OCHSNER Borehole heat exchangers with CO 2 Dr. Gerald Lutz

© Dr. Gerald Lutz The Geothermal Heat Pumps market in Central & Eastern Europe Bratislava, 12. Nov. 2007

OCHSNER Borehole heat exchangers with CO2


Dr. Gerald Lutz



Contents:

Benefit of using CO2 as heat transfer medium

Functionality of a CO2 - tube

Installation example of a CO2-tube



Classification of renewable energy sources

Quelle: EHPA (European Heat Pump Association) classification of ambient heat



Different variants for the energetic use of ambient heat from the ground

Quelle: Ehrbar, M. ;Peterlunger, A.: Pumpenlose Erdwärmesonde: Schlussbericht Potenzialabschätzung, Machbarkeitsstudie energetisch und wirtschaftlich, Interstaatliche Hochschule für Technik Buchs, (o.J.) Buchs, S.8f.

Heating of air by leading it through a gravel zone

Groundwater as a heat source

Direct expansion/flat collectors

Glykol- and water- heat pipes

Heat pipes without circulation pumps



Quelle: Ochsner


• highest COP. •A constant temperature from + 8 °C to + 12 °C

The groundwater is pumped from the delivery well to the heat pump and from there 15 meters to the sink well.



Quelle: Ochsner


•refrigerant cycle of the heat pump is used directly•no heat exchangers from brine to R 407C needed•Also no brine cirulating pump is needed With the brine system the brine circulates

• in horizontal collector tubes, or

• in trenches



Quelle: Ochsner


The brine circulates in earth taps around 100 m deep









Heat pipes without circulation pumps using CO2



Benefit of CO2 as a heat transfer medium

CO2 is non-toxic

not flammable

Greenhouse relevance is neclectable (compared to other refrigerants !) (GWP=1)

Ozon deplating potential (ODP=0)

not water endangering

cheap

no special regulations for its disposal

Benefit of using CO2-tubes



Disadvantages of conventional working fluids(Prophylen,- oder Ethylenglykol)

Very exact definition of the glykol concentration

missing addition of inhibitors is resulting in corrosions

Benefit of using CO2-tubes



Thermodynamic characteristics of CO2- subcritical and transcritical cyclic process

high volumetric cooling capacity (6 – 8 times higher as f.e. R407C, R717)

small volumetric flow rates smaller pressure losses

smaller tube profiles

low critical temperature 31,1°C, and a high critical pressure 73,8 bar.

Difficult to use within the refrigerant cycle because of flow temp. of >35˚C.

Changing of steam pressure with 1 bar/K.

Pressure of more than 100 bar with flow-temp. of >30˚C



Transcritical CO2-process (Lorentzen Prozess)

Rieberer, R; Halozan,H.: CO2 als Kältemittel, Institut für Wärmetechnik TU-Graz (2004)



Comparison of CO2 with other refrigerants

Refrigerant ODP GWP Critical temperature[°C]

criticalpressure [bar]

R744 (CO2) 0 1 31,1 73,8

R134a 0 1300 101 40,7

R407C 0 1525 86,7 46

R410a 0 1725 72,1 49,2

Potential to ozon layer destruction and greenhouse effect

Critical temperature and critical pressure



Functionality of CO2- tube

Prinzip des Wärmerohres (Vgl.Ochsner)

Principle of a heat pipe:

heat pipe transports warmth between heat source and a heat consumer

heat transfer medium is CO2) The heat transfer medium takes up heat energy –

ascends as steam inside the pipe (Thermosyphonprinzip)

delivers the energy in the heat exchanger

condensation of CO2

CO2 descends



CO2-tube coupled with as direct expansion heat pump

Kältekreis einer Direkterwärmungs- Wärmepumpe gekoppelt mit einer CO2-Sonde. Ochsner Wärmepumpen GmbH

Refrigerant circulates in the cooling head and evaporates there

highest performance

largest working reliability



Single tube system/ double tube system

Einrohrsonde/Zweirohrsonde. Vgl. Ehrbar, M.)

Danger of interruption

liquid und CO2-steam

If diameter is to large

Separation of liquid and gas phase



CO2-tube high-grade steel pipe: Maximum capacity and length – dependency on tube dimension

FKW Hannover Prof.H. Kruse

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40Rohrinnendurchmesser [mm]

Th

eore

tis

che

ma

x. E

ntz

ug

slei

stu

ng

[kW

]

0

10

20

30

40

50

60

70

80

90

100

Fil

mlä

ng

e [m

]

1 Rohr

2 Rohre4 Rohre

8 Rohre



Quelle: Objektdaten und Anlagenart des Installations-Beispiels

Installation-example: object data

Objektdaten

Heated area 160 m²

Construction method

Low energy house

Heat demand ~ 33 W/m²

Number of persons 3



Quelle: Objektdaten und Anlagenart des Installations-Beispiels

Heating system

Heat pump OCHSNER Golf GMDW 7

Heating capacity(E0/W35)

6,4 kW

Heat source Ground source direct expansion, 1 CO2-tube

Heating mode monovalent

Distribution system Floor – and wall heating system

Flow temperature max. 35°

hydr. decoupling 300 Liter buffer vessel

Hot water supply OCHSNER Europa 303

heating system



Drilling

Quelle: Errichtung einer Bohrung für die Einbringung einer CO2-Wellrohrsonde (Ochsner GmbH)

borehole with depth of 100 m



Tube

Quelle: CO2-high-grade steel pipe (Ochsner GmbH)

100 m

ambient heat 15 C

developing pressure 50 bar

pressure resistant, flexible high-grade

steel pipe

CO2 diffuses by conv. PE tubes



CO2-tube – installation tunnel

Quelle: Ochsner



Bringing in of the tube

Quelle: Einbringung der CO2-Wellrohrsonde (Ochsner GmbH)



Connection of the CO2-tube

Quelle: CO2-Erdwärmesonde (Ochsner GmbH)

Distance CO2-tube – heat

pump not more than 25 meters.

Refrigerant leading pipes and cooling head have to be isolated



Seasonal Performance Figure

Quelle: Monthly performance figure and seasonal performance for heating season 2006/2007 (Ochsner GmbH)

4,8

4,13,9 3,9 4 3,9 4,1 4,1

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

Performance Figures

Oct. 06 Nov. 06 Dec. 06 Jan. 07 Feb. 07 Mar. 07 Apr. 07 SPF



Advantages of CO2-as a heat transfer medium

no circulating pumps: higher SPF than conventional earth tubes

(conventional pumps have a running capacity of 200 W

with SFH ~ 360 kWh 15-20% higher JAZ)

environmental friendlyness: lower CO2-emissions because of higher working reliability

by closed cycle without mobile parts

lower investment costs

Advantages of the CO2-tube



Thank you for your interest!

OCHSNER Borehole heat exchangers with CO 2 Dr. Gerald Lutz

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