TermoPlus was determined to become 100% powered by renewables by 2018 and the project involved the use of ground source heat pumps and solar PV to cover all the energy and heating requirements of the site.
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CEO Jure Šacer explained the rationale: “It was much akin to the reason car manufacturers participate in racing events. By installing, owning and maintaining a system of our own, we could gather data, introduce improvements and get physical input that our simulation labs can’t offer. Not to mention the lower overheads and setting an example.”
A holistic approach
The Slovenian facilities total 1000 m². Back in 2007 the site used 61000 kWh of power from the grid and an oil fuelled boiler system that consumed 3000 litres of heating oil annually (a total annual cost of €12.500 in 2012 terms). CO2 output was at 130.748 kg pa.
After the heat pump installation in 2008 no heating oil was used at all. A ground water geothermal system was installed for heating and cooling along with a DHW heat pump that produces domestic hot water. Fan coils that enable cooling were installed as well as a mechanical ventilation heat recovery unit for the ventilation of the shop floor. The facade and building roof were also further insulated with doors and windows being upgraded.
An annual energy saving of 30% resulted in the use of 43.000kWh for heating, cooling, ventilation and production and zero oil. (total cost in 2012 terms: €4.700, down from €12.500).
In 2013 a 43kWp PV solar power plant was installed. As a result, in 2014 93% of all energy needs were covered by the solar PV power plant and a financial surplus from the feed-in tariff resulted in additional income.
After the implementation of these upgrades the Slovenian branch produced 23.648 kg of CO2 with all electric consumption. This is a total reduction of CO2 emissions of 107.100 kg per year, or 1.071 tonnes over 10 years.
The heat pumps
Two Gen 3 TermoPlus AQUApump ground-source heat pumps where used, one of which was equipped with a digital scroll variable output compressor. Also, a 300l TermoPlus DHW heat pump was used for hot running water.
A 18,05Kw Aquapump W25 DIGI EVI (COP (W10/W35): 4,80) was installed along with a 26,90Kw AQUApump W25 R (COP (W10/W35): 5,06).
The TermoPlus AQUApump W25 is a high-efficiency reversible water/water heat pump for central heating and cooling with a weather compensation controller. It made sense for one of the units to feature optimisation via a custom-developed scroll compressor.
Why a custom scroll compressor was used
Only digital scroll compressors offer variable compression. Simply put, they offer the advantage of digitally setting the output rate at which the heat pump operates, allowing for much more control over efficiency and power. By including one heat pump with a digital scroll compressor the system’s operational output could be fine-tuned to the desired levels. This has resulted in overall greater efficiency, particularly with lighter loads.
A test borehole a few metres from the building produced 15°C water at the depth of 5m. As a result, an open loop groundwater system that offered the highest COP and SCOP made sense. Alternatively a ground collector (closed loop) would have been employed instead. Currently the ground water temperature ranges between 12,5°C and 21°C, depending on the season.
A 4”, 15m deep borehole was then drilled and a submersible pump was inserted. PE pipes were laid to the plant room. Another borehole was drilled for the return of the ground water approximately 15m from the supply borehole.
To allow for active cooling, reversible heat pumps were used along with fan coils for the heating/cooling system. This allowed for heating and cooling in one system without the need for an additional water chiller.
Heat pumps and plant room
The two heat pumps were installed: a standard 25 kW heat pump and an 18 kW digital scroll heat pump with enhanced vapour injection. The digital scroll heat pump is used when less than 18 kW (3-18 kW variable) is required. When needs are between 18 and 25 kW the 25 kW heat pump is used (25 kW fixed). When needs are over 25 kW, both heat pumps work in cascade (26-43 kW variable). Both heat pumps were connected to a water filter and a submersible pump on one side and a 300l buffer tank on the other. The buffer tank was then connected to the 4-way manifold, where circulating pumps for fan coils, ventilation system and the radiators were connected.
Finally, a 300l DHW heat pump was then installed for the limited domestic hot water requirements and the old oil boiler was incorporated into the system as a (dormant) backup.
At the time fan coils were a natural choice for the office spaces, since both heating and cooling were needed. However, today underfloor heating would also accompany the fan coils for greater comfort during winter. Radiators had been in use for the bathrooms. For the shop floor, mechanical ventilation with heating/cooling coils was added beside fan coils.
Energy recycling through production testing
Another heat exchanger was installed on the supply line from the borehole just before the heat pumps to efficiently use the recycled hot water from the heat pump testing line. This pre-heats the ground water before entering the heat pumps.
The submersible pump was later replaced by an inverter driven pump, so that the pump speed and water volume would be driven according to the temperature differential set on the heat pump. Previously, the maximum water volume was constantly pumped.
The heat pump’s circulating pump for the flow to the buffer tank is also now speed controlled according to the desired delta T set on the heat pump controller.
Newer controllers and software were also added to the heat pumps, which offered remote maintenance and web control. Digital pressure transducers now constantly check high and low side pressure on the controller.
How the installation improved product development
The AquaPump series used in the installation were third generation units. At ISH 2017 TermoPlus launched the Gen 6 range. Some of the incremental improvements seen after three generations of refinements include improved control of the refrigerant circuit with electronic expansion valves and the introduction of microchannel heat exchangers with better transfer characteristics.
With the upgrade of the controller which now supports online control and speed control for circulation and submersible pumps (according to the temperature difference), seasonal efficiency of the heat pumps has increased by up to 15% (depending on the model).