Midea M thermal Mono Series Engineering Data page 44

To determine the maximum allowed water volume in the entire circuit, proceed as follows:
Determine the calculated pre-pressure (Pg) for the corresponding maximum water volume using the Figure 3-3.1.
Figure 3-3.1: Maximum water volume
3.3
2.8
2.3
1.8
1.3
0.8
0.3
0 50
Check that the total water volume in the entire water circuit is lower than this value. If this is not the case, the
expansion vessel inside the unit is too small for the installation.
Example 1
The unit is installed 5m below the highest point in the water circuit. The total water volume in the water circuit is 100 L. In
this example, no action or adjustment is required. The unit(16kW) is installed at the highest point in the water circuit. The
total water volume in the water circuit is 150L.
Example 2
The unit is installed at the highest point in the water circuit. The total water volume in the water circuit is 250L.
Result:
- Since 250 L is more than 230 L, the pre-pressure must be decreased (see table above).
- The required pre-pressure is: Pg(bar) =(H(m)/10+0.3) bar = (0/10+0.3) bar = 0.3 bar
- The corresponding maximum water volume can be read from the graph: approximately 310L.
- Since the total water volume (250L) is below the maximum water volume (310L), the expansion vessel suffices for the
installation.
When it is required to change the default pre-pressure of the expansion vessel (1.0 bars), following guidelines:
Use only dry nitrogen to set the expansion vessel pre-pressure.
Inappropriate setting of the expansion vessel pre-pressure will lead to malfunctioning of the system. Pre-pressure
should only be adjusted by a licensed installer.
If the expansion vessel of unit is too small for the installation, an additional expansion vessel is needed.
Calculate the pre-pressure of the expansion vessel: Pg(bar) = (H(m)/10+0.3) bar
The expansion vessel equipped in the unit should adjust the pre-pressure also.
Calculate the volume needed of the additional expansion vessel: V1=0.0693*Vwater/(2.5-Pg)-V0
Vwater: the volume of water in the system
V0: the volume of expansion vessel which the unit is equipped (8L)
3.3 Water Circuit Connection
Water connections must be made correctly in accordance with the labels on the outdoor unit, with respect to the water
inlet and water outlet. If air, moisture or dust gets in the water circuit, problems may occur. Therefore, always take into
account the following when connecting the water circuit:
Use clean pipes only.
202005
A1
A2
100 150 200 250
Midea CAC Confidential
A1: System without glycol
A2: System with 25% propylene glycol
Pre-pressure = pre-pressure of the expansion vessel
Maximum water volume = maximum water volume in
the system
300 350
M thermal Mono
43