ASPERN - POTENTIAL OF GEOTHERMAL ENERGY

POTENTIAL OF GEOTHERMAL ENERGY AS A SOURCE OF HEAT IN ASPERN SEESTADT

MICHAELA CERNA | ATRN | 2021/2022 FACULTY OF ARCHITECTURE CTU IN PRAGUE | STUDIO CIKÁN STUDIO HEAD: DOC. ING. ARCH. MIROSLAV CIKÁN ASSISTANT PROFESSOR: ING. ARCH. VOJTĚCH ERTL BUILDING TECHNICAL INSTALLATIONS CONSULTANTS: ING. ZUZANA VYORALOVÁ, ING. JAKUB DENK BACKGROUND PROVIDED FROM WIEN 3420 ASPERN DEVELOPMENT AG

Geothermal Energy Aspern Seestadt is an innovative development based on up-to-date ideas such as sustainability, ecology or subsidized housing, therefore an idea of using renewable energy sources comes to mind quite naturally. My semestral project explores the possibilities of using geothermal energy for heating of the buildings in Aspern. The goal was first to learn more about geothermal energy and the ways of extracting it in general, then looking closer at Aspern and using the information for designing an energy concept for the studio projects of my fellow students.

At lenght, there is a comparison of costs with traditional heat sources to see how the idea could correspond with the subsidized housing projects.

Geothermal energy is a renewable energy source that utilizes the heat from the Earth subsurface. There are different means of utilizing that heat depending mostly on the subsurface temperatures in a locality, also the depth from which the heat is extracted and whether is further used for heating or generating electricity. In Vienna it is meaningful to utilize near-surface geothermal energy by means of heat exchange elements placed in the subsurface and heat pumps. The energy obtained is used for heating and cooling of the buildings in combination with thermally activated building structures such as concrete slabs and walls.

..Architecture is not what is set and placed on the Earth by human beings, but the perpetual shaping of the Earth.

Architecture is the form which is forever emerging from the close embrace between living beings and the Earth.

Architecture is an Earth.“ - description of the piece „The Earth is an architecture“

by TVK, Biennale di Venezia 2021

Thermal Conductivity of the Subsurface in Vienna There could be differentiated three homogenous geological areas according to heat conductivity of the subsurface in the Viennese area. They are further classified by different depth ranges. The energy concept counts with 10 m deep piles and 130 m deep boreholes, therefore the numbers relevant for the concept are found mostly in the maps showing the heat conductivities in 0 – 30 m and 0 – 100 m. According that we can suppose heat conductivity from 1,7 to 1,9 W/m/K. (9)

less than 1,7 W/m/K 1,7 - 1,9 W/m/K more than 1,9 W/m/K

Thermal conductivity of the subsurface in 0 - 30 m of depth

(9)

Thermal conductivity of the subsurface in 0 - 100 m of depth

(9)

Thermal conductivity of the subsurface in 0 - 200 m of depth

(9)

Estimate of Geothermal Heat Potential in Seestadt The near-surface geothermal potential is quite high in Vienna.

Using geothermal probe fields the energy gain can reach up to 1500 MWh per year per hectare.(10) Considering this value, knowing the area of Seestadt and making an approximation of the heat loss of the whole area, we can suppose that there should be enough ground heat for the whole development.

351 900 MWh/year > 180 000 MWh/year

Geothermal energy potential 1500 MWh/year/ha(10)

Total area 234,6 ha (without the lake) -> energy potential on the area of 234,6 ha: 351 900 MWh/year

Total floor area 2,6 millions m2 -> total energy needed for heating: 180 000 MWh/year

Extracting of Geothermal Energy The near-surface geothermal energy is usually extracted by geothermal probes. Other solutions would be utilization by means of geothermal ground water, which is less effective because it demands more space, therefore the yield is lower, maximum of 200 to 300 MWh per hectare and year in Vienna(10). In Seestadt, where the building density is high, the optimal solution would be a combination of geothermal probes and geothermal piles. The main advantage of this solution is that it uses the piles as a part of the structure which probably would have to be constructed by all means. Therefore, also the costs would be lower than extracting heat only by means of geothermal probes.

Calculations and Methods The goal of this work wasn’t only to create an energy concept for the studio projects but also to bring some general conclusions.

Because of that, the concept works with whole urban blocks that are defined quite precisely by the Seestadt regulation plan and not with single buildings. The studio projects are designed along with the regulation, therefore I used them as a base of incoming data in order to be able do the calculations.

For calculation of heat loss of the blocks, I tried two different paths, first of them was envelope heat loss and second by using specific values of heat loss per flat or square meter. I found the values obtained by using the second method twice and a half as high as the values using the envelope of the building.

At the end I decided to use the envelope method as it is much more precise and round up the results quite a lot so there could be still a degree of generality. For example, in the block H1, in order to set its heat loss, I took the heat loss of the building with the highest area of envelope, which was around 190 kW. There are 5 buildings in the block, so I multiplied that number by 5, rounded up and got total heat loss approximately 1250 kW. That way the number still works for the specific urban block but it also could be adequate for the same block with a little different buildings, because there is a back-up. The heat needed for hot water is not taken into account.

For calculations of the amount of heat obtained from the ground, I first determined the number of geothermal piles and probes which are possible to allocate according to the structure of the buildings and the area of public space available. Towards determining the value of the heat yield I’m using table 1 from VDI 4640 which says specific number of kW per m of probe according to geology of the subsurface and its thermal conductivity. As mentioned before, the thermal conductivity is from 1,7 to 1,9 W/m/K(9) in our case, which means supposed yields around 60 W/m(4). For the Coefficient of Performance of the heat pumps I’m using 4,9 (8).

Energy concept for particular urban blocks

site plan of the given area, layout of geothermal piles and probes geothermal piles geothermal probes

F10 Area of urban block: 9 018 m2 Volume: 50 950 m3 Heat loss approximative: 500 kW Energy needs for heating: 957,6 MWh/year Number of geothermal piles (10 m deep): 161

-> heat gain from piles: 96,6 kW Number of geothermal probes (130 m deep): 20

-> heat gain from probes: 156 kW Geothermal heat gain: 252,6 kW Power needed for running the heat pumps: Power of heat pumps: Power that needs to be covered by additional heat source:

Geothermal energy covers 63,5 %

geothermal piles geothermal probes

64,8 kW 317,4 kW 182,6 kW

F11 Area of urban block: 6 019 m2 Volume: 94 750 m3 Heat loss approximative: 1500 kW Energy needs for heating: 2872 MWh/year Number of geothermal piles (10 m deep): 146

-> heat gain from piles: 87,6 kW Number of geothermal probes (130 m deep): 82

-> heat gain from probes: 639,6 kW Geothermal heat gain: 727,2 kW Power needed for running the heat pumps: Power of heat pumps: Power that needs to be covered by additional heat source:

Geothermal energy covers 60,9 %

geothermal piles geothermal probes

186,5 kW 913,7 kW 586,3 kW

F12 Area of urban block: 5 892 m2 Volume: 54 362 m3 Heat loss approximative: 400 kW Energy needs for heating: 766,1 MWh/year Number of geothermal piles (10 m deep): 159

-> heat gain from piles: 89,4 kW Number of geothermal probes (130 m deep): 22

-> heat gain from probes: 171,6 kW Geothermal heat gain: 261 kW Power needed for running the heat pumps: Power of heat pumps: Power that needs to be covered by additional heat source:

Geothermal energy covers 82 %

geothermal piles geothermal probes

66,9 kW 327,9 kW 72 kW

F13 Area of urban block: 5 389 m2 Volume: 48 189 m3 Heat loss approximative: 350 kW Energy needs for heating: 670,3 MWh/yea Number of geothermal piles (10 m deep): 150

-> heat gain from piles: 90 kW Number of geothermal probes (130 m deep): 20

-> heat gain from probes: 156 kW Geothermal heat gain: 246 kW Power needed for running the heat pumps: Power of heat pumps: Power that needs to be covered by additional heat source: Geothermal energy covers 88 %

geothermal piles geothermal probes

63 kW 309 kW 40,9 kW

H1 Area of urban block: 6 612 m2 Volume: 95 895 m3 Heat loss approximative: 1250 kW Energy needs for heating: 2394 MWh/year Number of geothermal piles (10 m deep): 166

-> heat gain from piles: 99,6 kW Number of geothermal probes (130 m deep): 60

-> heat gain from probes: 530,4 kW Geothermal heat gain: 630 kW Power needed for running the heat pumps: Power of heat pumps: Power that needs to be covered by additional heat source: Geothermal energy covers 63,3 %

geothermal piles geothermal probes

161,5 kW 791,5 kW 458,5 kW

How economical is geothermal energy?

In the following pages there are graphs comparing different energy sources and their combinations mostly from economical point of view. The calculations were done for the block H1 which need to cover around 40% by other energy source and the graphs are proposing different alternatives of this additional heat source. Also, there is always included an alternative that supposes the use of natural gas heating only for comparison. The option that considers heating only by geothermal heat pump and an air heat pumps probably would not be possible in reality but it is shown in order to explain better the economic differences of utilization of renewable and not renewable energy sources.

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Natural gas heating: 1250 kW

B: Geothermal piles + gas heating Gas heating: 1124,9 kW Geothermal heat pump: 125,1 kW Heat gain from piles: 99,6 kW Electricity: 25,5 kW

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Geothermal heat pump: 791,5 kW Heat gain from piles: 99,6 kW Heat gain from probes: 530,4 kW Electricity: 161,5 kW

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Gas heating: 458,5 kW

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air he at eat 26% h r i a e le c

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C: Geothermal piles and probes + gas heating

D: Geothermal piles and probes + air heat pump Geothermal heat pump: 791,5 kW Heat gain from piles: 99,6 kW Heat gain from probes: 530,4 kW Electricity: 161,5 kW Air heat pump: 458,5 kW Heat gain from air: 327,5 kW Electricity: 130,9 kW

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cumulative costs (millions of CZK)

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B C

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years 1

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break even point: around 6 years _comparing geothermal heat pumps and gas heating

A: 100% gas heating B: Geothermal piles + gas heating C: Geothermal piles and probes + gas heating D: Geothermal piles and probes + air heat pump

10

5

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plyn B C

tč piloty 2 520 251 Kč

5 174 720 Kč

4 972 800 Kč

3 635 883 Kč

6 703 222 Kč

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1 500 000 Kč

20 24 763 200 Kč

20 513 200 Kč

costs (not cumulative, millions of CZK)

25

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investment costs operating costs per year A: 100% gas heating B: Geothermal piles + gas heating C: Geothermal piles and probes + gas heating D: Geothermal piles and probes + air heat pump

Conclusion The solution proposed would cover more than 60% of the total energy needed for heating of each block, around 80% in blocks F13 and F12 which means that a major part of the heating energy could be produced by renewable source. Or even more in a combination with different sources such as air heat pumps or solar energy. The percentage is influenced mainly by the area of the envelope of the building through which heat is being lost, therefore there is needed more additional energy from other sources and also bigger number of geothermal probes in the building near the lake that are higher. Because the main part of the heat yields is obtained by the geothermal probes, an important factor is also if there is a sufficient width of streets around the building for placing the probes which should be at least 10 m far.

Quite obviously, the investment cost is higher than with a traditional energy source but the period of return of the initial investment can be around 5 or 6 years. And there are of course also the environmental advantages that come with utilizing renewable energy sources.

Sources (1) Erdwärmepotenzialkataster. Stadt Wien [online]. A-1010 Wien, Rathaus: Stadt Wien [cit. 2022-0112]. Dostupné z: https://www.wien.gv.at/stadtentwicklung/energie/themenstadtplan/erdwaerme/ (2) Wien Umweltgut. Stadt Wien [online]. A-1010 Wien, Rathaus: Stadt Wien [cit. 2022-01-12].

Dostupné z: https://www.wien.gv.at/umweltgut/public/grafik.aspx?bookmark=c1ctRgMpAEbwBQ1Gji-arR TnC7kxRMuDGdDhyVrcEud6y6DHaPzYbMoCOJyagxrmICVA-c (3) ČSN 73 0540- (730540)Tepelná ochrana budov - Část 2: Požadavky Praha: Úřad pro technickou normalizaci, metrologii a státní zkušebnictví, 2011. Třídící znak 730540.

(4) VDI 4640 -2 Thermal use of the underground - Ground source heat pump systems. 2001, s 43.

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