A guide to RV heating and cooling options and how they work
Achieving optimal temperature in your van — whether hot or cold — can be a bit like Goldilocks and the three bears. John Hughes takes a look at some of the best heating and cooling options on the market.
A comfortable temperature inside your van makes for a much more pleasant camping experience. There are a few appliance types available for heating and one type for cooling. Heating can be achieved with diesel heaters, gas heaters and reverse cycle air conditioners. Cooling is exclusively the domain of reverse cycle air conditioners. In this article, we enlist the help of Daniel Bennett, Product Manager at Leisure-Tec responsible for brands such as myCOOLMAN and Truma and Lisa Georgakis, Marketing Manager at NCE responsible for the Gree brand and many others.
We explore each type, their subcategories and learn about some of their pros and cons. The amount of space dedicated to each appliance is matched to its respective complexity and popularity.
Reverse cycle air conditioners
Most of this article is focused on reverse cycle air conditioners because they heat and cool and they are the most commonly found heating/cooling appliance found in Aussie vans. We previously covered fridges and had a close look at compressor fridges (if you missed that article, head here). This is relevant because a compressor fridge and a reverse cycle air conditioner are fundamentally the same thing. It is obvious that a fridge and an air con both cool but they also both heat.
This is how it works. Air cons have two heat exchangers. One of the heat exchangers is on the interior side of the van and the other heat exchanger is on the exterior side of the van. One heat exchanger (evaporator) absorbs heat out of the air creating a cooling effect. The other heat exchanger (condenser) dissipates heat into the air creating a warming effect. The clever thing is these heat exchangers can have their functionality reversed to either heat or cool the room — hence the name reverse cycle air conditioner.
The two heat exchangers are connected by pipes that circulate fluid (refrigerant) between them by a compressor. The functionality of the heat exchangers is reversed by changing the direction of the compressor. The heat exchangers do their thing thanks to the refrigerant constantly changing from a vapour to a liquid. The compressor pumps hot gaseous refrigerant to the heat exchanger acting as a condenser. The condenser is made up of a series of pipes exposed to the air. This sheds heat and partially cools and condenses the refrigerant to a liquid — hence the name condenser. The liquid refrigerant continues through the pipes (still being pushed by the compressor) to be forced through a valve allowing the liquid to expand. As the liquid expands it spreads over a larger area creating a pressure drop and corresponding drop in temperature. The depressurised refrigerant then flows into the other heat exchanger, another series of coils also exposed to the air evaporating from a liquid to a gas — hence the name evaporator. Evaporation causes heat to be drawn away from the air thus lowering its temperature. The gaseous refrigerant is then drawn back to the compressor to repeat the cyclical process.
What size air con for my van?
Daniel provided us with a rule of thumb that up to 18ft vans should use 2.4kW–2.8kW rated air cons and vans 18ft and above should use 2.8kW–3.5kW rated air cons. It would be understandable to assume that these ratings relate to electricity consumption, but they in fact are a measure of the capacity to transfer heat. Of course, there is a correlation between the amount of heat transfer capacity and electricity consumption, but it is not the same thing. Daniel provided us with a guide as to the respective continuous operation electrical power consumption of each heat transfer rating when cooling: 2.4kW ratings uses 0.6kW–1.0kW, 2.8kW uses 0.6kW–1.1kW and 3.5kW uses 0.8kW–1.6kW.
Pros and cons
A big advantage of a reverse cycle air conditioner is you only need one appliance to do cooling and heating. They are also arguably the safest and cleanest as there is no combustion involved as per diesel or gas appliances which we explore further on in this article. Reverse cycle air conditioners are completely reliant on electricity to run. Historically, this meant you could only use them when plugged into mains power in a caravan park or by running a generator. Now, more sophisticated self-contained electrical systems are becoming available in high-end caravans capable of running high-demand energy appliances such as air cons.
In simple terms, you need to be able to capture, store and deliver enough electrical power to make the air con run. A key component in this system is an inverter which converts 12V, 24V or 48V DC power stored in the van’s batteries into 240V AC power to run appliances. Inverters are rated in watt (W) or kilowatt (kW) indicating how much power they can deliver. This is often a constraint in the system. If the inverter can’t deliver enough power, you can’t run an air con. New developments in air cons are making it easier for inverters to cope with air conditioners.
Soft start vs traditional air cons
We quoted continuous operation electricity consumption in the numbers above. This is important for a couple of reasons:
Air cons are controlled by thermostats; this means they cycle on and off as the room temperature goes up and down. Therefore, when the air con is off it doesn’t use power and when it is on it does. This, in turn, means under most circumstances air cons will actually use less power on average than the continuous operation consumption number.
Depending on the type of air conditioner, some use more or less power than the continuous consumption number on startup. Traditional air cons use more power on start-up because it takes a lot of energy to get the compressor going. New generation air cons are known as soft starts because the compressors are capable of running at various speeds. Soft start compressors start at a lower speed and then gradually build up. This means they use less energy on startup. Soft starts enable you to use a lower-rated inverter than you would otherwise need. Just to complicate things soft start air cons are also known as inverter air cons. This is not to be confused with the inverter we have referred to above. It’s way too technical for this article but they are known as inverter air cons because the system has some fancy electronics that converts AC power to DC power and then inverts it back to DC to optimise variable speed performance of the compressor. Variable speed compressors also use less power overall because they don’t have to run flat out all the time like non-variable speed, traditional air cons.
Recent entrants to the soft start market include myCOOLMAN and Gree. Daniel tells us they have just launched their myCOOLMAN 3kW (heating and cooling) soft start model which has a continuous operation power consumption of 1.2kW but only requires 0.6kW on startup. More advantages of the new myCOOLMAN include a very low-profile design which minimises wind resistance and solar shadow on the solar panels. Other desirable features include optimised design to reduce noise, vibration and bolster energy efficiency. Lisa also tells us the Gree soft start air con is new to the market too. It has a cooling capacity of 3.6kW and a heating capacity of 3.4kW making it suitable for vans up to 27ft. At just 32.2kg it is a lightweight unit and also boasts an ultra-low profile for enhanced aerodynamics. The inverter-based variable speed compressor enables an optimisation of quiet operation and peak electrical efficiency.
Reverse cycle units — rooftop vs under bunk
Air conditioners are available in roof-mounted (self-explanatory) and under bunk versions which are fitted inside the van under furniture. We see a lot more roof-mounted air conditioners on vans as they have many advantages. Roof mounted air cons don’t eat up valuable storage space inside the van and they also tend to be more efficient, as air is able to flow more freely, particularly in cooling mode where air will fall down. The downsides to roof mounted air cons are they compete with solar panels for roof space, and they actually cast a shadow on solar panels reducing their efficiency. Plus, they do nothing to enhance aerodynamics. Daniel tells us under bunk air conditioners are gaining more share as hybrid vans grow in popularity. Most hybrids are pop-top caravans and having a rooftop air conditioner does make it appreciably harder to push up. Having the weight up on the roof is also not the ideal for centre of gravity when negotiating offroad conditions. Finally, roof mount air cons limit how many solar panels you can fit on the roof giving under bunk air air cons an advantage.
Getting the most out of the air con
Daniel tells us caravan air conditioners can generally cope well with temperatures up to 35°C. In temperatures above that you should really only expect the air con to take the edge of the heat. Better insulated vans and parking in the shade will optimise performance. On expected hot days, start the air con before ambient temperature maxes so the air con doesn’t need to work as hard. If you are powering an air con from a self-contained electrical system you can minimise the draw on the batteries by running the air con while driving to camp — most high-end electrical systems will include a DC-to-DC charger which uses the car's alternator to charge the battery.
Diesel heaters
Diesel heaters are quite popular because they are one of the simplest systems to use off-grid. We have seen that running an electrical heating/cooling device requires a sophisticated, expensive self-contained electrical system to deliver enough energy to power it. Diesel on the other hand is a very efficient method to store and convert energy. You can buy diesel just about anywhere and you don’t need much of it — diesel heaters typically consume roughly 200ml per hour. Diesel heaters have their own dedicated tank mounted on the outside of the van and they generally have a 10–15L capacity. For easy maths, a 10L tank provides approximately 50 hours run time (10 divided by 0.2 = 50). Plus, it is easy to top up your heater tank with a jerry can of diesel. Given that most tow vehicles run on diesel having a common fuel source is also a bonus.
The principle of how a diesel heater works is pretty simple. The diesel is fed from the external tank to the main unit inside the van containing a burner which converts the diesel into heat energy. Using a fan, air from the room is then circulated through the heater to warm it. The heater unit is generally located under a bed or seating and air is drawn through inlet vents into ducting. The air passes over a heat exchanger warming it and then it continues along ducting and exits the outlet duct/s. Continually passing air through the heater keeps the caravan warm. Diesel heaters do create exhaust fumes and they are piped out to the van exterior.
A common question is do diesel heaters smell? According to Daniel, they can give off an odour, particularly at the exhaust point, but regular servicing will help minimise this. To extend service life the heater burns more cleanly if run on a high setting and preferably not for short periods of time. Servicing is critical because a malfunctioning diesel heater could potentially put carbon monoxide into the room.
Gas heaters
The advantage of gas heaters is most caravanners already have LPG bottles on board. Gas can be used to power an installed heater, similar to a domestic heater. You will need to keep in mind that running a gas heater will consume a lot more gas than a cooker or hot water service. While gas heaters can be perfectly safe there is always some risk of explosion due to leaking unburnt gas or a faulty appliance generating carbon monoxide. Again, gas heaters should be regularly serviced by a professional to ensure their safety.
Combination water/space heaters
Another way to heat your van is to harness the heat from your hot water service. Most hot water systems only have a hot water outlet. Those designed for space heating also have a water inlet allowing the water to be continuously recirculated through a pipe loop. This continuously heated water is then passed over a heat exchanger to allow air to be warmed up and circulated with a fan. This system can be used with diesel, gas or electric heaters. Diesel and gas heater options are more off-grid friendly for most caravanners until fully self-contained electrical systems become more mainstream.
The wrap
Caravanners have a number of options when it comes to cooling and heating systems for their home on wheels. Reverse cycle air conditioners are the most popular as they are the only appliance capable of cooling and they also perform a heating function. The main drawback of reverse cycle air conditioners is they are not suited to off-grid camping unless you have a high-end self-contained electrical system or run a decent generator. Diesel heaters are the most popular alternative for off-grid heating applications. Less often used appliances include gas heaters or combination water/space heaters.
Thanks to the following companies who provided invaluable background information and images for this article:
- Leisure-Tec (myCOOLMAN and Truma products)
- NCE (Gree air conditioners)
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