Over the past decade, the number of radiant cooling systems designed, installed and commissioned has increased dramatically. More widely adopted in Europe, radiant solutions have seen steady growth in North America and more recently in Asia with projects in India, Malaysia, Singapore and Thailand. These cooling systems are gaining exposure and popularity for a variety of reasons.
Here are the top 5 radiant cooling benefits:
- Energy efficiency
- Superior thermal comfort
- Greater architectural flexibility
- Reduced operating and maintenance costs
- More effective control of ventilation
A hydronic cooling system can help dramatically reduce the energy consumption of a building through lower transport energy usage, more efficient operating modes, higher room setpoints, and lower transmission losses.
- Lower Transport Energy Usage: Because the heat-transfer capacity of water is much higher than that of air, a radiant system that uses a circulator to move water (in lieu of a fan to move air) can achieve the same heat transfer using significantly less energy.
- More Efficient Operating Modes: In addition to reducing energy consumption by utilizing pump power in lieu of fan power, an air-and-water system can also lower overall energy use by allowing the chiller to operate at more optimum modes. Typical chilled water temperatures for a hydronic system are between 55°F (12.7°C) and 63°F (17.2°C). Higher return water temperatures may allow the chiller to operate within a more efficient range. These higher operating temperatures also allow greater flexibility in chilled water sources. Potential alternative sources for chilled water may include fluid coolers, geothermal heat pumps or lake/bay water. The Exploratorium Museum uses water directly from the San Francisco Bay.
- Higher Room Setpoints: Because of the way the human body reacts to its surrounding environment, comparable levels of comfort can be achieved with a hydronic system at higher room temperatures (e.g., 78°F/25.6°C) than with a forced-air system at lower room temperatures. Therefore, a radiant cooling system, coupled with a dedicated outdoor air system (for ventilation, latent loads and supplemental sensible loads) can reduce a building’s total energy use by operating at higher setpoints.
- Lower Transmission Losses: With a conventional forced-air system, transmission losses can occur due to inadequate or poor insulation, and duct leakage. Distribution systems typically experience lower transmission losses. As a result of these factors, the total energy consumption of a building can be significantly reduced. Recent studies have shown total energy conservation for typical office buildings using hydronic cooling on the order of 17 to 53% below ASHRAE Standard 90.1-2010. The number of projects incorporating radiant cooling to achieve higher energy performance ratings continues to grow.
Superior Thermal Comfort
ASHRAE Standard 55-2010, Thermal Environmental Conditions for Human Comfort lists six factors that affect thermal human comfort: air temperature, radiant temperature, humidity, air velocity, clothing and metabolism. All-air systems attempt to maintain comfort by controlling air temperature and indoor relative humidity, ignoring the impact that radiant temperature has on human comfort. In typical settings, during low activity with light clothing and moderate air velocities, the human body transfers more of its sensible heat through radiation. Controlling floor temperatures and reducing surface temperature differentials results in reduced stratification and radiant asymmetry. Therefore, a thermal mass system that relies on radiation heat transfer can create a more comfortable environment compared to a system relying exclusively on convective heat transfer.
Greater Architectural Flexibility
With a hydronic cooling system embedded in the floor slab, the visible components, such as air handlers, ductwork, grilles, diffusers, etc. can be much smaller, allowing greater flexibility in the aesthetic architectural design. The space requirements for the mechanical system (e.g., mechanical room, roof space, ceiling space for ductwork) can be compacted, potentially reducing building floor-to-floor heights. Additionally, because a radiant slab can much more effectively deal with direct solar loads, temperatures in areas with high fenestration (e.g., lobbies, atria, etc.) can be more easily controlled with less noise and draft.
Reduced Operating and Maintenance Costs
The embedded tubing within the concrete slab requires no maintenance. The air-and-water system, including the chilled water source and distribution, requires no more maintenance than typical fluid-based systems. The smaller DOAS system — made possible by the radiant cooling system — translates to lower operating and capital costs (e.g., reduced fan horsepower, smaller filtration, smaller dehumidification equipment, etc.).
More Effective Control of Ventilation
In many heating, ventilation and air conditioning (HVAC)systems today, the air handling systems are sized to deliver airflow based on the total cooling and ventilation requirements of the spaces and occupants they are serving. These airflow rates are rarely the same, and controls are often ineffective in delivering the proper amount of airflow to satisfy both requirements simultaneously. For example, in some cases rooftop units are used to cycle on and off based on cooling demand, ignoring the continuous demand for ventilation air. In an air-and-water system, these two functions are decoupled. Decoupling these functions allows more exact ventilation control, ensuring that the occupants always receive the proper amount of outside air.
The Future of Cooling lies with Radiant Systems
Hydronic cooling solutions have increased in popularity over the last decade. The advancements in design, manufacture and installation combined with the pressure for architects to design cleaner, more efficient, more sustainable buildings have pushed radiant systems into the spotlight.
Many buildings like the Exploratorium Museum in San Francisco have achieved LEED’s certifications with the help of radiant cooling solutions. The traditional means of cooling through all-air systems is outdated, ineffective and wasteful. It is certainly perhaps the more familiar of the two but it is by no means the best or the most affordable. Radiant cooling is the future of cooling.