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)
How did you manage to aggregate the data into a graph from the Dimplex system?
The storage tank of that size is definitely a special case. Typically, people shower or bathe at 38-41°C (100-106°F), so why keep so much water heated to 50°C (122°F)? I would significantly lower that temperature setting.
And given the size, you should consider the risk of Legionella bacteria, unless there are 8 people showering daily.
The storage tank of that size is definitely a special case. Typically, people shower or bathe at 38-41°C (100-106°F), so why keep so much water heated to 50°C (122°F)? I would significantly lower that temperature setting.
And given the size, you should consider the risk of Legionella bacteria, unless there are 8 people showering daily.
guckuck2 schrieb:
How did you manage to aggregate the values into the graph for the Dimplex?
A storage tank of that size is quite unusual. Typically, people shower or bathe at 38–41°C (100–106°F), so why keep so much water at 50°C (122°F)? I would significantly lower that temperature.
And with a tank that size, you should consider the risk of Legionella bacteria, unless eight people shower daily. Well, I’m not an expert, but this is NOT a standard hot water storage tank. It’s a stratified tank. The hottest water is stored at the top and serves as water heating in a flow-through system. The bottom (I think about two-thirds) contains heating water.
So Legionella bacteria are absolutely NO ISSUE!
Thanks for the link about the network expansion.
Yes, it is a stratified storage tank. How are the layers distributed? With 850 liters (225 gallons), the issue of the large size remains. Either the domestic hot water storage is unusually large for a single-family home, or the buffer for the underfloor heating is very big (or both 🙂) — although the latter is ideally 0 liters (0 gallons) 🙂
Yes, it is a stratified storage tank. How are the layers distributed? With 850 liters (225 gallons), the issue of the large size remains. Either the domestic hot water storage is unusually large for a single-family home, or the buffer for the underfloor heating is very big (or both 🙂) — although the latter is ideally 0 liters (0 gallons) 🙂
A
Alessandro5 Nov 2021 08:41RotorMotor schrieb:
First of all, you need to give up on achieving temperature differences of more than three degrees within the thermal envelope!
For example, sleeping at 18°C (64°F) and having the bathroom at 23°C (73°F) just isn’t feasible.
Trying to reach that will only lead to frustration.
Interior doors and walls simply aren’t insulated. I don’t want to let that stand as is. I have 23°C (73°F) in the bathroom, 18.5°C (65°F) in the bedroom, and 21.5°C (71°F) in the hallway. The bathroom and bedroom are right next to each other. Of course, I’ve throttled the two heating circuits in the bedroom down to 0.2 liters per minute (0.05 gallons per minute).
BUT I also use ERR because I don’t want to give up on comfort.
As @Daniel-Sp wrote, you should find out the heating curves of the mixing valve and the heat pump and share them here.
I would also lower the domestic hot water temperature from 50°C (122°F) down to 45–48°C (113–118°F).
R
RotorMotor5 Nov 2021 09:03Alessandro schrieb:
In the bathroom 23°C (73°F), in the bedroom 18.5°C (65°F), and in the hallway 21.5°C (71°F). The bathroom and bedroom are directly next to each other.Please explain how you manage this and how you measure it. Also, what types of walls and doors are between these rooms?
Ah, and how is the building envelope constructed?
Alessandro schrieb:
I don’t want to leave it like this. I have 23°C (73°F) in the bathroom, 18.5°C (65°F) in the bedroom, and 21.5°C (70°F) in the hallway. The bathroom and bedroom are right next to each other. Of course, I have throttled the two heating circuits in the bedroom down to 0.2 l/min (0.05 gallons per minute).
BUT I also use ERR because I don’t want to give up comfort.
As @Daniel-Sp mentioned, you should find out the heating curves of the mixer and the heat pump and share them here.
I would also reduce the domestic hot water temperature from 50°C (122°F) to 45–48°C (113–118°F). I find that very interesting too. And even though it wasn’t for long, I almost managed to keep this for the last three days. The bedroom was at 19/19.5°C (66/67°F), the hallway at 21/21.5°C (70/71°F), and the bathroom at 23/23.5°C (73/74°F).
I found that very optimal. Two starts of the heat pump per day, each lasting about 2.5–3 hours. Which is still a rather high consumption considering the outside temperatures (around 8 kWh/day) — and that feeling it’s only for the warm bathroom. I think an additional heater during those times could save a lot on household energy consumption.
But to be specific again:
- Did you actually increase the heating in the bedroom a bit, despite wanting it as cold as possible there (is that your goal)? Do you have an ERR in the bedroom as well? If yes, what is it set to? Does it regulate at all?
- What average supply or return temperature do you have when the pump is off? At what temperature does the pump turn on and up to what temperature does it heat?
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