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Garald

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  1. I'll probably have to do that myself then. I guess all laser thermometers are born equal?
  2. Weather Underground states the temperature at a nearby weather station to have been 13C when we got started (8:30am) and about the same when I dropped by, but it peaked at 19C in the afternoon. Really not great, but we did what we could - we'd even programmed things in advance so that we would get a spot of cool weather. The first full week in June will be about the same - that will be our last chance to hire someone to use a thermal imaging camera and not get garbage, I take. Before we tested the walls with a laser thermometer (Wednesday morning) I took care to heat the entire house up to 30C. We did get very different results on different walls. All recent windows were surprisingly good (they were about 29C) but the walls were all over the map, from 20C to 30C, if I remember correctly. (25C seemed typical; only a couple of nasty spots got 20C).
  3. Got the keys on Tuesday. The morning of the purchase, I set the heater on low, and set the thermostat to 26C. When I went back in the evening, the house was properly overheated, in spite of its poor insulation, and the heater showed 40C as the water temperature. (Of course it may have gone higher; the heaters felt somewhat warmer than 40C, though not by that much - I could put my hand on them for an arbitrarily long time.) It wasn't a cold day - just a rainy spring day, with sun for a couple of hours in the afternoon. The previous owners told me that they never put the heater at a level beyond medium (which seems to correspond to 60+epsilon), and that seems to have been quite enough even in winter, even though the insulation is quite bad. All in all, I suppose that's evidence that a low-to-medium temperature will suffice, right? The radiators are largeish (except for those in the main library, which also has southern exposure and a chimney). I had a long talk with the architect on Wednesday while she checked every wall with a thermometer. We'll probably choose 15-20cm of alveolar insulation (synthetic), except for a wall with humidity issues, where we plan on using hemp-based insulation, and a few places where we don't have much width to work with and we'll use cork (or something as high-performing as cork). Sounds reasonable? We haven't got thermal images yet - I'm trying to hire a certified technician to do that, so that I can get the subsidies you are supposed to get in France when you undertake major energy-efficiency renovations.
  4. Right, I'm going to be working on all three. Or rather, I'll be helping the architect a bit on the first two, and watching her work on the last one; she's a ventilation expert. I'm getting the keys in ten days' time, and then we get started with a thermal camera.
  5. Well, but it is becoming the thing - Passivhaus and so forth; the question is whether get any of that to any perceptible extent when renovating an old building.
  6. Well, I said it was veering off-topic, but it *is* solar thermal, after a fashion, with a wooden tank full of books instead of water, and serving both as solar panel and as a radiator.
  7. Oh. I was assuming 0 light reflectance. So, the conclusion should really be: it is not necessarily stupid of thinking of bookshelves with solid-wood back panels that are relatively dark (varnished, painted, it may not matter)?
  8. And on books, right, I would never put them in a basement. Direct sunlight indoors is not that bad - at most, the spines will get discolored over the years. I don't recall that actually happening to me - though come to think of it, my Springer volumes do seem to be of many different shades of yellow now... At any rate, since I've barely noticed, it's not a problem I would think important.
  9. Let me see. Consider a fairly sunny winter morning in late December, with sunlight falling head-on to bookcases directly in front of them (this is essentially what the simulation shows), transmitting about 10 W/m^2 to the bookcases. It's actually hard to choose whom to believe about the volumetric specific heat of different kinds of wood - if you believe that, as is often stated online (e.g. https://tinyurl.com/4hmedzr9), the specific heat of pine is 2300J/kg C (at which humidity?) then IKEA pine would have a volumetric specific heat (heat capacity) of 0.92*10^6 J/m^23C - yet, according to https://tinyurl.com/yc72tjhz (which looks like a serious source), even oak barely achieves 0.85*10^6 J/m^2 C at 10% humidity. Well, let us say that we have empty bookcases with backpanels that are made of 2cm of solid wood with volumetric specific heat 0.8*10^6 J/m^3 C. That gives us 16kJ/C per square meter of surface. Since 10 W/m^2 means 36 kJ/hour m^2, we see that the backpanels are getting 2 C warmer every hour, for, say, 2 hours. Surely that's good - that means that the bookshelves are absorbing not so very little heat without breaking a sweat. What difference will they make on the room temperature, or on the energy radiated in the course of the day to someone directly in front of them? I don't know. What is also clear is that a flimsy backpanel would not absorb all that heat (its temperature would change significantly and quickly, and then its heat-absorption properties would change). Of course there are also books, but they don't cover the backpanel entirely. The moral, I guess, is that it is not actually stupid of thinking of having bookshelves with solid-wood back panels, if they are going to have sun shining directly on them on sunny but cold winter mornings, and you'd like the heat back later in the day. Putting 3mm cork sheets on the back of those panels may be overkill (since the temperature of the backpanel will have risen by at most 4C or so) or not - I do not know. Or am I interpreting this wrongly?
  10. Sorry, winter *morning*. 15 W m^{-2} is slightly optimistic but not wrong, at least not on a sunny day. See http://susdesign.com/windowheatgain/index.php Bit counterintuitive, in that the peaks for March and October are higher than those at other times - why is that? Bit funny that 15 W/m^2 should give very little rise in temperature, given that that's not what it happens in the summer, and, if the app is right, one doesn't get more than 10 W m^{-2} then. Latitude 49 N, orientation SES.
  11. I wouldn't be worried about March or October - most people already have their heating on by then - or April, since then only the lowest part of the long wall is exposed. (The left wall is occupied in part by a mantelpiece.) In September, the issue is mainly light falling obliquely between 7:30 and 9:30am, from the right window to the left part of the long wall; heat transfer should be less because of the sharp angle (together with the low altitude), no? Closely related if somewhat off-topic: I am planning on installing floor-to-ceiling built-in bookcases. When I was a few days younger, and even more naive, I went around asking how should I go about choosing the material for the bookcases (and so forth) so that they would absorb a bit of heat during winter mornings (which is when they would be fully exposed to direct light head-on - low-altitude, but still) and release it during the day. I was told that I was being silly, in that it is a better idea to let the sun heat water rather than wood. It didn't seem like an either-or to me (do you make bookcases out of water?), but that obviously pointed me in the direction of solar thermal. Now I'm back to where I started. It's hard to get consistent information on the heat capacity of wood (in part because it depends on several different factors), but apparently it is descent - if I understand correctly, the volumetric heat capacity of oak is somewhere between half that of concrete (http://www.international-agrophysics.org/Thermal-properties-of-wood-and-wood-composites-made-from-wood-waste,142472,0,2.html) or about that of concrete, and the same is true of dense pine (the heat capacity per gram is about the same as that of oak). Of course direct light coming through a window on a winter night just doesn't carry that much power, but even if someone sitting or lying down in the reading nook were to gain 1° C, that would be something. Haven't done any computations that would tell me whether that's the right order of magnitude. At any rate, maybe there's a point to this: bookcases of dense, dark-ish wood, with, say, cork behind the back-panels to provide a bit of insulation. But then perhaps the effect would be negligible, and I might as well choose light-wood bookshelves to get more light in the rest of the room. Can people eyeball this? As I was saying, an order-of-magnitude feeling for things should be enough to tell what makes sense.
  12. Oh, I just treated a window as an opening. I'm just showing where direct light falls, not how much of it does! There has to be a tiny error due to refraction, but all mesures were taken by the architect to the nearest 5cm anyhow (the real estate agent was in a hurry), so I was not going to bother. We will probably make an opening at a particular place in the long wall (an opening to be hidden behind a cabinet door, that is) to let direct light into the bedroom on winter mornings. For detailed modelling of light (with serious work on reflection), there are various front-ends using Radiance (https://www.radiance-online.org/). I found all the ones I tried to be kludgy, and the back-end itself a little archaic - there went an evening. I couldn't see whether there was any way to make it do what I wanted it to do (showing where direct light fell). I don't know what sort of professional software there is for thermal modelling. In the end I found it easier to write my own program in Python/SageMath (using the Pysolar library to compute altitude and azimuth as a function of time, and the Three.js library to get the animation running). I put the clock on the wall because the Sagemath-Three.js interface is somewhat incomplete - it wouldn't let me put the time on the corner of the picture, as something extradiegetic, so to speak.
  13. I was just talking a friend who has more experience than I of the practical side of things (well, same friend as above). He essentially said that he thinks of solar thermal as something for large families. Makes sense: who else needs lots of hot water during the summer?
  14. PS. Knowing how to program is good for something in this context. Here's a simulation I did last weekend of sun exposure in my new library (the largest and most important place in the house): https://webusers.imj-prg.fr/~harald.helfgott/simulcurie/21_6_2021.html (summer solstice) https://webusers.imj-prg.fr/~harald.helfgott/simulcurie/21_8_2021.html https://webusers.imj-prg.fr/~harald.helfgott/simulcurie/21_12_2021.html
  15. a) I have no idea of who the radiator manufacturer was. b) Primitive solution: if only it were still cold outside, I suppose I could just run the radiators at full blast and see whether they overheat the place (that would be a good thing, since it would indicate a lower temperature might be sufficient). I suspect they will; the place was well-heated during the first visit in a cold day in January, and insulation was and is terrible, so, once I insulate the place well... (Of course sales in France take forever. My architect is hoping for the last cold wave of spring so that she can check for thermal bridges.) I'm in pure maths (not strictly speaking a science). Did a double degree in maths and computer science (which *really* is not a science) before doing my postgraduate studies in maths. I would like to believe I am not completely illiterate in physics, but I'm not quite sure that's true, and at any rate it depends on the subarea. I *think* I am a quick study in physics (well, you'd expect it it from someone in math, particularly analysis and allied areas) but that may just be Dunning-Kruger.
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