Cascade Heat Pump with Recirculation for Large Temperature Lift

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Solution Overview

Problem

Existing caloric heat pumps face challenges in achieving a large temperature lift due to the limited temperature change of caloric materials, which is typically between 2 and 10 K, making them inefficient for applications requiring significant temperature changes, such as in motor vehicles.

Innovation Solution

A cascade heat pump system with multiple stages (n≥2) is designed, where each stage has a heat pump with a flow divider that splits the coolant flow between a hot side and a cold side. The system includes recirculation lines that connect the second coolant outlet of one stage to the coolant inlet of a preceding stage, enhancing the temperature lift and efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a single-stage caloric heat pump is used, then the device complexity is low, but the temperature lift is limited to 2-10 K

Engineering Contradiction:

Improvetemperature liftVSAvoiddevice complexity

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The heat pump system is divided into multiple stages (n≥2), where each stage contains a heat pump unit with a flow divider that separates coolant flow into hot and cold sides. This segmentation allows the temperature lift to be accumulated across stages, achieving a total temperature lift that is the sum of individual stage lifts, thereby overcoming the 2-10 K limitation of single-stage systems.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements a nested structure where heat pump stages are arranged in series, with each stage nested within the overall cascade system. The coolant flow path is nested such that the outlet of one stage feeds into the inlet of the next stage, allowing temperature transformations to be compounded through the nested stages.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Temperature

If multiple heat pumps are connected in parallel to increase temperature lift, then the temperature lift increases, but the device complexity and space requirements increase significantly

Engineering Contradiction:

Improvetemperature liftVSAvoidspace requirements

Core Design Contradiction:

TemperatureVSArea of stationary object

Solution Approach 1:

Multiple heat pump stages are merged into a single cascade system where coolant flows sequentially through each stage. The flow dividers within each stage merge the hot and cold coolant streams, allowing the system to achieve the temperature lift of multiple independent heat pumps while occupying the space of a single integrated unit.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent transitions from a parallel arrangement of heat pumps (requiring significant horizontal space) to a series cascade arrangement that utilizes the temperature dimension vertically. Each stage operates at a different temperature level, with coolant progressively transformed through the stages, achieving high temperature lift within a compact footprint.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Temperature

If the coolant flow is divided between hot and cold sides in each stage, then the temperature lift is multiplied, but the usable coolant flow is reduced

Engineering Contradiction:

Improvetemperature liftVSAvoidusable coolant flow

Core Design Contradiction:

TemperatureVSQuantity of substance

Solution Approach 1:

The patent ensures continuous useful action by recirculating the coolant through the cascade system. The coolant that exits the hot side of one stage is fed into the inlet of the next stage, maintaining continuous flow and maximizing the utilization of the coolant throughout the system, thereby preserving usable coolant flow despite the division at each stage.

Inventive Principle:

Principle #20Continuity of useful action

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

The cascade heat pump system achieves a significant multiplication of the temperature lift by concatenating multiple stages, allowing for a larger usable coolant flow and increased efficiency, which is essential for applications requiring substantial temperature changes, such as in motor vehicles.

Implementation Method 1

each heat pump has a hot side and a cold side and a flow divider, wherein the flow divider is equipped to divide a coolant flow entering the coolant inlet between the hot side and the cold side

Methodology Applied

Scientific EffectHeat conduction: Conduction (thermal)

Implementation Method 2

The cascade heat pump system achieves a significant multiplication of the temperature lift by concatenating multiple stages

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Data Source

PatentUS12264855B2Cascade heat pump and method for heating or cooling a coolant by means of a cascade heat pump

Publication Date: 2025.04.01 VOLKSWAGEN AG

AI summary

In order to provide a cascade heat pump with which a large temperature lift can be provided with high efficiency, a cascade heat pump comprising n stages where n≥2 is proposed. Each of the n stages has a heat pump with a coolant inlet, a first coolant outlet, and a second coolant outlet. Each heat pump has a hot side and a cold side and a flow divider to divide a coolant flow entering the coolant inlet between the hot side and the cold side. The first coolant outlet of the heat pump of each stage i, where i=1 . . . n−1, is connected to the coolant inlet of the heat pump of a subsequent stage i+1. The second coolant outlet of the heat pump of at least one subsequent stage i+1 is connected by a recirculation line to the coolant inlet of the heat pump of a preceding stage.