help needed

Mikesolar · 01-14-16, 07:08 PM

Well, In some ways i am the luddites, luddite. This is especially true when it comes to anything that needs programming which brings me to the problem in hand and my asking for help.

I have an A2W heat pump that I want to heat/cool a single tank with. It is to be based on outdoor temp. I need it to heat the tank (W signal, setpoint of 45C) anytime the outdoor temp is below 17C (adjustable). That is the warm weather shutdown point. It will also need to cool the tank (Y and O signal) anytime the outdoor temp is over 25C (again, adjustable, with setpoint of 7C). Also, it will need to switch off the A2W HP when it hits -15C (also adjustable) and turn on W2 which is the back up electric boiler. Oh yea, I should also have some way to let it know to turn on the back up boiler if the house drops below perhaps 14C, which would indicate a faulty HP.

I am absolutely useless with arduino so I wonder if any of you certifiable geniuses could help me write the code.

I don't think there is anything else the wee beastie needs to do as the t-stat will control turning on pumps and fans.

Please, pretty please.....

jeff5may · 01-15-16, 10:17 PM

Well, I don't know how much of a genius I am, but I can try all day long. If I had stayed in the IT field in the 90's, I would probably be richer and much better at hard coding than I am now.

The main logic to decide what to turn on and off, during what conditions is not all that difficult to code. But the peripheral stuff isn't so simple. I have some preliminary questions for you:

Does the outdoor unit have its own defrost control?

What kind of display or visual interface will the controller use?

What kind of sensors (and how many) will be used?

What kind of user inputs will the controller take (buttons, keypad, keyboard, etc.) to change settings or modes?

How simple or elaborate the answers to these questions are will have a large impact on the complexity of the control program.

Mikesolar · 01-16-16, 06:09 AM

Well Jeff, you, AC, BBP, etc seem to be moving right along and can work out bugs in the programming. It's just something I start tuning out when forced to look at and I wish it weren't so.

I don't have to control the operation of the HP in any way other than to turn it on or off based on outdoor temps. The industry standard in the HVAC industry is a 10k thermister and i have lots of them from other projects (check out Tekmar controls, for one) so many people build around those.

In the most simplest of designs, there would be no interface, just something programmed from the computer and put into action but that's no fun, I guess, so it probably should have something that shows the temps at least. Anything more than that is optional.

I have tried to find an existing control that does this but to no avail.

It only need 2 thermisters, one for the tank temp and one for the outdoor temp and optionally, one for room temp to be able to turn off W1 and turn on W2 in case the house starts getting too cold.

Acuario · 01-16-16, 10:30 AM

Sounds pretty straight forward to me. How are your soldering skills as you'll need to make up a bit of circuit for the thermistors, the rest should be pretty much 'plug and play'. Also, do you know if your thermistors are PTC or NTC as this will affect the code.

Acuario

Mikesolar · 01-19-16, 06:56 PM

My soldering skills are fine so, no problem on that front. The thermisters are 10k NTC and i have the graphs for them,

What did you have in mind?

Acuario · 01-20-16, 03:31 AM

Here is a schematic of what you could do. You can find all the bits on ebay.

Search 1x4 key membrane for the keyboard or you could build your own.

Search for I2C 16X2 for the display

Search arduino relay 2 module for the relay. I'm assuming a simple 'heat/cool' switch to change the operating mode of the heat pump.

I put in solid state relays for the main heat pump and electric boiler control.

For the inside temperature you could either use an electro magnetic thermostat or another NTC thermistor - I've included a thermistor.

The bits you'll need to build are the thermistor ones - a bit of stripboard and a few wires is all you need to assemble. The rest is plug and socket using DuPont cables.

Mikesolar · 01-20-16, 05:55 AM

Thanks Aquario:

What i currently have is a normal t-stat which takes care of the heat/cool pumps and anything on the load side. The HP has terminals for W (heat), Y (cool) and O/B (REV valve). It takes care of it's own circ pump to the tank which comes on with any call for heat or cool. For the backup boiler I just need to provide a dry contact.

For the programming, I would like the be able to have the arduino recognize the outdoor temp and tell the HP to turn on in either mode, without the owner having to go down twice a year and remember to flick a switch. I think that should just be a programming item (?)

Also, how come you use SSR instead of regular relays?

jeff5may · 01-20-16, 08:58 AM

Ok, so you're going to have 3 thermistor sensors: indoor, outdoor, tank temps. To do what you want, you will need either 3 or 4 relay outputs: backup heat(w2), reversing valve(o), and either w/y or separate w and y. Me like 4 way relay modules. For one, you can hear them click. They are cheaper, too.

For your program, the structure should be pretty simple. It will be something like this:

Setup
define variables, inputs and outputs
set initial conditions
display welcome message
startup delay

Loop
read inputs
change variable values based on control logic
update outputs and display if necessary

Acuario · 01-20-16, 10:24 AM

Quote:

Originally Posted by Mikesolar

Also, how come you use SSR instead of regular relays?

I prefer SSR's for switching loads for a several reasons:
1. They have zero cross detect so no big electrical spikes or need for snubber circuits
2. They don't need a transistor driver circuit to switch them on/off
3. No contact wear due to arcing
4. Silent operation (not important in noisy environments)

They are also as cheap or cheaper than a conventional mechanical relay.

For low current switching I do use conventional relay modules. I know the commonly available relay modules are rated at 10A but I'm not sure I'd be happy putting 10A through one, just personal caution.

Some questions:
1. What do you need to provide (voltage and power wise) to the W, Y and O/B inputs? Is it mains power?
2. Why is there a separate connection for the rev valve if there are separate wires for heat/cool? Do you have a schematic of the machine?
3. It sounds like the 'regular t-stat' is already in use so will the room temperature come from a separate stat or from an NTC (this is for the failure detect you require)?
4. Does the hp look after its own power failure/restart and defrost cycles?

Mikesolar · 01-26-16, 09:31 AM

HPs in North america, like our forced air heating systems, have a W for heat, Y for the compressor, O/B for the the reversing valve (which is dependent on where the unit is destined to be placed. In the American south, the RV is usually set to cooling, power off as it is a cooling dominant climate and in the great white north, it is the other way around. Having both available means it can be tailored to specific needs). Where I am, O will power the RV to cool. So, on a cooling call, the stat will call for a fan, Y and O and in heating (in this case) it will only call for W. This is all outside of the control of the arduino which is just needed to switch over the HP from heat to cool at specific temps and turn on the electric boiler.

The HP does look after all it's own functions including switching the circ pump to the buffer tank.

The HP has 24Vac which runs to the stat so there is 24V at any switched pin.

No extra power is needed other than to provide power to the Arduino.

The reason for regular relays is that I do need some DPDT ones to switch off a heating circ pump on the buffer tank when the back up boiler is running (which has it's own pump). This is one of the outputs from the arduino which reads the outdoor temp at -15C and will shut off the HP in favor of the electric boiler.

The programming is quite house specific and I have determined that the HP will easily heat this house down to -15C but it is not great when colder than that.

At one time I did find some reed relays that would work directly with the max pin current of the arduino but they were not DPDT so i didn't buy them. It may be available.

Drawing will be coming soon of the wiring.

01-14-16, 07:08 PM	#1
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	help needed Well, In some ways i am the luddites, luddite. This is especially true when it comes to anything that needs programming which brings me to the problem in hand and my asking for help. I have an A2W heat pump that I want to heat/cool a single tank with. It is to be based on outdoor temp. I need it to heat the tank (W signal, setpoint of 45C) anytime the outdoor temp is below 17C (adjustable). That is the warm weather shutdown point. It will also need to cool the tank (Y and O signal) anytime the outdoor temp is over 25C (again, adjustable, with setpoint of 7C). Also, it will need to switch off the A2W HP when it hits -15C (also adjustable) and turn on W2 which is the back up electric boiler. Oh yea, I should also have some way to let it know to turn on the back up boiler if the house drops below perhaps 14C, which would indicate a faulty HP. I am absolutely useless with arduino so I wonder if any of you certifiable geniuses could help me write the code. I don't think there is anything else the wee beastie needs to do as the t-stat will control turning on pumps and fans. Please, pretty please.....

01-20-16, 03:31 AM	#6
Acuario Apprentice EcoRenovator Join Date: May 2011 Location: Tortosa, Spain Posts: 221 Thanks: 2 Thanked 81 Times in 46 Posts	Here is a schematic of what you could do. You can find all the bits on ebay. Search 1x4 key membrane for the keyboard or you could build your own. Search for I2C 16X2 for the display Search arduino relay 2 module for the relay. I'm assuming a simple 'heat/cool' switch to change the operating mode of the heat pump. I put in solid state relays for the main heat pump and electric boiler control. For the inside temperature you could either use an electro magnetic thermostat or another NTC thermistor - I've included a thermistor. The bits you'll need to build are the thermistor ones - a bit of stripboard and a few wires is all you need to assemble. The rest is plug and socket using DuPont cables. Attached Thumbnails

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

01-15-16, 10:17 PM	#2
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Well, I don't know how much of a genius I am, but I can try all day long. If I had stayed in the IT field in the 90's, I would probably be richer and much better at hard coding than I am now. The main logic to decide what to turn on and off, during what conditions is not all that difficult to code. But the peripheral stuff isn't so simple. I have some preliminary questions for you: Does the outdoor unit have its own defrost control? What kind of display or visual interface will the controller use? What kind of sensors (and how many) will be used? What kind of user inputs will the controller take (buttons, keypad, keyboard, etc.) to change settings or modes? How simple or elaborate the answers to these questions are will have a large impact on the complexity of the control program.

01-16-16, 06:09 AM	#3
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	Well Jeff, you, AC, BBP, etc seem to be moving right along and can work out bugs in the programming. It's just something I start tuning out when forced to look at and I wish it weren't so. I don't have to control the operation of the HP in any way other than to turn it on or off based on outdoor temps. The industry standard in the HVAC industry is a 10k thermister and i have lots of them from other projects (check out Tekmar controls, for one) so many people build around those. In the most simplest of designs, there would be no interface, just something programmed from the computer and put into action but that's no fun, I guess, so it probably should have something that shows the temps at least. Anything more than that is optional. I have tried to find an existing control that does this but to no avail. It only need 2 thermisters, one for the tank temp and one for the outdoor temp and optionally, one for room temp to be able to turn off W1 and turn on W2 in case the house starts getting too cold.

01-16-16, 10:30 AM	#4
Acuario Apprentice EcoRenovator Join Date: May 2011 Location: Tortosa, Spain Posts: 221 Thanks: 2 Thanked 81 Times in 46 Posts	Sounds pretty straight forward to me. How are your soldering skills as you'll need to make up a bit of circuit for the thermistors, the rest should be pretty much 'plug and play'. Also, do you know if your thermistors are PTC or NTC as this will affect the code. Acuario

01-19-16, 06:56 PM	#5
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	My soldering skills are fine so, no problem on that front. The thermisters are 10k NTC and i have the graphs for them, What did you have in mind?

01-20-16, 05:55 AM	#7
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	Thanks Aquario: What i currently have is a normal t-stat which takes care of the heat/cool pumps and anything on the load side. The HP has terminals for W (heat), Y (cool) and O/B (REV valve). It takes care of it's own circ pump to the tank which comes on with any call for heat or cool. For the backup boiler I just need to provide a dry contact. For the programming, I would like the be able to have the arduino recognize the outdoor temp and tell the HP to turn on in either mode, without the owner having to go down twice a year and remember to flick a switch. I think that should just be a programming item (?) Also, how come you use SSR instead of regular relays?

01-20-16, 08:58 AM	#8
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Ok, so you're going to have 3 thermistor sensors: indoor, outdoor, tank temps. To do what you want, you will need either 3 or 4 relay outputs: backup heat(w2), reversing valve(o), and either w/y or separate w and y. Me like 4 way relay modules. For one, you can hear them click. They are cheaper, too. For your program, the structure should be pretty simple. It will be something like this: Setup define variables, inputs and outputs set initial conditions display welcome message startup delay Loop read inputs change variable values based on control logic update outputs and display if necessary

01-26-16, 09:31 AM	#10
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	HPs in North america, like our forced air heating systems, have a W for heat, Y for the compressor, O/B for the the reversing valve (which is dependent on where the unit is destined to be placed. In the American south, the RV is usually set to cooling, power off as it is a cooling dominant climate and in the great white north, it is the other way around. Having both available means it can be tailored to specific needs). Where I am, O will power the RV to cool. So, on a cooling call, the stat will call for a fan, Y and O and in heating (in this case) it will only call for W. This is all outside of the control of the arduino which is just needed to switch over the HP from heat to cool at specific temps and turn on the electric boiler. The HP does look after all it's own functions including switching the circ pump to the buffer tank. The HP has 24Vac which runs to the stat so there is 24V at any switched pin. No extra power is needed other than to provide power to the Arduino. The reason for regular relays is that I do need some DPDT ones to switch off a heating circ pump on the buffer tank when the back up boiler is running (which has it's own pump). This is one of the outputs from the arduino which reads the outdoor temp at -15C and will shut off the HP in favor of the electric boiler. The programming is quite house specific and I have determined that the HP will easily heat this house down to -15C but it is not great when colder than that. At one time I did find some reed relays that would work directly with the max pin current of the arduino but they were not DPDT so i didn't buy them. It may be available. Drawing will be coming soon of the wiring.