Daikin Applied (UK) Ltd.
REV A
– PAGE 9. SECTION 11 ADDED. 11/03/14
Page 29 of 37
Condensate Removal from Steam Coils
When air, water, or other product is heated, a modulating steam pressure control valve
can regulate the temperature or heat transfer rate. Since pressure and temperature do
not vary at the same rate as load, the steam trap capacity, which is determined by the
pressure differential between the trap inlet and outlet, may be adequate at full load, but
not at some lesser load.
Analysis shows that steam pressure must be reduced dramatically to achieve a slight
lowering of temperature. In most applications this can result in sub-atmospheric pressure
in the coil, while as much as 75% of full condensate load has to be handled by the steam
trap. This is especially important for coils exposed to outside air, since sub-atmospheric
conditions can occur in the coil at outside temperatures below 0ºC (32ºF) and the coil will
freeze if the condensate is not removed. There are detailed methods for determining
condensate load under various operating conditions. However, in most cases, this load
does not need to be calculated if the coils are piped as shown in the figure below and this
procedure is followed.
The steam trap should be 0.3 to 0.9m (1 to 3ft) below the bottom of the steam coil to
provide a hydraulic head of approximately 0.5 to 1.5 psig (3.5 to 10.3kPa above atm.).
Location of the trap at less than 300mm (12in) minimum usually results in improper
drainage and operating difficulties.
