greenhouse heating heat buffer

[cortejuan]

Hello,

I am a newcomer, crazy plants more or less exotic. I own two greenhouses, an old (30 years) heated conventionally (electricity and gas) and a new I want to heat thanks to an external water reserve of 2000 liters perfectly insulated. It will be connected inside the greenhouse to a car radiator system and fan continuously operating via a central heating pump. Associated with a reserve of water 800 liters buried in the greenhouse, this set should limit the consumption of electricity during the very cold nocturnal periods and cool the air during the sunny periods.

I started to read the posts on the phase change which had already seduced me during the construction of the first greenhouse, but I have not yet found the rare bird: a very cheap product "little" chemical and tilting at 10 degrees (cold greenhouse).

In fact, I try to get a passive energy greenhouse by capturing the maximum of diurnal calories (and largely harmful in winter) to restore them at night.

I await your advice and comments.

cordially

[dedeleco]

What greenhouse volume or dimensions, in principle not too big, their insulation, past heating consumption old let's fix the ideas ??

Have you evaluated the heat stored in your 2m3 or 0,8m34 balloon compared to the extreme needs of each greenhouse that must always stay at more than 10 ° C?
The balloon is perfectly isolated (what thickness and duration) for a night and a day but not much more.

The ideal solution is the solar with important thermal buffer as under the earth which if of great dimension makes it possible to keep the heat of the summer for the winter !!
Example that works in Canada:
http://www.dlsc.ca/borehole.htm
http://www.dlsc.ca/index.htm
other:
http://www.icax.co.uk/alternative_energy.html
http://en.wikipedia.org/wiki/Seasonal_thermal_storage
http://www.icax.co.uk/articles.html
https://www.econologie.com/forums/post183841.html#183841

The difficulty for a house is to have a heater over 20 ° C.
While for your greenhouse you want at least 10 ° C, and the earth deeper than 2m depth has a temperature equal to the annual average of 10 to13 ° C because it stores the heat of summer on the surface to lose it on the winter months !!
So an underground heat exchanger ensures at least 12 ° C in winter, but the only problem of the Canadian well is its size to provide the necessary energy on the winter and the cold on the summer, without the earth becoming too cold in winter and too hot in summer.

For a greenhouse it takes a lot less, especially with solar heating of the greenhouse and the earth underneath so excess heat in summer and autumn spring.
A m3 of earth stores about 1000KJ / ° C and therefore your energy needs minus the solar input in winter set the volume of earth to be heated in summer for the winter, as well as the surface of thermal sensors in summer with the greenhouse that is one.
The needs depend a lot on your area and the altitude !!

[dedeleco]

Read also and ask for his practical experience cuicui very useful:
https://www.econologie.com/forums/post179142.html#179142

[Did67]

Old-style greenhouses often had concrete worktops at their height: thermal inertia.

The watering ponds were inside: the temperate water for the plants and served again as thermal flywheel ...

So much for the liabilities.

Today metal and plastic replace all that ....

I am also a fan of plants which clutter up my whole house; I am thinking of a cold greenhouse: rainwater tank buried below but without insulation: "deported" inertia; lean on a concrete wall and / where upturned agglomerates filled with sand and / or mud brick stabilized on the north face ...

[Christophe]

If you have enough space: a large volume of water inside the greenhouse and in a container that is resistant to frost constitutes a passive radiator "frost-free" almost free ...

Around 0 ° C, you will recover the latent heat of this tank free of charge.

But I do not know if that's what interests you ...

[cortejuan]

Hello everybody

Thank you for your answers and advice.

Here are some technical data:

My greenhouse is aluminum profile (painted by me) 4 safety glass mm thick. Its floor area is 15 m2 and its volume is 32m3. Question winter insulation, it is fully lined with plastic bubble held 2 cm of the wall. It is currently heated with electricity and / or gas and oil.

My thermal storage system is composed of two IBC tanks of 1000 liters each connected to each other. Water entering into one outgoing by the other. They will be at 2,5 m from the greenhouse, leaning against a wall. They will be placed on a concrete slab covered with high density polystyrene, itself covered with an anti-punching material (probably a light concrete screed). Everything will be totally isolated with high density polystyrene sheets (10cm mini thickness). To hide this horror, all will be dressed in wood imitating a small cottage.
Inside the greenhouse, there will therefore be a height aluminum car radiator combined with two fans of different power. These allow to differentiate diurnal exchanges (necessarily fast, powerful fan) of nocturnal exchanges (slower, less powerful fan).

A central heating circulator will ensure the transportation of calories.

Since the greenhouse behaves like an excellent solar collector (the soil is in the ground), I hope on a clear day in winter to go up to 30 degrees for an outside temperature of 0 degrees for two or three hours a day (data verified yesterday) .

So to be less optimistic, I estimate that if the average temperature maintained in the greenhouse is 10 degrees, under the action of the sun, the air can go up smoothly to 20 degrees per day not too covered (denied today) or the degree gain is 10 (-2 out + 8 in) without heating).

But good on this basis of a difference of 10 degrees in / out, it gives me for my 2000 liters of water, 23 kWh of energy to distribute during the night.

Even by dividing this energy by two, it assures me, if not to stay at 10 degrees, at least never to freeze the night. I should therefore reproduce the climatic conditions of the Mediterranean strip (Menton region).

The must is to associate with water phase change materials as indicated in the thread on the use of palm oil. On this subject, unless I have not read correctly, no one has mentioned the emulsification of the oil in the water to create a new material, a phase change (perhaps) different). To go further, why not use saponification to increase even slightly the CC of water?

My region is Franche-Comté, which in winter has very cold but often very sunny periods (semi continental climate at the edge of the Rhone Valley).


cordially

[Gaston]

But good on this basis of a difference of 10 degrees in / out, it gives me for my 2000 liters of water, 23 kWh of energy to distribute during the night.

If you use the greenhouse to heat the water, you cool the greenhouse ...
So the temperature of the water in the tanks will not reach the temperature that would have reached the greenhouse without the use of the system.

In other words, to be able to collect 23kWh in your greenhouse during the day is that without the sampling system the temperature would be much higher.

In the end, the energy stored in the tanks will probably be much lower than you expect

I find like others before me that it is a very complex system to ultimately increase the thermal inertia of the greenhouse ...
By "simply" putting a tank of 1000 liters of water at the bottom of the greenhouse, you would probably achieve roughly the same result ...

[cortejuan]

Thank you for the answer,

Regarding the reserve, I have already (850 liters) and without exchanger system (radiator + circulation) it does not work, I just experienced it. A power failure to remove any heating in my two greenhouses, the outside temperature was -8 and morning waking in the greenhouse equipped with the reserve, it was -2 degrees. In the neighboring greenhouse with no water supply, the result was exactly the same (-2 in the greenhouse).

Regarding your comment, it's true and false ... Indeed, the temperature will drop (it is also the goal to avoid heat stress) but the thermal efficiency of the greenhouse will increase significantly because when the air in the The greenhouse is at 30 degrees while outside it is zero degrees, the losses are considerable (otherwise it showed as in a good sensor at 70 degrees or more). So if I capture the calories as they are generated, the temperature will drop, increasing the thermal efficiency of the greenhouse.

Finally very simply, I do not have access with a shovel in my garden, so the buried reserve was planned under the greenhouse, but my kidneys said no ...

cordially

[dedeleco]

water that costs nothing.

Water costs the tank and the land costs only to stir, good exercise shovel for health if you train regularly.
Other if the earth is deep it is possible to drill holes with a mass, a drill or a hand-held grinder to spin there tubes of copper exchangers (to go back in tube of protective steel), even a few meters, or even of shallow depth (50cm), which allow to heat the earth on the 15m2 and m3 of earth under (even 50 cm do 7m3, free tank) without stirring (A few holes per m2 (easy if the soil is good arable soil (deep alluvial soil) where one can easily push an iron pipe by hand with a mass 1m depth.
An exchanger (pipe or old home or car radiators recovered) in the greenhouse and a small photovoltaic circulator to circulate in the earth tubes allows to heat the earth when the greenhouse is too hot to recover this heat even months after if the tubes go down to more than xNUMXm depth (and at least one week to 1cm).
In addition the tropical plants will always have their roots warmer to more than 13 ° C like in tropical region, because otherwise they will be to that of the region 10 ° C even less in winter.

[dedeleco]

in winter, in the continental zone, the temperature can rise quickly to 30 degrees or more, which is particularly harmful for wintering plants, so we must quickly eliminate this energy and the water seemed to me, by its thermal conductivity and its capacity, more efficient than the ground.

Both, water and soil are complementary, everything depends on the installation and the system of exchangers in the ground.
The isolated water is of course a few days (day for night) but keep the enormous heat in excess of the summer for the winter, requires to use the slow diffusivity of the earth that does not exceed 3m of diffusion length on 4, 6 months to a year to store it in large volumes in depth.
It is necessary to calculate the energies in game very different in summer (10 to 15KW on 15m2 of greenhouse with sun) and in winter (5 to 10 times less ????).
.
(Diffusion length varying as square root of time, or in 4 months, twice that in a month and in a month than 5,5 times that in a day and in 3 months is 120 days this length is only 11 times that in one day, from 15 to 30cm to 1,7 to 3m approximately following the ground)
http://fr.wikipedia.org/wiki/Diffusivit%C3%A9_thermique
max info in German
http://de.wikipedia.org/wiki/Temperatur ... %A4higkeit
So if the earth is loose with the possibility of driving vertical tubes with a mass, it is interesting to heat it as much as possible in accessible depth and at a very low price, because this heat recovered by natural air conditioning from the ground in summer will be softened in early winter at least (if not deeper) for cheap at all.

The immobilized air insulators (wool, polystyrene, etc.) are only good for a few days at most, because their diffusivity is fast and the necessary thickness is believed to be the time and not the square root of this time and the earth. better keeps this heat on longer times for much less expensive.

The most effective insulation is a composite of alternating layers of light insulator (air) and earth (or water) which will combine a low thermal conductivity with a high heat capacity to reduce the thermal diffusivity to the minimum possible (conductivity ratio on overall capacity) and then the diffusivity of this composite will be 4xdiffusivity of the earth multiplied by Kair / Kterre (K thermisic conductivity ) 4 to 5 times lower and so we go from 3m to 1 m or 0,75m thickness of this optimal insulation in the long term to keep summer on winter if the volume of the tank is much greater than that of the earth in the composite insulation.
http://en.wikipedia.org/wiki/Thermal_diffusivity
http://fr.wikipedia.org/wiki/Diffusivit%C3%A9_thermique
http://de.wikipedia.org/wiki/Temperatur ... %A4higkeit
http://fr.wikipedia.org/wiki/Conductivi ... _thermique
Thus with optimum insulation of 1m of max thickness of alternating layers (1 to 3 cm) of air wool and immobilized water one can keep the heat on 4 months in large pool-type containers.
But with much less work, just as much use the earth just with earthen holes and a thickness of spontaneous earth insulation of 3 m instead of 1m.

For the circulator everything depends on the power and the flow required but also a combination of both is optimal, because with sun is saved and without sun can recover heat inaccessible without electricity.
It can be mounted gradually, electric heating and if everything works well add solar.