Custom Cut Pinwheel Makes a Useful HVAC Duct Flow Meter

Everyone is familiar with pinwheels, and few of us haven’t crafted one from a square of paper, a stick, and a pin. Pinwheels are pretty optimized from a design standpoint, and are so cheap and easy to build that putting a pinwheel to work as an HVAC duct flow meter seems like a great idea.

Great in theory, perhaps, but as [ItMightBeWorse] found out, a homemade pinwheel is far from an ideal anemometer. His experiments in air duct flow measurements, which previously delved into ultrasonic flow measurement, led him to try mechanical means. That calls for some kind of turbine producing a signal proportional to air flow, but a first attempt at using a computer fan with brushless DC motor failed when a gentle airflow couldn’t overcome the drag introduced by the rotor magnets. But a simple pinwheel, custom cut from patterns scaled down from a toy, proved to be just the thing. A reflective optosensor counts revolutions as the turbine spins in an HVAC duct, and with a little calibration the rig produces good results. The limitations are obvious: duct turbulence, flimsy construction, and poor bearings. But for a quick and dirty measurement, it’s not bad.

Looking for an outdoor anemometer rather than an HVAC flow meter? We’ve got one made from an old electric motor, or a crazy-accurate ultrasonic unit.

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Measuring Air Flow with Ultrasonic Sensors

Measuring air flow in an HVAC duct can be a tricky business. Paddle wheel and turbine flow meters introduce not only resistance but maintenance issue due to accumulated dust and debris. Being able to measure ducted airflow cheaply and non-intrusively, like with this ultrasonic flow meter, could be a big deal for DIY projects and the trades in general.

The principle behind the sensor [ItMightBeWorse] is working on is nothing new. He discovered a paper from 2015 that describes the method that measures the change in time-of-flight of an ultrasonic pulse across a moving stream of air in a duct. It’s another one of those “Why didn’t I think of that?” things that makes perfect sense in theory, but takes some engineering to turn into a functional sensor. [ItMightBeWorse] is using readily available HC-SR04 sensor boards and has already done a proof-of-concept build. He’s getting real numbers back and getting close to a sensor that will go into an HVAC automation project. The video below shows his progress to date and hints at a follow-up video with more results soon.

Here’s wishing [ItMightBeWorse] the best of luck with his build. But if things go sideways, he might look to our post-mortem of a failed magnetic flow meter for inspiration.

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Heat Pump Gets Brain Transplant; Such is Life in Latvia

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.

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A little too icy.

[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.

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Hackerspace Takes Fume Extraction Seriously

At first we laughed at the ridiculously over-the-top fume extraction system this hackerspace built for itself. Then we thought about seriously questionable donation rolls of solder some of the members managed to find and bring in. The kind of roll where the local greybeard assures you that a Californian State Trooper has permission to shoot you if you try to take it into the state, but damn does it solder well. They may be onto something is all we’re saying. But on a serious note, for a communal space like this one, a great air quality plan makes the place a lot more pleasant, if not safer at the same time.

The build uses a regular boost fan for its main suction and pulls the fumes out to a place the members aren’t. Knowing hackerspaces that could be anything from an empty alley to vents on the building’s roof. It’s actually an interesting challenge to solve in a rented space (please share your own solutions for “daylighting” to the outside in the comments).

The frame is made from ducting and dryer hose. Since there aren’t really fittings for this. Most of the joints were designed in OpenSCAD and 3D printed. At each end of the tube a computer fan provides another little boost of airflow. We like the stands to position each end of the hose at the fume source. All of it is powered by a distribution box of their own making with the juice being fed with repurposed Ethernet cables to the fans at the ends of the hose.

It’s a nice build and likely extended the life of a few of the more electronically active members in the space. Especially if the retired radio enthusiasts decide to do their fifty year anniversary garage cleaning and gift upon the space their findings.

Arduino Replaces Bad AC Thermostat, Hacker Stays Cool

Most of North America has been locked in a record-setting heat wave for the last two weeks, and cheap window AC units are flying out of the local big-box stores. Not all of these discount units undergo rigorous QC before sailing across the Pacific, though, and a few wonky thermostats are sure to get through. But with a little sweat-equity you can fix it with this Arduino thermostat and temperature display.

We’ll stipulate that an Arduino may be overkill for this application and that microcontrollers don’t belong in every project. But if it’s what you’ve got on hand, and you’re sick of waking up in a pool of sweat, then it’s a perfectly acceptable solution. It looks like [Engineering Nonsense] got lucky and had a unit with a low-current power switch, allowing him to use a small relay to control the AC. The control algorithm is simple enough – accept a setpoint from an encoder, read the temperature sensor, and turn the AC on or off accordingly. Setpoint and current temperature are displayed on an OLED screen. One improvement we’d suggest is adding a three-minute delay between power cycles like the faceplate of the AC states.

This project bears some resemblance to this Arduino-controlled AC, but it seems more hackish to us. And that’s a good thing – hackers have to keep cool somehow.

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HVAC techs – Hackers who make house calls

It’s been said that hackers are enamored with complex networks. In the 60s and 70s, the telephone network was the biggest around, singing a siren song to an entire generation of blue-boxing phone phreaks. I started a bit closer to the house. As a child I was fascinated by the heating system in the basement of our home: a network of pipes with a giant boiler in the middle. It knew when to come on to provide heat, and when to kick on for hot water. I spent hours charting the piping and electrical inputs and outputs, trying to understand how everything worked. My parents still tell stories of how I would ask to inspect the neighbors heating systems. I even pestered the maintenance staff at my nursery school until they finally took me down to see the monstrous steam boiler which kept the building warm.

My family was sure I would grow up to be a Heating Ventilation and Air Conditioning (HVAC) tech. As it turned out, electronics and embedded systems were my calling. They may not have been too far from the truth though, as these days I find myself designing systems for a major manufacturer of boiler controls and thermostats.

Recently a house hunt led me to do some HVAC research on the web. What I found is that HVAC techs have created a great community on the internet. Tradesmen and women from all over the world share stories, pictures, and videos on websites such as HVAC-Talk and HeatingHelp.

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This Little Amiga Still Runs School District’s HVAC

It’s the rare tech worker that manages a decade in any one job these days – employee loyalty is just so 1980s. But when you started your career in that fabled age, some of the cultural values might have rubbed off on you. Apparently that’s the case for an Amiga 2000 that’s been on the job since the late ’80s, keeping the heat and AC running at Grand Rapids Public Schools (YouTube video link.)

The local news story is predictably short on details and pushes the editorial edge into breathless indignation that taxpayer dollars have somehow been misspent. We just don’t see it that way. “If it ain’t broke, don’t fix it,” is somewhat anathema to the hacker ethos. After all, there’s no better time to “fix” something than when it’s working properly and you can tell if you’ve done something wrong. But keeping an important system running with duct tape and wire ties is also part of the hacker way, so we applaud [Tim Hopkins] and his colleagues at the GRPS Facilities and Operations Department for their efforts to protect the public purse. And a round of applause is also due not only to the Amiga design team, who produced a machine that can run for nearly three decades, but also to Johnson Controls, whose equipment – apparently a wide area radio modem linking the HVAC systems in the district’s buildings – is being run by The Little Amiga That Could. Sounds like they built stuff to last way back when.

So when this machine is finally retired, here’s hoping they give it a good sendoff. Perhaps we’ll see it with some other Amigas at some future Vintage Computer Festival. Or maybe it’ll be one of those active retirees and start a career in the music industry.

[Thanks Thinkerer!]