computerSaysNo
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Tldr[1] at the end of the post.
My local bus company are soon to receive a batch of Volvo BZL DD vehicles (Double Deck buses on the electric Volvo BZL chassis), and I noted with disappointment that they will still have opening hopper windows like the previous diesel buses had. This suggests to me that the vehicles will not have saloon air conditioning.
It was my understanding that conventional diesel buses and coaches used electricity passed through resistors to create heating in the saloon (alongside waste heat from the engine). As a short explanation: a wire or cable has a low resistance, allowing electricity to pass through it with ease. The electricity will then encounter the resistor element; this has a high resistance to the passage of electricity, and so when electricity passes through it the current is consumed and heat is released. The efficiency of this is roughly 100% i.e. 1KW of electricity put into the heater generates 1KW of heat energy.
This is obviously fine with a diesel engine as the alternator (converts rotation from the engine into electricity) is constantly running so there's generally an abundance of electricity. However with electric vehicles, electricity needs to be rationed, and so a heating system with greater efficiency would, I would have thought, been an obvious choice. Enter the heat pump.
Heat pumps work by moving heat around. Air Source Heat Pumps, as would be installed on moving vehicles, take in a medium-temperature air flow, and split it into a warm air flow and a cool air flow.
An electrically-driven compressor compresses refrigerant in pipes, causing it to heat up. The airflow is passed around those pipes, transferring the heat energy from the compressed refrigerant to the air. The refrigerant at this point then is compressed but no longer hot. When it is allowed to decompress, it expands and cools down in different pipes; (different) air flows around these pipes which transfers the heat from the air to the refrigerant. Thus the air is now cool, and the refrigerant is at roughly ambient temperature.
If heating is desired, as it would be in electric buses, the warm air is directed to the saloon and the cold air is dumped outside. If cooling is required, the cool air is directed to the saloon and the hot air is dumped outside. Heat pumps are more efficient[2] than resistance heaters as they use the electricity to move heat, rather than using it directly to create heat. Heat pumps are usually 200-400% efficient i.e. 1KW of electricity in gives between 2KW and 4KW of heat out (depending on various other factors).
An important additional benefit of heat pumps to passengers is that they can also cool the air.
Electric vehicles require heating and ought to use the most efficient method of doing so, which is heat pumps - this effectively means the vehicle would then be fitted with full climate control, however this can only be effective if passengers don't open windows and allow the treated air to escape.
Tldr, and my question, therefore, is this: what kind of heaters do Volvo or MCV, the bus body builder Volvo are partnered with, fit to their electric buses?
If resistance heating: why?
If heat pumps: why are the vehicles still fitted with opening windows?
[1]: "Tldr" = Too Long; Didn't Read. The Tldr section is a short summary at the end of the main body of text.
[2]: heat pumps set to heat are usually more efficient than resistance heating. There are exceptions to this but I'm going to say that those are outside the scope of this thread.
My local bus company are soon to receive a batch of Volvo BZL DD vehicles (Double Deck buses on the electric Volvo BZL chassis), and I noted with disappointment that they will still have opening hopper windows like the previous diesel buses had. This suggests to me that the vehicles will not have saloon air conditioning.
It was my understanding that conventional diesel buses and coaches used electricity passed through resistors to create heating in the saloon (alongside waste heat from the engine). As a short explanation: a wire or cable has a low resistance, allowing electricity to pass through it with ease. The electricity will then encounter the resistor element; this has a high resistance to the passage of electricity, and so when electricity passes through it the current is consumed and heat is released. The efficiency of this is roughly 100% i.e. 1KW of electricity put into the heater generates 1KW of heat energy.
This is obviously fine with a diesel engine as the alternator (converts rotation from the engine into electricity) is constantly running so there's generally an abundance of electricity. However with electric vehicles, electricity needs to be rationed, and so a heating system with greater efficiency would, I would have thought, been an obvious choice. Enter the heat pump.
Heat pumps work by moving heat around. Air Source Heat Pumps, as would be installed on moving vehicles, take in a medium-temperature air flow, and split it into a warm air flow and a cool air flow.
An electrically-driven compressor compresses refrigerant in pipes, causing it to heat up. The airflow is passed around those pipes, transferring the heat energy from the compressed refrigerant to the air. The refrigerant at this point then is compressed but no longer hot. When it is allowed to decompress, it expands and cools down in different pipes; (different) air flows around these pipes which transfers the heat from the air to the refrigerant. Thus the air is now cool, and the refrigerant is at roughly ambient temperature.
If heating is desired, as it would be in electric buses, the warm air is directed to the saloon and the cold air is dumped outside. If cooling is required, the cool air is directed to the saloon and the hot air is dumped outside. Heat pumps are more efficient[2] than resistance heaters as they use the electricity to move heat, rather than using it directly to create heat. Heat pumps are usually 200-400% efficient i.e. 1KW of electricity in gives between 2KW and 4KW of heat out (depending on various other factors).
An important additional benefit of heat pumps to passengers is that they can also cool the air.
Electric vehicles require heating and ought to use the most efficient method of doing so, which is heat pumps - this effectively means the vehicle would then be fitted with full climate control, however this can only be effective if passengers don't open windows and allow the treated air to escape.
Tldr, and my question, therefore, is this: what kind of heaters do Volvo or MCV, the bus body builder Volvo are partnered with, fit to their electric buses?
If resistance heating: why?
If heat pumps: why are the vehicles still fitted with opening windows?
[1]: "Tldr" = Too Long; Didn't Read. The Tldr section is a short summary at the end of the main body of text.
[2]: heat pumps set to heat are usually more efficient than resistance heating. There are exceptions to this but I'm going to say that those are outside the scope of this thread.
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