Designing a General Purpose Heat Pump Controller
 

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

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.

Best,

-AC_Hacker

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?

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

Hardware Requirements
 

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.

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

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

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.

OK, I can see that... Pretty high current, indicator LEDs for prototyping, the little black chunks are opto-isolators (I hope). Price seems pretty good.

Can you trigger the relays directly from an Arduino output??

OK, so how do you plan to use something like this relay assembly?

-AC

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

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

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.

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)


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.

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

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

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.

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

OK, I have the first-draft input list.

Additions/Subtractions/Modifications?

-AC

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)

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

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.)

Doug,

Thanks for your input.

Speaking only for myself, I think that the world-wide popularity and appeal of the Arduino IDE makes it a better choice, especially since there are millions of inspired youths all over the planet who are either competent with the Arduino IDE, or are well on their way to competency.

We are not only working to solve our local problem, we are also contributing to a vast pool of inspired enthusiasts, who, if we speak their language (Arduino, and eventually C++) may take what we do and create something beyond what we can imagine.

-AC

I had already put the RS485 option on the 'wish list' on post #2

Who is going to do the circuit design, circuit validation and CAD work for these added features? And should it be in rev 1?

By the way, there is a general engineering equation that predicts the reliability of a system. It is useful to note that in the denominator of this equation is the term n (for number of parts) squared. This means that if you double the number of parts, you have reduced the reliability of your system by a factor of four.

-AC

For such low frequencies, you can simply breadboard the circuit to test it. There's not much to go wrong with a simple buffered PWM output and buffered low pass filter anyways.

For the network interface, maybe it would be easier to just put in a "TTL" level (unbuffered) UART header to hook up to something like an OpenWRT router to handle the actual network interfacing.

item "Provide for a startup delay of the compressor"

This adjustable (up to 10 minutes) Delay on Make relay works great & are pretty cheap on Ebay.

Would control delay of compressor SSR.

http://ecorenovator.org/forum/attach...r-img_0190-jpg

I agree with this approach. If you want to control or read from this device, do it with one of these ways:

• UART/standard serial protocol
• USB (using arduino as a COM PORT, not a host)
• digital or analog pin (basic functionality)
• 1-wire interface (using a digital pin)

The main focus of this project is to make a unit that will perform the same functionality as your basic residential heat pump with digital thermostat or slave control. That being said, we can devise transparency and flexibility into this unit so developers who want exquisite functionality can take snapshots or xrays of the system to suit their requirements. We can include some registers or tables to monitor short-term and long-term data values and to provide a common location to read and write hardware states and maybe some error codes.

I am not opposed to adding extra modules to the controller. As long as the module is generic and widely available for cheap (like the CC3000 module), and will not interfere with the (basic) core operation of the controller, have at it. Start a thread, build a shield or module, make it work, include code that we can call from the basic module. If it proves worthy, we can include extra firmware to account for this device (if necessary) into the main sketch.

I realize there are a lot of tech savvy ecorenovators with a wide variety of specific skill sets that we will need help from to pull this project off. But this main module needs to be basic, cheap, and easy to assemble without expert skills. It needs to go together like duplo blocks. A lego block version would be too complex for some. The Technic or NXT/Mindstorm line version would definitely need to be an add-on shield or module.

As for downsizing the module, an arduino pro mini or pro micro 5 Volt module would have the same compatibility as a uno R3, without the shield pinout configuration. Getting much cheaper or smaller, we lose the USB port.

How about these flow sensors: $11

450 output pulses/liter

http://www.amazon.com/gp/product/B00...A1EX7LU0M6LM21

Product Description

DESCRIPTION:
Waterproof, heat resistance, pressure resistance, cold resistance
Easy to install
Frequency: F=4.8 * Q (L / Min) error: ± 2% voltage: 3.5-24VDC, current can not exceed 10mA, 450 output pulses/liters,
F=constant * units of flow (L / min) * time (seconds).
Flow range: 1-60L/min
Maximum current: 15 mA (DC 5V)
Working voltage range: DC 5～24 V
Load capacity:≤10 mA(DC 5V)
Operating Temp:≤80℃,Operating humidity:35%～90%RH
Allow compression: Water pressure >1.75Mpa
Insulation resistance: >100M OHM
Storage Temperature:-25～+80℃
Storage humidity:25%～95%RH
Output Waveform: Square Wave, output pulse signal
ROHS Compliant
Material: ABS Plastic
Color: Black
Cable length: approx. 15cm
INCLUDED:
1 x Flow Meter

Arduino - PulseIn

I have simple solid Arduino code using timed pulse for my CO2 sensor:

see 1st post in thread: http://ecorenovator.org/forum/conser...no-sketch.html

AC,

Here's a project page for the meter reader RS485 interface:
APMR by smakonin

It has been said the power industry is going to be using zigbee for its smart power meters with rf interface. Who knows for sure?

Power Meter

@ jeff5may

What do you mean by simple? don't you think that if we made a paper tutorial with pictures, then i think that the can solder there own print?

The arduino nano has his own usb port but the same pin layout as the mini pro. I used in other project it is easy to use.

stef

I really like the idea of a basic unit with snap-together modules.

I mean if the basic unit can run my heat pump, and jeff5may's air conditioner conversion, that is just fine.

Then if you wanted enhanced functionality, you could snap on extra modules.

The Arduino expansion 'pin + socket = shield' configuration seems like a great way to go. It is already developed and has super-wide acceptance. It would also make it easy for other hackers to develop enhanced-functionality modules. I mean proto board that conform to the Arduino configuration are available from multiple sources right now... no need to create one.

I like it that some Serbian kid could go down to his local Radio Shack equivalent and get started, or some girl in Nigeria could buy some incredibly cheap clone from ebay, and get started, all by simply downloading our freely-available code.


But I think that having the ability to easily configure the GPC for different configurations is vital, even more important that Xbee or Wi-Fi or cell-phone connectivity (not that it is mutually exclusive).

I have a brain-dead ASHP in the basement, I need to make it work. I need a GPC...

I have a small, simple GSHP that can feed a simple hydronic floor, I need a GPC...

My ultimate system will be a hybrid system that could handle a GSHP and also integrate it into a system that included a ASHP. I need a GPC...

We have a build going on right now in The Netherlands, by stef110 that is intended to integrate a solar heating system with an ASHP. He needs a GPC...

ditto buffalobillpatrick, He needs a GPC...

Also going on right now is a guy in England, wsexton1 who wants to do a GSHP and employ two different compressors. He needs a GPC...

The air conditioner-to-domestic-water-heater hack has proven to be surprisingly popular. It would be more popular yet if there was a GPC...

I also have the suspicion that randen's 3-phase monster also needs a GPC...

This project may not be easy, but the moment is definitely upon us...

-AC

Those cheap flow metres are OK for a while, mine has started playing up after around 4 months use. The impeller wheel sticks, so far I,ve managed free it several times by turning the circulation pump to full speed for a few seconds.
Maybe i 'm unlucky and got a duff one?

Arduino is the perfect platform on which to build a controller.

Yes, you should be able to load our sketch into a Nano and have it do the same thing. However, I wouldn't expect a 5th grader to be able to solder pins and breadboard and debug the thing to make it work. To someone with an intermediate or expert skill set, the task would be trivial in nature, but to a beginner or novice it would spell disaster.

The old-timers, with their "trade secrets" and "license necessary" attitudes are becoming a dying breed. With the advent of the internet and the information age, one can quickly look up how to do anything. There are multiple websites that operate just for this purpose.

However, just because you can look something up and be shown how to do it doesn't mean people will follow through. The reason why is simple: Joe Average is too lazy. Just look on any of the DIY websites that sell stuff. The kit forms of projects will always be readily available, while the more expensive, ready to use, prebuilt kits will more often than not be sold out. Who wants to solder and assemble when the finished product is available for 50% more?

My intent here is not to sell prebuilt kits, but assemble a short list of components that will work with a minimum of manual assembly. Someone should be able to go to radio shack, amazon or ebay and buy a couple of devices and have our basic set of components in a bag or box in ten minutes.

For example, from RadioShack:

• generic usb (arduino to pc) cable
• arduino uno r3 module
• Seeed Grove-Starter Kit for Arduino
• Seeed Relay Shield V2.0

For a grand total of around $100, buying name-brand stuff, at a store notorious for its high markup prices, a novice could rig this list to an ATX power supply harvested from any old computer and make a finished product. Granted, there would be some figuring involved in adapting the parts to the heat pump, but it could be done without much mayhem involved.

Again, from amazon:

• SunFounder 4 Channel 5V Relay Shield Module for Arduino UNO
• SainSmart C00 Kit with LCD Keypad Shield + UNO for Arduino UNO MEGA Duemilanove
• SunFounder Project Universal Starter Kit For Arduino UNO R3 Mega2560 Mega328 Nano
• 365buying DS18B20 Temperature Sensor - Waterproof Digital Thermal Probe Sensor DS18B20 (more than 1 piece)

Same thing, only cheaper grand total.

Don't we need more than 4 relays?

I just wrote a sketch that should work with that Amazon flow sensor, timing the pulses.

What flow sensor is better? They look to be $$$ for name brands.

Is your flow sensor required for fluid flow rate, or to verify that the pump is working?

-AC

A/C I thought it was your idea?
See pg1 post #2
That list also shows 6 relays.

I've not managed to source anything better yet, mine was fitted last October and works most of the time except for the sticking.
It may be because I only use the low end of the range 7-14 LPM. I,m using it as a flow switch for my cheap and nasty ashp as well as measuring the heat output in near real time with the help of a pair of waterproof ds18b12 temp sensors.

The 4 outputs for relays are:

• outdoor fan/ground loop pump
• indoor fan/hydronic loop pump
• compressor
• crankase heater/reversing valve

To make the reversing valve and the crankcase heater work together, off the same relay, they will both need to be active in heating mode. If they take different voltage, wire a transformer in.

This leaves room for customization. For example, if you wire your outdoor fan to the compressor, they will both run with each other. Then you can have a separate crankcase heater relay.

It would be a good idea to add spaces for extra relays.

I don't see the need for flow sensors, except for trying to measure COP or pumps in series.

I have installed dozens of pumps in hydronic systems & it becomes obvious pretty quick if a pump stops working, much tougher though when they are in series.

I would think that crankcase heater should be turned off when compressor starts.

Why can't both source & load water pumps be controlled by 1 relay?
Do they need to ever run independently?

Why can't the source & load water pumps AND compressor be controlled by 1 relay?

Power supply Requirements
 

OK, now for more conventions and constraints.
With the wide variety of configurations planned, it is possible to overload the Arduino board quite quickly. So I'll put out some rules. Feel free to comment on them, as they will probably change.

The Arduino chip and logic components attached to it must draw currents from the board. Input and output devices must also draw currents from pins on the chip. These currents must not exceed 20 mA per pin. The combined loads of all attached logic devices must run off the regulated 5 Volt pin when the unit is in standby (main power off). This includes shields and peripheral components such as sensors, displays, optocouplers, buffers, etc. The combined load when the unit is in standby must draw power from, but not overload, the USB port.

When the unit is powered on, the unit's power supply will enable separate voltage rails to power devices not directly attached to the microcontroller board. This includes relays, motors, contactors, pumps, etc. This power supply will also supply the board between 9 and 12 Volts DC to the power connector on the arduino board. The power supply may also have other source rails that may or may not be switched with the power state of the unit, but none of these except the 9-12VDC run supply mentioned previously will connect directly to the Arduino board!

What this means is that anything that could load down the Arduino and cause the unit to fail cannot run directly off the board. When line or mains power is lost, the unit should survive in standby mode and operate off a USB battery pack or attached cell phone for at least a couple hours before losing standby power. This feature will allow for blackouts, brownouts, and such so the unit will go right back to work when and if power is restored without losing its wits and memory.

jeff5may: "power is restored without losing its wits and memory"

Thats how they work without a battery.