Would a car air conditioning unit work on a boat?

[pearley]

My other half says car air a\c units draw off 4 to 6 horsepower from the engine, usually belt driven, that's about 3 to 5 kilowatts.

Having sold and installed car A/C since the 70s your other half is right but opening the windows does the same thing.

Edited July 23, 2015 by pearley

[Alan de Enfield]

Having sold and installed car A/C since the 70s your other half is right but opening the windows does the same thing.

 

Are you sure ?

Opening the windows draws 4-6 hp from the engine !!

[MtB]

Opening the windows doesn't lower the ambient temp inside the car to below that of the air outside, which is the whole point of air conditioning (in cars and boats at least).

[Guest]

Opening the windows doesn't lower the ambient temp inside the car to below that of the air outside, which is the whole point of air conditioning (in cars and boats at least).

.... In all installations surely?

 

Our new 'van will have air con but after researching before we bought it was pretty evident that a large volume like a caravan interior needs a pretty powerful unit to get it cooler than outside, and even then it's better if windows are CLOSED along with blinds. The 'van is 6.5 metres long internally.

 

It draws 4.7 amps on 240 volts.

 

A car air con only really works well because of the small volume of a car interior, I can't see it working at all in a boat unless it was in a very small cruiser, and even then under the conditions above.

[brassedoff]

i imagine it would cost a fortune in air con gas to fill that size of space with cool air.

 

plus you would have to keep every window and door shut, it would be costly.

 

extra diesel, loss of horse power, slower charging battery's

 

battery/alternator x 2 and engine wear would not be worth it, plus the air con pump would not last very long at all trying to cope with 50+ x the space it was designed to work in.

 

would not bother just get a vest and open the windows.

Edited July 23, 2015 by brassedoff

[Theo]

 

Are you sure ?

Opening the windows draws 4-6 hp from the engine !!

 

I have heard it maintained that opening the windows in a car so disrupts the air flow around it that running the air con is more fuel efficient. I have, of course, done no measurements on this but it is an interesting theory. A wind tunnel test would give the right measurements. I wonder if there is data for air resistance with windows shut cf window/s open.

 

N

[MtB]

.... In all installations surely?

 

 

No. True 'air conditioning' (as installed in buildings e.g. offices) not only regulates the temperature but the relative humidity and particulate content. (Dust and pollen particles especially.) Car air conditioning is a misnomer because it only reduces the temperature. One of the reasons manufacturers have take to describing it as 'climate control' instead of air con.

[Guest]

No. True 'air conditioning' (as installed in buildings e.g. offices) not only regulates the temperature but the relative humidity and particulate content. (Dust and pollen particles especially.) Car air conditioning is a misnomer because it only reduces the temperature. One of the reasons manufacturers have take to describing it as 'climate control' instead of air con.

That's strange, I have just bought a car that is described as having 'air conditioning' so has my daughter.

 

I thought that is why they had 'pollen filters' and quickly demisted screens.

[MtB]

Maybe your regulates humidity and particulates then!

(The 'air con' in my Vito mists up the windscreen rather than de-misting it.)

(As it reduces the air temp, the RH rockets to 100%)

[Guest]

Maybe your regulates humidity and particulates then!

(The 'air con' in my Vito mists up the windscreen rather than de-misting it.)

I can't recall a car that I have ever owned with air con that doesn't need a pollen filter change come service time TBH...

 

Ed , just googled Vito, now I understand

 

The actual difference between 'air con' and 'climate control' relates to how the temperature inside the vehicle is regulated.

 

'Air con' requires the temperature to be regulated via. human intervention, when it gets too cold or too hot a human has to intervene to change the temp. setting and/or the fan speed.

 

Climate control doesn't need this intervention, you simply need to set the desired temp. you would like the inside of the vehicle to be and the temp. and fan speed is sorted electronically. Some clever vehicles (like a Discovery we once had) allow different settings for both driver and front seat passenger.

Edited July 23, 2015 by MJG

[RLWP]

quickly demisted screens.

 

That one is a legal thing. ISTR some countries have a specific test that a new car has to pass

 

Even without aircon

 

Richard

[Guest]

That one is a legal thing. ISTR some countries have a specific test that a new car has to pass

 

Even without aircon

 

Richard

Apparently not in Germany....

[DHutch]

My 306 had a aircon (button was labeled a/c) that held a fixed temperature and didn't have a pollen filter, so nerrrrr...

 

 

Daniel

[Guest]

My 306 had a aircon (button was labeled a/c) that held a fixed temperature and didn't have a pollen filter, so nerrrrr...

Daniel

If it only had a single button, how did it maintain a fixed temperature please. Normally a dial to set the temp. that required adjusting and setting would be required, how could your system know what temp required setting, and how did it maintain and regulate that temp?

Edited July 24, 2015 by MJG

[Alan Saunders]

I can't recall a car that I have ever owned with air con that doesn't need a pollen filter change come service time TBH...

 

Ed , just googled Vito, now I understand

 

The actual difference between 'air con' and 'climate control' relates to how the temperature inside the vehicle is regulated.

 

'Air con' requires the temperature to be regulated via. human intervention, when it gets too cold or too hot a human has to intervene to change the temp. setting and/or the fan speed.

 

Climate control doesn't need this intervention, you simply need to set the desired temp. you would like the inside of the vehicle to be and the temp. and fan speed is sorted electronically. Some clever vehicles (like a Discovery we once had) allow different settings for both driver and front seat passenger.

That is how I understand it but I am not sure that Renault basic a/c can provide heating or demisting in winter. Renault do recommend that I run the a/c occasionally in winter to circulate the lubricant.

 

Basic car heating/cooling depends on the passengers sitting in a blast of cool/hot air rather than maintaining the general cabin temperature. Front seat passengers may roast/freeze whilst the rear seat passengers suffer the opposite

 

Generally, the pump may be mechanically driven from the engine and only works whilst the engine is running or an electric pump will be a huge drain on the batteries. Anyway, installing a/c involves some serious plumbing and charging kit that is not within my DIY skills or equipment.

 

A/C is nice idea but probably not practical for a boat without an adequate, continuously running generator.

 

Alan

[Guest]

That is how I understand it but I am not sure that Renault basic a/c can provide heating or demisting in winter. Renault do recommend that I run the a/c occasionally in winter to circulate the lubricant.

 

Alan

I think you might be confusing air conditioning with air cooling.

 

You can set the temp of what comes out of your heater to whatever you like but by switching your air con on you 'condition it too' ie dehumidify it and remove pollens and particulates.

 

That will quickly de mist your screen and give the system a work out.

Edited July 23, 2015 by MJG

[larkshall]

Well the book is clearly wrong!

I agree even though it is using salt water cooling which is far more efficient than heat shedding to atmosphere. The math doesn't work

[Alan de Enfield]

I like to try and understand things, and I am getting more confused as other manufacturers of air con provide figures that 'do not stack up'.

 

Truma (caravan air-con manufacturers) claim that their "Aventa" model is 2.4 Kw and uses 4.2 amps at 220/230 volt.

 

Another example

 

Amcor (a domestic air-con manufacturer) gives the following 'technical details'

 

Technical Information:

• 8000 BTU
• Cooling capacity - 2.34 KW
• 1-24 hour timer
• Quiet 2-speed turbo fan
• Noise dB - Noise Level: 48-55 db low/high mode(sound power method) EU label: max 64 dB (sound pressure method)
• 3-mode settings consists of Auto, Cool and Fan
• R410a "Green" refrigerant for improved cooling performance
• Thermostat range - 16-32°C
• Dehumidification - max - 24 L/Day
• Fan speed - 2
• Air flow (at high speed) - 380 m3/hr
• Power supply - 220-240V
• Energy rating: A
• Running power consumption - 890W
• Running current - 3.95 A

 

Is air-con cooling measured in a different way, or, are other manufacturers 'wrong' as well ?

Edited July 24, 2015 by Alan de Enfield

[Chewbacka]

A simple heater just converts fuel into heat, and if electric is basically 1kw in gives 1kw out. However air con is by heat pump and moves the heat from one place to another so can seem to give more cooling than it should. However if you look at the energy balance, it is less than 100% efficient. By this I mean the outside gets warmer and the inside gets cooler and the pump gets warmer as well which is where the energy is lost.

[Alan de Enfield]

A simple heater just converts fuel into heat, and if electric is basically 1kw in gives 1kw out. However air con is by heat pump and moves the heat from one place to another so can seem to give more cooling than it should. However if you look at the energy balance, it is less than 100% efficient. By this I mean the outside gets warmer and the inside gets cooler and the pump gets warmer as well which is where the energy is lost.

Ok - but how does an air-con 'consume' 890 watts but put out 2340 watts ?

[MtB]

A simple heater just converts fuel into heat, and if electric is basically 1kw in gives 1kw out. However air con is by heat pump and moves the heat from one place to another so can seem to give more cooling than it should. However if you look at the energy balance, it is less than 100% efficient. By this I mean the outside gets warmer and the inside gets cooler and the pump gets warmer as well which is where the energy is lost.

 

 

Actually I think this is right, and I was wrong. The figures quoted are technically possible. Although as larkshall says, they still seem improbably optimistic.

[Guest]

 

 

Actually I think this is right, and I was wrong. The figures quoted are technically possible. Although as larkshall says, they still seem improbably optimistic.

 

According to the spec. on our caravan air con (The Truma Aventa) it should draw over 10 amps, however in the manual it states it draws 4.2 amps and the minimum supply from the site bollard should be 6 amps (presumably to allow for other devices).

 

!0 amps is about average for caravan site bollards (some go up to 16 some are as low as 3 or 6). If it really did draw over 10 amps it would be unusable on a lot of sites, particularly if you add in a battery charger to the equation. So it would seem there is something 'different' about air condition units, though quite what it is I'm not sure.

[Chewbacka]

Air con units are heat pumps, so power in is just the power consumed by the pump. The work done by the pump shifts heat from inside to outside.

In fact some (maybe these days most) office aircon units can pump heat in either direction, so in winter they heat the office and in summer they cool it. The energy saving for heating compared to simple electrical heating can be significant. Why don't they use these for houses? Well the upfront investment cost is high, as is maintenance, and true energy saving is probably not much as you will now run the air con system during the summer, instead of opening the windows and moaning about the heat like I do :-)

 

http://energy.gov/energysaver/articles/heat-pump-systems

[cuthound]

Why not use a fan and some ducting to draw cooler air from the bilges and deposit it at ceiling height, so it can trickle down?

 

For a more permanent installation you could use ceiling mounted radiators connected to a closed circuit pumped glycol solution, and use a convoluted pipework system in the bilge to act as a heat exchanger?

[DHutch]

If it only had a single button, how did it maintain a fixed temperature please. Normally a dial to set the temp. that required adjusting and setting would be required, how could your system know what temp required setting, and how did it maintain and regulate that temp?

Button was an off/off button, dial had a feedback loop using a sensor and small circulation fan in the roof console with the map lights if you must know. Worked a treat.

 

Daniel

If it only had a single button, how did it maintain a fixed temperature please. Normally a dial to set the temp. that required adjusting and setting would be required, how could your system know what temp required setting, and how did it maintain and regulate that temp?

Button was an off/off button, dial had a feedback loop using a sensor and small circulation fan in the roof console with the map lights if you must know. Worked a treat.

 

Daniel