Energy/power audit

[Johny London]

Can anyone point me towards something to help me with an energy (or should that be power?) audit? Or is it just a question of writing everything down in a spreadsheet or whatever?

I'm aware I'll need to take average power drawn for each appliance, over the length of time its running for. Also any stuff sitting quietly on standby etc. But if it's an item that would only be running while either the engine or a generator is supporting it, should that be counted? Thinking about it - it's surprising how many powered devices have crept aboard lately...

 

[WotEver]

About three quarters of the way down the left hand list on Tony's helpful site:

http://www.tb-training.co.uk/cover.html

[mross]

http://www.thefitoutpontoon.co.uk/buying-building-canal-narrowboat-12v-leisure-battery-power-audit-working-out-amp-drain.html

It's a pen and paper job but the calculations are simple.

or here

http://www.waterwaysworld.com/advice/electrics.html

[cuthound]

No point in including things only on with the engine other generator.  

The idea of a power audit is to ensure your batteries are correctly sized for the lifestyle you intend (charging daily because you cruise every day or being able to stop at a place for say 4 days without having to charge batteries).

[WotEver]

13 minutes ago, Johny London said:

... if it's an item that would only be running while either the engine or a generator is supporting it, should that be counted?

If that is definitely the only time that it will be switched on then no. If there is any possibility that you might want to use it when the engine isn't running then yes. 

[WotEver]

5 minutes ago, cuthound said:

No point in including things only on with the engine other generator.  

The idea of a power audit is to ensure your batteries are correctly sized for the lifestyle you intend (charging daily because you cruise every day or being able to stop at a place for say 4 days without having to charge batteries).

Picking up on this point...

1. You do your energy audit.

2. You work out how you can replace that energy fully at least once a week (around 1.2 x that usage over a period of 8 hours). 

You must reconcile the above two points before you move on to the next step, which is to choose a battery bank at least 2.5 x the amount. 3 or 4 times might be better, depending on how often you will be charging. 

Edited March 3, 2017 by WotEver
Changed power for energy to avoid the pedants... Nick ;)

[larryjc]

16 minutes ago, mross said:

http://www.thefitoutpontoon.co.uk/buying-building-canal-narrowboat-12v-leisure-battery-power-audit-working-out-amp-drain.html

Slightly surprised by the advice about fridges in this article.   It says that a fridge rated at a draw of 5 amps and ignoring time under engine (6hours) then it will consume 120 AH per day.  I live on a boat in the Caribbean a few years back and our fridge was rated at a 5 amp draw but we never used more than half that as it only drew current when the thermostat switched it on (and it had a large freezer compartment).  On my current boat the fridge is probably only running for twenty minutes in the hour.  I've checked on my NASA BM1.

 

 

[nicknorman]

There are different types of electric fridge. For the absorption type (often 3 way gas, mains and 12v) the consumption is about right. But no-one in their right mind would use one of those on batteries! For a compressor fridge it's more like 30AH per day, although obviouslynit varies with ambient temperature and how often you open the door.

[larryjc]

Thats sort of what I was trying to say.  The advice - if you took it at face value, would grossly exagerate the energy requirements for a compressor fridge.  Mind you my last narrow boat had a three way and I loved it - always used the gas or mains options.  As a complete thread drift - why on earth can't you have them in narrow boats these days?  Caravans and campervans use them to this day.

Edited March 3, 2017 by larryjc
spelling

[WotEver]

3 minutes ago, larryjc said:

As a complete thread drift - why on earth can't you have them in narrow boats these days?  Caravans and campervans use them to this day.

Didn't we have a thread about this recently where it was concluded that you can?

[nicknorman]

I think it is along the lines of no self respecting gas safe chap will fit something not in accordance with the instructions. So if the manufacturer doesn't say it's suitable for boats, or worse, that it is unsuitable for boats, you're scuppered if you are a live aboard. Although you could always DIY and ignore the law if you wished.

[Robbo]

24 minutes ago, larryjc said:

Thats sort of what I was trying to say.  The advice - if you took it at face value, would grossly exagerate the energy requirements for a compressor fridge.  Mind you my last narrow boat had a three way and I loved it - always used the gas or mains options.  As a complete thread drift - why on earth can't you have them in narrow boats these days?  Caravans and campervans use them to this day.

If you have a decent electrical system of batteries and charging system then using a gas fridge seems daft.   Lugging around heavy bottles of gas on a regular basis vs for majority of the year you can just use the sun's power then it's a no brainer. 

[Johny London]

Thanks - I've made up a table to fill in - might have to have separate sections for standby hours and on hours. Plus there is a fair seasonal variation. As ever, the fridge features heavily - can't believe I'm spending money keeping the boat warm (coal) then paying again to cool down one little corner! It'll make better sense in the summer when a cold drink is really appreciated and some solar panels make an appearance!

[larryjc]

2 hours ago, Robbo said:

If you have a decent electrical system of batteries and charging system then using a gas fridge seems daft.   Lugging around heavy bottles of gas on a regular basis vs for majority of the year you can just use the sun's power then it's a no brainer. 

Well I had to 'lug around gas' on a permanent basis because I wanted to cook on something!!  With a gas fridge and cooking we got through one 13kg bottle a month on average.  The fridge was in the boat when we got it and worked very well with a plumbed in external vent.  Given the choice I would have one again.

[WotEver]

21 minutes ago, Johny London said:

Thanks - I've made up a table to fill in - might have to have separate sections for standby hours and on hours. Plus there is a fair seasonal variation. As ever, the fridge features heavily - can't believe I'm spending money keeping the boat warm (coal) then paying again to cool down one little corner! It'll make better sense in the summer when a cold drink is really appreciated and some solar panels make an appearance!

Forget the seasonal variations and go for the highest figures. Probably the winter (more lights etc). 

[Robbo]

43 minutes ago, larryjc said:

Well I had to 'lug around gas' on a permanent basis because I wanted to cook on something!!  With a gas fridge and cooking we got through one 13kg bottle a month on average.  The fridge was in the boat when we got it and worked very well with a plumbed in external vent.  Given the choice I would have one again.

Lug around gas around every 4-6 months for cooking only.  Gas fridges are not particular good, with electric you get a decent fridge and or fridge/freezer and nothing more additional as you still have to charge your batteries up anyhow.

[Robbo]

55 minutes ago, Johny London said:

Thanks - I've made up a table to fill in - might have to have separate sections for standby hours and on hours. Plus there is a fair seasonal variation. As ever, the fridge features heavily - can't believe I'm spending money keeping the boat warm (coal) then paying again to cool down one little corner! It'll make better sense in the summer when a cold drink is really appreciated and some solar panels make an appearance!

Size of the fridge, insulation and ventilation are key to low power fridges.  Don't get a bigger fridge than you really need, add more insulation around the fridge.

[WotEver]

35 minutes ago, Robbo said:

Size of the fridge, insulation and ventilation are key to low power fridges.  Don't get a bigger fridge than you really need, add more insulation around the fridge.

But be careful where you put the insulation. It's been reported here that some fridges apparently have their condenser on the side as opposed to the back. 

[Chewbacka]

3 hours ago, Robbo said:

If you have a decent electrical system of batteries and charging system then using a gas fridge seems daft.   Lugging around heavy bottles of gas on a regular basis vs for majority of the year you can just use the sun's power then it's a no brainer. 

Summer only boating - completely agree, but in winter an electric fridge is only going to run the batteries down and need a fair bit of shore power or other charging method.

[Robbo]

8 minutes ago, Chewbacka said:

Summer only boating - completely agree, but in winter an electric fridge is only going to run the batteries down and need a fair bit of shore power or other charging method.

You still have to charge the batteries in winter for other uses if your aliveaboard anyhow, 30ah's isn't that great amount if you have a decent charging regime.

[WotEver]

8 minutes ago, Robbo said:

You still have to charge the batteries in winter for other uses if your aliveaboard anyhow, 30ah's isn't that great amount if you have a decent charging regime.

Agreed.