Bosch Geothermal Heat Pumps Applications Manual page 19

Applications Manual
Because a Bosch geothermal heat pump operates in both
heating and cooling, it's rare that a particular series will
exactly match both the calculated cooling and heating load
calculations, except possibly in moderate climate locations
year round. Sizing a Bosch geothermal heat pump for
cooling is the industry-recommended method, regardless
of locale, since normally heating needs are less prevalent.
Most design methodologies prescribe this process, and it
is prevalent in the southern portion of the U.S.
However, in colder climates such as the northern portion
of the U.S., Bosch geothermal heat pump equipment
equipped with single stage compressors that is sized
for the cooling gain could result in short cycling in the
summer and poor dehumidi cation. A Bosch single stage
geothermal heat pump that is not running very often may
not provide suf cient dehumidi cation, and can result
in comfort and indoor air quality (IAQ) problems as well.
Additionally, single stage equipment which is sometimes
sized only for the cooling load could result in excessive
use of auxiliary electric heaters during winter, increasing
operating cost.
If a Bosch geothermal heat pump equipped with a single
stage compressor is sized for the full heating loss load
calculation in a colder climate, it will most likely be
over-sized for cooling needs. Bosch provides exceptional
two-stage geothermal heat pump equipment designed to
alleviate this occurrence. Our two-stage geothermal heat
pumps are equipped with a Copeland Two-Stage, Single
Speed compressor (Fig. 18).
Fig. 18 Bosch series two-stage geothermal heat pumps
This compressor can operate at approximately 67%
capacity in the cooling mode in colder climates during
the summer and provide increased dehumidi cation.
But, when cooling needs are excessive for that particular
climate (which is often the case) the Bosch two-stage
geothermal heat pump can shift to 100% capacity and
remove the heat from the structure. The use of these
two-stage Bosch geothermal heat pumps is recommended
for colder climates, as they will more closely match the
calculated heat loss of the home and therefore be able to
Bosch Thermotechnology Corp.
Bosch Geothermal Heat Pumps | 19
meet the heating needs of the structure better. This newer
technology may also include ECM blowers that can help
provide the appropriate capacities at design conditions
and at part-load conditions. Proper Bosch geothermal heat
pump equipment sizing is still important in this situation,
but installers are provided with exibility by utilizing the
two stage compressor geothermal heat pumps in northern
climates.
Regardless of location, local codes and/or electric
utility program requirements always supersede any
recommendations in this application manual.
Installers should always observe design conditions when
calculating structure cooling and/or heating loads. Most
heat gains and heat loss load calculations are based upon
1% (or 2.5%) of the time. Most load calculations are based
on the 1%, but always check with local authorities if in
question. This means that the outdoor temperature in the
summer is only hotter than the locale design temperature
1% of the time on average. Normally, the heating design
temperature is referred to as the 99% design condition,
and the cooling design temperature is referred to as
the 1% (or 2.5%) design condition. Either way, the load
calculation will provide a basis for designing a system
that will handle virtually all of the heating and cooling,
regardless of outdoor temperature.
The indoor design conditions should be based on
customer needs and requirements. As a default, installers
should observe the following nominal indoor design
conditions:
f
Summer cooling design point: 75ºF at 50% relative
humidity
f
Winter heating design point: 70ºF at 30% relative
humidity
The purpose in this method is simply establishing the
temperature differentials for use in the cooling and heating
load calculations.
Once the load calculation has been completed for
the structure for both heat gain and heat loss, the
installer must pay attention to the sensible and latent
loads determined from the load calculations. The load
calculation is typically based on peak load conditions (the
design day) for cooling. For summer cooling, this generally
occurs on a hot day and the peak sensible condition
results from the peak dry bulb at that time. If the weather
is not very hot or it is raining it is natural to expect the
outdoor condition may be in the low 80Fs with a higher
relative humidity (especially if it is raining or at night).
Since the equipment is normally sized for peak dry bulb
temperature during a hot day, it is typically oversized when
operating at non-peak, part-load duty (the other 99% of
the time), meaning that latent removal capability may be
short when really necessary.
Once a load calculation has been determined and the
Data subject to change