It's time for thermostats!

So, as far as a “single duty cycle” option, I don’t know of one for AC but many Samsung refrigerator have a feature called “Power Cool” and “Power Freeze”, which might do something similar. Based on the description on the website (and watching the one in my kitchen) it temporarily pushes the temperature settings inside the fridge down and activates the fan, overriding the normal settings and bypassing the normal shut offs. https://www.samsung.com/in/support/home-appliances/what-is-power-cool-function-in-samsung-convertible-refrigerators/

alphawhiskey

Awesome video! Thermostats are a good into into control theory (aka rocket science without the explosives). Control theory is all about sensing and reacting. The thermostat senses that the air is too cold and turns on the heat until it senses that it's too hot to stay on and tuns off. People want to turn the heat up all the way because in their mind, the system prioritizes accuracy over speed but in reality, the system is just naturally slow.

Yagsti

This video finally convinced me to become a patron. Love how you address these seemingly mundane technologies rather than just fancy gadgets. Informative and entertaining.

Clemens

The thermostat in my apartment is the old bimetalic style you described, but it adds this "longer cycles" control to control the duty cycle. Any idea how that works? https://i.imgur.com/H4qaPqk.jpg

Francis

When can I purchase a "Convicted Fun Sucker" pin? :D

Travis Snoozy

You managed to make household thermostats interesting. Good on you.

Our thermostat has a 5/2 program (you can set 2 cycles for the 5 weekdays and a different 2 cycles for the 2 weekend days for both heating and cooling). You can then override the program, which puts it into "HOLD" mode. This will maintain the overriding temperature until you press the "resume program" button, at which point it returns you to your normal temperature program already in progress. I think this is the closest to what the one twitter guy was looking for.

Mike Bird

Soooo.... yeah I'll be that guy for this one. I have a Carrier Infinity heat pump system, and it's the exception to the rule. It doesn't use the old school 4/5 wire setup, it's a serial data bus, and is variable speed on both the fan and the compressor motor. So turning it all the way up to 90 does in fact speed up both the circulation fan and the heat output. The damn thing sounds like a hurricane when it gets up to full speed. But most of the time it runs at a low speed and low compressor output so you don't even hear it running. But the motors in the compressor and air handler are driven by real PWM! Of course, it also means I have to use only Carrier stuff, I can't go just buy a thermostat at Home Depot, I have to use the $300 one Carrier sold me. Great video as always!

Neill Thornton

In retrospect this was a horrible idea, but when I was 8 or so years old (LBJ was still president) my dad remodeled our central heating system, including replaceing all the old thermostats. Because I was a science nerd, he let me collect the mercury and I actually brought it to school as a show and tell. Fortunately I soon lost interest in the mercury and it was soon disposed of (yes...likely a landfill...it was the 60's...cut me some slack). Of course if any of this happened today, there'd be HAZMAT suits, and suspensions from school, and all kinds of nasty things!

PWM assumes a fixed frequency, which the thermostats definitely don't have, so this is not PWM. As Alec also said, a PWM control system also features feedback, which is effectively the temperature measurement of the thermosensitive element, i.e. the bimetal strip, so you actually have a variable frequency, variable pulse width close loop regulator in the thermostat.

Ognyan Manchev

Ecobee has multiple temp sensors for averaging as well as reverting the temperature back to the scheduled temp after a set period of time if someone changes the set point.

Do you know how many times I've explained to people (mostly women) who have a car with automatic climate control that setting ti to max because you're cold will not heat the car up faster!? They don't get it. Let the technology work for you!!!

Patrick Bianchi

Great video! In the UK we use a combination of Timer and Thermostat - which Nest then merged together. However I have an older Nest, so it only covers the heating, and not the hot water. My Timer had a button called 'boost' which did exactly what you were talking about at the end. So for my hot water, I can press the boost button and it turns the boiler on for an hour to give me extra hot water outside of the timed cycle. However, it doesn't affect the timer itself. Interestingly in the UK there are very few homes that have A/C. It's mainly in business premises only, like Offices or shops/restaurants. Some homes *do* have it retrofitted but it's not something people install by default.

Mark Wayt

And my personal experience: A Honeywell connected, geofenced thermostat sounded like a good idea but is useless for shift workers. Home (asleep) during the day? Crank the heat up!

Michael Steeves

I'm an I&C engineer and I think you did a great job on an understandable level of explaining things. I do have a question on heat transfer and PWM. Wouldn't heat transfer be more efficient if there were a greater temperature difference? If so, a cooler heating element with PWM wouldn't be as effective. (This is a thermodynamics question that my I&C brain can't fully parse and a quick google just muddied things for me).

Michael Steeves

The difference between the On and Off points is called deadband. A small deadband results in more cycling but more accurate temperature control. A large deadband is not a good thing and isn't good for comfort. It is much easier to control with a digital thermostat.

Michael Steeves

Great video. Your delivery adds to the enjoyment. Thanks for making vids.

Hi Alec, how to you do these great videos! Oh, and on my PC, it's "," and "." to navigate frames. "" control the speed setting. May be a European thing? Speaking of European: would you care to spend time on Opentherm, as Thijs Dortmann also mentioned?

Paul Schuur

Maybe you didn't include it because you were mostly focussing on forced-air heating and cooling systems, but in Europe (or at least in the Netherlands) where forced forced-air heating and cooling is quite uncommon in residential buildings, on/off heating is largely becoming obsolete. Many new houses have in-floor heating, that warms the floors of the rooms in order to heat them by running warm water through long coils that are laid just below the actual floor. As you don't want to heat your floor to the maximum temperature your furnace can heat the water to and because most furnaces are more efficient when they're not run at full blast, most thermostats and furnaces support OpenTherm, which simply tells the furnace to what temperature it should heat the water. Newer versions can even tell the furnace to only run at a certain percentage of it's rated output. This often results in the furnaces simply staying on all the time, just at a very low output. This has the added benefit of a very constant temperature in the rooms. Another cool feature of OpenTherm is that the furnace can 'talk back' to the thermostat, allowing you to see diagnostics on the screen of your thermostat and change settings for hot tap water that the furnace also often provides.

Hi, Alec, re the "one cycle" question you answered, on our old mechanical central heating timer (not thermostat) we had a button we called the "gis-an-hour" button. One push would turn on the heating for a hour and then return to the regular programming. That was really useful - I wish we had something similar on our new 'Tado' system. Re PWM, w-a-y back at University College London, we built a PWM system to take the monochrome pictures from weather satellites, PWM them and display them on a storage oscilloscope. That was quite neat.

Stephen Bell

PWM vs Thermostats: the analogy is right but there is one major difference. PWM is used (in lieu of a slowly changing sine wave) because transistors waste energy — read, “get hot — when they are “half way open,” because then they act as a resistor. Whereas when a transistor is either fully “shut” or “open,” as in PWM, they waste much less energy and more of the power is used by the “load.” In a thermostat this is less important because the whole point of a heating element is, well, wasting energy. In other words, if we used a sine wave to turn the heating element on and off, the “switch” would get a lot hotter. But, who cares, as long as the two are in the same place, the heat output will be the same. I know this is a bit of an apples-and-oranges kind of a comparison but I think it nevertheless makes the point of PWM clear. A Class-D amp wastes less of its consumed energy on heating up and more on the speakers, because we want sound, not heat. (Of course 90%+ of that energy then becomes heat in the speaker coil, the rest sound waves that also heat up room. All energy eventually turns to heat).

Well... "merde" is French for "shit"

I installed a Nest (didn't accomplish anything - waste of money) and didn't know what the colors represented. Thanks for the informative video!

Mine calls that temporary hold (as opposed to permanent hold and vacation hold). It resumes the program on the next point with no recovery (where it turns on early so it reaches the next setpoint as the time arrives). We have some at work that do what the tweet asked almost - if you manually change the temp it's only effective for 15 or 30 minutes before resuming schedule.

What does "oh merde" mean? And "amiright" that this is the typo? Also, Ecobee thermostats (Nest's main competitor) does support the feature you mentioned in the end: when you change the temperature on the main screen, it activates a "temporary hold" where it's set to that temperature for a custom, pre-configured period of time, and then reverts to the normal program.

Sonic the Anonymous Hedgehog

Ah that was my bad. I put the new link in the text box but didn't replace the actual Patreon thing.

Technology Connections

Sorry about that! I just deleted the old version--I don't like leaving them both up there and either getting confused with which one is which, or risking the "duplicating content" strike that is apparently possible. Here's the updated link: <a href="https://youtu.be/ZZC0SP02PqY" rel="nofollow noopener" target="_blank">https://youtu.be/ZZC0SP02PqY</a>

Technology Connections

Hmm, I was watching the video and I got caught during your re-upload so it stopped. I was going to mention heat pumps (which are basically the same but 'heat' is a reversing valve) often have 2 stages - so my honeywell can call for stage 2 (full) when the temperature difference is larger like when you have a schedule change from 80+F down to say 76/77°F and even an 'emergency heat' mode (complete with red LED) which tuns on the electric heat strip to 'help' (mostly make the house smell like burning).

The huge video thumbnail here shows as "removed by the user"...looks like you haven't updated it.

Sonic the Anonymous Hedgehog

Made unavailable from youtube while watching... ..

Jacob Nelson

My "furnace" apparently have a dynamic heat output adjustment. It was cool at first, economic, but the only way to controls it is the proprietary thermostat, with only 2 "bus" wire. I have a wire i can bridge on the heater, but it turn it back to 0-100%. I'm very sad because i really wanted to controls it with home assistant.

Vlycop

watching youtube via xbox (or pretty much any youtube smart tv interface, they're all pretty much the same), there's no sane way to read the fast scrolling text. (other than get out a different device)

adcurtin

My parents' house was built in 1962. I wasn't born until 1970, but the mercury bulb thermostats were still working fine when I moved to Taiwan in 1996. When I was about 10, we would turn it on and I would take the cover off and sit and watch and record the times, eventually making a graph. What a nerd! It's very frustrating that AC is such an important part of life here, but so many people don't understand this. Great video, Alec!

I always assumed that they carried loads but nothing more than a relay's worth... I guess I assumed that a contactor would have another device before it rather than be directly controlled by the thermostat. Makes sense, though.

Technology Connections

Thermostat wire is sized like it is because it has to carry loads. Often times furnaces and most all common air conditioner and heat pumps have electrical contactors inside of them that take a not insignificant amount of current to run. Couple a few of those together and add something like a damper or relays, thermostat battery charging or the like, and you can overwhelm something like cat5 24awg cable very easily and risk fire potential. Likewise running a larger cable like 14 ga is just wasteful and expensive, as well as harder to work with.

Very punny!

Craig Kollai

Ah drat! And the second render is already done! I'm just gonna let that one stay in there...

Technology Connections

Not quite the same thing as a "single duty cycle" option, but the Nest can be used in a similar fashion with a schedule set and the "learning" turned off. If you set the temperature manually it will only stay at that manually set temp until the next set point on the schedule. So I often use that feature when I'm hot or cold from being outside knowing that the set point will reset to the normal scheduled setting within a relatively short time frame. But it could be well over an hour until the next scheduled set point and it can mess up the learning algorithm if you do it often enough, so definitely not the same thing.

Dylan Neu

Great video!

Professor Kroog

I had a toaster oven as a kid that I’m pretty sure ran on duty cycle. If you opened it mid-cooking, it’d never really get back up to the set temperature. Oh, and I have the exact same Honeywell thermostat as you showed first. Except I changed mine to Celsius.

Quinton Wilson

as ever, i'm pleased as punch i became a patron. thank you!

V.E. Griffith

You misspelled "because" in the second paragraph of the super fast scrolling text block :) And, no... I didn't know about the keyboard keys to skip forward and back a frame

Linh Pham

wow, this video is really COOL get it.

I always post this right when it's done, so captions usually happen the next day.

Technology Connections

Didn't publish the captions yet? Will it be available after the re-render?

Sonic the Anonymous Hedgehog