Hi,
has anyone used hubitat to defrost driveway? I would need a humidity and temp sensor to install to ground. Ground installation would be best for detecting the moisture on ground. Air moisture would be inaccurate. The sensor should be able to stay in rain.
Br.
Samuel
Nothing to add, but I wish I had that problem. Sometimes my slightly hilly driveway gets so icy that without the fine Nokian/Nordman studded tires, I couldn't get leave the house. One time, without the studded tires, I had to put some sand on the driveway. Pretty noisy though.
I wonder if a leak detector sensor could work? Something where the pins are on a wire to the detector which could be in the garage. Maybe mount it a small distance above the driveway surface. Ice would set it off, I would think. If it was raining so much that the conductors were bridged, the temperature would tell the system that it's likely rain and not ice.
I found this. Together with separate temp sensors those might work.
For defrosting I have casted ethanol pipes to concrete, which are heated with heat pump. Thres's heat exchanger between water and ethanol circuit.
Hubitat needs to manage with pumps, valves and valve for mixing cold ethanol so that the heat exchanger will not freeze.
Pumps are always in 230V, so only running rules must be made. There's also actutors for separate defroting circuits. I think easiest way to open separate circuits in defrosting should be 230v actuators and zigbee relays.
I think the hardest part will be mixing the water.
I think that is geared towards liquid water. I still like my idea. 
I would make sure you think carefully about safety. Depending on Hubitat, Zigbee, relays of dubious quality, etc...anything could happen.
Did the system come with controls, or are you doing this totally by yourself? Interesting project. Just curious...is the heat pump outside the house? You would think it gets cold enough there where the heat pump would be straining. Then again, it only has to get the ethanol somewhat above freezing, not warm enough to heat a building.
The heat pump is heating the water for heating, hot water and defrosting. There's separate tanks for hot water and heating. Heating water is used to heat heat exchanger to heat defrosting ethanol. So ethanol temperateure is mixed just enough to defrost the driveway. The heating water will still be as warm as needed to heat the house. If automation fails pumps for warm water will run and defrosting pumps will turn off, so ethanol circuit won't be able to freeze the heat exchanger.
@SamuelS Maybe not an ambient temp sensor but maybe a probe fitted into the concrete/blacktop of your driveway. So that when the concrete/blacktop hit's 32f/0 cel that it kicks on? You wouldn't have to worry about humidity...
Who wants it kicking on if there's no ice on the driveway?
Fair enough.... just a thought
Not something we need to think about too much down my way...
But my take on it would be first working out how to enable whatever kind of defrosting mechanism you want to utilise.... once you can trigger of that, then you can start to consider how to detect when to enact that automation.
Yeah. Now I'm just extrapolating, but, I think he's already got a heat pump for the house and domestic hot water. He's added pipes (plastic, like an ice skating rink, in reverse) in the driveway surface already. He want to tie it into his existing system. He's going to use a water(inside house)/ethanol heat exchanger of some sort to heat the ethanol just enough to melt the ice.
He's concerned about frost forming on the heat exchanger. I wonder if this is really a concern, depending on the type of exchanger. If a coil could be placed in the domestic hot water tank, the heat pump would automatically come on and heat up the water. If it was a shell and tube arrangement, I'd guess you'd have to put a sensor in the shell to make sure the water temperature didn't get close to freezing-run heat pump water circulation and if that wasn't sufficient, shut off driveway pump circulation.
I've thought about leaving my house in the winter and it has hot water heating, and what if the heat or power goes off? It's been suggested to me to substitute an ethanol mixture instead of water as the working fluid. I think that would be expensive, since I have a 100 gal buffer tank, plus boiler + distribution pipe. Plus, I think it's somewhat less efficient at heat transfer vs water.
Sounds like the easier option is to move down under... 
Yeah. For me, it would be so luxurious to have a heated driveway.
I wonder if this arrangement with the heat pump would be enough to keep snow from accumulating?
That would be great.
Maybe expensive to run, but hence...luxurious!
edit: You'd still have to think about the melted water...where would that flow, and for how long before it refroze? Would you need heat tracing in pipes? Above my pay grade.
In Northern Oz that come's as standard... though I expect it also comes built-in for southerners in the States as well....
While I hope to get ther one day... Central America would want to be good.....
There's 12kW heating melting power in driveway. Two 6kw circuits. Both circuits have separate valves so they can be controlled individually. I will not be defrosting the driveway in lower than -7C(will get more accurate after testing), because it rarely snows at those temperatures and air will be very dry.
So when temperature rises from -7 the ethanol can be even colder than that. If the pump turns on and there's no mixing valve, I could freeze the heat exchanger if the hot water is not running fast enough in other side of exchanger. That's why there should also be automation for water mixture. It's not for the situations when climate gets colde but vice versa, because then the ethanol can be much colder that freezing temperature of water.
Because of the heat pump the 12kw of deforsting power will take approximately 4kw in temperatures where it's used. So the luxury will not cost a fortune as it would be with electric heating. The other 6kw circuit it under a roof, so it will be used rarely. So in the end I would say, most of the time running it would take just 2kw of power to keep driveway defrosted.
My 'retirement project' a few years ago was putting in a pellet boiler. My memory is fading, but I know I have at least one mixing valve for boiler protection, so that water won't be circulating through the boiler if it is too cold. Totally mechanical.
Why not put one of those (in front?) of the water/ethanol heat exchanger? You'd have to get a low temperature mixing valve, compared with a boiler. But, then the temperature would never be allowed to get below a certain temperature, like 32F.
Then again, you mentioned mixing valve, so maybe there's a reason you can't use one.
2kw is like two coffeemakers. I should've made this my retirement project rather than the pellet boiler, which I hardly use.
I've tested the system without automation few times, just bu operating valves and turning on pumps by hand. The circulation pump seems to do the job preventing the freezing cold return liquid. The shunt valve can be closed when the pump is used. Most efficient system would be running the circulation pump only when the system is shut down.
To get the shunt valve working I would need at least 4 temp sensors. I just ordered potential free zigbee relays to use the valves and pumps. I would also need 0-10v dimmer switches to use the shunt valve opening.
With those I could have on/off contolled system. If I get that running, it would be easy to attach the on/off to operate by humidity and temp switch. But by hand, the driveway defrosts well, so hardware is working.
This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.
Download the Hubitat app
