Roberts Gorden CRV-B-2 Manual Do Utilizador

9

The building heat loss must be calculated in accor-
dance to accepted energy load calculation methods. 
ASHRAE (American Society of Heating, Refrigeration 
and Air-Conditioning Engineers) offers in-depth infor-
mation that is useful in calculating energy loads. The 
CRV-Series system input is determined in concert with 
the required radiant adjustment to heat loss and height 
adjustment factors.

The practice of applying an adjustment factor to heat 
loss calculations for radiant heating systems is well 
known within the radiant heating industry, having been 
used by manufacturers for over 25 years. A number of 
studies have been conducted to identify the values of 
the adjustment factor in the range of 0.8 to 0.85 
depending on efficiency (higher efficiency uses lower 
factor). This adjustment can be more thoroughly 
understood when considering the following radiant 
effect issues:

• Infrared energy heats objects, not the air.

• Lower ambient temperatures reduce the amount 

of air infiltration.

• Less air stratification with radiant heat.

• Lower ambient air temperatures reduce the trans-

mission heat loss through walls and roof.

• Elevated floor temperature provides a thermal 

reserve capacity.

• Increased mean radiant temperature allows occu-

pants to perceive thermal comfort at the reduced 
air temperature.

Each of these issues impacts favorably on the reduc-
tion of the installed capacity of the radiant heating sys-
tem. This fact, together with the realization that the 
standard ASHRAE heat loss calculation methods 
(particularly the transmission heat loss coefficients) 
have been developed specifically for conventional hot 
air systems, demonstrates the need for the heat loss 
adjustment factor.

• In general, a .80 adjustment factor should be 

used for CRV-Series systems.

As discussed above, the installed input capacity of 
radiant heating systems is typically reduced as com-
pared to the calculated heat loss due to the radiant 
effects associated with a properly designed radiant 

heating system. The ability of a radiant system to pro-
vide the advantages of these radiant effects rests 
largely with the ability of this system to establish a 
reserve heat capacity in the floor. Without this reserve 
capacity, radiant comfort cannot be achieved. (The 
exception is station heating/spot heating applications 
where sufficiently high levels of direct radiation are 
received from the heater.) The height adjustment fac-
tor is a means to insure adequate floor level radiant 
intensity to “charge” the floor heat reservoir.

Proportionately larger wall surfaces also remove 
energy from the floor to a larger degree, decreasing 
the heat reservoir.

The increased input capacity recommended by a 
height adjustment factor is not extraneous as com-
pared to the heat loss calculation. Rather, it is a real-
ization that in order to maintain radiant comfort 
conditions (and the economic benefits), a minimum 
radiant level must be maintained at the floor.

It is recommended that an adjustment to the heat loss 
of 1% per foot (3% per meter) for mounting heights 
above 20' (6 m), be added up to 60' (18 m). Above this 
height, additional correction overstates the BTU 
requirement as determined by the heat loss.

CORAYVAC

®

 Installed Capacity = Heat Loss x 

Radiant Adjustment x Height Adjustment

For CORAYVAC

®

 systems, a .80 radiant adjust-

ment factor is used.

The height adjustment is 1% per foot over 20' 
(3% per meter over 6 meters), or 1.10. 

∴CORAYVAC

®

 Installed Capacity = 350,000 

(Btu/h) x .80 x 1.10 = 308,000 (Btu/h)