ᐅ Heat Pump Calculation Formula Based on Heating Load

Hello, maybe someone has an Excel spreadsheet or formulas to help me calculate the theoretical energy consumption of my heat pump for a specific day?

The average consumption of 23 kWh/day seems a bit high to me for a new KFW55 house. I know there is still residual moisture in the building, but does that really make such a big difference?

What would really help me are formulas to estimate the consumption, or maybe my heat load calculation is a bit low.

Data:
KFW55 house with 132 m2 (1420 sq ft) of living space. December Lunos heat recovery ventilation, aerated concrete 42.5 cm (17 inches)
Footprint 9 m x 10 m (30 ft x 33 ft), 1.5 stories, ceiling height 2.59 m (8.5 ft)
3 people, including 1 toddler
Water-saving shower heads + Amphiro smart meter, max temperature 38°C (100°F)

Heat pump consumption over 18 days: 413 kWh
Average day/night temperature: 5°C / -1°C (41°F / 30°F)
Energy provider shutdowns twice for 1.5 hours each

Heat Pump
Rotex HPSU 308, 6 kW, 300 L (79 gallons) storage tank
Domestic hot water temperature set to 48°C (118°F)
COP A-7/W35 2.53 Heating capacity 4.2 kW
COP A2/W35 3.47 Heating capacity 5.5 kW
COP A10/W35 4.94 Heating capacity 8.6 kW
Standby heat loss at 60°C (140°F) kWh/24h: 1.3
Surface area of domestic hot water heat exchanger: 5.8 m2 (62 sq ft)
Average specific heat transfer: 2790 W/K
Domestic hot water volume: 27.8 L (7.3 gallons)
Storage charge/discharge heat exchanger
Volume: 12.4 L (3.3 gallons)
Surface area of charge heat exchanger: 2.5 m2 (27 sq ft)
Average specific heat transfer: 1200 W/K

Average room temperature: 21°C (70°F)

Heat load calculation
HT 83.11 W/K, HV 28.94 W/K, H Building 112.05 W/K
Building transmission losses (T Geb) 2681 W, Ventilation losses min (Vmin) 186 W, Ventilation losses actual (V Geb) 638 W
Building losses (N Geb) 3320 W, Heat load building (HL Geb) 3320 W
Building area (An Geb) 145.8 m2 (1570 sq ft), Building volume (Vn Geb) 384.0 m3 (13560 cu ft), Surface area (A) 388.9 m2 (4186 sq ft)
Heat load per area (HL Geb / An Geb) 22.8 W/m2
Heat load per volume (HL Geb / Vn Geb) 8.6 W/m3
HT 0.21 W/(m2·K)

I would like to calculate the following:
How many hours does the heat pump run, for example, during one day?
Energy consumption in kWh per day?
What effect does a temperature difference of ±1°C have?

Thank you very much

The electricity consumption alone doesn’t say much. What you need is the heat. Assuming the pump has a COP of 3, you would have about 81 kWh (kWh) of heat, including hot water, which is not unusual at these temperatures.

Isn’t there a formula?
For example:
If it’s -10°C (14°F) outside, then the heating energy demand is a certain amount.
The house loses a certain number of degrees per hour.
If the house temperature is 2°C (4°F) below the target, the heat pump switches on until it reaches 1°C (2°F) above the target and takes a certain amount of time to do so.

A rough estimate is possible.

You take the heating load and multiply it by the 'heating hours.'
For older buildings, this is usually around 2000. For new constructions, it’s closer to 1800.

Using 2000 and a heating load of 3.3 kW, you get about 6600 kWh of energy consumption per year.

Dividing this by the annual performance factor (seasonal performance factor), assuming a low value of 3, you would need to pay for 2200 kWh.

I currently pay 21.5 cents per kWh of electricity. So you would end up with estimated heating costs of around €473 per year.

What the original poster (OP) is aiming for cannot be calculated without specialized equipment. You need hardware for that.

Here is a heat meter. With it, you can analyze your heat demand depending on the outside temperature and check whether the values a) match your heating load calculation and b) correspond to your electricity consumption.

At 5°C (41°F) outside temperature and with your given (very good) heating load specifications, the heat demand (if I compare it with my consumption and heating load calculation) should not exceed 30 to 40 kWh. At this temperature, your heat pump should achieve a coefficient of performance (COP) of 3.5 (which is not outstanding) and therefore have an electricity consumption of a maximum of 12 kWh plus about 2 kWh for domestic hot water, totaling 14 kWh.

Your 23 kWh thus suggests:
- a poorly adjusted heat pump, resulting in a COP of about 2
- or a house with worse performance than stated in your calculation
- or very high domestic hot water demand
- or a malfunctioning mechanical ventilation with heat recovery system
- or unaccounted-for window ventilation
- and possibly residual moisture (which can have a significant impact)
- etc. There are many other factors to consider here.

Hello,
no matter how I try to calculate the average daily consumption, I always end up between 9 and 14 kWh.
Water consumption is not high; we monitor showering with the Amphiro Meter. Dishwashing is done with the dishwasher.
The mechanical ventilation with heat recovery is from Lunos, a standard system. Could it be that the wind pressure is too high and cold air is being pushed inside?
Window ventilation is not used because of the mechanical ventilation system.
There is definitely residual moisture, as it is a new build.
Does that really make a difference of 12 kWh?

Yesterday, I noticed the consumption was 26 kWh. The utility company cutoff was blinking on the system, the outdoor unit was not reachable, and frost protection was active. When the electrician replaced the meter, the outdoor unit was left without power. Could it be that the heat pump has been trying to defrost using the electric heating element for 1.5 hours or is operating in fault mode?

Thank you very much for the helpful tips.