Adequate heating of buses is tricky, and it is particularly the case with electric drivetrains. Clayton Herschel has an all-new infra-red system that it says is highly efficient and low maintenance
Ensuring that a bus interior is warm during cold weather has long been a challenge. At Euro 6 it’s even more of a balancing act, as the engine and exhaust run at a high temperature for the latter to function correctly, meaning that the harvesting of waste heat may be restricted.
Heating an electric bus is also contentious. A diesel-fired unit may be unacceptable, while resistance heaters and air-conditioning units compromise range.
In both of these cases and more, infra-red (IR) heating is an option.
That’s according to Clayton Herschel, which is working with bus manufacturers to develop the concept. It says that IR has several benefits over conventional heating.
“In the past it was easiest to use waste heat, but as engines became more efficient there was less of it,” says Director Dean Allsop.
“Waste heat is also less easy to come by in buses with engine stop-start, while for obvious reasons there is none in those with electric drivelines.
“In the latter, resistance heating is inefficient; in a single-decker it consumes up to 20kW, making it a non-starter.”
A different way
Clayton Herschel’s IR product is a new approach to heating buses, says Dean. “IR rays warm surfaces, not air. IR Panels are usually in the roof, but they can be mounted elsewhere, including in coves or sidewalls.”
Alexander Dennis and Wrightbus are currently working with Clayton Herschel on IR heating. Both manufacturers favour ceiling-mounted units and Clayton Herschel has thought hard about this strategy.
“When in use, the IR panel is hot. At the front of a single-decker that’s no problem, but where the floor is higher, or upstairs on a double-decker, it is undesirable. We fit lower output panels in these locations; they are 70W compared to 100W at the front of a single-decker and reach a much lower temperature.”
IR heaters are being tested at the moment. “There is an advantage over conventional heating systems in that we are not heating air that will potentially be expelled at the next stop,” says Dean.
“We are heating people’s skin and items on the bus; the analogy is that it is the same effect as the sun shining on you.”
Trials have shown that the temperature of items that the IR rays come into contact with rises to 17-18oc within an hour. Opening and closing the doors has no effect.
The benefits are…
“Advantages of IR systems include weight reduction; there is potentially a 40kg saving over hot water heaters,” he adds. The IR panel is around 1.5mm thick and it can be cut to a size and radius to suit.
“IR heating can also be fitted in the cab. As a result, no water is pumped beyond the engine compartment.
“We advise bus builders to also fit a heated windscreen, but IR heating creates less condensation than warm air and so it has a demisting effect anyway.
“They tell us that they are happy with that and we have retrofitted IR heating to some driver training buses in London. There have been no complaints.”
Further retrofits, in both diesel and electric buses, are likely, adds Dean. “We are talking to operators in London about it and they see the benefits that IR heaters give in terms of reduced costs.
“There are no maintenance requirements with IR heating and the panels have a 100,000 hour life. Where retrofits include the cab it may be necessary to upgrade the vehicle’s alternator, but other than that it is a simple task.”
Retrofit capabilities
Retrofitting IR heating is a fully viable option, says Dean. “We are looking at installing it into two BYD double-deckers with Metroline; it has been approved by Transport for London. The auxiliary diesel heaters will likely be left initially with but they may be removed later,” says Dean.
“In diesel buses we would probably leave the existing heating infrastructure in place because it is more troublesome than it’s worth to remove it.”
IR heating will prove most attractive in electric buses, however. It has a power draw that is much lower than either resistance heaters or air-conditioning, and individual panels can be switched off during the day or dependent on external temperatures to reduce power draw.
“There are other benefits of IR heating on electric buses. We can configure it to engage during opportunity charging, or when plugged in overnight.
“In the latter case, that reduces power draw during the day. The system can also be programmed to start an hour before the bus leaves the depot.”
So far IR heating is working well on a prototype basis. Within three months Clayton Herschel expects to be producing significant numbers of the panels at its Coventry factory.
“There is some scepticism because IR heating consumes a fraction of the energy of electric heaters, but we have done lots of work to ensure that the rays go where they are needed,” says Dean.
“Energy for heating has to come from somewhere, whether the bus is powered by diesel or electric. We are continuing to develop IR; not to gain efficiency, but to build it into the vehicle differently. There are a lot more benefits to it than there may first seem.”
