Control Board Operation - Harman Stove Company PB 105 Installation & Operating Manual

Control Board Operation

Aquastat Sensor - This sensor is located in the
aquastat well on the top of the water jacket. This sensor
along with the outdoor air sensor is what the control board
uses to regulate the feed rate based on these two observed
conditions. (Boiler Temp. & Outdoor Air Temperature)
Outdoor Air Temp. Sensor (OAT) - This sensor
is located outside the building (on the north side of the
house and out of direct sunlight). The Outdoor Air Sensor
is used to perform hot water reset based on outdoor air
temperatures.
When the OAT sensor is installed, at zero degrees F
(outside temperature), the boiler will operate at the tem-
perature set on the MAX. TEMP. knob. The boiler water
temperature will decrease by 1 degree F. for every 1
degree F. in temperature rise of the outdoor air.
NOTE: Pellet Boiler Outdoor Air Reset Operation
Graph located on page 22.
22
Operation
Setting The Boiler Temperature
Without the Outdoor Air Temperature Sensor Installed
To set the maximum boiler water temperature,
simply turn the Max. Temp. water temperature dial to the
desired setting. The control and the boiler will then per-
form to achieve and maintain the set temperature.
The Min. Temp. Knob simply becomes the boiler
mode switch, on or off. Turning the knob fully counter-
clockwise is the "OFF" position while turning the knob
clockwise past the 120 degree position is the "ON"
position.
With The Outdoor Air Temp - Sensor Installed
Maximum boiler temp setting is as described
above.
The MIN. TEMP. knob in addition to being the
mode setting (on or off) now also has the function of
setting the minimum boiler water temperature. This would
be the lowest boiler water temperature that you want to
have based on the following factors.
1.) Outdoor Air Temperature (OAT)
2.) Domestic Hot Water Use
3.) Overall Volume of the Heating System
NOTE:
Although the full operational scale of the boiler water
temperature setting is from 120 to 185 degrees F, in
most cases it would not be recommended to maintain a
boiler temperature less than 140 degrees F.
The PB105 is designed to withstand lower return water
temperatures however, extended return temperatures
below 130 degrees F can cause condensation in the
secondary ash chamber area and also in the venting
system both of which could cause damage in these
areas.
One Exception to this would be summertime operation with
a domestic hot water coil option. The boiler water tempera-
ture could be maintained at a lower temperature since there
would be no load from the heating system and recovery
would be quick.
NOTE:
If the system is run at the lower temperature settings,
conditions of the firebox, boiler tubes, secondary ash
chamber and venting should be monitored closely. If
any indications show excess condensation the boiler
water temperature will need to be increased until
condensation does not occur.
a.) Hot Water Coil Option
b.) Indirect Hot Water Storage