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In order to properly control a hot water heating system, the amount of heat
supplied to the building must equal the amount of heat lost by the building.
The amount of heat delivered into a building depends on the temperature of
the water in the heating unit and the surface area of the heating unit. Heat-
ing units with a small surface area, such as baseboard radiators, require a
higher water temperature than heating units with a larger surface area such
as radiant fl oors.
The amount of heat lost from a building depends on the outdoor temperature.
As the outdoor temperature becomes colder, the amount of heat a building
loses increases.
The operation of a hot water heating system can generally be improved by
adjusting the supply water temperature to the system as the outdoor tem-
perature changes. Using this approach, the heat input to the building can
be matched to the heat lost from the building. This method of controlling the
supply water temperature to a heating system greatly improves the comfort
of the system and is known as Outdoor Reset.
When an Outdoor Sensor is connected to the Radiant Mixing Control (RMC), the RMC provides outdoor reset. When operating in the outdoor
reset mode of operation, the installer must set the Outdoor Design Temperature and the Design Supply Temperature in order to establish
the relationship between the outdoor temperature and the supply water temperature. This is known as setting the Heating Curve.
SEQUENCE OF OPERATION
When the RMC receives a Demand and it is not in a WWSD, the RMC turns on the system pump and calculates a Mixing Target tem-
perature. The variable speed injection pump is then operated to maintain the Mixing Target temperature at the mixing supply sensor.
The boiler contact operates as described in the Boiler Operation section. The RMC also provides boiler protection as described in
the Boiler Operation section.
DEMAND
The RMC requires a demand signal before it will begin operation. The RMC can use either a powered or an unpowered demand
signal. Once a demand signal is received, the RMC displays the demand pointer in the
display and operates as described above.
Powered Demand
The RMC recognizes a Powered Demand Signal when 24 V (ac) is applied across the
Com and Heat Dem terminals.
Unpowered Demand
The RMC recognizes an Unpowered Demand signal when a switch is closed between
the Com and Heat Dem terminals.
SYSTEM PUMP OPERATION
The RMC has an internal system pump contact. This contact turns on when the RMC has a
mixing demand and is not in a WWSD. The integrated system pump as well as an external
boiler pump may be controlled by this relay. By providing proper fl ow in the boiler loop, the
boiler temperature can be accurately controlled based on the mixing load.
Outdoor Reset Mode of Operation
Outdoor Reset Settings
HEATING CURVE SETTINGS
In order to establish the heating curve, the RMC must be given two points to work with. The fi rst point is the Outdoor Reset Starting
Point and the second point is the Design Condition.
Outdoor Reset Starting Point
The Outdoor Reset Starting Point for the RMC is fi xed at 72°F (22°C). This means that when the outdoor temperature is 72°F
(22°C), the RMC calculates a required supply water temperature (Mix Target) of 72°F (22°C).
Design Conditions
The design conditions represent the supply water temperature required to satisfy the heating system on the typical coldest day of
the year. These are the conditions that are used when calculating the size of the heating equipment needed to heat the building. The
Design Conditions are made up of an outdoor temperature (Outdoor Design) and a supply water temperature (Design Supply).
Com Heat
Dem
Boil Out
Powered
Demand
C
24 V (ac)
R
Switch
Com Heat
Dem
Boil Out
Unpowered
Demand
Switch
