In Germany, we have every year about 1000 kWh/m² sunshine (equivalent of 100 l diesel / m²) but most of it is available in summer when we do not need heating. By storing this thermal energy (TES), we are able to overcome the winter with what we have collected in summer. The easiest medium is liquid water with its high specific heat (water 4182 J/kgK compared to concrete 800 J/kgK). A typical method is working with a large pit, covered with thermal insulation (PTES) although other methods are also available. A nice introduction is given in the following paper.

Newly installed PTES with polymeric cover

Like described, large difficulties are present with the thermal insulation in the cover. Indeed, polymeric foams absorb large quantities of humidity while also spontaneous deforming is present due to the high water temperature and concentration of rain water on the cover. For that reason, the temperature of the water is limited to 75-80°C.

To improve efficiency, it makes sense to use cellular glass and 95°C water to increase the thermal energy content of the PTES. However, to protect the stainless heat exchangers and to avoid biological contamination, the water is kept of pH=9, which stimulates the corrosion of soda lime glass and so cellular glass. For that reason, the cellular glass should be protected against this corrosion. Stainless steel foil has a large corrosion resistance in hot alkaline water and has a matching thermal expansion coefficient with (cellular) glass. GLAPOR proposed a modular solution on the ISEC 2022 conference in Graz, Austria with the following poster.

By working with a modular system, we are able to assemble larger covers than possible today (100 x 100m) and a temperature up to 99°C is possible with these materials. On top of the cover, we can use typical flat roofing technology with polyurea and tapered solution to drain/guide the rain water. Moreover, a second function is possible with this solution, which can be a photovoltaic system, a large greenhouse (in situ heating), a swimming pool (in situ heating), … . This second function will be logic because most PTES will be located near cities, where the land is very expensive. This is certainly not possible with the polymeric solution like shown hereunder. The dramatic situation hereunder can never happen with a cellular glass cover.

The flat roof will be straightforward in the future because it can absorb the maximum of solar energy, independent on the orientation of the building. A flat roof on the other hand accumulates easily humidity in not-vapour-tight thermal insulation like XPS, EPS and mineral wool if there is no perfect vapour screen on the warm side. The perfect vapour screen does not exist and so perfect dry thermal insulation in a flat roof neither. Basically, the reason of this accumulation is the combination of a healthy humidity in house (50% relative), a cold winter and a waterproofing membrane induces humidity where the perfect vapour screen is absent (joints, poor labour, …)

For this reason, the cellular glass compact warm roof (warm roof = water proofing membrane on top of the thermal insulation) is known as the best solution on the condition that the joints are perfectly filled with bitumen. If these joints are partially not filled with bitumen, condensation of the present humidity induces in winter freeze and thaw. This causes open cells and the humidity enters almost permanent in the cells, increasing drastically the thermal conductivity. This has been observed by Prof. Dr. Hugo Hens, KU Leuven in the Belgian climate (interview November 17, 2022). This should certainly not happen when the joints are well filled with bitumen.

A cellular glass roof, installed with bitumen is hard to recycle at the end of its lifetime. In Germany it is not allowed anymore to use oxydized bitumens while installation with other bitumens is more difficult. As a consequence, the dry installation will become a necessity, even for flat roofs. This means that the surface cells have to be filled to be protected against freeze and thaw. According to Prof. Dr. Künzel, (Fraunhofer Holzkirchen, Stuttgart University and developer WUFI-software) (interview November 30, 2022) at least the top surface and sides of the cellular glass need to be coated against freeze and thaw damage. For the moment, there is no such cellular glass product available but some polymer coatings are straightforward.

If freeze and thaw resistant cellular glass should be available, we have the choice to install above (inverted roof) or under the water-proofing-membrane (warm roof). The major advantage of the inverted roof is that the water proofing membrane is protected against UV-light, temperature variations and mechanical damage. These are the causes that the membrane has a reduced lifetime on the warm roof. A nice paper states that the lifetime of a water proofing membrane at least doubles in an inverted roof compared to a warm roof.

Roof 4 is the inverted rood, roof 3 a warm roof with some ballast (protection) and roof 2 the unprotected insulated roof (typical compact roof). Roof 1 is the non-insulated roof. It is clear that an inverted roof with freeze and thaw resistant cellular glass has a life time of about 50 years after which the cellular glass blocks can be reused (no need for disposal or recycling). Using solar energy to the maximum will be a must and so the flat roof. The inverted roof is the logic choice due to its expected lifetime if freeze and thaw resistant cellular glass at (top and side surfaces) is available.

The inverted roof was originally patented by Dow Chemical for XPS like discussed in a previous post. However, XPS is a closed cellular structure based on polystyrene, which has a diffusion coefficient for water vapour, which is about 1 billion larger than in ordinary glass. For that reason, perfectly installed XPS absorbs humidity by diffusion in an inverted roof. This became even worse in the green roof, with its almost constant > 95% relative humidity, again according to Prof. Dr. Künzel by experiments and WUFI-simulations. In 20 years the thermal conductivity doubles and disposal is needed. This disposal is very expensive because the cost goes pro kg. After 20 years, XPS absorbs about 6 times its weight in a green inverted roof …

Although there are a lot of (negative and false) dogma about the inverted roof, in my opinion it will conquer the world with freeze and thaw (top and sides) resistant cellular glass. Disposal of the water proofing membrane after minimum 50 years and reuse of the cellular glass will be the arguments to get rid of the compact warm roof and its bitumen, causing a shorter life time and a high disposal cost. The first signs are already present. Austrian accredited expert Hannes Guggenberger states (telephone November 29, 2022) that he has already 4 years a good experience with a cellular glass inverted roof. If it works in the Austrian climate, I guess it works everywhere in Europe.

Installation of very light thermal insulation with a rendering on a new facade can in principle be done with an adhesive. However, most people don’t trust this because it depends on the state of the facade (wet by rain, contamination due to traffic, etc.). At that moment, they want mechanical fixings, which are anchored in the facade.

In case of a ventilated surface with more heavy thermal insualtion like cellular glass and with a heavy cladding, an improved mechanical fixing is needed.The patent of Willy Trittenbach, once a collegue is a nice example of such a very stable fixings. But stainless steel has thermal conductivity of 15 W/mK and GLAPOR cellular glass about 0.05 W/mK or a factor 300. This means that a 6mm screw cinducts the same amount of heat as a cylinder GLAPOR cellular glass with a diameter of 100 mm, which is a huge cold bridge. Besides the screw, also the legs are passing the cellular glass. The patents mention at least one fixing in every boards 450 x 600 or a cold bridge of about 10% of the thermal insulation. To remove this cold bridge, a new patent was taken.

This new patent eliminates works with a double layer insulation, separated by a board, which is fixed on the walls. In this case, there is no direct connection by a long screw between the surface of the thermal insulation and the wall.

However, in Germany ventilated facades have to be insulated with thermal insulation with melting point above 1000°C according to DIN 4102-17. Check the German product datasheet before ordering the thermal insulation in case of Germany.

In 2022, it is 90 years ago that Professor Ilya I. Kitaygorodsky presented cellular glass at the All-Union conference on standardization and production of new materials in Moscow. Therefore, BELGLAS BV conducted some research about this man, with which we share a common respect for cellular glass.

Professor Isaak Ilyich Kitaygorodskiy was the founder of the Department of Chemical Technology of Glass and Sitals at the D. Mendeleev University of Chemical Technology of Russia. In the following, I copy a part of an interview with Vladimir Nikolaevich Sigayev.

The Department of Glass is a legendary one. It was founded almost 90 years ago, in 1932, by the famous Soviet scientist, technologist #1 in the field of glass, Isaak Ilyich Kitaygorodskiy. Suffice it to mention that the ruby stars of the Moscow Kremlin were created on the basis of his developments related to glass coloring processes. I should remind you that the towers of the Kremlin were originally decorated with two-headed eagles. The builders of communism got to them only in 1937, and the eagles were replaced by metallic stars, which, however, were not visible at night and did not make a good impression at all. Therefore, it was decided to replace them by ruby-colored glass stars which fitted perfectly well into the architectural appearance of the Kremlin. It was a very beautiful design that complemented the brilliant work of Aristotle Fioravanti. 

Let us return to the foundation of the department. 1932 was a landmark year not only in the context of its founding. It was the same year when the famous article by William Zachariasen, the largest scientist of crystal chemistry, who laid the foundation for the theory of the glassy state structure, was published. By the way, this two-page work remains the most cited article in glass science to date. 

Kitaygorodsky, the founder of the department, worked as a chief engineer at a glasswork in Zaprudna near Moscow before the events of the 1917 revolution. Kitaygorodsky set up the production of light bulbs at this, judging by the preserved photographs, quite ruined facility. In fact, as they say today, he started the process of import substitution, and beginning from 1913 Russia has been using domestic light bulbs. After 1917, when the entire country was electrified under the GOELRO plan, they began to be called “Ilyich bulbs,” referring not to Isaac Ilyich, but to Vladimir Ilyich, which I find a major historical injustice. 

Later, the activity of the department covered all the variety of glass technologies, including all the new challenges coming from the needs of instrumentation, medicine, and ecology. The main challenge was related to the improvement of sheet glass and organization of its multitonnage production (95% of all glass production is oriented on the creation of window sheet glass, i.e., glass used in architecture). The problem of sheet glass production was finally resolved with the aid of the so-called float technology, which makes it possible to obtain nearly perfect glass sheets up to six meters wide by melting the glass mass into liquid tin. In Russia, this problem has been solved when foreign companies came to the Russian market such as “AGC,” “Guardian,” “Pilkington,” etc. It is difficult to overestimate the contribution of Kitaygorodsky and his students in the development of sheet glass, electrovacuum, medical glass, foam glass, and seals.

Today, a lot of research about cellular glass is again performed in Russia. I guess that our spiritual father will be pleased.

The inverted roof has the thermal insulation on the waterproofing membrane. A better but less known name is the Protected Membrane Roof (PMR). Another contraction was IRMA (Inverted Roof Membrane Assembly), which was once a registered trademark of the Dow Chemical Company. Moreover, Dow Chemcial company had once a patent on the inverted roof. It was filed in 1965, which means that there was no absolute freedom to install this type of roof in the USA untill 1985.

The patent describes that the thermal insulation has to be watertight and should not absorb humidity. It is a surprise that this patent showed up 24 yeasr after the invention of the XPS. The patent mentions also cellular glass in its introduction: The thermal insulating layer, employed in the practice of the present invention, beneficially is a closed cellular material which is substantially water impermeable. Particularly beneficial and advantageous, for use in the pres ent invention, are cellular plastic foams of a closed cell configuration including styrene polymer foams, styrene acrylonitrile copolymer foams, styrene-methylmethacry late copolymer foams, polyvinyl chloride foams, poly ethylene foams and other water impermeable materials available in cellular foam form which are well known to the art. Foam glass is particularly advantageous when it is desired to omit a protective layer over the thermal in sulating material. A protective layer beneficially is employed when synthetic resinous organic cellular thermal insulating layers are utilized. Such organic materials are generally subjected to decomposition when exposed to weather and more particularly when exposed to Sunlight.

Cellular glass can not be used in freezing countries because freezing water in the open cells on the top surface will induce cracking and water absorption. For that reason, cellular glass was only used under the water proofing membrane like shown in the many applications of GLAPOR cellular glass. However, if your are able to solve the problem of open cells at the surface of cellular glass, the way is open to use cellular glass in an inverted roof. The advantages in these sustainable times are clear.

Since less than one year, a patent was published, which claims to solve this problem. This patent from a Belgian inventor works with a mineral protective coating on the cellular glass surface.

This patent does not refer to the original inverted roof patent but is on the other hand very extended. It describes a few detailed methods how to prepare a mineral protective coating on the cellular glass. All these coatings are based on alkali silicate solutions with mineral fillers and even some testing in a climatic chamber for facades is included. The coating is proven to be resistant to UV, higher temperatures and freezing water. I guess that a mineral coating, based on hydraulic lime could also be suited. I used it once for a “sculpture” and it survives already 15 years in a Belgian climate, even the horizontal part.

Choosing between a warm roof (thermal insualtion under the water proofing membrane) or an inverted roof is choosing between the risk for damage / wear at the thermal insulation or damage / wear of the water proofing membrane. I guess that the second risk is at least more acute. An inverted roof needs ballast on the thermal insulation, which makes the roof construction more expensive. But Germany is going in the direction to make ballast on the water proofing membrane an obligation for every flat roof.

If the roof construction can bear ballast and cellular glass with a mineral coating is available, an inverted roof with loose-laid cellular glass is the most durable solution. Indeed, the life time of the membrane will be very long (no UV, stable temperature and no mechanical damage) and recycling at the end of the roof life (building life) will be much easier. These coated cellular glass blocks can be found at Hytherm CG and I guess other suppliers of cellular glass will follow. In the UK, non-combustible thermal insulation is an issue since the incident with the Grenfell Tower, while the inverted roof with the combustible XPS was very popular there. Mineral coated cellular glass is there a big opportunity today.

In my opinion: “The warm roof is dead, hurray the inverted roof”

In the mean time, we learn the above patent has been aborted.

Recently, a nice YouTube-movie appeared about full printing a 3D-house. The house was put on GLAPOR cellular glass gravel, while the flat roof was insulalted with GLAPOR-boards.

The movie shows the use of cellular glass gravel and the printing of the house, layer by layer. In fact, the house was printed by only two people and a huge cement mortar printer. The challenge was to develop a mortar, which allows printing but which does not flow after printing.

More information about the printing can be found in another YouTube movie.

The company Jahan Ayegh Pars in Isfahan, Iran started with the production of cellular glass due to its unique properties and because it is was hard to get in Iran. I am a little bit surprised about the name because they must be aware about Pittsburgh Corning.

Just like IZOSTEK , STESS and GLAPOR, a family take the initiative to develop a process and build the production facility. Further, they organize succesfully a sales environment. In this case, the company already produces mineral wool, ceramic wool and PIR industrial technical insulation.

In this case, I also measured the gas composition in the cells to check for closed cells and to estimate the thermal conductivity, which is not published. The cells are indeed 100% closed and I estimate the thermal conductivity to be 0.046 W/mK for the 115 kg/m3 density and 600 kPa compressive strength. Although recycled glass is used without remelting, JAP achieved a low H2 content below 3%. In view of the low energy cost, labour cost and recycled glass use, I estimate the production cost of this material between 50 and 70 €/m3. In the Middle East, such a producer can be a game changer. A chromatogram is given hereunder.

We are 100% sure that we hear much more about this porducer in the near future.

To understand fully the unique properties of the different types of cellular glass, it makes sense to read some more didactic books for glass science. I found these books on the Internet and I guess I am allowed to mention them.

The first work I like to advise is the under graduate student book of James E. Shelby. I got sympathy for the book by its definition of a glass: A glass can be defined as “an amorphous solid completely lacking in long range, periodic atomic structure, and exhibiting a region of glass transformation behavior”. Any material, inorganic, organic, or metallic, formed by any technique, which exhibits glass transformation behavior is a glass.

The second work is a little bit more academic. About glass is a shorter but more difficult version of the above one. 

Cellular glass can be foamed from different glass compositions. The history of the glass composition is the perfect introduction how the world evolved from colored glass beads to optical fibers. This topic is interesting because cellular glass is the best method to recycle all kinds of glass. 

Knoppix is well known as a live-LINUX in Germany, which allows to taste LINUX on a CD or DVD, without writing on the hard disk of your PC. Any possible damage on your Windows-system is excluded. Klaus Knopper started in 1998, already 23 years ago as a LINUX and open source software consultant. He also developed his own LINUX, KNOPPIX on a live CD/DVD and later on a USB-flash drive. Since USB 3.0, such a flash drive is fast enough for a gentle opeation.

This standard KNOPPIX USB-drive (XTRA-PC) is delivered by SoftwareFair for 23.85€ in Germany, delivery included within 2 days. After plugging into an (old) PC and booting for the US-drive, the LINUX system runs. The orginal PC-XTRA does not allow writing on the USB-flash drive, which means that extra installed programs are lost after shutdown. For that reason, you will find on the desktop a button to make a copy of the USB-flash drive with an overlay up to maximum 65GB. Once booted with the new USB-flash drive, all work and installed programs will be saved on the USB-flash drive. This USB-flash drive can be used on any Windows of Mac computer, every where on the world, even without internet connection with all your work included.

The USB-flash drive system contains a preinstalled an enormous amount of open source software. Libreoffice (Office replacement), GIMP (Photoshop replacement), a terminal emulator, Chromium webbrowser and a File explorer are a few examples. I included a FORTRAN compiler, which allows to run all my old programs, Texmaker (to work with Latex to write my book), YAD to generate a graphical interface and Anydesk to be able to take over PC’s of my customers all over the world. All this software is easily loaded from the Debian site but don’t forget to run first the “sudo apt update” command before installation.

As a service, BELGLAS sells this USB-flash drive with possibly all the FORTRAN programs, with and without source, I have written about cellular glass annealing, foaming, thermal shock, pipe thermal insulation, … . By nature, when your PC is booted with this USB-flash drive, all the programs will run for sure.

At last but not at least, I like to thank Klaus Knopper, who developped this valuable tool.

In a previous post in 2016, we already reported on this move of Windows. At that time, a real BASH – shell was available. In this application, only text based programs without GUI could be run. Today, we have WSL2 (Windows Subsystem for Linux), which works with a real Linux-kernel and allows to call GUI-programs from the command line.

WSL-Ubuntu can be run as in a terminal of  (as an example) MobaXterm. The X-server of MobaXterm (free for home-use) makes the GUI possible. We have succesfully installed and used

• GNU FORTRAN
• Mousepad and Gedit editors
• GNUplot to show our data
• LibreCad to make 2D drawings
• Qpdfviewer to show pdf-files
• Krusader to search and navigate in the filesystem.
• Zenity to write BASH scripts with GUI

It is possble to enter the Windows filesystem, which is mounted under /mnt and in this way, Linux and Windows-applications can be run on the same files. A C-complier and Python2 and python3 interpreters are already standard availbale with WSL-Ubuntu. The ordinary scientist has everything for his standard scientific work with this WSL-Ubuntu.

We may speculate about Windows 11. Will it be totally based on LINUX and in that way make all other LINUX-distros unnecessary? I would not be surprised. In the mean time, I enjoy the feeling that a community of free of charge working programmers clearly influence the decision of a large multinational.