Heat pump glossary
The words the heat pump course uses, from COP to weather compensation, in plain English.
- COP (coefficient of performance)
- How much heat a heat pump gives out for each unit of electricity it uses, measured at one set of conditions.
- SCOP (seasonal COP)
- A heat pump's efficiency averaged over a whole heating season, rather than at one moment.
- Air source heat pump
- A heat pump that takes heat from the outside air through a fan-driven outdoor unit.
- Monobloc heat pump
- A heat pump with all its refrigerant sealed inside the outdoor unit, so only water pipes run into the house.
- Split system
- A heat pump with an outdoor and an indoor unit joined by refrigerant pipes.
- Refrigerant
- The fluid inside a heat pump that picks up heat outside and gives it up to the heating water.
- Heat loss
- The rate a room or house loses heat on a cold design day, in watts, which sets the size of the heating system.
- U-value
- How easily heat passes through a wall, roof, floor or window, in watts per square metre per degree of difference.
- Design temperature
- The cold outdoor temperature, and the room temperatures, a heating design is worked out for.
- Short cycling
- A heat pump switching on and off too often, usually because it's too big for the house or the system holds too little water.
- Flow temperature
- The temperature of the water leaving the heat pump to go round the radiators or underfloor heating.
- ΔT (delta T)
- A temperature difference. For a radiator, it's the gap between the mean water temperature and the room.
- Weather compensation
- A control that sets the flow temperature from the outdoor temperature, warmer when it's cold and cooler when it's mild.
- Underfloor heating
- Pipes laid in or under a floor that warm the whole floor surface, so a room can be heated with cooler water.
- Heat pump cylinder
- A hot water cylinder with a coil large enough to heat the stored water from a heat pump's cooler primary water.
- Legionella cycle
- A planned run that heats the stored hot water hotter than usual, to help control legionella bacteria.
- Unvented cylinder
- A hot water cylinder fed straight from the mains and run under pressure, with no open vent or tank in the loft.
- Inhibitor
- A treatment added to heating water to slow corrosion and scale inside the system.
- Magnetic filter
- A filter on the heating pipework that traps magnetic sludge from corroding steel and iron parts.
- Glycol
- An antifreeze mixed into the heating water of some heat pump systems to protect outdoor pipes from frost.
- MCS
- A certification scheme and quality mark for small-scale renewable systems such as heat pumps, and the businesses that fit them.
- Boiler Upgrade Scheme
- A grant in England and Wales towards replacing fossil fuel heating with a heat pump or biomass boiler.
- Competent person scheme
- A government-authorised scheme in England and Wales whose members can self-certify certain building work instead of applying to building control.