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Bosch Geothermal Heat Pumps
Bosch Thermotechnology Corp.
Data subject to change
Applications Manual
Example 2:
In this example, we will examine the Bosch four (4) ton
geothermal heat pump unit as the possible selection
for this application. Our goal is to provide more heating
ability with the geothermal heat pump compressor and
associated ground heat exchanger than using auxiliary
heat. Using the Bosch four (4) ton geothermal heat pump
will also result in a lower structure balance point allowing
the compressor heat to meet the structure heating needs
to a lower outdoor ambient temperature. We will also
examine the cooling performance for this situation as well.
At rst glance, we nd that this selection exceeds the 3.3
ton (40,000 Btu/h) cooling capacity criteria normally used
for sizing for cooling. However, using a system with a two
stage compressor may prove bene cial in this case.
We nd when looking at the Bosch four (4) ton geothermal
heat pump system data (Table 10) cooling capacity at full
load, we see that at an Entering Fluid Temperature (EFT)
of 50°F (the typical shallow groundwater temperature for
the location is 47°F per Bosch Geo Solutions software)
and at 75°Fdb, 63°Fwb (typical load calculation criteria
for cooling), the total capacity of the Bosch four (4) ton
geothermal heat pump is 52,460 Btu/h, with 38,150 Btu/h
sensible capacity (73% of total capacity). This leaves
14,310 Btu/h latent capacity. The installer should meet
100% of both sensible and latent capacity of the calculated
cooling load. The sensible load is 24,000 Btu/h and this
Bosch four (4) ton geothermal heat pump provides 38,150
Btu/h. The latent load is 8,000 Btu/h and this Bosch four
(4) ton geothermal heat pump provides 14,310. Therefore,
this Bosch four (4) ton geothermal heat pump will comply
with typical minimum sizing criteria selecting the unit to
meet cooling load requirements. As the Bosch four (4) ton
geothermal heat pump will not be operating at the cooling
outdoor design temperature of 88°F except during the
warmest summer days, the Bosch four (4) ton geothermal
heat pump will revert to low cooling or part load capacity
most of the cooling run time. This will improve humidity
removal and still meet the structure heat gain, even
though the Bosch four (4) ton geothermal heat pump is
theoretically oversized. The increased cooling capacity
of the unit also allows an increase in heating capacity
provided by the compressor during winter months, more
closely aligning with the structure heat loss in a colder
climate.
Example 2:
f
Heating Dominate Climate
f
Minneapolis, Minnesota
[typical entering fluid
temperature (EFT) of 47°F]
f
Load Calculation Sensible Heat Loss
= 65,000 Btu/h
(outdoor design temperature = -11°F; indoor design
temperature = 70°F)
f
Load Calculation Sensible Heat Gain
= 24,000 Btu/h
(outdoor design temperature = 88°F; indoor
temperature = 75°F)
f
Load Calculation Latent Heat Gain
= 8,000 Btu/h
f
Total Heat Gain (Sensible plus Latent)
= 32,000 Btu/h
(slightly larger than a 2-½ ton unit)
f
Per Manual S, 25% larger than the total cooling load
= 1.25 x 32,000 Btu/h = 40,000 Btu/h
f
Maximum Bosch water-to-air geothermal heat pump
size
= 3.3 tons (40,000 Btu/h Cooling Capacity)
Unit selected:
Bosch four (4) ton
If the summer outdoor temperature approaches the actual
cooling design temperature of 88ºF, the Bosch four (4) ton
geothermal heat pump will shift to high cooling or full load
capacity to meet the structure cooling needs, even though
they may be less than in a warmer climate. In this case, the
Bosch four (4) ton geothermal heat pump selected meets
approximately 164% of the maximum limits, per ACCA
Manual S.
Examining the part load speci cations for the Bosch
four (4) ton geothermal heat pump (Table 11) at 50°F
EFT (the typical shallow groundwater temperature for
the location is 47°F per Bosch Geo Solutions software),
we nd that at 75°Fdb, 63°Fwb the unit will produce
a total capacity of 40,350 Btu/h with 33,980 Btu/h
sensible capacity (84% of total capacity). This leaves
6,370 Btu/h latent capacity. During milder summer days,
this Bosch four (4) ton geothermal heat pump will run in
part load and still provide the necessary cooling needs
for the structure. This operation mode will require less
electrical power to operate and will enhance latent heat
removal (dehumidi cation), resulting in improved indoor
temperature and air quality conditions.
