Modeling of Horizontal
GSHP System for
Greenhouse Heating
Murat AYDIN,1,2 A.Gültekin2 1International Geothermal Center Bochum
2Istanbul Technical University, Energy Institute
Ground Source Heat Pumps (GSHP)
and
Ground Heat Exchangers (GHE)
• Ground Source Heat Pump (GSHP) is one of the best
efficient space heating and cooling system (USEPA).
• Heat load of a space is extracted (in heating) from
ground or injected (in cooling) to ground.
• There are two common methods for GHE
• Vertical
• Horizontal
Horizontal GHE
Vertical GHE
Horizontal
Ground Heat Exchangers (GHE)
• Horizontal Ground Heat Exchangers (GHE) have some
advantages:
• easy to apply,
• cheaper than vertical GHEs
• Also have some disadvantages:
• Need wider area than vertical ones,
• Lower performance in cold days.
Slinky GHE Spiral GHE Helix GHE
Heating-Cooling of Greenhouses
Depending on the plant growing, inside air has to be controlled continuously,
They need heating or cooling most of time in a year,
Heating and Cooling expenses one of the highest expenses,
Some of them are far from the natural gas network.
Identification of the Problem
An efficient heating and cooling system needs the greenhouse,
There is not any available larger spaces,
Greenhouses floor can be used as heat source/sink,
Sensitivity of calculation is important because of products.
Working Scheme
Experimental Study
Modeling in COMSOL
Fitting the Experiment
to Model
Extending to results to field
scale
Test System using in Experimental Study
Sýc. Sensörü
(3B - D)
TOPRAK ALTI ISI
DEÐÝÞTÝRÝCÝSÝ
Sýc.Sensörü
(1 - G)
Sýc.Sensörü
(3B - D)
Sýc. Sensörü
(3A - G)Topraktan dönüþ kollektörü
Topraða gidiþ kollektörüSU
TANKI
MOBÝTES
MOBÝL TEST CÝHAZI
KONTROL
PANELÝ
T
Elektrik
Rezistanslarý
4 x 3kw
KUYU4
100m
Sýcaklýk
SensorüDebimetre
Pompa
6
4
T
Oto. Hava Purjörü
Genleþme Tanký
ISI
POMPASI
8-27 kw
mFiltre 2
T
5
1
3
T
Fig. Mobile Test Vehicle and its connection to the slinky GHE.
SAMPLE SLINKY GHE
SINK (A BHE)
HEAT PUMP
8-27 kW
WATER
TANK
MOBILE TEST VEHICLE
CONTROL
PANEL
Eectrical
Resistances
4 x 3kW
Flowmeter Temperature
Sensor
Auto. Air Purge
Pump
Filter
Expansion Vessel
Ground Flow Coll.
Ground Return Coll.
Experimental Study Results
4
5
6
7
8
9
10
5 15 25 35 45 55
T [
oC
]
t[h]
4-6 May Horizontal Slinky Test, Tg:6 oC, 10lt/min
TreturnTflowT2T1
Fig. Changings in temperature sensors during the test,
T1 is located on the closer to flow side on PE pipe,
similarly T2 is located on the closer to return side.
Air & Ground Conditions
Test time 04-06 May
Total duration 57 h
Amb. temp. during the test 12 - 22 oC
Avg grou. temp. at 0.5m depth 19 oC
z =-2m temp. before the test 11 oC
Test Data
Inlet fluid temp. to GHE Tg= 5.6 oC
Avg. return temp. from GHE Td =7.0 oC
Avg. fluid temp. in GHE 6.3 oC
Flowrate 𝑄𝑣 = 9.9 lt/min
Temp.diff. between slinky GHE and ground
at z =-2m 4.7 oC
Average heat load 𝑞 = 999 W
Ave. heat load in unit trench 𝑞 ′ = 91 W/m
Table: Air and ground conditions.
Modeling
Fig. COMSOL model box for one Slinky GHE.
(6m x 10m x 25m) Fig. Slinky GHE.
Pinch (p) 0.25m
Diameter (d) 1m
Inlet diameter of pipe (di) 0.026m
Outlet dia. of pipe (do = dp) 0.032m
Total length of pipe 100m
Total trench length 11m
≈
Governing Equations
COMSOL Heat Transfer Module, “Heat Transfer in Solid
QqTCt
TC pp
u
)TT(hq amb 0
Governing equations in the ground:
Upper Boundary Condition
GHE Boundary Condition T=Tavg-exp
Computation
Fitting Modeling Results to Experimental
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
500 1000 1500 2000 2500 3000
Hea
t L
oad
[W
]
t [min]
)TT(mcq returnflowpSlinkyGHE
Heat load is calculated following eq.:
Extending the results to field scale
Fig. Field Application of Slinky GHE.
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
20 25 30 35 40 45 50 55
Time [h]
Experimental Results - Heat Load
Numerical Model - 3D Slinky Model
Numerical Model - 3D Plate Geometry
3D Slinky GHE
3D Slinky Plate Geometry
totalq
Effect of distance between GHEs
0
1000
2000
3000
4000
5000
6000
7000
8000
0 500 1000 1500
Time [h]
totalq
distance
between
GHEs Fig. Heat load for one line(100m), for yearly working condition
100m
Degrees of Freedom : 963773 (plus 287540 internal)
Solution time app. ~ 8min (Intel i7-4510U-2GHz+8GB Mem.)
3m
2m
1.5m
1m
Simulation Results
Fig. Simulation results.
Distance
between
trenches
[m]
Obtainable heat load
from ground [kW]
Given Heat to
Greenhouse
[kW]
One
Layer
Double Layers Total Heat
(COP:4)
1 172 309 412
1.5 149 275 366
2 136 258 344
3 117 228 304
Table. Heat value obtained from the 60m x 80m field at the
end of the 2400h non-stop running condition.
Conclusions
• A horizontal ground heat exchanger system model is built for a greenhouse.
• Slinky geometry is used as vertically that can be located in narrow trench easily.
• Experimental results of a sample vertical slinky is imported in COMSOL and using them in the model, the
model is validated.
• It is shown that double layer with 1.5m distance between each loop is given best performance for 60mx80m
application field.
• Up to 366 kW heat energy can be supplied to greenhouse with gshp system.
• This system can be used for auxiliary system with other resources and yearly acclimating cost of the
greenhouse can be decreased considerably.
Thank You For Attention
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