COMPARATIVE STUDY AMONG HYBRID GROUND SOURCE HEAT PUMP SYSTEM, COMPLETE GROUND SOURCE HEAT PUMP AND CONVENTIONAL HVAC SYSTEM Page: 4 of 7
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5%
16%
8%
68%
3%
SPA &Dometic Water
Heating
Loop Pumping
100% Outside Air UnitCooling tower
Figure 8. The energy summary from utility company
According to the well comparison, we can say the modeling
results are trustworthy and reasonable. In the next section, the
calibrated building model installed with different HVAC
system is simulated and the energy comparison results are
presented.
5. RESULTS AND DISCUSSION
After the validations above, the validated building model
and system model are set up well. In order to reseach the
advantage and disadvange of HyGSHP compared with other
type of HVAC system, the building model with the alternative
complete GSHP and ASHP system is simulated. And Fig. 9
and Fig. 10 (screenshot from TRNSYS plotter) shows the
ground temperature (red line) and subhourly exiting water
temperature of GHX for the validated HyGSHP system. Then
the HyGSHP system is substitued by the complete ground
source heat pump system which contain 245 boreholes with
200 ft depth with total estimated 250 tons capacity.
From Fig. 9 and Fig. 10, with the same HVAC system
capacity, the exiting water temperature of complete GSHP has
lower fluctuation and is controlled more effeciently than the
exiting fluid temperature of HyGSHP. The reasons are as
follow:
First of all, these two HVAC systems, the spacing of
boreholes and the inlet mass flow rate of GHX is set as the
equal for the HyGSHP and GSHP.
And according to the heat convection Eq. (1):q = h A ( Tsurface - TfIuid)
complete ground source heat pump discharges more heat into
ground; therefore, the outlet temperature Toutlet is lower than
than for HyGSHP when the fuild goes through the ground heat
exchanger ( see Fig. 9 and Fig. 10). This may explain why the
case of HyGSHP resulted in a higher ground temperature.q = 11 c ( Toutlet - Tiniet)
(2)
Where,
Im, mass flow rate
C, thermal conductivity
Figure 9. Plot of hourly ground temperature and EWT for
HyGHSP
' Simltion rrme .U6f0 00 jhr1,J
Figure 10. Plot of hourly ground temperature and EWT
for GHSP(1)
Where,
q, energy transfer rate
h, convection heat-transfer coefficient
Tsurface, surface temperature of U-TUBE
A, surface area of U-TUBE
Because the complete ground heat exchanger with
lengthened ground heat exchange length has the larger surface
area of U-TUBE of ground heat exchanger than surface area
of U-TUBE of the HyGSHP, more heat is transferred from
fluid to the ground in the GSHP that the heat transferred in the
HyGSHP.
Therefore, according to the Eq. 2, with the same mass flow
rate and thermal conductivity for GSHP and HyGSHP,Annual
energy
consumption
(KWH)700000
600000
sooooo
400000
300000
200000
100000I
GHSP HyGSHP ASHP
Figure 11. Comparison of annual system energy
consumption among three types of system
(Note: the total consumption include the main loop
pumping water source heat pump (or air source heat pump)4
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Zhu, Jiang & Tao, Yong X. COMPARATIVE STUDY AMONG HYBRID GROUND SOURCE HEAT PUMP SYSTEM, COMPLETE GROUND SOURCE HEAT PUMP AND CONVENTIONAL HVAC SYSTEM, article, November 1, 2011; United States. (https://digital.library.unt.edu/ark:/67531/metadc845909/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.