Excerpt from “Manual sturgeon hatchery” – Daniel TABACARU (the book can be ordered here)Thermal Balance Aquaculture
Description of the thermal stability of the system
The Sturgeon species that determine the heat and power pattern of our project, to have the most balanced energy approach, is centrally located in the natural environment in the Danube basin at 44 degrees latitude and in the Volga River basin with a central location at 45 degrees latitude.
At these coordinates on the globe between 44 and 45 degrees latitude, regardless of longitude, the solar radiation per m2 is around 1400 kWh per year.
In fact almost all of Europe, except for the northern areas, is bathed in solar radiation between 900 and 1400 kWh/year. In the United States of America we find this correspondence on the 45 degrees longitude axis starting with the eastern coast in the Ontario, Erie, Huron, Michigan, Superior, Nipigon, through Minnesota, South Dakota, Montana, Idaho and Oregon lakes area.
In order to not complicate the calculations and have a weighted energy average with coverage for other latitudes around the central value of 45 degrees we propose the amount of 1,000 kWh/year.
The incidence of sunlight at this latitude to the horizontal plane is, with little variations, between 21 degrees at the winter solstice and 72 degrees at the summer solstice.
Between these coordinates we have four seasons.
Our culture species needs a thermal range with a maximum of 22 ° C during summer and a minimum of 4 ° C during winter. Although the thermal tops at these coordinates in extreme situations bring us over 40 ° C in summer and minus 20 ° C in winter we all know that these values are not constant but exceptions to the rule.
I personally conducted an extensive study referring to the temperatures in the Danube Delta, where the largest flocks of sturgeon species, Acipenser ruthenus, are detected, to the minimum and maximum daily temperatures in the time span of 4 years starting in 2005.
The conclusions with regard to the average values of temperature between the daytime maximum and the nighttime minimum are:
Negative values – 35 days with negative values in November, December, January, February and in which the day-night average temperatures have zero values of ° C or lower. The longest period of consecutive values of 0 ° C and negative values was for 11 days.
The negative peak reached during this period as an average of the negative temperatures was – 5.5 ° C.
Positive values – 43 days distributed in June, July, August and September when day-night temperatures had average values above 22 ° C or higher.
The longest period of consecutive values above 22 ° C was 7 days.
The positive peak reached during this period as an average of the positive temperatures was 25.55 ° C, with 3.55 ° C more than the maximum put under discussion.
The calculations for 2006, 2007, 2008 present themselves the same.
Besides the extremes mentioned above we have a temperature that is ideal for raising sturgeon. I believe at this moment you are asking yourselves a very serious question, namely: what to do with these extremes and how do we protect the fish from frost and excessive heat if their comfort range is between 22 ° C and 4 ° C.
The answer is extremely simple: The fact that we have one or two days with negative temperatures doesn’t substantially alter the temperature in the water found in volumetrics of tens of cubic meters, which is also found in solar type spaces where the temperature is kept positive at an average of 2 – 8 °C in the winter and through ventilation, a weighted temperature in the summer.
And most importantly, through the exchange of water from the culture ponds with soil water that has the average winter-summer temperature of 11 ° C. Yes, the lowly and wise nature helps . In the winter we will warm past the limited 4 ° C with water from the soil, in the summer we will cool over 22 ° C with the same soil water. For the rest of the year we in the comfort zone (of the fish) and we will not have energy consumption for heating or cooling.
If we dive deeper into the thermodynamic analysis of the whole system we see that our greenhouses foils that cover the fish ponds are impervious to solar infrared radiation.
Fish do not need sunlight but cold special light that will be installed in the areas of culture. Instead the greenhouses that will contain AquaPonics crops will have a transparent foil medium specific to greenhouse cultures.
Even these greenhouses are equipped with thermal compensators buried at ground level (180 m3 tanks), which will keep the temperature constant in hot days. On the other hand the shelves of culture are thermally insulated causing the high greenhouse temperatures to be kept out of the hydraulic circuit.
I know some of you are skeptical about the ability to grow fish, plants, bacteria and this without any outside energy input except the thermal energy stored in the soil at a depth of only 30-60 meters. You yourself can experiment the miracle of thermal energy stored in the ground by measuring the temperature from your own pool found at ground level and seeing how long it takes for the water to gain or lose 1 ° C with no thermal heating contribution.
Without making the thermal calculation an end in itself in this project, we will present only those important factors that were taken in the initial calculation of the thermal stability desired in the system in the range of growing the sturgeon species Acipenser ruthenus :
Temperature – a status parameter illustrating the thermal heating of the bodies;
The thermal field – it is a general calculation with reference to a particular space from the perspective of specific temperatures of objects in space. It can exist when the temperature does not change or variably when one or all of the embedded temperatures change;
Isothermal surface – defined as the amount of points with the same temperature in a space;
Isothermal line – it is the geometric place of all the points equal to the temperature in a plan;
Temperature gradient – it is a virtual size with which temperature changes are expressed;
Amount of heat – it represents the amount of energy and is measured in joules (J) or in specific traditional units like calories (cal) or kilocalories (kcal);
The heat flux density or specific heat flow – is the amount of heat that passes through an area in a unit of time;
Coefficient of thermal assimilation – it indicates the ability of materials to absorb heat;
Thermal inertia index – it reflects the ability of heat accumulation or heat release from the material elements;
The phase angle of thermal oscillation – in the variable thermic regime, due to the thermal inertia of the elements, temperature fluctuations that occur on a face of a body are experienced later on the other side;
These elements were analyzed from the perspective of the main modes of heat transmission (conduction, convection, radiation) and it demonstrates that in the above-mentioned range the thermal stability is satisfied with the condition of using automatically controlled loops and analyses with trends at a highly rigorous resolution.
This will be achieved through measurements with a high resolution degree, thus providing an opportunity to examine the system’s trends at a basic level taking early preventive decisions to stabilize.
In other words, when the temperature is measured at a tenth of a grade through repeated measurements, one can see any imminent trend of temperature increase or decrease by making the right decision based on the manifested trend.
For this, the measurement loops must include the system’s oscillating filtering algorithms, it must have a high level of resolution and accuracy, it must have immunity to “noise” in the case of measurements in the current loop 4 -20 mA.
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