Designing a General Purpose Heat Pump Controller

[AC_Hacker]

Originally Posted by takyka

AC,

With the smallest sufficient DC cap, the arduino can survive few hundred ms without power. I have never tried, but read in a book, the compressor can stop, or at least slows down so much, it will not spin up again without Pressures equalize. With optocoupler you can count each individual AC cycle.
It's cheap, and really just 4-5 components to add.

The flow sensor has some resistance, sure. I didn't measure it. I have the 1" version it has proximately half of the crossection blocked. The wheel turns so easy, if you blow into it gently it immediately spins up. For me, the small penality in COP would be acceptable for the added safety. I know about flow switches, but 5-10 times more expensive, and having a tongue in de way of the flow which generates resistance too.

T.

T,

I just ordered two of THESE_FLOW_SENSORS form ebay.

As BBP indicated, these will make it easier to calculate COP.

Here we go...

-AC

[AC_Hacker]

Originally Posted by jeff5may

AC,
I bought this one:
Arduino Shield List: DFRobot LCD Shield

jeff5may,

I just ordered one, too, FROM_THIS_PLACE.

This should be interesting, 'cause the buttons will give us access to a menu system, and will allow modification of values of strategic variables.

Should result in a real class act!

This is gonna be fun.

* * *

So jeff5may, with this LCD display, and its I/O buttons, AND with the reluctantly recognized necessity of flow measurement sensors, do you still think that the UNO will have enough pins to service all the inputs & outputs?

-AC

[Ormston]

As refrigerant pressure is directly related to its temperature could temperature sensors not be used(thermistor or digital) instead of pressure switches/transducers?
Also a mechanical thermostat could be mounted on the condenser input line and evaporator water outlet and wired inline with the compressor relay coil to shutdown the compressor in the event of over temp/pressure or freezing ground loop water.

Safety circuits should never rely on software.

For compressor stalled protection would a motor thermal overload not be suitable? One should really be used anyway to protect against the compressor jammed or simply overpressure, motor capacitor failed/disconnected and so on.

Steve

[NiHaoMike]

Use I/O expanders and you'll have a lot of I/Os to go around. Or go right for an ARM based solution and be able to run a RTOS with ease.

[takyka]

Originally Posted by Ormston

As refrigerant pressure is directly related to its temperature could temperature sensors not be used(thermistor or digital) instead of pressure switches/transducers?
...
Steve

It is not correct. Boiling point is related to pressure and temperature. But if you pass that point you can rise temperature for the wapor, without increasing pressure. Think about compressor discharge temperatures. You can't set any temperature limit on discharge line which is safe for low superheat case but high enough for high superheat case.

Originally Posted by Ormston

Safety circuits should never rely on software.
Steve

Good point, thank you! Everybody has to decide, how much the safety worth.

T.

[takyka]

Originally Posted by AC_Hacker

T,
I just ordered two of THESE_FLOW_SENSORS form ebay.
-AC

Good move! You can't imagine, how much these helps to find the best COP.
Only thing, your simple controller is not that simple anymore!

T.

[AC_Hacker]

Originally Posted by tc

...Only thing, your simple controller is not that simple anymore!

Curse you Takyka!

This was suppose to be simple.

-AC

[jeff5may]

Originally Posted by AC_Hacker

jeff5may,

I just ordered one, too, FROM_THIS_PLACE.

This should be interesting, 'cause the buttons will give us access to a menu system, and will allow modification of values of strategic variables.

Should result in a real class act!

This is gonna be fun.

* * *

So jeff5may, with this LCD display, and its I/O buttons, AND with the reluctantly recognized necessity of flow measurement sensors, do you still think that the UNO will have enough pins to service all the inputs & outputs?

-AC

For your air-source outdoor unit, it will work. For my self-contained unit, it will work. The main difference is thermostat control vs. slave control via a wire or serial comms.

You got a different version of the lcd module than I did. If it ships like the picture shows, that is. I did some testing on my LCD shield and it is definitely a version 1.0. The one in your pic is a version 1.1, which is supposed to have a fix for the backlight built onto the board. Either way, the code I am using will work with both versions the same. You just comment out one part of the code or the other to make the keypad read correctly (I guess they used different parts in the voltage divider for the keypad pin in the different revisions also).

It's going to take me longer than I thought to make the sketch for this project. Mainly me fighting with the arduino IDE to get it to like what I'm writing. It looks like I'll be making it one big file instead of a bunch of smaller pieces. Every time I try to add something, it doesn't wanna work. Navigating between modules leaves a lot to be desired, and you have to define all the types and variables in the main sketch anyway. Once I get something posted, the more experienced code warriors can divide it up so it looks nice.

[NiHaoMike]

Arduino is really meant for (very) simple projects.

[MN Renovator]

I disagree, the Arduino has been used on some projects that I consider to be quite advanced. I've seen them in many electric vehicle applications such as motor controllers, battery monitoring/management. I don't see why it wouldn't function well if its fed well programmed instructions and uses the inputs and outputs to their desired abilities.

Even a simpler PICAXE type control could -probably- do the job if you can program in a compact way and don't demand too much from them. The limitation with the PICAXE is more along the lines of the types of inputs it supports and the general smaller amount of sotrage memory it has for you to program into. I'd personally pursue the Arduino myself, more versatility.