FR2519750A1 - Gas to gas air conditioning heat exchanger - has adjacent parallel channels formed by concertina shaped bent sheet to heat air entering building - Google Patents

Abstract

The heat exchanger is a gas/gas type with parallel flow. It is used to heat fresh air entering a building from the stale exhaust air. Parallel walls are fitted in a heat insulated chamber to form gas flow channels. The parallel walls are made by bending sheets into concertina form, with semicircular bends. The wall width is more than five times the pitch dimension, which is less than 4cms. One of the walls can be dismounted and the sheets are held by transverse concertina shaped strips (6).

Description

 The present invention relates to a heat exchanger between the fresh air injected into a building and the stale air extracted therefrom.

 The present invention is both a method of recovering thermal energy from the hot air extracted from a building and a technological device making it possible to integrate in an original way a high performance air exchanger inside a residential, office, school or other building, provided that this building benefits from air renewal, by controlled mechanical ventilation.

The process
The process is based on the theory of the heat exchanger with parallel counter-currents.

Let qi be the injected air flow (m3 / h)
qe the extract air flow (m3 / h)
Let mi = 0.34 qi Let S: the total area of trade
k: the wall exchange coefficient.

si me = mi = m

The efficiency of such an exchanger is written:
(outlet temperature - inlet temperature) injected air
# = inlet temperature - inlet temperature
air extracted from the injected air if me # mid

if me = mi = m

These values assume that the exchanger is perfectly isolated from the outside environment.

Applied in the case of an exchanger between fresh air and stale air in a building: - me 5i1 mi when there are parasitic air inlets through windows-
very or doors and / or when mixing with stale air,
to increase the inlet temperature, the fumes
of a heat producing device.

- me s mi when the quantity injected is strictly extracted.

This is the case for example of an electric heated building
three times and whose exterior joinery is
very airtight.

It is observed that the yields are independent of the inlet temperatures of the fresh air and the extracted air.

 But obviously the outlet temperature of the fresh air will be higher the higher the inlet temperature of the stale air. The need for additional heat will therefore be even smaller.

 It is also observed that the efficiency of the exchanger is all the better as the exchange coefficient k of the exchange wall is large and that the exchange surface is large.

If mi <me

 However, it is known that the fouling of the exchange surfaces, that very low velocities ((at 0.30 m / s) of air circulation along the exchange surfaces and that an excessively large thickness of the air gap between the exchange surfaces, are factors which generate very significant decreases in the value of k.

 One of the original features of the process and the technological device presented is that it takes these conditions into account in a manner specifically adapted to the building, with the aim of obtaining a yield practically close to 0.8.

 In order to better clarify this very important point of the invention, one can examine by way of example, and without this being limiting, the case of a collective residential building.

 A stairwell generally distributes 4 apartments per floor, the overall living volume of which is Vha.

Let y = Volume of air renewed per hour
Living space
Suppose to simplify the presentation qe = qi = yVha Dlod: m = me = mi = 0.34 yVha
The yield is written

For a given value of X (objective to be reached), we find

 If the building has n levels, the total habitable volume is equal to n x Vha.

The previous relation is then written

 It can therefore be seen that if one assigns a heat exchange surface S proportional to Vha of each level, the value of the yield defined in objective is not modified.

 Another originality of the process and the device presented is to apply this theorem by placing the exchanger vertically in the height of the building. Its performance will then remain constant regardless of the number of floors in the building (for a given renewal rate y).

The two essential originalities described above of the process generate the following technological device
- The exchanger is designed by elements with a floor height
can be integrated for example at the bottom of a stairwell
or in any other place allowing these
elements vertically one above the other at the
way of a sheath.

avec la condition : si mi > me alors 5 doit être choisi

- The exchanger is designed so that the thickness of the air knives
between two exchange surfaces is as small as possible (4 4 cm) and so that the speeds of the injected air
as that of the extracted air are greater than 0.30 m / E
- The dimensions of the exchanger are calculated as
next
Data: strongly desired
volume of fresh air injected per hour: qi
volume of stale air ejected per hour: qe
Hence mi = 0.34 qi
me = 0.34 qe
Values to be determined: kS, Ae, Ai k practically does not depend (taking into account the constraints
adopted) as the material of the surface
exchange
S exchange surface
Ae passage section of the extracted stale air
Ai passage section for injected fresh air

with the condition: if mi> me then 5 must be chosen

avec la conditipn 5 ( 1
Dans les deux cas (vitesses ) 0.30 m/s)

If mi <me then
If mi = me

with conditipn 5 (1
In both cases (speeds) 0.30 m / s)

and distance between two exchange plates d 4 4 cm
We note that inequalities can always be
satisfied.

Technological device
The original features of the process described above are embodied by the technological devices described below.

Only the original features of the device are described. The construction details not described belong to the usual and known technology.

 Plate 1 shows that the exchanger can be arranged, for example, vertically at the bottom of the stairwell of a residential building, and over its entire height. This position is indicative. Other choices are possible depending on the configuration of the building.

 Plate 2 shows a current exchanger element of height h corresponding for example to a stage height h.

ussi
Plate 2 shows the current section of a current exchanging element of height h.

 The outer shell of the exchanger consists of a fixed part 1 sealed in the construction and a removable panel 2 accessible.

 This envelope can be made of angles and sheets of metal or plastic (PVC for example).

 To satisfy one of the hypotheses of the process (non-exchange with the environment), the thermal resistance of this envelope must be greater than 2 m20 / W (7 cm of polyurethane foam for example).

 The exchange surfaces are formed by the exchange elements 3, 4, 5 ... as much as necessary (cf. calculations described above).

 Each exchange element is made up of a plate folded in the form of an accordion with a pitch of d cm.

 This thin sheet is made of steel, aluminum, PVC, or other material having a good quality of heat exchange.

 The number of steps d of each exchanger element is chosen so that the element is easy to handle.

 Plate 3 shows the details of the joints. It is indeed essential that the stale air does not mix with the fresh air.

 There are two types of seals.

 Detail 6 shows the vertical joint between the ends of each exchanger element 3, 4, 5 ... and the outer casing.

This seal consists for example of an extruded strip of neoprene or the like bonded to the bottom of the envelope. This strip ensures both the fixing of the exchanger elements and the vertical sealing by clipping.

 Detail 7 shows the horizontal joint between two superposed exchanger elements. The rib 9 of the sheet of exchanger elements 3, 4, 5 ... ensures the stiffening of this sheet in the current height. I1 also ensures, by suitable positioning of the first lower rib, and of the last upper rib, the clipping of a preformed joint strip 8 at the same pitch and at the same width as the exchanger elements. The sealing is completed by internal coating of the strips with a non-sticky paste.

 Plate 4 shows the details of the fresh air and stale air outlet at the top of the last level of the exchanger. Blanking plates (10) close off the volume offered & the stale air. This emerges through the front window 12 pierced in the front panel of the outer casing. The fresh air is recovered above the last exchanger elements and exits through the window (11).

 On these windows are bolted the ducts which will recover the two air streams.

 In the lower part of the 1st level of the exchanger, the device is the same but reversed.

Other solutions for recovering the air streams at the inlet and at the outlet of the exchanger can be adopted without altering the originality of the invention
- front fresh air outlet, rear stale air
- side or top outlets.

Exploitation of the technolozic process and device
The purpose of this presentation is to clearly specify the originalities of the process and the device.

 For example, assume an R + 4 residential building (5 levels) with a living volume of 750 m3 per level.

The air renewal rate is 0.55. Due to parasitic air inlets we will admit
qi = 750 x 0.55 = 412 m3 / h per level
qe = 1.05 qi = 433 m3 / h
mi = 0.34 x 412 = 140 W / O
me = 0.34 x 433 = 147 W / O
We want to make a yield exchanger = 0.80 which can be housed at the bottom of a stairwell 2.60 m wide. We calculate

We will admit, taking into account the periodic cleaning and the configuration of the exchanger: k = 5 W / m20
Hence: S = 513 = 103 m.

5
Taking into account the thickness of the envelope and the clearances which should be reserved at the lateral ends of the exchanger to ensure easy installation of the exchanger elements, the useful length of the exchanger is
L = 2.60 - 0.15 - 0.15 = 2.30 m
The speed condition # 0.30 m / s gives:
L x # 2 x 412 = 0.824 m
1,000
Hence: # # 0.824 = 0.36 m or # = 0.35 m
2.30
If we assume the floor height h = 2.70 m
Each exchange plate has a surface
s = Q xh = 0.35 x 2.70 = 0.95 m2
So you need a number of plates
p = 103 = 108 P o, g5
The step d is therefore worth
d = L = 2.30 = 0.021 m
p 108
Let d = 2 cm
We check d 4 4 cm
If this condition was not satisfied, one of the data would have to be modified.

(In general L)
For reasons of handling of the exchanger elements, the 108 exchange plates are produced by 5 "accordions of 17 steps each (an odd number is required) and one of 23 steps.

 Always for reasons of maneuverability of the drying elements, each element can be cut in half in the height of a stage (possibly).

The cleaning of the exchanger elements is then carried out as follows
. removing the front panel (2)
. unclipping the horizontal joint strips
. unclipping of the exchanger elements of the joint strips
vertical
. cleaning of the elements by sandblasting (the accordion effect
can be used to open each step)
reassembly by reverse operation.

Claims (10)

 1. Parallel current gas / gas heat exchanger intended in particular for reheating the fresh air entering a building by the stale air which is extracted therefrom, characterized in that it comprises a series of parallel walls arranged in a thermally insulating enclosure, said parallel walls delimiting with the walls of the enclosure spaces inside which the two gases circulate.  2. Heat exchanger according to claim 1, characterized in that the parallel walls are obtained by accordion folding of a sheet in a regular pitch.  3. Heat exchanger according to claim 2, characterized in that each folding zone is in a semicircle.  4. Heat exchanger according to claim 2 or claim 3, characterized in that the width of the walls is greater than five times the value of the pitch.  5. Heat exchanger according to any one of claims 2 to 4, characterized in that the pitch is less than 4 cm.  6. Heat exchanger according to any one of claims 1 to 5, characterized in that one of the walls of the enclosure which is orthogonal to said parallel walls is removable.  7. Heat exchanger according to any one of claims 2 to 6, characterized in that it comprises a series of sheets folded in accordion, joined by longitudinal joints along a wall of the enclosure orthogonal to the walls parallel.  8. Heat exchanger according to any one of claims 2 to 6, characterized in that it comprises a series of sheets folded in accordion joined by transverse joints constituted by strips folded in accordion at the same pitch as the sheets and clipped on the sheets between the ribs presented by each sheet in the vicinity of its ends.  9. Heat exchanger according to any one of claims 1 to 8, characterized in that the spaces delimited by two successive parallel walls are alternately closed and open at their ends so as to allow the entry or exit of one gases beyond the parallel walls, while side windows in the vicinity of these ends provide entry or exit of the other gas.  10. A method for carrying out a heat exchange between two gases, characterized in that an exchanger is used according to any one of claims 1 to 9, and the gases are circulated alternately in opposite directions in the different spaces defined between the parallel walls.