The Altecnic (Caleffi) SATK32 Heat Interface Unit is an advanced HIU solution engineered for district heating and communal systems, offering precise control of domestic hot water (DHW) and space heating while actively protecting network efficiency.
Designed for modern low-carbon systems, including heat pump-led networks, the SATK32 integrates intelligent controls to address key challenges such as low ΔT performance, return temperature control, and peak load management.
What is the SATK32?
The SATK32 is a heat interface unit (HIU) that connects a property to a central heating network. It transfers heat from the central system to provide:
- Hot water on demand
- Controlled space heating
Its indirect twin plate heat exchanger design keeps the primary network separate from the building’s internal systems, improving reliability and performance.
System design and application
The SATK32 utilises an indirect twin plate heat exchanger configuration, providing full hydraulic separation between:
- Primary network
- Domestic hot water circuit
- Secondary space heating system
This ensures improved network stability, reduced contamination risk, and compatibility with variable flow systems.
Typical applications:
- District heating schemes
- Multi-residential developments
- Low-temperature heat pump networks
- CIBSE CP1-aligned systems
Key performance features
- Return Temperature Limitation (RTL)
The SATK32 incorporates active return temperature control, a critical requirement for compliant and efficient heat networks.
- Independent RTL setpoints for heating and DHW
- Automatic modulation of secondary flow temperatures
- Maintains designed ΔT under varying load conditions
Design impact:
- Prevents elevated return temperatures
- Supports compliance with CIBSE CP1 best practice
- Improves plant efficiency and diversity performance
Unlike conventional HIUs, the SATK32 ensures return temperatures remain controlled even under low load conditions, in poorly balanced secondary systems, and when emitters are restricted or oversized.
- Primary Flow Rate Limitation
The unit allows specification of maximum primary flow rates during heating operation.
Benefits:
- Prevents over-extraction from the network
- Maintains system diversity assumptions
- Protects against coincident peak demand scenarios
This is particularly valuable in high-density residential schemes and networks with constrained plant capacity.
- Intelligent Load Modulation
The integrated controller dynamically adjusts:
- Secondary flow temperature
- DHW output
- Primary energy draw
Outcome:
- Stable operation across variable demand
- Reduced risk of network inefficiency
- Improved seasonal performance
Controls and integration
Integral Controller
The SATK32 features a programmable controller capable of:
- Independent heating and DHW control
- Weekly scheduling (heating + preheat)
- Adjustable RTL setpoints
- Auto/manual operation modes
BMS Connectivity (MODbus)
Full MODbus compatibility enables:
- Remote commissioning and parameter adjustment
- Real-time monitoring of system performance
- Fault diagnostics and historical analysis
Available data points include:
- Flow rates and temperatures
- Valve positions
- Pump operation
- Fault logs and occurrence tracking
This supports integration into central energy management strategies.
Preheat (keep warm) strategy
The SATK32 includes a configurable preheat function designed to:
- Reduce DHW response times
- Minimise standing losses
Operational modes:
- Always OFF
- Always ON
- Time-controlled scheduling
Importantly, preheat operation is governed by return temperature logic, ensuring no compromise to network efficiency and compliance with low return temperature strategies.
Mechanical and installation considerations
The SATK32 is designed with practical installation in mind, featuring a compact, wall-mounted form suitable for apartment applications. It offers reversible pipe connections for top or bottom entry, a fully insulated casing to minimise heat loss, and provision for retrofit heat meter installation via an included spool piece. An integrated wiring centre further simplifies installation and commissioning.
Technical pParameters
- Max primary pressure: 16 bar
- Max secondary pressure: 3 bar
- Primary ΔP range: 50–600 kPa
- Max operating temperature: 85°C
- Electrical supply: 230V / 50 Hz
- Pump: UPM3 15-70
Materials:
- Stainless steel pipework
- Steel expansion vessel
- Insulated steel enclosure
Product range
Optional specification items
- Energy metering integration
- Primary flushing bypass
- Secondary isolation valve kits
- First fix brackets for staged installation
- Weather compensation (external sensor required)
Comparison to conventional HIUs
Consultant benefits
Specifying the SATK32 supports improved network efficiency through low return temperatures, alignment with CP1 and heat network best practice, reduced risk of plant oversizing, enhanced controllability and commissioning flexibility, and future-ready integration with smart energy systems.
About Altecnic
Founded in 1987 near Stafford, Altecnic is a leading UK supplier of hydronic solutions for commercial and domestic markets. As part of the Caleffi Group, its products serve a wide range of sectors while meeting all UK and European standards.
To find out more about Altecnic, please visit: www.altecnic.co.uk/