Vacuum Insulaon for Window 201 Buuildin Teechnologie OffifficPeee Revvie Pictures of NREL’s transparent vacuum insulation for windows. The pictures show that the evacuated components are transparent while providing superior insulation in a flexible structure that can be retrofitted to installed windows. Image of vacuum capsules on low-e coated films and 3M#Pres(ge#70# 3M#Pres(ge#90# Glass# glass, after multiple sprayed layers. Lin Simpson, [email protected] Naona Rennewabl Ennerg Laaborator Project Summary Compevely Selected Award FOA 823 Key Partners: Inial TRL 2: laboratory validaon inial principles Engaging commercial companies that can provide Final TRL: 5: Reasonably realisc integraon for tesng key strategic alliances for manufacturing and specific market applicaons. Partners include Timeline: vacuum capsule, low-e film, and window Start date: October 1, 2013 manufacturers. Planned end date: 2015 Key Milestones 1. Assess vacuum insulaon materials with less than 0.007 W/m-K thermal conducvity; September 30, 2014 2. Deliver VI with low-e for external tesng; Project Goal: September 30, 2015 This effort is assessing the impact vacuum Budget: insulaon (VI) will have for window applicaons Total DOE $ to date: $750,000 FY14 & 15 using novel evacuated materials (that are so small as to be invisible) integrated with low-e coated Total future DOE $: $0 plasc films. The ulmate goal is to develop materials that have R-5 to R-20 insulaon values Target Market/Audience: and have the correct form factor for easy This effort addresses the large installed windows integraon with installed windows (i.e., flexible, retrofit and inexpensive high performing new thin, and applied like nng products). windows markets to substanally improve fenestraon and building envelope energy effici2 ency. Purpose and Objecves • Problem Statement: Buildings use ~40% of the energy and produce ~40% of the CO2 emissions in the United States (US) today. – Windows can account for 30% to 50% of the energy losses in buildings. • It could take decades and trillions of dollars before replaced with highly insulang windows. • Thus substanal need for retrofing installed windows to improve energy efficiency. – This effort is assessing vacuum insulaon (VI) for window applicaons using novel evacuated materials (that are so small as to be invisible) integrated with low-e coated plasc films. – Goal: develop R-5 to R-20 insulaon that has the correct form factor for easy integraon with installed windows (i.e., flexible, thin, and applied like nng products). • Target Market and Audience: This effort addresses the large installed windows retrofit and inexpensive high performing new windows markets to substanally improve fenestraon and building envelope energy efficiency. – Could save 1 to 3 quads of energy annually in US. • Impact of Project: The project creates R-5 to R-20 transparent VI films that ulize nano- to micrometer sized vacuum capsules integrated with standard low-e coated flexible window plascs. – Near-term impact path: quanfy insulaon, transparency, cost, and other performance criteria to idenfy high-value market opportunies to support inial transion to commercial products. – Intermediate-term impact path: Work with commercializaon partners to opmize manufacturing and performance for specific applicaons – Long-term impact path: Work with commercial and residenal building communies to develop rapid market penetraon strategies to help decrease energy use and CO2 emissions as quickly as possible 3 Background: “Standard” Thermal Conducvity Calculaons • Calculated thermal conducvity of Classic Thermal Conductivity capsule materials using ”standard” Literature Results thermal dynamic assumpons – Assumes no radiave transport at 20 °C – For conducon only: through air & capsule material – Thermal conducvity directly related to the true density (ρt) of the capsules • Ρt = [1−(d/D)3] ρ0, – d is the average internal diameter, Typical assumption that thermal – D is the average external diameter, and – ρ0 is the density of shell part excluding hollow conductivity directly related to cross part sectional area of solid material and air; dominated by TC of solid material. In effect, to reduce the TC of the system: 1. increase the ratio of d to D and 2. Increase the stacking coefficient of capsules, which also means to reduce the true density and increase the amount of capsules. 4 Overestimates Solids TC by >10X Progress: Insulaon Beer Than Calculaons & Vacuum, WHY! • “Standard” TC assumpons: _________________ _____________________________________________________________________ Air conduction – Over-esmates solid conducon contribuon. ~25 mW/m-K – Wall thickness and amount of solid material not the issue – Conducon through solid components bole necked at small contact points. • True for most porous insulaon • Radiave and gas convecve/conducon Note: “air” (not solids) heat transport much larger in pure vacuum between solid materials Aerogel and open spaces than in insulang including with vacuum structures: materials being developed for this project. capsules! Solids 2-5 nm • Convecon not applicable with small diameter (micron) spaces Pores with air • Conducon through air largest component <100 nm diameter Literature results of capsules w/ air inside Note TC of solid components of perlite, aerogels, and capsules all over 10 time lower than “standard” model predicts!! 5 NREL’s Approach to Achieve High Insulaon Values • Use <100 nm sized vacuum capsules In vacuum, point contacts – Needed for transparency – Decreases pore sizes between capsules between adjacent • Decrease pore sizes with air to decrease air thermal short circuit. capsules have high – Perhaps < 10 mW/m-K with capsules thermal resistances • Evacuate capsules decrease TC – Perhaps < 5 mW/m-K With air between • Increase evacuated volume to >80% capsules, effective TC that – Perhaps < 3 mW/m-K of air and capsule • Low-e coangs to reduce IR coupling – Perhaps < 1 mW/m-K • Minimize capsule contact area Note space between • Perhaps organic molecules used for self-assembly decreases evacuated capsules is conducon as well (i.e., Kapitza resistance, phonon interference) “air” not solid material! Overall Approach: Use basic processes and materials to form smooth vacuum capsule layers with structure that minimizes thermal conductivity • Possibly maintain thin flexible plastic sheets properties. • Inexpensive and scalable to high throughput manufacturing. • Demonstrate transparent R-5 to R-20 films Key Issues: Thermal conductivity measurements below 20 mW/m-K Distinctive Characteristics: Highly insulating transparent film will be a game changer for windows, resulting in substantial energy and CO2 reductions 6 Progress: Ultra low TC Measurements an Issue • Spent substan;al ;me trying to accurately measure low TCs of porous materials o Hot Disc system provides reasonable TC values for standard non-porous materials – Measurement very reproducible, but “contact” issues with porous materials may be problem o Working with “NIST” standards and alternave measurements o Need to work through thin film versus bulk issues as well o Appears to give reproducible “relave” TC values to provide processing feedback 200" Literature"Values" 150" Hot disc overestimates the Hot"Disc"Measured"Values" thermal conductivity of 100" porous materials with air or vacuum in the open spaces 50" between the solid materials by 10 mW/m-K or more. 0" Thermal(Conduc/vity((mW/m7K)( Cork" May have more issues with PMMA" Aerogel" NIST"1459" materials that have smaller NIST"1450d" contact areas with sensor Foam"Insula5on" (e.g., vacuum capsules). Air"in"Vacuum"Capsules" 7 Accomplishment: Low Thermal Conduc4vity Measurements • Must go to evacuated materials to validate measurement systems to below 10 mW/m-K o Materials have lower thermal conduc;vity when air removed o Hot Disc systemacally has higher measured TCs – Clearly overes;mates TCs. All levels of vacuum? – Systemacs may be good enough to get relave TC values 45" Open"Cell"Polyurathane" 45" VIP"Aerogel:"No"Carbon"8" 40" Literature" 40" Literature" VIP"Aerogel"Hot"Disc" 35" Open"Cell"Polyurathane" 35" Measure" 30" Hot"Disk" 30" VIP"Aerogel"w/"Carbon" 25" 25" Literature" 20" 20" 15" 15" Should be ~ 4 mW/m-K Should be ~ 5 mW/m-K 10" 10" 5" 5" Thermal(Conduc/vity((mW/m7K)( Thermal(Conduc/vity((mW/m7K)( 0" 0" 0.1" 1" 10" 100" 1000" 10000" 100000"1000000" 0.1" 1" 10" 100" 1000" 10000" 100000"1000000" Pressure((millitorr)( Pressure((millitorr)( 8 Accomplishment: NREL Vacuum Capsule Measurements • NREL working to validate hot disc to very low thermal conduc;vity measurements (e.g., < 0.005 W/m-K). • Hot Disc measurements of vacuum capsules are higher than literature values. (pressures in graphs are for outside the vacuum capsules) • Clearly NREL’s evacuated materials have lower TCs – As much as factor of 3 decrease in TC – Inside capsules evacuated to ~10-7 torr 40" Literature"of"Panel"of" 40" Hot"Disc"Measured" Capsules"with"Air"Inside" 35" 35" Evacuated"Capsules"Bulk" Literature"of"Capsules"with" 30" Air"Inside" 30" Hot"Disc"Measured"Capsules" 25" Hot"Disc"Measured"Capsules" 25" with"Air"Inside,"Bulk" with"Air"Inside,"Bulk" 20" 20" 15" 15" 10" 10" 5" 5" Could be <1 mW/m-K Should be <2 mW/m-K Thermal(Conduc/vity((mW/m7K)( 0" Thermal(Conduc/vity((mW/m7K)( 0" 0.1" 1" 10" 100" 1000" 10000" 100000"1000000" 1" 10" 100" 1000" 10000" 100000" 1000000" Pressure((millitorr)( Pressure((millitorr)( 9 Accomplishment: NREL Vacuum Capsule Insulaon • Vacuum capsule insulaon 5 mes beer than aerogels or fumed silica. – TC of solid vacuum capsule components less