ASPERN - POTENTIAL OF GEOTHERMAL ENERGY by ATC

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 %