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2005 Boreal Geothermal Inc.
www.boreal-geothermal.com
BOREAL
® Electronic Control Board
Theory of Operation
The Boreal ACDX heat pump operates on the principle
of a buried multi loop condenser / evaporator assembly to
exchange energy to and from the earth as required by the sea-
son.
When heating is required the heat pump uses all loops
(typically 1 per ton) in parallel to extract heat from the
ground. During the cooling mode when the buried loops are
acting as a condenser, the number of loops in operation at any
one time must be controlled in accordance with their tempera-
ture for proper operation of the heat pump.
To accomplish this Boreal Geothermal Inc. has designed
an electronic control board to monitor and control all aspects
of the ACDX heat pump operation.
The BOREAL CONTROLLER BOARD (hereinafter
called BCB) has been designed to operate the heat pump with
the highest reliability and efficiency without the main micro-
processor being directly connected to the heat pump and it's
associated AC noise which can cause erratic operation. We
have isolated all INPUTS, OUTPUTS and the POWER SUP-
PLY from the AC supplies in the heat pump so that AC noise
is not a problem.
All the inputs for thermostat functions are optically cou-
pled to the BCB where they are transferred to a +5v or 0v
signal for the microprocessor. The BCB reads the voltage on
each of it’s inputs and determines what functions are required
based on this information.
Thermostat inputs
NOTE
: The thermostat chosen should be a good quality
two-stage heating, one-stage cooling heat pump style thermo-
stat. If the stat is a mercury bulb style unit the heating and
cooling anticipators must be set completely out of the circuit
so that they will not affect the run time of the ACDX heat
pump
By allowing the 24v AC thermostat to operate the con-
troller board instead of the heat pump’s controls directly we
improve reliability in two ways:
1. The stat does not have to handle any current from
compressor relays, loop solenoids etc. In our system, direct
connection to the stat could put loads on the stat which would
shorten it's life. With the 24v signal we send, only a few milli-
amps of current are required.
2. It is impossible to for the installer to short anything
during the installation of the thermostat. Crossed connections
some erratic manner but would not damage the controller
board.
The BCB has all the time delay functions of a conven-
tional electronic thermostat built into its program and all indi-
cator lights function normally.
The eight (8) terminals going to the thermostat from the
BCB are as follows:
3. G -
indicates blower required
2. B -
indicates mode switch in (HEATING)
5. Y -
compressor operation required
4. W -
indicates (ELECTRIC HEAT) required
6. O -
indicates mode switch in (COOLING)
7. L -
Lock-out indicator light.
1. R -
has 24v hot signal continuously.
1. C -
common
For example: When the mode switch (cool-off-heat-EM
heat) is set to OFF the BCB does not see 24v on either "B" or
"O" terminals and therefore knows the system is in the OFF
position.
If the BCB sees a signal on "B" it knows the mode
switch is set to HEAT and will bring on the compressor when
the thermostat is turned up and the thermostat makes a contact
with the "Y" terminal.
If there is no “B” terminal on your thermostat or if the
unit is a ACDX-to-Water machine
Similarly by moving the selector switch COOL, a 24v
signal on the "O" terminal indicates that COOLING mode has
been entered which activates the reversing valve, the NO liq-
uid line solenoid and 1 cooling loop. When "Y" is made by a
contact closure of the stat the compressor is activated.
A 24v signal on "G" will activate the system fan (FAN
switch set to "ON")
A 24v signal appearing at "W" (terminal designated as
second stage heating) during any time except when the
MODE selector is in COOLING will bring on the supplemen-
tary heat.
There are adjustable time delay's built into for every
function that the BCB looks after. These time delays can be
changed in the field by a serviceman with a laptop computer
and a serial cable. (A list of printouts available from the BCB
are included in appendix.)
High & Low Pres. Controls and Loop Pressure Limit
Switch Inputs
The BCB has another terminal block on the middle left
