heat loss

Which British Standard covers the method for the calculation of design heating loads?

• BS EN 12828:2003

• BS EN 12831:2003

• BS EN 14336:2004

• BS EN 1264-1:1998

Answer explanation

BS EN 12831:2003 specifically outlines the method for calculating design heating loads, making it the correct choice among the options provided.

What is the measurement of the U-value?

• w/m²K

• kj/m°C

• w/kg/K

• J/m³/K

Answer explanation

The U-value measures thermal transmittance and is expressed in watts per square meter per Kelvin (w/m²K). This indicates how much heat is lost through a material, making w/m²K the correct unit for U-value.

What is the correct formula to determine the heat loss from a space through air changes and ventilation?

• m² x At x 1.33

• m² x At x U-value

• m³ x QTY x At 0.33

• m³ x U-value x QTY x 3

Answer explanation

The correct formula for heat loss through air changes is m³ x QTY x At 0.33. This accounts for the volume of the space (m³), the quantity of air changes (QTY), and the temperature difference (At), multiplied by a factor of 0.33.

What are the likely effects of oversizing a heating system?

• Reduced energy usage, as systems produce enough heat quickly before shutting off for longer periods

• Reduced life expectancy of heat emitters, which often overheat due to higher temperatures

• Greater risk of burns/scalds, due to excess temperatures within the system and increased boiler combustion efficiency

• Reduced energy efficiency, as boilers ‘hunt’, and greater initial outlay costs

Answer explanation

Oversizing a heating system leads to reduced energy efficiency as boilers cycle on and off frequently ('hunt'), causing higher initial costs and inefficient operation.

What is the most suitable external design temperature for a house with normal sheltered exposure in England and Wales?

• -1°C

• -3°C

• -4°C

• -5°C

Answer explanation

The most suitable external design temperature for a house in England and Wales is -1°C. This temperature accounts for typical winter conditions, ensuring adequate heating design without excessive energy use.

What is the correct formula to determine the heat loss through a surface such as a wall or window?

• m² x Δt x 1.33

• m² x Δt x U-value

• m³ x QTY x Δt 0.33

• m³ x U-value x QTY x 3

Answer explanation

The correct formula for heat loss is m² x Δt x U-value, where m² is the area, Δt is the temperature difference, and U-value represents the thermal transmittance of the surface.

A radiator has a temperature of 70°C at the inlet and 50°C at the outlet. What is the MWT of the radiator?

• 20°C

• 40°C

• 50°C

• 60°C

Answer explanation

The Mean Water Temperature (MWT) is calculated as the average of the inlet and outlet temperatures. MWT = (70°C + 50°C) / 2 = 60°C. Therefore, the correct answer is 60°C.

You are trying to determine the correct size of an expansion vessel for a typical domestic central heating system. The system is installed in 22mm and 15mm copper. Which of the following methods could be used to give an approximate system volume?

• 2 litres per kW of the boiler

• 4 litres per kW of the boiler

• 6 litres per kW of the boiler

• 10 litres per kW of the boiler

Answer explanation

The correct method to estimate the system volume for a domestic central heating system is 6 litres per kW of the boiler. This provides a reliable approximation for sizing the expansion vessel.

What is the term given to the radiator within a central heating system which is the furthest from the heat source?

• The content circuit

• The shunt circuit

• The hydraulic circuit

• The index circuit

Answer explanation

The term for the radiator furthest from the heat source in a central heating system is the index circuit. This component is crucial for ensuring even heat distribution throughout the system.

What is the formula used to determine the flow rate for a circuit?

• kg/s = kW / 4.19 x Δt

• W = kg x SHC x Δt

• kW = 4.19 / kg x 1.33

• Litres = kW x SHC / Δt

Answer explanation

The correct formula for flow rate is kg/s = kW / (4.19 x Δt), which relates mass flow rate to power and temperature change. This choice accurately represents the relationship needed to calculate flow rate in a circuit.