Calculating volume required to change temp

[seangee]

Geek question alert
Is this a simple arithmetic calculation (as long as you are using litres and celcius )?
I usually stand my vats in a sink of hot water till they reach the right temperature. Today I have to change all 4 tanks so I thought I'd short cut by using a kettle of RO water.

Since it is a low volume of kettle water and I couldn't be bothered to account for how much the water cools between the kettle and reaching the vat, and the vats actually hold a little more than stated (and I haven't measured them) I just used 20% more kettle water than I calculated to raise 25 litres from 20.8C to 25C.

The water ended up a little cooler than expected (23.5) but still close enough to use without any further adjustment. Is it valid to assume I can just use a formula and this would apply to my 10 litre vats and still hold true when the starting temp is lower?

 

[AilyNC]

Geek question alert
Is this a simple arithmetic calculation (as long as you are using litres and celcius )?
I usually stand my vats in a sink of hot water till they reach the right temperature. Today I have to change all 4 tanks so I thought I'd short cut by using a kettle of RO water.

Since it is a low volume of kettle water and I couldn't be bothered to account for how much the water cools between the kettle and reaching the vat, and the vats actually hold a little more than stated (and I haven't measured them) I just used 20% more kettle water than I calculated to raise 25 litres from 20.8C to 25C.

The water ended up a little cooler than expected (23.5) but still close enough to use without any further adjustment. Is it valid to assume I can just use a formula and this would apply to my 10 litre vats and still hold true when the starting temp is lower?

Variables would be temp of tap water and maybe the room.

But generally speaking 1.5 litres of kettle boiled water into a 10 litre bucket would have my temp at 29/30C. This is when my tank is in ich treatment.

So you're formula of 20% is 2 litres of boiling water mixed with 8 litres of cold water. That'd be too hot in my set up. Maybe 1 litre of boiling to 9 cold would do it.

Trial and error until you find the amount that works

 

[seangee]

So you're formula of 20% is 2 litres of boiling water mixed with 8 litres of cold water. That'd be too hot in my set up. Maybe 1 litre of boiling to 9 cold would do it.

No I meant 20% extra hot water. For 10 litres my formula was 9.5 litres cold water and 0.5l kettle water. By extra 20% I meant 9.4 cold and 0.6 hot.
But I seem to have got really close by assuming the kettle water is 88C rather than 100 by the time i have poured from the kettle into a jug and from the jug into my water containers. Don't want to risk my thermometers by putting them into boiling water but I reckon that's close enough to see me through winter. I will still have to measure the water in my vats every week because they are in an unheated room. When it gets colder I will bring them into a living room the night before water change so I don't have to raise the temp by too much.

 

[mbsqw1d]

Could you add heaters to the vats? Put them on a 7 day timer to perhaps kick in the day before water change? (How big are these vats?)

 

[mhancock]

With the same ratios and starting temperatures you'd get the same results.

If you want to predict what will happen, it will be the mean of the two temperatures taking into account the amount of both.

((Temp A x volume A) + (Temp B X volume B))/(volume A + volume B)

 

[seangee]

Could you add heaters to the vats? Put them on a 7 day timer to perhaps kick in the day before water change? (How big are these vats?)

My vats are really just jerry cans. 4x25l and 9x10l. So probably not practical, and quite expensive. Using the kettle worked pretty well. Knowing I can calculate how much water to add to each will save me a ot of time over continuously adding a bit and re-testing.

 

[seangee]

With the same ratios and starting temperatures you'd get the same results.

If you want to predict what will happen, it will be the mean of the two temperatures taking into account the amount of both.

((Temp A x volume A) + (Temp B X volume B))/(volume A + volume B)

Pretty much exactly what I did. The unknown is temp A (assuming that's the kettle). A few degrees difference has quite a big effect. Its nowhere near 100 degrees by the time I mix it and at room temp boiling water cools quite quickly when you only have a small volume.

Luckily somewhere close is good enough because I really can't be bothered to include cooling rates in the jerry can, or in the tank once the lid is off with the heater turned off while I remove water. In every case the tank ended up within 1.5 degrees of where it started after the water change - and that's good enough for me.

 

[seangee]

Biggest bang for buck is certainly increasing RO production capacity. Right now I still have 115 litres worth of empty water containers. I have changed 3 of the tanks so far. The 4th will happen tonight, although its one of the little tanks its still another 40 litres of water I'll be using.