Designing a General Purpose Heat Pump Controller

[AC_Hacker]

Originally Posted by NiHaoMike

An option to control VFDs (via RS232, PWM, or an analog voltage) would be nice.

I think we should initially focus on a general purpose controller for 'lowest common denominator' systems. Achieving that simple goal, so that there actually is a basic general purpose controller, that can be deployed by 'just anybody' is no trivial task.

NiHaoMike, I agree it would be nice to include a VFD interface for future revisions. That would be highly desirable. I think that a separate development thread should be initiated toward achieving that end. To my knowledge very few people have cracked that nut, and if they have they have remained very quiet about it. But it is a need that should be met, and made public for future revs.

-AC

[AC_Hacker]

I spent a bit of time looking for similar projects.

I didn't see any that had reached fruition, but there's a trail of interesting ideas along the way.

Plenty of attempts to control minisplits via LED siginals...

This link is called a Tinker's Rambling, but unfortunately the tinker may have rambled into the deep gloomy forest where he sank into quick sand.

Thus link, Home Heating Monitor, has a few pics (horrible focus) of attempts at monitoring an oil heating system.

Here's one called Monitoring of My Heat Pump that has monitoring, but no control.

Here is a

four part YouTube instructible

, that uses an Arduino to control an apartment heat pump that is not his own property. So the hacker has resorted to servos to make changes rather than directly hacking in and seizing control of the 'electrics' of the machine.

* * *

So, I have not found a project that is quite like what we are proposing here. I'm not saying that it doesn't exist, I'm just saying that I couldn't find one.

I searched in sufficient detail that I was coming across EcoRenovator discussions on the need for such a thing.

So, there is the possibility that we are out here, pretty much on our own, and nobody is going to do it for us...

BTW, I just did a search for "relay board shield" and found that there are quite a few shields that will plug right into an Arduino...

What do you think about this?

RELAY SHIELD

-AC

[AC_Hacker]

Since we are mulling over various power switching options, it might be useful to see how many microprocessor pins and switches (relay/SSR) we need at this point...

Maybe an initial tally could be useful.

Originally Posted by AC_Hacker

As for myself, I would like a GSHP controller that, as a very minimum requirement would:

• Provide for a startup delay of the compressor
• Monitor the output of the evaporator HX
• If evaporator HX output temp was equal to or less than 37F the compressor would shut down for a selectable period off time (10 minutes for starters) while the water pumps keep running

1. startup compressor: I think an SSR for this output (digital-out pin for the micro) SSR has opto-isolator
2. monitor output: needs an analog-in pin to read a thermistor, or a digital-in pin to read a 1-wire sensor (and 1-wire library)

Originally Posted by jeff5may

...In addition to AC's requirements, I would like the controller to do these things:

• Have the option for reverse cycle (heating and cooling modes)
• Short cycle protection (compressor lockout)
• Air or water source operation (selectable or configured)
• Freeze protection (water source) or defrost (air source - compressor lockout or active reverse cycle)

NOTE: My requirement for HX monitoring = your 'freeze protection' and your need for 'defrost sensing' = my 'freeze protection', so depending on the application, these functions are so similar the we could use the same hardware, and maybe sufficiently similar software, so that some variable(s) could be switched to tailor behavior.

3. Reverse cycle: this would call for two digital-out pins, and two relays
4. Freeze protection: this would call for a sensor pin (analog-in or digital-in)

You didn't mention it, but if your unit is going to be outside, you may need a crankcase heater, which would add:

5. thermistor or 1-wire sensor and an analog-in pin or digital-in pin. since we've previously call out a 1-wire library, no need to repeat.
6. digital-out pin and a SSR or fairly beefy relay.

Originally Posted by jeff5may

I suggest we include a few "sugar cube" relays to directly control smaller devices, such as fans, pumps, or valves.
To control components that require more current than the relays can supply, a contactor or SSR can be added into the circuit. For that matter, the contactor or whatever can be wired to slave off a sugar cube relay.

7. fan control: digital-out pin & relay
8. pump control: digital-out pin & relay
9. valve out control: digital-out pin & relay
10. Contactor: difital-out pin, relay, contactor (this may be the same as my item #1?)

jeff5may, in previous conversations, you said you wanted a read-out display

Do you still?

That could call for:
11. a LCD display unit which could call for an LCD library, I2C library (maybe), 1 digital out pin with I2C option, or maybe 6 digital-out pins for direct control option.

12. Should we include an Arduino Uno?

What am I missing so far?

There is a possibility that as this design develops, it may become complex enough that some of the functions could be handled by slave processors, like a Teensy or equivalent, saving pins and program space for the main micro-brain.

-AC

[stef110]

This is a great project i really like to join.
For my own HP i was already started to design and make the circuit on breadboard. My idea was to place this print inside the house next to the HX and run a cable to control the outside components.
The things I want on my board:

-Relay for compressor
-Relay for fan
-Relay for 4way valve
-Relay for circulation pump
-input for flow switch so i am sure that water is circulating
-input for an S0 power meter to measure power usage.
-two rs485 bus lines one for outside sensor print, and one to
communicate with my other heating controller.
-2x16 lcd display
- some led's and push button to test


My idea was to control everything with the arduino nano. Witch is just a arduino uno but then smaller and easy to include on you own circuit board.
I designed circuit boards before and make the first prints at home.
I have very good experience with one wire sensors i use them also for my wood stove system for all the sensors it only require one input of an arduino.

I think it is an good idea to make an list of the outputs we want, and a list for the inputs the functions are "software issues" but also good to place them in a third list!

stef

[Daox]

You guys are right, I jumped the gun. What you should really do is make a list of features or functions that you need the controller to perform. Once you have a list of the features and functions, you can start selecting hardware that meets your requirements.

I suggest having this list (as well as all the other decided upon design info) on the 1st page of this post so that you can always reference it easily.

[AC_Hacker]

Welcome aboard stef110. This is going to be fun!

Daox's & stef110 idea sounds like a good plan...

I'm waiting to hear back from jeff5may, as he might have ideas & additions.

Then I'll edit the requirements so far into the 2nd post (subject to revisions, of course)...

But I do think that beginning to enumerate inputs & outputs & required libraries & pin requirements & possible hardware helps to shape ideas... and also to foresee potential dead ends.

As long as we haven't started ordering parts, we can stay flexible.

-AC

[AC_Hacker]

OK, I have the first-draft input list.

Additions/Subtractions/Modifications?

-AC

[buffalobillpatrick]

A/C Great thread idea, just what I need.

I really like 10K NTC thermisters for temp. sensors, they are cheap, stable & don't jump around.

I have several sketches running on Arduino Uno, reading multiple analog sensors (pots & 10K NTC thermisters) & controlling multiple relays.

These 16-channel multiplexor breakout boards are very handy, as I quickly ran out of analog input pins:

8-Channel relay module, Arduino can provide enough current to energize these from digital pins and these can then control SSR's

Good stable pots for setting analog levels (the cheap ones are junk)

[doug30293]

Is there a specific reason for not considering an off-the-shelf PLC? The Automation Direct Click series, for example, is available in a multitude of I/O configurations, it's stackable, software is free, and it is easy to program

Doug

[NiHaoMike]

Originally Posted by AC_Hacker

I think we should initially focus on a general purpose controller for 'lowest common denominator' systems. Achieving that simple goal, so that there actually is a basic general purpose controller, that can be deployed by 'just anybody' is no trivial task.

NiHaoMike, I agree it would be nice to include a VFD interface for future revisions. That would be highly desirable. I think that a separate development thread should be initiated toward achieving that end. To my knowledge very few people have cracked that nut, and if they have they have remained very quiet about it. But it is a need that should be met, and made public for future revs.

-AC

The hardware for it is very simple. RS232/RS485 is just bringing the UART to a common 9 pin connector via a level shifter and is useful for far more than just VFDs. PWM is just bringing a PWM pin to a screw terminal with some sort of buffer circuit in between. Then add an active low pass filter (literally just a resistor, capacitor, and opamp) and you also have analog output. A little more circuitry and it will also do 4-20mA output.

We can put in the hardware first and worry about the software later. We can also add WiFi capability with a CC3000 module. You can simply leave the spot blank if you're not going to use it. It's common practice in hardware engineering to provision in as many features as the space and time allow. Also use the highest end processor that is compatible with the footprint during development, then downgrade for going into production. (For a one off, just keep the high end processor as its cost - a few dollars - is practically nothing as far as the total system cost is concerned.)