Modeling and Design of Net ZEBs as Integrated Energy Systems - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 82

Geothermal systems may be used to provide both heat and cool using
air-to-water heat pumps.
In “Wet” installations, the oldest form of modern radiant floor systems, the
tubing is located within a solid floor. The tubing or cable can be inserted in
a thick concrete foundation slab or in a thin layer of concrete, gypsum, or
other material installed on top of a subfloor.
In “Dry” floors, the cables or tubing run in an air space beneath the floor.
Usually a dry floor is faster and less expensive to build; it is characterized
by lower thermal inertia but requires higher operating temperatures. These
installations are usually easier when planning retrofit actions and can often
integrate acoustic solutions.
One of the main features of radiant floor heating (mostly in wet
installations) is the uniform temperature conditions from floor to ceiling
and the reduced thermal stratification (Olesen, 2002). Floor heating
systems usually provide superior comfort conditions for occupants as air
movement in the environment and vertical temperature gradient are very
low and the thermal mass limits the temperature fluctuations; moreover,
the working fluid average temperature is low, which allows for a wide set
of solutions for the heating source (also district heating or geothermal heat
pump systems can be used). On the other hand, the thermal mass causes
the system to react slowly to temperature changes. Overheating can be
an issue in poorly controlled zones; these systems usually have difficulties
dealing with frequent setpoint temperature adjustments. Radiant cooling
fluid temperatures must also never be lower than 13-15 °C to ensure
comfort and avoid the formation of interstitial moisture. Predictive control
is one efficient strategy to optimally control radiant heating in TABS
(thermal massive systems). Ventilation and humidity control may be done
separately.
Practical applications of active BITES systems with radiant heating/cooling
are presented in this topic. They include a hydronic BITES system installed
in an institutional Net ZEB, Research Support Facility (RSF) building
(Section 7.3), in the National Renewable Energy Laboratory (NREL) of the
Department of Energy of the United States, a hydronic BITES system in
the residential Net ZEB, Leaf House (Section 7.2), and a ventilated BITES
system adopted in a residential near Net ZEB, ÉcoTerra (Section 7.1).