Boiler performance monitoring
A pulse counter on the fuel meter coming in, a heat meter on the way out, and the firing state that tells you which periods are worth comparing.
- Measure
- Fuel or electrical input, delivered heat, flow and return temperature, firing state
- Calculate
- Boiler energy monitoring by firing state: heat out against energy in, over the same period
- Sensors
- ZPC-20, counts the gas meter's pulses, up to 40 Hz ZPC-2X datasheet (PDF, opens in a new tab)
- On site
- ZGW-20 Gateway, keeps the input, the output and the state together ZGW-20 datasheet (PDF, opens in a new tab)
Hardware for a boiler efficiency measurement
One meter for the energy going in, one for the heat coming out, and a way to tell when the burner was firing.
The gas or oil meter's pulse output, which is the energy going in
Pulses down to 10 ms wide, up to 40 Hz, inputs to 35 V DC, mains powered
The heat meter on the flow, which is the useful energy coming out
Reads the meter's own energy, volume and temperature records
Holds the input, the output and the state, and calculates the ratio by state
If the circuit has no heat meter
Flow and return temperature where there is no heat meter to read them from
2 steel pipe probes, 2 m leads
±0.2 °C from 0 to 70 °C, ±0.5 °C from −40 to 105 °C, 2 m leads
If the controller has a published register map
Firing state, stage, setpoint and lockout from the burner or plant controller
ZPC-20, ZHM-21, TES-22 and ZMB-31 share one enclosure with different terminals inside, so the ordering code is what you specify.
Input, output and the state between them
A ratio needs both sides on the same clock, and a state that says whether the two periods being compared were doing the same job.
| Position | What it tells you | Reference | Sensor |
|---|---|---|---|
| Fuel input | The energy entering the boundary, in the units the meter registers | Record the pulse weight and whether the figure is gross or net calorific energy ZPC-2X datasheet (PDF, opens in a new tab) | ZPC-20 (on this page) |
| Delivered heat | The useful energy the circuit received | The heat meter's own calculated record ZHM-21 datasheet (PDF, opens in a new tab) | ZHM-21 (on this page) |
| Flow and return | The temperature lift, and the operating regime the boiler ran at | A matched pair, both on the same circuit TES-2X datasheet (PDF, opens in a new tab) | TES-22 (on this page) |
| Firing state | Which periods were firing, standby, cycling or locked out | A control command is not proof of flame or of delivered heat ZMB-3X datasheet (PDF, opens in a new tab) | ZMB-31 (on this page) |
Gross or net, chosen once. A gas volume becomes energy through a calorific value. Write down which basis is used, and use the same one on both sides of any comparison.
Steam is a different calculation. A temperature difference across water does not describe steam. Mass flow and the thermodynamic state are needed, and the condensate boundary with them.
Above 70 °C the probes read to ±0.5 °C. LTHW flow commonly runs at 70 to 82 °C, which is outside the pipe probe's ±0.2 °C band. A flow and return pair measured with surface probes on an 80 °C circuit carries that wider error on both readings, so a small lift is the case to treat with most care.
How to compare boiler input and output
Take both totals over the same interval, and quote the operating state with the result.
Efin = pulses × pulse weight × calorific value
ratio = Qout ÷ Efin- Efin
- input energy over the interval, kWh
- pulse weight
- units of gas or oil per pulse, from the meter
- calorific value
- energy per unit of fuel, from the supplier
- Qout
- delivered heat over the same interval, kWh
Worked example
A gas meter registers 1,000 pulses at 0.1 m³ per pulse over a day: 100 m³. At 10.9 kWh per m³, that is 1,090 kWh in. The heat meter rose by 905 kWh over the same day, a ratio of 0.83. It is a ratio for that day at that load, not a combustion efficiency.
In Edge
One calculated sensor converts pulses to input energy, a second divides delivered heat by it, and the firing state is kept as its own point so the periods can be separated afterwards.
Commissioning checks
Check the two meters before the ratio is discussed.
-
The pulse weight is the meter's
Read the pulse weight from the meter's own plate or manual, and compare a counted period with the meter's display.
Pass when the counted volume matches the display over a bounded period.
-
The heat meter reads as it displays
Compare energy, volume and temperatures in Edge with the meter's display at the same moment.
Pass when every value and unit matches.
-
Both sides share a clock
Compare the timestamps of the input and output readings over one interval.
Pass when the interval boundaries line up, and neither side lags by more than one interval.
-
The firing state is true
Watch the burner or its indication while the state point changes.
Pass when the state changes when the plant does, and standby is not recorded as firing.
-
The boundary is written down
List what is inside the measurement: which auxiliaries, which circuits, which fuel basis.
Pass when somebody else could reproduce the same ratio from the list.
What this measurement does not tell you
This is an input and output ratio at the boundary you chose. It is not a combustion measurement.
- It does not calculate or certify combustion efficiency, flue losses, emissions or burner safety.
- Steam and condensing systems need thermodynamic and condensate boundaries this arithmetic does not have.
- A calorific value from a supplier's average is not a measurement of the gas that was actually burnt.
- Boiler control, water treatment, pressure systems and statutory inspection stay with the competent specialists.
Sources and related guides
Sources
- Improve your boiler's combustion efficiency, steam tip sheet 4 (opens in a new tab) US Department of Energy, Advanced Manufacturing Office. Combustion efficiency, stack loss and the excess air a fired boiler is judged on.
- Benchmark the fuel cost of steam generation, steam tip sheet 15 (opens in a new tab) US Department of Energy, Advanced Manufacturing Office. The fuel and output figures a boiler efficiency number has to be built from.
- ZPC-2X Pulse Counter datasheet (opens in a new tab) EpiSensor. Specifications, ranges and ordering codes.
Related
- Heat pump performance monitoring Application guide Measure delivered heat and every electrical input inside one boundary, then calculate heat pump COP and a seasonal performance factor you can defend.
- Electric boiler demand response Application guide Shed electric heating stages against measured stored heat, prove each stage actually opened, and measure the recovery the site pays for afterwards.
- Equipment performance monitoring boundaries Knowledge Base Define input, useful output, operating state and time boundaries for pumps, compressors, boilers, chillers and heat pumps.
- Pulse frequency and counter-rollover estimator Engineering tool Check pulse frequency, counts per reporting interval and how long a counter takes to roll over.
Reviewed by EpiSensor Engineering on . Revision 4.
Work out what a boiler's existing meters can tell you
We will check the pulse output, see whether the heat meter can be read as it stands, and size the kit.