FR2512182A1 - METHOD FOR REMOVING HEAT FROM MOVING AIR AND PRECIPITATION - Google Patents

Abstract

Method for extracting heat from flowing air or from precipitation, such as rainwater or dew, characterised in that there is arranged on as high as possible a point of a building, in particular on a roof ridge, a heat collector flowed through by a cooled liquid, in particular a naturally forced-convective tube bank heat exchanger, with a high outer heat transmission coefficient between air or water and heat exchange surface of the heat collector, and the cooled liquid which is heated as it flows through the heat collector is utilised as heat transfer medium.

Description

Process for extracting heat from moving air and precipitation.

The growing trend for long known reasons in the construction field to abandon conventional fossil fuel heating in favor of so-called soft energy heating for living quarters using heat pumps. heat and solar heating systems has caused a multitude of process and device developments regarding collectors
(collectors) required for this purpose.

 An evaluation of the efficiency of the two aforementioned soft heating systems can be made exclusively according to the climatic conditions of the moment - we consider here only Europe. It is certain that in sunny regions, such as in southern countries, the solar heating system is very efficient. In northern European regions, on the other hand, the number of days of sunshine per year is so reduced that there can no longer be any question of the efficiency of solar collectors (it is certainly very audacious to speak of an efficiency of collectors even in overcast conditions, i.e. in case of diffuse radiation).

 In northern European regions, the heat pump is therefore the only gentle alternative to conventional heating systems. Among the heat sources entering the Coptic line, ground water, surface water or pond water, soil and outdoor air, from which the heat necessary for heating can be extracted, by means of suitable thermal sensors, it is the last mentioned which should be the most interesting in the future.

 There are two reasons for this: firstly unlike outside air, water is only available on an exceptional basis and the soil is becoming more and more scarce due to the fact that land is measured more and more sparingly ; on the other hand, in the envisaged northern regions, the atmospheric conditions are good for the implementation of air heat sensors; because there are constantly more or less strong and relatively hot wind conditions (the efficiency of an air sensor depends on the intensity of the moving air). The definite drawback of heat pumps based on the heat of the air resides in the fact that they can only function in a bivalent way (fossil fuel heating systems remain necessary as a complement, because at outside air temperatures below 0 C, the efficiency of the collector at air becomes too low).

 In any case, around 70 tonnes of heat needs can still be covered by a heat pump in the northern regions of the European continent.

 Taking into account the preceding considerations, many firms have developed a multitude of air thermal sensors, a closer examination of which reveals however either too low efficiency or too high cost price or even the two drawbacks. So far there is a lack of an air thermal sensor which is optimum both in terms of efficiency and of its maintenance, construction and investment costs.

Here is how an air thermal sensor is composed and works: The essential elements are hollow bodies, generally tubes or pipes in which flows a water-glycol mixture (glycol as an antifreeze additive) serving as a coolant. From the outside, air blows over the bodies as it passes. On its path in the hollow bodies, the coolant heats up from an inlet temperature of -6 "to -8 C under the effect of the heat released by the air to the hollow bodies, to reach a temperature output from 0 to about 100C depending on the temperature of the atmospheric air. The mathematical relation which describes this process of heat transmission is written (I) Q = kFtm where
Q (kcal / h) denotes the heat transmitted by
hour
k (kcal / m2h K) denotes the coefficient of
heat transmission
F (m2) designates the collector area
thermal
# tm (C) denotes the mean difference of
temperatures between the coolant
and the air.

Among the three quantities which determine the quantity Q of heat transmitted, A tm is not, k is to a certain extent united and F is largely influenced. Atm is determined on the one hand by the temperature prevailing in the air and on the other hand by the evaporation temperature of the refrigerant which evaporates in the heat pump. If we consider the equation of determination of the heat transfer coefficient kR for example for tubes, we have
1 (II) kR =
1 da + da ln da + 1 oi i di 2tR di
(calculated on the external surface of the tube) and we note that for predetermined dimensions of the tubes (da, di) and for predetermined flow rates in the tube (oCi), only the quantities a (external heat transfer coefficient ) and (heat conductivity of the tube) remain as variables. The external heat transfer coefficient Ga a depends mainly on the speed of the wind, which can be influenced in a limited way, with which the wind blows on the tube.Also have influence on C ba the arrangement of the tube and its orientation relative to wind direction. By properly choosing the constituent material, one can determine the thermal conductivity tR (copper is by far the best material but also the most expensive).

To have a determined heat transmission capacity, established according to the maximum needs of a dwelling, the sensor must be arranged taking into account the aforementioned non-limited and partially limited variables such as the surface, the wind speed, the construction method. of the sensor, its arrangement and the materials of the hollow bodies. The aim here is to make the sensor as efficient as possible, silent and sober, discreet, inexpensive and easy to install. Naturally, not all of these criteria can be fully achieved, but a good collector or collector is characterized by the fact that it achieves the greatest possible number of these criteria in an almost optimal manner.

 The air collectors known up to now are divided into heat exchangers with technical and natural forced convection. In the first group, a fan draws outside air at high speed through the heat exchanger.

 This system has as a definite advantage the high capacity of heat transmission and therefore its efficiency due to the high air speed, the use of copper tubes and strips.

However, it is thermally disadvantageous that the thermal sensors installed at the bottom of wells in the basement cannot be reached by rain or sun.

 The major drawbacks, however, are the additional energy consumption of the fan, its noise, especially annoying at night, and the need for frequent maintenance (due to the narrow distribution of tubes and strips, the network becomes clogged quickly due to dust and leaves sucked as well as by the icing which obstruct and in extreme cases cut the passage of air through the network).

Depending on the climatological circumstances, a greater or lesser amount of condensation forms, which must be constantly removed. The price of such a forced circulation technical convector
LWW.T (air-water heat exchanger) is also not low. In all cases this type of sensor is unsightly installation.

 Because of the serious drawbacks of air-water heat exchangers with technical forced convection, we have imagined a multitude of air-water heat exchangers with natural forced convection based mainly on wind or moving air.

 The major drawback of air-water heat exchangers with natural forced convection is that they do not extract the latent heat to a large extent from the outside air. The main reason for this is the improper construction from the technical point of view and the incorrect orientation of the sensor from the point of view of the quickest possible loading by the moving air. In addition, the majority of known air-water exchangers are constructed in an expensive manner (special constructions), that is to say at great expense and requiring fairly good maintenance.

 In the design of the air-water heat exchanger according to the invention, we started with the objective of fulfilling the criteria indicated above, which are decisive for the evaluation of a sensor, as optimally as possible.

Since air in northern terrestrial regions must be used as a decisive coolant, care was taken to make the most of its heat content when designing the new sensor. However, this can only be achieved if high heat transmission is obtained between the air and the tubes (according to equation (II), the external heat transfer opposes the greatest heat resistance). In an air-water heat exchanger with natural forced convection, this goal is achieved by the following measures 1) The exchanger is installed at the greatest distance
possible from ground level in an environment not
disturbed to use a wind speed too
as high as possible.

2) The exchanger has been designed so that for all
parts of its tube network there is a
great heat transmission.

3) The heat exchanger is installed so that it
undergoes the breath of the wind at the optimal speed
during most of the heating period.

 These requirements gave rise to a compact multi-row tube bundle heat exchanger which is installed horizontally a little above the highest point of the house, namely above the roof ridge (Fig. l). A multiplicity of rectilinear tubes successively offset is assembled into a compact bundle whose distribution is precisely defined (Fig. 2). Preferably, the bundle of tubes is placed on a gable roof (roof in a gable) and transverse to the direction of the prevailing wind. As a result, the packet receives freely, that is to say without hindrance from solid bodies or delimiting surfaces (cross current) the blast of wind a priori relatively strong at these heights. A positive factor here is the inclination of the roof.The slope of the roof acts as a constriction of the passage section according to Bernouilli which causes a considerable acceleration of the wind flow in the smallest section - in this case the roof ridge - so that the wind hits the tube bundle at an even higher speed (Fig. 3).

 For the multi-row tube bundle sensor, considered as much as possible in the direction of blowing, the tubes of which are arranged according to a defined, offset distribution, a type of heat exchanger has been chosen which is distinguished by transmission coefficients of heat has medium high (compared to the exchange surface) (the cross-current which is presented here is practically as good as a pure counter-current) and this type of exchanger has proven its best in the chemical industry (see GDI, Gd4 of VDI-Warmeatlas 1953).

By considering the enormous volume of air and thus the calorific content of the wind which passes by the sensor of heat of the air, we can admit that all the tubes of the bundle i.e. from the first to the last row of tubes, are struck by air at the same temperature. This is of great importance if we consider equation (I) for transmitted heat. Nusselt's law of equality for a beam struck purely transversely is formulated as equation (I) in -GDI. If we apply this to the case considered, we obtain as a function of the wind force external heat transmission coefficients between 30 and 100 ir These values are
m ";h; k are far superior to those of air at rest with
kcal oC m2wk ;;
In this case, no account has even been taken of the fact that the exchanger according to the invention uses a transverse or crossed counter current which is even better than a simply transverse or crossed current.

 When the main wind direction changes, that is to say in the event of a 90 "deviation from the transverse current, the external heat transfer coefficient drops. When the striking or blowing angle is acute , and only reaches 200 (therefore a flow almost parallel to the tube bundle), the external heat transfer coefficient still reaches 50 g of the coefficient valid for a flow transverse to 900 (cf. GcI of VDL-Warmeatlas 1953).

This means that even for a house whose transverse orientation with respect to the prevailing wind is not ideal, we still obtain coefficients of external heat transmission which are good.

 According to equation (I-I), it is always necessary to look for a heat exchanger in which the three thermal resistances taken in isolation for the external heat transmission> thermal conduction, and the internal heat transmission are roughly of the same magnitude.

 Calculations in this regard for the new sensor have shown that by using high density polyethylene (HDPE) absolutely weather resistant to make the tubes, the thermal resistance is the greatest. From a thermal point of view, however, it is not justifiable to use very expensive copper tubes. An HDPE pipe whose thermal conduction value would be slightly improved would be sufficient here with regard to the desired resistance relationships. This slight improvement is brought by an HDPE tube weakly provided with metal powder, preferably aluminum powder (on this subject see the application filed the same day on behalf of the applicant).

 The efficiency of the tube bundle heat exchanger according to the invention is however ensured not only in the event of wind but also in rain and fog. In the event of rain, the tube bundle is exposed in such a way that constant humidification of all the pipes is ensured. Before the rain reached the tiles, it flooded the superimposed tubes or - in the case of oblique rain - succeeding one behind the other. The heat transmission of a constantly renewing thin film of water is particularly intense (see Nusselt's theory of surface water).

Relations are also good in fog, where a thinner film of water is formed anyway. With regard to efficiency as a solar collector, we also come up against the same limitation as for all the other collectors protected from the wind, namely that on windless days a significant transmission of heat is only obtained by solar radiation. .

 For the construction of the air thermal sensor according to the invention, it should be noted that: it was oriented for a cheap manufacturing of the sensor as well as for its quick and easy installation. This is why no new fastening element has been designed, but rather those which already exist on the market have been used in the form of inexpensive mass articles.

 The collector must have essentially the same length as the ridge of the gable roof which it must fill. As lower and upper limits, lengths of 5 m and 20 m can be mentioned respectively.

 Packages of more or less long tubes must obviously be fixed stably on the roof ridge, especially taking into account the strong thrust caused by a strong wind, which gives rise to forces with a high horizontal effect. These forces act like the self-weight of the sensor as continuous extension loads. These loads are taken up by special load-bearing chassis, which are installed approximately every running meter.

 These supporting frames each include a plate 1 of synthetic material pierced about 10 to 20 mm thick, a horizontal carrying tube 2, two vertical supporting tubes 3, 3 'and two telescopic spacer tubes 4 , 4 '(Figure 4).

All plastic sheets have the same dimensions and the same perforation patterns; they consist of a weather-resistant synthetic material, preferably a duroplast reinforced with PVC by a hard body, by wood or by a fabric, this duroplast being based on phenol or melamine resin. This corresponds to a desired distribution for the tubes or tube bundles (Fig. 2). The plastic plates are used for free guiding, fixing and exact spacing of the tubes between them. The tube bundle is made up of a multitude of parallel tube loops of the same length. The length of the individual loops is calculated in such a way that the liquid coolant on its route through the tube loops is heated by the air to a defined outlet temperature, which is slightly below the air temperature. number of rows connected in parallel is calculated from the power required for the sensor. The perforation model shown in FIG. 2 gives rise to a sensor with thirteen loops (number of holes in the vertical row of holes). Each loop consists in this case of six ends of straight pipes (each time an oblique row of holes for a loop) and the corresponding number of elbows (the length of the sensor and that of the calculated loop provides the number of ends of straight pipes and elbows). The elbows are also molded parts in HDPE which are each time welded to two ends of pipes to be connected together.

 This connection method takes into account the possible expansion of the pipes under the effect of heat. The loops are each arranged in an oblique plane (see Fig. 2 shape of the pattern of parallelogram perforations), because they must be filled without air bubbles by means of the fluid coolant. In the ends of the pipes located at the bottom, (row of holes on the right in Figure 2), the liquid coolant enters and runs through the straight, horizontal tube sections of each loop in successive stages higher and higher, from right to left, exactly against the air flow (therefore cross-counter current). The air possibly still arriving in the loops can go up to the highest section of tube and exit via the deaeration valve 9 '(Fig.5, fA) of the manifold 10.The manifold 10 and the distributor 11, both made of copper, have float valves 9, 9 'at the head for deaeration of the loops. The distributor pipe and the manifold are both arranged on the front face of the tube bundle (Fig. 5, 5A), the pipes of which are also fixed axially on this side. In the other holes of the plastic plates, the tubes are fixed axially loosely, so that they can slide in these holes in the event of thermal expansion or contraction.

The actual tube support frame, as shown in Figures 4 and 6, is made of fire-galvanized steel tubes. The supporting tube 2 tal horizon to which the plastic plate 1 is fixed by means of screw brackets 5 zinc plated with fire (see detail
Fig.6A), is held by the vetal support tubes 3, 3 '. These in turn are supported on the two horizontal telescopic tubes 4, 4 '(two tubes inserted one into the other according to the staging of their diameter). At their ends, the telescopic tubes each have a flange or flange 6, 6 'provided with through holes for wood screws. The telescopic tubes are stretched between the wooden rafters of the roof space (parallel to the roof ridge) and are screwed in. The perpendicular tubes between them are connected to each other by means of stirrups, as shown in Fig.7 , 7A.

 The 3.3 'waterproof tubes can be passed through the roof by the use of a so-called antenna tile 7, 7' (Fig. 4, 6; special tile for passage TV antenna support tubes). The seal between the tube and the antenna is made by means of a rubber lining 8, 8 '(Fig. 4, 6). As it is imperative to offset the antenna tile properly and that the offset of the rafters already exists, the two however not being identical, it is not guaranteed that the support tubes will always be located halfway between the rafters. For this reason, the connection between the support tube and the telescopic tube must always be possible at any location thereof by means of a fixing bracket. So you need a telescopic tube because the distances between the rafters often differ greatly from each other. It should be emphasized again that all of the items described here are serial items found on the market and which are relatively inexpensive to acquire.

 The fluid coolant is brought in and out as shown in FIG. 5: the inlet and outlet pipes 12, 13 also pass through antenna tiles 7, 7 ′ to a collecting pipe and a distributor pipe respectively. 10, 11 and their passage is sealed by means of rubber linings 8, 8 '.

 To stiffen the entire load-bearing construction, a fire-galvanized copper tube 14 (Fig. 5, 6) is provided which connects all the plastic plates together (by means of stirrups). 15 screwed to each of the plates).

 FIG. 1A shows a preferred embodiment of the construction carrying the bundle of tubes of the heat sensor; each time between two tube-carrying frames there is further provided one or more plastic plates 1 ', which are fixed to the copper tube 14 only from above.

For a greater distance from the support frame between them, they must avoid bending of the tubes by heating, for example due to more intense solar radiation.

 To complete the description of embodiment, it is still necessary to briefly emphasize the advantage of the sensor according to the invention having regard to the following criteria a) The efficiency of the sensor is optimal.

b) The sensor is absolutely silent and does not ask
no maintenance.

c) We cannot say that the sensor goes unnoticed,
but it does not bother due to its construction
compact (about 0.5 m above the top of the
roof ridge).

d) The sensor is easy to install because it can be
largely made in advance (weight per meter
is a few pounds).

e) The sensor is very inexpensive due to the
the inexpensive elements that make it up and its ease
mounting.

 It should also be noted that everything that has been said has been the subject of prototype tests.

 It is understood that the invention is not limited to the details described above and that many modifications can be made thereto without departing from the scope of this invention.

Claims (23)

 1. Process for extracting heat from moving air and / or precipitation, such as rain water or dew, characterized in that it is placed as high as possible in a building, in particular on the roof ridge, a heat sensor traversed by a cooled liquid, in particular a heat exchanger with a bundle of tubes and with naturally forced convection, having a high coefficient of external heat transmission between the air and / or the water and the heat exchange surface of the sensor and in that the coolant which is being heated as it passes through the sensor is used as the heat transfer agent.  2. Method according to claim 1, characterized in that the thermal sensor is installed so oriented at the highest point of the building that it is struck by the wind at the highest possible speed and transversely during most of the heating period.  3. Method according to claims 1 and 2, characterized in that the thermal sensor is placed in a place where its heat exchange surfaces are wetted as abundantly as possible by precipitation.  4. Method according to any one of claims 1 to 3, characterized in that a thermal sensor is used whose individual thermal resistances (a) between the outside air and the heat exchange surface  external mique (b) inside the exchanger wall and (c) between the internal heat exchange surface and  the heat transfer agent, are as small as possible  and about equal magnitude.  5. Method according to any one of claims 1 to A, characterized in that the thermal sensor is arranged in the form of a compact tube bundle heat exchanger with several rows horizontally a little above the ridge d 'A sloped roof and transverse to the direction of the prevailing wind, the tubes of the heat exchanger being preferably arranged one behind the other.  6. Device for carrying out the method according to any one of claims 1 to 5, characterized by a thermal sensor traversed by a coolant, in particular a heat exchanger with a bundle of tubes and naturally forced convection, with an external heat transfer coefficient between air and / or water and the heat exchange surface of the thermal sensor, which is placed at the highest possible point in a building, in particular - on the ridge of a roof.  7. Device according to claim 6, characterized in that the thermal sensor is arranged at the highest point of the building transversely to the direction of the wind which blows during most of the heating period, that is to say say as much as possible across the direction of the prevailing wind.  8. Device according to claims 6 or 7, characterized in that the thermal sensor is arranged in a place where its heat exchange surfaces are wetted as much as possible by precipitation.  9. Device according to any one of claims 6 to 8, characterized in that the thermal resistances of the thermal sensor considered in isolation (a) between the outside air and the surface. exchange  external thermal (b) inside the wall of the exchanger and (c) between the internal exchange surface and the medium  or heat transfer agent are as small as possible and approximately equal in size.  10. Device according to any one of claims 6 to 9, characterized in that the thermal sensor is arranged horizontally in the form of a heat exchanger with a bundle of tubes with several rows a little above the ridge of a roof. in a boat transverse to the direction of the prevailing wind, the tubes of the heat exchanger being preferably arranged one behind the other.  11. Device according to any one of claims 6 to 10, characterized in that the thermal sensor is made of a weather-resistant material.  12. Device according to any one of claims 6 to 11, characterized in that the heat sensor exchange surfaces consist of synthetic or plastic material, in particular high density polyethylene (HDPE), which contains a good conductive filler heat, preferably a metal powder or granulate, in an amount sufficient to improve the thermal conductivity.  13. Device according to claim 12, characterized in that the filler is constituted by a powder or an aggregate of copper or aluminum.  14. Device according to any one of claims 6 to 13, characterized in that the tube bundle heat exchanger is provided with support frames which comprise a perforated plastic plate (1), a horizontal support tube (2 ), two vertical support tubes (3, 3 ') and two extendable telescopic spacer tubes (4, 4') for fixing the device between two rafters of the roof.  15. Device according to one of claims 6 to 14, characterized in that the thermal sensor is provided with deaeration valves (9, 9 ').  16. Device according to claim 15, characterized in that the deaeration valves (9, 9 ') are produced in the form of float valves at the head of the collecting pipe (10) and / or the distributor pipe (11) of the 'tube bundle heat exchanger.  17. Device according to any one of claims 14 to 16, characterized in that the horizontal support tube (2) is connected in its middle or centrally to the plastic plate (1).  18. Device according to any one of claims 14 to 17, characterized in that the vertical support tubes (3, 3 ') bear on the telescopically extendable spacer tubes (4, 4') and in that the spacer tubes are provided with flanges (6, 6 ') at their ends.  19. Device according to any one of claims 14 to 18, characterized in that the telescopic extendable spacer tubes (4, 4 ') are fixed horizontally between the rafters of the roof parallel to the roof fate.  20. Device according to any one of claims 14 to 19, characterized in that the support tubes (3, 3 ') pass in a watertight manner through pierced tiles (antenna tiles) (7,' ) fitted with a seal.  21. Device according to any one of claims 6 to 20, characterized in that the length of the tube bundle heat exchanger corresponds approximately to that of the roof ridge.  22. Device according to any one of claims 14 to 21, characterized in that at least one head tube (14) is installed fixed on the head sides of the plastic plates (1, 1 ') to stiffen the of the supporting structure of the thermal sensor.  23. Device according to any one of claims 14 to 22, characterized in that one or more plastic plates (1 ') are additionally arranged between two supporting frames, these plates being fixed to the head tube (14) only at the top.