16 Heat Flow
Mk8 MM Manual Page | 287
16.6 Hot Water Flow Metering
Heat Flow Metering is the measurement of the amount of heat being transferred to the water by a hot water
boiler. If the stack losses and the standing losses of the boiler at any moment are known then the remaining
energy is transferred to the water.
From the Exhaust Gas Analyser (EGA):
stack losses = 100 combustion efficiency
Radiation losses are specific to the boiler, 1% radiation losses are typical for a packaged boiler operating at
Maximum Continuous Rating (MCR). The loss is constant regardless of boiler output.
At 50% firing rate the radiation loss is equal to 2% of the energy input.
The total heat input at any given time is given by the Heat Flow Metering so the instantaneous heat input to
the water we can be calculated, and by integrating these values we can get a totalised value for hot water
flow.
16.6.1 Hot Water Flow Calculation
Efficiency % = 100% Stack loss +
Radiation Losses × 100
Firing Rate
Useful Heat into Water = Total Heat ×
Efficiency
100
Volume Flow in lbs/hr =
Useful heat MBTU/Hr
SP Ht BTU/lb/°F × (Flow Temp – Return Temp)
Volume Flow in cu ft Hr =
Volume Flow in lbs hr
Density of Water at Return Temperature
Since 1 cu ft Hr = 0.124676 US GPM
Volume Flow in US G. P. M. = Volume Flow in cu ft Hr × 0.124676
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