Switchroom · Thrapp Hill · 2026
A room with a load and no people in it
Thrapp Hill Distribution
A sealed switchroom has a large sensible load and almost no moisture in it. Nobody breathes in there, nothing is cooked in there, and the fresh-air rate is zero because the room does not need one. The air recirculates at about 24 °C and 30% relative humidity, which puts its dew point at 5.4 °C.
The coil surface sits at 11 °C. Air cannot condense on a surface warmer than its own dew point, so this coil takes 20 kW of heat out of the room and not one gram of water. Its sensible heat ratio is 1.00 — not approximately, exactly — and its drain pan is dry every hour of the year.
We fitted the drain anyway, with a float alarm on it. If that alarm ever goes off, something about the room has changed and somebody should be told.
The coil on this job
Coil 02 — sensible only
CCU-1, Thrapp Hill
Close control, full recirculation, sealed room with no fresh-air provision.
| dry bulb | humidity ratio | RH | enthalpy | |
|---|---|---|---|---|
| Air on | 24 °C | 5.53 g/kg | 30% | 38.2 kJ/kg |
| Air off | 12.3 °C | 5.53 g/kg | 63% | 26.3 kJ/kg |
| Duty | 20 kW total | 20 kW sensible | 0 kW latent | SHR 1.00 |
| Condensate | none — the coil surface is warmer than the entering dew point, so no water can leave the air | |||
Same problem, different building?
Ring us or book the survey. Either way the first thing we do is measure what is actually happening in the room.