Technical data
50 | Project planning manual for heat pumps for heating and domestic hot water preparation | 01.2012 www.dimplex.de
4.2 Water-to-water heat pump
4.2 Water quality requirements
Irrespective of any legal regulations, the ground water should not
contain any substances that could form deposits. iron (<0.20 mg/
l) and manganese (<0.10 mg/l) limit values must be adhered to to
prevent iron ochre sedimentation from forming in the heat source
system.
Experience has shown that contamination with grains larger than
1 mm (organic components in particular) can easily cause dam-
age. Granular material (fine sand) does not deposit if the speci-
fied water flows are adhered to.
The dirt trap included in the scope of supply of the heat pump
(mesh size 0.6 mm) protects the evaporator of the heat pump; it
should be installed in the heat pump inflow.
ATTENTION!
Fine, colloidal contaminants that cause the water to become turbid also
tend to stick and can deposit in the evaporator, thereby impairing heat
transfer. These contaminants cannot be removed cost-efficiently using a
filter.
The use of surface water or water containing salt is not permissi-
ble. Your local water utility company can provide general infor-
mation regarding the possible use of ground water.
a) Water-to-water heat pumps with welded stainless steel
coil heat exchangers (Table 4.1 on page 49)
It is not necessary to carry out a water analysis with regard
to evaporator corrosion if the annual mean temperature of
the ground water is below 13 °C. In this case, only the val-
ues for iron and manganese have to be complied with (sed-
imentation).
At temperatures over 13 °C (e.g. waste heat recovery), a
water analysis must be carried out in accordance with Table
4.2 on page 50 and the resistance proven for the stainless
steel evaporator of the heat pump. If one characteristic in the
column "stainless steel" is negative "-" or two characteristics
are "0", then the analysis should be considered to be nega-
tive.
b) Water-to-water heat pumps with copper-soldered stain-
less steel plate heat exchanger
Irrespective of any legal regulations, a water analysis ac-
cording to Table 4.2 on page 50 must be carried out to de-
termine the resistance for the heat pump's copper-soldered
evaporator. If one characteristic in the column "copper" is
negative "-" or two characteristics are "0", then the analysis
should be considered to be negative.
NOTE
If the necessary water quality is not achieved or if this cannot be guaran-
teed long-term, we recommended installing a brine-to-water heat pump
equipped with an intermediate circuit.
Table 4.2: Resistance of copper-soldered or welded stainless-steel plate heat exchangers to substances contained in the water
"+" Normally good resistance
"0" corrosion problems can arise, particularly if several factors receive a evaluation of "0".
"-" Should not be used
[< smaller than, > larger than]
Evaluation
characteristic
Concentration
range (mg/l)
Copper
Stain-
less
steel
> 13°C
Evaluation
characteristic
Concentration
range (mg/l)
Copper
Stain-
less
steel
> 13°C
Substances that
could form deposits
(organic)
00 Oxygen
< 2
> 2
+
0
+
+
Ammonia
NH3
< 2
2 to 20
> 20
+
0
–
+
+
0
Hydrogen sulphide
(H2S)
< 0.05
> 0.05
+
–
+
0
Chloride
< 300
> 300
+
0
+
0
HCO3- / SO
4
2
-
< 1
> 1
0
+
0
+
Electr. conductivity
< 10 µS/cm
10 to 500 µS/cm
> 500 µS/cm
0
+
–
0
+
0
Hydrogen carbon-
ate (HCO3-)
< 70
70 to 300
> 300
0
+
0
+
+
0
Iron (Fe), dissolved
< 0.2
> 0.2
+
0
+
0
Aluminium (Al), dis-
solved
< 0.2
> 0.2
+
0
+
+
Free (aggressive)
carbonic acid
<5
5 to 20
> 20
+
0
–
+
+
0
SULFATE
up to 70
70 to 300
>300
+
0
–
+
+
0
Manganese (Mn),
dissolved
< 0.1
> 0.1
+
0
+
0
SULPHITE (SO3),
free
< 1 + +
Nitrate (NO
3
), dis-
solved
< 100
> 100
+
0
+
+
Chlorine gas (Cl2)
< 1
1 to 5
> 5
+
0
–
+
+
0
PH value
< 7,5
7.5 to 9
> 9
0
+
0
0
+
+