Have you ever noticed how sunlight can make a room feel like a sauna even with the air conditioner on? The main problem with traditional ACs is that they only allow setting a single temperature, foregoing other crucial factors that may significantly affect how we feel. According to ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), aside from temperature, all of these components make up our thermal comfort: Indoor Humidity, Thermal Radiation (Sunlight) and Time of Day. Another super important factor that isn't on ASHRAE's list but is definitely a big player, is Outdoor Weather. Different combinations and levels of each factor create a shift in our environment, and ultimately in how we feel. To make things a bit easier to understand, we’ve created the Factor Series – focusing today on one that many of us may not even pay attention to: Sunlight, or Thermal Radiation.
How does thermal radiation even work? What is it?
Thermal radiation is one of four ways of heat transfer (others are conduction, convection and latent heat); it is basically a process where energy is emitted by a heated surface and is subsequently absorbed. It’s important to note that thermal radiation will not heat the air much, but will focus on the objects/people - we feel the heat when the sun is shining as well as when the fireplace or stove are on at home, and so will other objects in our house. The rate or strength at which a body radiates or absorbs thermal radiation depends on the type, color or material; certain objects will become strong emitters or reflectors. Ever wonder why you feel so hot wearing black in the sun? A blackened surface is a super strong absorber and emitter!
What happens next? That’s right - heated bodies (whether of animate or inanimate objects) will in turn warm up the air, which means the final effect of radiation on our environment is a 2-step process. This is why sometimes the temperature seems to be ok, but the way we actually feel is amplified by the sun shining through the window.
What does thermal radiation mean for comfort and why is it so important?
Now that we have a picture of what thermal radiation is, it’s easy to see how it will affect our comfort and create the imbalance we all struggle with. At home, we have 2 main sources of radiation: windows and walls. On a sunny, bright day you will notice this a lot more; a study by MY Chan and CW Mak in Hong Kong, found that fully glazed windows introduce a large amount of solar radiation, transmitting up to 84% of the sun’s heat indoors. Our walls, normally white (another stronger absorber/emitter), can also act as heating components, and depending on the time of day or position of our windows, may create quite a few “hotspots”, influencing the mean radiant temperature and affecting thermal comfort. Another study, by E. Arens et al., suggests that the impact of strong sunlight can be equivalent to changing your AC’s set-point temperature by as much as 1.5°C! All of this will obviously make us feel uncomfortable even if we use the AC; more than anything, it will leave us confused - how and when should we adjust the AC to meet our needs?
What can I do to make sure sunlight doesn’t leave me uncomfortable?
There are a number of things you can try to do to minimize the effects of sunlight/radiation on your comfort, and some of them will also save you some energy! Obviously a major player to assist us is our beloved air conditioner, with which you can adjust the temperature to try and find your comfort sweet spot. Here are some ideas:
How can I better use my air conditioner to battle the effects of sunlight?
Clearly, no one can diss using the AC, especially in Summer or humid periods. But with so many options, how will you be able to make the right decisions to ensure your comfort? Sure, you can adjust the AC whenever you feel uneasy, but due to the delicate impact of sunlight this could be a bit tricky. When trying to optimize your thermal comfort, you’ll want to take everything into account - including the time of day and degree of luminosity, which can greatly influence how you feel. A smart AC controller can help you; when choosing a controller, your best bet is to opt for one with a sunlight/luminosity sensor and time of day data to account for the warmest hours. This way you can be sure you’re not missing out on that extra factor that may cause imbalance in your comfort!
We’re sure you can now see how sunlight plays a role in our comfort and well-being; while it may feel like a minor change to our environment, combined with other factors it can greatly affect us without us ever pin-pointing to the cause. Some of us may be more sensitive to these minimal changes and ultimately get frustrated when our AC or shut blinds just don’t give us the comfort we need.
Finding the balance and being able to control and maintain an optimal environment is what we all want– so if you’re convinced, now’s the time to take charge of your comfort and start looking for smart solutions with a multi-factor approach to ensure your home stays in the best shape!