Radiant Cooling Systems

Hydronic PEX-based System

The most effective way to optimize thermal comfort and energy use. 

Typically designed in conjunction with radiant heating, radiant cooling works by circulating cooled water through the same network of pipes where warm water circulates during winter. The cooled surfaces evenly absorb heat energy to create perfect comfort using little energy.

Suited to Many Climate Regions
Early on, radiant cooling was best suited for arid regions, however, advances in system design and control capabilities have led to successful installations in various climate zones.

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How it Works

Studies by building technology experts, including DOE and UC Berkeley’s Center for the Built Environment, recommend radiant cooling as the technology with greatest potential for energy savings at competitive or reduced investment costs. 1,2

Radiant cooling works best in a tightly sealed building that integrates radiant with a downsized forced-air system to meet the building’s fresh air requirements. With optimized design, two cooling systems, each doing what it does best, are more efficient and cost effective than one.

Separating Cooling Components for Maximum Efficiency
Effective cooling requires removal of heat energy from solar gains, electrical equipment and people (sensible load) as well as humidity (latent load). A hydronic radiant system takes advantage of the superior heat transfer properties of water to very efficiently absorb heat energy, while air-based cooling efficiently removes excess humidity. By shifting some of the cooling load to the radiant system, air handling equipment and ductwork can be significantly downsized.

Just as decoupling building loads fine tunes efficiency, breaking down how humans experience temperature fine tunes comfort. Mean radiant temperature (i.e., the average of the surfaces surrounding you) and air temperature (i.e., the thermostat setpoint) combine to create operative temperature (i.e., the temperature you feel). With its expansive cooled surfaces, radiant cooling lowers mean radiant temperature, allowing thermal comfort to be achieved with a slightly higher setpoint than in 100% forced-air systems. This elevated air temperature results in energy savings on the total cooling load required by the building.

Achieving Optimal Radiant Cooling Output
A radiant cooling system is designed similarly to a radiant heating system, with minor adjustments in pipe diameter and pipe spacing. The capacity of a radiant cooling system depends on factors such as insulation, pipe spacing, floor construction and indoor air temperatures. Under optimal design conditions, capacities of a floor system up to 16 Btu/h∙ft² can be achieved,3 with more typical capacities in the 8 to 12 Btu/h∙ft² range. Ceiling systems can achieve nearly double this output.

The main difference between radiant cooling and radiant heating system design is a heightened awareness of humidity control. Careful control of humidity and water temperature is essential to reduce the risk of condensation. By using an integrated design team approach including architects, engineers and contractors from the early phases of a project’s design, many buildings have realized superior energy performance with REHAU radiant heating and cooling systems.

Increasing Capacity With Bidirectional Conditioning
In REHAU radiant cooling systems, RAUPEX pipe is typically integrated into an insulated floor slab, providing unidirectional conditioning to a single adjacent space. For interior levels where bidirectional conditioning of spaces above and below is desired, the layer of insulation can be omitted. Often referred to as thermally activated slabs (TAS) or thermally activated building systems (TABS), this emerging design option increases the capacity of the radiant system. In addition, “charging up” the thermal mass can take advantage of off-peak electrical rates.

1 Building HVAC Systems Volume III: Energy Savings Potential,Roth, et al. Energy Consumption Characteristics of Commercial, DOE, July 2002.
2 Moore, et al. Radiant Cooling Research Scoping Study, Center for the Built Environment, University of California, Berkeley, April 2006.
3 Olesen, Bjarne. Radiant Floor Cooling Systems, ASHRAE Journal, September 2008.

Installation and Performance

This diagram of a typical commercial radiant cooling system illustrates two installation configurations: A TAS method (Thermally Activated Slab) in the upper floor and a standard in-slab construction with an insulation barrier in the lower floor. Supply lines from the energy source are colored blue; return lines are colored red.

1. RAUPEX® pipe
2. PRO-BALANCE® manifold
3. Room thermostat / humidity sensor
4. System controller
5. Surface sensor
6. Outdoor air sensor
7. Main control
8. Valves
9. Temperature sensor
10. Circulator pump
11. Mixing valve
12. Energy supply (e.g., geothermal heat pump)

The capacity of a radiant cooling system depends on factors such as insulation, pipe spacing, floor construction and floor covering. Under optimal design conditions, capacities of up to 16 Btu/h ft² can be achievedwith more typical capacities in the 8 to 12 Btu/h ft² range.

In radiant cooling systems, RAUPEX® pipe is either integrated into a floor structure with insulation to condition the space above or without insulation to condition the space above and below.

Design Factors
Designing and installing a radiant cooling system can be straight forward, especially when integrating with a radiant heating system. A focus on controlling humidity levels and water temperatures is essential to reduce the risk of condensation associated with radiant cooling.

Radiant cooling works best in a tightly sealed building, so you will typically need supplemental ventilation, either to meet the building’s fresh air requirements or to meet peak cooling loads. 

For assistance with design, visit our Design Support page.

*Olesen, Bjarne. Radiant Floor Cooling Systems, ASHRAE Journal, September 2008.


Just as ground temperatures keep the walls of your basement slightly cooler and therefore absorb heat from the rooms, a radiant system embedded in your building structure can have a similar effect, providing even, comfortable cooling to your space.

Increases Thermal Comfort
The human body feels at its best when it can regulate at least 45% of its heat emission via radiation. Radiant cooling provides a comfortable environment by optimizing the surface temperature of the occupants’ surroundings and efficiently absorbing unwanted heat from the space.

Improves Energy Efficiency
By surrounding you with cooled surfaces, radiant cooling allows you to feel comfortably cool with your thermostat set a few degrees higher. This can significantly reduce energy consumption. For the ultimate in efficiency, couple radiant cooling with geothermal. The moderate water temperatures required by a radiant cooling system are precisely the temperature ranges in which a geothermal heat pump operates most efficiently.

Improves Air Quality
A radiant cooling system can greatly improve air quality, making it ideal for hospitals, nursing homes or any facility in which air quality is critical. Also, radiant cooling can handle the entire cooling load or be used to cover the base loads in traditional cooling applications. 

Reduces Life Cycle Costs
A hybrid radiant-forced air cooling system may cost a little more upfront, but its superior energy efficiency will result in a short payback period and lower operating costs. In more arid climates where air handling equipment can be downsized dramatically, a hybrid design can actually reduce initial investment costs. You can also expect lower maintenance costs with a hybrid system.

Radiant With Geothermal

A natural synergy...
If you’re considering using our RAUGEO ground loop system, you’ll also want to look at radiant heating and cooling, and vice versa. There’s a natural synergy between the two.

Here's why: In order to provide comfortable room temperatures, radiant heating works well with relatively low water temperatures and radiant cooling works with moderate water temperatures. It’s precisely in these temperature ranges that your water-to-water geothermal heat pump operates most efficiently.

So, by combining RAUGEO with REHAU radiant heating and cooling, you’ll enjoy the greatest comfort at the lowest operating cost. You’ll also appreciate the reliability of REHAU quality components from the geothermal probe to your thermostat, including durable PEXa pipes, secure joints and manifolds with individually controlled circuits.

It could be all you need for total comfort.
In many cases, a properly designed geothermal-radiant system can provide enough energy to heat and cool your entire space even in extreme temperatures.