(Updated May 2017)
Air conditioning a caravan – how aircon works
As with a fridge, an air conditioner is not a sort of back to front heater. It does not cool air directly. It is basically a pump that moves heat from where you do not want it – to where it does not matter.
Reverse cycle units double as heaters. Here again they do not heat air as (say) does a gas heater. They ‘harvest’ heat energy from outside and move it to where it’s wanted. They can do this even at temperatures close to freezing. Such heat energy is greater than many suspect. Except in extreme cold, a reverse cycle air conditioner supplies over twice the heat energy than it draws in doing so. Some supply close to four times. It is far more efficient than heating air directly.
The Australian-made Kimberley Kamper has optional (virtually) all-solar powered air conditioning. Pic: Kimberley Kampa.
Air conditioning a caravan – care needed when buying
Whilst high efficiency is feasible, many caravan air conditioners fall short of that. Air conditioner efficiency is shown as the ratio of its heating or cooling energy to its energy usage. This is shown as a Star rating. The actual energy usage is shown on the product labels in kilowatt hours a year. Also listed is the draw at maximum rated output.
Currently, many units for air conditioning a caravan are barely on this scale. Some are not on it at all.
The top (domestic) reverse cycle 230 volt ac units are highly efficient. They are often ‘do-it-yourself’ fitted to caravans and motor homes. Currently, by far the most efficient is the 2.5 kW US7 unit made by Daiken. The unit produces a rated 2.5 kW of cooling and 3.6 kW of heat from 0.42 kW and 0.62 kW respectively. It is almost silent in operation. It’s costly to buy but you save more than the extra cost in solar and battery capacity. The US7 has a 7-star rating.
Such energy rating is very much price related. Air conditioning a caravan is not an area for eBay bargains.
Air conditioning a caravan – from solar
Given 750 watts of dedicated solar modules, air conditioning a caravan from solar alone is feasible for day time use. Night time use (as well) necessitates about twice that solar capacity. It also requires 800-1000 amp hour battery capacity. Weight limitations necessitate that being LiFePO4. These are smaller and lighter, but cost about three times more than other batteries.
An alternative, or supplement for air conditioning a caravan is to use an inverter/generator. A Honda or Yamaha unit assists, or wholly run the system. It charges the batteries via a 230 volt charger. Here too, LiFePO4s work well. They accept huge levels of charge without harm.
Quiet diesel-powered generators (e.g. Onan) cost a lot more, but last forever. Fuel costs $2 to $3 an hour, but so-charging a battery bank, needs only need an hour or so morning and evening. Some diesel generators are water cooled: so you may also have semi-free hot water.
Fuel cell technology will eventually be a more economic and silent back up for solar. My constantly updated article Fuel Cells reports progress. Currently, however, they cost far too much for most to consider.
Air conditioning a caravan – further information
The design and installation of air conditioning a caravan in caravans and RVs generally is too large to cover in article form. All you need to know, however is covered in Caravan and Motorhome Electrics. (It is even used by auto electricians as their working guide.) For RV solar see Solar That Really Works!. Solar Success is for home and property systems. My Caravan & Motorhome Book covers all aspects of RV usage.
Readers worldwide confirm the cost of my books is repaid many times over. It enables you to get systems right the first time. I have both an engineering and writing/publishing background of over 50 years. (About the author).