2
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 HWE-SS.
The installer fits the HWE-SS to a specific building by adjusting the Reset Ratio. With
a curve of 4 (2:1 reset ratio) a 2-degree change in outdoor temperature will change the
circulating hot water temperature by 1 degree; at an 11 curve (1:3 reset ratio) an outdoor
change of 1 degree will change the water temperature by 3 degrees. Most buildings
with baseboard radiation require a curve of 6, 7, or 8. Radiant heat applications usually
require a lower curve. An external T-Stat input can be used to shut the heating system
down when the thermostat is satisfied. 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
Reset Ratio
Offset
Radiators (Steel & Cast Iron)
1.00 (OD) : 1.00 (SYS)
0˚F
Baseboard (Finned copper tube& Cast Iron)
1.00 (OD) : 1.00 (SYS)
0˚F
Radiant (High Mass/Concrete)
4.00 (OD) : 1.00 (SYS)
-10˚F
Radiant (Low Mass/Joists)
2.00 (OD) : 1.00 (SYS)
-10˚F
Fan Coils & Air Handlers
1.00 (OD) : 1.00 (SYS)
20˚F
An optional domestic hot water input is provided for systems where an indirect tank provides DHW. During a DHW call, the HWE-SS will
maintain a constant set point of 200°F regardless of outdoor temperature or the status of the optional external thermostat. The DHW pump
will be enabled whenever there is a call for DHW. The heating system pump can be programmed to turn off during the first hour of a DHW
call. This allows the DHW tank to be satisfied quickly.
Mounting the Controller
• The HWE-SS DIGI-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 HWE-SS in a convenient location near
the unit to be controlled.
• Mount the HWE-SS 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 HWE-SS to the 1900 box or the extension skirt.
• Mount Display Section back to the Base Section. Tighten the Display Cover Mounting Screws.
Wiring
Wiring Power Input
The HWE-SS is designed to accept
ONLY A SINGLE POWER SOURCE
. It can be wired to either 120VAC using the two Black
wires or 24VAC using the right most two terminals on the terminal block on bottom of the control. Heat-Timer recommends the
installation of a Surge Suppressor and a Power Switch before the Power Line connection for safety and ease of service.
120VAC
• Attach line voltage, 120VAC, to the two Black wires extending from the back of the HWE-SS. Remember to use the power line
from a different source than the equipment being controlled.
WARNING
The HWE-SS can accept only one source of power: 120VAC or 24VAC.
If more than one power source is applied, the unit may be damaged.
T1
T2
T3+
COM
COM
T3- EXT+ EXT- P+ P- COM 24VAC
Display Cover Mounting Screws
Display Section
Base Section
Base Mounting Holes
Input Terminals 24VAC optional power input
N.O.
S.P.S.T. Output Wiring
120VAC Power Wiring
120VAC Power Source
BLACK
BLACK
Boiler
Output Wiring
N.O.
YELLOW
T1
T2
T3+
COM
COM
T3- EXT+ EXT- P+ P- COM 24VAC
24V
AC
Comm
24VAC Power Wiring
Shield
Shield
System T
emp
Outdoor Sensor
Sensor Wiring
T1
T2
T3+
COM
COM
T3- EXT+ EXT- P+ P- COM 24VAC
Enable/Disable
Wiring
T1
T2
T3+
COM
COM
T3- EXT+ EXT- P+ P- COM 24VAC
Input Terminals
{
{
{
{
{
{
Temp
er
atur
e S
ensor
30°F - 250°F
Temp
er
atur
e S
ensor
30°F - 250°F
Temp
er
atur
e S
ensor
150°F - 950°F
Ex
ter
nal Enable/D
isable
Shut
do
wn
Pr
essur
e,
V
acuum,
and
4 -20mA
24V
A
C P
o
w
er Supply
N.O.
ORANGE
System Pump
Output Wiring
N.O.
VIOLET
DHW Pump
Output Wiring
T1
T2
T3+
COM
COM
T3- EXT+ EXT- P+ P- COM 24VAC
DHW Call
Wiring
T1
T2
T3+
COM
COM
T3- EXT+ EXT- P+ P- COM 24VAC
Setback/Boost
Wiring
Outdoor Temperature (in °F)
70
60
50
40
20
30
0
-10
10
-20
120
140
130
150
160
170
180
200
190
210
220
100
110
12 11
10
9
8
7
6
4
3
2
5
1
1:4 1:3
1:2
1:1.5
1:1.25
1:1
1.25:1
1.5:1
2:1
3:1
4:1
8:1
W
at
er
T
em
pe
ra
tu
re
(i
n
°F
)
Reset Ratio Curves
Reset Ratios are presented as
Outdoor : Water
