Filter
Top Products
36 TRG-TRC001-EN
notes
period four
Air Quantity
Some designers prefer to set the supply air temperature at 55°F or use a 20°F
temperature differential (Room DB – Supply DB) without regard for the actual
sensible heat ratio of the room.
Using our same example, let’s examine how this has the potential for creating a
problem. Assume that the building design changes to use a much-higher-
quality glass that will reduce the sensible portion of the design load from
80,000 Btu/hr to 47,000 Btu/hr. This reduces the SHR to 0.70.
Plotting this new SHR line on the psychrometric chart, we find that the SHR line
crosses the coil curve at approximately 49°F DB (D).
If the system is arbitrarily designed with a 55°F supply air temperature D’, the
resulting room conditions will fall on the 0.70 SHR line drawn through D’. The
resulting room conditions A’ will be 78°F DB, 57% RH. This arbitrary design
practice results in a higher room relative humidity than desired.
%WXKUVHQVLEOHKHDWJDLQ
%WXKUODWHQWKHDWJDLQ
%WXKU
%WXKU
6+5
$UELWUDULO\8VLQJ)6XSSO\$LU
Figure 58
$
$
&
&
%
%
'
'
)
)
'
,
'
,
$
,
$
,
$UELWUDULO\8VLQJ)6XSSO\$LU
)
)
6
+
5
6
+
5
Figure 59