© 2010 D 270 - 08/10
10 of 24
Fancoil (3)
A fancoil terminal unit or Air Handling Unit (AHU) consists of a hydronic heating coil and
either a fan or blower. Air is forced across the coil at a constant velocity by the fan or
blower, and is then delivered into the building space.
Fin-Tube Convector (4)
A convector terminal unit is made up of a heating element with fins on it. This type of
terminal unit relies on the natural convection of air across the heating element to deliver
heated air into the space. The amount of natural convection to the space is dependent
on the supply water temperature to the heating element and the room air temperature.
Radiator (5)
A radiator terminal unit has a large heated surface that is exposed to the room. A radiator
provides heat to the room through radiant heat transfer and natural convection.
Baseboard (6)
A baseboard terminal unit is similar to a radiator, but has a low profile and is installed at
the base of the wall. The proportion of heat transferred by radiation from a baseboard is
greater than that from a fin-tube convector.
WARM WEATHER SHUT DOWN (OCC AND UNOCC)
The warm weather shut down (
WWSD
) disables the space heating system during warm outdoor weather. There is a separate
WWSD for both the occupied and the unoccupied periods. When the outdoor air temperature rises above the
WWSD
setting, the
control turns on the
WWSD
pointer in the display. When the control is in
WWSD
, the
Boiler Demand
pointer is displayed if there is
a boiler demand. However, the control does not operate the heating system to satisfy this demand. The control does respond to a
DHW demand and operates as described in section E.
Section E1: Domestic Hot Water Operation
DHW DEMAND
A DHW Demand is required in order for the control to provide heat to the DHW system. A
DHW aquastat or setpoint control is used as a switch in the DHW demand circuit. Once
the control detects a DHW demand, the DHW Demand pointer turns on in the LCD and the
control operates the boiler to provide a sufficient boiler supply water temperature to the
DHW tank. The control operates the pumps as described below.
The control registers a DHW Demand when a voltage between 24 and 230 V (ac) is applied
across the
DHW Demand
terminals (2 and 3).
2
3
Com
Dem
DHW
Dem
24 to 230 V (ac)
N
L
BOILER TARGET DURING DHW GENERATION
The DHW demand overrides the reset water temperature, except when the reset water temperature requirement is higher than that
of the DHW tank. When the control receives a DHW demand through an aquastat, the boiler target
temperature is at least as hot
as the DHW heat exchange setting (
DHW XCHG
).
DHW MODE AND PRIORITY OPERATION
The control has four different modes of DHW operation, which depends on the piping arrangement of the DHW tank. It is often
desirable to limit or even stop the flow of heat to the heating system when the DHW tank calls for heat. This allows for a faster
recovery of the DHW tank.