Hot and Cold

Pet Peeve #231: When people want a room to cool down rapidly, so they set the thermostat to 52 degrees.

I mean, come on. That’s just not how AC works, right?

Air conditioning is either on or off. It’s either working its little heart out trying to cool your room, or it’s waiting for the temperature to rise about the amount you set on the thermostat.

As long as the thermostat is set to something under the current temperature, then the AC will come on at full cooling power. All you do by setting the thermostat lower is use more energy when you forget to reset it to a reasonable temperature later.

But now I have a question.

How do electric stoves work?

That is, if I need medium heat, would I get there faster by turning the stove on high? Or does it work in the same way as the AC?

Someone figure this out for me.

7 Responses to Hot and Cold

  1. BruceS September 20, 2010 at 11:23 am #

    I did a little research on this, and I’m still not sure, but I think you’re right. Back in the good ole days, the thermostat was essentially a bimetallic coil connected to a mercury switch, so it was definitely either on or off. Modern thermostats and their associated heating and cooling systems aren’t quite so simple. My boiler is designed to run in either of two modes, depending on how badly the heat is needed. The more efficient mode is used when the desired temperature isn’t too far off the current, while a less efficient mode is used to quickly get the temp up. I didn’t find anything similar for cooling systems, but I can easily see where it could work similarly. On a side note, what does the “Max” mode on my AC do; just run the fan faster?
    As for electric stoves, you’d have to be more specific. My current stove has elements that are obviously switched on and off by a controller. Even if you turn it to its maximum setting, you’ll see the element switch off. There doesn’t seem to be any in-between setting on the element itself—it’s either on or off, like my car’s throttle. I think (I should look this up) that the older design used something like a rheostat as the control, to directly vary the amount of current going through the coils. With that system, turning it to “High” for a minute, then down to “Med” will get the stove to medium temp faster than just going to “Med” right away.

    • admin September 20, 2010 at 1:35 pm #

      Hmm, well I can’t be more specific because I have no idea about how my stove works and I’m far too lazy to find out. That’s why I asked you people to do it!

      Now you tell me you’ve failed because I didn’t give you enough information. Sigh. I thought social media had all the answers, but I guess I was wrong.

  2. Michael Silver September 20, 2010 at 1:56 pm #

    This is a great question. I’m too lazy to go test on my stove top.

    I *thought* stove top elements had variable heat, but the radiant glass-top’s did not. No idea about the inductive stove tops. Gas obviously does. I can’t imagine a stove comprised of only metal elements can’t offer variable heat.

    I also don’t see why an AC can’t have variable output. Surely the fan could utilize variable input. Perhaps there is no energy savings in doing this since the fan could be running indefinitely. In other words, it’s more efficient to only have an on/off.

    This is now going to bug me until I research it further.

  3. admin September 20, 2010 at 2:15 pm #

    All I ever wanted was for this to bug people until they answered it. I’m so happy!

  4. Kevin September 21, 2010 at 10:13 pm #

    For every electric non-inductive stove top I’ve ever encountered, there’s a rheostat varying the resistance across the load. Even in the smooth, glass-top ranges, it’s still a coil of wire, but it sometimes encased in a ceramic disk to spread the heat more evenly. Some also have halogen lights embedded in there to more quickly bring the temperature up, since that was a common complaint about electric versus gas.

    If you were just measuring the surface temperature of the range, it wouldn’t make a difference if you selected high or medium, as temperature should ramp equally up to the selected power, and then level off. I imagine the ceramic disk would modify the ramp time slightly, but not by a noticable amount.

    If your goal is to get water to boil, however, it will boil more quickly if you were to select high, then trim the power when you got the water to the desired temperature. The coil would get hotter than the desired state, but it would take awhile to transfer all that energy to the water, and you don’t mind if you get localized hot spots when you’re boiling water, because it will all even out pretty quickly.

    If your goal was to heat up mac & cheese, however, you’d be better served letting the coil ramp up and just wait for the heat to be distributed evenly, because localized hot spots would tend to scald the cheese on the edges before it had transferred to the middle.

    And SOME (not many, and certainly not in my price range) air conditioners actually do have multiple units that are activated based on the target temperature. If you select 50 degrees on a 70 degree day, they will sense that they are too far off target and will activate both units to more quickly bring the temperature in line. If the difference were 5 degrees, it would only activate one unit, sensing that it could get the job done that way. But that’s not normal, and not what drives the behavior you describe.

    What might drive that behavior is that they really do want the house to be below normal for awhile. When you walk into a hot hotel room on a hot day, perhaps what you want is for the room to be 50 for awhile, so you can cool down, and then you’ll set it back to 72 once you’ve lowered your body temperature. Of course, a cool shower would be more effective, if that’s the goal. But most likely, it’s like you said, we just want to crank it to 11 to get it there faster.

    • admin September 21, 2010 at 10:21 pm #

      Kevin! My man.

      I actually didn’t have a cooking goal at all. I just wondered…. But man, I sure could go for some mac and cheese.

  5. BruceS September 22, 2010 at 12:35 pm #

    Wow, Kevin is nowhere *near* as lazy as me!

    My stove is a GE non-inductive electric model with the glass top. If I select a high temp, it turns on the element for a while, then turns it off, then back on, etc. to maintain the temp. If I use a lower setting, the “off” periods are more of the time. It doesn’t appear to do the variable-flow approach. I don’t know if that’s an efficiency thing, of if they just thought it was cool to do it that way.

    That AC dual-compressor approach makes sense for a large application. I was actually speculating about a single compressor that would have multiple or variable levels of operation, but I don’t know if that’s done or not.

    When I want to cool off quickly, I do take a quick shower. It has the added benefit of removing excess sweat. Cooling off the whole house (or hotel room) seems like a great waste, but then again I’m cheap.

    No mac and cheese for me. I’d rather have the boiling water, and use it to make some tea and ramen soup.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Subscribe without commenting

Powered by WordPress. Designed by Woo Themes