HVAC Fan Run-On Control for Residual Heating and Cooling
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Solution Overview
Problem
Conventional HVAC systems waste energy due to the fan stopping abruptly after the heating or cooling unit shuts off, and existing solutions fail to efficiently handle floating or unknown thermostat signals, leading to continuous fan operation and inefficiency. Additionally, the need for Wi-Fi enabled thermostats can be cumbersome for homeowners, and existing devices cannot implement automated demand response without replacing the thermostat.
Innovation Solution
A plug-and-play energy saving controller (ESC) is introduced, which can be installed between the thermostat and the air handler, capable of extending fan run time after the heating or cooling unit shuts off, handling unknown thermostat signals, and providing Wi-Fi enabled automated demand response, allowing for energy-efficient operation without replacing the existing thermostat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the fan stops abruptly after the heating or cooling unit shuts off, then the HVAC system operates simpler, but energy is wasted because residual heat or cooling capacity is not delivered to the conditioned space
Solution Approach 1:
The controller predicts the fan run time extension before the heating or cooling unit shuts off. By calculating the residual energy in the heat exchanger or cooling coil and the rate of energy transfer to the conditioned space, the system determines in advance how long the fan should continue running to deliver this residual energy, preventing waste without requiring complex real-time adjustments
2Ease of operation
If the thermostat fan output signal is in floating or unknown state when thermostat is shut off, then the thermostat design is simpler, but the HVAC system may remain on or fan runs continuously due to high impedance state being misinterpreted as ON state
Solution Approach 1:
The energy saving controller acts as an intermediary device installed between the thermostat and the air handler unit. It receives the fan output command signal from the thermostat, processes it through circuitry that converts floating or high impedance states into known 24 vac or 0 vac states, and then sends the processed signal to the air handler. This intermediary function allows the thermostat to remain simple while ensuring reliable HVAC system shutdown
3Extent of automation
If Wi-Fi enabled thermostat with automated demand response is installed, then energy management capability is improved, but installation complexity and cost increase for homeowners
Solution Approach 1:
The system segments the automated demand response functionality into a separate plug-and-play energy saving controller device that interfaces with the existing thermostat. This allows Wi-Fi enabled automated demand response capability to be added without replacing the thermostat itself. The new device communicates with the thermostat through standard wiring interfaces, dividing the complex functionality into modular components that can be installed independently
Data Source
AI summary
An energy saving controller configured for mounting between a thermostat and the controller for an air handler unit having a fan and at least a member of a group consisting of a heater and a compressor, the energy saving controller including a temperature probe for reading the temperature of a room where the thermostat is located and being configured to control the air handler unit based on a demand response request received from a utility provider via the Internet and an input from the temperature probe.