Page 138 - Low Temperature Energy Systems with Applications of Renewable Energy

Effective use of heat pumps for various heating applications 127

3.5.6 Economic comparison of the efficiency of various heat
sources
A comparison of different types of heat pumps is carried out according to an economic
criterion, i.e., by the equivalent fuel consumption B b in kg/s for the generation of the
specified thermal power Q 0 in kJ/s or kWt. Fuel consumption (in coal equivalent) for a
boiler is:

Q 0
B b ¼ ; (3.3)
29:3$h b
where 29.3 MJ/kg is the heat of combustion of coal fuel equivalent; h b is the boiler
efficiency.
For a vapor-compression heat pump (VCHP) with an electric drive:

Q 0
B HP ¼ (3.4)
29:3$h $h $COP HP
e
el
where h el is efficiency of an electric generating plant; h e is efficiency of power transfer
in transmission lines and networks.
For an absorption heat pump (ABHP):

Q 0
B ABHP ¼ ; (3.5)
29:3$M$h g

where M ¼ Q 0 /Q g ; Q g is the heat added in the generator; h g is generator efficiency.
For the purpose of comparison, noting that the quantity Q 0 /29.3 is a constant, we
obtain:
Boiler:

1 1
B b ¼ ¼ ¼ 1:11 kg=s. (3.6)
h 0:90
b
Vapor compression heat pump:
1 1
B HP ¼ ¼ ¼ 1:06 kg=s. (3.7)
h $h $COP HP 0:33$0:95$3
e
el
Absorption heat pump:
1 1
B AHP ¼ ¼ ¼ 0:65 kg=s. (3.8)
M$h g 1:7$0:9