Radiant Cooling and Heating Systems

Radiant heating or cooling is a concept that has been in practice for longer than we realise.

Archeological digs in Asia and the Aleutian islands of Alaska reveal how the inhabitants drafted smoke from fires through stone covered trenches which were excavated in the floors of their subterranean dwellings. The hot smoke heated the floor stones which then radiated into the living spaces.

An ondol, also called gudeul, in Korean traditional architecture, is underfloor heating which uses direct heat transfer from wood smoke to the underside of a thick masonry floor. The main components of the traditional ondol are a firebox or stove accessible from an adjoining (typically kitchen or master bedroom) room, a raised masonry floor underlain by horizontal smoke passages, and a vertical, freestanding chimney on the opposite exterior providing a draft. The heated floor is supported by stone piers or baffles to distribute the smoke, covered by stone slabs, clay and an impervious layer such as oiled paper.

hypocaust was an ancient Roman system of underfloor heating, used to heat houses with hot air. Hypocausts were used for heating hot baths (thermae), houses and other buildings, whether public or private. The floor was raised above the ground by pillars, called pilae stacks, with a layer of tiles, then a layer of concrete then another of tiles on top; and spaces were left inside the walls so that hot air and smoke from the furnace would pass through these enclosed areas and out of flues in the roof, thereby heating but not polluting the interior of the room.

It doesn’t surprise me that these methods were in use probably since 5000BC (if wikipedia is to be believed). Most concepts that we now follow are actually age old methods that are so logical and obvious that it is a surprise that we ignored them for so long.

A radiant cooling (or heating) system refers to a temperature-controlled surface that cools indoor temperatures by removing sensible heat and where more than half of heat transfer occurs through thermal radiation.

-ASHRAE Handbook. HVAC Systems and Equipment. Chapter 6. Panel Heating and Cooling Design. ASHRAE. 2008.

The process of radiant exchange has a negligible effect on air temperature, but through the process of convection, the air temperature will be lowered when air comes in contact with the cooled surface.

The temperature people feel is an average of the air temperature in a room and the radiant temperature from the surrounding surfaces.With radiant cooling the room temperature can be reduced which reduces the convective cooling load.

This is a surface cooling system where the water tubes are placed in the roof slab that absorbs the heat from heat sources in the room.The Slab absorbs the heat and exchanges it with the circulating water. Typically the circulating water only needs to be 2-4°C  below the desired indoor air temperature.Once having been absorbed by the actively cooled surface, heat is removed by water flowing through a hydronic circuit, replacing the warmed water with cooler water.

The heat energy is emitted from a warm element, such as a floor, wall or overhead panel, and warms people and other objects in rooms rather than directly heating the air. For radiant heating systems, you can use any one of  the three commonly applied floor heating methods: radiant air floors (air is the heat-carrying medium), electric radiant floors, and hot water (hydronic) radiant floors or use radiant panels in walls and ceilings.

For further Information:

Radiant Cooling