Why don’t buses have air-conditioning?

It’s that time of year again with glorious hot weather on the way, so I thought I’d take the time to answer a question that is often asked by bus users here in the West Midlands.

Short answer

For the number of days per year when it would actually be useful, it is not worth the cost to UK bus operators to provide it.

Long answer

Air-conditioning (aircon) systems work best in a closed environment. Most cars and small vans have an aircon system installed, so anyone who has travelled in a car with one will understand how it works and the effect it brings.

A car aircon system only works effectively when the windows are left closed. Air within the cabin is circulated through the HVAC (heating, ventilation and air conditioning) system and is cooled as it passes through an evaporator, which is the reverse of a car heater, which warms the air using the hot water in the engine cooling system.

And therein lies the first problem: if a bus had aircon fitted and working, the interior saloon windows would need to be kept closed.

The second problem is that even if the windows were kept closed so the aircon system could effectively cool the cabin air, every time the bus stops and opens the door(s) to let passengers on/off, warm air from outside is allowed to enter the cabin, which then means the aircon system is continually working to maintain the desired interior temperature.

Coaches don’t have this problem, as they tend to travel long distances between stops, so aircon is more effective and useful to coach operators. Same applies to trains, as these now don’t have windows that passengers can open.

The other disadvantage to aircon systems is how they are powered. The compressor is the beating heart of the system, and it is driven by belts on the engine. As the engine has to work harder, it ends up consuming more fuel, as anyone who drives a car with aircon running can testify! More fuel means more costs to the operator to operate that vehicle and the service it runs on.

As electric vehicles don’t have a ‘traditional’ combustion engine with rotating parts to drive it, their aircon compressors are electrically powered, much like what you would find in your fridge-freezer at home, but on a bigger scale. As a result, using aircon in an electric vehicle consumes more battery power and thus reduces the operating range of the vehicle. Which in the case of buses is not very useful, as it limits the number of journeys they can complete before requiring recharging.

Aircon systems also require regular maintenance and servicing, which also increases engineering costs of maintaining vehicles.

In summary

The main reasons why UK buses don’t have air-conditioning can be summarised as follows:

Climate: The UK generally has a mild climate, and there are only a few days in the year when temperatures are extremely high. As a result, the need for air conditioning in buses is not as high as in countries with hotter climates.
Cost: Installing and maintaining air conditioning systems in buses can be expensive. Given that the UK does not experience extreme heat for long periods, the cost-benefit analysis may not always justify the investment in air conditioning systems for buses.
Energy efficiency: Air conditioning systems consume a significant amount of energy, which can increase fuel consumption and emissions from buses. In an effort to reduce carbon emissions and promote environmental sustainability, some bus operators may choose not to equip their buses with air conditioning.
Ventilation: Many buses in the UK are designed with windows that can be opened to allow for natural ventilation. While this may not be as effective as air conditioning in cooling the interior of the bus, it can still provide some relief on warmer days.

In addition to the above, you also have the effort that would be required to educate passengers about keeping windows closed on hot days, in order for the aircon to actually work properly!

So while it would be nice to travel on an air-conditioned bus on a hot day, the reality is that we don’t actually get very many hot days for it to be worthwhile.