A ton of Refrigeration (TR)
A ton of
refrigeration (TR) is a unit of heat extraction capacity of the
refrigeration or cooling equipment. Generally, TR is defined as the amount of
heat transferred to freeze or melt 1 short ton of ice at 0 deg. C in 24 hours.
1 TR is
approximately equal to 12000 BTU or 3024 Kcal/hr of energy/heat load.
The heat of the fusion of water is about 335 KJ/kg or 80.01 kCal/kg. 1 short ton is equal to
2000 lb or 907 kg.
Ans:
TR
is the amount of heat to be extracted from the system or process.
Assumption :
1. Air is 100 % dry at inlet
temp.
2. The system is well
insulated and Heat gain from the atmosphere is negligible.
Here
cooling duty of the heat exchanger is the amount of heat to be extracted and
heat added by a chilling water recirculation pump.
Let's
calculate the Chilling duty (Qa) of the heat exchanger.
Qa
= Air Flow rate x Cp of Air x ( Air in
temp – Air out Temp)
=
1000 x 0.24 x ( 45-10 )
= 8400 Kcal/hr
Qa
= 8400/3024 = 2.78 TR ------------------ I
Let's
calculate the chilling water flow rate (Mw) for Qa
Chilling water flow rate
(Mw) = Qa /( Cp x ( Chiller temp. Diff.)
Mw
= 8400 /(1*5) =
Mw
= 1.7 m3/hr ------------------------ II
Pumping
power (Shaft power) with about 30-meter liquid head and 30 % pump efficiency is
about 0.44 kWh. Assuming worse case that all pumping power (Qp) will be added to liquid which is about
0.44 kWh i.e. 378 kCal/hr ( 1 kWh = 860 Kcal).
Total
heat load on chiller is,
Qc = Qa+Qp
= 8400 + 378
= 8778 Kcal/ Hr
------------------------------ III
Chiller
Capacity = 8778 Kcal/hr i.e. 2.9 TR.
Note:
1. If air or gas is
saturated or has moisture then the heat of condensation will be added to
cooling duty to calculate actual chiller capacity.
