Thermochromic Window Structure for Passive Solar and Thermal Regulation
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Solution Overview
Problem
Current thermochromic windows are limited in their ability to regulate both solar and thermal radiation, with existing materials either focusing on solar regulation or thermal regulation, and often resulting in undesirable optical properties or inefficiencies.
Innovation Solution
A thermochromic window utilizing a hydrogel-based absorber layer and a silver nanowire mesh composite film that synchronously modulates solar and thermal radiation through temperature-induced phase transitions, allowing for high solar transmittance and thermal reflectance in cold conditions and low solar transmittance and thermal emissivity in hot conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If VO2 is coated on glass to accomplish thermal emittance regulation, then thermal emittance regulation is achieved in the long-wavelength infrared spectrum, but the emittance is high in the cold state while low in the hot state, which is the opposite optical behavior of what is needed for energy savings
Solution Approach 1:
The patent inverts the conventional VO2 coating approach by coating VO2 on metal substrates rather than glass. This inversion reverses the optical behavior: the metal substrate reflects infrared radiation when VO2 is in its low-temperature insulating state, achieving high thermal reflectance in cold conditions. When VO2 transitions to its metallic state at high temperatures, the thermal reflectance decreases, allowing heat dissipation. This inverted configuration resolves the contradiction by achieving the desired optical behavior (high thermal reflectance in cold state, low in hot state) while maintaining energy savings.
Solution Approach 2:
The patent employs a composite structure combining VO2 thin film with metal substrates (such as aluminum or silver). This composite material approach allows the system to leverage both the thermochromic properties of VO2 and the high reflectance properties of metals. The composite structure enables simultaneous achievement of thermal reflectance regulation and structural stability, resolving the contradiction between energy efficiency and manufacturing feasibility.
2Loss of energy
If VO2 is coated on metals to reverse the optical behavior and achieve positive regulation, then thermal reflectance regulation is achieved with correct optical behavior, but the regulator becomes opaque and not suitable for windows
Solution Approach 1:
The patent applies local quality by creating a multi-layer composite structure where different layers perform different functions. The VO2 layer (with thickness of 5-50 nm) provides thermochromic modulation in the infrared region, while the metal substrate provides structural support and enhanced reflectance. The layer thickness and material composition are locally optimized to achieve high thermal reflectance modulation while maintaining visible light transmittance above 70%, thus resolving the contradiction between thermal regulation performance and optical transparency.
Solution Approach 2:
The patent utilizes parameter changes by precisely controlling the thickness of the VO2 layer (5-50 nm) and the properties of the metal substrate. By adjusting these parameters, the system achieves optimal balance between thermal reflectance modulation and visible light transmittance. The thin VO2 layer allows visible light to pass through while still providing effective infrared reflection when in the insulating state, resolving the contradiction between thermal regulation and optical transparency.
3Loss of energy
If hydrogel is used for solar regulation through phase separation, then solar transmittance is strongly regulated in visible and NIR regions, but the phase separation mechanism can only shape the incident spectrum up to the near infrared region, so it cannot fulfill thermal radiation regulation across the entire incident spectrum
Solution Approach 1:
The patent merges two different mechanisms: the phase separation mechanism of hydrogel for solar region regulation and the thermochromic mechanism of VO2 for thermal infrared region regulation. The hydrogel component provides strong solar transmittance modulation in the visible and near-infrared regions through phase separation, while the VO2 component provides thermal reflectance modulation in the long-wavelength infrared region. This merging of mechanisms enables simultaneous regulation across the entire solar and thermal spectrum, resolving the contradiction between solar regulation effectiveness and spectral coverage versatility.
Solution Approach 2:
The patent creates a multi-functional system where the window coating performs multiple functions: solar transmittance regulation via hydrogel phase separation, thermal reflectance regulation via VO2 thermochromism, and structural support via metal substrate. This universal system addresses both solar energy management and thermal energy management across the entire spectrum, resolving the contradiction by making the system versatile enough to handle both short-wave solar radiation and long-wave thermal radiation.
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 window achieves efficient indoor temperature regulation in all weather conditions, with enhanced energy savings by dynamically adjusting solar and thermal properties, providing up to 6.8 times more energy savings than existing technologies.
Implementation Method 1
temperature-induced phase transitions
Implementation Method 2
thermochromic window
Implementation Method 3
thermal reflectance
Implementation Method 4
thermal radiation
Implementation Method 5
hydrophobic-hydrophilic transition of the absorber
Data Source
AI summary
A solar and thermal regulating window structure including: an optically-transparent housing frame; a reversible liquid absorbent material layer positioned in the housing frame; a thermally-reflective layer having high solar transmittance and high thermal reflectance positioned over the liquid absorbent material layer; a liquid, being absorbed in the liquid absorbent material layer below a selected transition temperature, and being positioned over the liquid absorbent material layer above the selected transition temperature, such that when below the selected transition temperature, the window structure facilitates indoor solar heating through solar transmittance during daytime and facilitates indoor heat insulation through thermal reflectance during daytime and nighttime, when above the selected transition temperature, the window structure facilitates indoor heat dissipation through thermal emission; and an optical film with high transmittance for both solar and thermal radiation, configured to seal the liquid absorbent material layer, liquid, and thermally-reflective layer in the housing frame. The window structure enables passive all-day thermal management in different climates.