2 4 |
Bosch Geothermal Heat Pumps
Bosch Thermotechnology Corp.
Data subject to change
Applications Manual
Examining the corresponding full load heating data
(Table 6) for the Bosch three (3) ton geothermal heat
pump (compressor operating at 100% ability), we nd that
at 50°F EFT (the typical shallow groundwater temperature
for the location is 47°F per Bosch Geo
Solutions software) and 70°F Entering Air Temperature
(EAT) (return air temperature), we determine the total
capacity for heating is 35,970 Btu/h. Our calculated heat
loss at design conditions is 65,000 Btu/h at -11°F outdoor
temperature. We will be able to meet approximately 55%
of the structure heat loss with the three (3) ton unit
capacity at design conditions if the outdoor ambient falls
to -11°F. Examining the actual bin hours for Minneapolis,
MN (see Table 5), we nd that the Bosch three (3) ton
geothermal heat pump providing compressor heating will
operate until the structure balance point of approximately
20°F outdoor temperature without auxiliary heating being
required.
Capacity Data - Full Load Heating
Entering
Fluid Temp.
(F)
Entering
Air Temp.
(F)
Total
Capacity
(MBtuH)
Power
Input
(kW)
Heat of
Abs.
(MBtuH)
COP
50
60
38.04
2.33
30.08
4.8
60
42.34
2.47
33.92
5.0
70
46.64
2.60
37.75
5.2
80
50.93
2.74
41.59
5.5
50
70
35.97
2.37
27.87
4.4
60
40.03
2.51
31.46
4.7
70
44.09
2.65
35.05
4.9
80
48.16
2.79
38.64
5.1
50
80
33.55
2.42
25.27
4.1
60
37.33
2.57
28.57
4.3
70
41.11
2.71
31.87
4.4
80
44.89
2.85
35.17
4.6
Tab. 6
(EFT Range (Standard) 25F to 80F)
The structure balance point is the outdoor temperature
for the particular structure where heat output from the
compressor meets the heat loss of the structure due to
construction details. The compressor will not be able to
meet the heat loss requirements for the structure at this
outdoor ambient of approximately 20°F or lower.
Supplemental heating (electric coils) will be necessary
to provide heating assistance to the compressor at this
structure balance point outdoor temperature and below,
energizing for longer time periods as outdoor ambient
drops. When outdoor temperatures are warmer than 20°F
and heat loss is excessive (i.e., doors open, windows open,
etc.), these supplemental heaters will energize, but will
occur only for a short period of time. The supplemental
heaters will also operate in the emergency heat mode
if the compressor fails. These heaters must be sized to
meet the total structure heat loss at design conditions
to adequately provide emergency heating if necessary.
The size of heater should typically meet 90% of the heat
loss of the structure minimum (58,500 Btu/h) at design
conditions. This will be a 17 kW heater minimum. The
installer should therefore install a 20 kW electric heater for
this application.
If the EFT falls at the installation location due to
outdoor climate conditions, the installer can determine
the approximate heating ability of the Bosch three
(3) ton geothermal heat pump as well from published
speci cations (Table 7). Examining the “Low Temp
Heating” full load data for the Bosch three (3) ton
geothermal heat pump, we nd that at 30°F EFT and
70°F Entering Air Temperature (return air temperature),
the full load heating capacity (compressor operating at
100% ability) of the Bosch three (3) ton geothermal heat
pump will be 27,310 Btu/h. This provides approximately
42% of the structure heat loss at design conditions. Since
outdoor temperatures will not be at design conditions but
approximately 1% of the time, the unit will be operating
at higher outdoor ambient temperatures. The auxiliary
or supplemental electric heater installed in the unit will
provide the necessary supplemental heating capacity to
help the compressor maintain 70°F in the structure. The
auxiliary heaters may be energized longer when outdoor
ambient temperatures are cooler during heating months.
If the installation location in Minneapolis, Minnesota is
experiencing milder (warmer) winter days, the three (3)
ton unit will be able to operate at part load conditions.
The installer can determine the capacity of the unit at
these conditions as well.
Capacity Data - Full Load Low Temp Heating
Entering
Fluid Temp.
(F)
Entering
Air Temp.
(F)
Total
Capacity
(MBtuH)
Power
Input
(kW)
Heat of
Abs.
(MBtuH)
COP
25
60
26.76
1.99
19.96
3.9
30
28.87
2.06
21.83
4.1
40
33.08
2.20
25.58
4.4
25
70
25.32
2.03
18.39
3.7
30
27.31
2.10
20.15
3.8
40
31.29
2.24
23.66
4.1
25
80
23.62
2.07
16.55
3.3
30
25.47
2.14
18.16
3.5
40
29.18
2.28
21.39
3.7
Tab. 7
(Antifreeze required)
(EFT Range (Standard) 25F to 80F)
