H
Havanna8621 Jun 2022 11:07Hello everyone, thank you in advance for your interest!
We are planning to renovate a building from 1936. Ultimately, it will undergo a complete renovation and be well insulated.
For the question at hand:
Underfloor heating is planned for all rooms. At the moment, we are considering an air-source heat pump (unfortunately, alternatives are too expensive right now). The roof will be extensively equipped with photovoltaic panels (14 kWp).
I do not currently have a U-value calculation available. I am mainly interested in your opinion on whether you think my proposed heating system makes sense.
Requirement:
The heat pump should provide heating as well as domestic hot water. Possibly, a wood stove with a water jacket will be integrated in a few years.
My initial thought is that the heat pump runs more efficiently the less work it has to do. This means that if the underfloor heating is operated with, for example, 23°C (73°F) supply temperature, the heat pump should not have to work much harder than 25°C (77°F).
To take advantage of the photovoltaic system, a generously sized buffer tank will be used.
The heat pump would keep the buffer tank at 25°C (77°F), preferably during the day, and depending on solar surplus, the heat pump could also work harder at times and raise the buffer temperature to higher levels (for example, 40°C (104°F)).
That covers the heating system.
Now there is always the question of how to achieve the temperature lift for the domestic hot water, especially considering the risk of legionella bacteria.
My idea is to draw water from the buffer tank in the same way as for the heating system and install two domestic hot water stations. Two units only for the purpose of locating the domestic hot water stations close to the points of use (kitchen and bathroom). I would then place a solar-powered instantaneous water heater before each station, so depending on the buffer temperature, it can raise the temperature from 25°C (77°F) (or possibly higher) to 50–60°C (122–140°F).
In this system, I believe a very simple buffer tank can be used, without heat loops.
According to my concept, this system should have comparatively low installation costs because it is very simple and contains little complex control technology. Therefore, it should also be relatively low-maintenance. I am aware that the instantaneous water heaters will cause costs when operating without solar surplus. However, in my estimation, these costs should be balanced out because the heat pump can continuously operate efficiently within its ideal “comfort range.”
Looking ahead, there is also a plan to connect a wood stove with a water jacket to the system, which would raise the buffer temperature and reduce the workload on the instantaneous water heaters.
Open for criticism and suggestions ;-)
Stefan
We are planning to renovate a building from 1936. Ultimately, it will undergo a complete renovation and be well insulated.
For the question at hand:
Underfloor heating is planned for all rooms. At the moment, we are considering an air-source heat pump (unfortunately, alternatives are too expensive right now). The roof will be extensively equipped with photovoltaic panels (14 kWp).
I do not currently have a U-value calculation available. I am mainly interested in your opinion on whether you think my proposed heating system makes sense.
Requirement:
The heat pump should provide heating as well as domestic hot water. Possibly, a wood stove with a water jacket will be integrated in a few years.
My initial thought is that the heat pump runs more efficiently the less work it has to do. This means that if the underfloor heating is operated with, for example, 23°C (73°F) supply temperature, the heat pump should not have to work much harder than 25°C (77°F).
To take advantage of the photovoltaic system, a generously sized buffer tank will be used.
The heat pump would keep the buffer tank at 25°C (77°F), preferably during the day, and depending on solar surplus, the heat pump could also work harder at times and raise the buffer temperature to higher levels (for example, 40°C (104°F)).
That covers the heating system.
Now there is always the question of how to achieve the temperature lift for the domestic hot water, especially considering the risk of legionella bacteria.
My idea is to draw water from the buffer tank in the same way as for the heating system and install two domestic hot water stations. Two units only for the purpose of locating the domestic hot water stations close to the points of use (kitchen and bathroom). I would then place a solar-powered instantaneous water heater before each station, so depending on the buffer temperature, it can raise the temperature from 25°C (77°F) (or possibly higher) to 50–60°C (122–140°F).
In this system, I believe a very simple buffer tank can be used, without heat loops.
According to my concept, this system should have comparatively low installation costs because it is very simple and contains little complex control technology. Therefore, it should also be relatively low-maintenance. I am aware that the instantaneous water heaters will cause costs when operating without solar surplus. However, in my estimation, these costs should be balanced out because the heat pump can continuously operate efficiently within its ideal “comfort range.”
Looking ahead, there is also a plan to connect a wood stove with a water jacket to the system, which would raise the buffer temperature and reduce the workload on the instantaneous water heaters.
Open for criticism and suggestions ;-)
Stefan
D
Deliverer23 Jun 2022 22:09I couldn’t help but smile a little when I first read your thread title and then your post! :-)
I expected a simple design but encountered probably the most complex system ever. Wow. So here’s my take:
Water jacket fireplace: Absolutely not. It costs a huge amount of money, requires a massive buffer tank (more on that later), harms the environment, and can’t even serve as a backup during power outages.
A heat pump shouldn’t run “a little” but run efficiently. One that runs very little is oversized. So first, renovate and then have the heating load calculated precisely (room by room). Not by an energy consultant, but by an engineering firm. ONLY then should the underfloor heating be planned and the heat pump selected accordingly. “Accordingly” means not larger than the heating load.
Photovoltaics and heat pumps have nothing to do with each other. Please consider them separately. Install photovoltaics as large as possible. An electric car alone can easily use 30 kWp. A heat pump as well. So only let the roof area (including north-facing sections) limit the size.
Buffer tank: A good heating system doesn’t have an enormous buffer tank, it has none. ZERO. The heat pump connects directly to the heating circuit. Everything else is a compromise that costs money and reduces efficiency.
Legionella issues don’t exist in single-family homes if the hot water tank is not oversized. Legionella control programs don’t help. A fresh water station is fine but it should be separate from the heating system in its own tank. The rest of your ideas were too complex for me to follow.
Simple installation with minimal control is exactly right. No individual room controls, no actuators, no mixing valves, no bypass valves, no buffer tanks, no heat pump control via photovoltaics. Produce hot water at midday, slightly overheat the screed by two degrees Celsius (4°F) during the day. Done.
Sorry for the blunt words, but you’ve really gone 180° off the planned path.
I expected a simple design but encountered probably the most complex system ever. Wow. So here’s my take:
Water jacket fireplace: Absolutely not. It costs a huge amount of money, requires a massive buffer tank (more on that later), harms the environment, and can’t even serve as a backup during power outages.
A heat pump shouldn’t run “a little” but run efficiently. One that runs very little is oversized. So first, renovate and then have the heating load calculated precisely (room by room). Not by an energy consultant, but by an engineering firm. ONLY then should the underfloor heating be planned and the heat pump selected accordingly. “Accordingly” means not larger than the heating load.
Photovoltaics and heat pumps have nothing to do with each other. Please consider them separately. Install photovoltaics as large as possible. An electric car alone can easily use 30 kWp. A heat pump as well. So only let the roof area (including north-facing sections) limit the size.
Buffer tank: A good heating system doesn’t have an enormous buffer tank, it has none. ZERO. The heat pump connects directly to the heating circuit. Everything else is a compromise that costs money and reduces efficiency.
Legionella issues don’t exist in single-family homes if the hot water tank is not oversized. Legionella control programs don’t help. A fresh water station is fine but it should be separate from the heating system in its own tank. The rest of your ideas were too complex for me to follow.
Simple installation with minimal control is exactly right. No individual room controls, no actuators, no mixing valves, no bypass valves, no buffer tanks, no heat pump control via photovoltaics. Produce hot water at midday, slightly overheat the screed by two degrees Celsius (4°F) during the day. Done.
Sorry for the blunt words, but you’ve really gone 180° off the planned path.
It is exactly as @Deliverer says.
Apparently, you’ve been talking too much with HVAC/plumbing engineers who design 6-12 unit multifamily buildings? (My brother-in-law is one of those.) They install fresh water stations because of the legionella issue, but those have no place in a single-family house.
Usually, there isn’t even 3 liters of water standing in the pipes from the source that could promote legionella growth. If you have a guest bathroom with a small hand basin and 40m (131 feet) of piping that’s only used three times a year, just open the tap occasionally. By the way, circulation systems don’t belong in a house either, just like electronic room thermostats.
Many heat pumps come with a combined storage tank. However, the underfloor heating itself doesn’t require a separate storage tank; the volume of water in the underfloor heating system plus the screed serves as sufficient storage.
Alternatively, put a 100 kWp solar system on the roof, use only tankless water heaters and infrared heaters—that’s simply the easiest solution 🤨
Regarding the water buffer tank chimney: You can do that in an old house with “high temperature technology,” meaning no surface heating and high flow temperatures. But it’s relatively expensive and might be a DIY project (a friend of mine did that in an old building combined with an old oil heating system).
Apparently, you’ve been talking too much with HVAC/plumbing engineers who design 6-12 unit multifamily buildings? (My brother-in-law is one of those.) They install fresh water stations because of the legionella issue, but those have no place in a single-family house.
Usually, there isn’t even 3 liters of water standing in the pipes from the source that could promote legionella growth. If you have a guest bathroom with a small hand basin and 40m (131 feet) of piping that’s only used three times a year, just open the tap occasionally. By the way, circulation systems don’t belong in a house either, just like electronic room thermostats.
Many heat pumps come with a combined storage tank. However, the underfloor heating itself doesn’t require a separate storage tank; the volume of water in the underfloor heating system plus the screed serves as sufficient storage.
Alternatively, put a 100 kWp solar system on the roof, use only tankless water heaters and infrared heaters—that’s simply the easiest solution 🤨
Regarding the water buffer tank chimney: You can do that in an old house with “high temperature technology,” meaning no surface heating and high flow temperatures. But it’s relatively expensive and might be a DIY project (a friend of mine did that in an old building combined with an old oil heating system).
H
Havanna8624 Jun 2022 11:33Okay... Thanks for the clear words!
Critical feedback really helps to avoid mistakes!
My approach was:
But not even a small storage tank to save solar energy for the evening hours? It should not be charged during the day if the photovoltaic yield is too low anyway. In that case, the heat pump can supply the underfloor heating directly and bypass the buffer tank?
Would a hot water heat pump be the better choice then? (the basement is insulated on the walls, but since it is not living space, there are no rooms here)
So charge a buffer tank around noon with the heat pump that is only responsible for domestic hot water?
Then I would still need instantaneous water heaters or a hot water heat pump if the buffer tank has not been charged to the appropriate temperature...
Okay... Good point about electricity... We will reconsider an alternative (a stove with less heat storage mass and without a water jacket).
Critical feedback really helps to avoid mistakes!
My approach was:
- not to install a combined storage tank or layering tank, since I find it energetically questionable to generate high temperatures with the heat pump when the electricity is drawn from the grid
- therefore, hot water and heating should be separated
Deliverer schrieb:
Buffer tank: A good heating system does not have a large buffer tank, but none at all. ZERO. The heat pump goes directly into the heating circuit. EVERYTHING else is a stopgap solution that costs money and efficiency.
But not even a small storage tank to save solar energy for the evening hours? It should not be charged during the day if the photovoltaic yield is too low anyway. In that case, the heat pump can supply the underfloor heating directly and bypass the buffer tank?
i_b_n_a_n schrieb:
Apparently you have talked too much with MEP planners who design 6-12 unit multi-family buildings? (my brother-in-law is one of them)
Because of the legionella issue, they install fresh water stations
Would a hot water heat pump be the better choice then? (the basement is insulated on the walls, but since it is not living space, there are no rooms here)
Deliverer schrieb:
Make hot water at noon, preheat screed by two degrees during the day. Done.
So charge a buffer tank around noon with the heat pump that is only responsible for domestic hot water?
Then I would still need instantaneous water heaters or a hot water heat pump if the buffer tank has not been charged to the appropriate temperature...
Deliverer schrieb:
Water jacket stove: Absolutely not.
Okay... Good point about electricity... We will reconsider an alternative (a stove with less heat storage mass and without a water jacket).
H
Havanna8624 Jun 2022 11:35i_b_n_a_n schrieb:
Apparently, you have talked too much with MEP planners who design multifamily residential buildings with 6-12 dwelling units? (my brother-in-law is one of those)
They install fresh water stations because of Legionella issues, but those have no place in a single-family house. Oh, right.
I mainly deal with people who plan schools and functional buildings...
You’re overcomplicating things. For the scale of a single-family house, all of this is unnecessary and inefficient.
As @Deliverer wrote: first improve the building’s energy performance. Then have the heating load calculated. Based on that, design the heating system and heat pump (usually underfloor heating with an air-to-water heat pump) accordingly and definitely avoid oversizing.
Only design a domestic hot water storage tank (!= buffer tank, which is misleading).
One heat pump then supplies the domestic hot water storage tank (for potable water) and the heating system.
The screed and heating system together act as your thermal buffer, which you can heat slightly more during the day as needed, so you can heat less at night.
All rooms are regulated to maintain an average target temperature, and then keep additional features to a minimum.
That’s how you save the most and achieve efficiency—both in terms of initial costs and operation.
As @Deliverer wrote: first improve the building’s energy performance. Then have the heating load calculated. Based on that, design the heating system and heat pump (usually underfloor heating with an air-to-water heat pump) accordingly and definitely avoid oversizing.
Only design a domestic hot water storage tank (!= buffer tank, which is misleading).
One heat pump then supplies the domestic hot water storage tank (for potable water) and the heating system.
The screed and heating system together act as your thermal buffer, which you can heat slightly more during the day as needed, so you can heat less at night.
All rooms are regulated to maintain an average target temperature, and then keep additional features to a minimum.
That’s how you save the most and achieve efficiency—both in terms of initial costs and operation.
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