The Fix
Anytime new hardware is added to an older system, especially a
former steam heating system, it’s good practice to install a dirt separator to
minimize sludge migration to the new hardware. The old piping should also be
flushed out with an appropriate surfactant to remove as much sludge as
possible.
The mod/con boiler with compact heat exchanger will not like the
low flow rates that will occur in the original design when only one thermostatic
radiator valve is open (or partially open). This is corrected by hydraulically
separating the boiler circuit from the distribution system with a pair of
closely spaced tees. It could also be accomplished using a hydraulic separator.
The latter would provide air and dirt separation for the system and thus
eliminate need to install separate air and dirt separators.
An ECM-based variable speed, pressure-regulated circulator is
shown in the distribution system. This circulator will vary its speed as needed
to maintain proportional differential pressure across the distribution system
as the thermostatic radiator valves open and close. An alternative would be use
of a fixed speed circulator with differential pressure bypass valve. However,
the pressure-regulated circulator will ultimately have the lowest lifecycle
cost through reduced electrical consumption.
The thermostatic radiator valves should be installed on the supply
side of the radiators. This helps prevent heat migration from the supply piping
into the radiators. The valves shown have angle pattern bodies. This keeps the
thermostatic head far enough from the radiator to minimize convective
interference that could cause erratic operation of the valve.
Manually operated air vents are shown at the top of each radiator
to aid in purging the system.
Finally, a supply temperature sensor that regulates boiler
modulation is shown on the supply side of the distribution system (downstream
of the closely spaced tees). This allows the boiler to modulate based on the
true water supply temperature to the radiators.
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