What is Radiant Heating/Cooling?
- There are basically three modes of heat transfer. Conduction. Convection. Radiant. Conduction is heat transfer when objects are in contact with each other. Imagine if you take your hand and you touch a hot coffee mug, that heat will transfer from the coffee mug directly onto your hand because there’s a contact there.
- Convection has more to do with heat transfer via air movement. So, when looking at a more conventional air conditioning systems where convection is being forced by blowing air into a space, or even natural convection where natural ventilation is occurring based on the differences in density of the air because of the buoyancy, a natural flow exists. A hot air balloon is an example of convection in action.
- Radiant is very different in that unlike convection, radiant heat transfer doesn’t rely on the air itself. It’s actually heat transmitted through electromagnetic waves. So, heat transfer occurs even though you’re not seeing a difference in actual air temperature.
How do Radiant Systems Work?
- The system itself is actually quite simple. We’re taking advantage of the thermal mass, whether it be a concrete slab or even a wood floor, to control the surface temperature. As long as we can create a temperature difference between the surface temperature and the space temperature, we’re always going to be driving heat transfer in one direction or the other. So, we would have a network of tubing embedded into a concrete slab. Then, we circulate water through that network.
- By controlling the temperature of the water we’re circulating, we’re able to control the temperature of the slab. If that slab temperature is warmer than the space temperature, then naturally by the second law of thermodynamics, we’re going to get that radiation effect from that slab to the space. With chilled water, we’re able to create a cooler slab temperature. Because of that temperature difference, we’re able to absorb the heat that’s in this space and create a cooler environment.
- Radiant heating and cooling systems are typically more efficient than conventional systems. Because of this, there has become more interest in the use of radiant systems, particularly in commercial applications. Devin Avalon (Business Development Manager at Uponor North America) told JM Engineering Founder, John Melvin, on the How Great Buildings Work Podcast that, “You can see by comparing a radiant system versus a commercial airside system, the studies have shown that a radiant system can be between 17% to 43% more energy efficient (Lawrence Berkeley National Labs). Other studies have shown that radiant systems can be over 50% more energy efficient.
- There was a recent grant that the California Energy Commission granted to study radiant systems. They were interested in studying radiant systems because they found that over 50% of the net-zero buildings that were installed in California incorporated some sort of radiant heating or cooling strategy. So, there is a lot of opportunity for radiant systems. Again, we’re talking about a system where we’re circulating water through that network of tubing instead of using a lot of fan motor horsepower to blow air. We’re using pumps and circulators. Because the heat transfer capacity of water is so much greater, we’re able to more effectively and efficiently move those BTUs and create these comfortable spaces.”
Are There Health Benefits of Radiant Heating/Cooling?
- There are many different health benefits of a radiant heating and cooling system. This is mainly because we’re creating this very comfortable environment without having to rely heavily on air that’s being blown through ductwork or through the fusers. Engineers hear a lot about different issues with indoor air quality. Certainly, ventilations important in managing. At the same time, by relying less on an air system to deliver cooler warm air, we can create an environment that is healthier.
- Along those lines, one of the ways is to use what’s called a dedicated outdoor air system. This is where a radiant system is providing all of the heating and cooling. All of the air being delivered is just the ventilation air, which is being exhausted to the outside. So, we’re not recirculating germs in one place. This is a huge benefit in a school. Schools are basically germ factories. If we’re exhausting the air rather than recirculating it through, then hopefully we’re delivering a cleaner air stream to the students.