Process and device for controlling the thermal and electrical output of integrated micro combined heat and power generation systems

Abstract

Microprocessor-based control sub-systems which control the thermal and electrical output of integrated micro-combined heat and power generation (M-CHP) systems used to supply domestic electrical power, domestic space heating (SH) water, and domestic hot water (DHW). The M-CHP system uses a microprocessor controller to control the internal operating conditions, such as pump speeds, gas flow rate, and evaporator outlet temperature. Controlling these parameters enables setting the capacity of the system at any instant in time, thereby permitting load following, using a variable capacity operation. The controller also monitors through sensors a number of additional safety controls and system protection devices, such as relays/contactor of the alternator to grid, and electrical trips to the feed pump, the oil pump, the hydronic pump, the blower, the gas valve, the expander bypass valves, and other electrically powered devices in the system.

We claim:  
     
         1 . A control subsystem for governing the operation of a cogeneration system configured to operate with an organic working fluid, said system having a plurality of functional devices including at least a heat source, an expander having operatively coupled to a generator to produce electricity, a condenser in fluid communication with said expander and adapted to heat a hydronic heating system, and a pump configured to circulate said organic working fluid from said condenser through piping in thermal communication with said heat source such that heat transferred therefrom superheats said organic working fluid to provide superheated organic working fluid vapors to said expander, said control subsystem comprising a programmed processor operatively coupled at least to said pump and said heat source, and adapted to operate said pump and said heat source in response to a call for heat, causing said organic working fluid in said piping in thermal communication with said heat source to be superheated and provided to said expander.  
     
     
         2 . The control sub-system according to  claim 1 , wherein said functional devices of the cogeneration system further include a power grid contactor adapted to connect the electrical power output of said generator with a power grid and an electrical load, wherein said controller is further operatively coupled to said generator and said contactor for receiving and monitoring electrical power output from said generator, and connecting/disconnecting said electrical power output with said electrical load.  
     
     
         3 . The control subsystem according to  claim 1 , further comprising a plurality of sensors each providing a sensor signal indicative of a parameter of the cogeneration system, said controller coupled to said plurality of sensors and adapted to at least monitor the operation of said functional devices of the cogeneration system.  
     
     
         4 . The control subsystem according to  claim 3 , further comprising an operator interface coupled to said controller enabling modification of the operation of said controller in monitoring said functional devices and operating characteristics of the cogeneration system through entry of information via said operator interface.  
     
     
         5 . The control subsystem according to  claim 4 , wherein said operator interface includes a data acquisition and communications subsystem enabling data logging and reporting of said operating characteristics of said functional devices of the cogeneration system.  
     
     
         6 . The control subsystem according to  claim 5 , wherein said a data acquisition and communications subsystem includes a modem for reporting at least alarm conditions of said cogeneration system.  
     
     
         7 . The control subsystem according to  claim 3 , wherein said parameters include at least three of condenser inlet temperature, condenser outlet temperature, hydronic fluid flow, hydronic supply temperature, expander inlet temperature, expander inlet pressure, feed pump inlet temperature, feed pump inlet pressure, power module power output, evaporator inlet temperature, gas flow, expander outlet temperature, outdoor ambient temperature, feed pump speed (drive frequency), protection relay trip, level 1 trip failure, and level 2 trip failure (failed to re-start).  
     
     
         8 . The control sub-system according to  claim 3 , further comprising a plurality of control points, said controller being operatively coupled to said control points of said cogeneration system associated with functional devices thereof, said controller responding to said sensor signals to control said functional devices to thereby vary operating conditions of the cogeneration system.  
     
     
         9 . The control sub-system according to  claim 3 , wherein said controller operates under program control for acquiring said sensor signals and generating control signals for application to said functional devices of said cogeneration system.  
     
     
         10 . The control sub-system according to  claim 9 , wherein said controller operates according to said program control and at least acquires and takes into account an outdoor ambient temperature reading from one of said sensors before generating said control signals.  
     
     
         11 . The control sub-system according to  claim 10 , wherein said controller determines a set-point for a hydronic supply temperature in the hydronic heating system from said outdoor ambient temperature reading.  
     
     
         12 . The control sub-system according to  claim 11 , wherein said controller establishes said set-point according to a linear scale from  25 ° C. at an outdoor temperature of 20° C. to 75° C. at an outdoor temperature of −20° C.  
     
     
         13 . The control sub-system according to  claim 11 , wherein the heat source comprises a gas valve and a burner, and wherein said controller uses said set-point to operate the heat source in a variable capacity mode by modulating the gas valve on the burner to maintain actual hydronic supply temperature as sensed by one of said sensors at said set-point.  
     
     
         14 . The control sub-system according to  claim 13 , wherein said controller further prevents working fluid in the liquid state from entering the expander by coordinating a fuel flow rate (heat input rate) to the burner with a feed flow rate of the working fluid exiting the feed pump.  
     
     
         15 . The control sub-system according to  claim 14 , wherein the functional devices further include an evaporator fluidly connected to said expander by said piping and heated by said heat source, and said controller controls said fuel flow rate and said feed flow rate to maintain an exit temperature of the evaporator at 310° F. (154.4° C.).  
     
     
         16 . The control sub-system according to  claim 1 , wherein the functional devices further include a hydronic pump circulating fluid in the hydronic heating system to and from heat exchange piping of the condenser, and wherein said controller controls the hydronic pump at a speed that maintains a pressure difference between the supply and return of the fluid to the heat exchanger piping of the condenser at a preselected value for optimal thermodynamic performance of the hydronic heating system.  
     
     
         17 . The control sub-system according to  claim 1 , wherein the functional devices further include an evaporator fluidly connected between the feed pump and expander, and a desuperheater fluidly connected between the expander and condenser, said desuperheater having a return to the evaporator, and a switching valve provided in the piping for directing the organic working fluid either to the desuperheater or the evaporator directly, and wherein the controller controls the switching of the switching valve.  
     
     
         18 . The control sub-system according to  claim 1 , wherein the expander is selected from a positive displacement expander and a scroll expander.  
     
     
         19 . The control sub-system according to  claim 1 , wherein the functional devices further include a bypass valve and a shutoff valve in the piping to bypass and shutoff said superheat working fluid vapors from entering into the expander, the piping including a bypass loop connected between the bypass valve and condenser, and wherein said controller controls the opening/closing of the bypass valve and shutoff valve at least in response to startup and shutdown conditions of the cogeneration system.  
     
     
         20 . The control sub-system according to  claim 19 , wherein said shutdown conditions include a heat call satisfied signal, a startup sequence failure, or exceeding a related preset value for an expander inlet temperature, an expander inlet pressure, a feed pump inlet temperature, a feed pump inlet pressure, a protection relay trip, or a power module temperature.  
     
     
         21 . A control subsystem for governing the operation of a cogeneration system configured to operate with an organic working fluid, said system having a plurality of functional devices at least including a heat source, an expander having operatively coupled a generator to produce electricity, a condenser in fluid communication with said expander, and a pump configured to circulate said organic working fluid from said condenser through piping in thermal communication with said heat source such that heat transferred therefrom superheats said organic working fluid to provide superheated organic working fluid vapors to said expander, said control subsystem comprising: 
 a plurality of sensors each providing a sensor signal indicative of a parameter of the cogeneration system;    a plurality of control points; and    a programmable controller coupled to said plurality of sensors and to said control points of said cogeneration system associated with functional devices thereof, said controller responding to said sensor signals to control said functional devices of the cogeneration system to thereby vary the operating characteristics of the cogeneration system.    
     
     
         22 . A control system in combination with a cogeneration system having a plurality of functional devices and using an organic working fluid to heat a hydronic heating system and produce electrical power, the combination comprising: 
 a plurality of sensors for providing electrical sensor signals indicative of operating parameters of the cogeneration system;    a plurality of control points associated with said functional devices to change the operating parameters of the cogeneration system; and    a programmable controller coupled to the electrical sensors and to said control points of the system associated with said functional devices, said controller responding to the sensor signals and generating a plurality of control signals to control the operation of the functional devices; said controller defining a plurality of interactive control loops each generating a control signal for controlling a different one of said functional devices as a function of variation in a sensor signal supplied to the controller relative to at least a set-point value for a control loop for the hydronic heating system, wherein the set-point is determined by said controller from receiving an outdoor ambient temperature sensor signal from one of said sensors.    
     
     
         23 . A method of controlling the thermal and electrical output of integrated micro-combined heat and power generation systems used to supply domestic electrical power, domestic space heating (SH) water, and/or domestic hot water (DHW), and which converts heat energy contained in superheated vapors of an organic working fluid to mechanical energy, and distributes the superheated vapors under pressure to at least one functional device having a heating need which varies over time, comprising: 
 monitoring over a period of time an ambient outdoor temperature to determine said heating need by said at least one functional device; and    changing in response to said ambient outdoor temperature indicating at any given time that a different amount of said superheated vapors than that being delivered to said at least one functional device is so needed to satisfy said heating need.    
     
     
         24 . The method according to  claim 23 , wherein there are a plurality of process control sensors communicating with a controller programmed to change operating parameters of said system in response to said ambient outdoor temperature in order to furnish said at least one functional device a supply of said superheated vapors.  
     
     
         25 . The method according to  claim 24 , wherein said ambient outdoor temperature is used to determine a desired hydronic supply temperature for a hydronic fluid and said amount of superheat vapors is varied to heat said hydronic fluid to said desired hydronic supply temperature.  
     
     
         26 . The method according to  claim 25 , further comprising sensing an actual hydronic supply temperature via at least one of said process control sensors, and adjusting a firing rate of a burner used to heat said organic working fluid in order to bring said actual hydronic supply temperature into line with said desired hydronic supply temperature.  
     
     
         27 . The method according to  claim 26 , further comprising increasing said firing rate if said actual hydronic supply temperature is too low, and decreasing said firing rate if said actual hydronic supply temperature is too high.  
     
     
         28 . The method according to  claim 26 , further comprising sensing via at least one of said process control sensors temperature of said superheated vapors and adjusting flow rate of said working fluid past said burner to maintain said temperature of said superheated vapors within a desired operating parameter.  
     
     
         29 . The method according to  claim 28 , wherein said desired operating parameter for said temperature of said superheated vapors is 310° F. (154.4° C.).  
     
     
         30 . The method according to  claim 28 , wherein said flow rate is increased if said temperature of said superheated vapors is above said desire operating parameter, and decreased if said temperature of said superheated vapors is below said desired operating parameter.