by Collyn Rivers
Caravan Air Conditioning
Caravan air conditioning or motorhome is becoming increasingly feasible, even via solar. This article by Collyn Rivers shows how.
For caravan air conditioning, the most efficient air conditioners are reverse cycle units. These heat as well as cool. Whilst doing either, they move far more heat energy than the electrical energy they draw. This may seem contrary to the laws of physics but it’s not.
Caravan air conditioning – how aircon works
As with a fridge, an air conditioner 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. They do not heat air as (say) does a gas heater. Instead, 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 suspects. 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.
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 draw. It is shown as a Star rating. The actual energy draw is shown as kilowatt-hours a year. Also listed is energy drawn at maximum output.
Currently, many RV air conditioners are barely on this scale. Some are not all. The best (domestic) reverse- cycle units are highly efficient. They are often owner fitted.
Currently, the most efficient is the Daiken 2.5 kW US7. It provides 2.5 kW of cooling and 3.6 kW of heat from 0.42 kW and 0.62 kW respectively. The unit is almost silent. It’s costly, but you save more than the extra cost in solar and battery capacity.
Energy rating is price related. Air conditioning an RV is not an area for eBay bargains.
Caravan air conditioning – from solar
Given 750 watts of dedicated solar modules, air conditioning an RV from solar alone is feasible during daylight. Night-time use (as well) necessitates about twice that 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 energy source for RV air conditioning is an inverter/generator. A Honda or Yamaha unit can assist, or wholly run the system. It can do so directly. Or charge batteries via a 230-volt charger. Here too, LiFePO4s work well. They accept huge charging current.
Quiet diesel-powered generators (e.g. Onan) are costly but last forever. They charge a typical RV battery bank in an hour or so morning and evening. Some diesel generators are water-cooled. If so you may also have semi-free hot water.
Fuel cell technology will eventually be a more economic and silent back up for solar. Currently, however, fuel cells are too costly for most RV owners to consider.
Further information
The design and installation of caravan air conditioning is too large to cover in article form. All you need to know, however, is in RV Book’s Caravan & 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. The 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 a now over 60 years. (About the author).
