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10 SYSTEM WATER CONTENT
MINIMUM SYSTEM WATER CONTENT
For correct unit operation, there must be a suitable amount of water in the system. A sucient quantity of water not only ensures machine stability, but also helps avoid a high
number of hourly compressor start-ups.
To calculate it, use the formula: Unit rated cooling capacity (ton) x table value (gal/ton) = Minimum system content (gal).
NRP 2-PIPE SYSTEM 0800 0900 1000 1250 1400 1500 1650 1800
Minimum water content allowed SYSTEM SIDE gal/ton 9.2
Minimum water content allowed DHW SIDE gal/ton 9.2
Recommended water content SYSTEM AND DHW SIDE gal/ton 13
NRP 4-PIPE SYSTEM 0800 0900 1000 1250 1400 1500 1650 1800
Minimum water content allowed COOLING SIDE gal/ton 6.5
Minimum water content allowed HEATING SIDE gal/ton 9.2
Recommended water content COOLING AND HEATING
SIDE
gal/ton 13
Note: the water content referred to in the tables corresponds to the amount of water eectively useful for inertial purposes; this value does not necessarily coincide with the
entire system water content, and must be calculated on the basis of the system layout and operating modes.
Some examples are given below, but they do not cover all the possible situations.
Example 1: for a 4-pipe multifunction unit with primary circuit (heating and cooling) and secondary circuit, where the zone pumps of the secondary circuit may (even just
occasionally) be disabled, the water content of the primary circuit alone is considered the amount useful for count purposes.
Example 2: for a 2-pipe multifunction unit with an intermediate circuit (DHW side) that works on an intermediate heat exchanger for DHW production, and a secondary circuit
and boiler downstream from the heat exchanger, the water content of the secondary circuit and the DHW storage tank can only be considered part of the useful amount if
both the following conditions are met:
1. the intermediate heat exchanger is suitably sized on the basis of the machine capacity;
2. both pumps (primary and secondary) are always active or are simultaneously commanded on the basis of the temperature of the water in the DHW storage tank (meas-
ured by an SSAN probe).
On the system circuit of a multifunction unit for 2-pipe systems, example 1 applies.
If you are in any doubt, please refer to the relevant technical documentation or contact the AERMEC Technical-Commercial Service.
NOTICE: Under no circumstances does the unit have to be operated when water ow rate on the heat exchanger is below the minimum water ow rate or above the
maximum water ow rate, under penalty of the warranty expiration. Aermec cannot be held responsible for any malfunction of the units which are operated outside
the established limits of water ow rate and for their consequences
NOTICE: Under no circumstances does the unit have to be operated in a system in which the content of the water circulating is below the MINIMUM SYSTEM WATER
CONTENT, under penalty of the warranty expiration. Aermec cannot be held responsible for any malfunction of the units which are operated in a system in which the
content of the water circulating is below the MINIMUM SYSTEM WATER CONTENT and for their consequences
NOTICE: in the case of several units connected in parallel, the designer must ensure that the conguration of the system and the management logic adopted do not
cause too frequent START/STOP cycles and / or sudden changes in the water ow rate of the groups in operation
ATTENTION It is recommended to design systems with high water content (minimum recommended values shown in tab), in order to limit:
— The hourly number of inversions between operating modes
— Drop in water temperature during winter defrost cycles.
MAXIMUM SYSTEM WATER CONTENT
Units with the hydronic kit mounted come standard with the expansion vessel set at 21.8 psi, the pressure relief valve and the water lter mounted.
The maximum system water content depends on the capacity of the expansion vessel and on the calibration of the pressure relief valve.
Size 0800 0900 1000 1250 1400 1500 1650 1800
Hydronic kit
Expansion vessel number A no. 2
Expansion vessel capacity A gal 6.6 6.6 6.6 6.6 6.6 6.6 6.6 6.6
Pressure relief valve A n°/psi 1/87.0
The table gives an example of the maximum water content calculated at the indicated operating conditions and only to protect the unit.
If the volume of water in the system is higher, add another expansion vessel of the correct size.
System water temperature max/min °F 104/39.2
Hydraulic height Ft 98.4 82.0 65.6 49.2 ≤40.19
Expansion vessel pre-load psi 46.4 40.6 33.4 26.1 21.8
Water content maximum gal 574.3 699.0 823.7 948.4 1,017.6
System water temperature max/min °F 140/39.2
Expansion vessel pre-load psi 46.4 40.6 33.4 26.1 21.8
Water content maximum
gal 258.4 314.4 370.9 426.9 457.5
The data in the table refer to units with a 6.6 gal. expansion vessel.
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