Abstract
A possible system for heating and cooling of a train compartment has been modelled and simulated. This
system is a turntable HVAC unit developed at SINTEF, which is reversing the airflows to provide either
cooling or heating. It has two gascoolers and two evaporators for separate treatment of ambient and
recirculated air. The entire HVAC unit is rotated 180° to switch from heating to cooling mode. Carbon
dioxide, CO2 (R744) is a sustainable working fluid for such systems.
R744 systems have a large potential for expansion work recovery. If unrealized, this results in large
throttling losses at high ambient temperature operation. An ejector is therefore added to the heat pumping
circuit. In order to simulate the steady state and transient operation mode of the turntable HVAC unit a
simulation model was built using Modelica as programming language. The refrigerant cycle including the
ejector system was modelled based on the TIL-Library. Main focus of this study is the investigation of the
ejector system performance at different ambient conditions and required heat and cooling capacities.
Simulations were performed for the air reversing HVAC unit based on the heating and cooling demand when
operated in 5 European cities representing a wide climatic diversity. The COP for cooling mode ranges from
2 to 4.5, depending on load and occupancy rate. The COP in heating mode ranges from 6 to 2. The efficiency
decreases with reduced occupancy rate. The annual energy saving potential are calculated for all the 5 cities
of the study, compared to current HVAC systems for trains.
system is a turntable HVAC unit developed at SINTEF, which is reversing the airflows to provide either
cooling or heating. It has two gascoolers and two evaporators for separate treatment of ambient and
recirculated air. The entire HVAC unit is rotated 180° to switch from heating to cooling mode. Carbon
dioxide, CO2 (R744) is a sustainable working fluid for such systems.
R744 systems have a large potential for expansion work recovery. If unrealized, this results in large
throttling losses at high ambient temperature operation. An ejector is therefore added to the heat pumping
circuit. In order to simulate the steady state and transient operation mode of the turntable HVAC unit a
simulation model was built using Modelica as programming language. The refrigerant cycle including the
ejector system was modelled based on the TIL-Library. Main focus of this study is the investigation of the
ejector system performance at different ambient conditions and required heat and cooling capacities.
Simulations were performed for the air reversing HVAC unit based on the heating and cooling demand when
operated in 5 European cities representing a wide climatic diversity. The COP for cooling mode ranges from
2 to 4.5, depending on load and occupancy rate. The COP in heating mode ranges from 6 to 2. The efficiency
decreases with reduced occupancy rate. The annual energy saving potential are calculated for all the 5 cities
of the study, compared to current HVAC systems for trains.