The electricity a heat pump uses is the heat it delivers to the building divided by the unit's efficiency ratio. The instantaneous ratio is the COP; the average over a heating season is the SCOP. For example, in a house that needs 12,000 kWh of heat in a winter, a system with a SCOP of 4 uses about 3,000 kWh of electricity, and a system with a SCOP of 3 about 4,000 kWh. That ratio is set not by the power on the unit's label but by the building's heat demand, the outdoor temperature and the temperature of the water sent to the heating system.
What determines consumption?
The calculation has two sides. The first is the building's demand: insulation, windows, climate and the household's habits decide how many kilowatt-hours of heat are needed in a season. That figure is independent of the unit; the same house needs the same heat whether it has a boiler or a heat pump. The second is how much electricity the unit uses to produce that heat, and that depends on the conditions it works under. We explain where the heat comes from, and why it is more than the electricity used, in our article what is a heat pump.
The power figures in technical tables are often misread. The table for the 12 kW model of the Poyraz series, for example, lists a maximum power input of 3.7 kW. That is the upper limit the unit can draw under the hardest conditions and is used to size the electrical connection; it is not the average consumption. For most hours of the heating season, the outdoor air is milder than the design temperature, and the unit runs at part load, below that figure.
COP and SCOP
COP: a single operating point
The COP (coefficient of performance) is the ratio of heat delivered to electricity drawn at a given moment, and it must always be read together with a condition. In catalogue notations such as A7 / W35, A is the outdoor air temperature and W the leaving water temperature: outdoor air at +7 °C, water at 35 °C. The design points of the AD series are written the same way; for Poyraz it is A −7 / W 55, meaning −7 °C outdoor air and 55 °C water. The same unit has a clearly higher COP at A7 / W35 than at A −7 / W 55; putting two COPs measured under different conditions side by side is misleading.
SCOP: a whole season
The SCOP (seasonal COP) takes into account the range of outdoor temperatures the unit meets over a heating season, part-load operation and defrost periods. In Europe it is calculated to the EN 14825 standard. The standard defines three reference climates, average, colder and warmer, and values are usually given separately for 35 °C and 55 °C water. To estimate annual consumption, the figure to use is the SCOP, not the COP. In a province such as Kars or Erzurum, you should expect a lower value than a SCOP stated for the average climate.
Outdoor temperature
A heat pump takes heat from the outdoor air and carries it into the water. The bigger the temperature difference between the outdoor air and the water, the more work the compressor has to do. The upper limit set by physics shows this clearly: the COP of an ideal heat pump equals the absolute temperature of the hot side divided by the temperature difference between the two sides (the Carnot limit). Real units reach only part of that limit, but their efficiency moves in the same direction.
In cold weather capacity also falls, and extra energy is spent melting the ice that builds up on the outdoor coil. That is why the unit must be chosen for the climate. The Boran series was designed with its vapour injection (EVI) compressor and economiser to hold its capacity at −25 °C, and Ayaz with its two-stage cascade circuit to produce 75 °C water at −30 °C. Installing a unit chosen for the mild Marmara winter in Erzurum means losing both capacity and efficiency on the coldest days.
Leaving water temperature: the biggest lever
The variable the user can influence most is the temperature of the water sent to the heating system. A rough comparison with the Carnot limit: with the outdoor air at 0 °C, an ideal heat pump making 35 °C water has a COP limit of about 8.8, and one making 55 °C water about 6.0. Real units reach lower figures, but the direction does not change: the cooler the water, the less electricity it takes to deliver the same heat.
That is why underfloor heating is the most efficient system for a heat pump; 30–40 °C water is enough. In buildings with radiators, the water temperature needed drops as radiator surface grows or insulation improves. A control that sets the water temperature according to the outdoor air, a heating curve, does the same job automatically: on mild days the water cools down too. Domestic hot water, on the other hand, is made at 45–55 °C, so it is produced at a lower COP than space heating.
A worked example
To see the method in figures, let us set up an example. The values below are assumptions, not measured data for a particular unit.
Example: assume a detached house in the Marmara region that is heated today by a gas boiler. Say the boiler burns 1,300 m³ of natural gas in a winter. One cubic metre of natural gas carries about 10 kWh of energy; taking the boiler efficiency as 90%, the house uses about 11,700 kWh of heat in a season. That demand does not change when you switch to a heat pump.
- Underfloor heating, 35 °C water: assuming a seasonal SCOP of 4.0, 11,700 / 4.0 ≈ 2,900 kWh of electricity.
- Radiators, 55 °C water: assuming a SCOP of 3.0, 11,700 / 3.0 = 3,900 kWh of electricity.
In the same house, for the same heat, the difference of about 1,000 kWh comes from the water temperature alone. Let us add domestic hot water: assume a household of four, 40 litres of 45 °C water per person per day and 15 °C mains water. With Q = m·c·ΔT, that is 160 L × 30 K × 1.163 Wh/(L·K) ≈ 5.6 kWh a day, or about 2,000 kWh of heat a year. Taking the COP for hot water as 2.5, this means about 800 kWh of electricity a year. To turn the total into a bill, simply multiply the kilowatt-hours by your own tariff.
Let us also look at the coldest hours. Say the house loses 9 kW at −7 °C, and assume the COP drops to 2.8 under that condition: the unit then draws about 3.2 kW. That figure is useful for sizing the electrical connection; annual consumption is decided by the seasonal calculation above.
Two levers that reduce consumption: inverter and water temperature
Inverter compressor: A fixed-speed compressor runs at full power whatever the demand and switches on and off frequently; some energy is lost at every start. A DC inverter compressor adjusts its speed to the load at that moment. Since the load is below the design value for most of the season, the unit runs at low speed for long periods, and because the heat exchangers are generously sized for that smaller load, efficiency rises too. Poyraz, Boran and Vaha have DC inverter compressors and BLDC fans; the Mega central system adjusts its capacity steplessly between 10% and 100%.
Water temperature: Choose the lowest leaving water temperature that keeps the rooms comfortable. With a correctly set heating curve, the water cools down by itself on mild days. In homes with underfloor heating, deep night setbacks rarely pay off; to recover the heat lost overnight, the unit has to run at full power with hotter water in the morning. Correct capacity belongs on this list as well: an undersized unit leans on a backup heater on cold days, and its seasonal efficiency falls.
Two additions are possible. In summer, the HİDREM indoor unit transfers the heat it removes from the rooms into the water in its tank, so no extra energy is spent on domestic hot water. On the panels of HİDRA and HİDREM, energy use is tracked daily, monthly and yearly, so the effect of a setting can be seen without waiting for the bill. If there are photovoltaic panels on the roof, shifting the unit's operation to sunny hours reduces the electricity drawn from the grid; we cover this in our article on solar energy with a heat pump.
A calculation for your own building
The way to estimate annual consumption correctly is to know the building's heat demand and to choose the unit for the climate and the heating system. You will find which series suits which climate in our heat pump selection guide, and the technical tables of the models on our heat pump products page. If you send the consumption of your boiler over recent winters and your heating system type through our quote request form, we will do this calculation with you for the model we propose.
