Modeling and Design of Net ZEBs as Integrated Energy Systems - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 81

2.2.3.1 Radiant Heating/Cooling Systems Integrated with Thermal
Mass
Unlike air-conditioning systems that condition spaces primarily through
convection, radiant systems (ASHRAE, 2007) condition the floor, ceiling,
or walls, which in turn either radiate heat directly or absorb heat from
occupants or objects, while also having a significant convective component
when the heat flow is upward (cooling ceiling or heating floor). Heated
floors have been used since the first millennium B.C. (Bean, Olesen, and
Kwang Woo, 2010); for example, around 300 B.C. the Romans started to
use them extensively. The system called “Hypocaustum” was defined by the
furnace (hypocausis) and a series of flue passages realized under the floor
by means of pillars carrying a slab (i.e., like a ventilated concrete slab).
In modern times, starting from the 1950s and the 1960s, radiant heating
installations started to increasingly appear in Europe in the residential
sector, but taking into consideration that buildings were not well insulated,
the resulting operating temperature of the working fluid was higher than
today's standards. Then, at the end of the 1970s, the introduction of plastic
pipe for floor heating facilitated more widespread use of floor heating,
especially in Germany, Switzerland, Austria, and the Nordic countries.
Three types of radiant floor heating exist: radiant air floors (air is the
heat-carrier), electric radiant floors, and hot water radiant floors. All three
types can be further subdivided by the type of installation: those that profit
from the large thermal mass of a concrete slab floor (these are called “wet
installations”); and those in which the radiant floor tubing is located
between two layers of plywood or under the finished floor or subfloor (“dry
installations”). Air-heated floors (like VCS) are often characterized by slow
response; however, they can be coupled with air heating systems.
Hydronic (liquid) systems are the most popular radiant heating systems. In
thesesystemsheatedwaterispumpedfromaheatingsourcethroughtubing
laid out in a pattern in the floor massive layer (usually at its bottom). In
some systems, the temperature in each room is controlled by regulating the
flow of hot water through each tubing loop, through the use of motorized
zoning valves. For hydronic floors it is recommended to use water at about
35 °C, while for cooling using water at a temperature lower than 15 °C
should be avoided (ASHRAE, 2007; Olesen, 2002) to avoid condensation
problems. These temperatures make the use of solar assisted heat pumps
or solar combi-systems a good option for producing hot water in Net ZEBs.