HVAC /Heat Pump Controls

[Wittmann]

So after  replacing some cheap  hvac circuit boards,  twice,  and seeing the price go astronomical  I am  retrofitting  my Heat Pump/AC and Air handler with a micro plc,   AB  820,  a 3 phase blower motor, and a VFD.  Now I have a basic idea of how the system operates,  I can write a program using a PID block to control my fan speed,  etc.   As far as I know,   the compressor   starts and runs when heating and cooling is called for.  I am not sure if there is a pressure switch for the fluid to control that on/off   and pressure cut out safety switches to protect the compressor etc.    If any1  has knowledge of  HVAC operation,     and you have time to do a short write up for me so I can program,  plz do so. 

[Lipfert]

On 3/30/2022 at 4:35 PM, Wittmann said:

So after  replacing some cheap  hvac circuit boards,  twice,  and seeing the price go astronomical  I am  retrofitting  my Heat Pump/AC and Air handler with a micro plc,   AB  820,  a 3 phase blower motor, and a VFD.  Now I have a basic idea of how the system operates,  I can write a program using a PID block to control my fan speed,  etc.   As far as I know,   the compressor   starts and runs when heating and cooling is called for.  I am not sure if there is a pressure switch for the fluid to control that on/off   and pressure cut out safety switches to protect the compressor etc.    If any1  has knowledge of  HVAC operation,     and you have time to do a short write up for me so I can program,  plz do so. 

I used to know this stuff thirty years ago ! Not really up to speed right now.

S!

[Wittmann]

A good start.  Some wiring and cleanup to finish.  Right now. I will be using 4 or 5 contact inputs to vfd for some preset speeds. When i get my dp transmitters. and thermistors I will switch the vfd speed over to pid control using modbus. This will free up. Some relay outs which i will then use to replace my sprinkler system controller

[Wittmann]

Up and running since I posted last.  Took some work. On figuring out the wiring.  So now all control is via allen bradley micro 820 plc,  the blower motor is a heavy duty 3 phase,  using a vfd for speed control.  Cost me less than half what the parts would have been oem,  and then they would have just been the same cheap hvac components

[Vonrd]

Sorry, way out of my realm of knowledge. 

Glad you worked it out.

[Lipfert]

Kameraden,

Are you using a capacitor starter for the motor?

S!

[Wittmann]

Benn awhile since I remembered this post.   Lip,  I"m using a cap start for the compressor. And outdoor fan.  The blower fan, no cap.  No sense in it as I run the blower 24/7. For air filtration purposes.  And just speed up if cooling or heating is called for.    

On the filtration front.   I run a 3"  merv 13. With a carbon coating.  If your unit can use a thicker. Filter than the standard 1" thick,   do so.  It has much more surface area 2"  up to 5,  you have less drag on your fan,  it will flow better,  performance will increase.  The thicker filters cozt more. But last much longer.   If you use 1 inch. And you go thicker. You can increase the merv rating and not see any performance loss.

 

[Lipfert]

13 hours ago, Wittmann said:

Benn awhile since I remembered this post.   Lip,  I"m using a cap start for the compressor. And outdoor fan.  The blower fan, no cap.  No sense in it as I run the blower 24/7. For air filtration purposes.  And just speed up if cooling or heating is called for.    

On the filtration front.   I run a 3"  merv 13. With a carbon coating.  If your unit can use a thicker. Filter than the standard 1" thick,   do so.  It has much more surface area 2"  up to 5,  you have less drag on your fan,  it will flow better,  performance will increase.  The thicker filters cozt more. But last much longer.   If you use 1 inch. And you go thicker. You can increase the merv rating and not see any performance loss.

 

Wittmann,

Thanks for that information, my unit takes a 16 x 25 x 4 size. I just checked that the ones I have right now are MERV 11. I've updated my Amazon choice and will buy the MERV 13 with carbon next time. We had a Trane S9X2 installed last year with a new Trane XR13, like the unit so far.

S!