Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to an arrangement ~r the transfer
of heat from the exhaust air leaving an enclosed volume, such as a mine or
the like, to the input air to said volume, comprising a liquid filled
circuit with at least one first circulation pump at least one first heat
exchanger arranged in contact with the input airflow and at least one second
heat exchanger arranged in contact with the exhaust airflow.
There is an advantage to be gained by recovering the heat contained
in the exhaust air leaving dwelling houses, industrial premises, mines et-
cetera. One known method of achieving this objective to a certain ex~ent,
is to arrange a heat-exchanger in the exhaust air duct or line, which cools
the exhaust air and consequently absorbs part of its heat content, and to
arrange a heat exchanger in the air input duc~ or line, in order to heat up
the input air. The two heat exchangers are coupled together through a
circuit containing a circulation pump. As heat transfer medium in the
circuit, it is possible to use a liquid such as a water-glycol mix~ure so
; that the heat transfer medium is prevented from freczing in the heat ex
changers in the situation where the air temperatures are extremely low.
One problem occurring with this kind of known arrangemen~ is that
it is not possible to cool the exhaust air to too great an ex~ent without
2~ the liquid content which is always present in the warm exhaust air, con-
densing on the surface of the heat exchanger which cools this air, so that
it forms frost or ice on the heat exchanger if the exit temperature of the
exhaust air becomes low. Frost formation or icing on the surface of the
exhaust air heat exchanger impedes heat transfer and also increases the
resistance in the exhaust air duct. This icing or frost formation can
ultimately lead to blockage of the exhaust air duct. This phenomenon
imposes a limit on the extent to which the exhaust air can be cooled and
-- 1 --
-
~:' ., .' , ,, ' .: ' '
,
.
~ ,: '' '
therefore upon how much heat can be recovered.
In a particular example, the exhaus-t air from a mine is at a tem-
perature of about 7C. As soon as the exhaust air is cooled down to the
neighbourhood of 0C by the exhaus~ air heat exchanger, frost and ice begin
to form on ~he heat exchanger surfaceA If the input air to the mine has a
temperature of for example -25C, then only about 25% of the total heat
energy supplied to the input air can be recovered if severe frost formation
and icing on the exhaust air heat exchanger is to be avoided. It is an
objective of major importance from the economic and fuel policy points of
view to develop arrangements which will increase the fraction of recov-
erable heat energy without any risk of malfunctioning in the arrangement due
to icing or frost formation.
According to one aspect of the present invention there is provided
in an apparatus for transfer of heat from warm exhaust air leaving an en-
closed volume such as a mine via an exhaust conduit to cold input air supplied
to said volume via a supply conduit comprising a glycol-water filled circuit,
a circulation pump in said circuit, a first heat exchanger in said circuit,
arranged in said supply conduit, a second heat exchanger in said circuit, ar-
ranged in said exhaust conduit, the improvement comprising a heat store o
the stratified liquid-layer type, the hot side of which is coupled to the
hot side of the circuit and the cold side of which is coupled to the cold
side of said circuit, valve means for deflecting part of the ho~ circuit
liquid into said store during normal operation, and a shut off valve in said
circuit between the hot side of the heat store and said second heat exchanger,
whereby the flow of cold liquid through said second heat exchanger can be
interrupted such that the warm exhaust air will defrost said second heat
exchanger whilst said circulation pump feeds hot liquid from the heat store
- 2 -
":`
- ~ ,
.
through the first heat exchanger such that the heating of the input air flow
is maintained.
According to another aspect of the present invention there is pro-
vided an arrangement for the transfer of heat from the exhaust air leaving
an enclosed volume to the input air to said volume comprising:
a liquid-filled circuit having;
at leas~ one first circulation pump;
at least one first heat exchanger arranged in contact with said
input airflow;
at least one second heat exchanger arranged in con~act with said
exhaust airflow;
at least one by-pass line arranged in said circuit in parallel
with said second heat exchanger;
means for controlling the liquid flow through said second heat
exchanger; and,
layer type heat store means for supplying heat to said first heat
exehanger in the form of heat extracted from said exhaust air~ while
said second heat exchanger is disconnected for defrosting, having
the hot side thereof coupled to said liquid circuit between the
output of said second heat exchanger and the input of said first
heat exchanger and having the cold side thereof coupled to said
liquid circuit between the output of the first heat exchanger and
the input of said second heat exchanger, whereby said hea* store
constitutes said by-pass line.
In the accompanying drawings, which illustrate exemplary embodiments
of the present invention:
Figure 1 illustrates a first embodiment of the invention; and
~ 3 -
'' :- ,' ' '' , ~:
Figures 2 and 3 illus~rate two embodiments o the invention in which an
auxiliary heat source is provided in order to facilitate defrosting.
~ igure 1 schematically illustrates an enclosed volume 1 such as a
mine or the like, with an air supply duct 2 and an exhaust air duct 3. Fans
are normally provided, although not illustrated here, in order to circulate
the air through the volume 1 A first heat exchanger 4 is arranged in the
air supply duct 2. A second heat exchanger 5 is arranged in the exhaust
air duc~ 3. The heat exchangers ~ and 5 are connected into a closed, liquid
filled circuit 6. The liquid can consist of a water-glycol mixture. A by-
pass line is arranged across the second heat exchanger 5. A heat store 8 of
layer design is connected into the circuit 6 and its cold side connected to
the by-pass line 7. The circuit 6 exhibits a circulation pump 18 which
maintains circulation of the liquid through at least the firs~ heat exchanger
4. The circuit 6, between the heat store 8 and the second heat exchanger 5,
contains an element 9. The element 9 can be constituted by a shut-off valve
or a reversible circulation pump.
In operation of the installation shown in Figure 1, with the
temperature relationships set out for example in the drawing, after a rela-
tively short period of time icing and frost formation occur at the second
heat exchanger 5. As icing gradually begins to restrict heat exchange be-
tween the exhaust air and the liquid in the circuit 6, the valve 9 can be
closed down. This means tha~ the exhaust air, having for example a tem-
perature of 7C, brings about defrosting of the second heat exchanger
whilst the heat supply to the heat exchanger 4 is maintained by means of the
layer of hot liquid collected in the heat store 8. During the period of
operation in which defrosting is notin process, it is arranged, in other
words, that only part of the liquid heated up in the second heat exchanger is
~ . ' ' , ' ' '
.. ~
,
,
relayed ~directly) to the first heat exchanger ~, whilst the remaining
fraction of the liquid heated up in the second heat exchanger is stored in
the heat store for a period of time during which the valve 9 is kept closed.
In a situation where the element 9 is constituted by a reversible
circulation pump, the arrangement is such that the pump 9 normally pumps
liquid from the second heat exchanger 5 to the heat store 8. When the
second heat exchanger 5 is to be defrosted, the pump 9 is reversed so that
it pumps hot liquid from the heat store 8 through the heat exchanger 5.
In this case, thus ho~ liquid from the heat store 8 is pumped both through
the heat exchanger ~ and through that S. In this fashion, frost and ice
having formed on ~he heat exchanger 5 are thawed both ~rom the outside by
the warm exhaust air, and from ~he inside by the hot liquid from the heat
store.
An external heat source 10, such as an oil-burner unit, can be
arranged to reheat the input air prehea~ed in the heat exchanger ~, in order
to ensure that the air arriving in the enclosed volume 1 does not have an
undesirably low temperature. In this context, account must also be taken of
the situa~ion in the exhaust air duct since the exhaust air leaving the vol-
ume 1 should have a temperature normally exceeding 0C so that the heat ex-
changer 5 can also be defrosted by the supply of heat from outside, that is
to say that the relatively warm exhaust air can throw out the frost forming
on the plastic tube heat exchanger 5.
Referring now to Figure 2 there can be seen an arrangement generally
similar to that of Figure 1. However, in this case a second by-pass line
25 has been provided which is so arr~nged that is shunts the flow through
the circuit 6 ~rom a point between the circulation pump 18 and the first
heat exchanger ~, to a point between the first by-pass line 7 and the second
- 5 -
:
heat exchanger 5. The by-pass line 25 contains an auxiliary heat source 23
which may for example be designed as an i~nersion heater. In order to
control the flow distribution between the circuit 6 and the by-pass line
25, a first valve 20 is arranged in the line 25 and a second valve 21 at
the heat exchanger 4. The valves 20 and 21 are adjusted in such fashion
that a certain flow of hot liquid ~rom the heat s~ore ~ through ~he heat
exchanger 4 is maintained even when the heat exchanger 5 is being defrosted.
The immersion heater 23 heats up the liquid flow in the by-pass
line 25 to a level corresponding to the temperature reduction occurring in
the flow through the heat exchanger 5 whilst the latter is being defrosted,
with the result that the flow leaving the heat exchanger 5 and arriving in
the heat store 8 has a temperature which does not differ too radically from
the temperature in the hot section of the heat store 8.
Referring now to Figure 3, there can be seen an alternative method
of coupling the auxiliary heat source 23 into an apparatus otherwise in
accordance with Figure 1. In this instance, a by-pass line 7b has been
provided, which extends from a point between the circulation pump ~ and the
heat store 8, to a point between the by-pass line 7 and the second heat
exchanger 5. The flow distribution between the circuit 6 and the by-pass
line 7b is regulated by valves 20 and 21 which are arra~ged after the branch
between the by-pass line 7b and the circuit 6. The valve 20, 21 can of
course be designed as a ~hree-way valve and need not leak any flow into the
main circui~ 6 since the by-pass valve 7 ensures that circulation through the
heat store 8 and the first heat exchanger 4 is maintained for the time dur-
ing which the second heat exchanger 5 is being derosted.
