ᐅ Single- or Dual-Rate Meter in New Construction

Kaspatoo schrieb:
If you have a photovoltaic system, it might need its own meter (for example, definitely if you want to feed electricity back into the grid—at least that was the case for my in-laws)

No, that is not necessarily the case. Usually, a bidirectional meter is used (please don’t confuse this with a dual-rate meter—day/night). It is cheaper to maintain because there is only one meter, and less expensive to install due to lower space requirements in the panel. Additional sub-meters can be installed to measure self-consumption, heat pump usage, etc. These devices cost only about 20–30€ and are not calibrated or provided by the utility company; they are about the size of a circuit breaker.

Kaspatoo schrieb:
- for the air-to-water heat pump you might need a separate meter if you want to take advantage of a heat pump tariff from your electricity provider

Yes, that’s correct. Extra electricity for the heat pump requires a dedicated meter because household electricity should not be billed through it. However, if you have photovoltaics, this can be tricky and creates additional effort, as the heat pump might not benefit from the solar electricity produced, which is a significant factor in the profitability of the photovoltaic system.

Kaspatoo schrieb:
When measured together, the heating electricity is combined with household electricity. When measured separately, the heat pump’s electricity consumption is recorded independently from household electricity via a separate dual-rate meter.

Stop, dual-rate meter—that is an outdated concept from the days of night storage heaters and often does not make sense for heat pumps. Air-to-water heat pumps ideally run as little as possible at night, preferably not at all! Are you sure that is the product you are looking at? Here locally, both options are available: dual-rate meters for night storage heaters and single-rate meters for heat pumps. Dual-rate meters are usually more expensive than single-rate meters and greatly limit your choice of electricity suppliers (!!). Just check any comparison website you prefer and select a dual-rate meter option (if the site allows it). Usually, this ties you to the local utility company, which in my experience, besides reducing electricity demand, is the most important factor for saving electricity costs—avoid being locked into the local supplier!

Kaspatoo schrieb:
- either we have ONE dual-rate meter (dual = high tariff and low tariff), with different prices for high and low tariffs (assuming most household electricity is consumed during the day and at night basically only the heating uses power)

- or two separate meters where the air-to-water heat pump can run all day at the cheaper rate (i.e., a dedicated dual-rate meter for the air-to-water heat pump)

- the household electricity then has to be booked under a separate tariff

Or everything can be handled via a single meter in the standard way, with free choice of supplier. This offers maximum flexibility in supplier selection, no base fees for a second meter, no extra charges for dual-rate meters, and no need for additional panel space.

Kaspatoo schrieb:
Otherwise, let’s say you need 18,000 kWh of heat!.

More likely half of that, if at all. Unless you have 400 m² (4,300 sq ft) of heated living space or 20 people showering daily.

Kaspatoo schrieb:
Now you would need to know how much the air-to-water heat pump consumes at night. Let’s say, to approximate, the heat pump uses 50% of its electricity at night (low tariff) and 50% during the day (high tariff).

This assumption is the biggest flaw in your calculation, as it is based on incorrect premises. As already mentioned, the air-to-water heat pump should ideally consume little or no electricity at night because it operates most inefficiently then due to low outside temperatures! It should be set to run during the day. Night operation makes even less sense if a photovoltaic system is installed. Ideally, the heat pump should be configured (or dynamically controlled) to operate when the photovoltaics are producing a lot of power, maximizing self-consumption of solar electricity, or in other words, storing solar energy as heat inside the house.

Kaspatoo schrieb:
Costs and installation of an electricity meter vary between about 50 and 100€ each according to a quick Google search (beware of smart meters, I’m not very familiar with that topic).

Your electrician will probably charge more. The distribution panel also needs enough space; these meters are not cheap.

Kaspatoo schrieb:
I took the figure from an example calculation for heat pumps found online; if it’s less, the calculation can easily be adjusted accordingly. Your counterexample with 20 people showering is a bit exaggerated.

The heating energy demand of modern newly built single-family homes is between 7000 and 9000 kWh/year. The portion used for domestic hot water in homes with 3-4 people is about 1500 to 2000 kWh/year.
Even though my example with 20 people showering was a rough estimate, it actually fits quite well and is not exaggerated.

Kaspatoo schrieb:
And if it’s true, as you say, that heat pumps should hardly run at night, then a joint measurement as described above would make no sense at all.

The efficiency of an air-to-water heat pump mainly depends on the outdoor temperature, which is usually colder at night than during the day, right?

Kaspatoo schrieb:
On the other hand, a separate heat pump tariff that applies around the clock is still an advantage from my point of view.

Yes, that is possible. Everyone needs to calculate this individually. In this case, the savings would be about 10 to 20 € per year, not much more in your example, but with additional effort during the installation of the photovoltaic system, more space needed in the distribution board, and so on – in my opinion, it’s not worth it.
Also, read the fine print carefully. Some heat pump tariffs require that household electricity must be registered with the same supplier. At that point, the heat pump tariff becomes completely pointless.

4 people = 3,400 kWh for hot water plus standby losses according to Dr. Rüdiger Paschotta (RP Energy Encyclopedia). No upper limit.

It might be worth noting that with at least one dual-tariff meter, energy providers often want to install a disconnect switch that allows them to temporarily shut off the heat pump during peak load times.

This is the case for my sister, who regularly has little hot water available around midday and in the afternoon because it is used up in the morning and then shut off around noon.

Whether this also happens with separate metering depends on the energy provider. In the utility companies I mentioned, a similar clause applies even with separate tariffs. A heating technician told me, however, that this is usually not the case with separate metering.

Alex85 schrieb:

, it’s a small, uncalibrated box, costs 30€. You’ll probably get one or two anyway (photovoltaic)

What is the name of this box and where is it connected?

Meister keks schrieb:
What is the name of that box and where is it connected?

Try searching for “AC meter” and “DIN rail,” for example.