Well of Provence

The well of Provence is a geothermic exchanger which provides the function of estival or winter cooling of the Air ventilated. This system is also sometimes called Canadian well in reference to the function of winter pre-heating of the ventilated air.

The well of Provence is a mode of pre-heating/air-conditioning used in the passive Habitat.

Principle

The well of Provence consists in supplying a building in fresh air by making it circulate before in a buried conduit which according to the climatic conditions cools it or preheats it by using the thermal inertia of the ground. The air is used as Coolant while the tube is used as exchanging thermal while channeling the air to the building.

Mainly used as system of natural Air-conditioning, the well of Provence is also used the winter to preheat the entering air or to maintain except freezing a dwelling.

It is based on the simple report that the Température under ground:

is different from that of the air on the surface.
its variation can be modelled as the sum of two Oscillation S one annual (summer/winter) and the other day laborer (day/night).
its variation undergoes weaker Amplitude compared to its annual average more especially as the depth increases.
its variation day laborer, at a shallow depth, is out of phase in time compared to that of the air on the surface because of thermal inertia of the ground.

These reports are to be put in parallel with the following data:

the depth of the ground from which the temperature is regarded as except freezing is of approximately 60 cm in plain under the Latitude S metropolitan Frenchwomen.
the seasonal average temperature of the basement to 2 meters of depth approaches more the temperature of comfort (18-26°C) the summer that the winter (in plain under the metropolitan French latitudes).
the variations of the seasonal temperatures be/winter do not intervene practically any more starting from 10/15 meters of depth where the temperature remains quasi-constant throughout the year.

In practice, the tube will be buried at least 1,5 meter from depth and for this reason:

the tube is with the shelter of freezing.
the temperature variation day laborer with this depth is out of phase compared to that of surface.
the monthly average temperature with this depth varies during the seasons.

The passive process and being based on the Heat capacity of the ground, a well of Provence can be against-productive to preheat/refresh with certain parts of the day and/or year compared to the surrounding air. To avoid that, an entered of air in direct catch and a Vanne (manual or electric) is recommended to short-circuit the well.

Using the thermal principle of inertia, the system is all the more effective as the thermal amplitudes external day laborers are strong or that it faces extreme climatic events of short duration (ex: blizzard provided that the air intake is protected from snow).

Elements of the well

The heat exchanger: the tube

The tube constitutes a heat exchanger between a flow of air and the ground (or any other material having a mass Heat capacity important).

the circuit of air can be closed by forming a loop leaving under ground to return to the building. Advantageous on the thermal level, there remains effective even in wet weather. However, it does not contribute to the Renouvellement of the interior air and then requires a second circuit of air for the dwelling.

the circuit of air can be open while coming from outside. The summer, the Humid air coming from outside, preceding a Storm for example, according to the rate of Hygroscopy and of the temperature can condense on the walls of the tube. The Changement of state (Liquefaction) of the Steam in droplets taking place at constant temperature by restoring energy reduces the performances of the well limiting the fall of temperature of the flow of air (compared to a dry flow). During construction a constant slope of the tube will be necessary in order to evacuate it and to avoid having Stagnant water. It has to notice that a well of Provence is not very effective for the climates offering of the hot and wet seasons.

The tube must answer various constraints according to its environment:

To resist the Corrosion, the tube being in contact permanently with air and water.
To resist the crushing because of its hiding, of its immersion or a possible passage of a machine on the surface.
To resist light deformations to accompany a movement by ground without breaking.
not to be porous, nor permeable in order to avoid all Pollution coming from the interior or outside.
To resist a chemical or thermal treatment to cure an accidental pollution or possible a contamination of the flow of air by an agent present in the tube.
To have an internal wall smoothes in order to facilitate the evacuation of the condensates.

If the tube is not only one holding, the joints between the various sections must also answer these characteristics.

The thermal Conductivité of material composing the tube affects only very little the thermal efficiency of the system. The disadvised metal tubes because sensitive to corrosion hardly bring more than of the tubes in Polymère. It should be noted that the tubes in PVC Nf have an extruded layer inside which reduces heat exchange. For more effectiveness, there exist tubes in Polypropylène with a coextrudée interior layer presenting, moreover, of the properties Bactéricide S thanks to ions of Argent.

Air circulation

The operation of the well of Provence rests on the circulation of air in the tube which can take place:

passively is by an overpressure in entry of tube by positioning it for example side of the dominant winds and/or by creating a depression at exit of tube by using a chimney of Provence (solar chimney). These techniques do not consume energy but the operation of the well depends then on the Vent and the Ensoleillement. The dimensioning of the air intakes and the tube will have to be adapted and the regulation of the air will be done manually by obstruction (valve, diaphragm etc.). This process can be used to maintain out-freezing a building deprived of power supply for example.
or mechanically thanks to an adapted motorized ventilation. However, the legal requirement install a controlled mechanical Ventilation (VMC) in the dwelling houses, in good number of European countries, makes that a dedicated ventilation is seldom installed since one VMC can play this part. At the time of its installation the power of the VMC must take account of the additional pressure losses generated by the well . The flow chart of air in a house corresponding to an air intake and a single exit of air is that of the VMC double flow .

The flow of air has vocation to circulate in the building:

the building is made up only of only one part, the entry of the well directly will feed it. If it is about a dwelling, one VMC simple flow is enough.
the building is composed of several parts and/or of stages, the flow of entering air will have to be conveyed and distributed in the parts. The well of Provence requiring hermetically to close all the other air intake of the building, a VMC double flow in the case of a dwelling will be useful to guarantee a renewal of air constant and uniform in all the building and in particular in the kitchen - especially if the hotplate runs on gas. Such a system requires the installation of a mouth of aspiration or blowing in almost all the parts. In this case, the characteristics of the installation will have to be then studied not to propagate the its S from one part to another or the humming of ventilation.

The flow of entering fresh air acting as coolant, the sheaths distributing the air in the parts should be insulated are so that heat/freshness is not lost in the roof S or the basement, for example, during its advance.

The investment in a VMC double flow has another advantage to the level of the thermal profits to be the extension of a well of Provence . It allows the installation of an air-to-air heat exchanger which uses heat/freshness of the outgoing air to heat/refresh the entering air. Just like for the well the exchange is not always useful and a drain and a valve (by-pass) making it possible to short-circuit this exchanger more than are advised.

If the legislations in force generally impose a renewal rate of minimum air in the houses, on the other hand it is not interdict to increase the Fréquence by it in particular the summer. Selected mechanical ventilation will have ideally to be adjustable and sufficiently dimensioned so that its electricity consumption does not increase in a disproportionate way.

Protections against pollution

The Renewal of the interior air of a House or a Local of dwelling makes it possible to fight against internal pollution and the well of Provence by limiting the thermal losses contributes to it. The pollutants evacuated by the renewal have various forms in particular gas. They can be of human origin and related to breathing like the Carbon dioxide or of natural origin like the Radon. This last is not the only gas which is released from the ground but it represents a medical danger while being heavier than the air and especially a radioactive contaminant. Naturally present on all the continents and in all the areas, it is it of advantage in the zones granitic S, Volcanique S or uranium-bearing S and the national health authorities draws up the charts regularly of them. Because of its characteristics, it tends to accumulate in the depressions (hollow or little broken down places): the risk increasing with its concentration in the breathed air, it is there particularly Cancérigène for the Poumon S. an special attention in the design of the well of Provence must be given to the level of the Imperméabilité with this gas of the tube and its possible joints so that they do not become about it a diffuser in the building. However a well under operation dilutes these possible gas infiltrations with fresh air bringing the concentrations of radon to an acceptable threshold (with a radioactivity in lower parts of 150 Bq/m ³). The problem arises at the time of a stop prolonged or a use intermittently of the well, this dense gas more that the Air can be infiltrated slowly and accumulated in the tube: in this case, it is to better purge thanks to a by-pass rejecting it directly outside without passing by the building, before its restarting. Another solution consisting in reversing flows of air led to contaminate the tubes of food with the rejections of air of the house. It is to be noticed that this can occur naturally if the ventilation of the well is simply stopped without this last not being blocked. The possible proximity of a classified industrial park envisages normally a plan of Prévention in the event of catastrophe including of measurements of Confinement of which the stop of ventilations. In this case, that it is natural or mechanical ventilation must quickly be able to be stopped. In the first case, the well of Provence and possibly its by-pass must be able to be easily blocked. In the second case, an Interruptory easily accessible, a fusible or a differential Disjoncteur dedicated on the electric Control panel must allow a fast stop of the system. After an in particular chemical industrial catastrophe an special attention must be taken before the restarting of the well whose tube can have accumulated toxic heavy gases (ex: Dichlore).

If it is not protected by a Crépine, and Filtre S the well of Provence becomes the main door of the Nuisible S for the man (Rongeur S, Reptiles, Insecte S, Arthropode S, pollens…) who for some are vectors of Maladie if not troubles. Protections are installed outside inside with increasingly fine meshs . The finest filters, against the Pollen S for example if one wishes to protect oneself some, require more maintenance and must be more often changed under penalty of being clogged and stopping the air flow. By closing the access to these animals, the accumulation of organic matter and vegetable is limited by preventing the Excrément S, the storage of Aliment S, the accumulation of ground or of vegetable matters for the construction of Nid S. the filters also prevent the tube d'" aspirer" sheets and the Dust flying in the air. Without that, accumulation during the time of all these elements mixed with condensed water can form a substrate for Champignon S, Moisissure S and/or Bactérie S. the bad smells following the restarting of a well of Provence after a prolonged stop betray the presence of matters in Décomposition or Fermentation.

The evacutation of the Condensat S of the well, if it is done in a network of Waste water, requires the installation of a siphon. If not, the aspiration created by one VMC will not make the difference between the air coming from the well and that unhealthy from the sewer S bringing an health hazard and bad smells in all the ventilated building. To be effective and not to be him even source of pollution the siphon must remain full and nonstagnant water.

Maintenance and the Prévention remain however the best means of avoiding any pollution throughout the life of the installation. The servicing consists with the replacement and/or the cleaning of the filters under penalty of seeing increasing the pressure losses at the same time as the electricity consumption of the power station for the mechanized installations. The prevention passes by an examination of the tube at a regular frequency, triennial for example, in order to inspect its cleanliness and its integrity especially in the zones of pressure loss, as in bent.

Implementation and engineering

The output of the exchanger

The output of heat exchange between the flow of air and the ground depends on:

the nature of the basement : the thermal Conductivité of the grounds strongly varies according to the presence of water and its constancy. In the cases of sources or underground rivers the output is of advantage function of the temperature and the perenniality of these flows, the mass Heat capacity of water being definitely higher than that of the components of the ground. Strong precipitations in summer can clearly improve the output of the well after several weeks of dryness for example.

the dimensioning of the tube and air flow : heat exchange is all the more large as the rate of flow of the flow of air is low and the large surface of the tube. Air flow being directly related to the needs for renewal of fresh air for the building which is fixed at minima in the regular manner. Consequently the speed will depend only on the diameter of the tube. The heat-transferring surface as for it is function length and diameter of the tube. It is to be noticed that the length of the tube increases the line loads and influences directly the power necessary to the installation. The consumption of ventilation must remain with an acceptable power, the energy profit of the well must remain higher than the energy loads related to ventilation to justify such an installation.

the depth of the hiding of the tube : the more one goes down in the basement, the more the temperature is constant. It is necessary to find a compromise between output and cost of the earthwork, this compromise is generally found between 1 and 2 meters of depth.

the rate of hygroscopy of the flow of air in the tube.

Installation of the tube

To preferably envisage the evacuation of the condensates thanks to a constant slope (2% for example) in the direction of the flow of air.
To take guard with the punching tube related to the presence of hard body hidden with its direct contact, by using a filtered fill, a ground without stones or a sand bed for example. It is to be noticed that a sand bed, usually used to avoid the punching of the tubes, drains surrounding water and moisture does not preserve, which does not facilitate heat exchange between the ground and the tube.
To remove the air pockets under the bulges of the tube at the time of its installation in order to avoid a possible radon concentration to its proximity.
In the presence of an easily flooded ground in order to fight against the Thorough of Archimedes, to fasten the tube can avoid its rupture related to a strong deformation.
the tube must be sufficiently far away from the building to preheat/air-condition or another tube assembled in parallel. Being used as heat exchanger, the tube will use the mass close to the building by producing the reverse of the expected effect. For the same reasons, an installation exploiting several tubes in parallel will have sufficiently to space them from/to each other (from 1 to 2 meters) so that they do not return in competition, increasing in fact the cost of such an installation.

See too

External bonds

the Canadian well , www.construire-sain.com, 5/27/2007
the installation of the Canadian wells , www.puitscanadien.org, 5/27/2007
Canadian Well , fr.ekopedia.org, 5/27/2007
Bruno Herzog, To build his bioclimatic house , www.batirbio.org, 5/27/2007
the Canadian well (or well of Provence) , www.idéemaison.com, 5/27/2007
David Amitrano, Elements of dimensioning of an exchanger air/ground, known as Canadian well , University J. Fourier, Grenoble, 4/19/2006
www.puitscanadien.com , 5/6/2007
Earth Cooling Tubes , www.eere.energy.gov, 5/27/2007
the Canadian well , www.puits-canadien-home.com, 9/27/2007

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