Method and apparatus for determining critical pressure of variable air volume heating, ventilating, and air-conditioning systems

Abstract

A strategy for determining the critical supply duct pressure in variable-air-volume heating, ventilating, and air-conditioning systems that compensates for duct leakage and variable loads, enabling its use during normal system operation. The strategy consists of a static pressure sensor, an airflow sensor, a supply fan, a fan modulating device, a controller coupled to the static pressure sensor and the airflow sensor, and a data processing algorithm for analyzing results from a function test using these components. The functional test involves changing the supply duct pressure setpoint, waiting for equilibrium, recording pressure, flow, and time, then changing the supply duct pressure setpoint to the next setting in the sequence.

1 . An apparatus for determining a critical supply duct pressure of a variable-air-volume heating, ventilating, and air-conditioning systems comprising in combination: 
 said supply fan;    a fan modulating device coupled to said supply fan;    a static pressure sensor;    at least one airflow sensor;    a supply fan controller coupled to said static pressure sensor and said fan modulating device, said supply fan controller configured to regulate static pressure to a static pressure setpoint;    a calculator configured to determine a critical supply duct pressure.    
   
   
       2 . The apparatus of  claim 1  wherein said airflow sensor is located upstream of said supply fan.  
   
   
       3 . The apparatus of  claim 1  wherein said airflow sensor is located downstream of said supply fan.  
   
   
       4 . The apparatus of  claim 1  wherein said calculator uses data from said airflow sensor to compute said critical supply duct pressure.  
   
   
       5 . The apparatus of  claim 1  wherein said calculator uses data from said static pressure sensor to compute said critical supply duct pressure.  
   
   
       6 . The apparatus of  claim 1  wherein said calculator uses said static pressure setpoint to compute said critical supply duct pressure.  
   
   
       7 . The apparatus of  claim 1  wherein said calculator is configured to use a controlling-mode model.  
   
   
       8 . The apparatus of  claim 7  wherein said model of the controlling system behavior includes a leakage term.  
   
   
       9 . The apparatus of  claim 7  wherein said controlling-mode model includes a time-dependent term.  
   
   
       10 . The apparatus of  claim 1  wherein said calculator is configured to use a starved-mode model.  
   
   
       11 . The apparatus of  claim 1  wherein said calculator uses a least squares data fitting procedure.  
   
   
       12 . A method for determining a critical supply duct pressure of a variable-air-volume heating, ventilating, and air-conditioning system, the method including the steps of: 
 commanding a supply duct setpoint to a setting;    waiting for equilibrium;    measuring a supply airflow rate after equilibrium is reached;    repeating said commanding, waiting, and measuring steps for a sequence of said supply duct setpoint settings;    processing measured data with a calculator configured to determine a critical supply duct pressure from said data acquired.    
   
   
       13 . The method of  claim 12  further including the step of measuring a supply duct static pressure after equilibrium is reached and including said supply duct static pressure in said processing step.  
   
   
       14 . The method of  claim 12  further including the step of measuring a time at which equilibrium is reached and including said time at which equilibrium is reached in said processing step.  
   
   
       15 . The method of  claim 12  wherein said calculating step uses a controlling-mode model.  
   
   
       16 . The method of  claim 15  wherein said controlling-mode model includes a leakage term.  
   
   
       17 . The method of  claim 15  wherein said controlling mode model includes a time-dependent term.  
   
   
       18 . The method of  claim 12  wherein said calculating step uses a starved-mode model.  
   
   
       19 . The method of  claim 12  wherein said calculating step uses a least squares data fitting procedure.