Skip to content
☰ Havaxer
§
developer_board02
Examples

Theoretical

This is the installation the 02 was designed for: a complete HVAC controller for two circuits, each able to heat or cool, with domestic hot water. It uses most of the board and leaves a little spare.

Nothing here is firmware you can download. It is the shape of a working system - what goes where, and what the logic between them has to do.

Wiring

Terminal What to connect
TEMP1 outside temperature sensor
TEMP2 domestic hot water (DHW) temperature sensor
TEMP3 system supply, or buffer top, temperature sensor
TEMP4 circuit 1 supply temperature sensor
TEMP5 circuit 2 supply temperature sensor
TEMP6 spare - a room temperature sensor, for example
TRIAC1, TRIAC2 circuit 1 mixer, open and close
TRIAC3, TRIAC4 circuit 2 mixer, open and close
RELAY1 circuit 1 pump
RELAY2 circuit 2 pump
RELAY3 heat source controller - on means "start heating the supply water"
RELAY4 DHW changeover valve, and the DHW charge pump if the heat source does not provide it
SIG1, SIG2 spare 5 V outputs - an off-board relay for a DHW circulation pump, for example
OC1, OC2 spare mains inputs - an ordinary light switch reading a request for extra hot water, for example

What the logic does

With those connections in place, an application might work like this:

  1. Watch TEMP2. Below 42 °C, turn RELAY3 and RELAY4 on. Above 48 °C, turn them off.
  2. If circuit 1 is enabled, turn RELAY1 on. If not, turn RELAY1 off, TRIAC1 off and TRIAC2 on - closing the mixer.
  3. If circuit 1 is enabled, watch TEMP4. Below 26 °C, pulse TRIAC1 on for 3 seconds. Above 28 °C, pulse TRIAC2 on for 3 seconds. Wait 15 seconds before acting again.
  4. If circuit 2 is enabled, turn RELAY2 on. If not, turn RELAY2 off, TRIAC3 off and TRIAC4 on - closing the mixer.
  5. If circuit 2 is enabled, watch TEMP5. Below 34 °C, pulse TRIAC3 on for 3 seconds. Above 38 °C, pulse TRIAC4 on for 3 seconds. Wait 15 seconds before acting again.
  6. Watch TEMP3. If it falls below the minimum supply temperature that any enabled circuit needs, turn RELAY3 on. Turn it off once TEMP3 reaches that temperature plus 7 K, or after 60 minutes.
  7. Watch TEMP1 and adjust the required supply temperature of both circuits against it.

The 15-second wait between mixer pulses is what stops the loop chasing itself: a mixer valve takes time to move, and the water takes longer still to reach the sensor.

Every temperature and time above is an example. Real values depend on the plant, the emitters and the building - and getting them right is most of the work in an HVAC controller.