Heating potential

Infrared Heater vs. Space Heater Comparison

By using a 1,500W infrared heater at a bus stop it could provide an efficient and more direct method of warming commuters, especially in inclement weather. Unlike the traditional space heater, which primarily heat the air around them, infrared heaters emit electromagnetic waves that directly heat objects and people within their range. This fundamental difference of course makes infrared heating particularly more well-suited for something such as outdoor applications, where conventional space heaters struggle to retain heat due to constant air movement and heat dissipation. Infrared heaters do not rely on warming the air, so they are far less impacted by wind compared to space heaters, which lose significant efficiency as heated air is carried away. In an enclosed or semi-enclosed bus stop, a 1500W infrared heater can provide a more consistent and noticeable increase in warmth, making waiting times significantly more comfortable for commuters.

Impact of Reflective Coating on Heat Retention

The effectiveness of an infrared heater can be greatly enhanced by using something like a reflective coating on the bus stop's walls. These coatings would work by reflecting infrared radiation back into the shelter, trapping heat whilst minimizing the heat loss. This setup increases the heater’s overall efficiency, ensuring that more of the emitted heat is utilized and not dissipating due to wind conditions. With reflective coatings, the perceived warmth inside the shelter can be significantly improved, potentially adding an additional 5-10°F to the temperature inside compared to a setup without it. The combination of infrared heating and reflective surfaces ensures a more comfortable environment, even during colder and windier conditions.

Reflective coatings, such as aluminum-based materials or infrared-reflective paints, act similarly to a space blanket. Instead of allowing the warmth to dissipate into the air, these coatings redirect the infrared radiation back toward the people in the shelter, significantly improving heat retention and comfort.

Effect of Wind on Heating and Heat Retention

Wind speed plays a very crucial role in how effective the infrared heaters will be in outdoor settings. Below is a general estimation of how wind speed impacts the perceived effectiveness of a 1500W infrared heater at a bus stop for various wind speeds, both with and without reflective coatings being added onto the walls of the stop:

At 0 mph winds – In still conditions, an infrared heater can raise the temperature inside of the shelter by around 10-15°F. With reflective coating added, the temperature increase can additionally rise by 5-10°F, resulting in an even warmer and more comfortable environment. Making the potential total about 15-25°F.

At 10 mph winds  – A more lighter breeze can cause some heat loss in the system, but the reflective coating helps retain warmth, maintaining an increase of 8-12°F inside the shelter. The coating reduces heat loss by redirecting infrared radiation back toward the commuters inside adding about 5-7°F. Making the potential total about 12-19°F.

At 20 mph winds  – Without reflective coating, much of the heat will be lost due to the wind, and the perceived temperature increase will be 5-8°F. However, the reflective coating still helps at these speeds, ensuring a more consistent temperature. Adding a potential increase of 5-6°F despite the stronger winds. Making the potential total about 8-14°F.

At 30 mph winds – With even higher wind speeds, heat loss becomes more significant, and the perceived temperature increase may only be 2-5°F. Yet again though, the reflective coating helps to mitigate some of this heat loss, increasing the temperature by a potential of 2-4°F, providing some relief from the cold. Making the potential total about 4-9°F.

We were able to derive these estimates by using this simple formula: Temperature increase with coating = (Temperature increase from the heater) × (1 + heat retention percentage). With the base temperature of the heater being 10-15°F and the heat retention from the reflective coating being anywhere from 50-75% at a base case. Of course, as wind speeds increase these numbers have to be adjusted more and more since we know that higher speeds will lead to more loss in heat. So when we move from 0 mph to 10 mph that base heater temp needs to be reduced by about 20-30% due to wind conditions, while the reflective coating base case needs to be reduced to 30-50% instead of 50-75% at 0 mph winds. Then we jump forward to 20mph speeds and that heater base case is further reduced to about 30-50% heat loss whilst the reflective coatings base case remains at about 30-50% decrease from its base case. And the final 30 mph wind the heater base case is reduced by a whopping 50-75% in effectiveness while the coating remains at a decrease of 30-50% in its base case. Allowing us to derive the estimated temperature increases in the environment of a bus stop at various wind speeds. Of course, we went a little more generous in how much heat dissipation there would be to rather be safer than sorry, meaning that these temperature increases could be potentially even greater than the numbers stated for wind speeds above 0 mph. Providing even more heat than we have calculated than the ones above.

In calm conditions, a 1,500W infrared heater can provide a 10-15°F increase in temperature inside the shelter. With reflective coatings on the walls, this increase can be boosted by an additional 5-10°F, making the bus stop feel significantly warmer. In windy conditions, the reflective coating helps mitigate heat loss, ensuring that the temperature increase stays between 5-10°F higher than it would be without it, even when wind speeds reach up to 30 mph.

By combining infrared heating with reflective coatings, the heating system becomes much more resilient to wind and outdoor conditions, offering reliable warmth even during cold, windy days. The reflective coating ensures that heat remains concentrated inside the shelter, making it a more comfortable and efficient solution for commuters, even in harsh winter conditions. Showing how much better waiting at bus stops could potentially be if we were to implement these systems into the city's infrastructure.

Calculations used for the base case of 10-15°F for infrared at 0 mph:

T(air) = (P / (h x A)) x (9 / 5) --> (1500 / (10 x 20)) x (9/5) = ~13.5°F

• T(air) - Air temperature increase inside of the bus stop

• P - Heaters power in Watts

• h - Effective transfer coefficient in W/m^(2) (Varies based upon materials, insulation IE the reflective material, and wind assumed as 10 due to the average material used in Lakewood Bus stops and lack of wind in the base case)

• A - Total surface area for Avg. Bus stop in Lakewood in m^(2)

• 9/5 - Conversion of °C to °F​
  

  
  With a calculated total of about 13.5°F, we can see that the base case numbers are approximately correct; however, we know that numerous factors within the world can affect this number. So it's better to assume a range of numbers instead of a singular point, so we round it to about 10-15°F. This helps us better account for the multiple variables used, such as bus stops being constructed differently, varying wind exposure, different insulation, and many other potential variables.

Sources used:

Simon Fraser University - Steady Heat Conduction

Vaia - Steady State Heat Transfer

Abdullah Moubarak - Steady Heat Conduction

Wright State University - Steady Heat Conduction

Herschel - Infrared Heaters

Lukas Anselm Wille, Bjorn Schiricke, Kai Gehrke, Bernhard Hoffschmidt - Reduction of Heating Energy Demand by Combining Infrared Heaters and Infrared Reflective Walls

Ho Kun Woo, Kai Zhou, Su-Kyung Kim, Adrian Manjarrez, Muhammad Jahidul Hoque, Tae-Yeon Seong, Lili Cai - Visibly Transparent and Infrared Reflective Coatings for Personal Thermal Management and Thermal Camouflage

Hongmei Zhao, Yuyu Zhou, Xiaoma Li, Chunyan Liu, Xiaoling Chen - The influence of wind speed on infrared temperature in impervious surface areas based on in situ measurement data

Fluke - Wind Effects on Thermal IR Images