Service Training

Self Study Program 880153

The Heat Pump from Volkswagen
Design and Function

Volkswagen Group of America, Inc.
Volkswagen Academy
Printed in U.S.A.
Printed 7/2015
Course Number SSP 880153

©2015 Volkswagen Group of America, LLC.
All rights reserved. All information contained in this manual is based
on the latest information available at the time of printing and is
subject to the copyright and other intellectual property rights of
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Always check Technical Bulletins and the latest electronic repair
information for information that may supersede any information
included in this booklet.
Trademarks: All brand names and product names used in this manual
are trade names, service marks, trademarks, or registered trademarks;
and are the property of their respective owners.

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Basic Principle of the Heat Pump. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
The Heat Pump in the e-Golf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Function of the Heat Pump. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
System Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Knowledge Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Note

This Self-Study Program provides information
regarding the design and function of new
models.

Important!

This Self-Study Program is not a Repair Manual.
This information will not be updated.
For maintenance and repair procedures, always
refer to the latest electronic service information.

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Introduction
Heat pump technology has been used in buildings for many years to reduce heating and cooling costs. At Volkswagen, this
efficient technology is being used to produce heat in the e-Golf.
The heat pump system is a refrigerant circuit that is made up of numerous components. In this SSP, we will simply call it the
heat pump.
In cars with an internal combustion engine, the heat produced by the engine can be used to heat the passenger compartment.
Electrically driven vehicles, however, do not produce enough thermal energy to heat the vehicle interior.
Using a heat pump allows the heat from the outside air and the heat produced by the drive components to heat the vehicle
interior. As a result, less battery power is required by the electrical high-voltage heater, reducing energy consumption. The
range of the e-Golf with a heat pump is 30% greater with a heat pump than without one.

s532_006

1

Introduction
Physical Laws
What is heat?
Heat (mathematical symbol of Q, unit of joule) is a form
of energy that is transferred between two systems due to
temperature differences.
Heat always flows from a body of high temperature to a
body of low temperature.
Heat can be transferred through thermal conduction,
thermal radiation or convection.

Phase Transition

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The phases of water

There are three primary states of matter that substances
can change between due to temperature or pressure; solid,
liquid and gas.
Freezing

Condensation

Melting

Vaporization

To change its state of matter, a body must either absorb or
release thermal energy:
• Melting: The transition from solid to liquid state. Heat
is absorbed.
• Vaporization: The transition from a liquid to a gaseous
state. Heat is absorbed.
• Condensation: The transition from a gaseous to a
liquid state. Heat is released.
• Freezing: The transition from a liquid to a solid state.
Heat is released.

2

Solid

Liquid

Gas

Introduction
Heat Pump
General Information
Heat pump technology makes use of these laws.
Water flows downhill by itself, but needs to be pumped uphill. The same can be said of heat: it automatically “flows” from a
higher to a lower temperature level. Heat pumps use electrical energy to pump heat against the natural “temperature flow”
from a lower to a higher temperature level.
Task
Heat pumps transport thermal energy from one location to another. They have been used in buildings for a long time for
heating. Heat pumps have lower energy consumption, lower pollution levels and lower operating costs than traditional heating
methods.

Source of Heat
Heat Pump
Heating

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When reversed, this principle is used for cooling in refrigerators and air conditioning systems.

3

Introduction
Refrigerant
The heat pump uses R134a refrigerant. It is a chlorofluorocarbon (CFC) with a low boiling point. R134a is invisible in gas form
and is colorless like water when in vapor and liquid states.

Characteristics
F

• Designation:

tetrafluorethane

• Chemical formula:

CH2F-CF3

• Boiling point:

-26.5°C (at approx. 1 bar)

• Solidification point:

-101.6°C

• Critical temperature:

100.6°C

• Critical pressure:

4.056 MPa (40.56 bar)

F

F
C
C

H

F
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H

Pressure and Boiling Point
The boiling point is the temperature at which a substance changes from liquid to gaseous state. The boiling point of a
substance is always given at normal atmospheric pressure (1.01325 bar). The boiling temperature varies according to the
pressure. It falls at low pressure and rises at high pressure. This behavior is illustrated as an evaporation curve in the pressuretemperature graphs.
Water

R134a
bar

1.0

9

0.9

8

0.8

7
Pressure [bar]

Pressure [bar]

0.7
0.6
0.5
0.4
0.3

6
5
4
3
2

0.2

1

0.1

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0 10 20 30 40 50 60 70 80 90 100

-40

-20

0

20

40

60

These physical properties of R134a refrigerant are used in the heat pump. By specifically changing the pressure and the
temperature, the refrigerant is able to:
–– evaporate and absorb heat at ambient temperature or
–– condense and release heat at ambient temperature.

4

Basic Principle of the Heat Pump
Circuit Design
A heat pump basically consists of the following main components: a compressor, an evaporator, an expansion valve and a
condenser.
In the closed heat pump circuit, the refrigerant circulates and changes between liquid and gaseous state, transferring and
transporting heat. There is always a high pressure side and a low pressure side in this circuit.

Outside Air
(airflow/fan)
Expansion Valve

Evaporator
Cooled Air
Outside Air
(airflow/fan)

Electrical Power
Supply

Compressor
Heated Air for Interior

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Condenser

Function
• The compressor draws in cold, gaseous refrigerant at low pressure and compresses it under high pressure. The
temperature rises. In this phase, the refrigerant is gaseous and under high pressure at a high temperature.
• Cold air (airflow/fan) flows through the condenser. The refrigerant transfers heat to the air and condenses. The heated
air flows into the interior. In this phase, the refrigerant is liquid and under high pressure at medium temperature.
• The pressure of the liquid refrigerant is reduced significantly in the expansion valve. The reduced pressure leads to
partial evaporation of the refrigerant. After expansion, the temperature of the refrigerant is significantly lower than the
ambient temperature.
• In the evaporator, the pressure of the refrigerant being sprayed is further reduced and it evaporates. The heat of
vaporization required for this process is drawn from the warmer outside air, which then cools. The now gaseous
refrigerant leaves the evaporator.

5

Basic Principle of the Heat Pump
Phase Diagram of R134a Refrigerant

Pressure [bar]

This diagram represents the phases of R134a in a heat pump circuit. You can see the energy content, the pressure, the
temperature and the state of the refrigerant in each process. Other absolute values occur depending on the outside air
temperature and the heating requirement inside the vehicle.

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Energy Content (kJ/kg)

Gaseous Refrigerant

High-pressure Region

Wet Steam Region of Refrigerant

Low-pressure Region

Liquid Refrigerant

Line of Constant Temperature (temperature curve)

Gas/liquid Region Borderline

Explanation
A - B: compression
The refrigerant is gaseous; the pressure and the
temperature rise.
B - C: condensation
The refrigerant turns to liquid, the temperature falls
and the pressure remains constant.
C - D: expansion
The pressure reduction leads to partial evaporation of
the refrigerant and the temperature falls.

6

D - A: evaporation
The refrigerant becomes completely gaseous, the
temperature rises slightly and the pressure remains
constant.
K: critical point
The boiling line is to the left of the critical point and
the saturated vapor line is to the right of it.

The Heat Pump in the e-Golf
System Configuration
Components like the electrical air conditioner compressor, the evaporator and the condenser run the air conditioning system
in the e-Golf. The refrigerant circuit of the air conditioning system has been expanded for use with the heat pump to include
refrigerant lines, electrical expansion valves, pressure senders, temperature senders and a heat condenser.
Since the heat pump system for the e-Golf also uses the heat produced by the motor and the power and control electronics for
electric drive, a second expansion valve and a heat exchanger for the heat condenser are used in parallel to heat pump circuit.

Refrigerant Circuit
Pressure and Temperature Sensors

Expansion/Shut-off Valves

Condenser

Electrical Air Conditioner
Compressor

Heat Exchanger for Heat Condenser
Evaporator

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Heat Condenser

7

The Heat Pump in the e-Golf
Schematic Diagram of the Coolant and Refrigerant Circuits
This schematic diagram provides a basic illustration for subsequent descriptions of components and the functions of the heat
pump.
G395

V470

G829

N642

Refrigerant Circuit

Reservoir
N643

N696

G827

G826

N636

Condenser

N637

G828

Heat Condenser

N638

Evaporator

Heat Exchanger for Heat Condenser
G110

G787
Z115

Non-return Valve