<\/span><\/h2>\nDomestic hot water (DHW) integration<\/strong> is the technical process of connecting a heat pump system to the building’s potable water supply to produce, store, and distribute heated water for daily use. It defines how a heat pump generates usable hot water for taps, showers, bathtubs, and kitchen appliances \u2014 beyond its primary role in space heating.<\/p>\nIn a heat pump installation, DHW integration determines the system architecture for hot water generation. It covers the hydraulic connection between the heat pump, a storage vessel, and the distribution network. It also governs the control logic that manages when, how, and at what temperature hot water is produced.<\/p>\n
DHW integration is not a standalone product. It is a defined functional layer within a complete heat pump system. The integration quality directly determines energy efficiency, hygiene compliance, user comfort, and operational cost.<\/p>\n
\nDomestic hot water integration = the controlled coupling of heat pump thermal output to potable water heating and storage within a residential or commercial building system.<\/p>\n<\/blockquote>\n
<\/span>Core Purpose of DHW Integration<\/span><\/h2>\nThe core purpose of DHW integration is to supply sanitary hot water at legally required temperatures using heat pump technology as the primary energy source \u2014 replacing or supplementing conventional fossil-fuel boilers or electric resistance heaters.<\/p>\n
DHW integration serves three operational functions:<\/strong><\/p>\n\n- Thermal production:<\/strong> The heat pump extracts energy from an ambient source (air, ground, or water) and raises it to the temperature required for potable hot water.<\/li>\n
- Thermal storage:<\/strong> A buffer or stratified cylinder stores the produced heat and makes it available on demand without running the heat pump continuously.<\/li>\n
- Controlled distribution:<\/strong> The integrated controller manages temperature levels, priority switching, and reheating cycles to ensure uninterrupted supply.<\/li>\n<\/ul>\n
A correctly integrated DHW system reduces total system energy consumption. It shifts hot water production to low-tariff periods, coordinates with space heating demand, and prevents system conflicts that lead to efficiency losses.<\/p>\n
<\/span>Why Domestic Hot Water Integration Is Needed<\/span><\/h2>\nThe Energy Problem With Conventional Hot Water Systems<\/h3>\n
Traditional water heaters use electric resistance elements or gas burners to heat water. These systems operate at efficiencies close to or below 100%. Heat pumps achieve efficiencies of 250\u2013500%, expressed as a Coefficient of Performance (COP) between 2.5 and 5.0. Without DHW integration, a heat pump cannot deliver these gains for hot water \u2014 an electric immersion heater remains the default, negating much of the system’s efficiency advantage.<\/p>\n
Regulatory Requirements<\/h3>\n
European and national regulations mandate that heat pump systems must include hygienic hot water preparation at specific temperatures. Key regulatory frameworks include:<\/p>\n
\n- EU Energy Performance of Buildings Directive (EPBD):<\/strong> Requires nearly zero-energy buildings (nZEB) to cover domestic hot water demand through high-efficiency systems.<\/li>\n
- EN 806 \/ \u00d6NORM B 5019 (Austria) \/ DIN 1988 (Germany):<\/strong> Define sanitary installation standards for potable water systems, including temperature maintenance to prevent bacterial growth.<\/li>\n
- Legionella Prevention Regulations:<\/strong> In Austria, Germany, and Switzerland, potable water systems in multi-unit dwellings must comply with regulations requiring periodic thermal disinfection at 70\u00b0C or higher.<\/li>\n
- ErP Directive (EU) 2013\/814:<\/strong> Classifies and labels heating systems including heat pump DHW configurations by energy efficiency class.<\/li>\n<\/ul>\n
Failure to integrate DHW correctly creates hygiene risk and legal non-compliance.<\/p>\n
The Comfort Problem<\/h3>\n
A heat pump without integrated DHW management creates temperature conflicts. When space heating and hot water demand occur simultaneously, the system must prioritise one function. Without structured integration, this results in:<\/p>\n
\n- Cold showers during heating cycles<\/li>\n
- Excessive reheating cycles that reduce compressor lifespan<\/li>\n
- Inconsistent supply temperatures<\/li>\n<\/ul>\n
Proper integration solves this through priority control and storage buffering.<\/p>\n
The Efficiency Problem<\/h3>\n
Heat pumps operate most efficiently at low flow temperatures. Domestic hot water requires higher temperatures \u2014 typically 55\u00b0C to 60\u00b0C for storage, compared to 35\u00b0C to 45\u00b0C for underfloor heating. Without optimised DHW integration, the system runs at elevated temperatures continuously, degrading overall system COP.<\/p>\n
Smart DHW integration limits high-temperature operation to defined time windows. This protects compressor efficiency and reduces electricity consumption.<\/p>\n
<\/span>Key Features of DHW Integration in Heat Pump Systems<\/span><\/h2>\n<\/div>\n\n
\n\n\n| Feature<\/th>\n | Function<\/th>\n | Regulatory Relevance<\/th>\n<\/tr>\n<\/thead>\n |
\n\n| Priority control<\/td>\n | Switches system between heating and DHW mode<\/td>\n | Ensures supply continuity<\/td>\n<\/tr>\n |
\n| Thermal disinfection<\/td>\n | Periodic heating to 70\u00b0C to kill Legionella<\/td>\n | \u00d6NORM B 5019, DIN VDI 6023<\/td>\n<\/tr>\n |
\n| Stratified storage<\/td>\n | Layered temperature storage for efficiency<\/td>\n | Supports low-COP operation at draw-off<\/td>\n<\/tr>\n |
\n| Smart tariff integration<\/td>\n | Shifts DHW production to off-peak electricity periods<\/td>\n | Reduces operational cost<\/td>\n<\/tr>\n |
\n| Immersion heater backup<\/td>\n | Electric resistance element for peak or emergency demand<\/td>\n | Ensures supply during defrost or extreme cold<\/td>\n<\/tr>\n |
\n| Heat meter \/ energy monitoring<\/td>\n | Measures energy input for DHW production separately<\/td>\n | Required for subsidies in AT\/DE\/CH<\/td>\n<\/tr>\n |
\n| Anti-legionella timer<\/td>\n | Automated weekly or programmable thermal shock<\/td>\n | Legal compliance in multi-unit buildings<\/td>\n<\/tr>\n |
\n| Hygienic fresh water station<\/td>\n | Instantaneous heat exchanger avoids stored potable water<\/td>\n | Highest hygiene standard, no stagnation<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/span>Detailed Explanation of Features<\/span><\/h2>\nPriority Control<\/h3>\nDefinition:<\/strong> Priority control is the logic within the heat pump controller that determines which thermal demand \u2014 space heating or domestic hot water \u2014 receives system output first.<\/p>\nPurpose:<\/strong> It prevents simultaneous competing demand from overloading the heat pump and ensures that DHW storage is recharged within a defined time window.<\/p>\nHow it works:<\/strong> When DHW storage falls below the set threshold temperature, the controller switches the heat pump to DHW mode. Space heating is temporarily paused. Once the target storage temperature is reached, space heating resumes.<\/p>\nTwo primary modes exist:<\/strong><\/p>\n\n- Absolute DHW priority:<\/strong> DHW demand always overrides space heating. Used in systems with high and unpredictable hot water demand.<\/li>\n
- Parallel DHW\/heating operation:<\/strong> The heat pump serves both functions simultaneously. Requires higher system capacity. Used in larger installations with sufficient compressor output.<\/li>\n<\/ul>\n
Benefit:<\/strong> Eliminates temperature conflicts. Guarantees consistent hot water supply without manual intervention.<\/p>\nExample:<\/strong> In a family home with iDM heat pump systems, DHW priority is activated at 05:00. The cylinder recharges to 55\u00b0C before the morning peak demand. Space heating resumes after recharge is complete.<\/p>\nStratified Thermal Storage<\/h3>\nDefinition:<\/strong> A stratified storage cylinder (also called a layered or thermal stratification tank) stores hot water in distinct temperature layers \u2014 hotter water at the top, cooler water at the bottom \u2014 without mixing.<\/p>\nPurpose:<\/strong> Stratification maximises the usable hot water volume at the correct temperature while minimising the return temperature to the heat pump, preserving COP.<\/p>\nHow it works:<\/strong> Cold mains water enters at the base of the cylinder. The heat pump charges from the bottom upward using a low-velocity inlet. Hot water is drawn from the top. The temperature gradient remains stable between recharge cycles.<\/p>\nBenefit:<\/strong> A 300-litre stratified cylinder can deliver significantly more usable hot water than a 300-litre mixed tank at the same average stored energy \u2014 because the draw-off temperature at the top remains consistently high.<\/p>\nKey specifications to evaluate:<\/strong><\/p>\n\n- Tank volume (litres) \u2014 sized per EN 12897 or DIN 4708 based on occupancy<\/li>\n
- Standing heat loss (W) \u2014 lower values indicate better insulation<\/li>\n
- Connections for solar thermal or photovoltaic integration<\/li>\n
- Number of heat exchanger coils<\/li>\n
- Internal surface material (enamelled steel, stainless, or plastic-lined)<\/li>\n<\/ul>\n
Thermal Disinfection (Anti-Legionella Function)<\/h3>\nDefinition:<\/strong> Thermal disinfection is an automated procedure in which the stored water is heated to 70\u00b0C or above for a defined period to eliminate Legionella pneumophila and other pathogens.<\/p>\nPurpose:<\/strong> Legionella bacteria multiply in water stored between 25\u00b0C and 50\u00b0C. Normal heat pump operating temperatures for DHW (55\u00b0C storage) reduce but do not eliminate the risk in all system configurations. Thermal disinfection provides a periodic kill cycle.<\/p>\nRegulatory basis:<\/strong><\/p>\n\n- \u00d6NORM B 5019 (Austria): Mandates Legionella prevention concepts for buildings with central hot water supply<\/li>\n
- DVGW W 551 \/ VDI 6023 (Germany): Technical guidelines for drinking water systems, defining temperature maintenance and disinfection requirements<\/li>\n
- Swiss SVGW W3 Directive: Equivalent requirements for Swiss potable water systems<\/li>\n<\/ul>\n
How it works:<\/strong> The controller triggers the immersion heater or auxiliary heat source once per week (configurable). The entire cylinder volume is brought to \u226570\u00b0C. This is held for a minimum period (typically 3 minutes at the most distant draw-off point).<\/p>\nBenefit:<\/strong> Legally compliant operation in multi-unit dwellings, care homes, hotels, and any building with centralised hot water distribution.<\/p>\nPractical consideration:<\/strong> Thermal disinfection at 70\u00b0C cannot be achieved by a standard air-to-water heat pump alone at ambient temperatures below approximately 15\u00b0C outside air. A backup immersion heater or auxiliary boiler completes the cycle.<\/p>\nHygienic Fresh Water Station<\/h3>\nDefinition:<\/strong> A hygienic fresh water station (Frischwasserstation) is a heat exchanger module that heats potable water instantaneously on demand, rather than storing it. The heat pump charges a buffer tank with heating water. When hot water is drawn, a plate heat exchanger transfers heat from the buffer to fresh mains water in real time.<\/p>\nPurpose:<\/strong> Eliminates stored potable water completely. No stagnation occurs. Legionella cannot multiply in water that is not stored.<\/p>\nHow it works:<\/strong> The buffer tank stores heating water (non-potable circuit) at 50\u201365\u00b0C. A circulation pump activates when a tap is opened. The plate heat exchanger transfers heat to the mains water stream, raising it to the set point temperature (typically 45\u201355\u00b0C at the outlet).<\/p>\nBenefit:<\/strong><\/p>\n\n- Maximum hygiene \u2014 no stored potable water<\/li>\n
- Eliminates Legionella risk without thermal disinfection cycles<\/li>\n
- Consistent outlet temperature regardless of draw-off volume<\/li>\n
- Suitable for installations where water quality or storage hygiene is critical<\/li>\n<\/ul>\n
Use case:<\/strong> iDM heat pump systems can be configured with hygienic fresh water stations for residential and commercial applications where drinking water hygiene regulations are strict \u2014 particularly relevant in Austrian public buildings and healthcare facilities.<\/p>\nSmart Tariff and Load Management Integration<\/h3>\nDefinition:<\/strong> Smart tariff integration connects the DHW production schedule to dynamic electricity pricing, grid signals, or photovoltaic (PV) surplus detection. The system charges the DHW cylinder during low-cost or zero-cost electricity periods.<\/p>\nPurpose:<\/strong> Reduces the electricity cost of hot water production by shifting demand to cheaper time windows.<\/p>\nHow it works:<\/strong><\/p>\n\n- The heat pump controller receives time-of-use tariff data or a grid signal<\/li>\n
- DHW recharge is scheduled during off-peak hours (e.g., night-time rates)<\/li>\n
- PV surplus detection activates DHW production when solar generation exceeds building load<\/li>\n
- The cylinder acts as a thermal battery, storing solar energy as hot water<\/li>\n<\/ul>\n
Benefit:<\/strong><\/p>\n\n- Reduces annual DHW electricity cost by 20\u201340% in PV-equipped households<\/li>\n
- Increases self-consumption of photovoltaic generation<\/li>\n
- Reduces grid feed-in at low or zero tariff rates<\/li>\n
- Supports demand-side flexibility for grid operators<\/li>\n<\/ul>\n
Regulatory context:<\/strong> The EU Smart Readiness Indicator (SRI) framework (Commission Delegated Regulation (EU) 2020\/2155) rates buildings on their ability to manage energy demand flexibly. DHW smart tariff integration directly improves the SRI score.<\/p>\nImmersion Heater Backup<\/h3>\nDefinition:<\/strong> An immersion heater (electric resistance element) is an integrated backup heating element inside the DHW cylinder. It activates when the heat pump cannot alone reach the required temperature.<\/p>\nPurpose:<\/strong> Ensures hot water availability during:<\/p>\n\n- Thermal disinfection cycles (70\u00b0C requirement)<\/li>\n
- Extreme cold weather (reduced heat pump output)<\/li>\n
- Heat pump defrost cycles<\/li>\n
- Maintenance or fault conditions<\/li>\n<\/ul>\n
How it works:<\/strong> The controller monitors storage temperature. If the target temperature is not reached within a defined time window using heat pump output alone, the immersion heater activates automatically. It is sized to cover peak demand independently.<\/p>\nTypical sizing:<\/strong> 2 kW to 9 kW depending on cylinder volume and application.<\/p>\nEfficiency note:<\/strong> Immersion heater operation has a COP of 1.0. Frequent reliance on the backup element degrades overall system efficiency. Correct system sizing and insulation minimise activation frequency.<\/p>\n<\/span>Types and System Models<\/span><\/h2>\nIntegrated Monobloc DHW Systems<\/h3>\nDescription:<\/strong> The heat pump unit includes DHW production as a native function. The internal control logic manages heating and hot water as a unified system.<\/p>\nCharacteristics:<\/strong><\/p>\n\n- Single controller manages both functions<\/li>\n
- Factory-configured priority and temperature settings<\/li>\n
- Compact installation footprint<\/li>\n
- Lower hydraulic complexity<\/li>\n<\/ul>\n
Best for:<\/strong> New residential construction. Single-family homes. Installations where simplicity and compact design are priorities.<\/p>\nSplit System With Separate DHW Cylinder<\/h3>\nDescription:<\/strong> A dedicated DHW storage cylinder is connected hydraulically to the heat pump via a separate circuit. The heat pump charges the cylinder independently of the heating circuit.<\/p>\nCharacteristics:<\/strong><\/p>\n\n- DHW cylinder and heating buffer are separate vessels<\/li>\n
- Allows optimal sizing of each vessel independently<\/li>\n
- Greater flexibility in cylinder placement<\/li>\n
- Supports integration of solar thermal on the DHW coil<\/li>\n<\/ul>\n
Best for:<\/strong> Larger residential buildings. Retrofit installations where the cylinder must be positioned remotely from the heat pump. Systems combining solar thermal with heat pump DHW.<\/p>\nCombination Cylinder (Combi Tank)<\/h3>\nDescription:<\/strong> A single large cylinder integrates both the heating buffer volume and the DHW storage volume in one vessel, using internal coils, zones, or integrated heat exchangers.<\/p>\nCharacteristics:<\/strong><\/p>\n\n- Single vessel replaces two separate tanks<\/li>\n
- Reduces installation space significantly<\/li>\n
- Internal stratification manages heating and DHW zones separately<\/li>\n
- Heat losses from the heating zone can pre-warm the DHW zone passively<\/li>\n<\/ul>\n
Best for:<\/strong> Space-constrained installations. Passive house projects where thermal mass and heat retention are priorities. Renovation projects where only one cylinder location is available.<\/p>\nHygienic Fresh Water Station (Frischwasserstation)<\/h3>\nDescription:<\/strong> As defined in Section 5.4. No stored potable water. Buffer tank stores heating water only.<\/p>\nBest for:<\/strong> Multi-unit residential buildings. Healthcare, educational, or hospitality facilities. Installations with strict drinking water hygiene requirements.<\/p>\nDHW Heat Pump (Exhaust Air or Ambient Air)<\/h3>\nDescription:<\/strong> A dedicated DHW-only heat pump unit \u2014 separate from the main space heating heat pump \u2014 extracts heat from indoor exhaust air or ambient air to heat a dedicated cylinder.<\/p>\nCharacteristics:<\/strong><\/p>\n |