Half a croissant, on a plate, with a sign in front of it saying '50c'
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Solar/Antisolar Heating/cooling

Seperate warmth and coolth, making them more useful.
  [vote for,

Start with a thermal solar collector, and modify it so that it is radiatively insulated from terrestrial sources of infrared. That is, it can see the sky, but not trees, houses, the ground, etc.. This allows it to collect the sun's heat during the day, and radiate heat to the sky at night. This solar collector should be on one's roof, or on top of a tower. The height ensures it isn't shaded during the day, and better hides it from ground sources of heat at night.

At a more convenient location (perhaps ground level), place two thermally insulated pressure vessels. One will be a hot thermal reservoir, the other a cold thermal reservoir.

These reservoirs, and the solar collector, will be filled with a refrigerant... one whose freezing point is below any temperature that the system will ever experience.

Include a pump, and electronic thermostats at the top and bottom of each thermal reservoir, and the top and bottom of the solar collector.

Whenever the temp at the top of the solar collector is higher than the temp at the top of the hot tank, the pump is used to move liquid refrigerant from the bottom of the hot tank to the bottom of the solar collector. A check valve allows gaseous refrigerant to move from the top of the solar collector to the top of the hot tank.

Any time the pressure of the hot tank is above a certain limit, the pump is prevented from turning on... this prevents excessive heat/pressure from occurring in the hot tank or solar collector.

Whenever the temp at the bottom of the solar collector is below the temp at the bottom of the cold tank, a valve is opened, allowing the liquid refrigerant from the collector to move, by gravity, through a check valve, to the bottom of the cold tank. Another check valve allows gaseous refrigerant from the top of the cold tank to move to the top of the solar collector.

Excessive chilling isn't a concern, because we've selected a refrigerant with a very low freezing point, and excessive low pressure isn't a concern, because the external pressure is one atmosphere.

When the temp of the collector is between the temps of the tanks, heat can't move in either of the "wrong" directions, due to the various check valves.

Note that pumping is only needed during the day... thus, we can make good use of photovoltaic power. At night, we only need to open or close valves... this is easy to do using batteries that were charged during the day.

If the cold tank is placed below the level of the collector, but above the level where coolth is needed, heat can be passively moved from one's home to the cold tank using either a thermosiphon or heat pipe.

Similarly, if the hot tank is placed below where it's warmth will be needed, warmth can be passively moved into one's home via either a thermosiphon or heat pipe.

(Obviously, for both of these purposes, a thermostat should be used to regulate whether heat transfer is allowed to occur.)

If the cold tank is below the level where coolness will be needed, or if the hot tank is placed above where heat will be needed, active systems will be needed to get the heat where it needs to go.

goldbb, Oct 01 2009

(?) Double-ended thermosiphon http://img142.image...2/5907/39240923.jpg
[Freefall, Oct 08 2009]


       Which part(s) isn't/aren't feasible?
goldbb, Oct 06 2009

       The basic concept is sound, but the details of thermal storage need some work. Simple thermally insulated pressure vessels won't do; they just don't have enough thermal mass to make much of a difference. While you can store lots of heat, you need to pump that heat when the storage temp is higher than what the roof panel can create. Similarly, while you can cool by radiation, you'll need to pump heat out of the cold reservoir when it is colder than the roof panel. Since pumping heat requires energy, this will very quickly become inefficient.   

       If, on the other hand, you had a large thermal mass available (say, a big insulated block of concrete installed prior to building construction), you could store more heat, but at a lower temperature. Cold could be similarly stored by choosing a refrigerant mix which produces a slurry as one component freezes before the other. (glycol is good for this).   

       While your idea is good, it is already being done to a certain extent. Some large air conditioning installations run full-power at night, freezing a solution of glycol and water. During the day, the chiller is turned off, and the cold slurry is used to cool the building.
Freefall, Oct 08 2009

       Assuming that an insulated block of concrete (with tubes of refrigerant going through it) has a higher specific heat capacity (measured in joules of heat needed to raise one dollar of substance one degree) than that of an insulated tank of refrigerant, then it will be a better material for the thermal storage than a tank of refrigerant.   

       However, I don't see why the maximum temperature (of the hot thermal mass) would have to be lower.   

       I can see how the *rate* at which heat can be added to / removed from concrete might be lower the *rate* at which heat could be added to / removed from liquid refrigerant, since concrete isn't a speedy heat conductor (it takes time for heat to move between the tubes of refrigerant, and regions of concrete not near those tubes).   

       However, unless you expect concrete to crack or otherwise fail at high temperatures, I would expect the maximum *temperature* should be just as high with concrete as with liquid refrigerant.   

       (Considering how much heat can be stored in the form of latent heat of fusion, might not a tank containing a mix of waxes, with an appropriate range of melting points, be even better than concrete? That is, store high temperatures the same way one might store low temperatures.)   

       If the size of the hot thermal mass is sufficient, then the heat collected during sunny days will be enough to warm the house and heat the water through each night, and the cloudy days between the sunny days.   

       Since solar collectors in the sun can potentially get very hot, much hotter than the highest temperature we'll ever need to use, pumping heat shouldn't be necessary.   

       That is, we don't need to pump heat if we choose to only move heat into the hot thermal mass when the solar collector is hotter than the thermal mass.   

       Similarly, if size of the cold thermal mass is sufficient, then the cooling accomplished on clear, cloudless nights, will be enough to cool our home through each day, and through the cloudy nights between the clear nights.   

       Since the temperature of the night sky is 3 Kelvin (-270 Celsius), the solar collector (which, as mentioned, is shielded from terrestrial sources of heat) can potentially become very cold.   

       If we only move heat out of the cold thermal mass when the solar collector is colder than the cold thermal mass, no heat pumping is required.
goldbb, Oct 08 2009

       Thought I saw " Solar/Antisocial Heating/cooling "
normzone, Oct 08 2009

       goldbb, you're correct; you can store heat by melting a suitably chosen substance just as you can store cold by freezing a suitably chosen substance. As this technique is not new or novel, I made the assumption that the insulated pressure vessel was the novel feature, and your intent was to store a hot liquid where the vapor pressure would be raised to a point requiring a pressure vessel.   

       Your device could be reasonably realized as a double-ended thermosiphon (see link). You can put a heat exchanger for your hot storage in the top tank, and a heat exchanger for your cold storage in the bottom tank.   

       Note the positions of the one-way valves, oriented to flow counter-clockwise in the hot loop and clockwise in the cold loop.   

       When the panel is being heated, the water will convect with the upper tank. The water, having been cooled by giving up heat to your hot storage reservoir, will travel down the hot-side back pipe and into the panel again. This cycle is self-sustaining as long as the water in the bottom of the hot tank is cooler than the water in the panel.   

       When the panel is radiating to a clear sky, the water will convect with the lower tank. Water heated in the lower tank by taking heat from your cold storage reservoir will flow back up to the top of the panel through the cold-side back pipe. Again, this is self-sustaining as long as the panel is radiating.   

       The hot and cold tanks can flow between themselves, bypassing the panel; however, this will typically be prevented due to convective forces.   

       This system should work as long as the working fluid will stay liquid at both ends of the expected working temperature range.
Freefall, Oct 08 2009

       [+] saved me from reposting it, and better than mine, with the unpowered flow thing.   

       You could also plug your fridge/freezer into the cold-side (through a heat pump if the reservoir isn't all that cold), to reduce their electricity usage. The tanks only need be big enough to last through a few days of cloudy weather.   

       I'm not sure where //gaseous// or //pressure vessel// come in, though.   

       Why not just use water as storage medium ? Sure a clear night sky could get it sub-zero, but most refrigerants are poisonous, and you end up having to deal with ice buildup somewhere in the process.   

       Silica aerogel, apart from being the best thermal insulator, is transparent to infrared, so there's your trough insulation.
FlyingToaster, Jul 01 2015

       2020 and 13% of remaining western countries adopt goldbb's technology.   

       2021 worlds coldest recorded winter in western countries in decade.   

       2022 scientists begin considering the possibility that the artificial cooling actions taken to prevent global warming have backfired, and a rapid deterioration is expected, with no way to stop it. Even artificially heating the areas will just hasten earth spinning out of its delicate heat balance.   

       2023 fish in oceans seen with changed features fit for colder waters. Scientists looking into neo-Larmarkism after Darwinian theories fail to explain phenomena   

       2024 Sunni-Shia pact and the 3rd Irano-Arabia Kaliphate established. France capitulates to SUSHI. The Republic of American Atheists retreats to Berkeley University campus and is put under a four month siege by the New Salvation Army. Horrible storms across the north part of the planet stop most of the battles, while soldiers dig in on both sides of the Great Secular-Religious Divide along the Alps to play with their new iPhone 7.2
pashute, Jul 01 2015

       The sun could be used to heat air in solar panels to make a draft drawing air through earth tubes that would heat air up to 50 degrees where the air duct underground used geothermal heating and cooling and convection of air by the solar panel would drive the system in day time. I guess a small solar battery system for night. It could make it easier to heat and cool your home from 50 degrees rather than 90 or 20 depending on the weather out side.
travbm, Nov 07 2015


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