Outdoor Reset Control - Weil-McLain WMB-155C Manual

W
TM
AquaBalance
24 Controls and operation
Adjustments
Theory of Outdoor Reset Control
One of the key points to boiler efficiency, is to match the
heat generated by the boiler to the heat loss of the build-
ing to be able to obtain a given comfort level in the living
space.
You can obtain this efficiency by selecting a scale within an
operating programmed range of the boiler water tempera-
ture. These scale ranges are related to the outdoor tem-
peratures, and boiler water temperatures for the installed
radiation.
These "Outdoor Reset Control" curves are graphed
(and programmed into the control board) by outside
temperature from 68 degrees to -4 degrees F and boiler
water target temperatures from 86 to 194 degrees F (see
Figure 73, page 55), where the heat loss of the home, will
match the gradual increase in boiler water temperature as
the outside temperature drops.
The average heat loss of a home may meet the needs
(boiler water temperatures) of offset curve number 5
(Figure 75, page 55) to meet the heat loss at given outdoor
temperatures.
Another example would be a high heat loss structure, where
curve number 10 would drive up the boiler water tempera-
ture with a slight drop in outdoor temperature. (from 68
degrees F outside temperature to just a drop to 50 degrees F
outdoor temperature, see Figure 75, page 55)
An example of a structure with very little heat loss, (such
as a super insulated, high efficiency building) would be
curve number 1, where the outdoor temperatures continue
to drop, and the boiler water temperatures are in the low
range from 86 degrees to 104 degrees F.

Outdoor Reset Control

1. When the external outdoor sensor is attached to the boiler,
the system can work in Outside Temperature Compensation
mode. In OTC mode the temperature of the heating system
is controlled according to the external climate conditions,
this will insure a high degree of comfort and energy saving
all year round.
2. By using the CH buttons (Items 3 and 4 - Figure 64, page 50)
it is possible to set the maximum system water flow tempera-
ture for the installation.
OTC setting
1. To enter the OTC- reset mode, press OTC button (Item 6 -
Figure 64, page 50) for 5 seconds.
2. The display shows "CU" flashing Figure 71; to set Curve,
use the DHW buttons (Items 1 and 2 - Figure 64, page 50).
It can be varied from 1 to 10, in accordance with the chart
Figure 73, page 55. "O" means no OTC mode.
3. By pressing the CH push buttons (Items 3 and 4 -
Figure 64, page 50), the display shows "0F" flashing Fig-
ure 72; to set Offset, use the DHW push buttons (Items 1
and 2 - Figure 64, page 50).
54
M -
ALL OUNT GAS FIRED WATER BOILER
— C
OMBI
(continued)
Figure 71
DHW
It can be 68 or 104, in accordance with the chart Figure 74
or Figure 75.
4. To exit the OTC mode, press OTC button (Item 6 -
Figure 64, page 50) for 5 seconds.
Figure 72
CH
In the case of an outdoor sensor failure, the control
will continue to operate the boiler, but without the use of
the Compensation Curves, and an error message will flash
on the display (Fault 39 -please see Figure 99, page 78).
Upon replacement of the defective sensor the boiler will
resume the use of Compensation Curves .
OTC Exempt mode
By pressing the DHW+ and ECO buttons together for 10
seconds, it is possible to enter the OTC Exempt menu. The
display starts showing the value of the parameter OTC Exempt
(See parameter Number 1 63, page 97) flashing. By means of
the CH- push button it is possible to change value. By pressing
DHW+ and ECO buttons together for 10 seconds, it is possible
to leave the OTC Exempt Menu. If no action has been taken,
the control automatically leaves this mode after 2 minutes.
- 0 = installation non exempt from outside sensor connection;
- 1 = installation exempt from outside sensor connection;
Compensation curves
Curve numbers below refer to Figures 73, 74, & 75, page 55.
Curve number 1 is for a high efficiency home with very
low heat losses.
Curve number 5 is for an average home heat losses.
Curve number 10 is for a home with high heat losses.
Boiler Manual
Part number 550-100-305/1016