PTAC Thermostat Setback Control Using Room Thermal Response

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Solution Overview

Problem

Conventional thermostats fail to balance energy savings with occupant comfort by not adequately considering the room's thermal response rate and recovery time when reducing setpoint temperatures during periods of non-occupancy, leading to potentially uncomfortable temperatures upon re-occupation.

Innovation Solution

A thermostat system that measures the room's thermal response rate during maximum heat application to calculate a reduced setpoint temperature, ensuring energy savings while maintaining a comfortable recovery time by utilizing both heat pump and resistive heating sources as needed.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the setpoint temperature is reduced during non-occupancy periods, then energy savings are achieved, but the room may become uncomfortably cold when occupants return

Engineering Contradiction:

Improveenergy consumptionVSAvoidoccupant comfort

Core Design Contradiction:

Loss of energyVSEase of operation

Solution Approach 1:

The system performs preliminary measurements of the room's thermal response rate during periods when heating is actively applied. These measurements are stored and used to predict recovery time before occupants return, allowing the thermostat to calculate an optimal reduced setpoint temperature that ensures comfortable recovery without excessive energy consumption.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors the room's actual thermal response to heating and uses this feedback to refine predictions of recovery time. This feedback mechanism allows the thermostat to adjust the reduced setpoint temperature dynamically, balancing energy savings with the guarantee of comfortable recovery when occupants return.

Inventive Principle:

Principle #23Feedback

2Loss of energy

If the setpoint temperature is reduced significantly during non-occupancy, then energy savings increase, but the recovery time to comfortable temperature increases

Engineering Contradiction:

Improveenergy consumptionVSAvoidrecovery time

Core Design Contradiction:

Loss of energyVSLoss of time

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the setpoint temperature parameter dynamically based on occupancy status and predicted recovery time. By calculating the optimal reduced setpoint using measured thermal response data, the system achieves maximum energy savings while maintaining acceptable recovery time within the constraint of the measured thermal characteristics.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If the thermal response rate is measured during maximum heat application, then accurate recovery time prediction is achieved, but energy consumption increases during measurement

Engineering Contradiction:

Improvethermal response measurement accuracyVSAvoidenergy consumption during measurement

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The system performs thermal response measurements periodically rather than continuously, specifically during periods when maximum heating is already being applied for other reasons. This periodic measurement approach captures accurate thermal response data while minimizing additional energy consumption dedicated solely to measurement purposes.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system uses the existing maximum heating cycles that occur naturally during operation to perform measurements, rather than initiating separate measurement cycles. This self-service approach leverages already-planned heating events to gather thermal response data without requiring additional energy expenditure specifically for measurement.

Inventive Principle:

Principle #25Self-service

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach allows for significant energy savings while ensuring the room temperature recovers to a comfortable level within a reasonable time, striking a balance between energy efficiency and occupant satisfaction.

Implementation Method 1

a heat pump or 'compressor' which incorporates also some form of resistive heating

Methodology Applied

Scientific EffectHeat pump: Heat Exchanger

Implementation Method 2

heat pumps used in conjunction with heat strips or resistive heating apparatus

Methodology Applied

Scientific EffectResistive heating: Joule Heating

Data Source

PatentUS8141791B2Energy management improvement for a heating system with reduced setpoint temperature during no occupancy based upon historical sampling of room thermal response with highest power heat applied

Publication Date: 2012.03.27 COPELAND CANADA INC

AI summary

A thermostat apparatus for controlling a heat pump with supplemental resistive heating as typically contained in a Packaged Terminal Air Conditioning (PTAC) unit is disclosed which provides improvements in energy management by reducing energy usage as much as possible within user guidelines when the conditioned space served by the PTAC is not occupied. A reduced setpoint temperature determination is based upon measurements of thermal response within the conditioned space to application of supplemental or resistive heat, and utilizes supplemental or resistive heat in achieving a quick recovery when people enter the conditioned space, thus enabling a more reduced setpoint temperature when the space is not occupied.