In this second part of our feature on the evolution of RV heating systems we highlight North America and Australasia. We also look at crossover products from the automotive industry along with role of technology. We end with a glimpse into the future
Words Terry Owen
The RV scene in the USA and Canada has always been very different from that in Europe. For a start, caravans get called ‘travel trailers’ and motorhomes ‘coaches’ or ‘truck campers’. As well as tending to be much larger than their European cousins they tend to get used somewhat differently.
Americans like their hot water in quantity and the demand is often met with a tankless heater offering instant hot water. There are too many brands to mention each one individually so here we look at some of the more popular names.
One very popular brand is Aqua Hot (part of the Airxcel Group since 2019) and producing a wide range of combi heaters powered by diesel or propane, supplemented with electric elements. All are capable of producing continuous hot water without needing a storage tank. With power ratings from 17,000 – 65,600 BTU (5 – 19 kW) these are beefy units with dry weights 50 – 195 lb (23 – 84 kg) to match.
Another popular brand is Atwood, who became well known for their 6- and 10-gallon propane-fired water heaters, amongst other products. Atwood was purchased by Dometic in 2014. The water heaters live on under the Dometic brand.
Atwood also became well known for its warm air heaters. In the US these are often referred to as furnaces. There are two basic types. The direct discharge type blows air directly from the unit’s faceplate whereas the ducted type distributes the warm air through ducts in the ceiling or floor. Atwood’s furnaces continue under the Dometic brand with ratings up to around 41,000 BTU (12 kW).
Suburban began manufacturing RV heating systems in the 1960’s from its base in Dayton, Tennessee, becoming part of the Airxcel family in 1997. Today it offers a wide range of propane powered space and water heaters along with cooking appliances. Its water heaters include tank capacities of 4 to 16 USG (15 to 60 litres) whilst tankless models provide up to 60,000 BTU (17.6 kW) of continuous hot water.
Space heaters take the form of traditional furnaces with no less than five series on offer. Capacities range from 16,000 to 40,000 BTU (4.7 to 11.7 kW).
Other players include Elwell with its Timberline heating system. Aimed at class B and C motorhomes, the heater is powered by diesel or gasoline and uses glycol to transfer heat to blown air heat exchangers and a water heater.
Also on the scene, is ITR (International Thermal Research) with its Oasis diesel powered systems. Aimed at larger motorhomes these too are glycol based. The smallest boiler (Zephyr) weighs in at 48 lb (22 kg) dry and produces some 33,000 BTU (10 kW) for distribution to heat exchanger fans. It can also give continuous hot water at 1.0 USG (3.8 litres) per minute. At the other end of the scale is the mighty Oasis NE-S with 85,000 BTU (25 kW) and 3.0 USG hot water per minute.
Against this background Alde has been making inroads with its fully hydronic system based on the Compact 3020 boiler. With 18,700 BTU (5.5 kW) of propane heating and up to 1.9 kW of electric power, its small size and 14 kg dry weight make it a very attractive proposition. Those who want continuous hot water can specify the Flow option, which adds just 5 lb (2.3 kg) and delivers 0.9 USG (3.5 litres) per minute.
In recognition of the demand for instantaneous water heaters, Truma launched the AquaGo in 2014. It provides an infinite supply of constant temperature hot water from its 60,000 BTU (17.6 kW) propane burner. The AquaGo is technically a hybrid device as it contains a small tank to help with instant delivery and temperature stabilisation.
As well as being suitable for new installations, the AquaGo is designed as a direct replacement for the standard 6-gallon water heaters that have dominated the US market for many years. New installations can be specified with the Comfort Plus model, which adds a recirculation pump to the hot water circuit. This ensures that hot water is available at each tap as you turn it on. You don’t have to wait for it to be pumped from the boiler.
The AquaGo sells alongside four versions of Truma’s highly successful Combi heater. This can combine electric heating with propane to give blown air and hot water. It’s claimed to be the only forced air furnace available with an electric heat option.
Where diesel powered heaters are concerned the market in Australia and New Zealand is dominated by Eberspächer and Webasto, which are seen as premium brands. Eberspächer is marketed there by Dometic.
Next to these come the Chinese ‘Belief’ and Russian ‘Autoterm’ brands. Belief air heating products have been sold in Australia for about six years and have proved reliable, with outputs of up to 4 kW. The Russian-made Autoterm brand offers a small range of diesel air heaters with powers up to 4 kW. There is also a 5 kW hydronic diesel-powered heater designed to pre heat the engine or provide warm air via a heat exchanger.
Those looking for LPG powered space heaters will find ready availability of Truma’s Vario heat models, which can be supplemented by the addition of an electrically powered booster if required.
For water heating the Suburban brand offers its Nautilus on demand heater and the full range of Truma products is available. The Swift Appliance group manufacture in Australia and offer a 20/28 litre gas and electric water heater with a stainless-steel tank.
There is also the Chinese made Camec brand with a design echoing some American models.
The automotive influence
Eberspächer, Webasto and others
The idea of water and air heaters powered by petrol or diesel goes back to the 1930’s with the development of engine-independent heaters for passenger cars by Webasto. After the war production increased with companies such as Eberspächer, joining in. At this stage the main purpose of the heaters was to avoid cold starts and supply warm air to passenger compartments. However, it was quickly realised that they could also be used to drive or supplement the heating systems used in campers and boats. Using a readily available fuel that the vehicle needed anyway made a lot of sense and preserved precious LPG for things like cooking.
Today there is a huge choice of both air and hydronic heaters with more than enough power for even the largest of motorhomes. These heaters have another advantage too and that is their excellent power to weight ratio. A good example is the Webasto Thermo Pro 90, a hydronic device which can produce 9 kW from a dry weight of just 4.9 kg. (Image 13).
Combi type units are also available with water heating included. An example is Webasto’s Dual Top range. It comes with an 11-litre boiler and can be mounted inside or outside the vehicle. The electric option adds an extra 2 kW of power giving a total of 8 kW. It weighs in at 24 kg.
Eberspächer counters with its Airtronic blown air heaters.
It also offers the Combitronic air and water heater. This is driven by a hydronic heater with a calorifier for sanitary hot water and a fan matrix for warm air. It has an output of 5 kW and can be used with petrol or diesel fuel. Alde too gets in on the automotive platform with an engine heat exchanger that allows heat from the engine to enter its system and so warm the whole RV, not just the cabin.
The influence of technology
Advances in heater design have come about through two major factors. The first is experience. Each generation learns from the previous one and designs improve with time. The second is advances in technology that permit developments which were never possible previously.
An early technology influence on design was the advances in electronic circuitry which allowed for electronic ignition, along with better control and monitoring. These did away with the need for a pilot light or unreliable piezo push button ignition. What’s more, electronic flame detection could quickly shut off the gas supply in the event of flame failure. In short, electronic control brought with it improved safety, reliability, and end user convenience.
Another influence was the continuing development of high-performance plastics. Years ago, metal was the material of choice for heater casings and the like because of its ability to withstand heat. However, as plastics improved, they slowly began to displace metal. Not only did this offer an important reduction in weight, plastic also made it possible to produce one-piece mouldings and other shapes that were not so easy with metal.
An early example is Truma’s E heater series. It launched with metal casing in 1975 but today’s smaller and lighter successor, the VarioHeat, uses plastic.
Whilst improvements in heat exchanger design played a role in this development, advances in plastic technology were also key.
Arguably the biggest influence of technology on RV heater design has been the more recent implementation of technology borrowed from the world of computers. An early adopter was Whale in 2013 with its revolutionary iVan system. This employs a smartphone-like control panel in conjunction with Wi-Fi to control the water and space heating systems.
The use of Wi-Fi greatly reduces the amount of wiring required whilst the central control panel simplifies operation and cuts down on the number of components needed. However, despite the advantages of Wi-Fi, the RV industry has decided that the answer for rock solid connectivity with a minimum of wiring, lies with bus systems. Hence, we have seen the development and adoption of the CI-BUS, of which much has been written in this magazine and elsewhere.
A further major development has been the ability to control RV heating (and other systems) from anywhere using a smartphone. One of the early players here was Truma with its iNet system. Launched in 2016, it earned the industry’s European Innovation Award for that year. The beauty of the iNet system is that it uses simple text messaging to underpin its operation. This means it works anywhere there is a 2G phone signal; 3G, 4G and 5G are simply not required.
Since then, many other systems and technologies have appeared. The net result is that the end user has a degree of control unimaginable a few years ago.
The role of the climate chamber
Climate chambers have been around for years but their appearance in our industry was driven by the new insulation grading systems for caravans and motorhomes (EN 1645/6) introduced from model year 1999. For winter use, caravans are now classified according to being able to maintain an internal temperature of 20°C with an outside temperature of either 0°C or -15°C (- 5°C for motorhomes).
The slightly less stringent requirement for motorhomes is an acknowledgement that heating a cab with its single-glazed glass windows can be difficult. The ratings thus reflect not just the level of insulation but also the performance of the heating system.
Whilst it is possible to arrive at a rating for an RV using calculations alone, the PR advantages of proving it using a cold chamber are obvious. What’s more, with the help of thermal imaging cameras, any weak points in the insulation can be quickly identified.
A glimpse into the future
RVs of the future are expected to get smaller and lighter, and become increasingly powered by electricity alone. The all-electric motorhome is already a reality and, together with hybrid-powered vehicles looks set to dominate in the years to come.
LPG as a heating fuel will slowly wane due to its inconvenience and CO2 emissions. It will be largely replaced by electricity although some motorhome appliances may switch to diesel, where this is used as an engine fuel. One school of thought suggests that LPG might be replaced by bio-ethanol. The latter is carbon neutral and is easier to transport and store. Time will tell.
These changes pose significant challenges for RV heating companies. The days of the heavy and bulky combi units may be numbered for all but the larger RV’s. Instead, we may see de-centralised systems based on individual components, connected together but physically apart, secreted away wherever there is space. This approach means such components can be individually sized according to the needs of the vehicle, potentially saving weight.
Such systems lend themselves to hydronic operation, where a fluid can efficiently transport heat (or cooling) around a vehicle. To this end both Eberspächer and Webasto may be a little ahead of the game here. They already have lightweight electric heaters designed for the direct heating of fluids for plug in hybrids and pure electric vehicles. These heaters convert electricity into heat without loss.
The Eberspächer product relies on positive temperature coefficient technology (PTC) to prevent overheating. This is where the resistance of the heating element increases with temperature, so regulating the power drawn.
Webasto has a different technology. It says the heating layer of its device is ‘rapidly and precisely adjustable’ and that it ‘avoids interfering short term power spikes and converts then directly into heat’. It claims this is a clear advantage over PTC heaters.
The fact remains that both heaters are highly efficient at converting electricity into useable heat and do so in a compact, lightweight device that could be ideal for use in RV’s of the future.
Infrared heating works by using radiation to transmit heat. We’ve all experienced it when we walk out into warm sunshine. The radiation involved is not the harmful ionising type, but sits just below that of red light, hence the name infra-red or, infrared, as it’s more commonly referred to. Infrared heaters have been around for a long time, first coming to prominence for the industrial curing and drying of paints during the second world war.
As well as being a natural form of heat, infrared heating can be very efficient. That’s because it heats just the objects in its path and not the air in between. These objects can then re-radiate the heat to others that might not be directly in the path of the heater. The result of this efficiency is that infrared heating solutions often use less power than others.
Infrared heaters can be formed into a wide variety of shapes including very thin and light panels. This makes them ideal for all-electric RV’s – a fact that was recognised by Dethleffs in their all-electric concept RV, the e.home, first shown at Dusseldorf in 2017. It used infrared heating panels built into the floor, walls and furniture.
Phase change heat storage
The Dethleffs e.home also used something called phase change technology. This allows materials to absorb and store heat above a certain temperature and to release it when the temperature drops.
Phase change material have the advantage of a much higher energy density storage capability than those that don’t change phase. Also, the stored heat is released at an almost constant temperature. It’s the technology that’s used in those small hand-warming bags you might take to a football match. A liquid is triggered into crystallising and, in doing so, heat is steadily released. The process is reversed by heating the crystals until they become liquid again.
Heat pump technology
We already have heat pump technology in RV’s in the form of those reversible air conditioning units that can extract heat from the outside air and pump it into the RV. It may enter at high level, which is less than ideal, given that heat rises but it can still make quite a difference. For example, the Dometic, Truma and others each produce under-bench and roof-mount models that can output 1.7 to 3.0 kW in heat pump mode.
The advantage of heat pumps is their sheer efficiency. For every 1 kW of electricity used, approximately 3 kW is produced. Given that all-electric RV’s are on the way, this has to be a great way to heat them. On the other hand, heat pumps don’t work when the ambient temperature drops below freezing so some form of supplementary heating may be needed.
Another issue is weight, as compressors and drive motors are inevitably heavy items. However, compressor technology is improving and, in the next few years, we may well see hot water and climate control systems based on heat pump technology.
The hydrogen revolution
Vehicles powered by batteries alone are all very well but batteries tend to be expensive, heavy and space consuming. What’s more, lithium batteries also consume one of the earth’s scarcest resources – cobalt. Whilst technology advances will no doubt help to overcome some of these issues, there are those who think the long-term future lies with hydrogen power.
A vehicle fitted with a fuel cell and hydrogen tanks can produce its own electricity meaning that a much smaller battery is needed, just to smooth out the demands on the fuel cell. Such vehicles do exist but the cost of production and the lack of a hydrogen infrastructure have held them back so far.
If hydrogen technology catches on it raises the prospect of space and water heating powered by a good, independent, supply of electricity, or even by directly burning hydrogen. There is also the prospect of hydrogen replacing LPG for cooking. Swapping from LPG to hydrogen is not the easy switch you think it might be. Hydrogen burners need lots of fine nozzles rather than fewer larger ones. This is to prevent blow-back where the gas burns from the mixing jet rather than the burner itself.
Another factor is that hydrogen has a significantly higher flame speed than LPG and a greater flammability range. The traditional flame failure devices that rely on ionisation within the gas flame, don’t work with hydrogen. Couple these issues with the fact that hydrogen is likely to burn at a higher temperature, and significant engineering challenges emerge for appliance design.
We are already seeing plans for wind farms and solar arrays to use excess energy to produce hydrogen through the electrolysis of water. This ‘green’ hydrogen could be the key to powering the RV’s of the future.