Keywords: Hydronic Radiant Cooling, Building Conditioning, Radiant Conditioning, Concrete Core Cooling, Concrete Core Conditioning, Radiant Panel, Low-Energy Cooling, Bauverlag, Seminar, Kühldecke, Energy-Efficient Conditioning, Energy Efficiency, Hawaii, Resourcenschonende Gebäudekonditionierung, Heizung, Klima, Lüftung,

Berkeley CA 94707-0617


Hydronic Radiant Cooling

Hydronic Radiant Cooling separates the ventilation task from the thermal conditioning. Due to large radiant surfaces (e.g., the floor and/or the ceiling), the temperature level of the coolant is close to the room temperature. This allows to consider alternative cooling sources (e.g., ground coupling, cooling tower operation, night cooling) to assist or replace the chiller for the thermal conditioning task.

Due to the high heat capacity and density of water, thermal energy can be transported water in pipes with little pump power; saving approximately 70 to 80% of the fan power normally used to conditioning a building. This alone reduces the peak-power of the air-conditioning system by about 30 to 45%. (Compared to a “perfect”, leak-free all-air system)


For an office building in Los Angeles, less than 20% of the air transported by the fans might be outside air, the majority of the air is being recirculated to save energy.

Hydronic Radiant Cooling systems are “Air-and-Water” Systems, with an outside air ventilation system providing fresh air, and a hydronic thermal distribution system with a radiant heat exchanger providing the thermal conditioning (either heating or cooling).

Due to the separation of ventilation and thermal conditioning, much space can be saved in plenum height. This allows one to reduce floor-to-floor heights by up to 2 feet (0.6 m), which contributes to significant cost savings for the facade.

What if the pipes leak?
Leaking pipes or fittings are not a problem. How often do supply water lines or sprinkler lines leak? It is very rare. Ducts, however, are always leaky and lose significant amounts of energy due to air leakage.

How fast does the system respond?
That does depend of the system used. Panel systems and capillary systems respond immediately. Concrete core conditioning systems have lots of thermal mass, systems design is particularly crucial.

What is the heating/cooling power of the different systems?
Specific thermal power output depends on the system type as well as on the temperature difference between room temperature and water temperature. Due to radiant heat exchange, the installed power has to be simulated using numerical programs.
Suspended panel systems and capillary systems have higher heating and cooling power than concrete core conditioning systems (for details see Figures following the Q&A section.

What about “radiant asymmetry”?
Radiant asymmetry does not reach uncomfortable levels for cooled ceilings for temperature differences below 10 K (18 F).

How to avoid condensation?
Condensation takes place when the panel surface temperature is below the dew point of the room air. The ventilation system is being used to provide room air with dew points below or at panel supply water temperature.

Can the system be used in any type of building in every climate?
With a ventilation system controlling the humidity of the supply air, hydronic radiant systems can be installed independent of the outside climate.

Does the system show savings in all climates?
Yes, however, percentage savings are biggest in dry climates (for details see C. Stetiu: “Radiant Cooling in US Office Buildings,” Doctoral Thesis, University of California, Berkeley, 1997).

Who is going to install cooled ceilings?
The number of companies who have experience in radiant cooling installations is still very small in the US. We will be able to provide you with some contacts for panel ceilings installations.

Where do I get the equipment?
There are several US, Canadian and European panel manufacturers. Capillary tubes are only manufactured in Germany, and plastic pipe for Concrete Core Conditioning is manufactured in Europe and the US.

Who is going to design it?
We are glad you asked. We do! International Energy Studies provides you with the conceptual design including the heating and cooling load calculations based on numerical simulations, the panel selection or the location of the plastic tubes in the concrete slab, the requirements for the ventilation system, possible alternative cooling sources, and more.
If requested by the client, we will also supervise the installation of the ceiling.

There are three different hydronic radiant systems available:

Panel Systems
Capillary Tube Systems
Concrete Core Conditioning Systems


Hydronic Radiant Conditioning Systems


Suspended Panel Ceiling

Most common radiant system. Aluminum panels with copper pipes connected to the rear of the panel. Connection between the panel and the tube is critical for the heat transfer. Poor connections provide only limited heat exchange between the tube and the panel, which results in increased temperature differences between the panel surface and the cooling fluid in the tubes.

Capillary Tubes

Cooling grids made of small plastic tubes placed close to each other can be embedded in plastic, gypsum board, or mounted on ceiling panels.

Concrete Core Conditioning (CCC)

Tubes are embedded in concrete slab. The thermal storage of the concrete slab allows for peak load shifting, which provides the opportunity to use this system in association with alternative cooling sources. Due to the thermal storage, control is very limited. This leads to a relatively high surface temperature in the cooling mode, to avoid uncomfortable conditions in the case of a reduced cooling mode. Large surfaces, however, provide a reasonable cooling power even at surface temperatures close to room temperatures.

There are several examples worldwide for building conditioning with CCC. For Examples and Publications see the following pages.



This page was developed at IES by hef. Last changed on July 9, 1997
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