<\/span><\/h2>\nThe core purpose of a horizontal ground collector system is to make shallow geothermal energy accessible for residential and commercial heating.<\/p>\n
The ground at a depth of 1.2\u20132.0 metres maintains a near-constant temperature year-round \u2014 typically between 8 \u00b0C and 12 \u00b0C across Central Europe. The collector pipes harvest this low-grade thermal energy. The heat pump then raises it to useful heating temperatures of 35\u201355 \u00b0C. This process replaces fossil fuel combustion with a renewable, ground-stored energy source.<\/p>\n
Primary functions of a horizontal collector ground-source heat pump system:<\/strong><\/p>\n\n- Extract stored solar energy from the shallow subsurface<\/li>\n
- Supply space heating to low-temperature distribution systems<\/li>\n
- Provide domestic hot water (DHW) generation<\/li>\n
- Enable passive cooling (natural cooling) in summer<\/li>\n
- Operate as a renewable heating system compliant with EU and national energy regulations<\/li>\n<\/ul>\n
<\/span>Definition<\/span><\/h2>\nGround-Source Heat Pump (GSHP)<\/h3>\n
A ground-source heat pump (GSHP) is a mechanical refrigeration device that uses the earth as a thermal source in winter and a thermal sink in summer. It operates on the vapour-compression refrigeration cycle. The system achieves a Coefficient of Performance (COP) significantly higher than 1.0, meaning it delivers more thermal energy than the electrical energy it consumes.<\/p>\n
Technical classification:<\/strong><\/p>\n<\/div>\n\n
\n\n\n| Term<\/th>\n | Meaning<\/th>\n<\/tr>\n<\/thead>\n |
\n\n| Ground-Source Heat Pump (GSHP)<\/td>\n | Broader category; source is the earth<\/td>\n<\/tr>\n |
\n| Geothermal Heat Pump<\/td>\n | Often used interchangeably with GSHP in EU regulations<\/td>\n<\/tr>\n |
\n| Brine-to-Water Heat Pump (Sole-Wasser-W\u00e4rmepumpe)<\/td>\n | Technical designation in German-speaking markets<\/td>\n<\/tr>\n |
\n| Horizontal Collector System<\/td>\n | Specific installation variant using shallow, horizontal ground loops<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\nHorizontal Ground Collector (Fl\u00e4chenkollektor \/ Erdkollektor)<\/h3>\nA horizontal ground collector is a closed-loop pipe network installed in horizontal trenches at a depth of 1.2\u20132.0 metres below the surface. The pipes carry a brine mixture \u2014 typically water and propylene glycol or ethylene glycol \u2014 that circulates between the ground and the heat pump’s evaporator.<\/p>\n The collector absorbs geothermal energy stored in the topsoil. This energy originates primarily from solar radiation absorbed at the surface and conducted downward through the soil. The horizontal collector system exploits this near-surface thermal reservoir without requiring borehole drilling.<\/p>\n Installation<\/h3>\nInstallation refers to the complete technical process of designing, excavating, laying, connecting, pressure-testing, commissioning, and certifying the collector field and heat pump unit. It includes civil works, refrigerant pipework, hydraulic integration, electrical connection, and system commissioning.<\/p>\n <\/span>Purpose<\/span><\/h2>\nGround-source horizontal collector heat pump installation serves four interlinked purposes:<\/p>\n 1. Renewable Heat Generation<\/strong> The system replaces oil, gas, or electric resistance heating with a renewable energy source. Ground energy qualifies as renewable under the EU Renewable Energy Directive (RED III) when a Seasonal Performance Factor (SPF \/ Jahresarbeitszahl JAZ) above 2.5 is achieved.<\/p>\n2. Energy Efficiency Compliance<\/strong> New buildings in Austria (OIB Richtlinie 6), Germany (Geb\u00e4udeenergiegesetz GEG), and Switzerland (Mustervorschriften der Kantone im Energiebereich MuKEn 2014) must meet strict primary energy requirements. Ground-source heat pumps reliably achieve the SPF values required to comply.<\/p>\n3. Cost-Effective Long-Term Heating<\/strong> With no fuel costs and low maintenance requirements, horizontal collector systems deliver a predictable operational cost structure over a service life of 20\u201330+ years.<\/p>\n4. Cooling Capability<\/strong> In summer, the ground acts as a natural heat sink. Systems equipped for passive (natural) cooling use the cool brine to absorb heat from the building without activating the compressor \u2014 reducing cooling energy demand to near zero.<\/p>\n<\/span>Why Ground-Source Horizontal Collector Heat Pump Installation Is Needed<\/span><\/h2>\nThe Problem: Fossil Fuel Dependency in Building Heating<\/h3>\nHeating accounts for approximately 50% of total energy consumption in EU buildings. In Austria, Germany, and Switzerland, space heating and domestic hot water together represent the largest share of household energy expenditure. The majority of existing and new buildings still rely on gas and oil boilers that emit CO\u2082 and are exposed to volatile fuel prices.<\/p>\n The Regulatory Driver<\/h3>\nThe EU Buildings Directive (EPBD, recast 2024) mandates that all new residential buildings be near-zero energy buildings (NZEBs). Germany’s GEG 2024 requires that new heating systems cover at least 65% of their energy demand from renewable sources. Austria’s energy strategy targets fossil fuel phase-out in heating by 2040. These requirements create a structural, regulatory demand for ground-source heat pump systems.<\/p>\n The Practical Solution<\/h3>\nHorizontal collector systems address this problem where land is available. They deliver:<\/p>\n \n- SPF values of 3.5\u20135.0 in typical Central European climates<\/li>\n
- Full independence from natural gas and heating oil supply chains<\/li>\n
- Compatibility with underfloor heating, radiators, and domestic hot water<\/li>\n
- A proven, bankable technology with decades of operational data across the DACH region<\/li>\n<\/ul>\n
The Supply Gap<\/h3>\nDemand for ground-source systems significantly exceeds installer capacity across Germany, Austria, and Switzerland. Homeowners, developers, and energy planners require clear, reliable technical guidance for correct system selection, sizing, and installation. This content addresses that knowledge gap directly.<\/p>\n <\/span>Key Features of Horizontal Collector Systems<\/span><\/h2>\nHorizontal ground collector heat pump systems share a defined set of technical characteristics that distinguish them from other heat source options.<\/p>\n Core System Features<\/h3>\n\n- Closed-loop brine circuit<\/strong> \u2014 No ground contamination risk; the brine remains sealed within the collector loop<\/li>\n
- Shallow installation depth<\/strong> \u2014 Trenches typically 1.2\u20132.0 m deep; no deep drilling required<\/li>\n
- Large collector surface area<\/strong> \u2014 Typically 1.5\u20132.5\u00d7 the heated floor area of the building<\/li>\n
- Frost-tolerant operation<\/strong> \u2014 Brine temperatures can drop to \u22125 \u00b0C without system damage<\/li>\n
- Passive regeneration<\/strong> \u2014 The ground recharges naturally through solar absorption and precipitation<\/li>\n
- Long service life<\/strong> \u2014 PE-Xa or PE100 collector pipes rated for 50+ years of operational life<\/li>\n
- Silent outdoor operation<\/strong> \u2014 No outdoor unit; no noise or visual impact above ground<\/li>\n
- No air-source dependency<\/strong> \u2014 Performance remains stable regardless of outdoor air temperature<\/li>\n
- Reversible operation<\/strong> \u2014 Many systems offer passive or active cooling in the same installation<\/li>\n<\/ul>\n
<\/span>Detailed Explanation of Key Features<\/span><\/h2>\nThe Brine Circuit (Solekrais)<\/h3>\nDefinition:<\/strong> The brine circuit is the closed hydraulic loop connecting the horizontal collector pipes to the heat pump’s evaporator. It carries a heat transfer fluid \u2014 a mixture of water and antifreeze \u2014 that transports thermal energy from the ground to the heat pump.<\/p>\nPurpose:<\/strong> The brine absorbs low-grade heat from the surrounding soil as it flows through the collector. It enters the heat pump evaporator at 0\u20138 \u00b0C and returns to the ground at \u22122 to +3 \u00b0C after heat extraction.<\/p>\nBrine fluid specifications:<\/strong><\/p>\n<\/div>\n\n \n\n\n| Parameter<\/th>\n | Value<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Fluid type<\/td>\n | Water + propylene glycol (food-safe) or ethylene glycol<\/td>\n<\/tr>\n | \n| Antifreeze concentration<\/td>\n | Typically 25\u201333% by volume<\/td>\n<\/tr>\n | \n| Freeze protection to<\/td>\n | \u221212 \u00b0C to \u221215 \u00b0C<\/td>\n<\/tr>\n | \n| Operating pressure<\/td>\n | 1.5\u20133.0 bar<\/td>\n<\/tr>\n | \n| Pipe material<\/td>\n | PE-Xa or PE100 (cross-linked or high-density polyethylene)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\nBenefits:<\/strong> The closed-loop design eliminates any contact between the heat transfer fluid and groundwater. This meets the environmental protection requirements set by German Wasserhaushaltsgesetz (WHG) and Austrian Wasserrechtsgesetz (WRG).<\/p>\nPractical example:<\/strong> A 150 m\u00b2 residential home in Upper Austria typically requires a brine circuit with 400\u2013600 m of collector pipe, a circulation pump consuming 50\u2013150 W, and a brine volume of 100\u2013180 litres.<\/p>\nCollector Pipe Layout and Trench Design<\/h3>\nDefinition:<\/strong> The collector layout defines how the pipes are arranged within the excavated area. Three primary configurations are used: straight parallel runs, meandering (serpentine) loops, and spiral\/slinky coils.<\/p>\nPurpose:<\/strong> The layout determines the extraction power per square metre of land, the excavation cost, and the thermal regeneration rate of the soil.<\/p>\nStandard layout types:<\/strong><\/p>\n<\/div>\n\n \n\n\n| Layout Type<\/th>\n | Pipe Spacing<\/th>\n | Area Requirement<\/th>\n | Extraction Power<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Parallel straight runs<\/td>\n | 0.5\u20131.0 m apart<\/td>\n | High<\/td>\n | 10\u201320 W\/m\u00b2<\/td>\n<\/tr>\n | \n| Meandering (serpentine)<\/td>\n | \u2014<\/td>\n | Medium-high<\/td>\n | 15\u201325 W\/m\u00b2<\/td>\n<\/tr>\n | \n| Slinky\/spiral coil<\/td>\n | Compact horizontal<\/td>\n | Lower area<\/td>\n | 20\u201335 W\/m\u00b2<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\nBenefits:<\/strong> Slinky coils reduce the required land area by 30\u201350% compared to straight runs. This makes them suitable for plots where space is constrained but deep drilling is not feasible.<\/p>\nRegulatory note:<\/strong> DIN EN 15450 and the VDI 4640 guideline (Blatt 2) govern the design of horizontal collector systems in Germany. \u00d6NORM EN 15450 applies in Austria. These standards specify minimum extraction rates by soil type and required regeneration margins.<\/p>\nSoil Thermal Properties and Site Assessment<\/h3>\nDefinition:<\/strong> Soil thermal conductivity is the measure of how effectively the ground transfers heat to the collector pipes. It is measured in W\/(m\u00b7K).<\/p>\nPurpose:<\/strong> Soil type directly determines how much heat can be extracted per square metre of collector area. Under-sizing a collector based on incorrect soil data leads to system failure and ground freezing.<\/p>\nThermal conductivity by soil type:<\/strong><\/p>\n<\/div>\n\n \n\n\n| Soil Type<\/th>\n | Thermal Conductivity (W\/m\u00b7K)<\/th>\n | Extraction Power (W\/m\u00b2)<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Dry sandy soil<\/td>\n | 0.3\u20130.5<\/td>\n | 10\u201315<\/td>\n<\/tr>\n | \n| Moist sandy soil<\/td>\n | 1.0\u20131.5<\/td>\n | 15\u201325<\/td>\n<\/tr>\n | \n| Clay\/loam (moist)<\/td>\n | 1.5\u20132.0<\/td>\n | 20\u201330<\/td>\n<\/tr>\n | \n| Waterlogged soil<\/td>\n | 2.0\u20132.5<\/td>\n | 25\u201335<\/td>\n<\/tr>\n | \n| Rock\/gravel<\/td>\n | 2.5\u20134.0<\/td>\n | 30\u201345<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\nBenefits:<\/strong> Accurate soil assessment prevents system under-performance. Sites with high groundwater tables offer the highest extraction rates because water movement continuously replenishes soil heat.<\/p>\nPractical application:<\/strong> A site survey in Bavaria or Tyrol typically includes soil core sampling, local geology mapping, and review of existing hydrogeological data. iDM-certified installers conduct site assessments prior to system sizing.<\/p>\nHeat Pump Unit (W\u00e4rmepumpenaggregat)<\/h3>\nDefinition:<\/strong> The heat pump unit is the indoor mechanical component that compresses the refrigerant to raise its temperature. It connects the brine circuit (evaporator side) to the heating system (condenser side).<\/p>\nPurpose:<\/strong> The compressor is the energy-converting core of the system. It elevates the low-temperature brine energy to the temperature level required by the heating distribution system.<\/p>\nKey heat pump parameters for horizontal collector systems:<\/strong><\/p>\n<\/div>\n\n \n\n\n| Parameter<\/th>\n | Typical Value<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Rated heating capacity<\/td>\n | 6\u201360 kW (residential\/small commercial)<\/td>\n<\/tr>\n | \n| COP at B0\/W35<\/td>\n | 4.0\u20135.5 (ground 0 \u00b0C \/ flow 35 \u00b0C)<\/td>\n<\/tr>\n | \n| Seasonal Performance Factor (JAZ)<\/td>\n | 3.5\u20135.0<\/td>\n<\/tr>\n | \n| Refrigerant<\/td>\n | R410A (legacy), R32, R290 (propane), R454B<\/td>\n<\/tr>\n | \n| Max. flow temperature<\/td>\n | 55\u201370 \u00b0C depending on model<\/td>\n<\/tr>\n | \n| Compressor type<\/td>\n | Scroll (most common), inverter-driven scroll<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\nBenefits:<\/strong> Inverter-driven compressors modulate output continuously. This reduces electrical consumption, eliminates short-cycling, and maintains stable brine temperatures \u2014 all of which extend system life and improve JAZ.<\/p>\niDM product context:<\/strong> iDM Energiesysteme GmbH manufactures the TERRA series of brine-to-water heat pumps, engineered for horizontal collector integration. The TERRA range delivers rated COPs of up to 5.3 (B0\/W35) and is certified under EN 14511.<\/p>\nManifold and Distribution System (Verteilerstation)<\/h3>\nDefinition:<\/strong> The manifold is a central hydraulic distribution point where multiple collector loops connect to a single supply and return header feeding the heat pump.<\/p>\nPurpose:<\/strong> The manifold balances flow across all collector loops and allows individual circuits to be isolated for maintenance or repair.<\/p>\nManifold specifications:<\/strong><\/p>\n\n- Material: Stainless steel or high-grade plastic<\/li>\n
- Number of circuits: 2\u201312 collector loops per manifold<\/li>\n
- Location: Underground chamber or frost-protected building entry point<\/li>\n
- Flow balancing: Manual or automatic balancing valves per circuit<\/li>\n
- Access: Inspection cover at surface level<\/li>\n<\/ul>\n
Benefits:<\/strong> A correctly designed manifold ensures even heat extraction across the entire collector field. Unbalanced flow causes localised ground freezing and reduces overall system performance.<\/p>\n<\/span>Types and System Variants<\/span><\/h2>\nSeveral variants of horizontal collector systems exist. Selection depends on available land area, soil conditions, building heat demand, and local regulatory requirements.<\/p>\n Flat Horizontal Collector (Fl\u00e4chenkollektor)<\/h3>\nThe standard installation type. Pipes are laid in parallel trenches at 1.2\u20131.5 m depth. Trench width is typically 60\u201380 cm. This is the most common configuration in Austria and Germany.<\/p>\n Best for:<\/strong> Properties with generous garden or field area; soil with moderate thermal conductivity.<\/p>\nSlinky Coil Collector (Spiralkollektor)<\/h3>\nPipes are wound into horizontal spiral coils and laid flat in wider, shallower trenches. The coil configuration increases pipe length per metre of trench.<\/p>\n Best for:<\/strong> Properties with limited land area; installers seeking reduced excavation volume.<\/p>\nNear-Surface Geothermal Mat (Geothermie-Matte)<\/h3>\nPre-assembled mat systems consisting of a high-density grid of small-diameter PE pipes embedded in a geotextile carrier layer. These are rolled out and covered with backfill.<\/p>\n Best for:<\/strong> New construction sites where the collector can be installed during foundation landscaping; residential developments with standardised plots.<\/p>\nDual-Depth Horizontal Collector<\/h3>\nTwo pipe layers installed at different depths \u2014 for example, 1.2 m and 2.0 m \u2014 within the same trench. This doubles extraction power within the same surface footprint.<\/p>\n Best for:<\/strong> Sites with limited land but good soil thermal properties; medium-demand applications.<\/p>\nEnergy Basket \/ Energy Pile (Energiekorb)<\/h3>\nA compact vertical-horizontal hybrid: coiled pipe baskets installed in bored or excavated pits approximately 2\u20134 m deep. Multiple baskets connect to a common manifold.<\/p>\n Best for:<\/strong> Sites where trenching is restricted but shallow drilling is feasible; brownfield sites with limited surface access.<\/p>\n<\/span>Use Cases<\/span><\/h2>\nHorizontal collector heat pump systems serve a broad range of applications across the Central European building stock.<\/p>\n New Residential Construction (Einfamilienhaus \/ Neubau)<\/h3>\nApplication:<\/strong> Single-family homes with heat demands of 6\u201320 kW. The most common deployment context for horizontal collectors in Austria, Bavaria, and Switzerland.<\/p>\nWhy horizontal collectors work here:<\/strong> New construction allows collector installation during site preparation, before landscaping. Garden areas of 300\u2013800 m\u00b2 are typical and sufficient for collector fields serving 100\u2013250 m\u00b2 heated floor area.<\/p>\nRegulatory fit:<\/strong> GEG 2024 (Germany), OIB Richtlinie 6 (Austria), and MuKEn 2014 (Switzerland) all support GSHP systems as a primary renewable heating technology.<\/p>\nResidential Renovation with Garden Access (Sanierung)<\/h3>\nApplication:<\/strong> Retrofit of oil or gas boiler with a ground-source heat pump in existing single-family homes.<\/p>\nWhy horizontal collectors work here:<\/strong> Where the property has sufficient garden area, horizontal collectors avoid the cost and planning complexity of borehole drilling. The heat pump is installed in the existing plant room.<\/p>\nKey challenge:<\/strong> Existing radiator systems may require upgrades to operate at the lower flow temperatures (35\u201345 \u00b0C) that maximise heat pump efficiency. Low-temperature underfloor heating is the ideal distribution system.<\/p>\nMulti-Family Residential Buildings (Mehrfamilienhaus)<\/h3>\nApplication:<\/strong> Buildings of 4\u201320 residential units with collective heat demands of 20\u201380 kW.<\/p>\n | | | | |