HVAC Fan Controller With Variable Off-Delay for Energy Recovery
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Solution Overview
Problem
Existing HVAC systems waste energy due to inefficient fan control methods, where the fan is turned off too quickly, leading to unrecovered heat or cold, and the fan speed does not adapt to optimize energy delivery, resulting in increased operational time and energy consumption.
Innovation Solution
A microprocessor-controlled fan controller that determines system type and mode of operation to implement variable fan-on and fan-off time delays, increasing fan speed during heating and extending fan-off time based on compressor or heat source operational times, thereby optimizing energy efficiency and recovery of heat or cold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the fan is turned off immediately when the heat source or compressor is de-energized, then the operational time and energy use are reduced, but significant heat or cold energy is wasted and lost to the environment
Solution Approach 1:
The controller extends the fan run time beyond the point when the heat source or compressor is de-energized to preliminarily capture and deliver remaining heat or cold energy to the conditioned space before shutting down, preventing energy waste to the environment
Solution Approach 2:
The fan continues to operate after the heat source or compressor is turned off to continuously deliver the remaining thermal energy to the conditioned space, maintaining useful action until the energy is fully utilized rather than being lost
2Loss of energy
If the fan runs at low speed during heating mode, then energy consumption is reduced, but the heating efficiency and speed of delivering heat to conditioned space is decreased
Solution Approach 1:
The controller dynamically adjusts fan speed based on system mode and timing - using higher cooling speeds during heat exchanger warm-up to accelerate heating delivery, then transitioning to lower speeds for energy efficiency, optimizing both heating performance and energy consumption
3Productivity
If the fan speed is increased to deliver more heating capacity, then the heating efficiency is improved, but the fan energy consumption increases
Solution Approach 1:
The controller uses periodic high-speed fan operation during specific phases (heat exchanger warm-up and immediate post-shutdown) to maximize heating capacity delivery, then reduces to low-speed operation for the remainder of the heating cycle to minimize energy consumption while maintaining productivity
Data Source
AI summary
An efficient fan controller for Heating Ventilating Air Conditioning (HVAC) systems including at least one electrical signal input from thermostat or equipment control terminals with a microprocessor to control a switching device connected to a signal output to control a fan relay and operate a system fan. The microprocessor is configured to monitor a thermostat call for cooling/heating duration and determine a variable fan-off delay based on the cooling cycle or heating cycle duration, and at an end of a cooling/heating cycle energize the fan relay to operate the system fan for the variable fan-off delay. The fan controller can include a heat pump detection signal input and electrical signal inputs to connect to a thermostat heat terminal, heat pump reversing valve terminal, or compressor terminal. The fan controller can also include a normally-closed relay connected to the switching device to maintain continuity between the fan signal input and output.