house as heat storage

[free75degrees]

OK, so I in a way everybody uses their house as heat storage...

Let's say my tank temp is at 160*, it is early evening, I have a nice bed of coals with which I can easily get a gasification going, and I am thinking about loading the boiler with wood. Granted, I am a complete novice, but I think my strategy makes sense... I think I want to fill the boiler with enough wood to satisfy my heating demands for the evening and just barely get the tank to 180*. If I add too much wood, the boiler will idle when the tank gets to 180*, which would be bad. My thermostats are set to 70* and I am too lazy to raise the temperature when I realize I loaded too much wood.

However, I do have a nice ARM based controller a la nofossil, and I also have some nice digital temperature sensors gathering dust. Why not replace my thermostats with my temp sensors, hook them up to the controller, and write a program that basically says that if the house it at 70*, the tank is at 180*, and the boiler is still cranking out hot water, then go ahead and heat the house above the set temp of 70*? The boiler wants to burn, so why not let it? So what if the house gets a little warm, we would be effectively using the house as heat storage.

Does this sound like a good strategy?

 

[Nofossil]

It's not a bad idea, but beyond a certain point you're getting outside the comfort zone. Still, heating a couple of extra degrees will give you more time before it gets uncomfortably cool.

What I do is use two stage thermostats with remote setback. That gives me three different temperatures that I can control to from the same thermostat. When I'm heating with the wood boiler, I use the highest temperature. When I'm heating from storage, I use the second stage output, which is two degrees cooler. When I'm heating with oil, I use the setback temperature, which is five degrees cooler still. Of course, the goal is never to get to that point, and I typically stay in the two degree band between the stage one and stage two outputs.

 

[MrEd]

Were can I find out more about these "ARM controllers". I like the idea of having programmable logic for my (soon to be installed) woodboiler, solar, heat storage) setup. Are there many to choose from? or are all you folks using "the one"?

 

[free75degrees]

Were can I find out more about these "ARM controllers". I like the idea of having programmable logic for my (soon to be installed) woodboiler, solar, heat storage) setup. Are there many to choose from? or are all you folks using "the one"?

nofossil and I got ours from (broken link removed), although we got different models. I think he has a 7260 and I have a 7800. The 7800 is newer and faster, but costs a little more and the 72xx series should be plenty of power for this application. ARM refers to the type of processor used (I think ARM is a specification, not a brand name). There are other companies selling ARM based single board computers, but the Technologic Systems is probably going to be hard to beat for features and price.

These are basically blank slate computers with some programming tools pre-installed (linux, compilers, interpreters). In order to make it into a useful controller they need software. Nofossil wrote his software and I am in the process of writing mine. If you wanted to pursue this route, I would be happy to share my software with you and nofossil has posted his software on his web site, but even if you used pre-existing software it would require some pretty solid computer experience. I don't want to scare you away, but I also don't want you to get a $200-$300 paperweight. If you are still interested, we are here to help.

 

[MrEd]

Well programming doesn't scare me (thats what I did for 25+ years to make a living), but only on Windows/Intel platform. Do any controllers interface with a Windows PC? I'd love the idea of interfacing to my desktop and getting me reports that way. Do these controllers replace something else that you would need anyway? or are the controllers a new layer of technology that sits "on top off" all the other controls that are already there?

 

[Nofossil]

Well programming doesn't scare me (thats what I did for 25+ years to make a living), but only on Windows/Intel platform. Do any controllers interface with a Windows PC? I'd love the idea of interfacing to my desktop and getting me reports that way. Do these controllers replace something else that you would need anyway? or are the controllers a new layer of technology that sits "on top off" all the other controls that are already there?

There may be controllers that interface with a Windows PC, but not at the price point and power consumption of the Technologics units. The programming language of choice for these is C, and it requires a development system that's separate from the controller itself. Linux is much easier, but people have done it using a Windows development platform. In any event, you must use a cross-compiler (available free) because the Arm has a completely different instruction set than the Intel processor.

As free75degreessays, it's not at all for the faint of heart, but help is available if you choose to pursue this route. It's also important to realize that while there are lots of I/O boards available at very reasonable prices, there is some amount of soldering and light electrical design that's necessary to get sensors and relays interfaced with it.

In my case, I started out running my Arm controller 'on top' of the existing oil and wood controllers. I use failsafe relays so that if my controller dies, the system reverts to as-installed functionality. I've gradually gotten more confidence, and I'm giving my controller more responsibility as time goes on. For instance, it now controls the EKO circulator, which originally was managed by the EKO controller. Again, my failsafe relays give control back to the EKO if my Arm controller is dead.

My controller provides system level control functionality that neither boiler provides on its own. Without my controller these functions don't happen:

- Automatic selection of heat source (wood/tank/oil)
- Datalogging
- Management of two-stage thermostats and thermostat setback
- Heat Storage control (heat into and out of heat storage)
- Wood boiler inlet temperature protection
- DHW superheating
- Heat load balancing (zone priority, total heat load optimizing)
- Multispeed circulator control (match circ speed to EKO output)
- EKO preheat at fire start
- EKO heat purge after fire is out
- Oil boiler heat purge after demand is satisfied

There's probably a couple of others. None of these is necessary to have heat and hot water, and some of them could be provided in other non-controller ways. However, they add to comfort, convenience, and efficiency. And I get a kick out of figuring out how to do this sort of thing for minimum bucks.

 

[free75degrees]

There may be controllers that interface with a Windows PC, but not at the price point and power consumption of the Technologics units. The programming language of choice for these is C, and it requires a development system that's separate from the controller itself. Linux is much easier, but people have done it using a Windows development platform. In any event, you must use a cross-compiler (available free) because the Arm has a completely different instruction set than the Intel processor.

There is another option to cross-compiling. The ts7800 (not sure about the 72xx) comes with gcc, ssh, and ftp installed. I edit my source code on my windows machine using xemacs for windows, ftp the files to the ts7800, then use Putty (a free ssh client that runs on windows) to ssh on to the ts7800 to compile and run the program there.

 

[free75degrees]

Eventually I also plan on installing an irrigation system in my yard and I plan on using the ts7800 to control that as well. The NOAA offers a free webservice that supplies lots of nice weather forecast info and I think it would be really cool to have an irrigation system that would not turn on when rain is in the forecast. The weather info might also be useful to the heating controls, but I haven't quite figured out how I would use the info yet.

 

[free75degrees]

What I do is use two stage thermostats with remote setback. That gives me three different temperatures that I can control to from the same thermostat.

Yeah I guess that accomplishes the same thing. I need to look into how many btus it takes to raise my house by 1 degree to get a feel for how much heat a house holds as compared to the water tank.

 

[termite]

Anyone interested in data acquisition and control for their boiler might also want to look at some of the RS485 modules available. I am developing a system around rs485 daq modules for thermocouples, relays and I/O (digital and analog). Advantech and Nudam are two companies that manufacture these. I'm sure there are others. These modules accept acsii commands and return acsii data the pc.

So far I have the thermocouples installed and logging data. The other modules are installed and functional but not doing much right now. I hope to do all the boiler control this way by this winter.

Brief system topology:
I buried some cat5 along with the pex out to the boiler room. On the house side one twisted pair of the cat5 is connected to an rs485/network converter. The rs485/network converter is plugged into a hub under the house so I can communicate with the boiler from anywhere. On the PC I have a virtual com port set up for the converter.

The rs485 modules all reside on the same twisted pair and are individually addressable. I'm currently using Excel and VB and a freeware application called Windmill for logging and control.

I think these modules are a pretty good option for people (like me) that don't possess nofossil's programming skills but do have a wood boiler obsession.

When I have my new control system up and running I will start a thread to show it off.

 

[Nofossil]

What I do is use two stage thermostats with remote setback. That gives me three different temperatures that I can control to from the same thermostat.

Yeah I guess that accomplishes the same thing. I need to look into how many btus it takes to raise my house by 1 degree to get a feel for how much heat a house holds as compared to the water tank.

Unfortunately, the heat loss calculations don't provide an answer for that. It's pretty highly variable, depending on the volume of the house and the mass of the building materials. Safe to say that every little bit helps.

 

[Nofossil]

Anyone interested in data acquisition and control for their boiler might also want to look at some of the RS485 modules available. I am developing a system around rs485 daq modules for thermocouples, relays and I/O (digital and analog). Advantech and Nudam are two companies that manufacture these. I'm sure there are others. These modules accept acsii commands and return acsii data the pc.

So far I have the thermocouples installed and logging data. The other modules are installed and functional but not doing much right now. I hope to do all the boiler control this way by this winter.

Brief system topology:
I buried some cat5 along with the pex out to the boiler room. On the house side one twisted pair of the cat5 is connected to an rs485/network converter. The rs485/network converter is plugged into a hub under the house so I can communicate with the boiler from anywhere. On the PC I have a virtual com port set up for the converter.

The rs485 modules all reside on the same twisted pair and are individually addressable. I'm currently using Excel and VB and a freeware application called Windmill for logging and control.

I think these modules are a pretty good option for people (like me) that don't possess nofossil's programming skills but do have a wood boiler obsession.

When I have my new control system up and running I will start a thread to show it off.

I'd love to have a sandbox or sub-forum dedicated to controls and instrumentation. There are so many interesting products out there that no one can stay on top of it all.