ᐅ New Heat Pump for an Older Home Without Renovation

Nutshell schrieb:

I have a KFW55 house with solar hot water and gas (8600 kWh gas/year for heating and hot water) and underfloor heating. The new 6.8 kW split air conditioning system with 4 indoor units is currently used for heating. Managing peak load is one aspect, but I will turn off the air conditioning at -10°C (14°F) and switch to gas instead.

This is ideal: The gas boiler then operates efficiently in its optimal condensing range. The heat pump of the air conditioning runs efficiently at moderate temperatures. I can calculate when each system is more cost-effective based on my electricity and gas tariffs.

May I ask how satisfied you are with the solar hot water system? Feel free to reply by private message if this is off-topic for the thread.

Winniefred schrieb:

May I ask how satisfied you are with the solar system for hot water? Feel free to reply via private message if this is off-topic for this thread.

I am extremely satisfied with the solar hot water system. Supporting the heating system wouldn’t have made sense (whenever it produces energy, you don’t need it). That’s why I installed only 5 sqm (54 sq ft).

September 2022:
611 kWh total energy

66.3% (405 kWh) energy used for hot water:
59.1% (361 kWh) generated by solar
7.2% (44 kWh) generated by gas

28.2% (172 kWh) energy used for household, etc.:
172 kWh electricity from the grid

5.6% (34 kWh) energy used for heating:
34 kWh electricity for low-temperature heat pump from the grid

Conclusion:
I saved 361 kWh of gas, which amounts to $55 at the current gas rate. In one month!
If anyone asks me whether to choose solar thermal or photovoltaic, I would recommend solar thermal first. It’s a good solution and just two panels are enough for 2–3 people.
Photovoltaic doesn’t make sense for me because I’d have to finance it (I’m still paying off the mortgage) and I don’t have two electric cars yet (we’ll see by 2040). Two photovoltaic panels wouldn’t even generate close to $55 per month 🙂

Nutshell schrieb:

I am extremely satisfied with the solar hot water system. Heating support wouldn’t have made sense (whenever it provides energy, you don’t need heating). That’s why only 5 sqm (54 sq ft).

September 2022:
611 kWh total energy

66.3% 405 kWh energy needed for hot water:
59.1% 361 kWh solar generated
7.2% 44 kWh gas generated

28.2% 172 kWh energy needed for household, etc.
172 kWh electricity from the grid

5.6% 34 kWh energy needed for heating:
34 kWh electricity for air-to-air heat pump from the grid

Conclusion:
I saved 361 kWh of gas, which equals 55€ at the current gas rate. In one month!
If someone asks me whether to choose solar thermal or photovoltaic, I would first recommend solar thermal. It’s a good solution, and just two panels are more than enough for 2–3 people.
Photovoltaics don’t make sense for me because I would have to finance it (my house financing is still running), and I don’t have two electric cars yet (let’s see by 2040). Two photovoltaic panels don’t come close to saving 55€/month 🙂

Thanks! What did you pay for it?

We are also planning to install solar hot water in 2023. Combined with a masonry heater, possibly water-based. Then we could almost completely do without gas. In summer, the solar thermal would heat the water, and for the rest of the time, the heater and solar thermal would work together. That’s the plan, but everything still needs to be carefully planned.

Was included in the turnkey house price, no idea

Nutshell schrieb:

I am extremely satisfied with the solar hot water system. Adding heating support wouldn’t have made sense (whenever it provides heat, you don’t need it). So, just 5 m² (54 sq ft).

September 2022:
611 kWh total energy

66.3% or 405 kWh energy used for hot water:
59.1% or 361 kWh generated by solar
7.2% or 44 kWh generated by gas

28.2% or 172 kWh energy needed for household, etc.
172 kWh electricity from the grid

5.6% or 34 kWh energy required for heating:
34 kWh electricity used for air-to-air heat pump from the grid

Conclusion:
I saved 361 kWh of gas, which equals $55 at the current gas rate. In one month!
If someone asks me whether to choose solar thermal or photovoltaic, I would recommend solar thermal first. It’s a good solution, and just two solar panels are enough for 2–3 people.
Photovoltaics don’t make sense for me because I would have to finance it (I’m still paying off the house mortgage), and I don’t have two electric cars yet (we’ll see by 2040). Two photovoltaic panels don’t come close to generating $55/month 🙂

First, I don’t fully understand your energy calculation. You mix electricity and thermal energy without distinction.
What does the calculation look like for the entire year?

Besides, I think your setup as it stands is one of the least efficient variants. A more thorough plan could have achieved much better results.
1. You chose the classic (cheap) developer/general contractor approach with gas plus solar thermal.
2. Then you added a powerful air conditioning system.

From the start, it would have made more sense to focus on air conditioning as heating, a heat pump for domestic hot water, or a central instantaneous water heater combined with photovoltaics. That would have been truly effective and significantly more economical both in operation and investment.

1. You are choosing the classic (affordable) developer/general contractor option with gas plus solar
-> Affordable? It’s actually a proper Viessmann system with underfloor heating.

2. Then the big air conditioning unit was added
-> Yes, mainly because it got too hot in summer. Very unpleasant with a baby.

From the start, it would have made more sense to use air conditioning for heating, a domestic hot water heat pump, or a centralized instantaneous water heater for hot water, combined with photovoltaic panels.
-> I built in 2013. Back then, my gas costs were around 28–40€ per month, so manageable. Air-to-air heat pumps weren’t as efficient as they are today.