U.S. patent application number 10/959254 was filed with the patent office on 2006-04-06 for oil balance system and method for compressors connected in series.
Invention is credited to David N. Shaw.
Application Number | 20060073026 10/959254 |
Document ID | / |
Family ID | 35735189 |
Filed Date | 2006-04-06 |
United States Patent
Application |
20060073026 |
Kind Code |
A1 |
Shaw; David N. |
April 6, 2006 |
Oil balance system and method for compressors connected in
series
Abstract
A compressor system includes a first compressor, which has a
first low side oil sump, in a first shell and a second compressor,
which has a second low side oil sump, in a second shell. The first
and second compressors are connected in series. There is an oil
transfer conduit connected between the first low side sump of the
first compressor and the second low side sump of the second
compressor. The system also includes a normally open check valve in
the oil transfer conduit. A method for effecting oil balance in a
compressor system, the method includes establishing a first
compressor in a first shell having a first low side oil sump and
establishing a second compressor in a second shell having a second
low side oil sump. The first and second compressors are connected
in series. The method also includes positioning an oil transfer
conduit between the first low side sump and the second low side
sump and positioning a normally open check valve in the oil
transfer conduit.
Inventors: |
Shaw; David N.; (East
Falmouth, MA) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Family ID: |
35735189 |
Appl. No.: |
10/959254 |
Filed: |
October 6, 2004 |
Current U.S.
Class: |
417/245 ;
417/244 |
Current CPC
Class: |
F04B 41/06 20130101;
Y10S 417/902 20130101; Y10T 137/86139 20150401; F04B 39/0207
20130101; F25B 1/10 20130101; F25B 31/002 20130101 |
Class at
Publication: |
417/245 ;
417/244 |
International
Class: |
F04B 3/00 20060101
F04B003/00; F04B 5/00 20060101 F04B005/00 |
Claims
1. A compressor system comprising: a first compressor in a first
shell, said first compressor having a first low side oil sump; a
second compressor in a second shell, said second compressor having
a second low side oil sump; said first and second compressors being
connected in series; an oil transfer conduit connected between said
first low side sump of said first compressor and said second low
side sump of said second compressor; and a normally open check
valve in said oil transfer conduit.
2. A compressor system as in claim 1 wherein: said normally open
check valve permits oil flow between both of said oil sumps when
both of said compressors are off.
3. A compressor system as in claim 1 wherein: said normally open
check valve permits oil flow from said first oil sump to said
second oil sump when said first compressor is off and said second
compressor is on.
4. A compressor system as in claim 1 wherein: said compressor
system is a heat pump system, said first compressor being a booster
compressor and said second compressor being a primary
compressor.
5. A compressor system as in claim 1 wherein: said first shell has
a first inlet connected to receive gas from a low side of the
system, and said second shell has a second inlet connected to
receive gas from a low side of the system, said first compressor
has a discharge line connected at one end to said first compressor
and connected at the other end to said second inlet of said second
shell; and said second compressor has a discharge line connected at
one end to said second compressor and at the other end to the high
side of the system.
6. A compressor system as in claim 5 wherein: said normally open
check valve permits flow through said transfer conduit in both
directions between said first and second oil sumps when both of
said compressors are off; and said normally open check valve
permits flow through said transfer conduit from said first oil sump
to said second oil sump when said first compressor is off and said
second compressor is on.
7. A compressor system as in claim 6 wherein: said normally open
check valve is closed to prevent flow through said transfer conduit
from said second oil sump to said first oil sump when both
compressors are on.
8. A method for effecting oil balance in a compressor system,
including the steps of: establishing a first compressor in a first
shell having a first low side oil sump; establishing a second
compressor in a second shell having a second low side oil sump;
said first and second compressors being connected in series;
positioning an oil transfer conduit between said first low side
sump and said second low side sump; and positioning a normally open
check valve in said oil transfer conduit.
9. The method of claim 8 wherein: said normally open check valve
permits flow in both directions in said oil transfer conduit
between said first low side sump and said second low side sump when
both of said compressors are off.
10. The method of claim 8 wherein: said normally open check valve
permits flow in said oil transfer conduit from said first low side
oil sump to said second low side oil sump when said first
compressor is off and said second compressor is on.
11. The method of claim 8 including the step of: closing said
normally open check valve to prevent flow in said oil transfer
conduit when both of said compressors are on.
12. The method of claim 11 including the step of: stopping the
operation of said first compressor to open said check valve to
permit flow in said oil transfer conduit from said first low side
oil sump to said second low side oil sump.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to an oil balance system for
compressors connected in series. More particularly, this invention
relates to apparatus and a method for an oil balance system in
which each compressor is contained in a separate shell, and in
which each oil sump for each compressor is a low side sump, i.e.,
the inlet to each compressor is open to its respective shell, and
the outlet from each compressor is sealed to the compressor.
[0002] My prior U.S. Pat. No. 5,839,886, the entire contents of
which are incorporated herein by reference, relates to an oil
balance system for primary and booster compressors connected in
series for a heating/cooling or refrigeration system. The primary
compressor has a low side sump, but the booster compressor has a
high side sump (i.e., the inlet to the booster compressor is sealed
to the compressor, and the outlet from the compressor is open to
its shell. An open conduit extends between the oil sumps of the two
compressors to transfer oil from the sump of the booster compressor
to the sump of the primary compressor when the oil level in the
booster compressor exceeds a normal operating level.
[0003] My prior U.S. Pat. Nos. 5,927,088 and 6,276,148, the entire
contents of both of which are incorporated herein by reference,
relate to boosted air source heat pumps especially suitable for
cold weather climates. In the systems of these patents, a booster
compressor and a primary compressor are connected in series.
[0004] Most compressors will entrain and pump out some oil,
entrained in the refrigerant, during the normal course of
operation. So, for a system of series connected compressors housed
in separate casings, the pumped out oil will eventually return to
the first compressor in the system, thus tending to raise the oil
level in the sump of that compressor. As that oil level rises, this
will likely cause the first compressor to pump oil to the inlet to
the second compressor, so some oil will be delivered from that
first compressor to the second compressor in the system, thus
tending to prevent a dangerous loss of lubricant in the second
compressor. Various compressor designs react differently in regard
to this characteristic of pumping out oil entrained in the
refrigerant, and it is known to make modifications to specific
designs to enhance the tendency to pump out more oil as the level
of oil rises.
[0005] However, during the course of operation of a series
connected compressor system, such as the heat pump systems of my
U.S. Pat. Nos. 5,927,088 and 6,276,148, refrigerant/oil imbalances
can occur due to such things as, e.g., defrosting requirements,
extreme load changes, etc. These imbalances may lead to unbalancing
the oil levels in the two compressors; and this may result in
taxing the normal oil balancing tendencies beyond their normal
capabilities. Accordingly, it may be desirable to incorporate a
specific oil balance system in the series connected compressor
system.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention an oil balancing
system is incorporated in a series connected compressor system,
such as the heat pump system of my U.S. Pat. Nos. 5,927,088 and
6,276,148, wherein each compressor is housed in a hermetic casing
and has a low side oil sump. An oil transfer conduit extends from
the sump of the first compressor in the system (usually the booster
compressor) to the sump of the second compressor (usually the
primary compressor). When the first compressor is not operating and
the second compressor is operating, the pressure within the casing
of the first compressor is slightly higher than the pressure within
the casing of the second compressor, so oil will, as desired, flow
from the sump of the first compressor to the sump of the second
compressor when the oil level in the first sump exceeds the height
of the oil transfer conduit. However, when both compressors are
operating, the pressure in the shell of the second compressor will
be much higher than the pressure in the shell of the first
compressor, which could cause undesirable oil and/or flow from the
sump of the second compressor to the sump of the first compressor.
Accordingly, and most importantly, the oil transfer conduit has a
check valve which permits oil flow from the first compressor sump
to the second compressor sump, but which prevents oil and/or gas
flow from the second compressor sump to the first compressor
sump.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic of the oil balance system of the
present invention.
[0008] FIG. 2 is a sectional view of the oil balance check valve of
FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0009] The present invention will be described in the context of a
boosted sir source heat pump as disclosed in my prior U.S. Pat.
Nos. 5,927,088 and 6,276,148. However, it will be understood that
the present invention is applicable to any system of compressors in
series where the compressors each have low side oil pumps.
[0010] Referring to FIG. 1, a booster compressor 10 is housed in a
hermetically sealed casing 12, and a primary compressor 14 is
housed in a hermetically sealed casing 16. The compressors are
preferably reciprocating compressors, but rotary or other types of
compressors may be used. Each compressor is a low side sump
compressor. That is, the inlet to each compressor is open to the
shell of the compressor, and the outlet from each compressor is
sealed to the compressor. Each compressor/casing has an oil sump at
the bottom of the casing, the normal level of which is shown in
shown in FIG. 1. The oil in these sumps is used to lubricate the
compressors in ways presently known in the art.
[0011] An oil balance conduit 18 extends between the compressor
shells at the lower parts thereof. Oil balance conduit 18 is
positioned just slightly above the normal level of the sump oil in
booster casing 12. A normally open check valve 20 is positioned in
oil balance conduit 16. Check valve 20 permits oil flow from the
sump of booster casing 12 to the sump of primary casing 16 when
primary compressor 14 is on and booster compressor 10 is off or
when both compressors are off, but prevents oil flow from the sump
of primary casing 16 to the sump of booster casing 12 whenever both
compressors are on.
[0012] A conduit 22 is connected to the low side of a system (e.g.,
an evaporator in a heating or cooling system), to receive
refrigerant from the system low side. A branch conduit 24 is
connected to the inlet 26 to primary compressor casing 16 to
deliver refrigerant to the interior volume of casing 16 and to
primary compressor 14. A check valve 28 in conduit 24 controls the
direction of flow in conduit 24. Check valve 28 is preferably
normally open to minimize the pressure drop of the fluid flowing
through check valve 28 to primary inlet 26. Another branch conduit
30 connects conduit 22 to the inlet 32 to booster compressor casing
12 to deliver refrigerant to the interior volume of casing 12 and
to booster compressor 10.
[0013] One end of a booster compressor discharge line 34 is sealed
to booster compressor 10, and the other end of discharge line 34 is
connected to branch conduit 24 downstream of check valve 28,
whereby discharge line 34 delivers the discharge from booster
compressor 10 to primary inlet 26 and to the interior volume of
primary casing 16 and to primary compressor 14.
[0014] One end of a primary compressor discharge line 36 is sealed
to primary compressor 14 and the other end of discharge line 34 is
connected to the high side of the system (e.g., a condenser in a
heating or cooling system).
[0015] If the system includes an economizer, a conduit 38 would be
connected to conduit 24 downstream of check valve 28.
[0016] Normally open check valve 20 may be maintained normally open
in any chosen manner. Examples may be understood by reference to
FIG. 2 where valve 20 has a spherical chamber 40 in the segments
18' and 18'' of oil balance line 18. Chamber 40 is divided into
upper and lower segments by a wall 42 which has peripheral flow
passages 44. A ball 46 is loaded against wall 42 either by the
force of gravity, or by a light spring 48 or by magnets 50.
Regardless of the mechanism chosen, valve 20 is normally open to
permit flow in line 18 from booster casing 10 to primary casing 16
when the pressure in the interior volume of primary casing 16 is
essentially equal to or lower than the pressure in the interior
volume of booster casing 12. However, if the pressure in the
interior of primary casing 16 is substantially higher than the
pressure in the interior volume of booster casing 12, ball 46 will
be moved to engage a conical or spherical seat 52 to close the
entrance from line 18' to the upper segment of chamber 40, thus
blocking flow in oil balance line 18. In the operation of this
invention, check valve 20 must be open when primary compressor 14
is on and booster compressor 10 is off, and when both the primary
compressor 14 and the booster compressor 10 are off, and check
valve 20 must be closed when both the primary compressor and the
booster compressor are on.
[0017] Normally open check valve 28 may be held normally open in
the same manner as valve 20 if it is also mounted vertically.
However, if valve 28 is mounted horizontally, spring or magnetic
loading will be required.
[0018] When both primary compressor 14 and booster compressor 10
are off, the gas pressure in primary shell 16 and in booster shell
12 will be equal. Accordingly, oil flow in balance line 18 will be
bidirectional depending on the oil heads in the sumps of the
primary and booster shells.
[0019] In the heating mode of operation, the booster compressor is
off and only the primary compressor is operating at low heating
load on the system. In this situation, normally open check valves
20 and 28 are open; and the pressure in booster shell 12 is
slightly higher than the pressure in primary shell. Therefore, if
the oil level in the sump of booster shell 12 is higher than its
intended normal level, which means that the oil level in the sump
of primary shell 16 is lower than normal, oil will flow via balance
line 18 from the sump of booster shell 12 to the sump of primary
shell 16 to restore normal oil levels in both sumps. Also, if the
oil level in the sump of primary shell 16 is very high, which means
that the oil level in the sump of booster shell 12 is low, and the
pressure drop between the sump of booster shell 12 and the sump of
primary shell 16 is low enough, oil can flow via balance line 18
from the sump of primary shell 16 to the sump of booster shell
12.
[0020] At higher heating loads on the system, both the booster
compressor and the primary compressor will be operating. In that
situation, the pressure in the primary shell will be higher than
the pressure in the booster shell, because the discharge from
booster compressor 10 will be delivered via line 34 to casing 16,
check valve 28 will be closed, and system low side will be
connected via conduits 22 and 30 to the inlet 32 to booster shell
12. Accordingly, normally open check valve 20 will be closed, thus
preventing back-flow of compressed gas (which would go from the
discharge of booster compressor 10 to primary shell 16 and then
back to booster shell 12 via balance line 18 if check valve 20 were
open). However, the closure of check valve 20 also prevents oil
balance flow via line 18, which can lead to oil imbalance in the
sumps of the compressors, particularly creating a concern about low
oil level in the sump of primary shell 16.
[0021] Some oil becomes entrained in the circulating refrigerant
during the operation of the system. When both booster compressor 10
and primary compressor 16 are on, all oil entrained in the
refrigerant is delivered to the shell 12 of booster compressor 10,
where it tends to separate out and fall into the sump of booster
shell 12. If the oil accumulates in the sump of booster shell 12
above the predetermined normal level, operation of the booster
compressor will tend to agitate the oil to create a mist that will
be entrained in the refrigerant discharged from booster compressor
10. This entrained oil will be delivered to the interior of primary
shell 16, where it will tend to drop out from the gas due to
differences in gas and oil velocities upon entering into the
interior of primary shell 16. This separated oil will fall into the
sump of primary shell 16 to replenish the level of oil in this
sump.
[0022] Since this concern about low oil level in the sump of
primary shell 16 occurs only when both the booster and primary
compressors are operating, other steps can be taken to address the
potential problem in addition to relying on the mist and
precipitation action described in the preceding paragraph. One
solution is to program the system to turn off the booster
compressor for a short time (on the order of 2-4 minutes). As
described above for the operational state where the primary
compressor is on and the booster is off, this will result in
opening normally open valve 20, and any oil built up above normal
level in the sump of booster shell 12 will be transferred to the
sump of primary shell 16 via transfer line 18.
[0023] Also, during defrost cycling and cooling operation, the
booster compressor is off, and only the primary compressor is
operating. Thus, normally open check valve 20 will be open, and oil
balance transfer can take place from the sump of booster shell 12
to the sump of primary shell 16.
[0024] While a preferred embodiment of the present invention has
been shown and described, various modifications and substitutions
may be made thereto without departing from the spirit and scope of
the invention. Accordingly, it is to be understood that the present
invention has been described by way of illustration and not
limitation.
* * * * *