T9901018-1
Page 4 of 26
Because of the relatively high hydraulic pressure drops it may be cost effective to
incorporate two water pumps operating in series. Pump(s) need to be 230V/1ph/50Hz with
a total maximum current = 2A for all pumps combined. If the pump(s) total current is higher
than this an interface relay/contactor will need to be used.
If so required, the cooling duty can be reduced from 12kW and a smaller water pump
used. Dry cooling will still be achieved providing the room environmental conditions are no
higher than 24°C dry bulb with a relative humidity no greater than 40% and the chilled
water flow temperature entering the unit is no lower than 10°C. The following table gives
details for this:
Table 2
Cooling Duty
(kW)
Water Volume
Flow Rate
Water Return
Temperature
(
°
C)
Hydraulic Resistance
of water coil in
Thermoscreens Dry
Cooling Unit
(kPa)
Hydraulic Resistance
of heat exchanger in
Mitsubishi PUHZ
Outdoor Unit
(kPa)
m
3
/h l/min
11.5 2.6
44 13.8
24
10
11.0 2.0
33 14.8
14
6
10.5 1.6
26 15.7
9
4
Calculated for Water Flow Temperature = 10°C
In case of emergency, condensate could form on the cooling coil if there was a failure in
the air conditioning on site or environmental conditions in the server room went above
24°C/40%Rh due to some other circumstance, e.g. doors left open, extreme weather
conditions. To allow for this the Thermoscreens dry cooling unit is supplied with an integral
condensate drain tray and outlet pipe to drain condensate away from the unit. A gravity
condensate drain system extending to a suitable drain outside of the room must be
supplied and fitted by the installer in case this emergency situation were to occur. This
should be connected to the 15mm copper drain pipe that protrudes from the right-hand
rear of the cooling unit behind the plastic end cap. Condensate pumps are not
recommended but if a gravity drain system is impossible and a condensate pump is the
only alternative it must not be fitted at the dry cooling unit because of reliability issues with
these devices. If the condensate needs to be pumped to a higher level with a condensate
pump this should be done in a separate room away from the server room. If there was a
spillage of condensate at the pump, therefore, it will not occur in the server room. Suitable
condensate pumps are Peristaltic or Rotary Diaphragm type with a suction head. The
condensate pump needs to have the facility so it only operates if water is detected in the
drain tray. It should also have a pump overrun to empty the drain tray as much as
possible. We recommend the Blue Diamond rotary diaphragm type with cooling signal
sensor (drainStik) manufactured by Charles Austen Pumps Ltd. (
www.miniblue.co.uk
).
The condensate drain tray inside of the Thermoscreens dry cooling unit has a metal fixing
bracket located at the right hand end so a condensate sensor can be fixed in the tray in
the appropriate position by the installer. There is a rubber grommet with 9.5mm hole fitted
in the fixing bracket which will accept a 10mm diameter condensate sensor. Different size
grommets can be fitted by the installer to suit other condensate sensors or if the grommet
is removed a larger condensate sensor can be located in the 13mm diameter hole in the
fixing bracket and held with silicon sealant. See also the manufacturer’s instructions that
come with the condensate pump for further information.
Valuable or delicate equipment should not be placed beneath the dry cooling unit or
directly in the path of the cool air discharge from the unit.
