An economiser diagram is a drawing of the two paths through a shell boiler and the point at which they meet. Flue gas runs furnace to chimney, feed water runs tank to shell. The diagram below follows both, and the three temperatures marked on it are surface readings from our own survey of a Cochran package boiler.
Boilers/Cochran/End plate and economiser/Economiser/This page
The three temperatures on the diagram are readings taken with a thermal camera on the OUTSIDE of each item on a running boiler. They are not the temperature of the water or the gas inside. Feed pump 100 °C, economiser casing 126 °C, main stop valve 180 °C.
100 °C at the feed pump. The pump body and the piping either side of it sit at feed-tank temperature. Over the 4.22 m² of pump, valve, strainer and piping on that view the loss is 4,713 W.
126 °C at the economiser casing. What the casing shows is the heat that did not reach the water. Over 11.31 m² that is 18,327 W.
180 °C at the main stop valve. Saturated steam leaving the shell holds the valve body and its flanges close to steam temperature. The stop valve alone is 1,732 W over 0.60 m².
Read together the three points show the loss climbing with temperature faster than with area. The stop valve is one nineteenth the area of the economiser and sheds a tenth as much heat.
The same eight readings, sorted by temperature.
| Surface °C | W / m² | Area surveyed m² | Where it was read |
|---|---|---|---|
| 100 | 1117 | 1.49 | Cochran feed pump |
| 120 | 1499 | 5.32 | Cochran front door |
| 126 | 1620 | 11.31 | Cochran economiser |
| 130 | 1704 | 5.32 | Cochran end plate |
| 180 | 2888 | 0.90 | Cochran check valve |
Each row is one of our own surveys: the measured loss divided by the CAD area of the same surface. Nothing is interpolated. ISO 12241:2022 steady state, still air, emissivity from the FLIR survey.
Every figure on this page comes from the same chain: a radiometric camera reading of the surface, an area rebuilt in CAD from the surveyed machine, and an ISO 12241 calculation from those two. The instrument settings, the area allowance, the energy basis and the list of what was not measured are set out once, in full, on the method page.
Two paths and where they meet. Flue gas runs furnace, tubes, reversal chamber, economiser, chimney. Feed water runs tank, pump, check valve, economiser, shell. Heat crosses at the economiser.
Last in the gas path before the chimney and last in the water path before the shell. On the Cochran we surveyed that puts it directly behind the end plate.
No. All three are surface readings taken with a thermal camera on the outside of the item: feed pump 100 °C, economiser casing 126 °C, main stop valve 180 °C.
Feed pump, economiser casing and main stop valve. The feed tank, the furnace, the tubes and the reversal chamber are drawn to place the others and carry no reading from us.
The surveyed view this page came from, with every element on it.Open
→/ 02The view the economiser was measured on: 27,390 W bare against 1,425 W panelled.Open
→/ 03The water path of this diagram, item by item, at 100 °C.Open
→| Survey | FLIR S62 Pro, emissivity 0.90, reflected 25 °C, 3 m, full radiometric correction. UK commercial boiler house. |
| Geometry | Rebuilt in CAD from the surveyed machine. Area allowances are stated on the page they are used on and are allowances, not measured areas. |
| Calculation | ISO 12241 steady state. Heat loss is calculated from the measured surface temperature and the modelled area — it is not metered. Full method, basis and limits. |
Where surface loss sits inside the indirect method, and what 49.8 kW is against the fuel input.Open
→/ 02What has to be opened, how often, and who signs it off under PSSR 2000.Open
→/ 03Which machine this is, and why the losing surfaces differ between the two.Open
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