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II.10.7 VPF accessory – Variable primary Flow
The energy used for the cooling unit to work is an important component in the system costs, and reducing the unit consumption, especially with partial
load, is sometimes compromised by the pump unit operating constantly. The higher the absorption of the pumps used to maintain the proper flow of
water in the pipes the more this effect is noticed.
A solution that compensates for the problem of the energy absorbed by the pump units is using pumps driven by inverter technology, able to modulate
the flow rate G and reduce power consumption. This is how the systems with constant primary flow and secondary decoupled variable flow exist.
The introduction of the VPF system simplifies the systems, using a single primary variable flow circuit, in which inverter controlled pumps are installed as
the only pumps in the system; this solution generates complications related to the calibration, sizing of the venting section and system setting, which
burden the client and indirectly could affect the reliability of the machine.
The solution proposed by HITECSA combines the simplification of the VPF system, the reliability of the system solution with primary-secondary variable
flow circuits and the additional energy and cost savings derived from managing the primary with variable flow where energy saving depends on the
variation in flow rate ΔPa=f(ΔG)
The content of water in the primary circuit is very important since it stabilises system operation, the water temperature to the system and reliability of the
cooling unit over time (recommended minimum content of 7L/kw)
The cooling circuit is equipped with pumps on the primary side with inverter adjustment and the option to manage the inverter pumps from the system side.
In addition to significant energy savings, the solution with VPF technology by HITECSA also allows the design of the system's hydraulic circuit to be simplified
and the operating costs to be decreased.
The HITECSA solution offered for variable flow systems is innovative for several reasons:
• Stable flow rate modulation required by the system with guaranteed reliability for the chiller installed (even with system flow rate oscillation). The flow
rate can be modulated up to 20% by using pumps with an EC-type of motor
• Simplified system calibration operations
• Simplified design of the solutions to be applied to the terminals (balancing the number of 3-way and 2-way valves with adequate sizing of the venting
section)
• Maximising the efficiency of the cooling unit in each operating condition for the flow rate to be modulated on the system side following the route of
the load, as well as on the primary side, thereby minimising the pumping energy required for it to operate correctly.
• Possibility of simplified and reliable management of several units in parallel (the known problems related to flow variations in traditional VPF systems
when the cooling units are connected/switched off are avoided)
Below is a basic diagram of the VPF solution by HITECSA being used in the case of a single chiller
P/DP
Single or double pump controlled by a variable frequency inverter (pumps installed and controlled by HITECSA with a 0-10V signal)
Single or double pump, controlled by a variable frequency inverter to service the system. Adjustment is carried out by means of flow mod-
PI/DPI
ulation and is supplied by the user (with separate supply) and in this case, HITECSA is in charge of management via the analogue signal 0-
10V
TANK
Storage tank
V2
2-way adjustment valve
V3
3-way adjustment valve
∆P
Differential pressure transducer
NOTES on the installation:
1.
If a cooling unit with VPF technology is installed, a tank must be installed to guarantee minimum water content of 7 l/kw on the primary side. At least
20% of the flow must be guaranteed on the system side by installing a minimum number of terminals fitted with 3-way valves V3The probe to determine
the ∆P pressure differential is a standard supply. The installer can set the probe remotely in the most appropriate point in the system.
2.
Probes T1 and T4 are supplied and must be installed on the return side of the system, as shown in the figure: T1 before the hydraulic disconnector and
T4 after.
VPF
T1
T2
T3
T4
∆P
52
3.
HITECSA VPF Solution (Variable Primary Flow)
(0-10 V)
T
(T3)
OUT
P/DP
T
(T2)
IN
Primary side
pumps
EQPI3X
System side
pumps
PI/DPI
∆P
T4 T1
TANK
Disconnector
Probe ∆P
V2
V2
V3
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