot simply have a low stage machine discharging into glycol surge drum/ intercooler/PHE for glycol cooling.
As Josip mentions reciprocating compressor for efficiency & maybe price, but keep speed down to achieve best result in regards to reliability.
Small VSD screw also another option, as can run longer between service intervals.
Of course you need redundancy!
DX evaporators on freezer have been developed, as in past poor performance, this would keep ammonia charge to a minimum, hot gas defrost then can be used as water or glycol defrost seems a backward step, as if goes wrong big mess & ice everywhere.
Scrubbers have been developed for this purpose.

http://www.colmaccoil.com/new-techno...e-ammonia.aspx



This site also shows latest in technology with sensors & lots of other products & papers.

http://www.hbproducts.dk/en/hb-produ...rne,-australia


Air scrubber for ammonia

http://www.pollutionsystems.com/ammonia-scrubbers.html

https://www3.epa.gov/ttncatc1/dir1/ammonia.pdf

Thanks all for your contributions and inputs! Much appreciated.

@Cricri
The cost and impact associated with an ammonia/CO2 leak are a significant disadvantage and it would be difficult justifying taking on this risk, unless there are cost-effective ways to detect and isolate this problem.

@Josip
No decisions have been made. A key issue on this project are the safety issues surrounding the use of ammonia. The site itself will have potentially a significanf amount of people on site. As such, recirculating ammonia throughout the facility does not appear feasible at this stage. This has been the driver to minimise ammonia charge to the extent possible although thermodynamically and cost-wise it may not be the ideal solution. Thanks for highlighting the Temper secondary coolant. Have you used this before for low temperature loads? Is it considered food grade and suitable for use in food processing facilities such as propylene glycol?

@RANGER1
Thanks for sending through those details (scrubber and DX ammonia links). Interesting to see the developments in low temperature DX ammonia. Will have a good read of those. As highlighted above, the high population density both onsite and in surrounding buildings makes ammonia charge control and the prevention of ammonia emissions very important.

I am not familiar with the Temper coolants but have used a similar product called HyCool which was used in a UK fish market environment. They are food safe. Presently suitable down to -50°C.

http://www.srs-frigadon.com/hycool-fluids/