Recent content by PaulMuadDib

@erobz I have added the convective model (with h = 100 W/m²K, trying to find litterature about underground convection) in my excel sheet... it basically creates a small difference between the outward wall surface and the underground environment, and enables a small loss by radiation (significant...

Sorry @erobz, I misunderstood your question, the cooling phase will start from end of october to early febuary: mean temperature is 9.9°C during this period (while my underground garage stays around 13°C in a very stable manner from november to febuary)

Over the last year, the annual average was 16°C (in a shaded box outside)

I understand your model with the surface boundary condition, thank you @erobz. Solving it for ##T_s##, I get ##T_s=\frac {T + R.h\ T_{\infty}}{R.h + 1}## and if the product ##R.h## (##=\frac{L h}{k}##) is large (with your values ##R.h=2500##) then ##T_s - T_{\infty} \approx \frac{T}{R.h} =...

First simulation (conduction only) for paraffine/wax. With 4 ##m^3## of wax heated to 150°C, I initially store 550 kWh, I get 350 kWh 3 months later (63 % remaining, thanks to 210 kWh stored as latent heat) with a much more reasonnable insulation (no fire brick, 15 cm of rock wool and 15 cm of...

If the heat storage is underground, can I at least hope that convective heat losses are limited ? 🫣 The radiative heat loss already kills my hope in fact... I'm gonna heat the ground even with a good thermal insulator 🙄 Unless I can shield radiative losses in an economical manner ? In the same...

This an exploration of feasability (technical, economical) of a basic thermal solution storage, but I am not a specialist in this area ! I have a small pool I will no longer fill (water becomes scarce here, I am at 15 min from the sea). In winter, I use a heat pump and a small wood stove...

@Chestermiller Thank you for the correction of the time derivative ! @Demystifier I would have to add a radiative term $$\sigma e S (T^4 - T_{ext}^4)$$ where T and e are the temperature and the emissivity of the outer layer of the insulator ? (polyurethane). It seems indeed huge: for S = 15 m²...

Hello. These 1000°C are required to reach a sufficient heat amount (1800 kWh) initially, to get a minimum of 600 kWh 6 months later, but this will not be praticable (heat resistance of the tubular heat exchanger / TBE within the sand, dilatation, volume of the insulator, price,...). I don't know...

Hello there, My background is about signal processing, and after having installed a complete photovoltaic generator (7.2 kWp in 3 directions, Victron system) & storage (21 kWh of Pylontech batteries), heat pumps to heat the house (combined a small Jötul stove) and the domestic hot water, I am...

Hi there, I am not a thermal sciences specialist, and I try go get an idea of the insulation required to retain heat in a sand battery for a few months. I have a small pool (4 x 2 x 1.5 m) and I am questionning myself about two options: either converting this pool into a water storage or into a...