Flow Limits; Water Quality Requirements; Central Heating System; New Central Heating Systems - Riello RTC-80 Series Installation, Operation And Service Manual

2.8.2 Flow limits

RTC-80 boilers do not require a minimum flow rate in order to
maintain warranty. The boiler has been designed to operate with
a temperature difference between the supply and return of up
to 100 °F . Flow should be initiated with the start of the burner
to minimize temperature fluctuations and control deviations. The
field installed manual reset high limit (as required by CSD-1) must
be fitted to the instrument tapping of the heating supply, set to
210°F and electrically connected into the Control unit or the burner
enable/disable circuit directly.
RTC-80 boilers can operate with zero flow, and do not require a
minimum flow rate.
A minimum flow is recommended only to provide heat transfer,
and the maximum flow to prevent erosion.
Model
Maximum
RTC 1000-80
RTC 1300-80
RTC 1700-80
RTC 2300-80
RTC 3000-80
RTC 3800-80
RTC 4700-80
RTC 5500-80
(*) Units shown are in US Gallons.

2.8.3 Water quality requirements

The manufacturer recommends the use of water as heat transfer
fluid for the central heating system. A chemical treatment system
must be provided for this water.
The heat transfer fluid (water) for the central heating circuit must
conform to the quality parameters given in the following table:
Chemical and physical requirements of heating system water
ph
Hardness °fH / ppm
Electrical con-
μs/cm
ductivity
Chlorides mg/l / ppm
Sulphides mg/l / ppm
Nitrides mg/l / ppm
Iron mg/l / ppm
(*) values for water in system after 8 weeks of functioning
Flow Limits
Minimum
130 12 GPM (*)
160 15 GPM (*)
200 20 GPM (*)
290 30 GPM (*)
370 40 GPM (*)
480 50 GPM (*)
580 60 GPM (*)
690 70 GPM (*)
Initial filling Regular service
water water (*)
6-8 7.5-9.5
< 5° / 50 < 5° / 50
< 100
< 10 / 10
< 10 / 10
< 10 / 10
< 0.5 / 0.5
9
NOTICE:
If it proves impossible to treat the heating system water
supply properly because the water charging system is
automatic and uncontrolled, if there are no barriers
installed to prevent water oxygenation and if the heating
system includes an open expansion vessel, then the
boiler itself must be separated from the heating system by
means of a heat exchanger.
If the hardness of the water exceeds the value specified in the
table, it is mandatory to install a water softening system.
9
NOTICE:
− Chemical products used for water treatment must be com-
patible with applicable water pollution laws.
− Provided they are properly applied, these laws guarantee
the safe functioning of the heating system.

2.8.4 Central heating system

Possible causes for corrosion and limescale
Typical problems encountered in central heating systems include:
− the breakage of heated surfaces through overheating
caused by the thermal insulation of limescale deposits on
the water side
− oxygen corrosion
− deposit corrosion
− stray current corrosion
− diffused and localized acid corrosion.
The technical details provided in this section refer specifically to
domestic and industrial hot water heating systems with working
temperatures up to 210°F (99°C).

2.8.5 New central heating systems

Mistakes to avoid and precautions.
To eliminate contact between system water and the air, the fol-
lowing is required:
− ensure that the expansion vessel is a closed vessel, and
of the correct size and pre-charge pressure (the pressure
should be checked periodically)
− ensure that the system is always kept at a pressure high-
er than atmospheric pressure at all points (including the
pump suction side) and at all operating conditions (pre-
cisely because the seals, gaskets and joints in a water cir-
cuit are designed to resist pressure from within, but not to
resist a vacuum within)
− ensure that no part of the system is made from materials
that are permeable to gases (e.g. plastic pipes with no ox-
ygen barrier used in floor heating systems).
9
NOTICE:
The original system filling water and any topping up water
must always be filtered (using synthetic or metal mesh
filters with a filtration rating of no less than 50 microns)
to prevent sludge from forming and triggering deposit
induced corrosion.
9
NOTICE:
We recommend fitting an 80 mesh dirt filter externally to
the boiler return to prevent contamination of the boiler by
the water source.
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INSTALLATION