Functional Design of the mCCHP-RES System - Design for Micro-Combined Cooling, Heating and Power Systems - page 258

From the product data sheet choose the solar thermal collector with nominal
absorber area A ST n ciency g ST o . By knowing these data of the solar

collector, it is possible to determine the number of the solar thermal collectors
which is given by the equation:

and optical ef

A ST
g STo

n ST [ ð 20 Þ

A ST n

m 2 ]. The All solar thermal collectors can operate at a variety of flow rates in [l/h ·

flow rate will affect the pressure drop of the collectors and also change the tem-
perature increase across the panel. Generally a low m 2 )is

desired because it minimizes the pressure drop through the system resulting in
smaller pipes and less energy to run the pump. The

low rate (typically 30 l/h ·

flow rate selected needs to take

the heat exchanger into account to ensure suf cient heat transfer from the solar

system to the tank. The temperature increase across the collectors is driven by the
level of irradiation, the angle of the sun, and the outdoor temperature. Once the
energy output of the collector is known, the increase in temperature can be com-
puted with equation:

Q day
q

D# ¼ ð 21 Þ

V c

This increase in temperature across the solar collector is used in setting of the
solar controllers while the pump speed is varied to maintain this value.

B. Backup boiler (additional boiler)
The main technical characteristics of the back-up boiler are:

Thermal power [kW],

￿

Ef ciency g ST [%],

￿

Nominal volume flow of the hydraulic circuit [l/h],

￿

Max. operation pressure [bar].

￿

The required characteristic which is imposed by the system functioning, and
based on which the backup boiler is chosen from the market and embedded into the
system, is the maximum thermal power that must be supplied.
For sizing the backup boiler, the maximum thermal power should be determined
in the following steps:

(a) Determining the amount of energy produced by the backup boiler Q ad : max ,in
the month in which its load is the biggest:

Q ad : max ¼ A TFA q ad : max ½ KWh = month ð 22 Þ