Chiller performance with addition of Glycol

[Stormxtc]

Hi everyone,

I've been posed a question from one of my clients who has an existing chiller running at 6-12 degC split. He would like to reduce chiller leaving temp. to 3degC. To prevent freezing, he will also add approx. 20% Glycol.

The question is:
1) How will this roughly effect the capacity and efficiency of the chiller in terms of %

2) How will the above effect the performance of the cooling coil.

3) Will the overall system be better off?

Ball park % increase/decrease in chiller capacity and efficiency as well as cooling coil efficiency will be sufficient, no need for detailed calculations or analysis.

Thanks,

StormXTC

 

[imok2]

1) How will this roughly effect the capacity and efficiency of the chiller in terms of %

About 3% less capacity for chiller and coil

2.) Will the overall system be better off?
This will increase the pumping head about 23%

 

[Cooky]

I've run the comparison using a Carrier 120 kW chiller, in summary, the results are as follows...

With 20% ethylene glycol added and LWT of 3 deg.C

11 % reduction in cooling capacity
7.6 % reduction in COP
4.3 % increase in pressure drop through the evaporator

 

[quark]

20% EG for an LWT of 3⁰ is an overkill. Note that 10% is sufficient to take care upto 0⁰C(check Perry's Chemical Engineers Handbook).
Check this link

http://www.engineeringtoolbox.com/24_146.html

The main cause for reduction in performance, keeping other things constant, is due to lowering the temperature (derating the chiller).

Your pumping costs may increase by 10%. (the sp.gr may be high by 3% and as the specific heat is around 0.95 kcal/kg ⁰C you have to pump 6% more liquid)

Regards,




Eng-Tips.com : Solving your problems before you get them.

 

[Stormxtc]

Gentlemen,

Thank you very much for your advice and information, you have all been of great help.

Just for info., our client is a mushroom grower who would like to de-humidify the supply air as much as possible, hence the low CHW temperature.

Thank you all again,

Stormxtc

 

[MedicineEng]

I don't know where your client is installed, but if it is in a zone where the electricity is expensive or the wheather is temperate/sub-tropical, maybe you can consider an installation just for dehumidify by chemicals and then cool down that air already dehumidified.
You can save money in electricity bill.

PR

 

[Stormxtc]

Paulo,

The installation is just outside of Sydney, Australia. It is very dry and hot in summer (average high temp of 38degC) and cold in winter (average low temp. of 2-4degC).

What do you mean by dehumidifying by chemicals and where can I get more info on that? I may save elec. but how much capital costs are involved? I would need to work out payback.

Storm.

 

[MedicineEng]

Stormxtc:
I am not shure if this application is suitable for you, but where I work, Southeast China (Macau), tipically the weather is hot and humid so we need to dehumidify the air before we put it into the rooms. But if you have a hot Summer, you should spend a fortune in HVAC electricity to cool down from 38C to 3C.
The manufacturer of this systems is a dutch company called Kathabar (

http://www.kathabar.com).

What I can tell you is that we have two systems here (one 16 years old and other 3 years old) and after you understand the principle, the handling of the system is quite easy and stable.
I am not shure if they have a representative in Asia, but I know that beside our systems they also have some systems installed in gellatine plants in India. Even so, I have very good impressions about their service level.

Hope that helps.

PR

 

[quark]

I would prefer a solid desiccant dehumidifier to a liquid desiccant one. I used and also saw plenty of installations of Kathabar. The main problem with them is corrosion of ducting, cooling coils and the dehumidifier itself.

Moreover, I am cautious about using liquid desiccant dehumidifiers for either food or pharma applications. It is very difficult to find the traces of LiCl or LiBr in the air stream online. I got developed, with great difficult, one sensor to check the qualitative concentration of LiCl in air but that bloody thing also senses moisture.

Check with Munters at

http://www.munters.com

for solid desiccant dehumidification.

PS: The dehumidification by desiccants is isenthalpic which results in increased DBT of the treated air. So you do require additional tonnage in this case also.

Regards,


Eng-Tips.com : Solving your problems before you get them.

 

[MedicineEng]

Quark:
This is true for the old Kathabar installations (that is why we had to add a corrosion inhibitor to the LiCl solution). Actually all installation is in PP what reduces the corrosion problems.

PR

 

[wilg]

The old solid desiccant dehumidifier (Cargocaire) vs
liquid desiccant dehumidifiers (Kathabar) controversy.
Quark ....good points.
Back to the original question of 20% glycol, it
sort of comes down to maintenance costs of desiccant
wheel change out 10 years down the road and energy
required to operate the wheel, steam or electric
heat needed for wheel regeneration (dry out) vs
extra coil maintenance (flush out) and added pumping
costs. Also the initial capital costs of equipment.

 

[lilliput1]

I suggest you & your client define the required space condition required during the different phases of mushroom growing & compost formation. Temperature & humidity requirement would vary for the various stages. Humidity may be required to be high not low at some stage. You may have to cool & reheat to accomplish the dehimidification & space temperature requirement.