ᐅ Operating Cost Statement for Heat Pump in a Secondary Apartment

Hello everyone,

I urgently need your input.
We have a single-family house with a granny flat (secondary apartment), which is rented out.
Heating and cooling are provided by a Nibe F1145PC (geothermal system).

We have the following meters:

- "regular" electricity (total)
- "regular" electricity (granny flat)
- total electricity for the heat pump

- cold water (total)
- cold water for the granny flat
- hot water for the granny flat

- heating, compressor only (from the heat pump)
- domestic hot water, compressor only (from the heat pump)
- heat, including internal auxiliary heating (electric heating element in the heat pump)
- domestic hot water, including internal auxiliary heating (from the heat pump)

- heat meter before the underfloor heating of the granny flat

Sorry, I just can’t make sense of this.
How can I simply but fairly calculate the utility costs in the future?
I was advised that everything could be legally disputed except for the allocation of the heat pump electricity costs based on the living area.
The problem seems to be the energy recovery, the cooling, and the varying efficiency of the heat pump depending on the brine temperature.

I’m also wondering how passive cooling is measured. How is that accounted for?

The installer says he has no experience with heat pumps.
Nibe customer service told me to contact Nibe directly.
Nibe themselves say they can’t provide any information on this.

So now what?
I’m grateful for any advice.

Best regards,
Tito

A brief remark from NIBE:
"The information from your heat pump refers to the heat output. Therefore, you cannot use this data."

Does this mean I can only bill based on the total electricity consumption of the heat pump and then allocate it proportionally to people or area?

You need two heat meters, also one for your living area. Let’s say you use a total of 2400 meter units per year. Then you take the heating costs, including electricity and maintenance, calculate the cost per unit, and allocate the 2400 units between you and the tenant—you already have those numbers. That way it’s fair. An alternative would be to divide the costs based on square meters. K.

Nordlys schrieb:

You need two heat meters, including one for your residential area. Let’s say you consumed a total of 2400 meter units per year. You then take the heating costs, meaning electricity and maintenance, calculate the cost per unit, and allocate the 2400 units between you and the tenant based on your readings. That way it’s fair. An alternative would be to charge based on square meters. K.

Hello Nordlys,

Thank you very much for your reply.
But how do I determine the heating costs?
I only have the total costs for the heat pump from the separate electricity meter.
I can’t tell how much electricity was used for heating and how much for domestic hot water.

Total costs = (domestic hot water unit 1) + (domestic hot water unit 2) + (underfloor heating unit 1) + (underfloor heating unit 2) + (cooling unit 1) + (cooling unit 2)

Would it be acceptable to allocate the total heat pump costs based on floor area? That would solve it all at once, even if it’s not completely accurate.

You can’t separate the hot water costs. This is also not possible with a gas or oil heating system. Your heating costs consist of your heat pump electricity costs plus maintenance expenses.
With a gas heating system, the heating costs include gas charges, estimated electricity costs for the boiler, maintenance, and chimney sweeping. It’s similar with oil.
Yes, allocating costs per square meter is acceptable, although it is quite imprecise. It would be better to use heat meters that are integrated into the circuit. Karsten

Ok, understood...
So either allocate heat pump electricity costs per square meter or install additional heat meters.

Where exactly would I still need heat meters?
Before my underfloor heating? Nothing else?
Then I can compare the heat consumption of the granny flat and the house, but what would be the cost per kWh?
And how do I calculate the cost for hot water? I don’t have a hot water meter in my house... only the granny flat has one.

Topic cold water:
How should I handle that?
I have the total volume at the transfer point, but also a meter in the granny flat.
But I can’t calculate the difference, since cold water doesn’t only go into the house and the granny flat, but also to the heat pump.

Oh man, what a struggle.