Chapitre 4 Capteur Plan - Fr.en
Chapitre 4 Capteur Plan - Fr.en
Chapitre 4 Capteur Plan - Fr.en
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CHAPTER 4
THERMAL PLANE SENSOR
1. Introduction:
Lhot water permanently available brings a certain level of comfort, but even ifConsumption
does not represent the largest part of our home's budget, its bill (gas or electricity) can
sometimes reach amounts that we would prefer to spend elsewhere. However, owe all have
the experience of finding ourcontainer placed in the sun in the courtyard, or ourwarmer tap
water in summer. So, why not use this principle to heat our domestic water?Transforming
solar energy into hot water is today the best way to have yourhot water with clean use of
natural resources:ecological hot water, without combustion or greenhouse gas emissions. For
our country, using solar energy allows us to preserve fossil fuels and reserve their use for
more specific uses than the simple production of hot water.
While thermodynamic solar systems produce a temperature of around 500°C, the thermal
plane collector (commonly called a solar water heater) hardly reaches a hundred degrees. Like
tall surfaces illuminated by solar radiation,weprinciple lies in transformation,as efficiently as
possible, from solar radiation into heat bythe absorption of part of this radiation (by
conduction and convection), and its exploitation to produce domestic hot water (and not
electricity like the thermodynamic solar collector).Solar collectors can be simple unglazed
planar collectors, boxes or glazed type or complex mirror systems.They are considered a
future solution in the fight against global warming.
With contact or at a distance, any body exchanges energy in thermal form.This is the case
with radiant energy which comes to us from the sun. We described in paragraph???Stéphane
Boltzmann's lawwhich allows us to quantify thehe density of thermal radiation received by a
thermodynamic sensor.It is also the same process of energy capture by the glass wall of the
thermal plane sensor. In a flat sensor, this heat transfer is combined with two other transfer
modes: conduction and convection.
The energy intercepted by the solar collector, installed on a roof and facing south, is
converted into heatthanks to an absorber (body with very high absorption properties and very
low emissivity) placedee in a box closed by a window. The absorber transfers the heat to a
heat transfer fluid (generally water) circulating in the primary circuit, and is routed, depending
on the mode of use,to a storage tank (hot water tank).If necessary, an additional energy source
is connected to the tank to bring the water to the desired temperature.Thus, depending on the
design of the panel (plane or tube), the nature of fluid circulation, the type of installation, we
distinguish severalfamilies of sensors, including two main groups:flat fluid sensors and
“vacuum” tube sensors.[LAUGHTON C., ''Solar Hot Water: Design and Installation'',
DUNOD, 2012.]
Insulating sheath
Insulating heat
transfer fluid
- The heat pipe is an exchanger which uses the mechanisms for changing the liquid-gas state
of a fluid placed in a closed tube.The difference with the direct circulation sensor is that the
heat exchange takes place following a natural mechanism of evaporation and condensation
of a fluid; LThe principle is simple: by capturing the heat absorbed by the fin, the fluid
evaporates. It then rises to the upper part and gives up its heat by condensing by contact with
the heat transfer fluid of the installation which circulates in the upper part. Once again in the
liquid state, it then returns by gravity to the bottom of the tube, installed with a minimum
inclination.It allows the heat captured to be transmitted out of the tube to heat a fluid in the
collector.
This system is made up of thermal solar panels and a water storage tank. This is the model
most used in individual homes. In the case of our region, it can cover up to 80% of a home's
hot water production. In winter, where the level of sunshine is not sufficient, it is coupled with
a backup system.
The monobloc water heater, heis made up of a horizontal tank of variable capacity
connected to solar collectors (glazed or vacuum).It's aboutsimplest system: the thermal sensor
and the tank form a single unit,mounted on the same chassis. This type of water heater can be
installed on a roof or on a support located on the ground, outside the home.
Compared to this systemoperating in forced circulation, the thermosyphon solar water heater
remains simplerto install: no pump, regulator or expansion tank; it therefore simplifies
maintenance and significantly improves the lifespan of the solar system. On the other hand,
the forced circulation CES can, unlike the thermosyphon, be used in collective or industrial
uses, and does not need to be below the storage tank.
The water heaterunder pressure or drain,in this type of system, the heat transfer
fluid is constantly maintained at a pressure of 1 bar when stopped and 6 bars in operation
(sourcee+energy). Closed loop and forced circulation systems generally operate under pressure.
Often, we add a self-draining option. Thus, this makes it possible to extend the lifespan of the
system and to simplify its construction since they do not require a pressure gauge, an
expansion tank, a bleeder or a non-return valve (see. Paragraph ??)
Under pressure. To drain.
Figure 4.13 Operation diagrampressure and self-draining water heater (©e+energy)
Throughout its lifespan, a solar collector will be subject to climatic constraints and wear and
tear. It is therefore necessary to test and measure the reliability and durability of certain
parameters such as:
High temperature resistance: in order to determine what high level of sunlight the
sensor can withstand without breaking down (breakage of the window, degradation of the
insulation materials, etc.);
Frost resistance: If used in an environment where the temperature can drop below
freezing, it is essential to carry out frost resistance evaluation tests;
Thermal shock resistance: The objective is to evaluate the capacity to withstand
thermal shock (return to service on a hot, sunny day);
Good sealing performance: it is necessary to ensure that rainwater does not enter the
collector, following corrosion of the collector frame or loss of insulation;
Load resistance: evaluate whether the glazing and the sensor frame are able to
withstand a pressure load (effect of wind, snow, etc.);
Impact resistance: you need to know the tolerance for which a sensor can withstand
the effects of heavy impacts (hail, stone throwing, etc.)
For all these types of tests, there are international standards which specify thehe most
unfavorable real conditions to evaluate thermal performance.The table below shows the
nomenclature of Algerian testing standardsmeeting current international norms and
standards(source CEDER bulletin 029-06).
5. Sensor peripheral accessories:
Circuit lines: these are copper or simple steel pipes. Those of the primary circuit must
be well insulated in order to limit heat losses between the collectors and the storage tank;
A pump (circulator): its role is to ensure the circulation of the heat transfer fluid in
the loop;
The non-return valve: its function is to prevent an inversion of the primary circuit in
the event of the pump stopping;
The expansion tank: if a boiling phenomenon occurs, the expansion tank makes it
possible to absorb the eruption volume of the heat transfer fluid, without excessive increase in
pressure;
The safety valve: in the event of abundant sunshine (summer) and/or reduced
consumption, a risk of overheating in the sensors may appear. This requires the use of a
pressure gauge in order to limit the maximum pressure in the primary circuit (opening
pressures of 4 to 6 Bars);
Drain taps: they are placed at the lowest point of the circuit in order to be able to
completely drain the installation;
The traps: unlike drain taps, they must be placed at the highest points of the
installation, and thus allow air to escape from the pipes;
The Regulator: apart from the case ofthermosyphon systems,minimal regulation is
necessary in order to regulate the heat exchange process between the collector and the storage
tank. Saccording to the temperature difference measured by theprobe located in the thermal
sensor and another on the return to the outlet of the storage tank, the regulator controls
accordinglythe pump which sets the heat transfer fluid in motion.
Connection pipes Circulator Check valve Expansion tank
λis
Uar=
e is
Or𝜆𝑖𝑠 And𝑒𝑖𝑠 are the thermal conductivity and the thickness of the insulation on the back.
λis A lat
Ulat=
eislat A c
Or𝑒𝑖𝑠𝑙𝑎𝑡is the thickness of the insulation on its side faces
𝐴lat and 𝐴vs arerespectively, the surface of the side faces of the sensor and surface of the
sensor.
By summing the front, side and rear loss coefficients we obtain the overall loss coefficient Ut:
Ut = Uav + Uar + Ulat
We can then write the density of the total heat flux lost like this:
Qt= Ut (Tpm – Tam)
Tpm: absorber temperature,
Tam: ambient temperature.
Thus, the expression of the instantaneous efficiency of the sensor as a function of the average
temperature of the absorbing plate will be:
𝜂=𝜏𝑐.𝛼𝑝Gi -Ut(Tpm – Tam)
The sensors will differ from each other by the quality of the absorber𝛼𝑝,solar glass𝜏𝑐and by
that of the insulation of the sensorUt. All of these three properties will give the sensor
preferred temperature ranges.
ADVANTAGE INCONVENIENCE
Opaque flat sensor 1,Glazed plane sensor 2, Vacuum sensor 3
Simplified manufacturing, no body or glazing1.2. Very dependent on air temperature1.
Performing in summer1.2. Sensitivity to cold wind (absence of glazing)1.
Easy to install and integrate1,2,3. Need for larger surface area1.
Long lifespan1,2,3. Variation in yield depending on the season1,2.3.
Highly ecological1,2,3(no CO2 emissions). Aesthetics of the building (placed on a roof)1,2.3.
Energy savings1,2,3. Investment in a storage tank2,3.
Return on investment in 10 years1,2. Intermittent day/night, overcast weather1,2…
Minimal maintenance1,2. Need for additional energy1,2.3.
Possibility of combining with a PV panel2.3. Requires location on the ground or roof1,2.3.
Preserving fossil fuel reserves1,2,3. Sensitive to hail and frost1,2.3
Surface reduction of 25%3, Significant cost3
8. Calculation tools:
Among the numerous software programs for estimating the performance of different systems,
we will cite:
- CombiSun: Estimation of the performances of different combined systems under
different climates and loads.
- GetSolar and TSOL: Simulation of solar thermal installations
- LOGICLIP, POLYSun: Sizing of hot water installations
- SIMSOL: Simulation of collective solar installations
- SIMAPRO, EQUER, GaBi and TEAM: Life cycle, cost and environmental analysis
- CoDyBa, HOT3000, SUNCHART: Simulation of the energy performance of
buildings.