Energy Saving Measures for Automotive Air Conditioning (AC) System in the Tropics

Transcription

1 Energy Saving Measures for Automotive Air Conditioning (AC) System in the Tropics Alison Subiantoro, Ooi Kim Tiow, Ulrich Stimming International Refrigeration and Air Conditioning Conference at Purdue R-20, ID: 2116, July 16, 2014

2 TUM CREATE 2

3 TUM CREATE Developing cutting edge vehicle technologies Pioneering future transportation concepts Meeting the growing transport challenges and need for sustainable mobility 3

4 TUM CREATE RP 7 RP 7 - Air Conditioning and Power Management Developing an energy efficient air conditioning (AC) unit for Electric Vehicle (EV) in the tropics with no limitation in its driving range. Three strategies are discussed here: 1) A higher indoor temperature setting 2) A smaller temperature lift between the condenser and the evaporator diagram.png 3) To use a dehumidification system 4

5 Methodology (1) MATLAB programming language R134a and R1234yf REFPROP database Benchmark AC system:» Negligible pressure losses in the heat exchangers and the tubes» 10 C superheat at the compressor inlet» Compressor s total efficiency of 60%» Condensing temperature is 20 C higher than the outdoor temperature» 10 C sub-cooling at the expansion device s inlet» Isenthalpic expansion process in the expansion device» Evaporating temperature is 5 C lower than the dew point temperature of the indoor air condition 5

6 Methodology (2) Benchmark AC system schematic: hot, humid air Ambient Expansion device Condenser Evaporator Compressor cold, dry air Air warmer cool, dry air Car cabin 6

7 Methodology (3) Thermal loads in the cabin: 1. Solar irradiation» Constant at 1 kw/m 2» Exposed car window area of 2 m 2» Window glass transmissivity of Passengers body heats» Four (4) passengers, each 120 W of heat 3. Heat from the car body» Thermal conductivity of W/m 2.K» Effective area of 3 m 2 4. Air treatment (cooling and dehumidification)» Air flow rate = 0.06 kg/s» Car cabin = C, 60% rh» Outdoor = C, 80-90% rh 7

8 Strategies Strategies to reduce energy consumption of car air conditioned discussed here: 1) Higher indoor temperature setting 2) Smaller temperature lift between condenser-evaporator 3) Separation of cooling and dehumidification 4) Combined methods 8

9 Higher Indoor Temperature No additional component or major modification to the system Increasing indoor temperature from 20 C to 24 C reduces compressor power requirement by up to 22% and increases COP by up to 13% Energy saving is because of the higher required evaporating temperature 9

10 Smaller Temperature Lift Temperature difference between the condensing and the outdoor temperatures is reduced from 20 C to 10 C (no change in the evaporating temperature) Compressor power requirement can be reduced by more than 30%, COP can increase by up to 45% With a higher indoor temperature setting of 24 C, compressor power requirement is reduced by up to 45%, COP increases by more than 60%. A more efficient heat exchanger is necessary for this method. In the case simulated here, the effective area of the condenser needs to be doubled. 10

11 Dehumidification System (1) In a conventional AC system, fresh air is cooled to its dew point temperature (about 12 C) to remove the moisture In this studied case, the air is first dehumidified by using a dehumidification system before being cooled 11

12 Dehumidification System (2) Assume: evaporating temperature is 5 C below the corresponding dew point temperature (same as the benchmark system) Compressor power consumption can be reduced by more than 50% With a higher indoor temperature of 24 C, compressor power requirement can be reduced by up to 60% 12

13 Dehumidification System (3) With a dehumidification system, the evaporating temperature can be higher Assuming that the evaporating temperature is 5 C below the indoor temperature (not the dew point temperature), the power saving is more than 60% The effectiveness is highly dependent on the air flow rate. When air flow rate is halved, power saving is only 54%. When air flow rate is doubled, the power saving is as high as 68%. 13

14 Dehumidification System (4) The energy required for regeneration of the desiccant in the dehumidification system must be supplied from waste energy to make the energy balance positive In cars, this energy can be from the waste heat of the engine or from the condenser A design challenge in mobile applications is to design the device small and lightweight Another practical challenge is the need to rearrange the car components 14

15 Combined Methods Combining dehumidification system and a smaller temperature lift can save up to 65% of compressor power. When indoor temperature is 24 C, a dehumidification system is used and the temperature lift is smaller by 10 C, the compressor power requirement is reduced by up to 70%. 15

16 Summary No Method Higher indoor temperature (from 20 C to 24 C) Smaller temperature lift (from 20 C to 10 C difference at the condenser) Smaller temperature lift and higher indoor temperature (from 20 C to 24 C) Power Saving Potential COP Increase Potential Remarks 22% 13% No additional component is necessary 30% 45% 4 Dehumidification system 50% Dehumidification and higher indoor temperature (from 20 C to 24 C) Dehumidification and smaller temperature lift Dehumidification, smaller temperature lift and higher indoor temperature (from 20 C to 24 C) More advanced heat exchangers are required 45% 60% Same as remark (2) 60% 13% Same as remark (4) A dehumidification system is needed, external waste energy is used for regeneration, rearrangement of car components maybe necessary, effectiveness depends on operational air flow rate 65% 45% Same as remarks (2) plus (4) 70% 60% Same as remarks (2) plus (4) 16