Reliable and efficient
Electromobility is the future, but there are still many aspects that need to be dealt with. One of the key issues is the range that needs to be increased by continuously optimising all components. What’s more, electric buses do not produce waste heat that can be used to heat the passenger compartment. Electromobility therefore requires highly efficient auxiliary consumers and an integrated heating and cooling strategy.
The idea: an air-conditioning system for electric buses that increases the range and saves money on service and maintenance while adding ecological value at the same time.
The result: an integrated thermal management system for electric buses – 100% needs-based and customisable with maximum efficiency – the Konvekta CO2 heat pump.
- How does a heat pump work?
The principle is actually quite simple: heat or cold is extracted from a natural source of energy (air) to be used for heating in winter or cooling in summer.
1 KW energy becomes 4 KW power. (COP Coefficient of Performance = 3)
The Konvekta CO2 heat pump uses CO2 (R-744) as carrier.
The CO2 (R-744) refrigerant assumes the task of transmitting or transporting heat or cold in the circuit of the heat pump.
- Step 1: The CO2 (R-744) refrigerant “evaporates”
In the evaporator, the refrigerant “boils” at very
low temperatures and the energy/heat absorbed
during this process is stored.
- Step 2: The gas heats up under pressure
Now the volume of the CO2 (R-744) refrigerant
gas in the compressor is reduced = compressed.
This increases the pressure and the temperature
of the refrigerant.
- Step 3: The CO2 (R-744) refrigerant cools down and absorbs heat again
The hot refrigerant now flows to the gas cooler (condenser).
Here, the extracted ambient heat is transmitted to the interior of the vehicle and the refrigerant cools down.
- Step 4: “Decompression” through the expansion valve
The refrigerant is then decompressed to lower pressure and temperature through the expansion valve allowing it to absorb new heat from the environment.
The cycle thus restarts from the beginning.
The new Konvekta CO2 heat pump 2.0 is a comprehensive and load-synchronous thermal management system. This system consists of the roof unit and two new Konvekta energy carrier modules. The desired auxiliary consumers can be heated or cooled at the same time with these new components. For example, the front box and convectors in the interior can be heated and the batteries can be cooled at the same time. This way the second generation Konvekta CO2 heat pump can be customised to fit all bus types.
- refrigerant CO2 (R744)
- components developed in-house (e.g. heat exchangers)
- Energy Collect (Heat recovery from heat-generating components = 15 -20% energy savings)
- Konvekta control unit "CleverControl"
The energy consumption in comparison shows that of the possible variants of air conditioning an electric bus, the CO2 heat pump is the most energy-efficient.
The heat pump reduces energy consumption with zero emissions e.g. by 60% at -10°C in comparison to classic electric heating systems.
If you look at the entire year, including air conditioning, the energy requirement is reduced by more than 50%.
These energy savings could be used to increase the range. The increase in range depends upon the weather conditions and the type of the vehicle.
► Increasing the range up to 60 %
The heat pump requires a maximum of 50% of the drive power in comparison to an electrical heating device, therefore only half of the additional installed battery capacity will be required. Including the battery change that is required, this results a
► Saving of € 18.250 (in addition, the service life of the batteries will be increased)
The batteries can also be designed smaller, and at the same time their service life will ne increased. This represents another major benefit for the environment and a considerable cost saving.
Every system needs additional heating. The only question is how often you need additional heating.
If you look at the average climate in Germany, you can see that there is a temperature window from -13 ° C to 35. (travel time from 5:00 to 23:00)
The Konvekta CO2 heat pump 2.0 covers 100% of this window. That means: even at an outside temperature of -20 ° C it is pleasantly warm inside the vehicle and in summer it is still pleasantly cool even at 40 ° C.
With the other variants, additional heating is required very early on, this costs money or reduces the range of the vehicle.
The Konvekta CO2 heat pump requires no additional diesel heating and therefore no fossil fuels (e.g. diesel fuel). That means: there are no costs for heating the vehicle and no exhaust gases.
Other systems (e.g. a heat pump with R134a) very often require additional heating energy each year to air-condition the passenger compartment. This creates high costs. To heat a city bus for one year, you need the same fuel requirement as for a small family home.
In the area of service and maintenance, CO2 results in considerable cost and time savings. This is because there is no need to recover or dispose of this refrigerant (R744) after any maintenance or repair work.
The simple and safe handling of the R-744 means that service times are reduced by more than half compared to the R-134a. Since R-744 is not a chemical refrigerant, it is not subject to the ChemKlimaSchutzVO.
The acquisition costs for the refrigerant per kg are over 90% lower.
Another benefit is the use of UltraLight technology. The extremely light and stable high-performance material forms the basis for holding all components, which makes exchanging components extremely easy. Filters, fans and other components are replaced in a few seconds.
This results in an overall saving in service costs of approx. 70%.