Browse Forums Home Theatre & Automation 1 Jun 03, 2012 4:07 pm OK, I asked this general question over in the heating subforum to pretty-much silence ... so I'm wondering whether it's more of a question for the home-automation technology geeks? We're looking at how to heat the water for the under-floor heating we intend to install in our new house (not planned yet let-alone built). It looks like we might run into problems using the vacuum-tubes to directly heat the water, as we've got no pool or any expanses of concrete etc to absorb the unwanted heat in summer ... so I was wondering about smartly managing how to feed power to a heat-pump system from photovoltaics or off-peak and with full-rate power as a backup. Basically, there must be a way to configure it to use the juice generated by a photovoltaic array as the primary source, store heat in the floor tiles/screed, use a temp-sensor to decide whether it needs to switch over to mains power or off-peak (depending on the timing) or whether it can wait 'til the next day (or 'till off-peak becomes available) before it starts re-heating the water & pumping it 'round again. The logic required wouldn't be super-complicated, although you'd need to be a bit of an under-floor heating expert to set whatever the thresholds would be (ie. to program a controller). I asked a few under-floor heating people at the home-show, and they acted rather confused; eg. saying it wouldn't be possible because photovoltaics would only be generating ~12V (and seemingly ignoring how OTHER appliances are able to use the electricity you generate due to the inverter/switching systems that only feed the excess your house doesn't use back to the grid). Additionally - it'd be a neat trick if you could somehow switch all your houses' electricity usage over to off-peak when it became available, and back to full-price when that off-peak circuit turns off. But there're probably rules against that. So anyone know of home-automation products that're able to switch between power supplies for things like airconditioning, heating, etc? Or do any of the "smart house" services/experts know about how to implement this sort of thing? Re: Using home automation products to handle heating & power 2Jun 03, 2012 8:39 pm Hi I think you can probably simplify things by just connecting the solar panels to the grid as usual. Assuming that you are on a net tariff, you will either use your solar power or get paid for the excess that you export. If you try an use a system that connects it directly to your heating system you get the same result but much more complexity (plus the fact that inverters shut down if they don't detect incoming AC voltage as a safety precaution). You could operate a grid-disconnected solar system but then you waste the power when you don't need it. If you eliminate solar then you are just left with peak/off-peak switching. You could automate this with a change-over contactor and a sensor connected to the off-peak supply that told the system when off-peak was available. I would then have a user input that selected whether you only wanted to use off-peak power or whether you wanted to use peak and off-peak. You would then use the standard system thermostats to control heating and pumping. For what it's worth, in-laws had off peak in-slab hydronic heating in their house in the Snowy Mountains and they never had a problem with only using off-peak power. And yes, there are regulations on which loads can be connected to off-peak. Paul Re: Using home automation products to handle heating & power 3Jun 03, 2012 8:51 pm Sorry, I probably complicated the description in order to try & avoid over-complicating it. I assumed a net tariff, but some form of input to the heating timer/controller so the system "knows" when it's generating enough electricity such that you're not chewing through mega$ electrons when you could wait until off-peak cuts-in that evening. Of course my preference to all of this would be just to install vacuum-tube solar for the hydronic heating; but I believe we'd have problems in dissipating heat in summer (off to the heating/insulation thread to ask about that ...). With respect to your suggestions; I can see the logic behind what you say, but have zero idea of how you'd go about implementing any of it. Is this a "buy a CBUS system off someone and get some input and output devices programmed" solution? Re: Using home automation products to handle heating & power 4Jun 03, 2012 10:28 pm You could certainly do it with C-Bus, but it would be expensive. If you feel up to a bit of DIY then you could investigate boards like Arduino to host the logic. Actually detecting that you have a surplus of PV power would be tricky, and could change moment by moment as cloud cover and other household demand vary. Paul Re: Using home automation products to handle heating & power 5Jun 27, 2012 10:30 pm I think you could do this pretty easily (relatively - depends on your knowledge) using an HAI OmniPro 2. I have my HAI OmniPro system controlling my hyrdronic heating in the house, and also plan to put in a serial interface to control 6 zones of AC cooling in the house from my iPhone/iPad. The central wall unit I have controls the heating for the whole house in the winter. You can quite easily program macros to automate things. For example, I can tell my system to trigger a relay to open the garage door when a button I've configured is pressed, or when a code is received over serial input from the garage door keypad. My system also has an outdoor temperature sensor. In theory you could easily listen to the output from the PV cell and trigger a relay to cutover to the PV supply when there is adequate current flowing through. (its not much different than a macro to close the shades on a hot day). If the current drops below a certain level you could have the PV cell fail over to a mains supply. There's rules here in oz about the type of wiring you can DIY, so be careful that you know where you are doing - best if you have a sparky friend who can review & sign off on your work. my house blog: http://sugarloafdrivebuild.blogspot.com/ Building Standards; Getting It Right! 1. optional, you can but normally just use the earth from the main switch board 2. should be enough but the distance determines voltage drop - sparky should work it… 1 28821 Black on light wood does look good. Not sure if it will be as long lasting as a steel finish? 6 6354 Get some long brass machine screws and bolt right through the gate and put brass acorn nuts and washers on the other side. It will never come off 1 9083 |