Designing a General Purpose Heat Pump Controller

Hey guys I've been a lurker to these forums for a bit. I don't know anything about the technical parts about hvac stuff but i do know micro controllers, and arduinos. A arduino can definitely handle a controller for this application. If there is any doubt you can head over (diydrones dot com), you'll see that they wrote a complete Auto Pilot for Rc planes. its fully featured and from a computational standpoint i think it would be doing a lot more than this controller.

plus the Arduino has waaaaay more support(software, hardware). if you had all the parts you could prob have something up and running in the time it would take you to get a cross compiler set up for another Microcontroller

[Ormston]

Originally Posted by AC_Hacker

When communicating with the LCD, via I2C, you need to include the LCD library and also the I2C library, right??

Only library's to include are

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

Simple "Hello World" sketch compiles to 7,808 bytes with I2C or 5,882 bytes with standard connections.

I think the difference is the inclusion of the Wire.h needed to use I2C

Steve

[AC_Hacker]

Originally Posted by AC_Hacker

OK, I reluctantly ordered two flow sensors, and they arrived today.

I learned something today that may be of greater interest to N. American readers that others...

I went to a hardware store to explore my options when I integrate this 1" diameter flow sensor into my heat pump design.

I found that a 1" NPT female thread adapter will not thread all the way on. In fact, one PVC adapter only went on < one full turn. Another, a brass adapter, went on about 2.5 turns before stopping.

Then I took a close look at the threads and noticed that they are not tapered, the way NPT female threads are.

This means that it is a British Standard Pipe (BSP)thread (BSPP (British Standard Parallel Pipe, to be exact).

Both British standard and National pipe thread standards specify a thread taper of 1:16.

But as randen found out, the pitch of BSP and NPT are ever so slightly different.

However, I did find this INTERESTING_READING_HERE:

Threads
Here's a little primer on threads. You may find it useful.
NPT (national pipe thread) is the standard pipe thread in the USA. FPT (FMPT) and MPT (MNPT) simply denote female or male. Virtually all the NPT threads that you will find are 'tapered'.

BSPT (British Standard Pipe Tapered) or BSPP (British Standard Pipe Parallel) are the common pipe threads used in England and also in Europe. 'Metric' is a broadly used term to describe not only these threads but also other 'metric' threads used in Europe. The threads on our Italian equipment are BSPP although you will also see them called GAS. For example the spigots on small Italian tanks are BSPP.

Fittings with BSPP threads as well as adapters to NPT are available at places like McMaster-Carr. The bad news is that these adapters are quite expensive. The good news is that you rarely need an adapter because NPT fittings work just fine with BSPP or BSPT in almost all applications for winemaking or brewing. [You may read that you should not mix BSPP with BSPT or with NPT. You can ignore this warning if you are not using high pressure.]

The good news is that you can often mix NPT fittings (which are generally inexpensive) with BSPP or BSPT. For example, 1/2"NPT fittings work just fine with 1/2" BSPP (the thread on the small tanks). In this case, you are mixing tapered with parallel, so use teflon tape. The same is true for 1" NPT with 1" BSPP (the large tanks or the inlet/output of the small self-priming pump).

Tapered vs Parallel Threads.
If you look at male NPT threads, you will notice the diameter of the fitting is tapered, narrowest at the end. Parallel threads do not have a taper. The most important thing to understand is that tapered threads form a seal differently than parallel threads. Fittings with tapered threads seal on the threads. Use teflon tape on these type of threads to help make a good seal. On the other hand, parallel threads can either seal against a gasket or oring--do not use teflon tape--or on the threads--use Teflon tape if you want to seal on the threads. Garden hose thread GHT is another example of a parallel thread--the seal is made against a gasket---don't use Teflon tape.

Gas regulators connect to cylinders thru parallel threads. Do not use teflon tape.

Why does NPT work with BSPP?
Take as an example 1/2"NPT vs 1/2"BSPP. Both have 14 threads per inch so they match up quite well. The primary difference is in the pitch (angle of the thread) which is 60° vs 55°. Use a little teflon tape and they screw together and seal just fine. 3/4"NPT works well with 3/4" BSPP as well since the threads per inch is the same, 14.

"...almost all applications for winemaking or brewing..."

Hmmm......... but will they hold up for several decades when used for the purpose of heating a house???

If anyone in the Euro-Zone is reading this, do you know of inexpensive (maybe plastic) BSPP-to-NPT adapters or BSPP-to-barb fitting??

Best,

-AC_Hacker

[Mikesolar]

I've been using BSPP fittings for years on heat exchangers, boilers, and just about any European solar fittings, etc, etc. Search for DIN 16, 20, 25, 32, 40, 50 etc union nuts. They look just like the brass female fittings on washing machine hoses (but with a different thread) and are available from many Euro online dudes. Also they are all designed to be used with a sealing fibre washer. All the Euro pumps have this fitting too. Works so well I seldom use t-tape or NPT fittings unless I have to.

[AC_Hacker]

Originally Posted by Mikesolar

I've been using BSPP fittings for years on heat exchangers, boilers, and just about any European solar fittings, etc, etc.

Can you be a bit more specific?

Do you know of a supplier that has had what I am looking for (1" BSPP-to-1" NPT adapter)?

I'm unsure what "DIN is, let alone the 16, 20, 25, 32, 40, 50 etc. union nuts" might mean.

-AC

[Mikesolar]

Originally Posted by AC_Hacker

Can you be a bit more specific?

Do you know of a supplier that has had what I am looking for (1" BSPP-to-1" NPT adapter)?

I'm unsure what "DIN is, let alone the 16, 20, 25, 32, 40, 50 etc. union nuts" might mean.

-AC

The benefits of being Canadian, I suppose. We went officially metric in the 70s, (as America was supposed to also do, but didn't for some reason), so many of us are able to flip back and forth from metric to imperial.

DIN is the German industrial standard and you will see in on a lot of things but what the Germans don't like to admit is that much of it was based on the British standards, haha.

The metric pipe sizing is always OD of the tube and then wall thickness and the standards are as I noted above, 12, 15, 16, 18, 20, 25 etc. Common ones for us in the heating and solar world would be 16 (5/8"), 20 (3/4"), 25 (1"), 32 (1.25"), 40 (1.5") and 50 (2").

For example, if you look at any European grundfos pump, they come typically in sizes DIN25 (many solar pumps), DIN 32 and DIN 40 (most heating pumps). All European boiler connections are like this too (DIN 20 connections)

They do NOT use pipe dope or t-tape on these fittings as they are all unions with a gasket like you find on some antiscald valves (Honeywell and Apollo for sure). Any heating component that has a union connection is using a metric thread. They were all adopted from European norms.

I don't know of any adapters like what you are looking for but they may exist. More common is to find the female "nut" with the "tail piece" that is made for either metric or imperial pipe sizes, then you can solder to whatever size pipe you want and it is always removable without cutting the pipe.

There are also some corrugated stainless steel tubing that we use for solar and available from solar suppliers (and others) that have this thread on either end for easy connection. They usually come with an EPDM gasket.

I will ask my euro buddies if they have seen metric to imp threaded bushings but I doubt it. Viessmann used to take a metric brass union and re-tap an NPT thread for the north american market but gave up on that years ago. I may still have some but to me, anything like that is just bulky and unnecessary.

I used to make all my adapters from brass to go with the standard nuts on my lathe as needed so I have a selection of stupid, oddball fittings in the shop. When I see the trouble many eco-renovators are having putting water lines on the HX, I think Randen should provide a service making custom ones (don't shoot me dude, haha)

[Acuario]

Originally Posted by AC_Hacker

In considering NiHaoMike's comment about including two independent RS485 ports... Do we actually require these on our most basic controller? Are two RS485 vital to functioning? How will they be used? Can someone explain to me why one RS-232 would not be sufficient?

Hi All,
I've not been around for a while, work, getting married, more work and so have read through this topic with interest.

I agree with NiHaoMike's comments about pic v Arduino, many more versions of pics to chose from and many come on useful pre-built development boards that contain lots of extra goodies such as rtc's, eeproms, led/lcd drivers etc...

One very important point to be aware of when selecting the device you are going to use (Arduino vs pic) is the amount of memory available for the code. Unless you are writing it in assembler then you are likely to find it rapidly disappears as you add more functions, i.e. comms routines, keyboard routines, lcd, sensors, relays, watchdog etc... as compilers are not the most optimized beasts in the world.

So, why not RS232? Basically it's 1 to 1 so you need a channel for each connected device, with RS485 you can connect multiple devices to the same bus. There are ready built modules available very cheaply on ebay. I'm not sure why you would need 2 x RS485's though as with a properly designed comms protocol 1 should be sufficient. I use the same RS485 to control 2 heatpump slave controllers and a solar hot wáter system from the same central controller.

A comment about restart; there are several scenarios that can result in a restart; controller software failure (should be rebooted using a watchdog timer), power outage, user switches it off then back on in a short time etc..
So the delay timer that was suggested will work but that means every time the unit is started there is an x minute delay. This is ok for a restart but not for the initial startup from cold. This is why you would need the RTC as part of the software main loop should involve storing the current time. When the software is reset it can read and compare to determine if it has recently been run or not and then take the appropriate action.

An RTC is also useful although not essential in reverse cycle defrost and (should you add a centralised controller) for programming the unit to work during certain hours.

From my experience and re the discussion re DS18B20 vs thermistor/LM35 etc. I used the 18B20 BUT regret having done so (I will be changing them at some point). I'm not 100% sure why but they seem to be unreliable in my applications, possibly due to power line or environmental noise (EMC), I have also found that the changes in timing cause problems when the devices are very hot (as they are in the solar wáter panels).

A suggestion on schematic and PCB design tools, I use KiKad for both, it's free and has a pretty active developer fórum.

Acuario

[buffalobillpatrick]

I see that my "stupid questions" aggrivate jeff5may. TS

I don't know much about Heat Pumps & thus the requirements.

I do have MY following HP controller Arduino Uno programmed, debuged, & running solid.



/************************************************** ******
*
* ARDUINO SLAVE HP Controller.
*
* The MASTER Heating System controller powers this ARDUINO
* ON or OFF as Heat Pump is needed.
*
* This code controls 2 Relays and reads/displays 12x 10K NTC Thermisters
* and 1x MQ-2 GAS sensor
*
* IN SETUP:
*
* STEP #1
* Tells HEAT_SYS_MASTER Arduino that SLAVE "IS NOT HUNG" via ALIVE_RLY_R1
*
* STEP #2
* HP is started after a delay, via HP_RLY_R2
*
* In the Main Loop, 12x temperature sensors
* are read & displayed, continuously
* Takes 63.25 sec. / loop
*
* In the custom_delay function,
* The Source OUT water tempereature and the MQ-2 GAS Sensor are checked.
* If either are out of range, then code turns off both relays,
* & hangs until the MASTER powers OFF this SLAVE Arduino
*
* Change History:
* 07/30/14 Changed POT Heater over to hardware control &
* implemented new sample averaging method.
* 08/02/14 Added Custom_delay & MQ-2 GAS sensor
*
************************************************** ******/

[AC_Hacker]

Originally Posted by buffalobillpatrick

I see that my "stupid questions" aggrivate jeff5may. TS

I don't know much about Heat Pumps & thus the requirements.

I do have MY following HP controller Arduino Uno programmed, debuged, & running solid.

/************************************************** ******
*
* ARDUINO SLAVE HP Controller.
*
* The MASTER Heating System controller powers this ARDUINO
* ON or OFF as Heat Pump is needed.
*
* This code controls 3 Relays and reads/displays 16x 10K NTC Thermisters
*
* IN SETUP:
*
* STEP #1
* The Compressor is Heated up to required temperature via COMP_HEATER_RLY_R1
*
* STEP #2
* The Source & Load water pumps are started via WATER_PUMPS_RLY_R2
* after a delay, HP_SOURCE_IN water temp. is checked for being warm enough
* If not, the code turns off all relays & hangs #1
* doing nothing until the MASTER powers this SLAVE OFF
*
* STEP #3
* COMPRESSOR_RLY_R3
* The Compressor is started after a delay, in case of power glitch
*
*
* In the Main Loop, 16x temperature sensors are read & displayed over&over
*
* If the Source OUT water tempereatur drops below safe Temp.
* then code turns off all relays & hangs #2
* doing nothing until the MASTER powers this SLAVE OFF
************************************************** ******/

Great!

Where is the code?

-AC

[jeff5may]

Originally Posted by buffalobillpatrick

I see that my "stupid questions" aggrivate jeff5may. TS

I don't know much about Heat Pumps & thus the requirements.

I do have MY following HP controller Arduino Uno programmed, debuged, & running solid.

/************************************************** ******
*
* ARDUINO SLAVE HP Controller.
*
* The MASTER Heating System controller powers this ARDUINO
* ON or OFF as Heat Pump is needed.
*
* This code controls 3 Relays and reads/displays 16x 10K NTC Thermisters
*
* IN SETUP:
*
* STEP #1
* The Compressor is Heated up to required temperature via COMP_HEATER_RLY_R1
*
* STEP #2
* The Source & Load water pumps are started via WATER_PUMPS_RLY_R2
* after a delay, HP_SOURCE_IN water temp. is checked for being warm enough
* If not, the code turns off all relays & hangs #1
* doing nothing until the MASTER powers this SLAVE OFF
*
* STEP #3
* COMPRESSOR_RLY_R3
* The Compressor is started after a delay, in case of power glitch
*
*
* In the Main Loop, 16x temperature sensors are read & displayed over&over
*
* If the Source OUT water tempereatur drops below safe Temp.
* then code turns off all relays & hangs #2
* doing nothing until the MASTER powers this SLAVE OFF
************************************************** ******/

I don't ever remember calling anyone stupid in these forums. What fascinates me is I don't know if you are accusing me of being smart or just showing off.

I think it's great that you have developed something that works for you. Please post a well commented source code so others can steal your genius. If they have the same needs as you, and a similar system, it might work.

Sorry that I haven't posted any code yet, but I'm trying to make something here that isn't a one-trick pony. There's plenty of that widely available today for sale cheap enough. I'm trying to make something universal, where anyone can go buy an uno, a relay module, an lcd button shield, and have what they need to start hacking. Upload the sketch, set parameters via lcd shield, run like magic. Set what you want at will.

So far, the unit will work as follows:

1. mode 1
   

   heating thermostat
   cooling thermostat
   auto change-over thermostat
   relays control o,w,y,g as in standard HVAC
   thermometer is either ds1820 or thermistor, autodetected by uno
   config and setpoint saved in eeprom in case of reset or pwr failure

   mode 2
   

   slave device, no thermostat
   relays control compressor,reversing valve,crank htr/indoor fan or pump,outdoor fan/pump
   hard-wired thermistor sensors for defrost, ambient temp reading
   time + temp defrost cycle
   compressor lockout timer

   mode 3
   

   all of the above, dependent on wise usage of pins
   self- contained, standalone unit
   can also accept heating and cooling calls from elsewhere.

I'm working on the sketch in my free time and learning a whole lot in the process. I'm trying not to call or write any custom libraries, which makes writing this sketch much more difficult. However, it will make further development that much easier later. Plus, any casual user will be able to find the source file, modify it if they want, compile it with whatever they want, and stick it in their device (which may or may not be an uno board) and have quick, instant operation. Once I have something that doesn't run out of memory, that works like it should,I will post the entire source so everyone can download it and stick it straight into their unos. Meanwhile, I MAY discuss abstracts and methods with you all for advice or direction.

I'm glad others are working in parallel with me on their own adaptations of this project. I see this basic stamp growing into a full featured device, like Takyka has developed, without a huge amount of labor or expense. I wouldn't expect it to cost thousands of dollars like a commercial product would, or take years to develop. Keep the show and tell coming, and please keep us updated on your progress. This stuff is fun!