How much to electrify a small barge?

[Bargebuilder]

12v DC compressor fridges are often referred to as more efficient than 230V AC, but I've read that. " The motor on a Danfoss compressor is actually AC. The controller takes DC input and inverts it to variable frequency AC to run the compressor"

 

The relative efficiencies of different fridges is to do with their volume, the degree of insulation, the design (top openers lose less cold air) and features such as self de-frosting. People's own experience also depends on the number of times they open the door and how warm their boat is.

 

The most efficient fridge I had was a very efficient freezer converted to operate at 4⁰C instead of it's designed -18⁰C. Freezers, of course, have much better insulation than most fridges. Its on cycle was just a few minutes each hour all the time the door remained closed.

[David Mack]

15 hours ago, Bargebuilder said:

Could heat recovery be applied to a boat instead of leaving windows open?

I suspect the electricity consumption would be a killer for a boat off grid.

[GUMPY]

1 hour ago, Bargebuilder said:

The most efficient fridge I had was a very efficient freezer converted to operate at 4⁰C instead of it's designed -18⁰C. Freezers, of course, have much better insulation than most fridges. Its on cycle was just a few minutes each hour all the time the door remained closed.

Absolutely and simple to do with an external stat.

Chest freezers converted are even more efficient as the cold air doesn't pour out when you open them.

 

[Bargebuilder]

11 minutes ago, GUMPY said:

Absolutely and simple to do with an external stat.

Chest freezers converted are even more efficient as the cold air doesn't pour out when you open them.

 

I used the replacement fridge stat to power up a dedicated inverter only when it was needed, so there was no waste of 12 volt through quiescent inverter current draw; a super efficient solution to refrigeration.

28 minutes ago, David Mack said:

I suspect the electricity consumption would be a killer for a boat off grid.

BPC make a single room unit that will process 6 litres per second and draw only 3.4 watts. Much bigger volumes are possible with consequent increase in power consumption.

 

I suppose it depends on how much power you generate, but heat recovery would be a luxury on an off grid boat, but then, so is a refrigerator in midwinter.

[David Mack]

15 hours ago, Gybe Ho said:

Internal cabin temp is 20 degrees for 16 hours and 15 degrees for 8 hours

Unless you have underfloor heating or a fan system which takes hot air from ceiling level and blows it down to the floor, the air temperature just above the floor will be much lower than this, and hence the downward heat loss will also be less both with and without floor insulation than you have calculated, and so your postulated coal saving will also be less.

3 hours ago, cheesegas said:

Your average 90 litre under counter 12v fridge will only draw 60w or so when the compressor is running. 250w is a lot in comparison to this - bear in mind the air con compressor is likely to have a much longer duty cycle too. 

And for a typical narrow boat, electric fridge use represents about half the total daily electricity consumption, so something around 4 times that is substantial!

[GUMPY]

30 minutes ago, Bargebuilder said:

I used the replacement fridge stat to power up a dedicated inverter only when it was needed, so there was no waste of 12 volt through quiescent inverter current draw; a super efficient solution to refrigeration.

Except to do it that way you need a second inverter of at least 1kw to cope with the start up current, when a Victron draws less than 0.2A or less than 5Ah a day when in search mode it's hardly worth it.

[cheesegas]

1 hour ago, David Mack said:

Unless you have underfloor heating or a fan system which takes hot air from ceiling level and blows it down to the floor

In winter I put a little 120mm computer fan attached to a PWM controller at the front of the boat at ceiling height, aimed about 45 degrees down. Runs 24/7 on about half speed, pulls less than 0.1a and makes a massive difference. I’ve measured it too, moved some Ruuvi tags so ones on the floor, one at gunnel height and one on the ceiling. 

[Francis Herne]

3 hours ago, Bargebuilder said:

12v DC compressor fridges are often referred to as more efficient than 230V AC, but I've read that. " The motor on a Danfoss compressor is actually AC. The controller takes DC input and inverts it to variable frequency AC to run the compressor"

Setting aside the overhead of running a 12V-mains inverter, note the "variable frequency".

The controller can drive the motor as required for the load, which is quite a bit more efficient than simply wiring a single-phase motor directly across a constant AC supply as in old-school mains fridges and reduces the startup power demand spike.

 

Modern high-efficiency mains fridges often have compressor motors driven at a variable frequency by an inverter on the control board in the same way. Adding an 12V->240V inverter in front of one of them gives you a slightly silly chain of DC->AC->DC->AC conversions, and I suspect finding a way to power the inverter on demand as you've done would be less straightforward.

[Gybe Ho]

1 hour ago, David Mack said:

Unless you have underfloor heating or a fan system which takes hot air from ceiling level and blows it down to the floor, the air temperature just above the floor will be much lower than this, and hence the downward heat loss will also be less both with and without floor insulation than you have calculated, and so your postulated coal saving will also be less.

 

 

I updated my worked calculation notes to acknowledge this uncertainty but do not know how to update the calculation to factor in the temp gradient.

 

It is worth pointing out that heat loss through the floor contributes to the temp gradient and better insulation would reduce that. I do know that people feel the cold settling below gunwale height and carpets are viewed as a quick fix. 

[Bargebuilder]

2 hours ago, GUMPY said:

Except to do it that way you need a second inverter of at least 1kw to cope with the start up current, when a Victron draws less than 0.2A or less than 5Ah a day when in search mode it's hardly worth it.

Not quite right: a cheap 850w quasi works perfectly and is a fraction of the cost of the Victron to which you refer.

 

5Ah a day isn't much, but after two weeks of dull, misty, November days with very little solar, it can make a difference. 

1 hour ago, Francis Herne said:

suspect finding a way to power the inverter on demand as you've done would be less straightforward.

 

Actually, it's very straightforward: you just supply 12v to an 850w quasi inverter via a relay that is controlled by a 12v thermostat, the probe of which you insert into the freezer through the drainage hole in the back.

 

We didn't have a big Victron on board that remained on 24hrs a day, so the above was a cheap and efficient solution.

[Gybe Ho]

3 minutes ago, Bargebuilder said:

Not quite right: a cheap 850w quasi works perfectly and is a fraction of the cost of the Victron to which you refer.

 

5Ah a day isn't much, but after two weeks of dull, misty, November days with very little solar, it can make a difference. 

 

I thought Victron implemented a technical trick where they run the invertor in a low drain (AES?) standby mode that senses for demand 1 ac cycle in 50.

[cheesegas]

10 minutes ago, Gybe Ho said:

 

I thought Victron implemented a technical trick where they run the invertor in a low drain (AES?) standby mode that senses for demand 1 ac cycle in 50.

It does, but the microprocessor needs to be awake which consumes power. 3w nominal for a Multiplus 1600 I seem to remember, but feel free to check the manual…

 

3w = about 6ah per 24hrs @ 12v. 

[Bargebuilder]

22 minutes ago, cheesegas said:

It does, but the microprocessor needs to be awake which consumes power. 3w nominal for a Multiplus 1600 I seem to remember, but feel free to check the manual…

 

3w = about 6ah per 24hrs @ 12v. 

 

Which is about half of what the converted freezer to fridge consumed in 24 hrs, so for me, it was worth having a dedicated cheap inverter. Clearly not worth it if you have an inverter running 24hrs anyway.

[GUMPY]

2 hours ago, Bargebuilder said:

Not quite right: a cheap 850w quasi works perfectly and is a fraction of the cost of the Victron to which you refer.

You must have been lucky, a few years ago when I tried this I went through ten 1kw inverters none of which would reliably start a 230v fridge. Freezer may draw less start up  current but I doubt it.

[Bargebuilder]

18 minutes ago, GUMPY said:

You must have been lucky, a few years ago when I tried this I went through ten 1kw inverters none of which would reliably start a 230v fridge. Freezer may draw less start up  current but I doubt it.

Mine is a Sterling unit and has been working for the last 8 years. I haven't had the need to try other makes, so I don't know if Sterling inverters are happier to put up with short surge currents than other makes.

[MtB]

1 hour ago, GUMPY said:

You must have been lucky, a few years ago when I tried this I went through ten 1kw inverters none of which would reliably start a 230v fridge. Freezer may draw less start up  current but I doubt it.

 

I've been mucking about with a cheapo £80 fridge rated at 60W, a 600W Sunshine PSW inverter and a Fogstar 12V 100AH LiFePO4 battery. 

 

If I power up the inverter and let it stabilise first, it will just about start the fridge when I connect it. If I turn the fridge on first then power up the inverter (as though the fridge stat was booting the inverter via a relay), the inverter fails to boot up, throws an error and sulks. 

 

 

 

 

Edited August 7 by MtB

[GUMPY]

47 minutes ago, Bargebuilder said:

Mine is a Sterling unit and has been working for the last 8 years. I haven't had the need to try other makes, so I don't know if Sterling inverters are happier to put up with short surge currents than other makes.

Sterling did "produce" a 600w inverter that would start a fridge but that was 30 years ago.

2 minutes ago, MtB said:

 

I've been mucking about with a cheapo £80 fridge rated at 60W, a 600W Sunshine PSW inverter and a Fogstar 12V 100AH LiFePO4 battery. 

 

If I power up the inverter and let it stabilise first, it will just about start the fridge. If I turn the fridge on then power up the inverter (as though the fridge stat was booting the inverter via a relay when it turns on), the inverter just throws an error and sulks. 

This is exactly what I found ten times over.

[Bargebuilder]

1 hour ago, GUMPY said:

Sterling did "produce" a 600w inverter that would start a fridge but that was 30 years ago.

This is exactly what I found ten times over.

My 850w Sterling is powered up by the thermostat. The freezer, now fridge, is permanently 'on' because it's thermostat wants to get the temperature down to -18⁰c. The moment the sterling powers up it has to cope with the surge demand from the compressor, which it has done without any issues for 8 years. Obviously, Sterling inverters are tougher than some other makes.

[cheesegas]

35 minutes ago, Bargebuilder said:

My 850w Sterling is powered up by the thermostat. The freezer, now fridge, is permanently 'on' because it's thermostat wants to get the temperature down to -18⁰c. The moment the sterling powers up it has to cope with the surge demand from the compressor, which it has done without any issues for 8 years. Obviously, Sterling inverters are tougher than some other makes.

Sterling seem to be a bit of a crapshoot. Some of them will go for years and years, but quite a few explode prematurely with no inbetween it seems! Failure mode on the low frequency ones seems to be a FET blowing its front off, although I did see one that had managed to melt itself so thoroughly it was impossible to determine what went bad.

[Bargebuilder]

17 minutes ago, cheesegas said:

Sterling seem to be a bit of a crapshoot. Some of them will go for years and years, but quite a few explode prematurely with no inbetween it seems! Failure mode on the low frequency ones seems to be a FET blowing its front off, although I did see one that had managed to melt itself so thoroughly it was impossible to determine what went bad.

Sterling make inverters in the UK in the Midlands, so presumably they comply to UK manufacturing standards. Can they be more unreliable than the many imported inverters out there?

[cheesegas]

10 minutes ago, Bargebuilder said:

Sterling make inverters in the UK in the Midlands, so presumably they comply to UK manufacturing standards. Can they be more unreliable than the many imported inverters out there?

More reliable for sure, I was just commenting on the odd failure pattern; catastrophic explosion within a couple of years or quietly dying after many many years!

[IanD]

12 minutes ago, Bargebuilder said:

Sterling make inverters in the UK in the Midlands, so presumably they comply to UK manufacturing standards. Can they be more unreliable than the many imported inverters out there?

From what I've read about them Sterling inverters are better designed and built than a lot of the cheap no-name Chinese junk, but not as well-designed and built as the more expensive professional gear like Victron.

 

As usual, you get what you pay for... 😉

[cheesegas]

1 minute ago, IanD said:

From what I've read about them Sterling inverters are better designed and built than a lot of the cheap no-name Chinese junk, but not as well-designed and built as the more expensive professional gear like Victron.

 

As usual, you get what you pay for... 😉

 

16 minutes ago, Bargebuilder said:

Sterling make inverters in the UK in the Midlands, so presumably they comply to UK manufacturing standards. Can they be more unreliable than the many imported inverters out there?

Forgot to mention - I haven't seen inside that many Sterlings, but the build quality does seem to vary a fair bit, which may account for getting a dud or not. They also use cheap no-name electrolytics and have some questionable practices like having very crude protection circuitry.

[Bargebuilder]

7 minutes ago, IanD said:

From what I've read about them Sterling inverters are better designed and built than a lot of the cheap no-name Chinese junk, but not as well-designed and built as the more expensive professional gear like Victron.

 

As usual, you get what you pay for... 😉

 

With the efficient way that the internet disseminates information, I imagine that if they were that unreliable, they'd be struggling to stay in business. 

 

 

[IanD]

14 minutes ago, Bargebuilder said:

 

With the efficient way that the internet disseminates information, I imagine that if they were that unreliable, they'd be struggling to stay in business. 

 

Why? Everything and anything comes in various qualities from cheap low-quality to expensive high-quality, and people choose which is more important to them, cost or quality.

 

Sterling gear is lower-end but not as low as some, cheapish but not the cheapest. If you want better quality and reliability, spend more.

Edited August 7 by IanD