How to use water heater diagrams:
Air Speed. Starting from 2000 m3/h on the air flow scale draw a vertical line 1 till the air speed axis which makes about 3.75 m/s.
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Supply air temperature. Prolong the line 1 up to the point where it crosses the outside air temperature (blue curve), e.g. -20°C; then draw a horizontal line 2 from this point to the left till crossing water in/out temperature curve (90/70 °C). From this point draw a vertical line 3 to the supply air temperature axis on top of the graphic (+20°С).
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Heating coil capacity. Prolong the line 1 up to the point where it crosses the outside air temperature indicated as red curve (e.g., -20°С) and draw a horizontal line 4 from this point to the right to the intersection of water in/out temperature curve (e.g., 90/70 °С). From this point draw a vertical line 5 up to the scale of heating coil capacity (37.0 kW).
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Water discharge. Prolong the line 5 down to water discharge axis at the bottom of the graphic 6 (0.46 l/s).
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Water pressure drop. Draw the line 7 from the point where line 6 crosses the black curve to the pressure drop axis (6.7 kPa).