ᐅ Ground Source Heat Pump for a 200 m² Single-Family Home with Underfloor Heating, KfW55 Standard – Settings and Optimization
Created on: 4 Nov 2021 20:21
G
grericht
Hello. We moved into our new single-family house in March. I didn’t make any adjustments to the heating system at that time. Now that the temperatures are rising, I’ve started to take a closer look at it.
House details:
Heating system details (descriptions from the invoice):
My previous attempts:
Questions:
Personal preferences:
House details:
- Single-family house with a (heated) basement + 2.5 floors (usable gable roof/also underfloor heating) -> 4 heating circuits
- approximately 200 m² (2150 sq ft) of underfloor heating
- 2 bathrooms WITHOUT additional heating
- kfw55 energy standard
- ventilation system with heat recovery
- Currently 2 rooms in the basement are unoccupied/unutilized + the technical room
- There are also 2 children’s rooms in the attic that are unoccupied/unutilized
Heating system details (descriptions from the invoice):
- High-efficiency brine/water heat pump Dimplex SI 8TU
- High-efficiency brine system SZB 140E for brine/water heat pump with electronically controlled brine circulation pump Yonos Para 25/1-10
- Multifunctional storage tank Geysir MTL-WP650 efficiency class B (150 mm (6 inches) insulation thickness) with connection options for multiple heat generators, with layering plate for large volume flows, capacity 850 liters (225 gallons), domestic hot water preparation using counterflow principle with stainless steel heat exchanger, including differential temperature controller and flow sensor for hot water tapping system
- Hydraulic connection of the heat pump to the multifunctional storage tank with precision steel pipe 28x1.5 mm (1.1x0.06 inch) including insulation, 1 zone charging pump Dimplex UPH 75-25P with shut-off set, switchable between heating and domestic hot water charging
- Integration of the heating system with heating circuit sets Easyflow DN 25 R1" with EPP insulation type 2 including 3-way mixing valve, mixing valve actuator and circulation pump Grundfos UPM3 Auto
- (ERR in 3/4 of the rooms) - currently switched off
- Cooling station Dimplex PKS 14 Econ for passive cooling via geothermal probes, consisting of heat exchanger, brine circulation pump, cooling modules for network operation with heat pump manager and temperature sensor
- Room temperature controller Dimplex Smart RTC, for optimizing weather-compensated control via a reference room
My previous attempts:
- Domestic Hot Water:
- I first focused on the domestic hot water preparation. Initially, it was set to 50°C (122°F) with a 2° hysteresis. For Dimplex, this means that heating started again at 48°C (118°F). This setup was basically fine, but even without any hot water use, heating occurred 2-3 times a day. Since the pump ran only very briefly, the average summer consumption was about 0.7 kWh/day.
- I then experimented with lowering the temperature, setting lockout periods, and increasing the hysteresis. Our "optimal consumption" turned out to be 50°C (122°F) and 7° hysteresis with lockout from 8 pm to 5 pm. This sometimes resulted in the pump not running for an entire day. However, energy use was only reduced to 0.5 kWh/day, meaning hardly any consumption reduction at the cost of noticeable comfort reductions. Currently, I am at 48°C (118°F) and 4° hysteresis with lockout from 10 pm to 5 pm. Since we mostly use hot water in the evening, this works well. For bathing or higher demand, the water is reheated if necessary. I am currently experimenting with 5 or 6 degrees hysteresis, as the heat loss during ongoing heating operation seems lower and we might be able to skip a day sometimes. We’ll see...
- Now, regarding the heating, my attempts:
- All ERRs switched off, heating circuits opened roughly by feel, and tried to adjust by regulation. Control was via fixed return flow temperature, which I tested between 23 and 26°C (73°F and 79°F). The consumption and COP results were very satisfactory. Unfortunately, I couldn’t get the bathroom above 22°C (72°F) without other rooms becoming too warm (rooms quickly reached 22°C, which I find too high).
- Turned the ERR back on in the children’s rooms.
- After a one-week vacation during which I completely switched off the heating, I started over. I tried the recommended approach of fully opening the warmest room (bathroom) to about 2.2 liters/min (0.58 gallons/min) and then increasing the temperature until satisfied. But this meant the heating was massively oversized?! The heat pump came on about 20 times for 10-15 minutes each, the supply temperature was nicely between 30 and 33°C (86°F and 91°F) but the temperature felt like it never really got away from the heat pump’s threshold. I am attaching a picture of the behavior.
- Suspecting insufficient flow and hesitant to adjust the heating pump, I slowly opened other rooms slightly.
- I also tried increasing the fixed temperature to 27 or 28°C (81°F or 82°F) and used hysteresis to make the pump run less often but longer. I am now quite satisfied with the temperatures in the house. However, the numbers still look a bit odd to me. I believe there are now many rooms/areas/storage volumes with such low flow that “cooled down” mass just circulates in the loop and eventually reaches the return line repeatedly. I don’t mind that but I also do not want to risk any damage. I will attach another picture.
- Lastly, I reduced the temperature at night and in the morning so the heating starts at favorable times. Currently, two starts of about 2-3 hours each are sufficient.
Questions:
- Am I completely off track here or are these approaches generally valid? Unfortunately, I can’t really rely on the heating engineer. He is surely competent but firstly hardly reachable and secondly probably overwhelmed by such optimization considerations.
- What about rooms that are unused? Should I use the screed as a buffer and keep them slightly heated (<0.5 liters/min (0.13 gallons/min)) anyway?
- I increasingly believe that managing the large temperature difference between the bathroom at 23°C (73°F) and the rooms at 20.5°C (69°F) is not well controlled – is there really no alternative to an additional heat source? We only use the bathroom for about 2 hours and in the evening for 4 hours at 23°C (73°F). Otherwise, 21-22°C (70-72°F) would definitely be sufficient there.
- Any tips on settings?
Personal preferences:
- The underfloor heating is off in the bedroom – yet it quickly reaches 19-20°C (66-68°F), which is almost too warm.
- In the 3 children’s rooms, the ERR closes from 5 pm to 3 am (for sleeping – with time delay)
- Other rooms 20-21°C (68-70°F)
- Open-plan kitchen/living room 21-22°C (70-72°F)
- Bathrooms 23°C (73°F)
A
Alessandro11 Nov 2021 11:58What does a structured measurement look like? Please explain it to me. Unfortunately, I only have 15 years of experience in measurement, control, and regulation technology...
The bedroom does not get warmer than 18.5°C (65.3°F) with windows and doors closed. What is so difficult to understand about that?
The shading is half lowered (slats).
The bedroom does not get warmer than 18.5°C (65.3°F) with windows and doors closed. What is so difficult to understand about that?
The shading is half lowered (slats).
R
RotorMotor11 Nov 2021 12:00Alessandro schrieb:
What does a structured measurement look like? Please explain it to me.For example, average values for each room over the course of a day.Taking into account or at least mentioning external influencing factors such as outside temperature, wall construction, windows open, direct sunlight, showers, electric heaters, hairdryer, and so on.
Alessandro schrieb:
The bedroom does not get warmer than 18.5°C (65°F) with windows and doors closed. What is so hard to understand about that?Except that you measured 19.5°C (67°F).A
Alessandro11 Nov 2021 13:05RotorMotor schrieb:
For example, average values for each room over the course of a day.
Considering or at least mentioning external factors such as outside temperature, wall construction, open windows, direct sunlight, showers, electric heaters, hairdryers, ...
That you measured 19.5, after all. I set the maximum temperature value for each room. Without factoring in influences like sunlight or occupancy, as those are not constant factors.
Average values are pointless.
The 19.5°C (67.1°F) was measured after 8 hours of sleep!
The maximum value for the bedroom is 18.5°C (65.3°F).
R
RotorMotor11 Nov 2021 13:18Alessandro schrieb:
I set the maximum temperature value for each room. Without considering external factors like sunlight or occupancy, because those are not constant.
Average values don’t make any sense.
The 19.5°C (67°F) was after 8 hours of sleep!
The maximum value for the bedroom is 18.5°C (65°F). Sorry, but I don’t follow.
How can the maximum value be lower than the measured value?
And what do you mean by setting this value?
Measurements come from devices, not from setting a value.
Average values are very useful in a house, because as we can see you are otherwise including disturbing factors in your measurements. Since a modern house reacts very slowly, averages are exactly the right approach!
A
Alessandro11 Nov 2021 13:36Let me explain it using a different example:
A meeting room is used daily by a varying number of people.
One day, it is used by 2 people; on another day, by 10 people, including laptops and other devices.
On some days, it is occupied for 2 hours; on others, up to 12 hours (again with a varying number of occupants).
Due to the heat generated by the people (similar to what happens during sleep) and the devices, the temperature sometimes reaches 23°C (73°F), and other times, with full occupancy over several hours, up to 28°C (82°F).
Should I regulate or heat based on the average temperature? According to that, I would never need to turn on the heating.
However, if I enter the room alone in the morning (which, according to your statement, wouldn’t need heating), I would be freezing cold.
That’s why a maximum temperature is set for rooms, which the heating system regulates with its supply temperature!
For my bedroom, this is set at 18.5°C (65°F), which isn’t exceeded when the room is unoccupied…
A meeting room is used daily by a varying number of people.
One day, it is used by 2 people; on another day, by 10 people, including laptops and other devices.
On some days, it is occupied for 2 hours; on others, up to 12 hours (again with a varying number of occupants).
Due to the heat generated by the people (similar to what happens during sleep) and the devices, the temperature sometimes reaches 23°C (73°F), and other times, with full occupancy over several hours, up to 28°C (82°F).
Should I regulate or heat based on the average temperature? According to that, I would never need to turn on the heating.
However, if I enter the room alone in the morning (which, according to your statement, wouldn’t need heating), I would be freezing cold.
That’s why a maximum temperature is set for rooms, which the heating system regulates with its supply temperature!
For my bedroom, this is set at 18.5°C (65°F), which isn’t exceeded when the room is unoccupied…
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RotorMotor11 Nov 2021 13:55I won’t go further into the somewhat absurd example of 28 degrees in the meeting room. It doesn’t even make sense in theory.
Here is the answer: YES.
As already mentioned, a (modern) house is very slow to react in terms of indoor temperatures (apart from open windows and doors).
The exterior of the house is insulated, and the interior has large thermal masses.
Therefore, it takes a long time (many hours to days) for changes to have an effect.
This is also exactly why everyone advises deactivating the ERR and setting fixed flow rates.
Opening and closing valves briefly simply doesn’t make sense with such a sluggish system.
What does it mean to set this temperature?
Of course, you can choose a desired temperature, but whether it is reached without active/external cooling is questionable.
This could actually be tested with an experiment!
If you are on vacation, try recording the temperatures of the rooms.
My expectation would be that temperature differences between rooms within the thermal envelope turn out to be very small.
Alessandro schrieb:
Should I control/heat according to the average temperature now?
Here is the answer: YES.
As already mentioned, a (modern) house is very slow to react in terms of indoor temperatures (apart from open windows and doors).
The exterior of the house is insulated, and the interior has large thermal masses.
Therefore, it takes a long time (many hours to days) for changes to have an effect.
This is also exactly why everyone advises deactivating the ERR and setting fixed flow rates.
Opening and closing valves briefly simply doesn’t make sense with such a sluggish system.
Alessandro schrieb:
That’s why a maximum temperature is set for rooms, according to which the heating regulates its supply temperature!
In my bedroom, this is 18.5°C (65°F)! This temperature is not exceeded when the room is unoccupied....
What does it mean to set this temperature?
Of course, you can choose a desired temperature, but whether it is reached without active/external cooling is questionable.
This could actually be tested with an experiment!
If you are on vacation, try recording the temperatures of the rooms.
My expectation would be that temperature differences between rooms within the thermal envelope turn out to be very small.
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