greenhouse heating heat buffer

Solar thermal energy in all its forms: solar heating, hot water, choosing a solar collector, solar concentration, ovens and solar cookers, solar energy storage by heat buffer, solar pool, air conditioning and solar cold ..
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cortejuan
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by cortejuan » 30/11/13, 18:21

Hello,

For those who are interested...


here is a record of the thermal variations in my greenhouse (in bold) in my living room (above) and outside (below).

We note several things: a peak at 25 degrees despite an outside temperature of 3 degrees. we also notice rapid oscillations before and after around 10 degrees, it is gas heating in the absence of thermal buffer. After switching on the buffer, the oscillations have a greater period around 11 degrees. The more time passes, the more the temperature of the water in my tanks drops and the oscillations become more and more asymmetrical (the fall in temp does not move, it is the re-setting that takes more time) and from a certain temperature corresponding to the equality between input and loss, there are no more oscillations and the temperature in the greenhouse slowly drops until the gas comes to compensate.

I note that in my case, the difference in temperature of my thermal buffer - evening-morning- practically corresponds to the difference between the temperature in the greenhouse (10 to 11 degrees) and the average night temperature. So if it is 0 degrees at the start of the night, I know that a buffer initially at 50 degrees will be 39 degrees the first morning, then 28 degrees the next morning, then 17 (if nothing changes of course). So we might think that we should be able to hold without heating the water for about 4 days. In fact, below 20 degrees of temperature of my water reserve, the power supplied cannot compensate for the night losses and the system while working is no longer regulated.

So basically I do an outbreak every two days when the temperature does not drop below -5 degrees (no experience at -10 for now). Around a few night degrees I can recharge every 3 days or more.

My device asks me a few questions which I will discuss a little later.

cordially

Image
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cortejuan
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by cortejuan » 03/02/14, 21:46

Hi,

always for those interested,

I made some estimates of the capacity of my greenhouse to collect solar energy.

Basically, on days like today (direct sunlight from 12h to 17h) my 900 liters of water gain roughly 2,5 degrees. More precisely, today, for an initial water temperature of 14,1 in the morning, at sunset (around 5 a.m.), the temperature was 16,9 degrees or 2,8 degrees increase, the temperature outside rotating around 7 degrees.

Note that despite forced ventilation to improve the heat transfer from the air in the greenhouse to the water reserve, the temperature in the greenhouse rose to 32 degrees, triggering the automatic ventilation openings.

So it works but the efficiency is low and increasing the forced ventilation would be detrimental for the plants.

Here are my observations, I will try to improve efficiency, but if you have ideas, I am taker by recalling that I am limited in place (I can possibly add a car radiator).

cordially
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Aumicron
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by Aumicron » 04/02/14, 09:42

Interesting return.

Too bad indeed to need to open the vents. Not knowing your greenhouse in detail, a purely theoretical idea would be to make a honeycomb polycarbonate roof and at a certain temperature threshold to recover the air in these plates to heat your pad.
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cortejuan
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by cortejuan » 04/02/14, 16:43

Hello,

I think that improving the efficiency of energy transfer requires designing the greenhouse with this in mind. My greenhouse is a commercial greenhouse of ACD brand with cathedral security glass on the roof so I don't touch it (for now).

But the idea of ​​polycarbonate used as a sensor may be worth digging ...

cordially
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cortejuan
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by cortejuan » 03/03/14, 10:44

Hello,

some news...

yesterday sunshine from noon to 12 p.m., i.e. 17 a.m. Outdoor temperature between 5 and 8 degrees. Temperature of the 9 liters of water in the greenhouse at 900 noon: 12 degrees. Water temperature at 12.5 p.m .: 17 degrees, i.e. a gain of 17,8 degrees or 5,3 kWh of stored energy.

But above all, very marked smoothing effect. The temperature in the greenhouse decreases slowly until 20 p.m. when the thermal regulation is restarted. My second greenhouse without this system cools almost instantly.

It would have to be done again, I would store twice as much water in the greenhouse. Note also that the humidity created by this mass of lukewarm water is corrected by the drying effect due to the very strong condensation in the exchanger during the period of sunshine.

So far everything is OK.

cordially
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cortejuan
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by cortejuan » 24/09/14, 18:34

Hi,

some news from the front, I recall the principle: 2000 liters of carefully insulated water are heated by the sun and via an exchanger heat (at night) and cool (during the day) the interior of the greenhouse.

In cold, foggy and persistent periods, caloric storage is quickly consumed and must therefore be supplemented by an external source. Having refused the electric radiator, I added in series an external boiler (wood), allowing to raise the temperature of the 2000 liters to more than 30 degrees storage, which I will consume on an average of 3 days in winter.

The serial assembly was not a good idea because the heating of the boiler involved a circulation of water in the exchangers of the greenhouse, so roughly a part of the calories which should have been stored was evacuated in the greenhouse, during the day when the need is zero. In addition I had to turn off the thermostats and force the system, in short it was not the foot.

So I separated the greenhouse heating circuits and the boiler circuit. To improve the exchange in the boiler, I replaced my small electric car pumps with a higher flow water pump.

With a flow rate of more than 2000 liters per hour, the water leaving the boiler comes out hardly hotter than that which returns.

The advantages of the system:

- the system is protected from overheating (water at a temperature below 50 degrees in the stove pipe)
- the efficiency of the stove is improved
- the system is independent of the thermostatically controlled greenhouse heating which can operate independently.

Anticipated and unforeseen disadvantages:

- planned: electricity consumption during the heating phase of the boiler. The brass turbine pump chosen (which has existed in its current form for over thirty years) consumes around 350 watts. Gaining 10 degrees (e.g. going from 20 to 30 degrees) will take about 4 hours and a sack of wood.
- unexpected: the thermostat integrated in the pump trips from 34 degrees because the pump is installed in the tank enclosure and is at water temperature.

My next intervention will be to create an opening in the insulation at the level of the pump fan so as to cool it with outside air in order to reach a storage temperature of 40 to 45 degrees.

That said, the result is there. the subtropical plants are in excellent health, no doubt due to the gentle ventilation mechanisms and the low thermal gradients throughout the volume (which is not the case with electric heating). This year, good production of mandarins and large production of passion fruit (more than 170 and second fruiting in progress)

cordially
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beaver faithful
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Registration: 23/10/13, 22:58

Heated and insulated greenhouse




by beaver faithful » 06/11/14, 18:38

Hello Cortejuan, all,

I have a similar project that I describe here:
http://forum.apper-solaire.org/viewtopi ... highlight=

Hoping that we can cross our experiences .....
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cortejuan
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by cortejuan » 16/12/14, 12:00

Hello,

really interesting especially when you can recover the calories lost from the house. In my case, the greenhouse is far from the house otherwise I would have used the heat pump to heat the greenhouse.

On my project, I continue to explore my technique to measure the disadvantages and advantages.

- Regarding the recovery of calories accumulated in the soil in summer via my 900 liter water reserve, it does not work or rather it works badly ...

Basically, during the summer, solar calories made it possible to raise the water to around twenty degrees for 2 months. Without solicitation, the temperature slowly decreased to 17 degrees around September. When temperatures dropped and the heating system turned on, the temperature in the greenhouse reserve has dropped to 11 degrees in recent days. The important point is that in the absence of stress, the temperature hardly rises, demonstrating that the inertia of the heated floor in summer is far too great to respond to temperature drops and thermal leaks from the greenhouse.

So in short and extrapolating my experience, hope to heat a greenhouse, even putting it out of frost with cans of water, it does not work, the effect will certainly not be zero but insufficient to avoid freezing in the greenhouse. These canisters should be combined with very strong ventilation to extract the calories.

Likewise, heating the greenhouse with the heat accumulated in summer in the ground would require terribly improving the heat exchange with a battery of boreholes like the Canadian device dear to dedéleco.

Another problem, a too hot reserve has the drawback of high evaporation and a very humid greenhouse. I did a test by heating the 900 liters so that they regain their 17 degrees. Despite the cover of my reserve (not airtight), the water evaporates and it drips everywhere.

That said, it would have to be done again, I would increase the capacity of my reserve in the greenhouse, not to recover the summer calories but simply to simplify my installation (I have two external tanks of 1000 liters each that I had to isolate ).

Finally, the overall system works quite well, when it is cold, I soar every two or three days in order to raise the water in my external tanks to around thirty degrees, the ambient humidity is very low (I am forced to water the soil).

Regarding the greenhouse reserve, even if as I said the heat captured in the soil is not very recoverable, it ensures a gentle temperature at the roots of exotic plants which can perhaps explain the double fruiting of my passionflower this year.

I try this year vanilla, guavas, annone, mango and banana (madness is never far away).

cordially

And good Christmas everyone
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beaver faithful
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Registration: 23/10/13, 22:58




by beaver faithful » 28/12/14, 23:06

Good evening everyone,

Thank you for this Cortejuan return.
To see all that you try to grow in your greenhouse, that makes you dream!

Reheating in cold weather, as at this time, is without a doubt a big challenge!

I guess you have to fear for your plants right now!

I also embarked on a slightly crazy project to power my future greenhouse among others:
http://www.oliomobile.org/viewsujet.php ... 48#p240548

Happy Holidays to all !
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cortejuan
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by cortejuan » 29/12/14, 18:09

Hi,

Bravo for your project a little crazy as you say but I love it frankly. At the time I had been seduced by sterling engines and I dreamed of making one for cogeneration.

Regarding temperatures, you're right, I have my eye on the thermometer (wireless, so in the living room).

Everything is going pretty well even if I have to do an outbreak every day or two to maintain 10 degrees despite the -10 last night.

The next step will be the creation of a solar thermal collector to gain a few more free degrees.


cordially
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