MyStat Overview & Initial Setup

| Overview

The MyStat thermostat is designed to be compatible with most HVAC systems that operate with standalone heating and cooling. It uses industry-standard connections to control these appliances effectively.

This versatile device can manage single-stage heating or cooling with a fan, or up to three stages of either heating or cooling, thanks to its four onboard relays. It utilizes the 75F proprietary RF communication, ensuring seamless integration with existing 75F solutions. Additionally, the MyStat can function in standalone mode, programmable via a Central Control Unit (CCU).

Equipped with an occupancy sensor, as well as temperature and humidity sensors, the MyStat enables demand-controlled conditioning of the specific zone it manages, optimizing comfort and efficiency.

| Features

• Universal outputs 
• Universal Inputs
• Energy Efficient: Advanced occupancy sensing optimises comfort and reduces energy waste.
• Compact Design: MyStat is adaptable for various HVAC setups, offering reliable control without intrusive equipment.
• Integration: Seamlessly fits into the 75F ecosystem via a robust wireless mesh network.
• Enhanced Connectivity: Includes RS485 communication for wired BACnet and Modbus integration, plus support for wireless door/window sensors. (Yet to be implemented)
• Effortless Updates: Over-the-air firmware updates through the 75F Central Control Unit (CCU).
• Low Power Consumption: Designed to minimize energy usage for sustainable operation.

| Compatible Applications

• 2 Pipe Fan Coil Unit
• 4 Pipe Fan Coil Unit
• Rooftop Package Unit
• Heat Pump Unit

| Precautions

• Polarity Warning: Incorrect polarity wiring with a shared transformer can damage powered devices.
• Power Safety: Always turn off the power before connecting or disconnecting wiring.
• Circuit Board Protection: Ensure powered wires do not touch the circuit boards.
• Code Compliance: Install in accordance with all state and local codes.
• Assembly Caution: Do not assemble the front to the back plate while the device is powered on.
• Auto-Calibration: MyStat requires seven days to auto-calibrate and reach a steady state.
• Sensor Care: Avoid mechanical stress on the CO2 sensor for accurate readings.

| Mounting instructions

• Position the MyStat mounting plate and the back plate (if the gang box is vertically fixed) over the gang box. Ensure the back plate covers the gang box completely, then secure both plates to the wall gang box using the PHP screws provided.
• Align the MyStat top plastic with the mounting plate and push it to lock into place.
• Use the socket head screw provided in the box to secure the MyStat to the mounting plate.

| Dis-Assembling

• Remove the socket head screw.
• If the MyStat is wall-mounted, grasp the front plastic with both hands and gently pull it away from the wall.

| Wire Saver Mode

A wire saver module in HVAC systems offers several benefits, primarily by eliminating the need to run a new wire (C-wire) to the thermostat, thus simplifying installation and potentially reducing costs. These modules act as a splitter, allowing 24V systems to function with fewer wires by utilizing existing ones. 

The MyStat, when clubbed with the Wire Saver accessory, intelligently expands a traditional two-relay setup into a three-relay configuration. This allows for the addition of a new control point without the need for running additional wires, offering both flexibility and cost savings in installation.

Mystat V1 Wire Saver Illustration

Mystat V2 Wire Saver Illustration

Advantages

The following are a few advantages of the Wire Saver mode:

• Reduced Installation Costs: The primary benefit is avoiding the expense and effort of running a new C-wire, especially in older homes where it might be difficult or impossible to do so.
• Simplified Installation: Wire saver modules can make installing a smart thermostat easier, particularly for those without a C-wire connection.
• Compatibility: Many wire saver modules are compatible with various thermostat brands and both heat pump and conventional HVAC systems.
• Enhanced Functionality: Certain modules enable the transmission of multiple signals over a single wire pair, providing additional control features. 

Energy Savings: While not a direct energy-saving feature, the ability to easily install a smart thermostat (which can lead to energy savings through optimised heating and cooling) is facilitated by the wire saver. 

Note: This feature requires the controller to be powered with a 24V AC supply. The system will not support this functionality on alternate power inputs.