These systems use a structure’s architectural elements to maintain comfortable spaces that are energy efficient and help achieve decarbonization goals.
By Hailey Mick and Kim Bliss
Industry experts agree that decarbonizing buildings—whether new construction or renovations of century-old structures—is a critical step to meeting global climate goals. One solution that is gaining significant interest in commercial building design and construction is radiant heating and cooling combined with geothermal ground source heat pumps (GSHPs).
How Radiant Heating and Cooling Works
In a radiant heating and cooling system, heated hot water or chilled water circulates through a network of flexible, durable polymer pipes (PEX) that are embedded in the concrete slab. By simply controlling the flow and temperature of the water, the system efficiently and effectively controls the temperature of the slab, transferring heat in one direction or another—out from the slab to radiate heat for warmth and into the slab to absorb heat for cooling.
One common question that arises regarding radiant cooling is: When heating a space, it makes sense to heat from the floor, but shouldn’t cooling come from the ceiling, because heat rises, right? Actually, no, heat does not rise. Hot air rises due to buoyancy based on the differences in density.
If heat doesn’t rise, what direction does it go? To answer this question, we need to look at the second law of thermodynamics. More specifically, we need to look at the second formulation of the second law known as the Clausius statement, which states that heat will always naturally go from a high state to a low state (unless an outside source is influencing it).
For example, grabbing a hot coffee cup will transfer heat to your hand, but grabbing a cold glass will transfer heat from your hand to the glass, leaving you feeling cold. Hence, it does not matter if the surface being controlled is the floor, wall, or ceiling; as long as there is a temperature difference (a delta T) between the controlled surface and the object and people within the space, there is always going be heat transfer.
Combining Radiant Heating and Cooling with Geothermal GSHPs
The heated or cooled water from the geothermal ground source heat pump is what circulates through the PEX pipes in the radiant system, and combining these two systems for indoor climate (or even outdoor snow melting or turf conditioning) offers significant energy advantages.
Geothermal systems regularly achieve a COP (coefficient of performance) of 3 to 5 or higher, making them significantly more efficient than conventional HVAC systems. For example, in a heating application, a closed-loop geothermal system can actually provide free heat because it recharges the ground. For cooling, a typical chilled water system recirculates at 42°F, and radiant cooling systems operate at 58°F. Each degree the supply water increases can save between 1.5 and 3 percent in energy, which helps lower greenhouse gas emissions.
Additionally, both radiant and geothermal GSHP systems are long-lasting and require very little maintenance. For example, a radiant heating and cooling system uses corrosion-resistant PEX piping, which is highly durable, sustainable, and lasts for decades. In fact, studies indicate the carbon footprint of PEX is lower than copper when considering material extraction, processing, and installation. According to the Journal of Cleaner Production, “Energy and global warming potential reductions for PEX piping compared to copper piping (average for copper pipes types K, L, and M) are 44 percent and 64 percent.”
Other benefits include low operating costs, space optimization (minimal ductwork), and superior thermal comfort. The comfort stems from the fact that radiant most closely aligns with the ideal heating curve for the human body. Plus, when the system is in the floor where people are located, it provides instant comfort instead of wasted energy up in the ceiling (for heat, specifically).
Radiant cooling systems can also benefit from radiant ceiling panels to absorb heat that rises up in a space. The high-temperature cooling concept used by radiant cooling can also reduce the load on the equipment, allowing for smaller-sized heat pumps that do not consume as much electricity.
In addition, radiant systems provide uniform temperatures without drafts or noise, and because they are installed in zones, they can provide precise temperature control for occupants in different spaces. Plus, radiant systems support indoor air quality because they circulate conditioned water through the floor, ceiling, or walls instead of using fans that blow air as well as dirt, dust, allergens, and bacteria throughout a space.
In Conclusion
Combining radiant and geothermal GSHP systems is an efficient, resilient solution for heating and cooling. Water is safe and easy to use, has a high thermal capacity and low viscosity, requires less monitoring, and is better for our environment.
These systems are an intelligent solution that integrate architecture and sustainable HVAC design, using a structure’s architectural elements to maintain comfortable spaces that are energy efficient and help achieve decarbonization goals.
About the Authors
Hailey Mick is a business development manager with Alliance Air Products, a member of DAIKIN group, and can be reached at hailey.mick@allianceairproducts.com.
Kim Bliss is the technical and marketing content manager at GF Building Flow Solutions, a provider of Uponor-branded products, and can be reached at kim.bliss@georgfischer.com.
The opinions expressed in this article are those of the authors and not the American Society of Plumbing Engineers.
