The Onyx 15mm x 1/2" Angled White TRV (Thermostatic Radiator Valve) is a type of valve used in heating systems to control the flow of hot water into a radiator. 

Angled: The valve is designed with an angled connection, making it suitable for radiators with side connections, where the pipework comes out of the wall or floor at an angle.

Size: The 15mm connection is for the incoming pipe, while the 1/2" connection attaches to the radiator.

Thermostatic Radiator Valve (TRV): This type of valve automatically controls the flow of hot water into the radiator based on the temperature of the room. It helps maintain a desired temperature and improves energy efficiency by reducing overheating.

Energy Efficiency: By preventing overheating and allowing for individual room temperature control, TRVs can reduce overall energy consumption and lower heating bills.

Comfort: They provide a more consistent and comfortable room temperature, avoiding the extremes of too hot or too cold.

This specific type of TRV is commonly used in domestic and light commercial heating systems to control the temperature of radiators.