lp-548 Rev. 000 Rel. 004 Date 1.11.19
11
Register 40003/AV2 needs to receive the rate
command as follows: Acceptable range is 0 to
100. Value needs to be greater than 15 for the
appliance to fire.
When the command is 16, the appliance will
run at minimum fan speed (firing rate). When
the command is 100 the appliance will run at
max fan speed (firing rate) If the command
value is anywhere between 16 and 100, the
appliance will run at a fan speed proportional
to the command sent between minimum and
maximum firing rates.
NOTE:
To ensure proper operation, resend the
configuration bits to holding register 40001 /
AV0 prior to issuing a command.
Figure 6 - Firing Rate Curve
E. Example #4 - Hot Water Generation
Hot water generation can be accomplished
using one of two methods when an appliance is
Holding Registers
Definition
BACnet Decimal
Value
MODBUS Decimal
Value
HEX Value
Action
40001 / AV0
Configuration
26
26
001A
Set configuration to read 40002, 4 and 5
40002 / AV1
Coils
16
16
0010
Enables Tank Tstat (00 00 disables appliance)
40004 / AV3
Tank setpoint
130.0
1300
82
Sets setpoint to 130.0F
40005 / AV4
Tank
temperature
150.5
1505
96
Passes tank temp from remote sensor (ex: 150.5F) to tank
Table 17 - Example #3
NOTE:
To ensure proper operation, resend the configuration bits to holding register 40001/AV0 prior to issuing a command. For proper
hexadecimal conversion of rate percentage, please refer to the rate and temperature conversion section of this manual.
To ensure that the appliance can properly respond to a call for hot water generation, the following holding registers must be set in addition
to other commands:
*The appliance will not respond to the internal DHW limit while the Tank Temperature AND Tank Enable is being written from
MODBUS/BACnet!
connected to a BMS system, DHW with direct control, and DHW with remote control.
DHW with Direct Control
This is the typical installation with a hot water generator in close proximity to the appliance with the tank thermostat, or tank temperature
sensor, wired to the terminal strip or Customer Connection Board of the appliance.
DHW with Remote Control
This installation may or may not have the hot water generator in close proximity to the appliance. Its sensors and thermostat values are only
available through the MODBUS communication bus.
F. Cascade
In order to operate the appliance in cascade with MODBUS or BAC/net communications, configure the master appliance. Connect the
remaining appliances in the cascade through the normal cascade communications wiring. Cascade control can then be accomplished
automatically through the master appliance.
NOTE: With MODBUS or BAC/net communication connected only to the master appliance, only total cascade information can be seen
through the communications link. Information from the follower appliances is limited to follower appliance rate command, supply
temperature, fault code, and fault status.
If you want to see complete data from each follower, or use the master to control cascading of multiple appliances, each appliance will need
a MODBUS or BAC/net communication board. If this is implemented, remember that each appliance will present its data as Appliance 1. You
must then use the Appliance’s address to determine which follower you are accessing.
G. Temperature Conversions (MODBUS Only)
The MODBUS adapter passes temperature data to the appliance in degrees Fahrenheit. Also, to accommodate decimal places, the decimal
value must be divided by 10.
In some BMS systems, the data sent over the MODBUS is passed as an unsigned 16-bit integer (16BIT UINT). This poses no problem unless the
data becomes negative, such as temperatures below zero. In this case, the compliment has to be calculated as follows:
Example for WRITING negative temperature values to the appliance:
Temperature to be sent over MODBUS = -22
o
F.
First multiply by 10-22 X 10 = -220.
Calculate compliment 65536-220 = 65316. Data to be sent is a decimal value of 65316.
