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# Estimating Glycol Amount in Chiller/FCU System

## Estimating Glycol Amount in Chiller/FCU System

(OP)
Hello,

Is there a rule of thumb for calculating the amount of Glycol required in a chiller system?

I know that the proper way is to calculate the volume of the system. A lot of the pipework sizes are unknown so this is not possible.

The hotel has 100 fan coil units and is powered by a 460.75kW chiller.

On the back of the Glycol pack (Sentinel X500) it says a 30% solution will protect down to a temperature of -11°C. The temperature does not drop below this level so this protection level is fine.

Any help at all will be appreciated, thank you.

### RE: Estimating Glycol Amount in Chiller/FCU System

all devices (i.e. coils) have a volume per manufacturer, all pipes have known volume. So there you go.
If the plans etc. are not detailed enough, you just have to fill in until it is full.

If this is an existing system, make sure to drain all old fluid.

### RE: Estimating Glycol Amount in Chiller/FCU System

Or you could just drain down the entire system and re-fill it with a known, mixed 30% propylene glycol mixture till it's full again. Or just keep adding and draining off fluid till testing indicates a 30% mix. Or do some real engineering and do a proper estimate and calculation to start, in order to determine the minimum amount of glycol you need, then slowly add that to the system and check the mixture, then top it up as required.

### RE: Estimating Glycol Amount in Chiller/FCU System

(OP)
Thank you for your responses. The system is existing but we have replaced the chiller...

I suppose the starting point is to measure the existing percentage of glycol in the system then I can calculate how much extra needs to be added... can you recommend a cheap glycol refractometer?

### RE: Estimating Glycol Amount in Chiller/FCU System

I don't have a specific manufacturer recommendation, but you should aim for one that is correct, not cheap. They are only in the hundreds of $. Some of them under$100. At least google tells me that. As i said above, they may be +/- 5%
The contractor that replaced the chiller sure has one. If this is a glycol system, the maintenance crew also should have one.

at that occasion they also should check the pH value and general condition of glycol, check all strainers, dirt separators etc. the last thing you want is 50 year un-maintained glycol compromising your new chiller. Maybe a whole system refill is a good idea.

for determining required solution, keep in mind glycol has a slush temperature and a burst temperature. Obviously burst will break equipment and pipes. If winter operation is not required, you can go into slush conditions. but if you need winter operation (i.e. IT cooling), you need to stay above slush conditions.

Also keep in mind manufacturers have specific glycols for chilled, heated, or solar systems based on the expected temperatures. If that system is very old, don't rely on that being good.

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