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 14:32I don’t understand what you’ve been trying to explain to me all this time?!
Room temperature is not determined based on an average value! Over what period? At what outdoor temperature?
What do you do if, during the period when you are calculating the average temperature, the sun is shining directly inside all the time? Do you then set it to 24°C (75°F)?
You use a maximum temperature that each room should reach with windows and doors closed, without occupancy and without solar gain.
By the way, this is a simplified way to describe how heat load calculation and heating curve design work, but I’m sure you know that.
Or have you ever seen a calculation that includes, for example, the living room being occupied on average by 3 people between 7:00 p.m. and 11:00 p.m.?
You can see that it works in my case. I don’t know what you’re doubting...
Room temperature is not determined based on an average value! Over what period? At what outdoor temperature?
What do you do if, during the period when you are calculating the average temperature, the sun is shining directly inside all the time? Do you then set it to 24°C (75°F)?
You use a maximum temperature that each room should reach with windows and doors closed, without occupancy and without solar gain.
By the way, this is a simplified way to describe how heat load calculation and heating curve design work, but I’m sure you know that.
Or have you ever seen a calculation that includes, for example, the living room being occupied on average by 3 people between 7:00 p.m. and 11:00 p.m.?
You can see that it works in my case. I don’t know what you’re doubting...
R
RotorMotor11 Nov 2021 15:19Alessandro schrieb:
I don’t understand what you’ve been trying to explain to me all this time?! I just want to point out mistakes that ultimately lead to inefficient operation of heating systems. 🙂
But this is not meant personally against you.
Specifically, my point was that within a “well” insulated house, large temperature differences cannot occur.
Since the rooms are not insulated, the “basic law of heat exchange” applies.
That means the warmer room transfers heat to the cooler one.
The cooler room can only get colder if it also loses heat.
This can only happen to the outside, either through open windows or poor insulation.
Both cause energy waste.
Alessandro schrieb:
You don’t set a room temperature based on an average value!
...
By the way, this is also how heating load calculation and heating curve design work in simplified terms, but you surely know that. Here your two statements contradict each other.
Because exactly an average target temperature, e.g. 20°C (68°F), is set.
Alessandro schrieb:
Over what period? At what outdoor temperature?
What do you do if during the period when you want to calculate the average temperature the sun shines continuously?
Do you then set the temperature to 24°C (75°F)?
You take a maximum temperature that should be reached in each room with windows and doors closed, without occupancy and without solar gains. In this part, I don’t understand what you’re trying to say at all.
As I’ve mentioned several times already: the system is slow to respond.
So there’s not much to “control”.
Closing the valve because the sun is shining doesn’t help!
Alessandro schrieb:
It works, you can see that with me. I don’t know what you’re doubting... No, it measured 19.5°C (67°F).
And just because you temporarily lower the temperature by opening a window doesn’t mean you have overridden the basic law of heat exchange.
A
Alessandro11 Nov 2021 16:21RotorMotor schrieb:
My main point was that in a well-insulated house, large temperature differences cannot occur.
Since the rooms are not insulated, the “basic law of heat exchange” applies.
This means the warmer room transfers heat to the cooler one.
The cooler room can only get colder if it also loses heat.
This can only happen to the outside, either through an open window or poor insulation. By the way, the hallway thermostat and the bedroom thermostat are mounted on the same wall at exactly the same height — just on opposite sides, of course.
Just keep the windows closed for 72 hours and avoid cooling the rooms excessively by ventilation, and you will see that your bedroom becomes noticeably warmer.
If you throw the windows wide open and let the room cool down completely, it is of course obvious that the underfloor heating with minimal flow won’t warm up the room in 8-10 hours. However, this does not change the fact that in a modern new build, with _normal_ heating behavior, you won’t achieve a 5K (9°F) difference between adjacent rooms.
If you throw the windows wide open and let the room cool down completely, it is of course obvious that the underfloor heating with minimal flow won’t warm up the room in 8-10 hours. However, this does not change the fact that in a modern new build, with _normal_ heating behavior, you won’t achieve a 5K (9°F) difference between adjacent rooms.
A
Alessandro12 Nov 2021 09:13I have already done that. It wasn’t a full 72 hours, but 48 hours. It’s possible that the temperature might be a bit higher over 72 hours, but that doesn’t reflect our daily routine. Who is usually away from home for 72 hours?
That has nothing to do with it; it’s just meant to show you that your statement like "no problems at all" is not that simple. Because by ventilating heavily and cooling down, you are affecting the thermal envelope of your house.
I could also say, "I have KfW 40 and 40°C (104°F) supply temperature but don’t get above 20°C (68°F) room temperature," only to later admit in a few posts that I keep all the windows in the house tilted open 24/7.
I could also say, "I have KfW 40 and 40°C (104°F) supply temperature but don’t get above 20°C (68°F) room temperature," only to later admit in a few posts that I keep all the windows in the house tilted open 24/7.
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