Ammonia glycol system

[mechman]

We are considering an indirect nh3 glycol system for cold and freezer rooms.
I would like to know the drawbacks of such system?
What is the possibilities of hot water defrost, are seperated integrated hot water coils required and feasable?

I kindly like to hear your oppinion or experience with such system

[RANGER1]

mechman,
Depending on room temps in freezer would say its possible, but much more expensive to run.
You have to run lower suction pressures to cool glycol or which ever product is suitable.
Also running big glycol pumps uses power.
You can use warm glycol to run through air coolers to defrost units, water is messy if done the old fashioned way.
Normally glycol on rooms say around -5 c & above, ammonia on freezer side of things.

Lets see what others say!

[hookster]

There is some energy loss with this system but they are far more user friendly i.e contained ammonia circuits and only secondary distribution circuits in warehouse. Large buffer storage can reduce peak loading and on a large circuit it is cost effective to go with inhibited salts over glycol.
Controls are simplified too and maintenance & installation costs are lowered as non refrigerant specific trades can be used for secondary circuits. Disadvantage is that pipe sizes are increased to carry the duty required but they are low pressure.

Defrosting is highly efficient if an energy recovered hot brine defrost is utilised.
Systems can be designed to push hot/cold for defrosting through evaporators or another method is to use small closed loop defrost circuits on evaporators although this requires some electrical input or other heat source if available. (same evaporator coils used for defrost and cooling circuits on both designs)

If system is required to grow organically with the storage facilities then this is the best value system for future expansion. The refrigerant plant is inherently more stable due to high fluid volumes and less dramatic fluctuations.

Pump losses can be reduced with pressure regulated inverters. A well designed system would bleed freezer returns into the chill loop.

Capital outlay though is higher than a pumped ammonia LT / HT system but over a long term it has a better cost value.

[mechman]

Thks gents
Hookster-please elobarote on the defrost options- i am not with you 100%
what do you mean with push hot/cold?
for the seperate circuit does the blower require a dedicate defrost coil or the same cooling coil.

so glycol is abetetr prospespect for meduim temp rooms?

thks

[hookster]

Hi mechman

The push system uses a hot glycol supply that is used to drive the cold glycol into for example your chill circuit out of the evaporator. Control changeover when return probe from evap detects warm flow and diverts to hot defrost return. End cycle of defrost is reversed with warm glycol driven from evap with cold supply until return sensor detects cold return and diverts back to cold circulation. (hope this makes sense )

closed loop defrost has a small accumulator (sized for evap fluid volume) and electric heating, for example on defrost demand. The 3 ports shut cold flow and returns. Accumulated storage is allowed to flow in loop through evap. The accumulator only has low heat input requirements.

cooling coil is used on both applications

[mechman]

thks
i other words glycol require much more piping, bigger return line and bigger defrost as well as defrost return
how does the valve stations cost compare?

[neal]

For the freezer, what about LPR with reverse cycle defrost. And the glycol, a LPR with plate heat exchanger.
Both an option if the amount of ammonia on site is an issue.

[RANGER1]

There is some energy loss with this system but they are far more user friendly i.e contained ammonia circuits and only secondary distribution circuits in warehouse. Large buffer storage can reduce peak loading and on a large circuit it is cost effective to go with inhibited salts over glycol.
Controls are simplified too and maintenance & installation costs are lowered as non refrigerant specific trades can be used for secondary circuits. Disadvantage is that pipe sizes are increased to carry the duty required but they are low pressure.

Defrosting is highly efficient if an energy recovered hot brine defrost is utilised.
Systems can be designed to push hot/cold for defrosting through evaporators or another method is to use small closed loop defrost circuits on evaporators although this requires some electrical input or other heat source if available. (same evaporator coils used for defrost and cooling circuits on both designs)

If system is required to grow organically with the storage facilities then this is the best value system for future expansion. The refrigerant plant is inherently more stable due to high fluid volumes and less dramatic fluctuations.

Pump losses can be reduced with pressure regulated inverters. A well designed system would bleed freezer returns into the chill loop.

Capital outlay though is higher than a pumped ammonia LT / HT system but over a long term it has a better cost value.

i asked someone who knows & he suggests 25% more in power to run such a system with freezer duty.
You could also consider CO2 for freezer duty.

[mad fridgie]

Depending upon the application, I would consider a binary ice system (slush), on the refrigeration side more power used compared to direct, but is no different to glycol. How ever saving can be made on pump uses, piping size and coil size. (latent energy changes means reduced fluid mass flow.) also is excellent for thermal storage (much less storage is required), and by load shifting, could offset the higher refrigeration running costs.
The refrig equipment capital is expensive, but install may be lower.

[RANGER1]

i asked someone who knows & he suggests 25% more in power to run such a system with freezer duty.
You could also consider CO2 for freezer duty.

Refering to glycol or brine for freezer

[AMP]

[...] closed loop defrost has a small accumulator (sized for evap fluid volume) and electric heating, for example on defrost demand. The 3 ports shut cold flow and returns. Accumulated storage is allowed to flow in loop through evap. The accumulator only has low heat input requirements.

cooling coil is used on both applications

Just remember that electric heating resistances are not mandatory in centralized installations. You can install a heat exchanger after the condenser which will heat up the glycol and subcool the ammonia, so there is an additional efficiency gain during some hours per day. How many time per day? Of course this will depend on how many hours you consider to heat the glycol to the required temperture for defrosting.

[AMP]

i asked someone who knows & he suggests 25% more in power to run such a system with freezer duty.
You could also consider CO2 for freezer duty.

If you are considering a CO2 system, which means you are going for a cascade system, why don't you consider a two stage system in the ammonia/glycol installation?

CO2 systems, under my point of view, only have sense when you need to go to -45 ºC on evaporation temps. In a system with plate freezers (whether horizontal or vertical) you can evaporate between -35 ºC or -40 ºC with no problems and the efficiency of the ammonia is still good, so there is no sense to avoid the ammonia/glycol or ammonia/brine systems. You can prepare a single stage or two stage system evaporating at -40 ºC and obtaining a glycol at -35 or - 36 ºC. Higher initial investment but better efficiency and easier to find people prepared to make maintenance.

[RANGER1]

If you are considering a CO2 system, which means you are going for a cascade system, why don't you consider a two stage system in the ammonia/glycol installation?

CO2 systems, under my point of view, only have sense when you need to go to -45 ºC on evaporation temps. In a system with plate freezers (whether horizontal or vertical) you can evaporate between -35 ºC or -40 ºC with no problems and the efficiency of the ammonia is still good, so there is no sense to avoid the ammonia/glycol or ammonia/brine systems. You can prepare a single stage or two stage system evaporating at -40 ºC and obtaining a glycol at -35 or - 36 ºC. Higher initial investment but better efficiency and easier to find people prepared to make maintenance.

So it cost more to install & more to run, so what advantage does it have?

Ammonia is best for freezer, reasons why mechman does not want to use it, who knows!

[AMP]

So it cost more to install & more to run, so what advantage does it have?

Ammonia is best for freezer, reasons why mechman does not want to use it, who knows!

I fully agree with you. Ammonia is the best for freezing.

The only reason I see to combine it with glycol or CO2 it is reducing the amount of ammonia in the installation. For example, in vessels it is quite useful due to safety legislation, but on shore, the best is using ammonia directly on the evaporator.