Differential Controller Ver 3.x

A three-channel temperature controller that prioritises heating of domestic hot water from the lowest cost source.

Overview

The controller manages three input sources:

1. Solar accumulation tank
2. Solid fuel boiler (wood gasification)
3. Electric resistive heater (immersion)

If the domestic hot water temperature is below a preset limit, the controller checks whether an input source temperature is above a preset delta. Sources are tried in the order listed above, always preferring the cheapest option.

Basic function

The controller conserves the domestic hot water temperature and prevents it from dropping as output from solar systems or boilers cools. It transfers heat through tank heat exchangers while maintaining DHW temperature integrity.

Mode of operation

Four LED indicators show system status:

• STORE — solar heating DHW
• IMMERSION — electric heating
• BOILER — solid fuel heating
• POWER — device operational

Configurable parameters

• Preferred DHW temperature (60-90 C)
• Delta (temperature differential threshold)
• Hysteresis (prevents valve cycling)
• Minimum operating temperature
• Clamping temperature
• Maximum DHW temperature (hard limit: 90 C)
• Valve exercising (every 28 days of non-operation)

Installation

Electrical connections

• 220VAC mains power
• Thermo actuator valve connections
• Immersion heater relay
• Thermal store pump relay
• Dallas DS18B20 temperature sensors (3-wire, 5VDC)

Sensor placement

• Boiler output in thermowell with thermal conductivity enhancement
• DHW tank in top section above heat exchanger

Configuration

Our products are local-control-only devices. Self-running; no internet connection required. Configurable with any device that can connect via a serial terminal. No application. No operating system. No cloud. No subscription.

Setup is via serial USB terminal at 9600 baud ASCII. Users assign sensor addresses and configure operational parameters through a menu-driven interface.

Technical specifications

• Processor: Atmel 328 microcontroller
• Power supply: Meanwell/Recom/Vigortronix quality unit
• Protection: ESD and electrical fast transient protection
• Valve draw: Siemens STA23, 21mA steady-state, 250mA startup
• Temperature sensors: Maxim DS18B20 (-55 C to +125 C range)
• Load capacity: 500mA maximum per channel

Errors and omissions excepted. No reliance can be made upon the accuracy of the information contained herein. Devices are prototypes only and are not for commercial sale. No liability can be accepted for any loss or damage arising from the use of any device or information provided.