High Limit Safety Cut-Out; Additional Function For Dhw Heating; Connecting The Dhw Circulation And Thermostatic Mixing Valve - Viessmann VITOSOL 200-FM SV2F Design Manual
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Solar System Design Guide
High Limit Safety Cut-out
The solar control units SCU124/224/345 and SM1
are equipped with an electronic temperature limiter.
A mechanical high limit safety cut-out in the tank is
recommended when the ratio of tank capacity to collector
absorber area is less than 1 USG/ft
reliably prevents temperatures above 200°F (95°C) in the
tank.
Additional Function for DHW Heating
In solar thermal systems with DHW storage, we recommend
heating the Solar preheat section of the tank to ≥ 140°F
(≥ 60°C) once a day (regardless of the cylinder volume).
Connecting the DHW Circulation and Thermostatic Mixing Valve
Single tank - solar preheat with DHW backup
Legend
A DHW circulation pump
B Automatic thermostatic mixing valve
C Check valve
D DHW circulation bypass line (required to prevent
heating of entire solar tank).
E DHW circulation line. Flow temperature
maximum 140°F (60°C).
F Cold water line to thermostatic mixing valve. Pipe
runs as short as possible, as these receive no flow in
winter.
G Dual coil tank heated by solar and boiler
H Single coil tank heated by boiler
I Single coil solar pre-heat tank
2
(40 L/m
2
). This
Example: 3x Vitosol 200-FM flat-plate collectors, 75 ft
2
(7 m
) absorber area DHW tank with 79 USG
(300 L) tank capacity.
79 USG / 75.3 ft
(300 L / 7 m
2
) = (42.8 L/ m
e.g. a high limit safety cut-out is not required.
We recommend that the heating operation take place in
the late afternoon. This will help ensure that the lower
tank area or the preheating stage is cold again following
the expected draw-offs (evenings and the following
morning) and can subsequently be heated up again by
solar energy.
Note: For detached and multi-family houses, this heat-up
is recommended, but not compulsory.
Check local codes to determine requirements for
this function.
Multiple tank - solar preheat in line with DHW tank
Design and Operation
2
= 1.05 USG/ft
2
2
)
2
87
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