Facilities: Cooling Systems - Energy Conversion and Management - page 212

Fig. 12.8 Example of air-to-air reversing heat pump
Example 1 Replacement of an absorption system by a rotating compressor system.
An absorption system with a rated capacity of 1,744 kW (496 tons) is installed in
a food-processing factory and it is fed by steam at 0.7 MPa. The actual refrigeration
capacity is 995 kW (283 tons) with a steam flow rate equal to 2,299 kg/h. The
replacement of this system by a rotating compressor is here examined from the
energy-saving point of view, on the assumption that end-user needs are satisfied in
both cases. The operating characteristics are detailed in Table 12.2 together with the
technical comparison.
Economic evaluation is in Table 19.4 .
Example 2 Heat recovery from condensation phase and lubricant oil cooling.
A refrigerating plant with screw compressors has a nominal capacity of
1,400 kW (397.7 tons). The input shaft power is 500 kW; the refrigerating plant
works 5,000 h/year at 70 % of the rated capacity for food conservation at low
temperature.
Heat recovery can be obtained in two ways: (1) from the condensation circuit by
means of gas/water exchangers and (2) from lubricant oil-cooling equipment.
In case (1), hot water at 40-45 C (104-113 F) can be obtained if the conden-
sation temperature is kept at 45-50 C (113-122 F), which is quite a high value but
still acceptable for screw compressors. Hot water can be used for heating purposes
in the HVAC plant of the site and the boiler-fed hot water circuit for integration,
when needed.
The recoverable heat is estimated equal to 60 % of the sum of the shaft power
and the refrigeration capacity at the average load, that is, 798 kW.