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TECHNICAL MANUAL

Chapter 16

- Operating limits

NGSi 05÷15

ENGLISH

The data in this manual are not binding and they can be modified by the manufacturer without notice.

Reproduction of this manual is strictly prohibited

HAPTER

PERATING

LIMITS

1 6 . 1

E v a p o r a t o r w a t e r f l o w r a t e

The nominal flow rate refers to a temperature difference of 5°C between the evaporator intake and outlet. The maximum permitted flow rate
occurs with a temperature difference of 3°C. Higher values may cause excessively high pressure drops. The minimum permitted flow rate
occurs with a temperature difference of 8°C (except for the model NGSi 05 for which a maximum temperature difference of 6.25°C is
allowed). Insufficient flow rates may cause excessively low evaporation temperatures, tripping the safety devices and causing the unit to cut
out, and in extreme cases even causing ice to form in the evaporator, leading to serious damage to the cooling circuit.
For greater precision, the table below shows the minimum flow rates to be assured at the plate heat exchanger to guarantee correct operation for
each model (N.B.: the water flow switch is provided as protection against failed tripping of the antifreeze probe due to low flow rate; it does not
guarantee the minimum water flow rate required for correct operation of the unit).

As a basic guide, if no other measurement systems are available, the correct flow rate for assuring the best performance from the unit can be
checked, with the circulator pump at maximum rpm, by using a pressure gauge to measure the pressure difference between the water return
and output lines on the unit’s external water connections, and ensure that this value is at least as high as the working heads shown on the
curves provided in Chapter 15 “Heat pump working heads” for the respective models.

1 6 . 2

C h i l l e d w a t e r p r o d u c t i o n ( s u m m e r o p e r a t i o n )

The minimum temperature permitted at the evaporator output is 5°; for lower temperatures, structural modifications must be made to the
unit. In this case, contact our technical department for the feasibility and specification of the modifications to be made depending on
requirements. The maximum temperature which can be maintained during normal operation at the evaporator outlet is 25°C. Higher
temperatures (up to a maximum of 40°C) can be tolerated in transients and during start-up. In all case, the maximum power drawdown is
during operation in heat pump mode with outlet water at 55°C and external temperature of -10°C.

1 6 . 3

H o t w a t e r p r o d u c t i o n ( w i n t e r o p e r a t i o n )

Once the system is in normal operation, the water intake temperature must drop below 25°C; except during transients or start-up, lower
values may cause system malfunctions with possible compressor failures. The maximum outlet water temperature must not exceed 55°C. At
this temperature, electricity drawdown and COP are optimised if the external temperature is over 5°C, although the unit is able to operate
down to the limit of -15°C.
For temperatures above those indicated, especially with low water flow rates, unit malfunctions may occur, or in the most critical cases the
safety devices may be tripped.

1 6 . 4

R o o m a i r t e m p e r a t u r e a n d s u m m a r y t a b l e

Units are designed and built to operate in summer mode, with condensation control, with an external air temperature between -10°C and
46°C. During operation in heat pump mode, the permitted external air temperature range is from -15°C to +40°C, depending on the outlet
water temperature as shown in the table below.

Operating limits

Model

NGSi 05

NGSi 07

NGSi 10

NGSi 15

Rated cooling power [kW]

5.67

8.93

11.90

14.36

Minimum water flow rate to by guaranteed [L/s]