Heat pump deployment in the UK is accelerating rapidly, but much of the equipment in use today is still shaped by cooling-led design assumptions inherited from first generation heat pumps. These first generation heat pumps typically operate at low temperature differences (∆T), rely on constant flow, and require heating systems to adapt around their constraints.
As heat pumps are applied at scale across heat networks, apartment buildings, and larger developments, those constraints are becoming increasingly visible. They show up in system complexity, oversized pipework, higher electrical energy use, and limited flexibility at peak demand.
In response, the industry is moving towards second generation heat pumps.
Second generation heat pumps are designed for heating-first operation, using high ∆T, variable flow rates, and natural refrigerants to align heat pump performance with real-world hydronic heating systems, rather than forcing systems to adapt to cooling-led equipment.
This shift affects not only equipment selection, but how heating systems are conceived, sized, and operated.
From cooling-led to heating-first design
First generation heat pumps were largely adapted from cooling platforms. They perform best at low ∆T, typically between 5 and 10 K, and depend on constant volume circulation to remain stable. In practice, this has often meant that heating systems are designed around the limitations of the heat pump rather than the demands of the building – the tail wagging the dog.
Second generation heat pumps reverse this relationship.
They are designed from the outset for heating applications, recognising that space heating and domestic hot water impose very different requirements on plant, controls, and distribution systems.
What defines a second generation heat pump?
Second generation heat pumps are characterised by a small number of deliberate design choices:
· They operate at higher system ∆Ts, typically around 30 K
· They use variable volume operation rather than constant
· They are designed specifically for heating rather than adapted from cooling equipment
· They prioritise natural refrigerants
· Primary circulation is managed within the unit, simplifying system design
Individually, these features are well understood. What is new is their integration into a single, heating-led system approach.
Why higher ∆T matters in practice
Operating at higher ∆T increases the amount of energy carried by a given volume of water. This improves the effectiveness of thermal storage without increasing storage volume, strengthening resilience and enabling meaningful load shifting.
Higher ∆T operation also reduces the volume of water that needs to be circulated. This lowers pump energy, enables smaller pumps and pipework, and helps maintain stable performance under part-load conditions. The outcome is lower installed cost, reduced electrical demand, and improved system efficiency.
Leaner systems, clearer responsibility
In many first generation systems, temperature lift is achieved across multiple components, requiring additional protection, blending, and hydraulic separation. This increases system complexity and operational risk.
Second generation heat pumps carry out the temperature lift in a single stage within the unit itself, made possible by multiple stages of heat exchange. System layouts become leaner, with fewer components and clearer performance boundaries.
For designers and operators, this reduces risk and improves confidence that installed systems will operate as intended.
Enabling hybrid energy centres
These characteristics also make second generation heat pumps well suited to hybrid energy centres.
When combined with electric boilers for peak shaving and thermal storage for flexibility, high ∆T heat pumps allow plant to be sized around peak demand without excessive generation capacity. They also support better use of variable electricity tariffs by decoupling heat generation from immediate demand.
This reflects a broader move away from single-technology solutions towards integrated energy strategies.
A change in systems thinking
The move towards second generation heat pumps signals a change in system thinking.
Rather than asking heating systems to accommodate cooling-led equipment, second generation heat pumps are designed to align with the realities of heating demand, distribution losses, and peak management.
This thinking underpins the development of the DELTA heat pump range and the wider DELTA Energy Centre, where high ∆T operation, hybridisation, and thermal storage are treated as core design principles.
As heat pump deployment continues to scale, the distinction between first and second generation heat pumps marks a shift from adapting heating systems to suit cooling-led equipment, to designing equipment that properly serves heating systems.
