Handbook of air conditioning and refrigeration / Shan K

8.28 CHAPTER EIGHT
2 and 6 in. (50 and 150 mm). The thickness of the floor slab has a significant effect on its thermal
storage and slow response to heating load changes. Floor coverings like carpet and wood affect the
overall thermal resistance of the floor panel. The water temperature, therefore, should be increased
accordingly in order to provide the required amount of heat that is released from the floor panel. An
insulating layer and a moisture barrier under the concrete slab are often needed to reduce the heat
losses, as shown in Fig. 8.9c.
Thermal Characteristics of Floor Panel
Pump
Boiler
According to ASHRAE Handbook 1996, HVAC Systems and Equipment, the heat flux of the radiant
heat transfer irradiated from a heating floor panel q r,Btu/h�ft 2 (W/m 2 ), can be calculated as
q r � 0.15 � 10 �8 (T 4 Rp � T 4 R,AUST )
where T Rp � absolute temperature of effective panel surface,°R (K)
T R,AUST � absolute temperature of area-weighted average temperature of unheated surfaces exposed
to panels (AUST),°R (K)
(8.13)
The heat flux due to natural convection flows upward from a heated floor panel q c,Btu/h�ft 2 (W/m 2 ), is
Floor
panel
(zone 1)
Control
value
(a)
Thermostat
T1 T2
Floor
panel
(zone 2)
q c � 0.31(T p � T a) 0.31 (T p � T a)
DDC
unit controller
(c)
Outdoor
TO
Boiler
TR
TS
Return
sensor
Mixing
valve
Concrete
Plastic
tube
Insulation
layer
Supply
sensor
T1
(b)
Supply main
T2
Return main
(8.14)
FIGURE 8.9 Hydronic radiant floor heating systems. (a) Zone control valves; (b) outdoor reset plus zone control valves; (c) floor panel;
(d) design nomograph. (Source: ASHRAE Transactions 1995 Part I, p. 1204, Kilkis and Coley. Reprinted by permission.)