heat-timer DIGI-SPAN VSP Elite Installation And Operation Instructions Manual page 2

Two sensors are used for outdoor reset, one to monitor the outdoor temperature,
and one to monitor the Secondary Loop circulating hot water temperature. When
the outdoor temperature falls below outdoor cutoff setting, the heating system is
activated and the Secondary Loop hot water temperature is increased proportionally
to satisfy the load. Should it get warmer outdoors, the hot water temperature is
automatically lowered by the control. If the outdoor temperature continues to rise to
the outdoor cutoff setting then the heating system is automatically turned off.
Because of the many different physical characteristics of buildings, and the type of
radiation, i.e., baseboard or radiant, the heat loss varies. In one building, a 1-degree
temperature change outdoors may require a change of 1 degree in heating water
temperature; for another it may require a change of 2, 3, or even 4 degrees in order
to gain the desired comfort level. This is known as the Reset Ratio. The middle chart
shows the wide range of Reset Ratios available for the VSP Elite.
The installer fits the VSP Elite to a specific building by adjusting the Reset Ratio
curve. With curve 4 (2:1 reset ratio) a 2-degree change in outdoor temperature will
change the circulating hot water temperature by 1 degree; at curve 11 (1:3 reset ratio)
an outdoor change of 1 degree will change the water temperature by 3 degrees. Most
buildings with baseboard radiation require curve 6, 7, or 8. Radiant heat applications
usually require a lower curve. Another, is a Setback input that will switch the
heating system to a lower set point determined by the Set Back setting.
Type of Radiation in Building
Radiators (Steel & Cast Iron)
Baseboard (Finned copper tube& Cast Iron)
Radiant (High Mass/Concrete)
Radiant (Low Mass/Joists)
Fan Coils & Air Handlers
The Boiler Return water sensor and well are provided
to avoid thermal shock to the boiler and, therefore, to
help prolong boiler life. If the sensor registers that the
boiler return water is colder than 120°F, the VSP Elite
immediately lowers the temperature of the circulating
heating water to reduce the load on the boiler,
allowing the return water temperature to rise.
Mounting the Controller
• The VSP Elite is designed to mount on a 1900
(4"x4") deep electrical box.
• If additional room is needed for wiring use the
extension skirt provided in the box.
• Place the VSP Elite in a convenient location near
the unit to be controlled.
• Mount the VSP Elite indoors and away from
excessive heat or cold.
• Partially unscrew the Display Cover Mounting
screws. This allows for its removal.
• Lifting the Display Section away from the base will unplug it from the Base section.
• Proceed with the power and output wiring instructions.
• Use the screws provided to mount the VSP Elite to the 1900 box or the extension skirt.
• Mount Display Section back to the Base Section. Tighten the Display Cover Mounting Screws.
Reset Ratio Offset
1.00 (O) : 1.00 (S) 0˚F
1.00 (O) : 1.00 (S) 0˚F
4.00 (O) : 1.00 (S) -10˚F
2.00 (O) : 1.00 (S) -10˚F
1.00 (O) : 1.00 (S) 20˚F
Base Section
T1 COM T2 COM T3+ T3- EXT+ EXT- P+ P- COM 24VAC
Input Terminals 24VAC optional power input
1:4 1:3
12 11
220
210
200
190
180
170
160
150
140
130
120
110
100
70 60 50 40 30 20
Outdoor Temperature (in °F)
Reset Ratio Curves
Reset Ratios are presented as
Outdoor : Water
Display Section
Base Mounting Holes
Display Cover Mounting Screws
2
1:2 1:1.5
10 9
8
1:1.25
7
1:1
6
1.25:1
5
1.5:1
4
2:1
3
3:1
2
4:1
1
8:1
10 0 -10 -20