Case study: ??centri_commerciali??
Cetra, a Bologna-based company belonging to the Galletti Group and specialized in air handling, inaugurated a new production facility in Altedo with a surface area of 5,000 m², of which 4,000 m² is covered floor space.
The point of pride of the new facility is its geothermal unit, which was completely designed and built as a result of the internal expertise and synergies of the Galletti Group, beginning from the analyses and dynamic simulations for determining the size of the probe field, up to designing the air conditioning system.
For the facility’s heating needs, it was decided to use a geothermal system with components constructed entirely by the Galletti Group’s companies. Before coming to a decision on the system, however, an in-depth study was conducted comparing the costs and benefits of the various possible solutions, beginning with determining the size of the probe field using a dynamic simulation (EED).
|
Annual heating energy needs |
67.4 |
MWh |
|
Winter peak power |
60.0 |
kW |
|
Annual cooling energy needs |
37.6 |
MWh |
|
Summer peak power |
60.0 |
kW |
|
Annual energy for DHW |
9.1 |
MWh |
Input data: Base thermal load
Input data: Peak load
Four possible alternatives were compared, to arrive at the final solution: the first possible solution with a dry expansion exchanger and pure water as the thermal carrier fluid, which would have required approximately 1800 m of probes; the second possible solution with a dry expansion exchanger and water with 25% propylene glycol, which would have required approximately 1100 m of probes; the third possible solution with a submerged exchanger and pure water, which would have required 1400 m of probes; and the fourth possible solution was a more conventional system with a methane gas boiler and a refrigeration unit.
Solution |
# 1 |
# 2 |
# 3 |
# 4 |
|
Type of exchanger |
Dry expansion |
Dry expansion |
Submerged |
Methane boiler |
|
Heat transfer fluid |
Pure water |
Water + glycol |
Pure water |
Comparing the installation costs of the probe field for the three different solutions with a geothermal heat pump, the least expensive solution was found to be the second possible solution (dry expansion, water + glycol), which has a cost of 68,000 euros.
However, when the annual operating costs are taken into account, which depend on the needs of the building for heating, cooling, and DHW (constant in all 4 cases), and on the performance of the machines, solution 3 allows a savings of 28% over solution 2.
In fact, the heat pumps’ COP/EER vary depending on the number of probes installed and, therefore, depending on the inlet temperature on the source side of the heat pump.
Therefore, the payback for solution 3 is only 5 years, also due to the higher expenses for installing the probes and for replacing the glycol, thus making it the most economical; it was the solution adopted for the heating plant for the Cetra facility.
