Arduino R290 Suction Line Superheat Calc.

[buffalobillpatrick]

Mike, Is this a good EEV?

http://www.emersonclimate.com/Docume...d-Electric.pdf

PID with PWM for 6sec. for the above EEV looks pretty easy.

Use a SSR that can withstand millions of cycles.

I also stole this code:

/********************************************************
 * Arduino PID Relay Output Example
 * The output is going to digital pin 6 which is controlling
 * a relay.
 * The current temperature, PSI etc............ is read via pin A0
 * 
 * The pid Library is designed to only output an analog value,
 * but the relay can only be On/Off.
 *
 * To connect them together we use "time proportioning control"  
 * It's a really a long duration version of Pulse Width Modulation (PWM).
 * First we decide on a window size (6000mS say.) 6 seconds
 * We then set the pid to adjust its output between 0 and that window size.  
 * Lastly, we add some logic that translates the PID
 * output into "Relay On Time" with the remainder of the 
 * window being "Relay Off Time"
 ********************************************************/



#include <PID_v1.h>
#define RelayPin 6    //D6
#define T_pin   A0    //A0

//Define Variables we'll be connecting to
double Setpoint, Input, Output;

//Define the Tuning Parameters
double Kp=2, Ki=5, Kd=1;

//Specify the PID links
PID myPID(&Input, &Output, &Setpoint, Kp, Ki, Kd, DIRECT);

int WindowSize = 6000;          //6 sec

unsigned long windowStartTime;


void setup()
{
  windowStartTime = millis();    //get current time

  Setpoint = 100;                //Desired Temperature, PSI, etc................

  //tell the PID to range between 0 and the full window size
  myPID.SetOutputLimits(0, WindowSize);

  //turn the PID on
  myPID.SetMode(AUTOMATIC);
}
 
void loop()
{
  Input = analogRead(T_pin);  //Pass current temperature as Input to PID
  
  myPID.Compute();

  unsigned long now = millis();  //get now time
  
  if(now - windowStartTime > WindowSize)
  { //time to shift the Relay Window
    windowStartTime += WindowSize;
  }
  if(Output > now - windowStartTime) digitalWrite(RelayPin,HIGH);   //ON
  else digitalWrite(RelayPin,LOW);                                  //OFF

}

[Mikesolar]

This is the one I have with me now, the SER-B.

I was looking into using some chinese ones like BradC was but haven't gotten around to it yet.

[Mikesolar]

Originally Posted by buffalobillpatrick

Mike, Is this a good EEV?

http://www.emersonclimate.com/Docume...d-Electric.pdf



[/CODE]

I'm not sure that it is a good valve for this purpose. I have a Danfoss equiv (that came with a controller) that is used for liquid injection for cooling the pot if the head pressure gets too high but i didn't think it was suitable for use as an EEV. EEVs are usually stepper motors, not solenoid valves, AFAIK.

[AC_Hacker]

Originally Posted by Mikesolar

I'm not sure that it is a good valve for this purpose. I have a Danfoss equiv (that came with a controller) that is used for liquid injection for cooling the pot if the head pressure gets too high but i didn't think it was suitable for use as an EEV. EEVs are usually stepper motors, not solenoid valves, AFAIK.

Yep, EEV for HVAC must be stepper (or servo, which would be too expensive, with no added benefit).

Tell me more about what you have in mind for the EEV?

-AC

[buffalobillpatrick]

"The Emerson EX2 pulse modulated electric valve is an electrically driven expansion valve that provides precise temperature control. It is designed for use with R-12, R-22,
R-134a, R-404A, R-407C and R-502 refrigerants. - See more at: http://www.emersonclimate.com/en-US/products/valves/expansion_valves/Pages/electronic_expansion_valve.aspx#sthash.AodE1Cgy.dp uf"

Did anyone read the link in post #21 ?

[AC_Hacker]

Originally Posted by buffalobillpatrick

...I've built the R290 PT Chart into the software, ...

Did you do a look-up table?

-AC

[AC_Hacker]

BBP,

Thanks for the thanks, but I am asking you if you did a look-up table?

Reason is that I crafted a single formula that will generate the R-290 P-T table, precisely, no need to interpolate.

One line of code, no table.

-AC

[buffalobillpatrick]

Please share that line of code!

Yes Look-up table sort-of

I looked at the table: HC-290 (PROPANE) PRESSURE - TEMPERATURE CHART

and entered the table data into the array in function:
float calc_R290_Saturated_Temp(float PSI, int Which_sensor)

//Array element [0]  contains Saturation_Temp *F for 30PSI,
//Array element [1]  contains Saturation_Temp *F for 40PSI,...................>
//Array element [27] contains Saturation_Temp *F for 300PSI,
//Array element [28] contains Saturation_Temp *F for 310PSI

float R290_Saturation_Temp[] = 
     {7.93, 18.80, 28.42, 36.91, 44.59, 51.63, 58.13, 64.21, 69.90, 75.27, 
      80.35, 85.18, 89.78, 94.19, 98.41, 102.50, 106.40, 110.20, 113.80, 
      117.30, 120.80, 124.10, 127.30, 130.40, 133.50, 136.50, 139.40, 142.20, 
      145.00};

[AC_Hacker]

OK, if you need to economize on code or get more precise, let me know.

In other words, what happens to 31psi, 32psi, 33psi, 34psi, 35psi, 36psi, (and all the fractional pressures in between), etc.

-AC

[AC_Hacker]

Originally Posted by buffalobillpatrick

Please share that line of code!

OK, I will.

It won't take too long, but I need to do some mandolin practice right now, got a gig coming up and I need to do some preparation.

I'll have the formula for you sometime later in the day (I need to re-create it).

Best,

-AC