Environmental Engineering Reference
In-Depth Information
Chapter 3
Solar Thermal Water Heating
I
NTRODUCTION
Solar thermal systems are an important use of solar energy. The use of solar
thermal applications has a long history: Archimedes is reported to have boiled
water using a concave mirror as early as 214 BC; thermal systems today still
represent the most cost-effective use of solar energy.
Solar thermal
signifies the thermal use of solar energy in general.
Therefore, a number of different technical applications exist. Besides building
space heating, water heating or industrial processes, solar thermal systems can
be used for cooling applications or electricity generation with solar thermal
power plants. The main operational areas are:
•
solar swimming pool heating
•
solar domestic water heating
•
solar low-temperature heat for space heating in buildings
•
solar process heat
•
solar thermal electricity generation.
Since these operational areas are very far reaching, this chapter discusses only
the main aspects of solar domestic water and swimming pool heating with
closed and open solar collector systems. The following sections require the use
of some thermodynamic quantities in the explanation of the principles. Table
3.1 summarizes the most important parameters and their symbols and units.
Table 3.1
Thermodynamic Quantities for Thermal Calculations
Name
Symbol
Unit
Heat, energy
Q
Ws (= J) or kWh
•
Heat flow
W
Temperature
ϑ
°C
Thermodynamic temperature
T
K (Kelvin, 0 K = -273.15°C)
Specific heat capacity
c
J/(kg K)
Thermal conductivity
λ
W/(m K)
Heat transition coefficient
k'
W/(
mK
)
W/(m
2
Coefficient of heat transfer
k
K)
W/(m
2
Surface coefficient of heat transfer
α
K)
