Heat pump performance monitoring
An M-Bus interface on the heat meter for delivered heat, electricity from a Class 0.5S meter on every input inside the boundary, and both totals over one period.
- Measure
- Delivered heat, heat-pump electricity, pump and auxiliary electricity, source and flow temperature
- Calculate
- Heat pump COP now, and a seasonal performance factor from matching totals
- Sensors
- ZHM-21, reads the heat meter's own energy record over wired M-Bus ZHM-21 datasheet (PDF, opens in a new tab)
- On site
- ZGW-20 Gateway, calculated sensors, with the inputs kept beside the result ZGW-20 datasheet (PDF, opens in a new tab)
Which electricity counts as input
A heat pump on its own looks better than the system it sits in. Decide up front whether source pumps, load pumps, controls and any backup heater are inside the ratio, and measure what you decided.
| Unit only | System | |
|---|---|---|
| Electrical input | The heat pump's own supply | Heat pump, circulating pumps, controls and backup heat |
| Answers | How the machine performs | What the heat actually costs to make |
| Watch for | A high figure that excludes the pumps | Auxiliary heat quietly carrying the load |
Hardware for a heat pump COP measurement
One interface for the heat meter, one electricity meter per supply inside the boundary, and the controller for the operating mode.
Reads the heat meter's delivered energy, volume and temperatures
2 m flying lead to the meter, 300 to 9,600 baud, up to 1,000 m of cable
The heat pump supply, and each pump or auxiliary heater inside the boundary
- Choose the CT rating per supply: 120 A split-core, or 300 A, 1 kA and 3 kA Rogowski coils
Class 0.5S to IEC 62053-22 for the meter and its CTs together
Calculates COP on site and keeps the heat and electricity records that made it
If the controller has a published register map
Operating mode, setpoint, defrost and compressor state from the heat-pump controller
If there is no trustworthy source temperature already
Source or outdoor temperature, which is what the performance has to be read against
1 waterproof probe, 2.5 m lead
±0.2 °C from −20 to 70 °C, ±0.5 °C from −40 to 105 °C
ZHM-21, ZMB-31 and TES-21 share one enclosure with different terminals inside, so the ordering code is what you specify.
What a defensible SPF is measured from
Four measurements, all on the same clock. If one of them is estimated, the figure inherits that estimate.
| Position | What it tells you | Reference | Sensor |
|---|---|---|---|
| Delivered heat | The energy the heat pump actually delivered to the circuit | The heat meter's own calculated energy record OMS | ZHM-21 (on this page) |
| Heat pump electricity | The input the machine drew, at its own supply | Class 0.5S metering with CTs sized for the supply ZEM-63 datasheet (PDF, opens in a new tab) | ZEM-65 (on this page), unit supply |
| Pumps and backup heat | The rest of the input, which is what separates the unit figure from the system figure | Every supply named in the boundary has its own meter | ZEM-65 (on this page), one per supply |
| Source and flow temperature | The conditions the performance has to be read against | ±0.2 °C from 0 to 70 °C on the pipe or in the source TES-2X datasheet (PDF, opens in a new tab) | TES-21 (on this page) |
| Mode and defrost | Whether the period being compared was space heating, hot water or defrost | Controller registers, with the model and firmware written down ZMB-3X datasheet (PDF, opens in a new tab) | ZMB-31 (on this page) |
Backup heat hides inside the total. An immersion or resistance heater on the same board makes the system figure fall without the heat pump changing. Meter it separately.
Defrost is part of the season. Excluding defrost periods flatters the result. Keep them in, and keep the state that says which they were.
How to calculate heat pump COP and SPF
The instantaneous figure uses rates. The seasonal figure uses totals over the same period, with nothing excluded.
COP = Qheat ÷ (Pheat_pump + Paux)
SPF = ΣQheat ÷ Σ(Eheat_pump + Eaux)- Qheat
- delivered heat, kW
- Pheat_pump
- heat-pump electrical input, kW
- Paux
- included auxiliary input, kW
- ΣQheat
- delivered heat over the period, kWh
- Eheat_pump, Eaux
- electrical energy over the same period, kWh
Worked example
A week's heat meter reading rises by 1,240 kWh. The heat pump drew 340 kWh and its circulating pumps 42 kWh over the same week. SPF = 1,240 ÷ 382 = 3.2. Leaving the pumps out would have given 3.6, for the same building and the same heat.
In Edge
Two calculated sensors: one divides the heat rate by the summed electrical rate for the live COP, and one holds the totals the seasonal figure is worked from. Set the stale-input threshold so a missing input suppresses the result instead of producing a plausible one.
Commissioning checks
Prove each input before the ratio is quoted to anyone.
-
The heat meter reads as it displays
Compare the energy, volume and temperatures in Edge with the meter's own display at the same moment.
Pass when every value and unit matches the display.
-
Every included supply is metered
Walk the boards and list each supply inside the boundary, then find its meter in Edge.
Pass when the list and the meters match, and anything left out is written down as excluded.
-
Every operating mode is labelled
Watch a space-heating period, a hot-water period and, if the weather allows, a defrost.
Pass when each period carries the right state, and the COP during defrost is not silently dropped.
-
A missing input withholds the answer
Disconnect one electricity meter or the heat meter for longer than the stale-input threshold.
Pass when the COP stops rather than continuing from the last good value.
-
One period by hand
Take the heat and electricity totals for a day and divide them on paper.
Pass when the hand figure matches the seasonal calculation for the same day.
What this measurement does not tell you
A performance figure describes the period, the boundary and the weather it was measured in.
- An instantaneous COP is not a seasonal figure, and neither is a manufacturer's rating point.
- A seasonal factor built on estimated heat output inherits the estimate's uncertainty, however precise the arithmetic looks.
- Comparing two seasons means comparing two weathers unless the source conditions are quoted with the figure.
- Monitoring approves nothing about the refrigerant, electrical, hydraulic or pressure design.
Sources and related guides
Sources
- OMS specification volume 2, primary communication (opens in a new tab) OMS Group. What a wired M-Bus heat meter sends, and how its records are addressed.
- Commission Decision 2013/114/EU, guidelines on calculating renewable energy from heat pumps (opens in a new tab) European Commission. The seasonal performance factor and the system boundary a heat-pump figure is measured across.
- ZHM-21 M-Bus Interface datasheet (opens in a new tab) EpiSensor. Specifications, ranges and ordering codes.
Related
- Chiller performance monitoring Application guide Measure chiller electrical input and delivered cooling over the same interval, calculate COP and kW per ton in Edge, and prove the numbers before using them.
- Wired M-Bus heat meter integration Application guide Read an existing heat meter over wired M-Bus: the settings that have to match, what each record means, and how to prove the reading against the display.
- Equipment performance monitoring boundaries Knowledge Base Define input, useful output, operating state and time boundaries for pumps, compressors, boilers, chillers and heat pumps.
- Heat-meter flow and return energy sanity check Engineering tool Estimate heat output from flow and temperature difference to check a heat meter reading.
Reviewed by EpiSensor Engineering on . Revision 4.
Settle which electricity counts before measuring SPF
We will agree the boundary, check the meter can be read as it stands, and size the electricity meters.