Where I’m at, the temps flip-flop day to day, even hour to hour. In the morning it’s 35° outside, and by evening it’s 79°. I gave up keeping up with the temps and shut my unit off for the time being.
My question is why can’t HVAC units be programmed to say that if the outside temp reaches n° and the inside temp reaches m° cold, turn on the heat; conversely, if the outside temp rises to n° and the inside temp reaches m°, then turn on the AC?
My thermostat already knows the outside and inside temp, but I still have to manually switch it back and forth. I want a system that I can just set it and forget it all year round.
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Control theory is a bitch
My thermostat has a hot and cold setting that will heat when cold and cool when hot- I can also set it to a mode based on outside temp or time of day. You might just need a smarter thermostat.
That absolutely 100% exists. In commercial buildings, this is the standard. Nobody has to go to the BMS (Building Management System) and tell it to switch to cooling or heating. It’s all automatic. Even higher end residential thermostats do it. A couple of years ago I had my gas furnace replaced with a heat pump/electric heat system and it automatically switches between heat and cool as I’ve programmed it.
Hell, you can get systems that are sophisticated enough that every individual room in your house has an independent thermostat that automatically maintains a different temperature in each room. Of course, that’ll require a separate VAV for each room, which isn’t common in residential buildings.
The primary reason you don’t see “smarter” systems in homes more often is because they’re more expensive. Most people leave the fan on their HVAC system on auto and just switch between hot and cold manually as needed. And for most people, that’s only a few times per year. Most people switch it to cool sometime in the Spring, then leave it there until the Fall when they switch back to heat.
A more complicated system is just paying more money for something you don’t really need.
Nobody has to go to the BMS (Building Management System) and tell it to switch to cooling or heating.
Depends on how shitty your contractors are and how cheap your construction team is ☹️
thermostats don’t run off what the temperature is outside.
usually, they have set points- heat comes on if the temperature goes below x, cooling/air conditioning comes on if it goes above y.
Does your system have a physical outside sensor for temperature? or is it pulling that information off the internet? your immediate location and how you’re situated on your property (plus things like how well your home is insulated, the color, how many windows you have… etc,) has more to do with how hot it gets inside. Or, for example, if you get a lot of sunlight coming in, it can heat up the house with it being horribly cold outside.
Regardless, if it’s not staying comfortable, look for a “heat and cool” option and then adjust the set points to within a more comfortable range. keep in mind that will cause energy costs to go up as it’s now actively heating or cooling more. (This time of year plays merry hell with HVAC systems,)
Most HVACs thermostats have a target temperature range and can toggle heating and cooling to stay within that range - usually with some minimum range logic to prevent constant swapping.
This is also a classic modern house problem. In areas with wild temperature sways like what you’re describing traditional house building would include hacks to capture and retain the cool air in the morning and shed as much excess heat as possible during the day.
When we lived in Puerto de la Santa Maria we’d throw open windows to create a cross breeze in the mid afternoon and keep the air flowing (assuming it didn’t get too cold) into mid-morning at which point we’d seal off the east facing windows and draw curtains over the windows and doors to keep the heat out - swapping to full enclosure as it got to just before lunch time - then opening east facing windows and leaving the west shut util it was time to start the cycle again.
It was unbearably hot in direct sunlight during the hot months but the house stayed cool - especially with thermally conductive tiles and stone being the primary exposed surfaces. As long as you properly cycled the house you could keep it comfortable and it was easy to adjust by airing it slightly less or letting more heat in.
Wooden houses with huge sliding glass doors in direct sunlight that have no shades or curtains can’t do this, however.
My friends family has a shore house we’ve gone to a few times. It’s an old house, built before a/c was a thing, and still doesn’t have any. We throw open some windows and the house stays pretty comfortable, it’s warm but not at all unbearable even when the temps are in the 80s, 90s, occasionally even over 100 (fahrenheit of course)
It does help that it’s at the shore so there’s basically always a nice breeze.
If your willing to get into the weeds, most HVACs are very basic, and you can easily make your own thermostat with a cheap relay board. That plus a microcontroller and some code (and/or homeassistant) and you can make it as smart as you like.
There are smarter thermostats, but they are usually more expensive.
If you do microcontroller, look up PID regulator functions. Stabilizes anything measurable with super basic math.
Mini split. Cools when its hot and heats when its cold. Very energy efficient and cheap to install.
Ecobee thermostats have an automatic feature that does that. I only use the dedicated heat/cool settings since there aren’t wild shifts like that in my area.
I tried that once but it wasn’t for me. If it’s been cold out and is suddenly warm, I’ll bask in the heat or open windows.
Actually I’m a bit annoyed that my car does that. I set the car thermostat to heat to a specific temperature but then it also cools to that temperature. I haven’t figured out if there’s a way to set it to heat (or cool) only
Higher trim cars have radiation sensors to help account for solar heat gain.
Honeywell has individual room sensors available that you can average or prioritize.
I think the real reason you don’t see them- the average person is too stupid to understand them and set them up.
Less about people being too stupid and more about people just not seeing the point. The average person touches the AC/Heat switch only a few times a year.
I personally love the days where it’s cool enough at night to open the windows and get the house temperature down. Means the AC the next day doesn’t have to do nearly as much (and thus my electric bill isn’t as high).
There are a lot of smart engineers that design those.
If you have an external temperature measurement it helps. But it can’t see the difference between a cloudy day and a sunny day.
If you connect it to an online weather service that helps, but it’s still hard for it to know how much the sun heats your home due to big south facing windows for example.
This is something AI could be useful for. Feed it forecast, inside, outside temp and let it figure out how to balance those against each other for your home. I’m not sure there are many systems like this on the market yet.
You don’t need to go to that level of complication.
Two sensors in combination, one that detects current heat input one that detects absorbed heat. These modules would be placed about the outer walls.
Then calculate how much heat is going to radiate into the building the rest of the day.
And it can compensate.
We don’t need to be more than a fraction of a degree off and a system like that would be amply accurate.
What kind of sensor do you suggest for measuring that? I’m genuinely curious why they are not industry standard.
My guess is price and/or robustness. The RTCs we use are cheap and durable.
Truly It’s not my line of work so I’m not going to start randomly recommending products, I don’t think it’s fair to talk out my ass hahaha
What I can say however, is the reason I was so bold in my assertion previously, was that I personally do a lot of hobbyist electronics, and wiring up temperature sensors is very simple. It’s very much a trivial aspect to basic circuitry, because heat is such an aspect. It’s in your most basic things from coffee pots to hair dryers but even down to smaller electronics, bulbs and projectors, everything really in its own way.
And then my father was a highly trained meteorologist with the government of Canada for 43 years and then another 10 of consultancy, they scouted him because he was the 100% in all courses math superstar at his university for his year.
My father taught me a lot about how heat is measured and it’s a huge concern in a way that the average weather watcher doesn’t understand. It’s talked about in Watts per Square Meter. So that could be how much heat a structure may absorb per square meter, or perhaps how much heat is dissipated per second in a certain wind.
That’s a major and primary concern of anyone in the agriculture industry, think for example a farmer that holds a barn full of cattle, he absolutely needs to know how much heat that building’s going to dissipate so he can plan for heating.
But it doesn’t end there, it goes into so many different areas where heat is an issue, and weather is the primary driver of heat transfer.
So I guess in summary, a solution is trivial, I’m not sure if there’s an official product, but we’re not talking rocket science! Edit: I guess in a way it’s pretty cool and it’s pretty complicated, but the thinkings has all been done by people smarter than me I’m just saying it can be put together and lots of people probably do this every day.
Edit2: I guess also my brother-in-law was a graduate of 4-year electronics program and he ended up working at our local eh price where he designed some forms of heating control systems but to what degree I know not. We talked a bit about some of the egghead stuff so I think in summary it’s doable.
My Nest thermostat does this. And I use Nest Sensors to adjust to temps according to time and location in the house.
