Capacity control for multi-stage compressors

• US 5,626,027 A
• Filed: 12/21/1994
• Issued: 05/06/1997
• Est. Priority Date: 12/21/1994
• Status: Expired due to Term

• Current Assignee: Carrier Corporation (Carrier Global Corporation)
• Original Assignee: Carrier Corporation (Carrier Global Corporation)
• Inventors: Kaido, Peter F., Dormer, Michael J.
• Primary Examiner(s): WAYNER, WILLIAM E
• Application Number:
  US08/360,483
• Time in Patent Office: 867 Days
• Field of Search: 62/175, 62/510, 62/228.3-228.5, 236/1 EA
• US Class Current: 62/175
• CPC Class Codes: F04B 49/007 Installations or systems with two or more pumps or pump cylinders, wherein the flow-path through the stages can be changed, e.g. from series to parallel centrifugal pumps F04D15/0072
• CPC Class Codes: F25B 1/10 with multi-stage compression with cascade operation F25B7/00
• CPC Class Codes: F25B 2400/074 with multiple cylinders
• CPC Class Codes: F25B 2400/13 Economisers
• CPC Class Codes: F25B 49/022 Compressor control arrangements

Abstract

In a positive displacement compressor having a plurality of banks, operation can be multi-staged or single staged. Single stage operation can be of a single bank or plural banks in parallel. Switchover between modes of operation is under the control of a microprocessor responsive to sensed inputs. During pulldown under ambient or condenser entering air temperatures of 100° F., or more, suction modulation is used to limit the suction pressure thereby permitting a switchover to two-stage operation and the use of an economizer.

Claims

1. In a refrigeration means under microprocessor control for cooling a zone including a closed circuit serially including compressor means, condenser means, economizer means connected to said compressor means, expansion means and evaporator means, a method for operating the refrigeration means during pulldown at high ambient temperature where the compressor means has three banks, a crankcase, a suction inlet connected to the evaporator, means for controlling mass flow to the three banks, and a discharge connected to the condenser comprising the steps of:

supplying gas from the suction inlet to the first and second banks;

supplying gas from the crankcase to a third bank of the three banks;

delivering compressed gas from the third bank to the discharge;

selectively connecting the first and second banks to either the crankcase or the discharge whereby when said first and second banks are connected to the crankcase they act as a first stage and the third bank acts as a second stage and when the first and second banks are connected to discharge they act as a single stage and the third bank acts as a single stage in parallel with the first and second banks;

sensing at least one of ambient and condenser entering air temperature;

sensing zone temperature;

sensing zone set point;

comparing zone temperature and zone set point and if the sensed ambient or condenser entering air temperature is on the order of 100°

F., or above, the sensed zone temperature exceeds the zone set point by 5°

F., or more, and the first, second and third banks are in single stage operation, performing the serial steps of;

reducing the capacity of said first and second banks to reduce crankcase pressure;

switching over from single stage to two-stage operation;

enabling the economizer whereby capacity is increased and the pulldown is speeded up.

2. The method of claim 1 further including the step of:

increasing the capacity of the first and second banks after the economizer is enabled.

3. The method of claim 1 wherein the step of reducing capacity of the first and second banks is achieved by suction modulation.

4. The method of claim 1 further including the steps of:

sensing pressure in the crankcase; and

using the sensed pressure for controlling said step of selectively connecting the first and second banks to the crankcase discharge.