C L I M A T E M A S T E R W A T E R - S O U R C E H E A T P U M P S
18
C l i m a t e M a s t e r W a t e r- S o u r c e H e a t P u m p s
Tr a n q u i l i t y
®
W a t e r- t o - W a t e r T H W S e r i e s
R e v i s e d : 0 2 J a n u a r y, 2 0 1 3
10
15
20
25
30
35
40
45
50
55
30
25
20
15
10
5
0
-5
-10 -15 -20 -25 -30
Outdoor Temperature, °C
Buffer Tank Temperature, °C
Maximum
Buffer Tank
Temperature
52°C
20°C
Minimum
Buffer Tank
Temperature
Building
Balance
Point
Temperature
Outdoor
Design
Temperature
Figure 11: Example Outdoor Temperature Reset
Table 6: Buffer Tank Interface Inputs
Setting Description
Range
Default
Buffer Tank Set Point
21-60°C
38°C
Buffer Tank Deadband
2-11°C
3°C
Outdoor Design Temp
-40-10°C
-18°C
Maximum Design
Water Temp
27-60°C
54°C
Minimum Design
Water Temp
21-49°C
21°C
Building Balance
Point Temp
10-21°C
16°C
The maximum design water temperature must be equal the buffer
tank setpoint. The buffer tank setpoint will override the maximum
design temperature if they are entered with different values.
Electrical - Controls
There are four outdoor reset variables used for
reducing the buffer tank setpoint. The outdoor
design temperature (ODT) is the OAT above which
setpoint reduction begins. The valid range for ODT
is -40°C to 10°C, with a default value of -18°C. The
maximum design buffer tank temperature (MaxBT)
is the maximum desired buffer tank setpoint at the
outdoor design temperature. The valid range for
MaxBT is 27-60°C, with a default value of 54°C. The
building balance point temperature (the temperature
at which heating is no longer needed) is the OAT at
which maximum setpoint (MaxBT) reduction will occur.
The valid range for building balance point is 10-21°C,
with a default value of 16°C. The minimum design
water temperature is the minimum desired buffer tank
setpoint at the building balance point temperature.
The valid range for minimum buffer tank temperature is
21-49°C, with a default value of 21°C. If an OAT sensor
is not detected (or if a thermistor error has occurred),
the buffer tank setpoint will not be reduced based on
the OAT value (i.e. the controller will use the buffer tank
setpoint as described in the previous paragraph).
Figure 11 shows an example outdoor temperature
reset curve for a climate that has an outdoor design
temperature of -20°C. At design temperature, the
radiant fl oor system needs 52°C water. However, when
the outdoor temperature is 20°C, the home needs no
heating (building balance point). In between -20°C
and 20°C, the water temperature in the buffer tank is
adjusted accordingly. For homes that are well insulated
and tightly sealed, the building balance point may be
13°C or lower, so the slope of the line changes based
upon settings at the user interface. The radiant fl oor
design temperature will also change the slope of the
line. If tighter pipe spacing is used, for example, the
water temperature at the outdoor design temperature
may only be 38°C. Again, as the settings are changed
at the user interface, the slope of the line will change.
As mentioned earlier, the lower the heating water
temperature at design conditions, the higher the
effi ciency (COP) of the heat pump. The combination of
a lower design temperature and outdoor temperature
reset can result in a signifi cant impact on operating
costs.
