Once an exotic component, solid state heat pumps or Peltier devices are now pretty mainstream. The idea is simple: put electricity through a Peltier device and one side gets hot while the other side gets cold. [DroneBot] recently posted a video showing how these cool — really cool — devices work. You can see the video, below.
Many things in physics are reversible, and the Peltier is no exception. The device is actually a form of thermocouple, and in a thermocouple a temperature difference causes a voltage difference. This is known as the Seebeck effect as opposed to the Peltier effect in which current flowing between voltage differences causes a temperature difference. It was known for many years, but wasn’t very practical until modern semiconductor materials arrived.
The best type of power outage is no power outage, but they will inevitably happen. When they do, a hacker with a house full of stuff and a head full of ideas is often the person of the hour. Or the day, or perhaps the week, should the outage last long past the fun little adventure phase and become a nuisance or even an outright emergency.
Such was the position that [FFcossag] found himself in at the beginning of January, when a freak storm knocked out power to his community on a remote island in the middle of the Baltic Sea. [FFcossag] documented his attempts to survive the eight-day outage in vlog form, and although each entry is fairly long, there’s a lot to be learned from his ordeal. His main asset was a wood cook stove in the basement of the house, which served as his heat source. He used a car radiator and a small water pump to get some heat upstairs – a battery bank provided the power for that, at least for a while. The system evolved over the outage and became surprisingly good at keeping the upstairs warm.
The power eventually came back on, but to add insult to injury, almost as soon as it did, the ground-source heat pump in the house went on the fritz. A little sleuthing revealed an open power resistor in the heat pump control panel, but without a replacement on hand, [FFcossag] improvised. Parts from a 30-year-old TV transmitter were close at hand, including a nice handful of power resistors. A small parallel network gave the correct value and the heat pump came back online.
All in all, it was a long, cold week for [FFcossag], but he probably fared better than his neighbors. Want to be as prepared for your next outage? Check out [Jenny]’s comprehensive guide.
If you buy a used heat pump that was made in China and try to use it in Northern Europe, there are bound to be issues. If said heat pump ends up encased in a block of ice that renders it ineffective, you’ve got two choices: give up and buy a proper heater, or hack a new ice-busting brain board into the heat pump and get back to life.
[Evalds] chose the latter course, obviously, and in the process he gives us a pretty good look at how heat pumps work and how to overcome their deficiencies. In [Evalds]’ Latvia, winters can be both cold and humid, which can worsen an inherent problem with air-coupled heat pumps: they tend to ice up. As the outside coil is cooled to pick up as much heat as possible from the outside air, water vapor condenses out on the coils and freezes. Most heat pumps account for this by occasionally running in reverse, heating the outdoor coils to clear the ice buildup. [Evalds]’ had nothing more than a simple timer to kick off the defrost cycle, and it wasn’t keeping up with the Latvian winter. An Arduino replaced the OEM controller, and wired up to temperature sensors and an IR sensor that watches for ice buildup on the lower part of the coil, the heat pump is now much better behaved.
Of course it wasn’t as smooth as all that — [Evalds] has some hoops to jump through, including EMI problems and a dodgy Arduino clone. But he stuck with it and brought the heat pump back online, likely at far less expense than HVAC techs would charge for a service call.
Like so many other home appliances, it’s likely that even your air conditioner has a serial interface buried inside it. If you’re wondering why, it’s because virtually every microcontroller on the planet has a UART built in, and it’s highly useful for debugging during the development process, so it makes sense to use it. Thus, it was only a matter of time before we saw a hacked airconditioner controlled by a Raspberry Pi.
[Hadley] was growing frustrated with the IR remote for his Mitsubishi air conditioner; it can issue commands, but it’s a one way interface – there’s no feedback on current status or whether commands are received, other then the occasional beep or two. Deciding there had to be a better way, [Hadley] grabbed a Saleae Logic Analyser and started probing around, determining that the unit spoke 5 V TTL at 2400 bps with even parity. The next step was to start talking back.
[Ralph Doncaster] has a geothermal heat pump which is responsible for providing heat for his home. He’s been looking into some hacks that would make it more efficient and decided that the freon (R-22) needed to be tweaked. Some would say the stuff is bad for the environment, so he decided to go a different route. He replaced the Freon with propane, using this rig to make the fuel-grade propane more like cooling-grade propane called r-290.
He purchased the gauge set which is used whenever a technician services an A/C system (but you can also see it in this other A/C propane hack). That’s important because it’s responsible for making sure the old coolant is recaptured (his hose failure nixed this part of the plan) and the new coolant goes where it should at the correct pressure. But before dumping in propane from the local hardware store he needs to dry it out. Fuel-grade propane can have moisture in it, which can be bad for the cooling system. He bought a drier device, the grey bulb seen above, and soldered it on one end to a propane torch fitting and to a valve connection on the other. Now he could remove moisture as he pressurized the system.
Everything is working again, and the cooling side of the system gets much colder. He plans to do more testing as time goes by.
The heat pump which cools [Chris LeBlanc’s] home lacks the sort of control he was looking for. It’s just got a timer, which switches it off automatically. He wanted to the ability to schedule the cooling cycle like you would with a thermostat-driven arrangement. He ended up build his own controller to automate the cooling process.
The heat pump came with an IR remote control which provides the access point for the project. [Chris] set out to emulate the remote protocol which saved him the trouble of having to crack open the unit and wire in a controller. He went with the IR Toy from Dangerous Prototypes as this device is able to record and transmit IR signals — it’s basically a universal remote for your USB port. His Raspberry Pi, seen to the left, controls the system. It’s connected to the red IR Toy board via a USB hub which is used to interface a WiFi dongle as well. The system works alongside Google Calendar to allow [Chris] to schedule his home’s cooling just by adding an appointment. A Python script queries the calendar, then selects and sends the appropriate IR command. He shows off the build in the clip after the break.