andrews R18 Series, Technical Documentation Manual

Page: 15 / 71

18IP22B
7
Fig. 7 Heat exchanger
Fig.8 Pump and bypass with water connections
Heat exchanger
The heat exchanger (type 2-pass) is mounted on the chassis.
To ensure proper heat transfer of the combustion gases, the
copper fin tubes are arranged side by side and expanded
laterally into a mounting plate. The baffles on the copper fin
tubes optimize the efficiency of the heat exchanger. The stain-
less steel supply and return pipes together with the water mani-
folds form the heat exchanger and is
pressure tested at 16
bar . The R18 water heater is supplied with a primary pump ,
to ensure the optimum flow rate and a bypass (see fig. 8).
Primary pump
The primary circulating pump is sized to prevent the depositing
of limescale in the water heater under the following conditions.
Water hardness in ppm Maximum temperature in °C
0 - 80 90
80 - 250 85
250 - 350 80
350 - 500 60
Table 2 Maximum temperature