Fine Tuning Room Return Temperatures for Efficient Heat Pump Heating

[kr0ner]

Overview

Optimizing the return temperatures of individual heating circuits improves the efficiency of a heat pump system.
Lower and more uniform return temperatures enable the heat pump to operate with a higher coefficient of performance (COP).
Using Dallas DS18B20 temperature sensors attached to each return line allows precise monitoring and adjustment.

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Hardware Setup

The first image shows a heating circuit distributor equipped with DS18B20 temperature sensors.
Each sensor is clamped to the individual return line using 3D printed holders.

🔗 3D printable clamps: https://www.printables.com/model/1117829-hose-clip-for-6mm-ds18b20-probe/files

Example setup photo:

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ESPHome Configuration Example

Below is a minimal ESPHome configuration snippet for a DS18B20 sensor connected to GPIO1:

one_wire:
  - platform: gpio
    id: bus_ug_eg
    pin: GPIO1

sensor:
  - platform: dallas_temp
    one_wire_id: bus_ug_eg
    address: 0x18000000b9f5e328
    name: "Gäste Badezimmer Rücklauf Temperatur"
    id: gaeste_badezimmer_ruecklauf_temperatur
    device_class: temperature
    unit_of_measurement: "°C"
    accuracy_decimals: 1
    icon: mdi:thermometer
    update_interval: 5min

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Data Visualization and Adjustment

The second image shows the temperature profiles of various rooms over time.
After fine-tuning, most return temperatures are closely aligned, indicating balanced flow and heat distribution.
Only the bedroom remains slightly cooler, while bathrooms are kept a bit warmer for comfort.

Example temperature graph:

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Fine-Tuning Procedure

1. Measure Baseline
   Record all return temperatures under stable heating operation.
2. Identify Outliers
   Rooms with significantly higher return temperatures receive too much flow.
3. Adjust Flow
   Reduce flow in those rooms using the flow adjustment valves on the manifold.
4. Wait and Observe
   Allow several hours for the system to stabilize before making further changes.
5. Repeat
   Continue until all rooms show similar return temperatures (±0.3 °C).

🎯 Goal: Achieve uniform return temperatures while maintaining comfort.
Lowering the mean return temperature reduces compressor load and increases overall heat pump efficiency.

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References

• Dallas DS18B20 sensors : https://amzn.to/4u8ExHr
• 3D printed probe clips: https://www.printables.com/model/1117829-hose-clip-for-6mm-ds18b20-probe/files
• ESPHome documentation: https://esphome.io

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✅ Balanced flow and uniform return temperatures directly translate to better heat pump performance and lower energy costs.

[Schmidtjanroman]

Do you need a esp32 for every sensor or can you connect more sensors to one board?

[kr0ner]

1 spare GPIO for 20 sensors is enough if you power them via 3.3V

[Schmidtjanroman]

My plan was to use one ESP32 in every HKV, thinking about the effort it'll take to get this running and understood

[kr0ner]

I only have one ESP in the basement. The most time consulting part was to obtain the ID of every single sensor 😅 connect new sensor -> boot -> note down ID -> repeat
Took me and afternoon to install everything

[Oggy512]

How did you do the wiring, when all sensors are connected to the same GPIO?

[kr0ner]

They are all connected to GND and VCC and there is a 4.7k resistor between DATA and VCC. I run wires to the HKV and distribute the GND, VCC and DATA via Wago clamps

[hgN1337]

Hey, I wanted to ask how you ultimately assess the added value? Did it make a difference? I keep thinking about how sensible the approach really is, since all the rooms behave differently (size, north vs. south orientation, flooring, different starting temperatures, windows etc.). So were you able to reduce electricity consumption, regulate the temperature in the rooms better, or anything along those lines? ^^

[kr0ner]

I think so ^^ although I don't have the proof :D
The main killer is when the heatpump starts to cycle and goes ON - OFF - ON - OFF all the time.
Since my installation was never adjusted properly by the installer, the spread in return flow temp was around 5-6°.
Main problem was that the bathroom was fully opened and the two circuits there made up for 50% of the overall return flow temp value 2 x 3 l/min @ 28°, because the floor was saturated already. The other rooms barely contributed, because they had like 25° @ 1 l/min. So six other rooms contributed the same as the bathroom, which lead to the heatpump thinking the house is warmer than it actually is -> turned itself off, just to start soon after again.

Now I have set the bathroom to be 1° above the rest and the basement 1° below the average. All other rooms have a spread of 0.5°C which means they evenly take heat out of the system. I'm still in the process of tweaking.

[hgN1337]

Ah okay, mine was hydronically balanced but still had that start-stop behavior. It only really changed with the room sensor.

However i keep the project in mind for Next Winter