Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B1/00—Compression machines, plants or systems with non-reversible cycle
  • F25B1/04—Compression machines, plants or systems with non-reversible cycle with compressor of rotary type
  • F25B1/053—Compression machines, plants or systems with non-reversible cycle with compressor of rotary type of turbine type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B7/00—Compression machines, plants or systems, with cascade operation, i.e. with two or more circuits, the heat from the condenser of one circuit being absorbed by the evaporator of the next circuit
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
  • F04D27/02—Surge control
  • F04D27/0261—Surge control by varying driving speed
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
  • F04D27/02—Surge control
  • F04D27/0269—Surge control by changing flow path between different stages or between a plurality of compressors; load distribution between compressors
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
  • F04D27/02—Surge control
  • F04D27/0284—Conjoint control of two or more different functions
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B49/00—Arrangement or mounting of control or safety devices
  • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B49/00—Arrangement or mounting of control or safety devices
  • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
  • F25B49/027—Condenser control arrangements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/06—Several compression cycles arranged in parallel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2500/00—Problems to be solved
  • F25B2500/26—Problems to be solved characterised by the startup of the refrigeration cycle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2500/00—Problems to be solved
  • F25B2500/27—Problems to be solved characterised by the stop of the refrigeration cycle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2600/00—Control issues
  • F25B2600/02—Compressor control
  • F25B2600/025—Compressor control by controlling speed
  • F25B2600/0253—Compressor control by controlling speed with variable speed
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
  • Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Definitions

• HVAC heating, ventilation and air- conditioning
• Chilled water plants are employed to provide cooling for building comfort loads and for industrial process loads and are a major user of electrical power.
• Chilled water plants generally employ multiple chillers, and some chillers employ multiple compressors. This permits equipment to be staged to meet the changing loads, which usually vary from very low loading up to as much as 100% of plant capacity, depending on design and operating environment. Multiple chillers also permit designs that incorporate fail safe operation with backup available in case of a failure of one of the machines.
• a chiller consists of one or more compressors mounted on a set of heat exchangers which, along with additional piping, refrigerant and other equipment, cools a fluid that flows through one heat exchanger while rejecting the heat absorbed at a higher temperature to a fluid flowing through the second heat exchanger.
• the fluid flowing through both heat exchangers is usually water.
• Each set of one or more compressors and two heat exchangers is called a chiller, and medium to large chiller plants consist of multiple chillers.
• FIG. 5 is a simplified diagram of components of a conventional water chiller plant with four chillers (501-504) arranged in parallel and connected to chilled water pumping and piping system (520).
• Each chiller has an individual chiller controller (531-534) each of which is in communication with a controller (540).
• the individual chiller controllers may communicate via a network such as an Ethernet network.
• the central controller preferably has a processer and associated memory which are configured to read a computer program.
• the central controller may be a digital computing system, for example, a personal computer or a programmable logic controller.
• the central controller is configured to receive information from each individual chiller such as head pressure readings, fluid temperatures and the current vane settings.
• FIG. 1 illustrates the major components of a variable speed centrifugal chiller.
• Medium and large chiller plants typically employ from two to as many as a dozen or more such chillers for comfort conditioning applications or to serve process cooling needs in a manufacturing application.
• each chiller has one or more motor/compressor unit (109), which may be a hermetic type or open type.
• the motor or engine that drives the compressor is powered by a power unit commonly called a variable speed drive (110) that can vary the rotational speed of the motor or engine in the compressor unit.
• Each compressor draws low pressure refrigerant gas from the cooler (111) through a connection (112), compresses it, and discharges it as a higher pressure hot gas through a connection (113) into the condenser (114).
• hot gaseous refrigerant is condensed into a liquid by rejecting heat to condenser water that is supplied through a piping connection (140) from a cooling tower or some other means of conducting heat from the fluid.
• the condenser water flows through tubes in the condenser, absorbs heat from the refrigerant and cools it to a high pressure liquid.
• the heated condenser water then leaves the condenser through a piping connection (141) to return to the cooling tower or other method of heat rejection.
• the condensed liquid refrigerant then flows through an expansion device (133) that regulates the flow of refrigerant into the cooler (111), which is held at a low pressure by the operation of the compressor continuously drawing expanded gaseous refrigerant from it.
• the low pressure environment causes the refrigerant to change state to a gas and as it does so, it absorbs the required heat of vaporization from the chilled water circulating into the cooler via pipe connection (151), then through tubes in the cooler where the boiling refrigerant absorbs heat from the chilled water and the chilled water then exits through a pipe connection (152) at the desired temperature to cool the comfort or process loads to which the chiller plant is connected.
• the low pressure vapor is drawn into the inlet of the compressor and the cycle is continuously repeated.
• FIG. 1 is a cross section that shows in some greater detail the elements of the motor/compressor unit (see 109, 110 in Fig. 1 ) of a centrifugal compressor used in centrifugal chillers.
• the compressor unit consists of a motor or engine (210) that rotates a shaft upon which an impeller (212) is mounted that rotates within a housing (214).
• the compressor inlet (216) is connected to the evaporator (not shown) which may be configured in a number of variations.
• inlet vanes As the gas to be compressed, which is called “refrigerant,” is drawn into the compressor by the rotation of the impeller, it must first pass through inlet vanes (218) which are segmented.
• the vanes are closed and opened by coordinated rotation of each segment around its central axis (shown as a vertical axis in Fig. 2). We call this rotational position the current vane position or setting. When closed, only a small hole in the center of the segments is open for gas to pass.
• the vanes When the vanes are set to open, virtually the entire inlet area is open. As the vanes begin to close from full- open; their coordinated movement causes the gas flowing by to be rotated in the direction of the rotation of the compressor impeller (212).
• Variable speed compressors can reduce their operating capacity in two ways, first, by closing the inlet vanes as described above, and second, by slowing the speed of the compressor impeller.
• impeller rotational speed must always be maintained sufficiently high to maintain the flow of refrigerant gas through the impeller at the current pressure difference between the condenser and evaporator of the chiller. If the speed falls below a minimum speed that depends on this pressure difference across the impeller, the impeller will stall and flow will abruptly stop. The phenomenon in chillers is called "surging.” The impeller stalls and flow stops, this reduces the pressure difference and flow restarts only to stall again. Surging results in inefficient operation and can under some circumstances cause damage to elements of the compressor.
• the internal chiller or compressor controls of variable speed chillers incorporate some method of maintaining a minimum compressor speed that is usually based on the pressure across the impeller.
• a certain pressure differential across the compressor commonly called compressor "head”
• the impeller speed cannot be reduced due to a risk of stalling and surging, and at the same time a lower capacity is required from the chiller, then instead of slowing the speed of the impeller to reduce capacity, the impeller is maintained at the appropriate minimum speed and the vanes are closed to reduce the capacity, sacrificing efficiency of the chiller.
• the vane settings and the compressor (impeller) speed are coordinated so as to maintain a desired cooling capacity at current compressor head conditions.
• the vanes are employed to reduce capacity when compressor speed cannot be reduced due to the risk of an impeller stall condition.
• a current setting of the compressor vanes is employed in the decision to add or shed compressors, or to add or shed chilling units with single compressors, so that overall system capacity is achieved with optimal efficiency.
• Figure 1 is a diagram that shows the basic elements of a centrifugal chiller.
• Figure 2 is a diagram that shows the elements of typical variable speed centrifugal compressors.
• Figure 3 depicts a simple compressor or chiller add and shed decision flow chart that reflects prior art.
• Figure 4 is an example of a decision flow chart that reflects an embodiment of the present invention.
• Figure 5 is a simplified block diagram of a chiller plant.
• chillers that provide chilled water for comfort conditioning or process cooling are normally subject to very wide variations in cooling loads
• the ability to adjust capacity of individual chillers along with a method of sequencing chillers or compressors on and off line is employed to accommodate load changes and achieve efficient plant operation.
• the control of the capacity of each individual chiller is accomplished by internal chiller or compressor controls that maintain a predetermined temperature of the chilled water leaving the unit.
• the control of the number of chillers or compressors on line is dynamically accomplished by separate control algorithms, generally based on the loading or power draw of the online compressors. See my U.S. Patent No. 6,185,946 in which sequencing is based on comparing current point of operation to the curve of optimal efficiency, called the natural curve, of the device. Other methods are known, but these known methods do not account for characteristics of the internal controls that may result in a variation of compressor speed and vane control such that a point of operation is actually less efficient than expected.
• variable speed compressors have a property called a natural curve which is the curve of points of compressor capacity at which optimum compressor operating efficiency is achieved as a function of compressor head conditions. It is also known that the compressor head is a function of the chilled water and condenser water temperature and flow conditions and that the natural curve property can be applied to the entire chiller as a function of condenser water and chilled water temperature.
• chiller plant chillers the number and relative loading of chiller plant chillers, pumps, cooling towers, etc., depends not only on the plant loading, but also on the current operating conditions under which the plant must operate, most notably the ambient outdoor conditions to which the heat is rejected and the temperature at which the chilled water is supplied.
• the present invention discloses a new means of adjusting and improving the optimized sequencing techniques discussed in prior art.
• the sequencing of chillers is intended to ensure the total energy use for the chillers and heat rejection systems is continuously optimized. Chillers are sequenced on and off to keep the on-line equipment operating at all times as close as possible to the natural curve of that equipment which is the point of highest operating efficiency at the load condition.
• the previous methods can be more easily implemented and then automatically adjusted ensuring sequencing does result in optimum plant efficiency.
• Selection of the number of chillers or compressors online is aimed at maintaining the desired plant capacity while optimizing the overall energy use of the system.
• FIG. 3 A chiller sequencing flow chart for a plant employing one method (the natural curve method) of optimal chiller/compressor sequencing is shown in Figure 3 the enhanced method using this invention is shown in Figure 4.
• Figure 3 illustrates a portion of the logic used to control the adding and subtracting of chillers or compressors in response to changing operating conditions.
• the natural curve method of sequencing chillers which is based on calculated head pressure fractions and other current operating factors where the head pressure fraction is the ratio of the average current compressor head pressures compared to the design maximum for the operating compressor(s).
• the head pressure fractions may also be developed directly from the condenser and evaporator refrigerant temperatures or from the condensing and chilled water temperatures.
• the calculated compressor head pressure to add a compressor or chiller is made (312). This value is compared with the current head pressure fraction (314). If the calculation of the head pressure fraction of the existing system is greater than the current operating requirements, then a chiller or compressor is added to bring the system closer to its natural curve (318) and the remainder of the sequencing process is bypassed (320). If it is not, then the next step is to calculate the head pressure fraction to shed a chiller or compressor (340). This is then compared to the current operating head pressure fraction and if it is less than this current operating value, then a compressor or chiller is shed (346) before returning to the start of the process (348).
• Figure 4 is a chiller and/or compressor sequencing flow chart for a chiller plant consisting of multiple chillers and/or multiple compressors on each chiller wherein the natural curve sequencing method of Figure 3 has been enhanced with the method disclosed in this new invention.
• the first step in the sequencing decision path is to calculate the current HPFA value (412) and to compare this value with the current HPF of the operating chillers and/or compressors to see if adding a compressor or chiller is desired.
• the HPFA calculation is greater than the current HPF conditions, then it means the head conditions and capacity requirements are such that the online compressors are likely operating above their natural curves. In this operation, the compressors are at speeds above their most efficient for the current conditions to meet the capacity requirements. Thus, adding a compressor or chiller will reduce the speed requirements for each online compressor or chiller so the compressors will operate closer to their natural curve and plant efficiency will be improved.
• HPFA calculation is not larger than the current HPF value, then the program continues to the HPFS calculation (440), which is made and the result is compared to the current HPF value to see if a compressor or chiller shed action should be taken. If the HPFS calculation is less than the current HPF value, it means the online compressors are likely operating below their natural curves. At this operation, the online compressors are likely to be restricted by minimum speed, and their capacity is being controlled by closure of the inlet vanes. Thus, shedding a compressor or chiller will increase the capacity requirements for each online compressor or chiller so that vanes will open and plant efficiency will be improved by moving the operating point of the active chillers closer to their natural curve.
• digital computing system we mean any system that includes at least one digital processor and associated memory, wherein the digital processor can execute instructions or "code" stored in that memory.
• the memory may store data as well.
• a digital processor includes but is not limited to a microprocessor, multi-core processor, DSP (digital signal processor), processor array, network processor, etc.
• a digital processor may be part of a larger device such as a laptop or desktop computer, a PDA, cell phone, iPhone PDA, Blackberry® PDA/phone, or indeed virtually any electronic device.
• each of the display system, the presence detector and the web server comprises a digital computing system.
• the associated memory may be integrated together with the processor, for example RAM or FLASH memory disposed within an integrated circuit microprocessor or the like.
• the memory comprises an independent device, such as an external disk drive, storage array, or portable FLASH key fob.
• the memory becomes "associated" with the digital processor when the two are operatively coupled together, or in communication with each other, for example by an I/O port, network connection, etc. such that the processor can read a file stored on the memory.
• Associated memory may be "read only" by design (ROM) or by virtue of permission settings, or not.
• Other examples include but are not limited to WORM, EPROM, EEPROM, FLASH, etc. Those technologies often are implemented in solid state semiconductor devices.
• computer- readable storage medium (or alternatively, “machine-readable storage medium”) to include all of the foregoing types of memory, as well as new technologies that may arise in the future, as long as they are capable of storing digital information in the nature of a computer program or other data, at least temporarily, in such a manner that the stored information can be "read” by an appropriate digital processor.
• computer-readable we do not intend to limit the phrase to the historical usage of "computer” to imply a complete mainframe, mini-computer, desktop or even laptop computer. Rather, we use the term to mean that the storage medium is readable by a digital processor or any digital computing system.
• Such media may be any available media that is locally and/or remotely accessible by a computer or processor, and it includes both volatile and non-volatile media, removable and nonremovable media.
• a program has been stored in a computer-readable storage medium
• a portable digital storage medium may be used as a convenient means to store and transport (deliver, buy, sell, license) a computer program. This was often done in the past for retail point-of-sale delivery of packaged ("shrink wrapped") programs.
• Examples of such storage media include without limitation CD-ROM and the like. Such a CD-ROM, containing a stored computer program, is an example of a computer program product.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Control Of Positive-Displacement Air Blowers (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)

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Citations (3)

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• 2009
  • 2009-02-02 US US12/364,374 patent/US8291720B2/en active Active
• 2010
  • 2010-01-20 WO PCT/US2010/021534 patent/WO2010088118A1/en not_active Ceased
  • 2010-01-20 JP JP2011548078A patent/JP5579749B2/ja not_active Expired - Fee Related
  • 2010-01-20 KR KR1020117020462A patent/KR20110127176A/ko not_active Withdrawn
  • 2010-01-20 CA CA2751074A patent/CA2751074C/en not_active Expired - Fee Related
  • 2010-01-20 EP EP10736246.9A patent/EP2391856A4/en not_active Withdrawn
  • 2010-01-20 CN CN201080015499.3A patent/CN102365509B/zh not_active Expired - Fee Related
  • 2010-01-20 RU RU2011136463/06A patent/RU2011136463A/ru not_active Application Discontinuation
  • 2010-01-20 BR BRPI1008071A patent/BRPI1008071A2/pt not_active IP Right Cessation
  • 2010-01-20 MX MX2011008087A patent/MX2011008087A/es not_active Application Discontinuation
  • 2010-01-20 SG SG2011054152A patent/SG173151A1/en unknown
• 2011
  • 2011-09-01 CO CO11112540A patent/CO6420370A2/es not_active Application Discontinuation

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