Hello, I am currently trying to evaluate the advantages of gas versus electricity.
I’m assuming an annual demand of 5000 kWh including hot water.
What is a realistic seasonal performance factor (SPF) for 2 deep boreholes or for collectors just a few meters underground?
Heat pump costs around €310 for 1500 kWh => SPF 3.3
I have concerns about heat pumps regarding hot water production, as the efficiency is likely to be low when there is a temperature difference of 40-60°C (104-140°F). This is likely to reduce the overall seasonal performance factor, even though the SPF for underfloor heating at 25-30°C (77-86°F) can be above 4.5.
Is anyone’s practical experience available on this?
Gas costs are almost exactly the same at €310.
Purchase costs for gas:
- Gas boiler with solar and hot water 3000-5000 € ?
- Gas connection ? ?
Purchase costs for heat pump:
- Heat pump with hot water storage tank approximately 6000 € ?
- Deep borehole including installation 10,000 € ?
- Or ground collectors ? ?
+ BAFA subsidy 4500 €
Does it make sense to buy a separate air-source heat pump for hot water that is located inside the house and therefore has to heat from approximately 20°C (68°F) to 60°C (140°F)?
Or would it be better to purchase a heat pump with an integrated hot water tank and a solar connection, similar to a gas boiler?
If the operating costs (without photovoltaic system) are roughly the same, I would tend to choose the heat pump, since photovoltaic would allow additional savings in the future.
I’m assuming an annual demand of 5000 kWh including hot water.
What is a realistic seasonal performance factor (SPF) for 2 deep boreholes or for collectors just a few meters underground?
Heat pump costs around €310 for 1500 kWh => SPF 3.3
I have concerns about heat pumps regarding hot water production, as the efficiency is likely to be low when there is a temperature difference of 40-60°C (104-140°F). This is likely to reduce the overall seasonal performance factor, even though the SPF for underfloor heating at 25-30°C (77-86°F) can be above 4.5.
Is anyone’s practical experience available on this?
Gas costs are almost exactly the same at €310.
Purchase costs for gas:
- Gas boiler with solar and hot water 3000-5000 € ?
- Gas connection ? ?
Purchase costs for heat pump:
- Heat pump with hot water storage tank approximately 6000 € ?
- Deep borehole including installation 10,000 € ?
- Or ground collectors ? ?
+ BAFA subsidy 4500 €
Does it make sense to buy a separate air-source heat pump for hot water that is located inside the house and therefore has to heat from approximately 20°C (68°F) to 60°C (140°F)?
Or would it be better to purchase a heat pump with an integrated hot water tank and a solar connection, similar to a gas boiler?
If the operating costs (without photovoltaic system) are roughly the same, I would tend to choose the heat pump, since photovoltaic would allow additional savings in the future.
BeHaElJa schrieb:
We don’t have a pump either (all pipes under 3 L)
Regular water use happens everywhere except the bathtub – but the branch line comes off the upstairs bathroom and is 1 m long.
Just started the legionella program and turned on the heating element – heated the water up to 75°C (167°F). Then I read that you need to open all the taps for 3 minutes each... that caused the temperature to drop down drastically -.-
The experiment cost about 1.5 €. But okay – doing this every 3 months seems reasonable.Yes, that’s the trick. Heating up. Then open all your hot water taps full blast. For me, it takes less than 10 minutes until the hot water runs out.
As for the cost: it’s really not much.
And 75 degrees Celsius (167°F) is definitely sufficient. That’s enough to pasteurize the bacteria. They “thank you” by dying off.
If you do this regularly (as I mentioned, I have a calendar reminder, and from November to March I do it at least once a month, and again this April), you don’t have to worry about legionella anymore (or rather: the legionella should fear the homeowner, as it should be).
Best regards
Thorsten
PS: Thanks for confirming my suspicion that heat pumps have a similar program.
PS: This issue has only come up since everyone has become obsessed with saving energy due to the skyrocketing energy prices. I admit I’m guilty of that too.
Back when I was with my father, it was hardly a topic. Our hot water was set to 80°C (176°F). Wow. The scale buildup... well, you can imagine. The hysteresis ended at 67°C (153°F), and the burner (35 kW, or was it even 38 kW? Good grief... nowadays that would be enough for three houses) would roar and hiss to life. A few minutes later, the 250-liter (66-gallon) tank was back up to 80°C (176°F). Any legionella bacteria would have fled immediately. One by one. On foot. Another advantage: most of the time you could brew coffee or tea with tap water. grin.
Back when I was with my father, it was hardly a topic. Our hot water was set to 80°C (176°F). Wow. The scale buildup... well, you can imagine. The hysteresis ended at 67°C (153°F), and the burner (35 kW, or was it even 38 kW? Good grief... nowadays that would be enough for three houses) would roar and hiss to life. A few minutes later, the 250-liter (66-gallon) tank was back up to 80°C (176°F). Any legionella bacteria would have fled immediately. One by one. On foot. Another advantage: most of the time you could brew coffee or tea with tap water. grin.
BeHaElJa schrieb:
I'm not so sure about my geothermal drilling anymore; maybe a gas heating system would have been enough.I envy you. Geothermal drilling is just absolutely brilliant.
We couldn’t do that here. It wasn’t possible. That was made clear right when buying the plot.
I didn’t want an air-to-water heat pump.
A water-to-water heat pump wasn’t an option either—groundwater is very far away... burying a 300 sq m (3,230 sq ft) ground collector on the property with rock underneath (Bergisch slate): financially not a great idea.
A friend/colleague of mine also has geothermal drilling. Over 20 years, it definitely pays off. He operates at a COP of 5.7 (plus 6.3 kWp south-facing photovoltaic system)—when I see his heating costs for a house almost twice as large, it brings tears to my eyes. He pays less than $20 per month... incredible.
We are not concerned at all... The annual performance factor for domestic hot water is 3.7; for heating, it ranges between 5.2 and 5.6... well, the first winter still has to come. Monthly costs will probably be around €50 (about $54) for us... which is also fine and not a reason to panic, and by the way, it's as calculated.
BeHaElJa schrieb:
Monthly, it will probably be around 50 € for us... also okay and no reason to panic, and by the way calculated correctly.There is no reason to panic either.
50 € per month is definitely not a problem; all other expenses are much higher.
Besides, if you heat very environmentally friendly and are therefore part of the energy transition. Great. As I said, I envy you—I would like something like that too (just not an air-to-water heat pump, as no one has convinced me about these devices so far).
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