Large Glycol Systems

[Goober]

In a large commercial project..supermarket...cool store complex etc, what are the benefits, other than reduced refrigerant charge, of using chilled glycol circulating around the rooms/cabs instead of refrigerant? Medium temp obvioulsy. Personally, other than the Green PC image it portrays I can't see any other advantages.

Correct me if I'm wrong but if you a cool room that requires 10 kw of cooling and you have plant capable of providing 10kw cooling are you then not going to increase the power consumption by having to use a glycol pump to circulate glycol. Where as DX systems have no pump and same kw capacity. Am I missing something here in this glycol thing?

[Sandro Baptista]

Yes, you are right and it's not only that. You will must evaporating to a lower temperature in order to achieve a glycol temperature capable of cool the rooms. Lower evaporator implies less COP.

The benefits can also be, beside what you already said, the ease service to the water pipe and valves that almost any one can handled.

[NoNickName]

A glycol system has a much smaller refrigerant charge. It implies smaller and less polluting leaks.
It also implies a better overall load distribution, thanks to a greater heat inertia.
Clearly, it doesn't make much difference in a 10kW plant. But in a 100 or 500kW plant, the power input of the pump is fractional and almost negligible.

It is easier to setup and doesn't require separate superheating adjustment per cabinet or per room.

Also, regulation is much easier and more precise, with the adoption of modulating three way valves.

Finally, it is easier to scale and to upgrade.

All in all, I prefer a glycol system, although this isn't the mostly adopted layout these days.

[Sandro Baptista]

NoNickName,

The COP of the system is lower because you have to evaporate about 6K lower, depending of the design.

[charlie n]

We build flooded ammonia based chilled glycol systems up to 3000kW for indoor ski domes. I've also used glycol for medium temperature distribution warehouses. The biggest advantage is of course the reduced refrigerant charge and the separation of the refrigerant from the occupied spaces. The COP is not as good as a pump recirculated ammonia system of course but it is actually better than a DX system using any 400 series refrigerant. Nonickname's points about serviceability, and simplicity are also good reasons to use glycol. Animal fat such as butter can very easily absorb ammonia so a butter storage using chilled glycol can have lower insurance premiums making overall system cost more attractive.

[NoNickName]

NoNickName,

The COP of the system is lower because you have to evaporate about 6K lower, depending of the design.

Yes, but choosing one system or another is a matter of balancing between various requirements, one of which is of course COP.
One can partially recover the disadvantage with a lower condensing pressure or floating condensation.
In a compromise between advantages and disadvantages, choosing which way to go depends what weight you give to COP and what the other points I mentioned.

I forgot to mention that a glycol system, with a mixing valve to increase the delivery temperature, can also be used for space conditioning, without the need for a separate chiller.

[Sandro Baptista]

Yes, NoNickName you're right I was just point the disadvantages of course there are many advantages as I also said on the my first post.

[Goober]

Cheers Guys,

Can understand it on Ski Domes, Ice Rinks etc, but not really on Supermarket cabs and coolroom complexes of the smaller nature (Sports Stadium sort of thing).

[coolhibby1875]

i have come across glycol in sainsburys and believe me its a nightmare

[NoNickName]

i have come across glycol in sainsburys and believe me its a nightmare

I don't see how that is possible. Could you please elaborate why?

[coolhibby1875]

I don't see how that is possible. Could you please elaborate why?

i will try and elaborate later, as it will take so long to type out

[kengineering]

Also, regulation is much easier and more precise, with the adoption of modulating three way valves.

How is this used? Ken

[750 Valve]

I agree with Sandro Baptista in the fact that COP suffers for the additional TD involved in chilling the glycol, the argument that you can offset it by floating heads is a mute point as you can do this to a DX system as well.

I also whole heartedly agree with coolhibby in that glycol systems in supermarkets are NASTY! We are about to rip one of the only 2 in Australia out (thank god), as per his point it will take a lot of time to elaborate just how bad they are but in a nutshell this particuar system, over time and from service has not had all the air removed from a Temper -40 LT system, the results are catastrophic - all SQD boxes being wire drawn in the valve seats, so too the flow valves. Cost of installation is much higher than DX and also energy usage is increased.... yes there is a reduced refrigerant charge but it is better achieved with R744 as a secondary these days.

[NoNickName]

Well, I don't think you are ripping a system up because the former engineer was not able to purge the air in the system.... ah ah ah... I think air vents are available down under as well, don't they?