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Thread: Calculate System Water Volume
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11-11-2010, 04:22 PM #1
Calculate System Water Volume
I was asked to calculate this particular system's water volume, non intrusively, the system was in operation. The idea was to determine precisely how much glycol by volume has to be charged into the system to achieve a 30% glycol mix.
We wanted to remove just the right amount of water before refilling but with just the right amount of glycol.
Doing so it easy - easier than one might at first imagine -how did I do it. All the required info is in the attached image.
I'm just thinking that someone else might get the similar pleasure from the problem.
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11-11-2010, 04:40 PM #2
Re: Calculate System Water Volume
I'll take a wild guess and say you measured the expansion per degree of temp change and then calculated how much water it would take to cause that much expansion.
Last edited by Gary; 11-11-2010 at 04:44 PM.
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11-11-2010, 05:41 PM #3
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11-11-2010, 06:11 PM #4
Re: Calculate System Water Volume
Nope... calculations are not my thing.
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11-11-2010, 07:30 PM #5
Re: Calculate System Water Volume
Most expansion vessel manufacturers base their calculations on 12litres per kW of cooling, or heating.
Brian - Newton Abbot, Devon, UK
Retired March 2015
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11-11-2010, 07:41 PM #6
Re: Calculate System Water Volume
Maybe per 100kW ?
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11-11-2010, 07:48 PM #7
Re: Calculate System Water Volume
Litres expansion vessel or litres water - I think you were refering to water?
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11-11-2010, 07:53 PM #8
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11-11-2010, 08:09 PM #9
Re: Calculate System Water Volume
delta T of water = Density 1 - Density 2= change per mass.
Exapansion vessel, V1P1=V2P2
Change in P2, you then calculate volume change in the vessel
Divide one by the other to give total mass of water in the system
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12-11-2010, 09:08 AM #10
Re: Calculate System Water Volume
Yeah - that's pretty much how it was done. Though I did include further estimates on the volume change of the piping and vessel and then temperature change of the nitrogen in the vessel - the overall piping volume reduction of the piping for about 2000 litres of water was about 2 litres.
You need pretty good accuracy when measuring the vessel pressure change because when a vessel is selected it is not only selected to accept the expanding liquid which the expanding piping can't accommodate but it must accept the expansion without causing the system pressure to rise much. The nearer your operating pressures to the relief valve pressures the larger the expansion vessel you need and so a smaller vessel pressure change during the expansion of the liquid and so the greater the resolution needed on your gauge.
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12-11-2010, 09:13 AM #11
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12-11-2010, 04:02 PM #12
Re: Calculate System Water Volume
I recently had a situation like that with an old air conditioning chilled water system without any expansion tank. To get a more precise system water volume we called in our water treatment contractor who used the salts desolution method. This is the method they used:
1. They induced a known quantity of salts in the water circuit.
2. After circulating the water for a period they took a measured volume of the water with the dissolved salts and measured the concentration of the salts.
3. Since concentration is xgrams per Volume of water the known concentration easily calculates into the system volume.
I hope this makes sense to you. This method I think is the closest you can get to precission with determining your system volume.
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12-11-2010, 08:37 PM #13
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Re: Calculate System Water Volume
I don't like idea of introducing salt in system.
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12-11-2010, 10:19 PM #14
Re: Calculate System Water Volume
The solution's density would be less so the pump would not create as much pressure.
The pressure drop through any dynamic principled measuring device should also be less - based in density - but then ice has a viscosity much higher than water
I dunno - perhaps some light reflecting instrument is required. You can't go on water level - that remains constant so long at the ice in the water is floating.
Hang on, if the fluid was in a closed circuit then I guess you could use the same ideas already discussed - degree of expansion based on the relative densities of ice versus water. The amount by which the water level rises would be 1/9 (I think) of the mass that is now ice and that would be compared to the known mass of water total in the system.
Go on - tell us
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12-11-2010, 10:39 PM #15
Re: Calculate System Water Volume
Did think of that with the glycol but then if the sample indicated you had to add more then you have to drain and thus waste an amount of glycol with the water you have to remove in order to make way for the remaining known quantity of glycol you have then determined is still needed.
By the way - I went to Alan Wilson High School in Rhodesia.
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21-11-2010, 05:24 PM #16
Re: Calculate System Water Volume
Without frost protection
Temperature 0 10 20 30 40 50 60 70 80 90 100 105 110 120 130 140 150 160 % expansion 0 0.13 0.37 0.72 1.15 1.66 2.24 2.88 3.58 4.34 4.7 5.15 6 7 8 9 10 Evaporation pressure -0.99 -1 -1 -0.9 -0.9 -0.8 -0.7 -0.5 -0.3 0.01 0.2 0.43 1 1.7 2.6 3.8 5.2 Delta n 0 0.64 1.34 2.1 2.5 2.91 3.8 Density 1000 1000 998 996 992 988 983 978 972 965 958 955 951 943 935 926 917 907
Antifreeze up to 20%
Temperature 0 10 20 30 40 50 60 70 80 90 100 105 110 120 130 140 150 160 % expansion 0.07 0.26 0.54 0.9 1.33 1.83 2.37 2.95 3.57 4.23 4.92 - 5.64 6.4 7.2 8 8.9 9.8 Evaporation pressure -0.9 -0.8 -0.7 -0.6 -0.4 -0.1 - 0.33 0.9 1.5 2.4 3.5 4.4 Density 1039 1037 1035 1031 1026 1022 1016 1010 1004 998 991 - 985 978 970 963 955 947
Antifreeze up to 34%
Temperature 0 10 20 30 40 50 60 70 80 90 100 105 110 120 130 140 150 160 % expansion 0.35 0.66 1.04 1.49 1.99 2.53 3.11 3.71 4.35 5.01 5.68 - 6.39 7.1 7.9 8.6 9.4 10 Evaporation pressure -0.9 -0.8 -0.7 -0.6 -0.4 -0.1 - 0.23 0.7 1.3 2.1 3.2 4.4 Density 1066 1063 1059 1054 1049 1043 1037 1031 1025 1019 1012 - 1005 999 992 985 978 970
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21-11-2010, 05:34 PM #17
Re: Calculate System Water Volume
This is the formula used for a quick calculation of water content
V=0.014*Q
The water content is in Liters and Q is chiller in Watts
.
This is, by my experience over sized but for the quick calculation is more than enough. Calculating by size of an expansion vessel shall give more water content because size of expansion vessel is dependent of the pressure. And you really newer know who has calculated the expansion vessel size. I have noticed that in Europe, project designers are mainly calculating the expansion size due to the water inlet and outlet temperature but the fact is that temperature for which expansion vessel should be calculated is few degrees less than maximum outdoor temperature.
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21-11-2010, 05:35 PM #18
Re: Calculate System Water Volume
I meat in case of cooling
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