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Energy source storage systems increase the efficiency of heat pump systems that are fed from anergy sources. They can be easily combined with near-surface geothermal applications or PVT systems, for example.
An energy source storage system can temporarily store environmental and geothermal heat and make it available to the connected heat pump for a certain period of time. If the ice store is almost completely frozen (up to approx. 85 %), it is regenerated, i.e. defrosted, using environmental heat sources such as PVT or waste heat. The cold from the ice can also be used to cool buildings. You can find out more about how an ice storage system works and the phase change in our blog post "Ice storage: efficient storage of energy from renewable sources".

Despite its relatively small volume of water, the energy source storage tank can temporarily store a considerable amount of energy in the form of crystallisation heat. For example, a water volume of 1 m³, used as an ice store, provides approx. 90 kWh, while a heating buffer with a volume of 7.5-8 m³ would have to be kept available, assuming a spread of 10 K! Of course, the buffer volume is reduced if the spread can be doubled. However, this also has negative consequences for system efficiency.
However, seasonal ice storage solutions usually require a lot of space and can therefore only be installed at considerable expense. "Seasonal" here means that the ice storage tank serves as the sole source of heat for longer if no regeneration from outside is expected or possible. As the storage tank is placed underground, the earthworks are considerable: to supply a house with 120 m² of living space, the ice storage tank must have a volume of 10,000 litres (10 m³) if it is to be used as a source over a longer period of time - and that has to be accommodated first. In addition, transporting and inserting the ice storage tank requires correspondingly large machines. 
However, even an ice store with a volume of 10 m³ combined with a 10 kW heat pump uses up its energy after approx. 8-10 cold days. With a lower heating load and smaller heat pump output, the stored source energy lasts correspondingly longer. This means that a larger volume and, ideally, more space reserve would be required for the heat exchanger used in order to get through a cold December and January without regeneration. 
Homeowners need to consider where the economically sensible limit is to be drawn. In many cases, a combination with an efficient heat or regeneration source is the better option. 
Nevertheless, every ice storage system must include a 100 % heating rod for winter operation, which must be able to take over the heating work when the heat source is exhausted. 

A new development from qficiency GmbH is particularly interesting for owners of detached houses and apartment blocks: the small ice store, the EQS®, differs from previous models:  

• How it works
  The qficiency EQS® is not designed as a seasonal storage tank, but for "pendulum operation": Depending on the time of year and outside temperatures, icing takes place overnight and in the early hours of the morning. During the day, the ice store is regenerated again if regeneration potential is available. There are many options available for this, e.g. geothermal baskets, storage probes, energy fences, PVT absorbers, energy from rainwater, grey water heat recovery, etc. During the season with particularly cold outside temperatures, the regeneration source is operated directly with a low load and a second heat generator provides support if required. 
• Small and powerful
  The EQS® is only 2.5 m³ in size (height 2,400 mm, diameter 1,225 mm, base plate 1,400x1,400 mm). It can be sunk into the ground or - with additional insulation - installed outside. The height of the EQS® shaft can be adjusted (5-15 cm). However, its specific heat exchanger output is - relatively speaking - considerably higher: (EQS® 3.13 kW/m³ vs. competition 1.18 kW/m³), which is ideal for the use of volatile regeneration sources such as PVT.
• Time and cost savings during installation
  The EQS® is delivered fully assembled. The low weight (approx. 220 kg) reduces transport costs, as the ice storage tank can be delivered with a small lorry (3.5-7.5 tonnes). Installation is also much easier as no crane is required. 
  If the EQS® is to be fully or partially sunk into the ground, the shallow excavation depth does not require a specialised civil engineering company, but can be carried out cost-effectively with mini excavators (e.g. by landscape gardeners). This also applies to the excavation of the connecting pipes. 
• There are therefore no additional costs for the customer for a low-loader or (mobile) crane and the earthworks are also inexpensive due to the smaller volume.
• Plug & play prefabrication in the factory with the highest quality standards
  The EQS® is manufactured by our sister company GRATEC GmbH at its factory in Rödermark near Frankfurt/Main. The process is characterised by high-quality materials (PE tank; corrugated stainless steel heat exchanger tubes) and careful workmanship. The standardised heat exchanger unit is already installed at the factory, without detachable connections (plug & play). Sensitive and safety-relevant processes such as pressure and leak testing or the installation of sensors are also carried out at the factory so that the installation schedule can be easily adhered to on site. 

The qficiency EQS® can be designed flexibly according to customer requirements. Thanks to flexible manufacturing processes, not only standard sizes but also customised solutions can be implemented quickly and easily. Smaller solutions due to technically limited excavation depths are given the necessary performance by combining several storage tanks. A second heat exchanger level can also be ordered, which enables a second regeneration source to be easily integrated directly into the storage tank. 
The combination with one or more powerful heat sources is necessary in order to be able to regenerate the ice storage tank quickly. There are different approaches to this. Each regeneration source has special properties which, when combined, mean that sufficient environmental energy can be provided for heat pump operation in every season. 

• Combination of PVT and EQS®: Regeneration of the small ice store via PVT systems or PVQ® (PVT absorber from qficiency) for the direct use of thermal yields from a PV surface (solar thermal component) and thermal yields from the condensation or crystallisation of air humidity and the direct temperature of the outside air.
• Geothermal yields from additionally installed or already existing geothermal probes, baskets, storage probes or surface collectors, which are only designed to provide regeneration energy over 45-60 days in winter and can otherwise only supply base load.
• Grey water applications: Heat recovery systems for grey water can also be integrated into the heat exchanger circuit of the EQS® to ensure highly efficient use of waste heat from wastewater.
• Waste water heat recovery: direct and indirect utilisation 
• Power-2-Heat system: Regeneration of the EQS® by an adjustable heating element that converts PV electricity into heat and feeds it into the storage tank.
• Integration of the EQS® in cold local heating networks and still utilising its own PVQ/PVT primarily for its own energy improvement of the system operation.