Tranquility THW - 50 & 60Hz R410A - ClimateMaster Geothermal Heat Pumps - Rev.: 30 June, 2008B
17
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°F to 50°F [-40°C to 10°C],
with a default value of 0°F [-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 80-140°F [27-60°C], with
a default value of 130°F [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 50-70°F [10-21°C], with a default value of
60°F [16°F]. 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 70°F-120°F [21-49°C], with
a default value of 70°F [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 12 shows an example outdoor temperature
reset curve for a climate that has an outdoor design
temperature of -4°F [-20°C]. At design temperature, the
radiant floor system needs 126°F [52°C] water. However,
when the outdoor temperature is 68°F [20°C], the home
needs no heating (building balance point). In between
-4°F and 68°F [-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 55°F [13°C] or lower, so the slope
of the line changes based upon settings at the user
interface. The radiant floor 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 100°F [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 efficiency (COP) of the heat pump. The
combination of a lower design temperature and outdoor
temperature reset can result in a significant impact on
operating costs.
Outdoor Temperature Reset Example
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 [°F]
Buffe
r
Ta
nk
Te
mpe
ra
ture
,
°C
[°F]
[50]
[59]
[68]
[77]
[86]
[95]
[104]
[113]
[122]
[131]
[86]
[77]
[68]
[59]
[50]
[41]
[32]
[23]
[14]
[5]
[-4]
[-13]
[-22]
Maximum
Buffer Tank
Temperature
52C [126F]
20C [68F]
Minimum
Buffer Tank
Temperature
Building
Balance
Point
Temperature
Outdoor
Design
Temperature
Figure 12: Example Outdoor Temperature Reset
Table 6: Buffer Tank Interface Inputs
Setting Description
Range
Default
Buffer Tank Set Point
70-140°F [21-60°C}
100°F [38°C]
Buffer Tank Deadband
4-20°F [2-11°C]
6°F [3°C]
Outdoor Design Temp
-40-50°F [-40-10°C]
0°F [-18°C]
Maximum Design
Water Temp
80-140°F [27-60°C]
130°F [54°C]
Minimum Design
Water Temp
70-120°F [21-49°C]
70°F [21°C]
Building Balance
Point Temp
50-70°F [10-21°C]
60°F [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.
