Electric v Gas

[Ducatiboy stu]

Yes, that's what my equation does.

Enthalpy of vaporisation of water is around 2.26 MJ / kg, so the energy required for boiloff =

2.26 MJ/ kg x (Vstart - Vend) (Eq 1)

Heat capacity of wort is around 4 kJ / kg / oC, (slightly less than water at 4.18 due to the sugar content), so the energy required to heat wort =

4 kJ / kg / oC x Vstart x Trise (Eq 2)

Heat of combustion of propane is around 50 MJ / kg,so the energy from burning gas =

50 MJ / kg x mass of gas burnt. (Eq 3)

Set T rise to 35 degrees, Eq 2 becomes

E = .014 MJ / kg x Vstart (Eq 2a)

Add eqns 1 and 2a to get

E = 2.4 MJ / kg x Vstart - 2.26 MJ / kg x Vend

Efficiency is thus (2.4 x Vstart - 2.26 x Vend) / 50 x mass of gas burnt*.

Multiply both sides by 100 / 50 to get

Efficiency (in percent) = (4.8 x Vstart - 4.52 x Vend) / mass of gas

which is where we started.


I presented the bare finished product above because experience says 99% of the audience hasn't followed this.






* The units are consistent so they drop out of the quotient. The vapour is substantially water so 1 litre lost = 1 kg. The heat capacity of wort is dependent on sugar content, as is the density but they move in opposite directions so assuming 1litre = 1 kg introduces a trivial error.

Thank god for people like you

I was really shit at math in school

 

[DWC]

While I'm not looking at full automation, I am looking into an (OMG another one!) arduino based controller as I've never been completely happy with the ramp/soak function of my PID. That will be a ways off yet. Electric will make that easier n I wont have to worry about having enough gas on hand

 

[Ducatiboy stu]

While I'm not looking at full automation, I am looking into an (OMG another one!) arduino based controller as I've never been completely happy with the ramp/soak function of my PID. That will be a ways off yet. Electric will make that easier n I wont have to worry about having enough gas on hand

Ah yes...the old " F$%#....Just ran out of gas 20min in to the boil.."

 

[Tony121]

Ah yes...the old " F$%#....Just ran out of gas 20min in to the boil.."

Call it a 20 min IPA...

 

[pcqypcqy]

I liked gas for the portability and cost of set up. For a gas bottle and burner, you're in for much cheaper than you would be to get an electrician out and pull the wires required. Your burner and bottle are also portable and useful for other things other than brewing.

I usually have another bottle around the place attached to the BBQ, so I always have some spare gas if one bottle kicks. Though I am waiting for the day when both go at the same time, then I'll be screwed. But that said I have a servo or a bunnings within walking distance so I can quickly swap during a brew if I have to.

Now that I have a permanent spot set up, I may look into upgrading the wiring to the shed to allow for the larger elements required. But again, this isn't purely for brewing, as I'd like to set up for welding and other things out there as well. I'll probably keep it all at single phase for simplicity and cost of the components involved.

Like most things, there's no "better" way, it depends on your situation and what you like/prefer/can afford.