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Epi-metheus14 Mar 2015 15:06Hello everyone,
We are currently in the early planning stage for building a new single-family house. It will be designed as a passive house. We are still unsure about the size and whether we might include my parents in the project, so I cannot provide any details about the heating demand or floor area yet. In general, I am wondering how to reconcile the low supply temperature of underfloor heating (which we want) with the hot water needs of 4-6 people in a passive house.
Since the heating energy demand in a passive house is very low and underfloor heating can operate with low supply temperatures, a heat pump would seem to be a good option for heating energy. However, the gap between 27°C (81°F) heating water and the >45°C (113°F) hot water—which due to legionella prevention might sometimes need to be increased to 60°C (140°F)—is quite significant. Which heating systems can economically cover these different temperature requirements?
Gas is probably the cheapest option to install, but at such low heat output levels, I am not sure if it makes sense. Personally, I find the option with photovoltaic panels and self-consumption using heat pumps quite appealing, and we would be willing to pay extra for a certain degree of independence. But which heat pump systems are suitable for the two different requirements (27°C (81°F) vs. 45°C (113°F))?
I have seen that there are domestic hot water heat pumps. But if the unit is located in the utility room (no basement), and in winter it cools down the house while producing hot water and takes warm air that the small-sized heating heat pump provides, wouldn’t that be counterproductive?
I would appreciate some recommendations for systems or combinations of different systems suitable for this purpose. Maybe also some links for further reading. The usual passive house sites tend to provide only very general information.
Best regards,
Christian
We are currently in the early planning stage for building a new single-family house. It will be designed as a passive house. We are still unsure about the size and whether we might include my parents in the project, so I cannot provide any details about the heating demand or floor area yet. In general, I am wondering how to reconcile the low supply temperature of underfloor heating (which we want) with the hot water needs of 4-6 people in a passive house.
Since the heating energy demand in a passive house is very low and underfloor heating can operate with low supply temperatures, a heat pump would seem to be a good option for heating energy. However, the gap between 27°C (81°F) heating water and the >45°C (113°F) hot water—which due to legionella prevention might sometimes need to be increased to 60°C (140°F)—is quite significant. Which heating systems can economically cover these different temperature requirements?
Gas is probably the cheapest option to install, but at such low heat output levels, I am not sure if it makes sense. Personally, I find the option with photovoltaic panels and self-consumption using heat pumps quite appealing, and we would be willing to pay extra for a certain degree of independence. But which heat pump systems are suitable for the two different requirements (27°C (81°F) vs. 45°C (113°F))?
I have seen that there are domestic hot water heat pumps. But if the unit is located in the utility room (no basement), and in winter it cools down the house while producing hot water and takes warm air that the small-sized heating heat pump provides, wouldn’t that be counterproductive?
I would appreciate some recommendations for systems or combinations of different systems suitable for this purpose. Maybe also some links for further reading. The usual passive house sites tend to provide only very general information.
Best regards,
Christian
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merlin66718 Mar 2015 16:57Hello,
Especially in a passive house, I would recommend a very precise sizing of the heat generator, because if the heat pump is too large, it will be difficult to regulate the system in a stable and energy-efficient way. If it’s too small, you will have to use a lot of electric backup heating. Many heat pumps can operate up to 60°C (140°F) supply temperature anyway, although it’s still not very efficient at that level.
In my case, when producing domestic hot water at an outside temperature of -14°C (7°F), the heat pump had a coefficient of performance of 2 (3 kW electric input for 6 kW hot water output).
My entire system looks like this: a 5.72 kWp photovoltaic system, an Ochsner air-to-water heat pump GMLW9+HK with a 350 L (93 gallons) buffer tank and a 300 L (79 gallons) domestic hot water storage tank, and ventilation with a brine preheater, enthalpy heat exchanger, and electric reheating coil. Because of the buffer tank, the circulation pump for the underfloor heating can keep running, so the house is heated continuously even while domestic hot water is being produced.
I have used about 2300 kWh of heating energy from mid-October until now. On top of that, there’s domestic hot water and defrosting energy (I don’t remember the exact numbers, but the total is about 3100 kWh). Over the winter, my system’s seasonal performance factor including the heating circulation pump, mixing valves, and touch panel was 3.1. If you look only at the compressor and outdoor unit (which is what’s typically stated in datasheets or seasonal performance calculations), it was 3.6—calculated over the entire year, it was 4.0. Let’s see what the summer brings. The difference between these numbers is mainly the power consumption of circulation pumps, mixing valves, touch panel, and control system, which accounts for about 130-140 kWh of electricity.
Another point: My entire system is located in the utility room, so the “waste heat” from the domestic hot water storage tank benefits the house heating. My air-to-water heat pump (almost slightly oversized) can operate down to -16°C (3°F) without using the electric backup heater based on my heating demand.
This first winter was mainly about finding the right heating curve and the correct flow rate for the circulation pump of the underfloor heating.
My main issue was that the original heating load calculation was very inaccurate because it assumed a blower door test result of 1.0, while in reality, it was 0.28. That makes a big difference in well-insulated houses.
Additionally, the ventilation system’s heat recovery efficiency was not exactly as expected because my brine collector is extremely oversized (the excavation didn’t help much), and therefore it delivered quite a good amount of heat even in winter (depending on outdoor temperature, up to 1.5 kW).
According to calculations with the updated data, my heating demand factor is about 11.5 kWh/a/m², but the real value is a bit higher because I don’t have a very warm climate but prefer it warm inside.
Best regards,
Christian
Especially in a passive house, I would recommend a very precise sizing of the heat generator, because if the heat pump is too large, it will be difficult to regulate the system in a stable and energy-efficient way. If it’s too small, you will have to use a lot of electric backup heating. Many heat pumps can operate up to 60°C (140°F) supply temperature anyway, although it’s still not very efficient at that level.
In my case, when producing domestic hot water at an outside temperature of -14°C (7°F), the heat pump had a coefficient of performance of 2 (3 kW electric input for 6 kW hot water output).
My entire system looks like this: a 5.72 kWp photovoltaic system, an Ochsner air-to-water heat pump GMLW9+HK with a 350 L (93 gallons) buffer tank and a 300 L (79 gallons) domestic hot water storage tank, and ventilation with a brine preheater, enthalpy heat exchanger, and electric reheating coil. Because of the buffer tank, the circulation pump for the underfloor heating can keep running, so the house is heated continuously even while domestic hot water is being produced.
I have used about 2300 kWh of heating energy from mid-October until now. On top of that, there’s domestic hot water and defrosting energy (I don’t remember the exact numbers, but the total is about 3100 kWh). Over the winter, my system’s seasonal performance factor including the heating circulation pump, mixing valves, and touch panel was 3.1. If you look only at the compressor and outdoor unit (which is what’s typically stated in datasheets or seasonal performance calculations), it was 3.6—calculated over the entire year, it was 4.0. Let’s see what the summer brings. The difference between these numbers is mainly the power consumption of circulation pumps, mixing valves, touch panel, and control system, which accounts for about 130-140 kWh of electricity.
Another point: My entire system is located in the utility room, so the “waste heat” from the domestic hot water storage tank benefits the house heating. My air-to-water heat pump (almost slightly oversized) can operate down to -16°C (3°F) without using the electric backup heater based on my heating demand.
This first winter was mainly about finding the right heating curve and the correct flow rate for the circulation pump of the underfloor heating.
My main issue was that the original heating load calculation was very inaccurate because it assumed a blower door test result of 1.0, while in reality, it was 0.28. That makes a big difference in well-insulated houses.
Additionally, the ventilation system’s heat recovery efficiency was not exactly as expected because my brine collector is extremely oversized (the excavation didn’t help much), and therefore it delivered quite a good amount of heat even in winter (depending on outdoor temperature, up to 1.5 kW).
According to calculations with the updated data, my heating demand factor is about 11.5 kWh/a/m², but the real value is a bit higher because I don’t have a very warm climate but prefer it warm inside.
Best regards,
Christian
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Bauexperte18 Mar 2015 17:31Hello Christian,
A true passive house does not have underfloor heating ... or any heat generator at all!
Regards, Bauexperte
Bauexperte-metheus schrieb:
The whole thing is supposed to be a passive house ... In general, I wonder how to reconcile the low supply temperature of underfloor heating (which is desired) and the hot water demand of 4–6 people.
A true passive house does not have underfloor heating ... or any heat generator at all!
Regards, Bauexperte
Just as a side note regarding legionella: This function is only necessary if the water in the storage tank remains stagnant for an extended period (e.g., in a holiday home or weekend house). In everyday use, it is not needed because legionella bacteria require a certain amount of time to develop. If you are on vacation for two weeks, you can run the legionella protection cycle once.
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