Note: Descriptions are shown in the official language in which they were submitted.
7959
Method of continuously regulating the_operation of a
ventilation plant and a ventilation plant for use in said
method
The present invention relates to a method of continuously
regulating the operation of a ventilation plant, compris-
ing an air supply blower and an air exhauster, and a ven-
tilation plant for carrying out said method.
In known ventilation plants of the above-mentioned type,
the air flow through the fans is often only adjusted once,
and it is then assumed that the ventilation plant will
continue to function satisfactorily even under other con-
ditions than those prevailing when the adjustment wasmade. Known ventilation plants have, however, proved to be
sensitive to changes in such factors as atmospheric pres-
sure and outside temperature and the associated changes in
air density and volume, which can negatively affect the
flow through the system~ This is especially true for the
presently more and more common type of ventilation plant
which passes the exhaust air through a heat exchanger for
heat recovery before being exhausted in~o the atmosphere.
In order to avoid the risk of decreased performance, the
invention relates to a method which continuously regulates
a ventilation plant. This is achieved according to the
invention which includes a method for preventing
disturbances of the ventilation air ~low in a ventila-
tion plant of the zero-pressure type comprising an air
supply blower and a fan-type air exhauster. The method
includes comparing the static pressure in the room to
be ventilated by the plant with the static pressure of
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the open air. The difference between the static pres-
sures is used as a regulating variable for controlling
the flow through one of the air supply blower and air
exhauster in such a way that this diEference is elimin-
ated, whereby disturbances in the ventilation flow arecompensated by the plant.
A construction in accordance with the present invention
includes a ventilation plant of the zero-pressure type,
comprising an air supply blower and a fan-type air
exhauster. Duct means lead from the air supply blower
to the room to be ventilated to the air exhauster, and
openings which blow air into and draw air out of the
room. A regulator means which provides an output signal
when the static pressure ln the room deviates from the
static pressure of the outside air is also provided.
Means are furnished for relaying the output signal, and
a regulator which receives the output signal causes
increases and decreases in the air flow through one of
the air exhauster and the air supply blower in response
to the output signal to compensate disturbances in the
ventilation flow.
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In order to facilitate a better understanding of the
invention, an embodiment thereof will be described below
with reference to the accompanying drawings, of which:
Fig.l is a section through a ventilated room showing the
principles for the ventilation thereof,
Fig. 2 shows schematically a ventilation plant, which can
be regulated with advantage by means of the method accord-
ing to the invention, and
Fig. 3 shows a cross-section through a regulator means
according to the invention.
In a ventilation plant of the type shown in Fig. 1, air is
blown in from an obliquely downwardly directed air supply
opening 5 and is exhausted through an exhaust opening 6.
lS With suitable flow rates through these openings, the
intended effect can be achieved, namely that a circulating
diffusing flow will be created in the air in the enclosure
to be ventilated, as is indicated schematically in Fig. 1.
This type of flow provides a mixing of the air in the room
and assure that the incoming air flow will be thoroughly
mixed with the air present in the room. This desired type
of flow has, however, proved to be quite instable and
therefore difficult to maintain continuously during the
operation of the ventilation plant.
It is not uncommon in known ventilation plants that under
certain operating conditions this circulating diffusing
flow is not produced. Rather, the air blown in proceeds
more or less directly to the exhaust opening. This means
that a portion of the air in the room, lying under an
imaginary line between the lower edges of the openings 5,6
will not be changed, and this constitutes a serious
disadvantage if the air supply is also intended to heat
the room. The thermostat in the room, which controls the
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temperature of the air blown in, is usually located below
said imaginary line and will, under these conditions,
indicate that the temperature in the room is too low, and
this will result in the exhausted air being heated more
and more to no use. Such a situation can thus have
disastrous consequences for the energy economy of the
plant. If the room is used for work producing
environmentally dangerous gases, this lack of air mixing
can mean that these gases will be concentrated more and
more in the lower portion of the room and thus constitute
an unacceptable danger to those present in the room.
The invention is based on the surprising insight that if
the static pressures of the outside air and the air in the
room are equal, the above-mentioned disruptions of the
circulation flow will not occur. By providing the
ventilation plant with control equipment which keeps these
static pressures equal, the plant can thus be continually
regulated during its operation. In order to provide this
continuous regulation, the room or building is provided
with a regulator means 8, which sends an output signal
when the static pressure in the room differs from the
static pressure of the outside air. This will be described
in more detail below. This output signal then regulates
the flow through one of the fans, preferably the exhaust
fan.
Fig. 2 shows schematically a ventilation plant of heat
recovery type, which can be controlled with advantage by
the method of the invention. The ventilation plant compri-
ses an air supply fan 3, which blows preheated air through
an afterheater battery 4, where the air is heated further,
and then through suitable ducts and openings 5 into the
room or rooms to be ventilated. Upstream of the air supply
fan is a burner 2 and a heat exchanger 1 disposed for pre-
heating the air drawn in from the outside. By means of an
,
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exhaust fan 7 air is drawn from the room or rooms through
suitable openings 9 and ducts. Upstream of the exhaust fan
is a heat exchanger 1 for recovery of the heat content of
the exhaust air. Preferably, this consists of a rotary
heat exchanger 1 which is partially placed in the inlet to
the air supply fan 3 and there functions as a preheater.
Such a plant functions in the following manner. The intake
outside air passes, before passing through the air supply
fan 3, first past a portion of the rotating heat exchanger
1. There the outside air is preheated, depending on the
outside temperature, the inside temperature, the efficien-
cy of the heat exchanger etc. and then passes through the
burner disposed upstream from the air supply fan. The bur-
ner is preferably thermostat controlled, so that the airreaches the air supply fan 3 at essentially the tempera-
ture which is to be maintained in the ventilated room.
Before the intake air is delivered to this room, it is
additionally heated a few degrees in the afterheating bat-
tery 4 disposed downstream of the air supply fan. This airis then blown through suitable openings or nozzles 5 into
the room or rooms to be ventilated and heated. The air
drawn from said room or rooms through suitable openings 6
is collected in a collection duct or the like and flows
through the portion of the rotary heat exchanger located
upstream of the exhaust fan 7. In the heat exchanger it
gives off a significant portion of its heat before passing
through the exhaust fan 7 to the atmosphere.
39 In plants of this type, the amount of air blown in by the
supply fan 3 should be equal to the amount drawn out by
the exhaust fan 7. This means in turn that the amount of
air delivered to the atmosphere by the exhaust fan should
be equal to the amount of air supplied to the room by the
air supply fan. ~t constant pressure the volume which the
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same amount of air takes up at different temperatures is
directly proportional to these temperatures. This means
that air expelled into the atmosphere by the exhaust fan
which has been cooled by the heat exchanger from ~20C
to -10C will have a volume corresponding to 90% of the
volume which the same air took up in the room if the pres-
sure in the room is equal to the pressure of the outside
air. If the heat exchanger insted cools the air from
~20C to 0C, the air expelled into the atmosphere
will have a volume corresponding to 93% of the volume
which the same air took up in the room. If the ventilation
plant is set when the outside temperature is such that the
heat exchanger cools the exhaust air from ~20C to
0C, and the outside temperature then drops so far that
~5 the air is instead cooled to -10C, if other conditions
remain unchanged, the exhaust fan, the volume flow rate of
which is constant at constant rpm, will exhaust too great
a volume of air. Quantitative calculations of the effect
that this will have on the system are very difficult since
many factors affect the result, such as changes in the
; total, static or dynamic pressure, changes in pressure
gradients in ventilation systems, etc. Qualitatively, how-
ever, it will be understood that a low pressure can arise
in the room and experience has proven that this can dis-
rupt the proper no-draft ventilation flow, i.e. the
circulating diffusing flows disappear and the incoming air
flows directly to the exhaust opening. If the outside
temperature rises, a high pressure can of course arise
instead.
In order to prevent subatmospheric or overpressures from
arising in the room and thus preventing proper mixing of
the air, the rotational speed of the exhaust fan is con-
trolled by means of a regulator, which preferably consists
of a reversible electric motor, the output shaft of which
moves the pulley of a variable speed belt transmission via
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a lever mechanism or the like. The control signal to the
reversible electric motor is sent by a regulator means 8,
which when there is subatmospheric pressure sends an out-
put signal which makes the motor rotate in a direction
which reduces the rotational speed of the exhaust fan and
which when there is overpressure sends an output signal
which makes the motor rotate in the other direction.
The regulator means consists of a hollow body 9 of a mate-
rial which is rigid at the prevailing pressures, for
example of hard plastic. The hollow interior of the body
is divided by a flexible membrane 10 into two chambers
11,12. One 12 of the chambers communicates with the out-
side air via a duct to sense its static pressure. The open
end of the duct leading to the outside air should suitably
be placed so as to be protected from wind. This duct is
suitably connected to chamber 12 by means of a conventio-
nal hose coupling, which fits in a coupling flange 14 on
the body 9, said flange surrounding an opening in the body
to one chamber 12. The other side of the body 9 has a
corresponding opening and connecting flange 13 to communi-
cate the other chamber ll to the inside air in the room.
It should be noted that the open end of the connecting
duct for the inside air should be placed so that the local
over or underpressures arising due to the dynamic pressure
at the supply or exhaust openings 5,6 do not affect the
regulator means.
The membrane 10 is provided at its central portion with a
contact plate 17 of a suitable electrically conducting
material, which is connected via a wire 20 to a terminal
block on the body. Directly adjacent the contact plates 17
on both sides of the membrane are contact means 15, 16
which extend from both the insides of the body. The con-
tact means can be made of electrically conducting copper
or of electrically insulating elements which have electri-
cally conducting contact plates at their ends, connected
to the terminal block wires, suitably running through the
contact means. The distance between the membrane contact
plate 17 and the respective contact means 15,16 when the
membrane is in its rest position, i.e. when the pressures
in the chambers lI, 12 are equal, can be set by virtue of
the fact that the contact means are axially displaceable
in the body 9. They can for example be screwed into threa-
10 ded sleeves 18,19 in the body, as is indicated in Fig. 3.
The selected position is fixed by means of lock nuts 21.
If so desired, a scale can be arranged on the contact-~
means, providing the set spacing corresponding to the over
or underpressure at which the respective electrical cir-
cuit is closed. In the example shown, the membrane contact
plate 17 is connected via the terminal block to a voltage
source and the wires from the contact means 15,16 are con-
nected via the same block to a relay (not shown) which
controls the rotational direction of the output shaft of
the reversible electric motor depending on which of the
circuits is energized. Other arrangements of the electri-
cal control circuits are, however, possible and the above
design is therefore only given as a non-limiting example.
The method according to the invention thus provides conti-
nuous regulation of a ventilation plant, which balances
the inflow and outflow of air so that the static pressure
in the room or rooms to be ventilated is kept equal to the
static pressure of the outside air. Even if the process is
primarily intended for ventilation plants with heat reco-
very, the method can of course also be used on other types
of ventilation plants, which for one reason or another
require continuous regulation.
A number of modifications are conceivable within the scope
of the invention. For example, the air supply fan can be
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regulated instead of the exhaust fan, but since ventila-
tion norms require a certain rate of air change it is pre-
ferable to balance the air flows by means of the exhaust
fan as described above. Furthermore, the amount of exhaus-
ted air can be regulated by a combination of fan and dam-
per regulation. Such combined regulation is particularly
suitable when a number of separate rooms are to be venti
lated. In this case the output signal from the regulator
means in the largest room or the room most sensitive to
change is allowed to control the exhaust fan, while the
control means in the other rooms control dampers or the
like at the exhaust openings in these rooms. It should be
noted here that the heat regulator means in the other
rooms need not be connected to the outside air. Rather the
"outside air collecting chamber" can be directly or
indirectly connected to the air in the largest room.
Finally, by virtue of the fact that the contact means in
the regulator means are adjustable, it is possible to
obtain the desired control accuracy and even obtain a
minimal non-disruptive overpressure to completely elimina-
te the risk of cold fall in the room.
