Calculate System Water Volume

[DTLarca]

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.

[Gary]

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.

[DTLarca]

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.

That's the one - the expansion vessel has a nitrogen charged bladder. Do you want to offer some calcs?

[Gary]

Nope... calculations are not my thing.

[Brian_UK]

Most expansion vessel manufacturers base their calculations on 12litres per kW of cooling, or heating.

[DTLarca]

Maybe per 100kW ?

[DTLarca]

Litres expansion vessel or litres water - I think you were refering to water?

[Brian_UK]

Litres expansion vessel or litres water - I think you were refering to water?

Yes, sorry, litres of water within the system per ....

[mad fridgie]

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

[DTLarca]

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

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.

[mad fridgie]

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.

One for you,
We have a binary ice solution., how would you determine the amouny of ice within the fluid!

[PRESS]

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.

[nike123]

I don't like idea of introducing salt in system.

[DTLarca]

One for you,
We have a binary ice solution., how would you determine the amouny of ice within the fluid!

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

[DTLarca]

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.

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.

[MilosBog]

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

[MilosBog]

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.

[MilosBog]

I meat in case of cooling