Hot Water revision notes
System selection, demand and storage sizing, reheat times, scald protection and fault diagnosis.
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System Selection & Design
Instantaneous and stored hot water compared
Trade-offs between heating water on demand and storing it in a cylinder.
Secondary circulation and cylinders for solar and heat pumps
Keeping hot water close to distant outlets, and how solar and heat-pump cylinders differ.
Vented and unvented hot water: choosing the system
How open-vented and unvented stored hot water systems differ and what drives the choice at Level 3.
Sizing & Storage Calculations
Cylinder reheat and recovery time (worked example)
Turning a coil or element power rating into how long a cylinder takes to recover.
Energy to heat a cylinder (worked example)
Applying Q = m x c x change in T to find the energy and time to heat stored water.
Estimating hot water demand and sizing a cylinder
A structured way to estimate daily and peak hot water demand and pick a storage volume.
Design Temperatures & Scald Protection
Commissioning & Fault Diagnosis
Handover & Maintenance
Connect hot-water demand to storage and recovery
Work through hot-water sizing questions by recording the demand, usable storage and heat available for recovery. Explain why a cylinder volume and a heater power answer different questions. Keep the stated temperatures and units visible throughout the working.
Use the cylinder heat-up calculator to check energy and time, then the unvented-cylinder diagram to trace the controls. The G3 discharge guide covers the safety route that must be considered alongside storage and heating.
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