Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Method and Apparatus for Satisfying Heating
and Cooling Demands and Control Therefor
This invention relates generally to methods and apparatus for
simultaneously satisfying heating and cooling demands.
Refrigeration apparatus or machines are frequently employed to
cool a fluid sucK as water which is circulated through various
rooms or enclosures of a building to cool these areas. Often, the
refrigerant of such machines rejects a relatively large amount of
heat at the condenser of the machine. This rejected heat is
commonly dissipated to the atmosphere, either directly or via a
cooling fluid that circulates between the condenser and a cooling
tower. Over a period of time, the rejected heat represents a
substantial loss of energy, and much attention has been recently
directed to reclaiming or recovering this heat to satisfy a
heating load or demand.
One general approach to reclaiming this heat is to employ a
booster compressor to draw and further compress refrigerant from
the condenser of the refrigeration machine. This further
compressed vapor is then passed through a separate, heat
reclaiming condenser. A heat transfer fluid is circulated through
the heat reclaiming condenser in heat transfer relation with the
refrigerant passing therethrough. Heat is transferred from the
refrigerant to the heat transfer fluid, heating the fluid and
condensing the refrigerant. The heated heat transfer fluid may
then be used to satisfy a present heating load or the fluid may be
stored for later use, and the condensed refrigerant is returned to
the cooling circuit for further use therein.
With refrigeration machines having both a cooling circuit and
heating circuit as described above, it is desirable to control the
heating and cooling circuits to meet varying heating and cooling
loads, and it is preferred to control the heating and cooling
circuits independent of each other so that variations in one
circuit do not affect the other circuit's ability to handle loads
placed thereon. However, difficulties arise when the heating and
cooling circuits are independently controlled. For example, if
the refrigeration machine is called on to simultaneously handle a
low cooling load and a high heating load, then the refrigerant
flow rate through the cooling circuit is comparatively small and a
relatively small amount of vapor is discharged from the compressor
of the cooling circuit. At the same time, the refrigerant flow
rate through the heating circuit is relatively large and a
relatively large portion of the refrigerant discharged from the
compressor of the cooling circuit is drawn into the booster
compressor and passed through the heating circuit. In fact, under
extreme conditions, the refrigerant flow rate through the booster
compressor may temporarily exceed the ra-te at which refrigerant is
discharged from the compressor of the cooling circuit. When this
occurs, the mass of refrigerant vapor in the condenser of the
cooling circuit decreases, decreasing the pressure therein. This,
in turn, decreases the pressure at the inlet of the booster
compressor. If this pressure falls to a very low level, the
temperature of the vapor discharged from the booster compressor
may become undesirably high, or the booster compressor may enter
what is known as surge conditions wherein there are periodic
complete flow reversals in the compressor, destroying the
efficiency of the compressor and endangering the integrity of the
elements thereof.
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These and other difficulties are overcome in accordance with the
present invention by reducing the refrigerant flow rate through a
booster stage compressor of a booster type refrigeration machine
when the pressure of refrigerant vapor in the high pressu~e side
of the cooling circuit of the machine falls below a predetermined
value. More specifically, the present invention relates to
apparatus for satisfying heating and cooling demands comprising a
cooling circuit including a mechanical refrigeration unit having a
low pressure side and a high pressure side, a heating circuit
including a booster compressor for drawing and further compressing
refrigerant from the high pressure side of the refrigeration unit,
and a heat reelaiming condenser for passing the fur-ther compressed
refrigerant vapor in heat transfer relation with a heat transfer
fluid to heat the fluid and condense the refrigerant vapor. The
apparatus also comprises a control for reducing the vapor flow
rate through the booster compressor when the pressure in the high
pressure side of the refrigeration unit falls below a
predetermined value.
This invention will now be described by way of example, with
reference to the accompanying drawing, which is a schematic
representation of a vapor compression refrigeration machine
incorporating teachings of the present invention.
Referring to the drawing, there is disclosed a schematic
illustration of refrigeration machine 10 employing teachings of
the present invention. Machine 10 includes, generally, cooling
circuit 12 and heating circuit 14. Cooling circuit 12, in turn,
includes primary compressor means such as first stage 16 of two
stage compressor 18, primary condenser 20, primary expansion means
22, and evaporator 24. Heating circuit 14 includes booster
compressor means such as second stage 26 of compressor 18, heat
reclaiming condenser 30, and auxiliary expansion means 32. Inlet
guide vanes 34 are provided to control the vapor flow through
-35 first stage 16 of compressor 18 and, thus, through cooling circuit
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12, while valve 36 is utilized to regulate the vapor flow through
second stage 26 of compressor 18 and, hence, through heating
circuit 14. Pressure sensor means 38, preferably including two
pressure switches 40 and 42, is in vapor communication with
primary condenser 20 to control valve 36 in a manner more fully
discussed below. Motor or drive means (not shown) is employed in
a manner which will be apparent to those skilled in the art to
simultaneously drive first and second stages 16 and 26 of
compressor 18.
In operation, first stage 16 of compressor 18 discharges hot,
compressed refrigerant vapor into primary condenser 20 via line
44. Refrigerant passes through primary condenser 20, rejects heat
to an external heat exchange medium such as water circulating
through heat exchange coil 46 located therein, and condenses. The
condensed refrigerant flows through primary expansion means 22,
reducing the temperature and pressure of the refrigerant. The
expanded refrigerant enters and passes through evaporator 24 and
absorbs heat from an external heat transfer medium such as water
passing through heat exchange coil 50 which is positioned within
the evaporator. The heat transfer medium is thus cooled and the
refrigerant is evaporated. The cooled heat transfer medium may
then be used to satisfy a cooling load, and the evaporated
refrigerant is drawn from evaporator 24 into line 52 leading back
to first stage 16 of compressor 18.
As described above, first stage 16 of compressor 18 and primary
expansion means 22 separate cooling circuit 12 into high pressure
side 54 and low pressure side 56, and booster inlet line 58 is
provided for transmitting refrigerant vapor from the high pressure
side of the cooling circuit to second stage 26 of compressor 18.
In the embodiment depicted in the drawing, inlet line 58 is
connected to primary condenser 20 and transmits a portion of the
refrigerant vapors passing therethrough to second stage 26 of
`35 compressor 18. Alternately, line 58 could be connected to
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discharge line 44. Second stage 26 of compressor 18 further
compresses the vapor transmitted thereto, further raising the
temperature and pressure of the vapor. This further compressecl
vapor is discharged into line 60, leading to heat reclaiming
condenser 30. The refrigerant vapor enters and passes through
heat reclaiming condenser 30 in heat transfer relation with a heat
transfer fluid such as water passing through heat exchange coil 62
disposed within the heat reclaiming condenser. Heat is
transferred from the refrigerant vapor to the fluid passing
through coil 62, heating the fluid and condensing the refrigerant.
The heated heat transfer fluid may then be employed to satisfy a
heating load. Refrigerant condensed in heat reclaiming condenser
30 passes therefrom back to cooling circuit 12 via return means
including auxiliary expansion means such as orifice 32 and
refrigerant lines 64 and 66. More particularly, condensed
refrigerant from heat reclaiming condenser 30 flows through
orifice 32 via line 64, reducing the pressure and tempera-ture of
the refrigerant. Refrigerant line 66 transmits refrigerant from
orifice 32 back to cooling circuit 12, specifically primary
expansion means 22 thereof, for further use in the cooling
circuit.
Guide vanes 34 may be controlled in response to any one or more of
a number of factors indicative of changes in the load on cooling
circuit 12 to vary the capacity thereof. For example, guide vanes
34 may be controlled in response to the temperature of the fluid
leaving heat exchanger 50 of evaporator 24. As -the cooling load
increases or decreases, guide vanes 34 move between minimum and
maximum vapor flow position~ to increase or decrease,
respectively, the vapor flow rate through first stage 16 of
compressor 18 and, thus, cooling circuit 12. Similarly, valve 36
may be controlled in response to any one or more factors
indicating changes in the load on heating circuit 14 to vary the
capacity thereof. For example, valve 36 may be controlled in
response to the temperature of the fluid discharged from heat
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exchanger 62 of heat reclaiming condenser 30. As the heating load
increases or decreases, positioning means 68 moves valve 36
between minimum and maximum vapor flow positiolls to increase or
decrease, respectively, the vapor flow rate through second stage
26 of compressor 18 and, hence, through heating circuit 14.
Positioning means 68 may be of any suitable type, for example an
electric, hydraulic or pneumatic device. Preferably, however,
positioning means 68 includes a reversible electric motor that is
selectively connected to a source of electrical energy to move
valve 36.
As discussed previously, when refrigeration machines of the
general type described above are called on to simultaneously
handle a low cooling load and a high heating load, the pressure at
the inlet of the heating circuit, or booster, compressor may
become very low. When this occurs, the temperature of the vapor
discharged from the booster compressor may become excessively high
or the booster compressor may enter surge conditions. In view of
this, machine 10 includes control means for reducing the vapor
flow rate through second stage 26 of compressor 18 when the
pressure in the high pressure side 54 of cooling circuit 12 falls
below a irst predetermined value or set point. More
specifically, the above-mentioned reducing means includes pressure
sensor 38 and positioning means 68. Positioning means 68 is
connected to sensor 38 and, as mentioned above, to valve 36.
Positioning means 68 and sensor 38 cooperate for moving valve 36
toward its minimum flow position to decrease the vapor flow rate
through second stage 26 of compressor 18 when the pressure of
vapor in primary condenser 20 falls below the first predetermined
value. Preferably, positioning means 68 continues to move valve
36 toward its minimum flow position if the pressure in primary
condenser 20 remains below the first predetermined value, further
reducing the vapor flow rate through heating circuit 14.
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With the above arrangement, the rate at which vapor is drawn from
primary condenser 20 by heating circuit 14 is reduced until that
vapor flow rate matches or becomes less than the rate at which
vapor enters the primary condenser via primary compressor 16.
This tends to maintain the mass of refrigerant vapor in primary
condenser 20 at or above a stable value. In this manner, the
pressure in primary condenser 20 may be maintained at or above a
level sufficient to prevent second stage 26 of compressor 18 from
entering surge conditions or from discharging vapor at an
excessively high temperature. Should the pressure in primary
condenser 20 rise back above the first predetermined level, sensor
38 ceases to cause positioning means 68 to move valve 36 toward
its minimum flow position. However, as will be apparent to those
skilled in the art, valve 36 may still be moved toward its minimum
flow position for other reasons such as a decrease in the load on
heating circuit 14.
In addition to the foregoing, preferably sensor 38 also senses
when the pressure in primary condenser 20 falls below a second
predetermined level or set point, greater than the above-discusse`d
first predetermined level. When this event is sensed, positioning
means 68 is prevented from moving valve 36 toward its maximum flow
position. This tends to prevent the rate at which vapor is drawn
from primary condenser 20 by heating circuit 14 from increasing
due to, for example, an increase in the load on heating circuit
14. This, in turn, tends to prevent the pressure in the primary
condenser from further decreasing. In case the pressure in
primary condenser 20 rises back above the second predetermined
level, sensor 38 no longer prevents positioning means 68 from
moving valve 36 toward its maximum flow position; and the valve
may be so moved, for example because of an increase in the heating
load on circui-t 14. In contrast, should the pressure in primary
condenser 20 continue to fall, for example, because of a further
reduction in the cooling load on cooling circuit 12, and the
pressure in the primary condenser falls below the first
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predetermined level, positioning means 68, as explained itl detail
above, is activated for moving valve 36 to decrease the vapor flow
rate through second stage 26 of compressor 18.
As will be apparent to one skilled in the art, pressure sensor 38
may be of any suitable type such as an electric, hydraulic, or
pneumatic device. Since positioning means 68 preferably includes
a reversible electric motor, pressure sensor 38 preferably
includes first and second pressure switches 40 and 42. Switch 40
senses when the pressure in primary condenser 20 falls below the
second set point to disconnect the electric motor from the source
of electrical energy to disable the motor from opening valve 36,
while switch 42 senses when the pressure in primary condenser 20
falls below the first set point to connect the electric motor to
the electrical energy source for closing valve 36. As shown in
the drawing, switches 40 and 42 are disposed in chamber 70 which
is in vapor communication with primary condenser 20 via tap-off
line 72.
Refrigeration machine 10 incorporating teachings of the present
invention may be effectively employed to prevent the booster
compressor from entering surge conditions or from discharging
vapor at undesirably high temperatures when the machine is called
upon to simultaneously satisfy a low cooling load and a high
heating load. Moreover, as may be understood from a review of the
above discussion, these beneficial results may be achieved in a
very reliable and inexpensive manner.
While it is apparent that the invention herein disclosed is well
calculated to fulfill the objects above stated, it will be
appreciated that numerous modifications and embodiments may be
devised by those skilled in the art, and it is intended that the
appended claims cover all such modifications and embodiments as
fall within the true spirit and scope of the present invention.
