- Free Cooling (with Geothermal Storage)

Based on the example of the Geothermal heat pump, let’s now consider that the cooling demand can also be supplied by free cooling, whenever this is possible. For doing so, a free cooling heat exchanger must be added. It is modelled as a separate technology, as we have already 3 modes in our brine-water heat pump technology (the current maximum number of modes).

 

Set-up summary

Energy Carriers

Energy Demands

Imports

Exports

Supply technology

Brine water HP 1

Brine water HP 2

Brine water HP 3

HEX waste heat to geothermal

HEX Free cooling

Generic Borehole

Electricity

 

X

 

Primary Input

(primary) Input

Primary Input

 

 

 

Geothermal heat

 

 

 

Input

 

 

(primary) output

Output

X

Ambient heat

 

X

 

 

Input

 

 

 

 

Heat 30-40°C

X

 

 

(primary) Output

(primary) Output

 

 

 

 

Cooling 10-20°C

X

 

 

 

 

(primary) output

 

(primary) output

 

Waste heat

 

 

X

 

 

Output

(primary) input

 

 

 

Set-up implementation

The free cooling has only two outputs, as it simultaneously creates cooling and heating by transferring heat from one medium to the other. The output of the free cooling HEX is directly the geothermal heat. This way, the technology can only operate when the geothermal sink is not fully loaded. For simplicity, pump electricity has been ignored. Of course, adding an electricity input and strongly increasing the efficiency of the outputs would allow to consider it (e.g. for an output efficiency of 1’000 %, 1 unit of electricity would be needed for producing 10 units of cooling).

 

- Free Cooling (with cold water storage)

Two cases must be considered here:

  • A storage without charging and discharging losses

  • A storage with charging and discharging losses

- Storage without charging and discharging losses

For a storage without charging and discharging losses (= charging / discharging efficiencies of 100%), it is straight forward:

Make sure that the charging and discharging efficiencies are equal to 100%

 

 

- Storage with charging and discharging losses

As the storage technology has the possibility to charge and discharge at the same time, this may result in losses. When set up incorrectly, the system can use this to destroy energy (by charging and discharging high quantities of energy). This behaviour is observed when it is profitable for a system to destroy energy, which is the case when free cooling is be used (and when the cost and CO2 emissions of operating the free cooling is lower than using the other systems, which is the idea of the free cooling). In this case, the storage must be possible only for the actively chilled water.

 

Set-up summary

Energy Carriers

Energy Demands

Imports

Exports

 

Supply technology

 

Brine water
HP 1

Brine water HP 2

Brine water HP 3

HEX waste heat to geothermal

HEX Free cooling

Generic Borehole

Virtual technology

Electricity

 

X

 

Primary Input

(primary) Input

Primary Input

 

 

 

 

Geothermal heat

 

 

 

Input

 

 

(primary) output

Output

X

 

Ambient heat

 

X

 

 

Input

 

 

 

 

 

Heat 30-40°C

X

 

 

(primary)
Output

(primary) Output

 

 

 

 

 

Cooling 10-20°C

X

 

 

 

 

 

 

(primary) output

 

(primary) output

Active Cooling

 

 

 

 

 

(primary) output

 

 

 

(primary) input

Waste heat

 

 

X

 

 

Output

(primary) input

 

 

 

 

Set-up implementation

 

In this case, the cooling must be separated into two energy carriers: (e.g.) Cooling and active cooling. This is done so that the cooling production and storage use another energy carrier (active cooling) than the energy carrier produced by the HEX Free cooling (cooling 10-20°C), which has for effect, that the cooling 10-20°C cannot be stored within the cold storage.

The following model is based on the free cooling without storage model (section 5.1.1.2)

 

From there on, the custom cooling energy carrier ‘active cooling’ must first be added to the energy carriers.

 

Under the tab supply technologies, the output of the mode 3 of the brine water heat pump is changed to ‘active cooling’.

 

The generic storage can be added, as a storage for active cooling.

Finally, to allow for the system to cover the cooling demand with the active cooling, a virtual technology is added, transforming active cooling into cooling 10-20°C (the energy carrier of the demand).

 

 

- Free Cooling as export

Finally, there are some cases where free cooling is to be used as a 'bonus', meaning that the tenants won't have guarantee that their building is cooled. In this case, this 'bonus' must be modelled as an export rather than a demand. Indeed, modelling it as a demand would force its production.  The system is simple: a brine water heat pump can work on a geothermal borehole. To regenerate this borehole, free cooling of the buildings can be used (reminder: a borehole modelled as a storage need to be charged and discharged).

 

Set-up implementation

Set-up summary

Energy Carriers

Energy Demands

Imports

Exports

 

Supply technology

Storage technology

Brine water HP 1

Brine water HP 2

HEX Free cooling

Generic borehole

Electricity

 

X

 

Primary Input

Primary Input

 

X

Geothermal heat

 

 

 

Input

 

Output

 

Ambient heat

 

X

 

 

Input

 

 

Heat 30-40°C

X

 

 

(primary) Output

(primary) Output

 

 

Cooling 10-20°C

X

 

 

 

 

(primary) output

 

 

Set-up implementation

 

First, the energy carrier for the free cooling must be added (in this case Cooling 10-20°C)

The capacity of the free cooling heat exchanger must be limited to avoid infinite production of (very cheap) low temperature heat.

Monthly time varying efficiencies can be used to further modulate this capacity for every month (by setting efficiencies lower than 100%). This must be done for both outputs.