Refrigerant Circuits For HVAC Units

Abstract

Various embodiments of the teachings herein include methods for compensating for a disturbance in an HVAC systems. An example includes: determining a discharge coefficient c m based on the upstream pressure p u and the downstream pressure p d , wherein the discharge coefficient c m relates an actual flow {dot over (m)} at the determined position of the valve to maximum flow {circumflex over ({dot over (m)})} at the determined position; using a valve curve and the discharge coefficient c m and the determined position to estimate a flow through the valve at a predetermined position of the valve; calculating a deviation measure as a function of the estimated flow through the valve at the predetermined position and a value of expected flow at the predetermined position; comparing the deviation measure to a threshold value; and if the deviation measure is greater than the threshold value, producing a signal indicative of a disturbance in the refrigerant circuit.

1 . A method to compensate for a disturbance in a refrigerant circuit having a valve with an inlet port and an outlet port, a first sensor to generate a first signal indicative of a thermodynamic state of a refrigerant at the inlet port, and a second sensor to generate a second signal indicative of a thermodynamic state of the refrigerant at the outlet port, the method comprising:
 recording the first signal;   recording the second signal;   receiving a position signal indicative of a position of the valve;   processing the first signal to determine an upstream pressure p u ;   processing the second signal to determine a downstream pressure p d ;   processing the position signal to determine the position of the valve;   determining a discharge coefficient c m  based on the upstream pressure p u  and the downstream pressure p d , wherein the discharge coefficient c m  relates an actual flow {dot over (m)} at the determined position of the valve to maximum flow {circumflex over ({dot over (m)})} at the determined position;   using a valve curve and the discharge coefficient c m  and the determined position to estimate a flow through the valve at a predetermined position of the valve;   calculating a deviation measure as a function of the estimated flow through the valve at the predetermined position and a value of expected flow at the predetermined position;   comparing the deviation measure to a threshold value; and   if the deviation measure is greater than the threshold value, producing a signal indicative of a disturbance in the refrigerant circuit.   
     
     
         2 . The method according to  claim 1 , the method further comprising determining the discharge coefficient c m  as an exclusive function of the upstream pressure p u  and of the downstream pressure p d . 
     
     
         3 . The method according to  claim 1 , wherein:
 the refrigerant circuit includes a third sensor to generate a third signal indicative of a thermodynamic state of the refrigerant at the inlet port; and   the method further comprises:   recording the third signal;   processing the third signal to determine an upstream temperature t u ; and   determining the discharge coefficient c m  based on the upstream pressure p u  and the downstream pressure p d  and the upstream temperature t u .   
     
     
         4 . The method according to  claim 3 , the method further comprising:
 receiving a choice signal indicative of a choice of a refrigerant;   processing the choice signal to determine the refrigerant;   determining a back pressure ratio r b  as a function of the downstream pressure p d  and the upstream pressure p u ;   determining a critical pressure ratio r c  as a function of the upstream pressure p u , the upstream a temperature t u , and the determined refrigerant;   comparing the back pressure ratio r b  and the critical pressure ratio r c  to one another;   determining an application pressure ratio r a  as a maximum value of the back pressure ratio r b  and of the critical pressure ratio r c ; and   determining the discharge coefficient c m  based on the application pressure ratio r a .   
     
     
         5 . The method according to  claim 4 , the method further comprising:
 determining an isentropic expansion coefficient k as a function of the upstream pressure p u , the upstream temperature t u , and the determined refrigerant;   determining the critical pressure ratio r c  as a function of the isentropic expansion coefficient k;   comparing the back pressure ratio r b  and the critical pressure ratio r c  to one another;   determining the application pressure ratio r a  as a maximum value of the back pressure ratio r b  and the critical pressure ratio r c ; and   determining the discharge coefficient c m  based on the application pressure ratio r a  and the isentropic expansion coefficient k.   
     
     
         6 . The method according to  claim 4 , the method further comprising:
 receiving a numeric signal;   processing the numeric signal to determine a liquid pressure recovery factor F L  such that the liquid pressure recovery factor F L  is less than unity or equals unity;   determining a critical pressure p crit  based on the determined refrigerant;   determining a saturation pressure ratio r s  as a function of the upstream pressure p u , of the upstream temperature t u , and of the determined refrigerant; and   using the liquid pressure recovery factor F L  and the critical pressure p crit  and the saturation pressure ratio r s  and the upstream pressure p u  to determine the critical pressure ratio r c .   
     
     
         7 . The method according to  claim 6 , the method further comprising:
 determining a saturation pressure p s  based on the upstream temperature t u  and the determined refrigerant; and   determining the saturation pressure ratio r s  as a function of the saturation pressure p s  and the upstream pressure p u .   
     
     
         8 . The method according to  claim 7 , the method further comprising:
 determining a liquid pressure ratio factor F F  as a function of the saturation pressure p s  and the critical pressure p crit ; and   using the liquid pressure recovery factor F L , the liquid pressure ratio factor F F , and the saturation pressure ratio r s  to determine the critical pressure ratio r c .   
     
     
         9 . The method according to  claim 3 , the method further comprising:
 receiving a choice signal indicative of a choice of a refrigerant;   receiving a numeric signal;   processing the choice signal to determine the refrigerant;   processing the numeric signal to determine a liquid pressure recovery factor F L  such that the liquid pressure recovery factor F L  is less than unity or equals unity;   determining a back pressure ratio r b  as a function of the downstream pressure p d  and of the upstream pressure p u ;   determining a critical pressure p crit  based on the determined refrigerant;   determining a saturation pressure ratio r s  as a function of the upstream pressure p u , of the upstream temperature t u , and of the determined refrigerant;   using the liquid pressure recovery factor F L  and the critical pressure p crit  and the saturation pressure ratio r s  and the upstream pressure p u  to determine a liquid critical pressure ratio r cl ;   determining an isentropic expansion coefficient k as a function of the upstream pressure p u , the upstream temperature t u , and the determined refrigerant;   using the isentropic expansion coefficient k to determine a gaseous critical pressure ratio r cg ;   comparing the back pressure ratio r b  and the liquid critical pressure ratio r cl  and the gaseous critical pressure ratio r cg  to one another;   determining an application pressure ratio r a  as a maximum value of the back pressure ratio r b , the liquid critical pressure ratio r cl , and the gaseous critical pressure ratio r cg ; and   determining the discharge coefficient c m  based on the application pressure ratio r a  and based on the isentropic expansion coefficient k.   
     
     
         10 . The method according to  claim 9 , the method further comprising:
 determining a saturation pressure p s  based on the upstream temperature t u  and the determined refrigerant; and   determining the saturation pressure ratio r s  as a function of the saturation pressure p s  and the upstream pressure p u .   
     
     
         11 . The method according to  claim 10 , the method further comprising:
 determining a liquid pressure ratio factor F F  as a function of the saturation pressure p s  and the critical pressure p crit ; and   using the liquid pressure recovery factor F L , the liquid pressure ratio factor F F , and the saturation pressure ratio r s  to determine the liquid critical pressure ratio r cl .   
     
     
         12 . The method according to  claim 3 , wherein:
 the refrigerant circuit includes a fourth sensor to generate a fourth signal indicative of a thermodynamic state of the refrigerant at the inlet port; and   the method further comprises:   recording the fourth signal;   receiving a choice signal indicative of a choice of a refrigerant;   receiving a numeric signal;   processing the fourth signal to determine a vapour quality q u ;   processing the choice signal to determine the refrigerant;   processing the numeric signal to determine a liquid pressure recovery factor F L  such that the liquid pressure recovery factor F L  is less than unity or equals unity;   determining a specific volume v l  of a liquid fraction of the refrigerant based on the upstream pressure p u , the upstream temperature t u , and the determined refrigerant;   determining a specific volume v g  of a gaseous fraction of the refrigerant based on the upstream pressure p u , the upstream temperature t u , and the determined refrigerant;   determining a critical pressure p crit  based on the determined refrigerant;   determining a saturation pressure ratio r s  as a function of the upstream pressure p u , the upstream temperature t u , and the determined refrigerant;   using the liquid pressure recovery factor Ft, the critical pressure p crit , the saturation pressure ratio r s , and the upstream pressure p u  to determine a liquid critical pressure ratio r cl ;   determining an isentropic expansion coefficient k as a function of the upstream pressure p u , the upstream temperature t u , and the determined refrigerant;   using the isentropic expansion coefficient k to determine a gaseous critical pressure ratio r cg ; and   determining the discharge coefficient c m  based on the vapour quality q u , the specific volume v l  of the liquid fraction, the specific volume v g  of the gaseous fraction, the liquid critical pressure ratio r cl , and the gaseous critical pressure ratio r cg .   
     
     
         13 . A refrigerant circuit comprising:
 a condenser;   a compressor;   an evaporator;   a valve having an inlet port and an outlet port;   a first sensor to generate a first signal indicative of a pressure of a refrigerant at the inlet port;   a second sensor to generate a second signal indicative of a pressure of the refrigerant at the outlet port;   a third sensor to generate a third signal indicative of a temperature of the refrigerant at the inlet port;   a fourth sensor to generate a fourth signal indicative of a vapour quality at the inlet port; and   a controller communicatively connected to the valve, the first sensor, the second sensor, the third sensor, and the fourth sensor;   wherein the controller is configured to:   record the first signal;   record the second signal;   receive a position signal indicative of a position of the valve;   process the first signal to determine an upstream pressure p u ;   process the second signal to determine a downstream pressure p d ;   process the position signal to determine the position of the valve;   determine a discharge coefficient c m  based on the upstream pressure p u  and the downstream pressure p d , wherein the discharge coefficient c m  relates an actual flow {dot over (m)} at the determined position of the valve to maximum flow {circumflex over ({dot over (m)})} at the determined position;   use a valve curve and the discharge coefficient c m  and the determined position to estimate a flow through the valve at a predetermined position of the valve;   calculate a deviation measure as a function of the estimated flow through the valve at the predetermined position and a value of expected flow at the predetermined position;   compare the deviation measure to a threshold value; and   if the deviation measure is greater than the threshold value, produce a signal indicative of a disturbance in the refrigerant circuit.