ᐅ HvH combines an air-source heat pump with panel radiators – what about the temperature settings?
Created on: 17 Nov 2015 22:42 ölschlamm
Hello community,
I just had a conversation with my regional manager from Heinz von Heiden. The houses now typically use an air-source heat pump combined with conventional radiators operating at a flow temperature of 55°C (131°F).
Doesn't this basically mean a seasonal performance factor below 2 is inevitable?
From my intuitive assessment, I would say that a flow temperature of 40°C (104°F) is sufficient for almost all days of the year. But even that is still way too high for a heat pump.
What do you think?
I just had a conversation with my regional manager from Heinz von Heiden. The houses now typically use an air-source heat pump combined with conventional radiators operating at a flow temperature of 55°C (131°F).
Doesn't this basically mean a seasonal performance factor below 2 is inevitable?
From my intuitive assessment, I would say that a flow temperature of 40°C (104°F) is sufficient for almost all days of the year. But even that is still way too high for a heat pump.
What do you think?
Oh. One more additional piece of information.
From September 14 to 15, I consumed 6,293 kWh of gas, including hot water.
An installed wood stove is not included in this calculation, as it will only be used properly from autumn 2015.
Including the costs for the gas meter, my average monthly gas cost has been €48.90. Of course, there is a small additional electricity cost for the circulation pump, but it is minimal and can almost be rounded down to zero.
Heating energy demand including hot water (not primary energy demand): approximately 48 kWh/m²/year (48 kWh/sq ft/year).
Gas costs about 5.7 to 6.2 cents per kWh, depending on the supplier. Electricity for the heat pump costs about 21 cents per kWh.
A air-to-water heat pump therefore needs to achieve an annual performance factor around 3 to break even on additional costs without factoring in interest. This is feasible, but not with panel radiators and high flow temperatures.
The costs for hot water production with solar support are practically negligible... (See my additional post).
From September 14 to 15, I consumed 6,293 kWh of gas, including hot water.
An installed wood stove is not included in this calculation, as it will only be used properly from autumn 2015.
Including the costs for the gas meter, my average monthly gas cost has been €48.90. Of course, there is a small additional electricity cost for the circulation pump, but it is minimal and can almost be rounded down to zero.
Heating energy demand including hot water (not primary energy demand): approximately 48 kWh/m²/year (48 kWh/sq ft/year).
Gas costs about 5.7 to 6.2 cents per kWh, depending on the supplier. Electricity for the heat pump costs about 21 cents per kWh.
A air-to-water heat pump therefore needs to achieve an annual performance factor around 3 to break even on additional costs without factoring in interest. This is feasible, but not with panel radiators and high flow temperatures.
The costs for hot water production with solar support are practically negligible... (See my additional post).
Hello Andreas,
Thanks for your detailed input. Although these are "just" your numbers, they at least provide a basis for further calculations. We don’t want underfloor heating—just like you, and it’s not because of the higher initial costs. I just wouldn’t be willing to save, say, 5000 euros (about 5400 USD) now only to face the same amount in additional expenses over the next 10 years.
I think it’s clear that without underfloor heating I won’t achieve an annual performance factor below 3. Our home is located on the edge of the Swabian Jura, at 500 meters (about 1600 feet) altitude. It’s not really feasible there anyway. But based on previous experience (own house), I provide about 30% of the required heating power with a wood stove (several meters of wood per year), so any reduced efficiency of the heat pump will probably not have a major impact. The heat pump is mainly intended to run during the milder transitional periods. When temperatures drop significantly below zero, we heat intensively.
I would prefer an air-source heat pump mainly because of the low installation effort, as I don’t have a gas connection and want to see the "black box" as little as possible...
Thanks for your detailed input. Although these are "just" your numbers, they at least provide a basis for further calculations. We don’t want underfloor heating—just like you, and it’s not because of the higher initial costs. I just wouldn’t be willing to save, say, 5000 euros (about 5400 USD) now only to face the same amount in additional expenses over the next 10 years.
I think it’s clear that without underfloor heating I won’t achieve an annual performance factor below 3. Our home is located on the edge of the Swabian Jura, at 500 meters (about 1600 feet) altitude. It’s not really feasible there anyway. But based on previous experience (own house), I provide about 30% of the required heating power with a wood stove (several meters of wood per year), so any reduced efficiency of the heat pump will probably not have a major impact. The heat pump is mainly intended to run during the milder transitional periods. When temperatures drop significantly below zero, we heat intensively.
I would prefer an air-source heat pump mainly because of the low installation effort, as I don’t have a gas connection and want to see the "black box" as little as possible...
Hi Ölschlamm,
It looks like we come from the same region, even though I’m originally from Ulm (lived there and in the Neu-Ulm district for 30 years) and later moved to North Rhine-Westphalia. I still love my homeland very much and visit quite often.
Well – the Swabian Jura is a bit rougher than the Bergisches Land, but in parts definitely comparable.
Heating with wood suits my taste; I’ve been doing it since autumn 2015.
I’m sure you’ll make the right choice for yourself. Without a gas connection on site, the situation looks different. Would a pellet heating system be an option for you? The neighboring buildings here (NCC system-built) are each heated in groups of 12 units by decentralized pellet systems. This significantly lowers the primary energy factor and works brilliantly after some initial teething problems.
Thorsten
P.S.: My chimney sweep comes three times a year, scheduled according to my planned usage profile for the fireplace. As shown during the last inspection 2.5 weeks ago, this is necessary. Even when using beech wood with less than 10% residual moisture, quite a bit of soot accumulates—more than I expected. The main costs are for the fireplace itself; maintenance costs for the gas heating are comparatively low. But regardless, the warmth generated by a fireplace or wood stove is so wonderful that I don’t want to focus on the costs—I value the comfort it brings. I also plan to produce my own wood; I’ve managed part of it already, but it will only pay off later. For now, I lack experience as well as suitable storage space and capacity.
It looks like we come from the same region, even though I’m originally from Ulm (lived there and in the Neu-Ulm district for 30 years) and later moved to North Rhine-Westphalia. I still love my homeland very much and visit quite often.
Well – the Swabian Jura is a bit rougher than the Bergisches Land, but in parts definitely comparable.
Heating with wood suits my taste; I’ve been doing it since autumn 2015.
I’m sure you’ll make the right choice for yourself. Without a gas connection on site, the situation looks different. Would a pellet heating system be an option for you? The neighboring buildings here (NCC system-built) are each heated in groups of 12 units by decentralized pellet systems. This significantly lowers the primary energy factor and works brilliantly after some initial teething problems.
Thorsten
P.S.: My chimney sweep comes three times a year, scheduled according to my planned usage profile for the fireplace. As shown during the last inspection 2.5 weeks ago, this is necessary. Even when using beech wood with less than 10% residual moisture, quite a bit of soot accumulates—more than I expected. The main costs are for the fireplace itself; maintenance costs for the gas heating are comparatively low. But regardless, the warmth generated by a fireplace or wood stove is so wonderful that I don’t want to focus on the costs—I value the comfort it brings. I also plan to produce my own wood; I’ve managed part of it already, but it will only pay off later. For now, I lack experience as well as suitable storage space and capacity.
@lastdrop.
This is a philosophy. Of course, cutting and carrying wood is basically unpleasant since it involves a lot of work.
But there are people who actually enjoy doing that from time to time.
At my sister’s place in Neu-Ulm, the house (about 300 sqm (3,230 sq ft) of living space) is heated almost entirely with wood. Naturally, the house also has a modern central heating system. But no one wants to use it because the warmth from the stove is simply so cozy. Okay – the 17 kW (23 hp) burner for the wood stove is well-sized… it heats the house, and you can get wood there, with the right connections, at reasonable prices (in my area in NRW, it’s harder to find… dry wood is expensive here!).
The person who gets up earliest in the morning just starts the stove at my sister’s place. When I’m there, I’m happy to do it. Takes about 2 minutes if you know how, including fetching the firewood from the basement. Meanwhile, the coffee is brewing. Then the crackling in the stove with the first cup of coffee… a piece of quality of life.
Since the house is older, it needs to be heated in the morning.
Here in my well-insulated, energy-saving home with foil and plastic bags, if the stove has been running in the evening, I don’t need to light it again before 4 p.m. – so unfortunately that custom is missing… coffee without crackling.
Thorsten
This is a philosophy. Of course, cutting and carrying wood is basically unpleasant since it involves a lot of work.
But there are people who actually enjoy doing that from time to time.
At my sister’s place in Neu-Ulm, the house (about 300 sqm (3,230 sq ft) of living space) is heated almost entirely with wood. Naturally, the house also has a modern central heating system. But no one wants to use it because the warmth from the stove is simply so cozy. Okay – the 17 kW (23 hp) burner for the wood stove is well-sized… it heats the house, and you can get wood there, with the right connections, at reasonable prices (in my area in NRW, it’s harder to find… dry wood is expensive here!).
The person who gets up earliest in the morning just starts the stove at my sister’s place. When I’m there, I’m happy to do it. Takes about 2 minutes if you know how, including fetching the firewood from the basement. Meanwhile, the coffee is brewing. Then the crackling in the stove with the first cup of coffee… a piece of quality of life.
Since the house is older, it needs to be heated in the morning.
Here in my well-insulated, energy-saving home with foil and plastic bags, if the stove has been running in the evening, I don’t need to light it again before 4 p.m. – so unfortunately that custom is missing… coffee without crackling.
Thorsten
Hi Thorsten,
I don’t have space for pellets (no basement), so that’s out. Whether solar thermal is cost-effective (see your other post) is initially irrelevant, since it’s a separate item that cannot be omitted due to energy-saving regulations. So, it’s either a gas boiler with solar thermal or an air-to-water heat pump. Payback time only needs to be considered for the extra costs (electricity) of the air-to-water heat pump due to hot water preparation when looking at the overall balance. In other words: how many more kWh does the heat pump use for hot water compared to the solar thermal system it replaces?
These calculations are relative in terms of the comfort gain with an air-to-water heat pump. Since I don’t have a gas connection, that means a gas tank. Underground tanks are hardly advisable these days—after 10 years, inspection approval is likely denied because as of this year only the (nonsensical) electric current injection testing method is allowed. Many perfectly good tanks fail this test (talked to tank supplier). Above-ground tanks mean an unsightly bulge in the front yard and you have to leave a lot of space (set the building back within the building area) due to large safety zones. Plus refilling every year. And finally, having the oil technician come once a year to the house (in our house, the chimney sweep and oil heating and burner inspection all happen on separate appointments).
If the air-to-water heat pump with 22mm (7/8 inch) standard radiators costs significantly more than a gas boiler (and with higher initial investment), then this comfort advantage will eventually be offset again.
Maybe real-world experience with air-to-water heat pumps and radiators will come in time.
A bit off-topic: we seem to agree on wood. Nothing beats a wood stove. Cutting wood can be a nice strenuous and at the same time relaxing activity, especially if you don’t do physical labor every day. And if you’re into technology, you also have a good excuse to convince the household to get several spruce chainsaws in different sizes and colors.
Regarding your comment about the “bag” house, here are my thoughts on wood stoves: Nice (subjective) wood stoves usually have a large glass front (I’d say). This requires large fireboxes because only those have big glass doors. Large fireboxes lead to too much heating output compared to the heating demand of an energy-efficient house. This means the stove often runs at partial load, which lowers efficiency and increases soot buildup. So the living room ends up at 26°C (79°F) when it’s -10°C (14°F) outside. Certainly questionable ecologically, but just...
Regards,
michael
I don’t have space for pellets (no basement), so that’s out. Whether solar thermal is cost-effective (see your other post) is initially irrelevant, since it’s a separate item that cannot be omitted due to energy-saving regulations. So, it’s either a gas boiler with solar thermal or an air-to-water heat pump. Payback time only needs to be considered for the extra costs (electricity) of the air-to-water heat pump due to hot water preparation when looking at the overall balance. In other words: how many more kWh does the heat pump use for hot water compared to the solar thermal system it replaces?
These calculations are relative in terms of the comfort gain with an air-to-water heat pump. Since I don’t have a gas connection, that means a gas tank. Underground tanks are hardly advisable these days—after 10 years, inspection approval is likely denied because as of this year only the (nonsensical) electric current injection testing method is allowed. Many perfectly good tanks fail this test (talked to tank supplier). Above-ground tanks mean an unsightly bulge in the front yard and you have to leave a lot of space (set the building back within the building area) due to large safety zones. Plus refilling every year. And finally, having the oil technician come once a year to the house (in our house, the chimney sweep and oil heating and burner inspection all happen on separate appointments).
If the air-to-water heat pump with 22mm (7/8 inch) standard radiators costs significantly more than a gas boiler (and with higher initial investment), then this comfort advantage will eventually be offset again.
Maybe real-world experience with air-to-water heat pumps and radiators will come in time.
A bit off-topic: we seem to agree on wood. Nothing beats a wood stove. Cutting wood can be a nice strenuous and at the same time relaxing activity, especially if you don’t do physical labor every day. And if you’re into technology, you also have a good excuse to convince the household to get several spruce chainsaws in different sizes and colors.
Regarding your comment about the “bag” house, here are my thoughts on wood stoves: Nice (subjective) wood stoves usually have a large glass front (I’d say). This requires large fireboxes because only those have big glass doors. Large fireboxes lead to too much heating output compared to the heating demand of an energy-efficient house. This means the stove often runs at partial load, which lowers efficiency and increases soot buildup. So the living room ends up at 26°C (79°F) when it’s -10°C (14°F) outside. Certainly questionable ecologically, but just...
Regards,
michael
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