Air Conditioning Systems for caravans and motorhomes Words by Terry Owen, pictures by Alison Owen

What do we mean by air conditioning?
The generally accepted definition is a system that both cools and dehumidifies the air. This latter aspect is very important as lowering the humidity is a major factor in achieving comfort levels.

Air conditioning systems that work by refrigeration achieve these goals. The systems used are similar in principle to those used in domestic refrigerators. A refrigerant gas is compressed and cooled and the resulting cool liquid is then allowed to vaporise in a heat exchanger through which the air inside the van is passed. This vaporisation process produces a very cold gas which cools the heat exchanger. The air passing through the heat exchanger is thereby cooled and excess moisture condenses out so the resulting air feels much fresher and less humid.

Why fit air conditioning?
It is a fact that our climate is getting warmer and, in recent years, we have seen record summer temperatures. Indeed in August 2003, an all time high of 38.5 °C (101 °F) was measured at Brogdale near Faversham in Kent. With temperatures soaring towards these sorts of levels even shady pitches can become uncomfortably warm. And, whilst warm summer temperatures are not guaranteed for the UK they certainly are for many parts of mainland Europe, especially the popular camping destinations of Southern France and Spain.

In these sorts of climatic conditions the relatively lightweight construction of caravans and motorhomes means that they can heat up (and cool down) quickly making some form of temperature control important. (The white, cream or silver exterior finish found on 99.99% of all caravans and motorhomes plays a part in this by reflecting heat in the summer and reducing radiated heat in the winter.) Shady pitches and open windows can only do so much to keep the temperature down, beyond that air conditioning is needed.

Types of system available

Roof Mounted Most people are familiar with the roof mounted units from companies like Dometic (formerly known as Electrolux Leisure Appliances), Waeco and Telair. They are designed to replace an existing roof vent or fan making fitting an easy procedure. All that is needed is a good 230volt supply to operate them. Easy fitting and removal (perhaps to a new van), make these units by far the most popular on the market. The roof mounting position means the cooled air is right where you want it – i.e. at the highest point ready to cascade down cooling the inside of the van. The disadvantage is that air conditioning units can be quite heavy and putting such weights so high above the axle is contrary to good loading principles. It’s also important to check (via your dealer) that any given roof is strong enough to take the weight. It’s not the static loadings that are the problem but the dynamic ones created when bouncing down the road at 60mph or so. Of course roofs can be strengthened but this all adds to the cost. (Roof loadings are not normally a problem with motorhomes as most motorhome roofs are designed to be walked on.)
		The Dometic B1500 unit seen here came as a factory fit option on this 2003 Conqueror

Internally mounted (Truma Frostair)
These units are designed to floor mount in a bed box or similar space and preferably near the axle. This means they will have little effect on the outfit’s stability when on the move. Another advantage is that, for a given cooling capacity, Truma’s units seem to be a little bit lighter than other types. Cooling air is drawn in and expelled via the floor or side of the vehicle. Wiring is normally easy but ducting is required to take a proportion of the cold air to a higher level to be effective. With some van layouts this may be easy to achieve by hiding the piping inside existing furniture. However, where this is not possible, it may be difficult to achieve a neat installation.

Shoehorned into a rear bed bunk on this Challenger 490 is Truma’s mighty Frostair 2300		Here you can see 2 cold air outlets above the fire. Another is round the corner at higher level.		The wardrobe comes in handy for hiding the ducting.

Under floor (Trend Air)
These units are designed primarily for caravans and fit under the floor between the chassis rails thereby taking advantage of the relatively cooler air to be found here. This arrangement means that the only storage space lost within the van is that taken up by the ducting necessary to get the cooled air to the inside. Whilst the underfloor mounting will certainly help the stability of the outfit it could well clash with other items normally found in this area such as spare wheel carriers, water tanks and caravan movers. This (and the fact that I don’t think they’re imported into the UK any more) could explain why I’ve never seen one installed. They are available in Germany under the brand name Trend Air and tip the scales at a hefty 43 kg (95lb)

Power Requirements
All the units described here require 230 volts AC at around 3-4 amps. At first glance this would seem within the scope of many of the lightweight leisure generators that are so popular today. However the problem is that, when starting, a high current (typically15-20amps), is briefly needed to overcome the load on the compressor. This is beyond the scope of today’s leisure type portable generators. For caravanners this means finding a site with a mains hook up. Motorhome owners may however have more choice as some motorhomes have provision for an on board generator of reasonable capacity.

In the last couple of years or so some air conditioning units have been made available with dual 12 volt / 230 volt operation. This is achieved by means of an inverter that changes the 12 volt DC supply to a 230 volt AC one and is intended purely to allow motorhomes to operate their air con systems whilst being driven. The current required at 12 volts is far too high to make battery operation feasible

Weight, vibration and noise Significant advances in design over recent years mean that today’s units are lighter and quieter than their predecessors, but these issues cannot be ignored. At 25 – 45 kg air conditioning units can eat significantly into load margins, especially in those caravans already fitted with movers. The same effect is true with motorhomes particularly if an on-board generator is used to provide the power away from mains sites. Some units can be quite noisy when working at full load and, on busy sites, usage may be restricted to certain daylight hours. Whichever type you’re thinking of buying it’s always worth seeing if you can hear one in action beforehand.

Features
Most units come with multi speed fans and many have remote controls or even timers. It’s also possible to get inbuilt heaters for the cool summer evenings so often to be found in the UK. Remember more features can mean more weight, so choose carefully.

Costs
Air conditioning is never cheap because of the amount of engineering involved. The units described here cost £1, 000 or more, excluding fitting.

Useful web addresses:-

Dometic: www.dometic.com
Scan Telair: www.telecogroup.com
Truma UK: www.trumauk.com
Waeco UK: www.waeco.co.uk