U.S. patent application number 14/221702 was filed with the patent office on 2015-09-24 for variable refrigerant charge control.
This patent application is currently assigned to Lennox Industries Inc.. The applicant listed for this patent is Lennox Industries Inc.. Invention is credited to Eric Berg, Rakesh Goel.
Application Number | 20150267951 14/221702 |
Document ID | / |
Family ID | 54141757 |
Filed Date | 2015-09-24 |
United States Patent
Application |
20150267951 |
Kind Code |
A1 |
Berg; Eric ; et al. |
September 24, 2015 |
VARIABLE REFRIGERANT CHARGE CONTROL
Abstract
An apparatus and method for adjusting refrigerant charge level
are provided. The apparatus has a reservoir, a reservoir line, a
reservoir valve, and one or more side valves. The reservoir line
connects the reservoir and a liquid line, and has a connection to
the liquid line. The liquid line connects an indoor heat exchanger
and an outdoor heat exchanger. The reservoir valve is on the
reservoir line. The one or more side valves are on the liquid line.
In the method, an indicator of effectiveness of a refrigerant-using
system is calculated. The indicator is compared to a target
indicator of effectiveness. A refrigerant charge level is adjusted
to reduce the difference between the indicator and the target
indicator.
Inventors: |
Berg; Eric; (The Colony,
TX) ; Goel; Rakesh; (Irving, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lennox Industries Inc. |
Richardson |
TX |
US |
|
|
Assignee: |
Lennox Industries Inc.
Richardson
TX
|
Family ID: |
54141757 |
Appl. No.: |
14/221702 |
Filed: |
March 21, 2014 |
Current U.S.
Class: |
62/77 ;
62/292 |
Current CPC
Class: |
F25B 2400/053 20130101;
F25B 2400/054 20130101; F25B 2400/16 20130101; F25B 2400/19
20130101; F25B 49/02 20130101; F25B 2600/2519 20130101; F25B
2600/2523 20130101; F25B 2700/21163 20130101; F25B 13/00 20130101;
F25B 45/00 20130101; F25B 2700/195 20130101 |
International
Class: |
F25B 45/00 20060101
F25B045/00 |
Claims
1. An apparatus for adjusting refrigerant charge level, the
apparatus comprising: a reservoir; a reservoir line connecting the
reservoir and a liquid line, the liquid line connecting an indoor
heat exchanger and an outdoor heat exchanger, the reservoir line
comprising a connection to the liquid line; a reservoir valve on
the reservoir line; and one or more side valves on the liquid
line.
2. The apparatus of claim 1, wherein the one or more side valves
comprises an indoor side valve on the liquid line between the
indoor heat exchanger and the connection to the reservoir line.
3. The apparatus of claim 1, wherein the one or more side valves
comprises an outdoor side valve on the liquid line between the
outdoor heat exchanger and the connection to the reservoir
line.
4. The apparatus of claim 1, wherein the one or more side valves
comprises: an indoor side valve on the liquid line between the
indoor heat exchanger and the connection to the reservoir line; and
an outdoor side valve on the liquid line between the outdoor heat
exchanger and the connection to the reservoir line.
5. The apparatus of claim 1, wherein the reservoir valve and the
one or more side valves each comprise a solenoid valve.
6. The apparatus of claim 1, wherein the reservoir is above the
liquid line.
7. The apparatus of claim 1, wherein: a suction line passes through
the reservoir; and the suction line is connected to a
compressor.
8. A method for adjusting refrigerant charge level, the method
comprising: calculating an indicator of effectiveness of a
refrigerant-using system; comparing the indicator to a target
indicator of effectiveness; and adjusting a refrigerant charge
level to reduce the difference between the indicator and the target
indicator.
9. The method of claim 8, wherein adjusting the refrigerant charge
level comprises opening or closing a solenoid valve.
10. The method of claim 8, wherein: the indicator comprises a
subcooling value; the target indicator comprises a subcooling
value; and calculating the indicator comprises measuring a liquid
temperature and liquid pressure.
11. The method of claim 8, wherein: the indicator comprises an
energy efficiency ratio; the target indicator comprises an energy
efficiency ratio; and calculating the indicator comprises:
measuring an energy usage of a compressor; and measuring a heat
transferring capacity of the system.
12. The method of claim 11, wherein the heat transferring capacity
comprises a sensible capacity of the system.
13. The method of claim 12, wherein measuring the sensible capacity
comprises measuring an indoor airflow, a return air temperature,
and a supply air temperature.
14. The method of claim 11, wherein the heat transferring capacity
comprises a latent capacity of the system.
15. The method of claim 11, wherein the heat transferring capacity
comprises a total of: a sensible capacity of the system; and a
latent capacity of the system.
Description
TECHNICAL FIELD
[0001] This application relates to HVAC systems and, more
particularly, to HVAC refrigerant charge levels.
BACKGROUND
[0002] One area that has not been fully optimized in Heating,
Ventilation, and Air Conditioning (HVAC) systems is the refrigerant
charge level. Variable speed compressor technology greatly
increased the efficiency of HVAC systems by allowing the compressor
speed to be better adjusted to match the load on the system.
However, the refrigerant charge level (amount of refrigerant in the
system) in a conventional HVAC system remains the same regardless
of the load on the system. The refrigerant charge level is
therefore optimized for a single operating condition. It would be
desirable if a HVAC system could optimize its refrigerant charge
level for the current operating condition.
SUMMARY
[0003] In an embodiment, an apparatus for adjusting refrigerant
charge level is provided. The apparatus has a reservoir, a
reservoir line, a reservoir valve, and one or more side valves. The
reservoir line connects the reservoir and a liquid line, and has a
connection to the liquid line. The liquid line connects an indoor
heat exchanger and an outdoor heat exchanger. The reservoir valve
is on the reservoir line. The one or more side valves are on the
liquid line.
[0004] In another embodiment, a method for adjusting refrigerant
charge level is provided. An indicator of effectiveness of a
refrigerant-using system is calculated. The indicator is compared
to a target indicator of effectiveness. A refrigerant charge level
is adjusted to reduce the difference between the indicator and the
target indicator.
DESCRIPTION OF DRAWINGS
[0005] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
Detailed Description taken in conjunction with the accompanying
drawings, in which:
[0006] FIG. 1 depicts a HVAC system with a refrigerant charge
control apparatus;
[0007] FIG. 2A depicts the refrigerant charge control apparatus
configured for normal operation;
[0008] FIG. 2B depicts the refrigerant charge control apparatus
configured to fill a reservoir during cooling;
[0009] FIG. 2C depicts the refrigerant charge control apparatus
configured to fill the reservoir during heating;
[0010] FIG. 2D depicts the refrigerant charge control apparatus
configured to drain the reservoir using gravity;
[0011] FIG. 2E depicts the refrigerant charge control apparatus
configured to drain during cooling;
[0012] FIG. 2F depicts the refrigerant charge control apparatus
configured to drain during heating;
[0013] FIG. 3 depicts a HVAC system with an alternate refrigerant
charge control apparatus;
[0014] FIG. 4A depicts the alternate refrigerant charge control
apparatus configured for normal operation;
[0015] FIG. 4B depicts the alternate refrigerant charge control
apparatus configured to fill a reservoir;
[0016] FIG. 4C depicts the alternate refrigerant charge control
apparatus configured to drain the reservoir during cooling;
[0017] FIG. 4D depicts the alternate refrigerant charge control
apparatus configured to drain the reservoir during heating;
[0018] FIG. 5 depicts a method which a controller may perform to
use a subcooling value to control the refrigerant charge; and
[0019] FIG. 6 depicts a method which a controller may perform to
use an Energy Efficiency Ratio (EER) to control the refrigerant
charge.
DETAILED DESCRIPTION
[0020] In the following discussion, numerous specific details are
set forth to provide a thorough explanation. However, such specific
details are not essential. In other instances, well-known elements
have been illustrated in schematic or block diagram form.
Additionally, for the most part, specific details within the
understanding of persons of ordinary skill in the relevant art have
been omitted.
[0021] With reference to FIG. 1, depicted is a Heating,
Ventilation, and Air Conditioning (HVAC) system 100 with a
refrigerant charge control apparatus 101. System 100 includes
indoor unit 102, outdoor unit 104, and controller 105. Indoor unit
102 would be located inside a structure to be heated or cooled,
such as a building or refrigerator. Outdoor unit 104 would be
located outside the structure. This combination of an indoor unit
and an outdoor unit is generally used in residential HVAC systems
but may also be used in other applications, such as
refrigeration.
[0022] Prior to the operation of apparatus 101, HVAC system 100
operates conventionally. A continuous flow of refrigerant moves in
a loop through HVAC system 100. This loop may be called the "vapor
compression cycle." Compressor 106 compresses refrigerant in gas
vapor form, and then discharges the refrigerant through discharge
line 108. The compressed refrigerant gas vapor enters reversing
valve 110. Reversing valve 110 can change between a cooling
configuration, shown by solid lines, and a heating configuration,
shown by dashed lines.
[0023] In the cooling configuration, the refrigerant flows from
reversing valve 110 to outdoor heat exchanger 112. The refrigerant
flows through outdoor heat exchanger 112, releasing heat into the
outdoor air and condensing into a liquid. From outdoor heat
exchanger 112, the liquid refrigerant flows through liquid line
114.
[0024] Liquid line 114 has expansion device 116A and expansion
device 116B. Expansion devices 116A and 116B expand liquid
refrigerant flowing through them, reducing the pressure of the
refrigerant. However, due to check valves or the like, expansion
device 116A only acts on refrigerant flowing toward outdoor heat
exchanger 112, and expansion device 116B only acts on refrigerant
flowing toward indoor heat exchanger 118. Refrigerant flowing in
the opposite directions, through expansion device 116A toward
indoor heat exchanger 118 or through expansion device 116B toward
outdoor heat exchanger 112, bypasses the respective expansion
device and does not expand.
[0025] The liquid refrigerant bypasses expansion device 116A and
flows to expansion device 116B. Expansion device 116B reduces the
pressure of the liquid refrigerant flowing through it. The
refrigerant then flows through indoor heat exchanger 118, absorbing
heat from the structure and evaporating into a gas vapor. The
refrigerant then flows to reversing valve 110, where it is directed
through suction line 120 and back into compressor 106 to be
compressed again.
[0026] In the heating configuration, the refrigerant flows from
reversing valve 110 to indoor heat exchanger 118. The refrigerant
flows through indoor heat exchanger 118, releasing heat into the
structure and condensing into a liquid. From indoor heat exchanger
118, the liquid refrigerant flows through liquid line 114. The
liquid refrigerant bypasses expansion device 116B and flows to
expansion device 116A. Expansion device 116A reduces the pressure
of the liquid refrigerant flowing through it. The refrigerant then
flows through outdoor heat exchanger 112, absorbing heat from the
outdoor air and evaporating into a gas vapor. The refrigerant then
flows to reversing valve 110, where it is directed through suction
line 120 and back into compressor 106 to be compressed again.
[0027] Outdoor heat exchanger 112 may be called the outdoor coil.
Indoor heat exchanger 118 may be called the indoor coil. During
cooling, outdoor heat exchanger 112 may be called the condenser and
indoor heat exchanger 118 may be called the evaporator. During
heating, outdoor heat exchanger 112 may be called the evaporator
and indoor heat exchanger 118 may be called the condenser.
Expansion devices 116A and 116B may be expansion valves.
[0028] Refrigerant charge control apparatus 101 comprises reservoir
line 124, reservoir 126, reservoir valve 128A, indoor side valve
128B, and outdoor side valve 128C. Reservoir line 124 connects
liquid line 114 to reservoir 126. Reservoir 126 may be a tank which
holds excess refrigerant.
[0029] Reservoir valve 128A may be positioned on reservoir line
124. Indoor side valve 128B may be positioned on liquid line 114
between reservoir line 124 and indoor heat exchanger 118. Outdoor
side valve 128C may be positioned on liquid line 114 between
reservoir line 124 and outdoor heat exchanger 112. Valves 128A,
128B, and 128C can each be opened, to permit the flow of
refrigerant, or closed, to block the flow of refrigerant. Valves
128A, 128B, and 128C may be solenoid valves.
[0030] Indoor side valve 128B and outdoor side valve 128C are
called "indoor" and "outdoor" to identify their locations relative
to reservoir line 124 and heat exchangers 112 and 118. The "indoor"
and "outdoor" names do not identify whether the valves 128B-C are
indoors or outdoors. Indoor side valve 128B may be located indoors
or outdoors. Outdoor side valve 128C may be located indoors or
outdoors.
[0031] Refrigerant charge control apparatus 101 can be operated to
fill reservoir 126 with refrigerant from liquid line 114, reducing
the amount of refrigerant for compressor 106 to compress.
Refrigerant charge control apparatus 101 can also be operated to
drain refrigerant from reservoir 126 into liquid line 114,
increasing the amount of refrigerant for compressor 106 to
compress.
[0032] Controller 105 operates valves 128A, 128B, and 128C to
adjust the "refrigerant charge level," the amount of refrigerant in
the vapor compression cycle. Where valves 128A-C are solenoid
valves, controller 105 may send current through valves 128A-C
directly or send a signal that causes current to be sent through
valves 128A-C. Controller 105 may be a unit controller that
controls the overall operation of units 102 and 104, or may be a
separate controller that only controls the refrigerant charge
level.
[0033] With reference to FIG. 2A, depicted is a configuration 200A
of refrigerant charge control apparatus 101 in normal operation,
when reservoir 126 is not being drained or filled. Reservoir valve
128A is closed, indoor side valve 128B is open, and outdoor side
valve 128C is open. Refrigerant flows through liquid line 114 as it
would in the absence of refrigerant charge control apparatus 101.
In FIG. 2A, refrigerant would flow through liquid line 114 from
left to right during cooling and from right to left during
heating.
[0034] With reference to FIG. 2B, depicted is a configuration 200B
of refrigerant charge control apparatus 101. In configuration 200B,
refrigerant charge control apparatus 101 is configured to fill
reservoir 126 during cooling. Reservoir valve 128A and outdoor side
valve 128C are open, while indoor side valve 128B is closed.
Refrigerant 202 flowing from outdoor heat exchanger 112 through
liquid line 114 is blocked by indoor side valve 128B. Refrigerant
202 is instead forced through reservoir line 124 into reservoir
126. After charge is added to reservoir 126, refrigerant charge
control apparatus 101 may return to configuration 200A.
[0035] With reference to FIG. 2C, depicted is a configuration 200C
of refrigerant charge control apparatus 101. In configuration 200C,
refrigerant charge control apparatus 101 is configured to fill
reservoir 126 during heating. Reservoir valve 128A and indoor side
valve 128B are open, while outdoor side valve 128C is closed.
Refrigerant 202 flowing from indoor heat exchanger 118 through
liquid line 114 is blocked by outdoor side valve 128C. Refrigerant
202 is instead forced through reservoir line 124 into reservoir
126. After charge is added to reservoir 126, refrigerant charge
control apparatus 101 may return to configuration 200A.
[0036] With reference to FIG. 2D, depicted is a configuration 200D
of refrigerant charge control apparatus 101. In configuration 200D,
refrigerant charge control apparatus 101 is configured to drain
reservoir 126 using gravity. Indoor side valve 128B and outdoor
side valve 128C are open, allowing refrigerant 202 to flow through
liquid line 114 normally. Reservoir valve 128A is also open,
allowing gravity to drain refrigerant 202 in reservoir 126 into
liquid line 114. In FIG. 2D, refrigerant would flow through liquid
line 114 from left to right during cooling and from right to left
during heating. After charge is removed from reservoir 126,
refrigerant charge control apparatus 101 may return to
configuration 200A.
[0037] Because configuration 200D depends on gravity, to use
configuration 200D reservoir 126 should be placed above liquid line
114. As an alternative to configuration 200D, configurations 200B
and 200C can be used to drain reservoir 126 using a pressure
difference. Reservoir 126 may therefore be placed at the same
height as or lower than liquid line 114. If reservoir 126 is above
liquid line 114, gravity can still aid configurations 200B and 200C
in draining reservoir 126.
[0038] Referring to FIG. 2E, depicted is configuration 200C used to
drain reservoir 126 during cooling. Outdoor side valve 128C is
closed, blocking the flow of refrigerant from outdoor heat
exchanger 112 and reducing the pressure on the other side of
outdoor side valve 128C. Reservoir valve 128A and indoor side valve
128B are open. The reduced pressure draws refrigerant from
reservoir 126 into liquid line 114. After charge is removed from
reservoir 126, refrigerant charge control apparatus 101 may return
to configuration 200A.
[0039] Referring to FIG. 2F, depicted is configuration 200B used to
drain reservoir 126 during heating. Indoor side valve 128B is
closed, blocking the flow of refrigerant from indoor heat exchanger
118 and reducing the pressure on the other side of indoor side
valve 128B. Reservoir valve 128A and outdoor side valve 128C are
open. The reduced pressure draws refrigerant from reservoir 126
into liquid line 114. After charge is removed from reservoir 126,
refrigerant charge control apparatus 101 may return to
configuration 200A.
[0040] With reference to FIG. 3, depicted is a Heating,
Ventilation, and Air Conditioning (HVAC) system 300 with an
alternate refrigerant charge control apparatus 301. System 300 is
identical to system 100 except that apparatus 301 has been
substituted for apparatus 101. Refrigerant charge control apparatus
301 comprises reservoir line 124, reservoir 302, reservoir valve
128A, indoor side valve 128B, and outdoor side valve 128C.
Reservoir line 124 may connect liquid line 114 to reservoir 302.
Valves 128A, 128B, and 128C may be positioned as in apparatus 101.
Controller 105 operates valves 128A, 128B, and 128C to adjust the
refrigerant charge level.
[0041] Reservoir 302 may be a tank which holds excess refrigerant.
Suction line 120 passes through reservoir 302, and may pass through
the middle of reservoir 302. Refrigerant stored in reservoir 302
does not flow through suction line 120 into compressor 106. A tank
with a suction line passing through it is commonly called a charge
compensator.
[0042] With reference to FIG. 4A, depicted is a configuration 400A
of refrigerant charge control apparatus 301 in normal operation,
when reservoir 302 is not being drained or filled. Reservoir valve
128A is closed, indoor side valve 128B is open, and outdoor side
valve 128C is open. Refrigerant flows through liquid line 114 as it
would in the absence of refrigerant charge control apparatus 301.
In FIG. 4A, refrigerant would flow through liquid line 114 from
left to right during cooling and from right to left during
heating.
[0043] With reference to FIG. 4B, depicted is a configuration 400B
of refrigerant charge control apparatus 301. In configuration 400B,
refrigerant charge control apparatus 301 is configured to fill
reservoir 302. Reservoir valve 128A, indoor side valve 128B, and
outdoor side valve 128C are open. The refrigerant passing through
suction line 120 is cooler than the refrigerant passing through
liquid line 114. The temperature difference draws refrigerant from
liquid line 114 through reservoir line 124 and into reservoir 302.
After charge is added to reservoir 302, refrigerant charge control
apparatus 301 may return to configuration 400A.
[0044] With reference to FIG. 4C, depicted is a configuration 400C
of refrigerant charge control apparatus 301. In configuration 400C,
refrigerant charge control apparatus 301 is configured to drain
reservoir 302 during cooling. Reservoir valve 128A and indoor side
valve 128B are open, while outdoor side valve 128C is closed. The
closed outdoor side valve 128C blocks the flow of refrigerant
through liquid line 114, reducing the pressure in liquid line 114
after valve 128C below the pressure in suction line 120.
Refrigerant drains from reservoir 302 into liquid line 114 and
flows toward indoor heat exchanger 118. After charge is removed
from reservoir 302, refrigerant charge control apparatus 301 may
return to configuration 400A.
[0045] With reference to FIG. 4D, depicted is a configuration 400D
of refrigerant charge control apparatus 301. In configuration 400D,
refrigerant charge control apparatus 301 is configured to drain
reservoir 302 during heating. Reservoir valve 128A and outdoor side
valve 128C are open, while indoor side valve 128B is closed. The
closed indoor side valve 128B blocks the flow of refrigerant
through liquid line 114, reducing the pressure in liquid line 114
after valve 128B below the pressure in suction line 120.
Refrigerant drains from reservoir 302 into liquid line 114 and
flows toward outdoor heat exchanger 112. After charge is removed
from reservoir 302, refrigerant charge control apparatus 301 may
return to configuration 400A.
[0046] HVAC systems 100 and 300 are capable of both heating and
cooling. A system which can perform both may be called a heat pump.
In a HVAC system which is capable of one of heating or cooling, but
not both, one of valves 128B and 128C may be removed. In a HVAC
system which is only capable of heating, also called a heater,
indoor side valve 128B is unnecessary. In a HVAC system which is
only capable of cooling, also called an air conditioner, outdoor
side valve 128C is unnecessary. An exception is a refrigerant
charge control apparatus 101 which relies on configuration 200B or
200C to drain reservoir 126. In such an apparatus 101, both valves
128B and 128C are used even if the HVAC system is only capable of
one of heating or cooling.
[0047] Additionally, in a heater or air conditioner, reversing
valve 110 is unnecessary because the direction of refrigerant flow
does not reverse. Expansion device 116A is also unnecessary in an
air conditioner because refrigerant does not flow through liquid
line 114 toward outdoor heat exchanger 112. Expansion device 116B
is also unnecessary in a heater because refrigerant does not flow
through liquid line 114 toward indoor heat exchanger 118.
[0048] Refrigerant charge control apparatuses 101 and 301 are shown
inside outdoor unit 104. However, this is not necessarily the case.
Refrigerant charge control apparatuses 101 and 301 may also be
inside indoor unit 102.
[0049] Refrigerant charge control apparatuses 101 and 301 may fill
or drain their respective reservoirs by cycling between the normal
operation configuration and a fill or drain configuration. For
instance, refrigerant charge control apparatus 101 does not
necessarily change to configuration 200B, wait for reservoir 126 to
fill sufficiently, and then change to configuration 200A.
Refrigerant charge control apparatus 101 could alternately begin
cycling between configuration 200B and configuration 200A until
reservoir 126 fills sufficiently, then change to configuration
200A.
[0050] Depending on tubing size, using simple solenoid valves for
valves 128A, 128B, and 128C may result in refrigerant flow that is
too fast. In an embodiment, valves 128A, 128B, and 128C are
electronic flow valves with variable flow rates. When an electronic
flow valve 128A, 128B, or 128C is opened, controller 105 may adjust
the flow rate of the open valve to adjust the rate reservoir 126 or
302 fills or drains.
[0051] Compressor 106 is preferably a variable speed compressor,
which can operate at a wide range of possible speeds. Compressor
106 may also be a multiple stage compressor, which can operate at a
few discrete speeds. Compressor 106 may also be a single stage
compressor, which operates at only a single speed. However, the
benefit of adjusting the refrigerant charge increases with the
range of speeds compressor 106 is capable of. With a single stage
compressor 106, the benefit is very limited. The benefit is also
less with a multiple stage compressor 106 than a variable speed
compressor 106.
[0052] With a variable speed or multiple stage compressor 106, the
speed of compressor 106 increases when the load on the HVAC system
is high and decreases when the load on the HVAC system is low.
Generally speaking, when there is a relatively low load on the HVAC
system, the refrigerant charge level should be relatively high.
Ideally, only liquid refrigerant should leave the expansion device
which expands the refrigerant. This expansion device is 116B in the
cooling configuration and 116A in the heating configuration. If the
refrigerant charge level is too low, a mixture of liquid and gas
refrigerant will leave the expansion device, which will reduce the
performance of the evaporator coil.
[0053] Likewise, when there is a relatively high load on the HVAC
system, the refrigerant charge level should be relatively low. Less
refrigerant is needed to keep gas refrigerant from leaving the
expansion device which expands the refrigerant. At the same time,
unnecessary refrigerant increases the pressure of the refrigerant
in the vapor compression cycle and additional power is used moving
that excess refrigerant.
[0054] However, this inverse relationship between load and optimal
refrigerant charge level is only true in general. It is possible to
have too high a refrigerant charge level with a low load or too low
a refrigerant charge level with a high load. Thus, it is not
necessarily possible to determine whether the refrigerant charge
level should be increased or decreased solely from the present load
on the HVAC system.
[0055] With reference to FIG. 5, depicted is a method 500 which
controller 105 may perform to control the refrigerant charge level.
Method 500 uses a subcooling value to determine whether the
refrigerant charge level should be changed. When the gas
refrigerant passes through the condenser and changes into a liquid,
the temperature of the refrigerant falls but the refrigerant
remains at the same pressure. The subcooling value is the amount
the temperature falls below the saturation temperature of the
refrigerant for that pressure. The subcooling value is a measure of
the effectiveness of the system 100 or 300.
[0056] Controller 105 may have a memory which stores target
subcooling values for a given load on the HVAC system. The target
subcooling values represent an ideal subcooling value when the
refrigerant charge level is optimized for a given load. These
target subcooling values may be determined during testing or
simulation of the HVAC system.
[0057] At 502, controller 105 may measure the temperature and
pressure of the liquid leaving the condenser. At 504, controller
105 may calculate the subcooling value from the temperature and
pressure. At 506, controller 105 may compare the subcooling value
to the target subcooling value for the present operating load.
[0058] At 508, controller 105 may operate valves 128A, 128B, and
128C on charge control apparatus 101 or charge control apparatus
103 to adjust the refrigerant charge level. Whether to increase or
decrease the refrigerant charge level may be a matter of trial and
error for controller 105, based on whether the last adjustment to
the refrigerant charge level brought the subcooling value closer to
the target subcooling value. If the refrigerant charge level was
previously increased and the subcooling value is now closer to the
target subcooling value, controller 105 may continue to increase
the refrigerant charge level. Likewise, if the refrigerant charge
level was previously decreased and the subcooling value is now
closer to the target subcooling value, controller 105 may continue
to decrease the refrigerant charge level. However, if the
refrigerant charge level was previously increased and the
subcooling value is now further from the target subcooling value,
controller 105 may begin decreasing the refrigerant charge level.
If the refrigerant charge level was previously decreased and the
subcooling value is now further from the target subcooling value,
controller 105 may begin increasing the refrigerant charge
level.
[0059] To assist controller 105 in determining whether to increase
or decrease the refrigerant charge level, a liquidity sensor may be
added to the liquid line. The liquidity sensor may be an optical or
turbidity sensor which looks for bubbles through a side glass in
the liquid line. The absence of bubbles indicates there is
sufficient refrigerant charge level in the liquid line. Thus, if
the liquidity sensor finds the refrigerant is sufficiently free of
bubbles, controller 105 may always decrease the refrigerant charge
level.
[0060] With reference to FIG. 6, depicted is an alternate method
600 which controller 105 may perform to control the refrigerant
charge level. Method 600 uses EER (Energy Efficiency Ratio) to
determine whether the refrigerant charge level should be changed.
EER is the ratio of energy expended to the amount of heating or
cooling performed. The EER is an indicator of the effectiveness of
the system 100 or 300. The higher the EER, the more efficiently the
system is operating.
[0061] In a compressor driven by an inverter, the amount of energy
being expended can be obtained from the inverter driving the
compressor. In a compressor not driven by an inverter, the amount
of energy being expended can be measured from compressor current,
compressor voltage, and phase angle at the compressor. The amount
of heating or cooling performed is measured by a heat transferring
capacity of the HVAC system. The heat transferring capacity may be
the sensible capacity of the system, regardless of whether the
system is heating or cooling. If the system is cooling, the heat
transferring capacity may alternately be the latent capacity of the
system, or the total of the sensible and latent capacities of the
system.
[0062] The sensible capacity may be expressed as the product of
indoor airflow rate, a constant, and rise in air temperature. The
sensible capacity may therefore be calculated from the indoor
airflow, return air temperature, and supply air temperature. The
return air is the volume of air returned to indoor unit 102 from
the structure. The supply air is the volume of air passed over
indoor heat exchanger 118 and discharged to the structure. Indoor
unit 102 may have a return air temperature sensor where it receives
the return air and a supply air temperature sensor where it
discharges the supply air.
[0063] The latent capacity may be predicted from lab test data and
present conditions, such as indoor temperature, humidity, and
indoor airflow. Alternately, latent capacity may be predicted from
the rate of condensate (water vapor that is condensed on the
surface of the evaporator).
[0064] Controller 105 may have a memory which stores target EERs
for a given load on the HVAC system. The target EERs represent an
ideal EER when the refrigerant charge level is optimized for a
given load. These target EERs may be determined during testing or
simulation of the HVAC system.
[0065] At 602, controller 105 may measure the energy used by the
compressor and sensible capacity of the HVAC system. At 604,
controller 105 may calculate the EER from the energy used and
sensible capacity. At 606, controller 105 may compare the EER to
the target EER for the present operating load. At 608, controller
105 may operate valves 128A, 128B, and 128C on charge control
apparatus 101 or charge control apparatus 103 to adjust the
refrigerant charge level. 608 may be performed identically to 508,
except with the difference between the EER and target EER used in
place of the difference between the subcooling value and target
subcooling value.
[0066] The size of reservoirs 126 and 302 may vary depending on the
particular HVAC system. A reservoir should be large enough to
accommodate the difference between the largest and smallest optimal
refrigerant charge levels for the different operating loads of the
system.
[0067] It is noted that the embodiments disclosed are illustrative
rather than limiting in nature and that a wide range of variations,
modifications, changes, and substitutions are contemplated in the
foregoing disclosure and, in some instances, some features of the
present invention may be employed without a corresponding use of
the other features. Many such variations and modifications may be
considered desirable by those skilled in the art based upon a
review of the foregoing description of various embodiments.
* * * * *