Solar Thermal Information

19
This configuration allows the thermal mass of the water in
the upper portion of the tank to buffer the space heating
load, and thus helps prevent boiler short cycling. This
is especially beneficial when the distribution system is
extensively zoned.
ANTIFREEZE-BASED COMBISYSTEM #3:
The functionality of antifreeze-based system #2 can also
be achieved using slightly different hardware. Figure 4-6
shows a very similar solar subsystem to that used in
figure 4-4. The difference is an external stainless steel
brazed plate heat exchanger rather than an upper coil in
the storage tank.
Domestic hot water from the storage tank flows through
the external heat exchanger based on the operation of a
small bronze or stainless steel circulator (P3). This pump
can be configured for either constant-speed or variable-
speed operation. Figure 4-6 shows two different piping
arrangements based on how circulator (P3) is controlled.
If the speed of circulator (P3) is varied (as shown in the
upper portion of figure 4-6), it can meter domestic hot water
through the external heat exchanger such that the water
temperature supplied to the space heating distribution
system also varies. The higher the speed of circulator (P3),
the faster heat transfers across the heat exchanger and the
warmer the distribution system becomes.
air vent
w/ shut off
valve
solar collector array
solar
circulation
station
DHW
CW
solar storage tank

anti-scald
tempering 
valve
check
valve
relay
mod/con boiler
make-up water
AB
3-way 
diverter 
valve
A B
(P1)
(P2)
pressure-
regulated
circulator
heat source
circulator
relay
manifold valve actuator
thermostat
end switch leads from actuators
Bronze or stainless steel circulator. 
Speed varied to maintain suitable temperature
to the distribution system.
(P3)
zoned space heating circuits
check
valve
make-up water
AB
3-way 
diverter 
valve
A B
(P1)
(P2)
pressure-
regulated
circulator
heat source
circulator
relay
manifold valve actuator
thermostat
end switch leads from actuators
(P3)
zoned space heating circuits
fixed
speed
circulator
3-way
motorized
mixing
valve
piping using 3-way motorized mixing valve
piping using variable speed circulator (P3)
P&T
figure 4-6