System Controls and Zoning Flashcards

What is the primary function of a thermostatic radiator valve (TRV)?

Answer: To control water flow through a radiator based on room air temperature

A TRV senses the air temperature in the room and throttles the flow of hot water through the radiator to maintain the set temperature.

Why must a TRV not be fitted to the radiator in the room containing the room thermostat?

Answer: Both controls would compete to regulate temperature, causing short-cycling and inefficiency

If a TRV and room thermostat are in the same room, both will independently try to control the temperature, leading to conflict, short-cycling, and loss of accurate control.

Under Building Regulations Part L, at what minimum floor area does a new domestic heating system require at least two independently controlled temperature zones?

Answer: 150m²

Part L of the Building Regulations requires dwellings over 150m² to have at least two independently controlled heating zones to improve energy efficiency.

Why is an automatic bypass valve (ABV) essential in a system where TRVs are fitted throughout?

Answer: To prevent pump cavitation and boiler overheating when all TRVs are closed

When all TRVs close simultaneously, an ABV maintains minimum circulation through the boiler and pump, preventing pump cavitation and boiler thermal cut-out.

On a standard TRV head calibrated 1–5 with a frost symbol (*), what room temperature does setting 3 approximately represent?

Answer: 20°C

Setting 3 on most TRV heads corresponds to approximately 20°C, which is a typical comfortable room temperature for living areas.

What is the recommended temperature range for setting a room thermostat in a domestic property?

Answer: 18–21°C

A room thermostat is typically set between 18–21°C to balance occupant comfort with energy efficiency in UK homes.

What is the purpose of a lockshield valve on a radiator, and who should adjust it?

Answer: To balance system flow during commissioning; adjusted by the installer using a tool

A lockshield valve is set by the installer during commissioning to balance flow across all radiators and is protected by a cap to prevent unauthorised adjustment.