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