Ensures consistent flow to all emitters<\/li>\n<\/ul>\nPractical Application:<\/strong> For a 10 kW heat pump with a \u0394T of 5 K, the required volume flow is approximately 1,720 litres per hour. A 28 mm copper pipe or 32 mm multilayer composite pipe is typically selected for the main flow and return on this circuit.<\/p>\nCalculation Method:<\/strong><\/p>\nThe fundamental sizing formula is:<\/p>\n
\nQ = \u1e41 \u00d7 c_p \u00d7 \u0394T<\/strong><\/p>\n<\/blockquote>\nWhere:<\/p>\n
\n- Q = heat output (W)<\/li>\n
- \u1e41 = mass flow rate (kg\/s)<\/li>\n
- c_p = specific heat capacity of water (4,187 J\/kg\u00b7K)<\/li>\n
- \u0394T = temperature difference between flow and return (K)<\/li>\n<\/ul>\n
Hydraulic Balancing<\/h3>\n
Definition:<\/strong> Hydraulic balancing is the process of adjusting flow resistance across all parallel circuits so each receives its calculated design flow rate.<\/p>\nPurpose:<\/strong> Without balancing, the circuit with the lowest resistance receives the most flow. Rooms near the heat pump overheat. Rooms furthest from the heat pump receive insufficient heat. The heat pump operates outside its design parameters.<\/p>\nBenefits:<\/strong><\/p>\n\n- Eliminates hot and cold spots across zones<\/li>\n
- Stabilises return temperature to the heat pump<\/li>\n
- Reduces system noise from over-pressured circuits<\/li>\n<\/ul>\n
Practical Application:<\/strong> Balancing valves (e.g., Danfoss ASV, IMI Hydronic TA-STAD) are installed on each radiator return or underfloor heating manifold branch. Flow rates are set using a differential pressure gauge and adjusted to the values from the hydraulic calculation.<\/p>\nBalancing Methods:<\/strong><\/p>\n\n- Static balancing<\/strong> \u2014 manual adjustment of balancing valves using pre-set kv values.<\/li>\n
- Dynamic balancing<\/strong> \u2014 pressure-independent control valves (PICVs) automatically maintain design flow regardless of system pressure fluctuations.<\/li>\n
- Pre-setting balancing<\/strong> \u2014 thermostatic radiator valves (TRVs) pre-set to restrict flow before commissioning.<\/li>\n<\/ul>\n
Flow Temperature Design<\/h3>\n
Definition:<\/strong> Flow temperature design is the selection of the minimum supply water temperature at which the heating system meets its heat demand under design conditions.<\/p>\nPurpose:<\/strong> Heat pumps achieve higher COP at lower flow temperatures. A system designed for 35 \u00b0C flow temperature achieves a COP approximately 35\u201350% higher than the same unit operating at 55 \u00b0C.<\/p>\nBenefits:<\/strong><\/p>\n\n- Maximises heat pump efficiency and SCOP<\/li>\n
- Reduces electricity consumption<\/li>\n
- Qualifies the system for subsidy programmes that require low-temperature design<\/li>\n<\/ul>\n
Practical Application:<\/strong> Underfloor heating systems typically operate at 30\u201340 \u00b0C flow temperature. Low-temperature radiators operate at 45\u201355 \u00b0C. Fan coil units operate at 35\u201345 \u00b0C. The heating system designer selects the heat emitter type and dimensions it to meet the room’s heat load at the lowest practical flow temperature.<\/p>\nDesign Rule:<\/strong> For every 1 K reduction in heat pump flow temperature, COP improves by approximately 2\u20133%. Designing for 35 \u00b0C instead of 55 \u00b0C can increase SCOP by 25\u201340%.<\/p>\nDelta T (\u0394T) Calculation<\/h3>\n
Definition:<\/strong> Delta T (\u0394T) is the temperature difference between the flow pipe and the return pipe in a heating circuit.<\/p>\nPurpose:<\/strong> \u0394T determines mass flow rate and pump sizing. Heat pumps are designed for specific \u0394T ranges. Operating outside this range reduces efficiency, causes short-cycling, or damages the compressor.<\/p>\nBenefits:<\/strong><\/p>\n\n- Stabilises compressor operating conditions<\/li>\n
- Ensures accurate heat output to emitters<\/li>\n
- Prevents thermal shock to system components<\/li>\n<\/ul>\n
Practical Application:<\/strong> iDM heat pumps are factory-configured for a \u0394T of 5\u201310 K. A TERRA SLM 10 kW unit with a 5 K \u0394T requires a volume flow of 1,720 l\/h. The circulation pump, pipe sizes, and manifold must all be sized to deliver this flow at the design pressure drop.<\/p>\nPipe Insulation<\/h3>\n
Definition:<\/strong> Pipe insulation is the thermal barrier applied to distribution pipes to prevent heat loss between the heat pump and heat emitters.<\/p>\nPurpose:<\/strong> Uninsulated or under-insulated pipes lose significant heat in unheated building sections (basements, crawl spaces, service ducts). This increases the heat pump’s run time and energy consumption.<\/p>\nBenefits:<\/strong><\/p>\n\n- Reduces distribution heat losses to below 5% of system output<\/li>\n
- Prevents condensation on cold water pipes<\/li>\n
- Complies with building energy regulations<\/li>\n<\/ul>\n
Standards:<\/strong><\/p>\n\n- Germany (GEG 2023)<\/strong> \u2014 Minimum insulation thickness defined by pipe diameter and temperature range.<\/li>\n
- Austria (OIB Richtlinie 6)<\/strong> \u2014 Energy performance requirements include distribution loss limits.<\/li>\n
- Switzerland (SIA 384\/1)<\/strong> \u2014 Heating system planning standard with explicit insulation requirements.<\/li>\n<\/ul>\n
Practical Application:<\/strong> A 22 mm copper flow pipe in an unheated basement requires a minimum 20 mm insulation wall thickness (closed-cell elastomeric foam, \u03bb \u2264 0.040 W\/m\u00b7K) under German GEG requirements.<\/p>\nHydraulic Separation<\/h3>\n
Definition:<\/strong> Hydraulic separation is the physical decoupling of the primary heat pump circuit from the secondary heating distribution circuit.<\/p>\nPurpose:<\/strong> Heat pumps have fixed minimum flow rate requirements. Heating zones with thermostatic control open and close independently. Without hydraulic separation, zone valve closure can reduce primary circuit flow below the heat pump’s minimum, causing short-cycling or fault shutdown.<\/p>\nBenefits:<\/strong><\/p>\n\n- Protects the heat pump compressor from low-flow conditions<\/li>\n
- Allows independent control of primary and secondary circuits<\/li>\n
- Enables multi-zone heating without flow interference<\/li>\n<\/ul>\n
Methods:<\/strong><\/p>\n<\/div>\n\n
\n\n\n| Method<\/th>\n | Application<\/th>\n | Notes<\/th>\n<\/tr>\n<\/thead>\n |
\n\n| Hydraulic separator (low-loss header)<\/td>\n | Systems up to ~50 kW<\/td>\n | Simple, compact, cost-effective<\/td>\n<\/tr>\n |
\n| Buffer tank<\/td>\n | Systems requiring thermal storage<\/td>\n | Adds volume, stabilises cycling<\/td>\n<\/tr>\n |
\n| Plate heat exchanger<\/td>\n | Open systems or different fluid types<\/td>\n | Complete fluid separation<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\nPractical Application:<\/strong> iDM systems typically integrate a factory-configured hydraulic separator into the indoor unit or buffer cylinder, reducing installation complexity and ensuring correct primary circuit flow at all times.<\/p>\nExpansion Vessel and Pressure Safety<\/h3>\nDefinition:<\/strong> An expansion vessel is a sealed container that absorbs the volume increase of heating water as the system heats up, maintaining safe system pressure.<\/p>\nPurpose:<\/strong> Water expands by approximately 4% when heated from 10 \u00b0C to 70 \u00b0C. Without an expansion vessel, system pressure rises uncontrollably, triggering pressure relief valves or damaging components.<\/p>\nBenefits:<\/strong><\/p>\n\n- Maintains system pressure within the operating range (1.5\u20133.0 bar typical)<\/li>\n
- Prevents repeated water losses through relief valves<\/li>\n
- Protects heat pump heat exchanger from pressure surges<\/li>\n<\/ul>\n
Sizing Rule:<\/strong> Expansion vessel volume is calculated using total system water volume, maximum operating temperature, static fill pressure, and maximum allowable pressure. Undersized vessels cause chronic pressure relief valve operation and system water loss.<\/p>\nMaterial Selection<\/h3>\nDefinition:<\/strong> Material selection is the specification of pipe and fitting materials based on system temperature, pressure, fluid type, and installation environment.<\/p>\nPurpose:<\/strong> Different materials offer different advantages in heat pump installations. The choice affects installation cost, longevity, oxygen diffusion risk, and flexibility.<\/p>\nCommon Materials:<\/strong><\/p>\n<\/div>\n\n \n\n\n| Material<\/th>\n | Advantages<\/th>\n | Limitations<\/th>\n | Typical Application<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Copper<\/td>\n | High conductivity, proven longevity<\/td>\n | Higher cost, rigid<\/td>\n | Main distribution, primary circuit<\/td>\n<\/tr>\n | \n| Multilayer composite (PEX-Al-PEX)<\/td>\n | Flexible, oxygen-tight, easy installation<\/td>\n | Requires crimp fittings<\/td>\n | Secondary distribution, underfloor heating manifolds<\/td>\n<\/tr>\n | \n| Cross-linked polyethylene (PEX-a\/b)<\/td>\n | Flexible, freeze-tolerant<\/td>\n | Requires oxygen barrier for heating<\/td>\n | Underfloor heating circuits<\/td>\n<\/tr>\n | \n| Stainless steel<\/td>\n | Corrosion resistant, suitable for geothermal brine<\/td>\n | Higher cost<\/td>\n | Ground source brine circuits<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Critical Note on Oxygen Diffusion:<\/strong> Open heating circuits and PEX pipes without an oxygen diffusion barrier allow oxygen ingress. Oxygen causes corrosion of steel and cast iron components (radiators, pump housings). All pipes in closed heating circuits must use oxygen-tight materials or be fitted with a permanent oxygen barrier layer.<\/p>\n<\/div>\n<\/span>Types of Pipework Circuits in Heat Pump Systems<\/span><\/h2>\nPrimary Circuit<\/h3>\nThe primary circuit connects the heat pump’s refrigerant-to-water heat exchanger output to the system’s hydraulic separation device (buffer tank or low-loss header). This circuit:<\/p>\n | |