# Construction of underground heat accumulator

## Heat accumulator technical data

>> realization
Heat accumulator capacity (water temperature change from 75 to 55 degrees C): 202 megajoules

Heat accumulator capacity (water temperature change from 75 to 30 degrees C): 455 megajoules

Maximal power: 15 kilowatts

Water volume: 2420 litres

Water work temperature: 0... 75 degrees C

Depth: 2,4 metres

Width: 1,65 metres

## Heat capacity calculation

Specific heat capacity for liquid water is 4,18 KJ/(KG*K).

If the water temperature change is 20 degrees K (from 75 to 55 degrees C) and the water mass is 2420 kilograms:

accumulator capacity is 202 megajoules.

If the water temperature change is 45 degrees K (from 75 to 30 degrees C):

accumulator capacity is 455 megajoules.

**Other units**

**In kilowatt-hour (KWh)**

One kilowatt-hour is equal to 3,6 mega joule.

For temperatures from +75 to +55 degrees C, accumulator capacity is 56,1 kilowatt hours, and for temperatures from +75 to +30 degrees C accumulator capacity is 126,4 Kwatt-hours.

**In amper-hours (Ah)**

*(for comparison, with 12 volt electrical accumulator)*

One kilowatt-hour is equal to 83,(3) Amper from 12 volt electricity source during 1 hour. Or one kilowatt-hour is equal to 83,3 Ah for 12-volt accumulator.

For temperatures from +75 to +55 degrees C, accumulator capacity is 4675 Amper-hours, and for temperatures from +75 to +30 degrees C accumulator capacity is 10533 Amper-hours. (150 car electric accumulators)

## Heat accumulator sketch

Where is:

1 - liquid water

2 - spiral heat exchanger (copper pipe, diameter 20 millimeters)

3 - support for heat exchanger and thermometer

4 - thermometer

5 - thermal insulation

*XPS - Extruded polystyrene boards Fibran-Eco RF, dimensions 40x600x1250, thermal conductivity 0,035 Watt/(metre*Kelvin), thermal resistance 1,14 (sq.metre*Kelvin)/Watt*

6 - concrete

7 - concrete floor

8 - ground

9 - heat and cold pipes

10 - electric heater (800 Watt, 220 volt, length 1,9 metre)

11 - waste water-pipe

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