37
Minimum water content in the system
For correct operation of the unit, it is necessary to ensure a buffering on the system such as to comply with the minimum
operating time considering the greater between the minimum OFF time and the minimum ON time. In short, these con
-
tribute to limiting the number of times the compressors are switched on per hour and to preventing undesired deviations
from the set point of the delivered water temperature.
Larger amounts of water are in any case always preferable, because they allow a smaller number of starts and switch-
offs of the compressors, less wear of them and an increase in the efficiency of the system as a consequence of a reduc
-
tion in the number of transients.
where
V
min
is the minimum water content of the system [l]
P
tot
is the total cooling capacity of the machine [kW]
N: number of capacity reduction steps
ΔΤ: differential allowed on the water temperature. Unless otherwise specified, this value is considered to be 2.5K
ρ: density of the heat-carrying fluid. Unless otherwise specified, the density of water is considered
c
p
: specific heat of the heat-carrying fluid. Unless otherwise specified, the specific heat of water is considered
Considering the use of water and grouping together some terms, the formula can be re-written as follows:
For the N values, consider the following convention:
•
for units with 1 compressor N = 4
