Economic benefits of DUAL SOURCE technology in geothermal application

Producing thermal energy through a heat pump system involves a careful analysis of the source system, as the largest share of the benefits obtainable depends on this choice. Where the geothermal option has been assessed, in order to prioritize stability and performance aspects, the economic impact may be a deterrent to the investment that could make the choice of a less expensive system such as aerothermal energy.

However, there is an alternative. The DUAL SOURCE system makes it possible to greatly reduce the economic impact by the less use of geothermal probes, while retaining the benefits of using this mode of exchange even under the most disadvantaged conditions by combining the stability of the geothermal field with residual capacity of the aerothermal system.

Simply put a 50-50 (geothermal-aerothermal) system consisting of the heat pump mentioned in the project illustrated below. The aerothermal heat exchanger of the unit was deliberately maintained for two reasons. The first is that with a minimum investment you will have a backup system and the second is that in this way the resulting approach on the air side is about double, thanks to an improvement of the COP between 10% and 20% . It goes without saying that while on a little unit the cost of the aerothermal heat exchanger has a relative economic impact, for the opposite reasons it is necessary to carefully evaluate on large units.

At an outside temperature of -7°C and delivered to +35°C we develop 11.85 kWt with geothermal energy and 10.46 kWt with aerothermal part for a total of 22.31 kWt. Compared to pure aerothermal we have about a 17% advantage over a loss of only 6% compared to pure geothermal energy. Due to the same installed unit I get:

  • About 4 kWt more, which can make the choice on a smaller unit size
  • With equal consumption I have a COP that goes from 3.6 to 4.4
  • Additionally, we add a drop of more than 50% compared to waste energy for defrosting

Case study

We now present a real application case that compares a traditional geothermal system with a DUAL SOURCE, geothermal + aerothermal system in proportion 40% -60%, highlighting its economic savings. Model selected is COMPOUND.AQUA.S1.K30.410.

Initial data

  • Building 8 apartments - Treviso area ( Project temperature -5°C)
  • Radiant floor heating
  • Cooling fan coil
  • Heat pump power 28 kW

Energy over year

Month

Heating kWh

Cooling kWh

DW kWh

Total kWh

January

5917

 

1044

6961

February

4021

 

814

4835

March

2148

 

759

2907

Aprile

261

25

632

918

May

 

237

540

777

June

 

1910

433

2343

July

 

3228

404

3632

Aougust

 

2745

452

3197

September

 

806

566

1372

October

312

36

767

1115

November

2856

 

962

3818

December

5300

 

1041

6341

SINGLE SOURCE

Probe length (m) 552, number of probes 5 (max 120 m).

  • Cost of geothermal probes € 25,000.00
  • Connection and fill up costs € 6,000.00
  • Transport € 2.000,00
  • TOTAL € 33.000,00​

DUAL SOURCE 40-60

Probe length (m) 289, probes number 3 (max 120m). The remote exchanger and its cooling line (up to 5 m) and the COMPOUND device that simultaneously manage the two sources must be added to the system.

  • Cost of geothermal probes € 13,000.00
  • Connection and fill up cost € 4.000,00
  • Transport € 2.000,00
  • Remote air exchanger € 1,500.00
  • Fridge lines € 1.800,00
  • COMPOUND device € 700,00
  • TOTAL € 23,000.00​

From the values emerges a saving on the costs of the components of the source side of 30%!

Operating cost

From an energy saving point of view, we work with a demand of about 30,000.00 kWh / year between heating and hot water for sanitary use. Considering that the average monthly temperature (+3.75°C) for about 60 days (Dec./Jan.) is below the average temperature of the period (+7.60°C) and during which approximately 14,000.00 kWh. The average thermal power generated during the period is about 20 kW, of which 12 are taken from geothermal energy and the remaining 8 kW by air. Considering an increase in the average COP ranging from 4.5 to 5.5 (+ 18%) used at 70%, we get a final gain of 13%. As far as the economic savings are concerned, we stand for about 40% of the total airspace.

Conclusion

DUAL SOURCE technology is a great alternative to fully geothermal installations as it keeps most of the benefits by significantly reducing the value of the initial investment.