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
Alessandro5 Nov 2021 09:28Hallway
Bedroom
Bathroom (after 10 minutes of airing out)
The key is the thermostat hysteresis. I lowered it from 0.5 to 0.2 °C (0.9 to 0.4 °F) so that enough heating circuits remain open almost constantly, ensuring sufficient underfloor heating flow. Of course, the actuators open and close several times a day, but to me, the comfort is worth it.
Bedroom
Bathroom (after 10 minutes of airing out)
The key is the thermostat hysteresis. I lowered it from 0.5 to 0.2 °C (0.9 to 0.4 °F) so that enough heating circuits remain open almost constantly, ensuring sufficient underfloor heating flow. Of course, the actuators open and close several times a day, but to me, the comfort is worth it.
Alessandro schrieb:
As @Daniel-Sp mentioned, you should find out how the heating curves for the mixing valve and the heat pump look and share them here. This is probably a silly question, but can you tell me what "that" is?
Or I’ll try to explain it myself and you can correct me?
The heat pump heating curve refers to the temperatures at which the set sensor causes the heat pump to compress. It turns on when the set hysteresis is exceeded downward and turns off when it is exceeded upward.
If this is what you mean: I currently have it set to a fixed return temperature control. Up until last night, it was set to 28°C (82°F) with 2 setback periods and a 4°C (7°F) hysteresis. I thought that worked pretty well, although after the heat pump runs (during which the supply temperature was about 36°C (97°F) and the return temperature was heated up to 28 + 4°C (54°F) — and there were “weird” bumps in the heating curve), both supply and return temperatures dropped immediately to around 27–28°C (81–82°F). Then it took about half a day for the return temperature to fall down to 28 - 4°C (50°F).
Regarding the mixing valve heating curve: I can’t find any information about this in my documents. I can set a mixing valve hysteresis and a mixing valve operation time on the heat pump. The hysteresis is 0.5 K (0.9°F) and operation time is 2 minutes, which according to the heat pump manual is the standard setting. What exactly do these change? Am I correct in assuming that this means when there is a 0.5 K (0.9°F) difference between the buffer water and the supply temperature, the mixing valve runs for 2 minutes and mixes warm water into the heating circuit?
A
Alessandro5 Nov 2021 09:38What else do you want to optimize, @grericht, with 8kWh per day and 2 compressor starts? You have the desired temperatures in the rooms, ERR is active, and you have a buffer tank plus a mixing valve.
In my opinion, there’s nothing more to gain with the size of your house...
Maybe you can just set one heating curve that applies to both the heat pump and the mixing valve.
Take a photo of your heating curve settings.
It’s also important where your return flow sensor is located. Is it directly on the return pipe or in the buffer tank?
In my opinion, there’s nothing more to gain with the size of your house...
Maybe you can just set one heating curve that applies to both the heat pump and the mixing valve.
Take a photo of your heating curve settings.
It’s also important where your return flow sensor is located. Is it directly on the return pipe or in the buffer tank?
Alessandro schrieb:
What more do you want to optimize, @grericht, with 8 kWh per day and only 2 compressor starts? You have the desired room temperatures, ERR active, a buffer tank plus mixer.
In my opinion, there’s nothing left to improve at that house size... Hmm. I would have gratefully accepted that as a compliment a month ago. But now I have learned that my neighbor in a new build, using an air-to-water heat pump and a similar storage tank (just 850 instead of 650 liters (170/140 gallons)), managed to keep February last year under 7 kWh/day. And the average temperatures were more than 6°C (43°F) lower. His house is not much smaller. I think the heated/warm area is about the same. I don’t know if he has two bathrooms or if he has additional heating in the bathroom. I’m trying to find that out.
Basically, my main concern is to understand the system well. Unfortunately, my heating installer is not able to help with this, and I don’t think it’s really their responsibility to explain all the technical details to me.
Can you still tell me how you control the bedroom heating? Is the valve generally open at 0.2 liters per hour (0.05 gallons per hour) through your ERR, or is it usually closed and only opens if the bedroom starts to get too cold?
A
Alessandro5 Nov 2021 09:48Comparing yourself to others only causes confusion. Heating consumption is closely related to desired temperatures.
A 150kg (330 lb) man probably already feels too warm at 22°C (72°F) in the living room. My wife is still wearing three layers at 24°C (75°F) ;-)
That means: Maybe your neighbor is comfortable with only 20°C (68°F) in the living room and also accepts 20°C (68°F) in the bathroom.
Regarding your question: I ventilate my bedroom for 5 minutes right after getting up. After that, it takes until bedtime for the temperature to reach 18.5°C (65°F) and the ventilation system closes the circuits. I have two circuits with 0.2 liters per minute each in the bedroom.
A 150kg (330 lb) man probably already feels too warm at 22°C (72°F) in the living room. My wife is still wearing three layers at 24°C (75°F) ;-)
That means: Maybe your neighbor is comfortable with only 20°C (68°F) in the living room and also accepts 20°C (68°F) in the bathroom.
Regarding your question: I ventilate my bedroom for 5 minutes right after getting up. After that, it takes until bedtime for the temperature to reach 18.5°C (65°F) and the ventilation system closes the circuits. I have two circuits with 0.2 liters per minute each in the bedroom.
R
RotorMotor5 Nov 2021 09:49Alessandro schrieb:
BedroomAre bedroom windows always left open or what? Measuring the outside temperature wouldn't help much.Similar topics