So let's discuss the best sensor and practices for automating shades in the summer to help out the AC.
I have a Hue outdoor sensor just inside of a south facing window in a room I rarely use much. This window is double glass. Originally I have been playing around with automating the shades based on Lux but am noticing today the temperature portion of the sensor is also outputting useful data, maybe more useful. As the inside of the glass surpasses the AC setpoint, it seems to me it is time to close the shades. This seems more accurate (and cheaper sensor wise) than basing on Lux levels.
In my mind I think this would work in winter as well, although in my climate I would assume the glass is always a bit cold so I may need some adjustments.
I use a device that tracks the sun's position. If the sun would be beaming into my living room in summer, time to close the blinds. In winter, if the sun would be shining in it might be a good time to open them to get the extra heat.
The temp the sensor is reading is higher because the sun is shining on it. That’s heat radiation. It’s telling you the same thing as the lux sensor, which is that the sun is shining through the window.
How much does the temperature in the room rise when the sun is shining through the window?
My bedroom warms up by several degrees when the sun hits the windows in the afternoon (west/south facing windows).
So I have lux sensors placed on the window frames such that when a lux reading goes up beyond a set threshold (meaning the sun is shining directly though a window), the shade closes. When the sun is no longer shining directly though a window, the shade goes back up (until sunset).
I’m not sure why using the temperature on a multisensor that also measures lux would be an advantage.
It may work more accurately. More importantly, it would allow cheap contact/temp sensors to be used instead of lux. Many people may be using contact sensors on their windows already.
Report back your findings. I don't see why this wouldn't work perfectly. Temp equal to thermostat setpoint might be a little too early to close but it technically means the air at the window is a tiny bit warmer.
Fair point re: needing a dedicated sensor for lux, if one already has a contact sensor on the window that can measure temperature.
I still think it makes more sense to measure the illuminance level directly, if the goal is to close the shade when the sun is shining directly on the window.
This seems like creating a problem that doesn’t exist to use a device that adds complexity. If it’s AC season and the time of day, why wouldn’t you close the shades to prevent heat / reduce AC use. Conversely for when it’s Heat season. Regardless of if it’s cloudy - you’re still getting the thermal energy.
I have winter, summer and float modes. The modes run heat / AC / none which coordinates HVAC with shades / attic fan and adjust to doors - windows open so the HVAC isn’t running when they’re open, but if the temp exceeds X with doors / windows open HVAC fan will come on to circulate.
In theory, using temperature for the open/close decision can work. The difference between using temperature and illumination will be a matter of timing (lag).
The timing difference will be a function of the window construction (single, double, triple pane, plain vs low-e glass, etc. ). A triple pane window that is designed to restrict infrared and ultraviolet radiation from passing through the glass will prevent the interior space from heating up as quickly as a single pane plan glass window.
If you have an older house with old windows, try controlling the blinds with a temperature sensor. If you have high efficiency windows, the temperature control approach may not be quite as satisfying.
The answer to this question will be your best guide to designing the most efficacious solution. What are you trying to control, room brightness or room temperature? Choose a control sensor that best supports that goal.
Cost is definitely a factor that has to be considered as a part of the solution. Cost will often temper the efficacy or our solution. We can’t always justify the most effective solution. Most of the time good enough is the most optimal solution.
With all that technical mumbo-jumbo having been said, if what ever solution you choose works well enough, it’s a good solution.
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