OFTEC Heat Pump key terms

The ratio of heat energy delivered by a heat pump to the electrical energy it consumes at a given moment, measured under fixed test conditions. A COP of 4 means four units of heat per unit of electricity.

The ratio of total useful heat delivered over a whole heating season to the total electrical energy consumed across that season, including standby and auxiliary power. It reflects real installed performance better than a single COP figure.

A general measure of how effectively a heat pump converts input energy into delivered heat, expressed through COP or SPF depending on whether a snapshot or seasonal view is needed. It falls as the temperature lift increases.

The difference between the heat source temperature and the flow temperature the heat pump must produce. A larger lift demands more compressor work and lowers efficiency.

The temperature of the water leaving the heat pump or entering the heat emitters. Lower design flow temperatures improve efficiency and are central to good system design.

Any device that releases heat into a room, such as a radiator, underfloor heating circuit, or fan coil. Emitters must be sized to deliver the required output at the low flow temperatures heat pumps favour.

A room-by-room assessment of the heat escaping a building at design conditions, used to size the heat pump and each emitter. It accounts for fabric, ventilation, and internal and solar gains.

The low external temperature a heating system is sized to cope with, usually taken from national climate data for the location. It sets the peak load the heat pump must meet.

The outdoor temperature at which the heat pump's output equals the building's heat demand, below which a supplementary heater may be needed. Correctly set bivalent points limit inefficient electric backup use.

An additional heat source, often an electric immersion or boiler, that tops up the heat pump when demand exceeds its capacity. It should be sized and controlled to run only when genuinely necessary.

A secondary heating appliance provided so the building retains heat if the heat pump fails or is isolated. It may be the same device as a supplementary heater but serves a resilience rather than capacity purpose.

A tank of water connected into the heating circuit that adds thermal mass, helping the heat pump run in stable, longer cycles and preventing short cycling. It can also provide hydraulic separation between circuits.

Rapid repeated starting and stopping of the compressor because the system cannot shed or store enough heat. It wastes energy, increases wear, and is often cured by added volume or better controls.

Decoupling of the heat pump circuit from the distribution circuit, often by a low-loss header or buffer, so that flow rates in each can differ without interfering with one another.

The pipework and components carrying refrigerant or the heat-transfer fluid between the heat pump and the heat distribution system, including pumps, valves, and safety devices.

The heating distribution circuit on the building side of a separation component, serving emitters and often containing the circulating pump and controls for the space heating.

A buried pipe array, horizontal or vertical, through which a brine or water mixture circulates to absorb low-grade heat from the ground for a ground-source heat pump.

The closed loop of antifreeze solution that transfers heat from the ground, water, or air source to the evaporator of a heat pump. Its concentration and flow rate must be correct for reliable operation.

The heat exchanger in which low-pressure refrigerant absorbs heat from the source and boils into vapour. It is where useful environmental heat enters the refrigeration cycle.

The heat exchanger in which hot high-pressure refrigerant vapour releases heat to the heating water and condenses to liquid. It is where the heat pump delivers its useful output.

The component that raises the pressure and temperature of refrigerant vapour, driving the refrigeration cycle. It is the main consumer of electricity in a heat pump.

A metering device that drops refrigerant pressure between the condenser and evaporator, controlling how much refrigerant enters the evaporator and therefore the superheat.

The amount by which refrigerant vapour temperature exceeds its saturation temperature at a given pressure. Correct superheat settings protect the compressor and indicate correct charge.

The quantity of refrigerant contained in a system. It must match the manufacturer's specification; undercharge or overcharge degrades performance and can damage the compressor.

The amount by which liquid refrigerant temperature falls below its saturation temperature at condensing pressure. Measuring it helps confirm correct charge and condenser performance.

A control strategy that adjusts the heating flow temperature according to the outdoor temperature, so the system matches demand and runs at the lowest effective temperature.

A programmed relationship between outdoor temperature and flow temperature used by weather compensation controls. Its slope and offset must be set to suit the building and emitters.

The structured process of testing, adjusting, and documenting a newly installed heat pump system so it operates safely and to design performance before handover to the customer.

The formal stage at which the installer explains the system, its controls, and maintenance needs to the customer and provides documentation, manuals, and certificates.

Completion of the recognised commissioning checklist that records the installation details, test results, and declarations, providing a record for the customer and for compliance purposes.

Rules governing the handling, containment, recovery, and record-keeping of fluorinated greenhouse gases, including many refrigerants used in heat pumps. They impose certification and leak-check duties on competent persons.

A periodic inspection and testing of a refrigeration circuit for refrigerant loss, required at frequencies set by the charge size and refrigerant type under F-Gas rules.

The building regulation covering electrical safety in dwellings in England and Wales, requiring certain notifiable electrical work to be done by a competent person or notified to building control.

A registration allowing a business to self-certify that its work complies with building regulations without separate building control notification, covering defined work types.

A formal document issued after new electrical circuit work, recording the design, installation, and test results and confirming compliance with the wiring regulations.

A certificate used for small alterations or additions to an existing circuit that do not warrant a full electrical installation certificate, recording the work and test results.

A protective device that disconnects a circuit when it detects a small imbalance in current, reducing the risk of electric shock. Heat pump circuits often require RCD protection.

A switch that disconnects the heat pump from its electricity supply for safe maintenance. It must be accessible and clearly identified for service engineers.

The shortest period a compressor is allowed to run once started, set by controls to avoid frequent restarting. It protects the compressor and supports stable operation.

A programmed sequence in air-source heat pumps that temporarily reverses or alters operation to melt frost from the outdoor coil, maintaining heat transfer and efficiency.

A heat pump that extracts low-grade heat from the ground or groundwater via buried loops or boreholes, typically achieving more stable and higher efficiency than air-source units.

A heat pump that absorbs heat from outside air and upgrades it for space heating or hot water. Output and efficiency vary with outdoor temperature and defrost operation.