Renewable Heating Technologies
Core concepts
Renewable heating covers heat pumps (air source and ground source), biomass, solar thermal and hybrid systems. A candidate must understand:
- Heat pump fundamentals: the vapour-compression cycle (evaporator, compressor, condenser, expansion valve), and why coefficient of performance (COP) falls as the difference between source and delivery temperature increases. Seasonal performance factor (SPF) is the year-round measure.
- Emitter design: heat pumps work best with low flow temperatures, so larger radiators or underfloor heating are needed. This is a common design question.
- Biomass: pellet and log boilers, fuel storage, ash removal, and the need for a thermal store or buffer.
- Solar thermal: collector types (flat plate, evacuated tube), orientation and tilt, and the need for a twin-coil cylinder and anti-stagnation measures.
- System integration: buffer vessels, low-loss headers, and controls that manage two heat sources.
Traps
Questions often test the direction of the refrigeration cycle, or ask why COP is not a fixed number. Another trap is assuming a heat pump can simply replace a boiler on existing radiators without resizing emitters. Watch for confusion between COP (instantaneous) and SPF (seasonal).
Rule of thumb
A useful planning figure: a heat pump delivering at around 35–45 °C flow temperature will generally achieve a far better COP than one pushed to 55 °C or above - so always size emitters for the lowest practical flow temperature.