Designing a General Purpose Heat Pump Controller

[AC_Hacker]

The Homemade Heat Pump concept has had some notable success.

However, one link in the chain that is missing is an open-source general-purpose heat pump controller.

If such a controller existed, it could increase the success of people who undertake a homemade heat pump project.

Such controllers have been built and put into service since the 'Manifesto' thread started, but the design considerations and full final specifications (diagrams, photographs, schematics, PWB files, software, etc) were not sufficiently made public such that 'just anybody' could use them.

We want a design that is sufficiently complete so that 'just anybody' can make it work for them.

The goal of this thread is to design, test and put into service such a controller... modifications and improvements can follow.

There is a hazard that this discussion could become so diluted to the point that nothing is ever produced.

In other words, this thread is totally oriented toward developing a working device. This is not a 'talking shop'.

* * *

jeff5may & I have had some preliminary discussion, and have decided that it is time to open up our conversation to anyone who can contribute.

Here we go...

-AC & jeff5may

[AC_Hacker]

Seems to me that we need to start with a conversation about "scope" and desired results, specific enough that we can tell when we are moving in the correct direction.

EDIT: Below is a working list of inputs & outputs for the GPC (general purpose controller), based on desired functionality. Additions are invited.

• Relay for compressor
• Relay for crank case heater
• Relay for fan
• Relay for 4way valve
• Relay for ground loop circulation pump
• Relay for hydronic circulation pump
• Input for flow switch so i am sure that water is circulating
• Input for an S0 power meter to measure power usage.
• Input for frost sensor (or water HX output temp sensor)
• 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

Best,

-AC_Hacker

[Daox]

I agree defining the scope is crucial to starting the project. Answering questions like what do you all need to be able to control (motors up to X amps, etc)? Or, what kind of sensors are you going to be dealing with? 220V or 110V?

[AC_Hacker]

There are at least four projects that are in various stages of development that I am aware of, it could be useful if the people who are working on their projects could describe what they would like a controller to do...

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

-AC

[jeff5may]

Daox,
The actual brawny components residing in the machine will vary. They will differ depending on the specific application. However, the components on our controller should not. The controller module should be generic enough to fit the bill for a diverse range of end products. 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)

I suggest we include a few "sugar cube" relays to directly control smaller devices, such as fans, pumps, or valves. It may sound hokey, but relays last a long time, are predictable, and can be wired a jillion different ways, to whatever power source the controlled device needs to operate. 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.

[AC_Hacker]

Originally Posted by jeff5may

The actual brawny components residing in the machine will vary. They will differ depending on the specific application. However, the components on our controller should not. 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.

OK, this is good.

I do see all manner of SSRs, some smaller such as THIS_ONE, and THIS_ONE, and THIS_ONE.

I haven't designed much for any relays or SSRs except in my CO2 controller.

Is there a reason for electro-mechanical relays for the smaller devices and SSRs for the higher amp components?

-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

[AC_Hacker]

I have a couple of local guys who would like to get involved in PCB design for this project.

But if we wanted to stay with "off the shelf" stuff, HERE_ARE some possibilities regarding smaller relays & SSRs.

-AC

[jeff5may]

I like this one:
Amazon.com: SunFounder 4 Channel 5V Relay Shield Module for Arduino UNO 2560 1280 ARM PIC AVR STM32: Computers & Accessories

I was planning on using an Arduino Uno knock-off for my micro, so this board would attach like any other shield. This board will work with pretty much any microcontroller that spits out TTL for control. I believe they will need only 10 mA or less from the logic source per input.