Environmental Engineering Reference
In-Depth Information
Coeffi cient of Performance (COP) and Annual Coeffi cient
of Performance
The ratio of transient transmitted heat fl ow
Q
heating
to transient, usually electric, drive
power
P
is called the coeffi cient of performance
ε
Q
Q
QQ
heating
heating
ε =
=
P
−
heating
source
The abbreviation for coeffi cient of performance is COP. The power output
P
and the
refrigerating capacity
Q
source
of the low-temperature heat source together produce
the heat fl ow
Q
heating
:
QP Q
heating
=+
source
If, for example, a heat pump with electrically driven power
P
= 3 kW produces heat
fl ow of
Q
heating
= 9
kW
, the coeffi cient of performance is
ε
= 3. The difference of
Q
source
derives from the low-temperature heat source.
The coeffi cient of performance only applies to transient values. What is interesting
is the annual average. This is called an annual coeffi cient of performance.
= 6
kW
A high annual performance coeffi cient is essential for the ecological and economical
operation of a heat pump. With an annual performance coeffi cient of 4, for example,
a heat pump can cover a heating requirement of 10 000 kilowatt hours per year using
2500 kilowatt hours of electric energy. With an annual performance coeffi cient of
2, the requirement for electric energy rises to 5000 kilowatt hours.
Very good systems reach annual performance coeffi cients of about 4. In practice,
the values are often below this. Table 11.1 shows typical annual performance coef-
fi cients for different types of heat pumps from a fi eld test in Southern Germany.
Table 11.1
Typical annual performance coeffi cients for electric heat pumps
(Lokale Agenda-
Gruppe 21 Energie/Umwelt in Lahr, 2007).
Heat pump
Heat source
Annual performance
coeffi cient with
underfl oor heating
Annual performance
coeffi cient with
radiators
Brine/water
Ground
3.6
3.2
Water/water
Groundwater
3.4
3.0
Air/water
Air
3.0
2.3
The heat pumps that draw their heat from the ground produced the best values. The
annual performance coeffi cients for groundwater heat pumps were somewhat lower.
The reason is that it takes more pumping effort to extract groundwater than it does
to exploit heat from an enclosed brine loop in the ground. Furthermore, dirt traps
