Last modified by djahnie 2024-02-09 21:47:10
Created by Matthias Larisch 2021-11-17 15:01:35

:volcano: Heating system

Since beginning of Winter 2021, Kanthaus is powered by an air heat pump heating system, which means we heat fossil free only using electricity.

The outdoor unit is located in the garden outside of K20-0-1. Using a special liquid called refrigerant, it heats up water to send through our radiators, or domestic hot water (also called 'DHW') for showering and sinks.

The heat pump control panel is installed on the wall next to the Main Kitchen door in the hallway of K20-1.

:exclamation: General info for users

Heat pumps work fundamentally different from gas heaters. (Here's an article about how they work in general.) While gas heaters usually send really hot water through the radiators, the heat pump heating system's water temperature needs to be as low as possible. That means:

  • You can not heat up a room quickly - expect a room to become pleasantly warm only 1-2 days after turning on the radiator
  • Much of the temperature control is set centrally. Thus, turning the knobs on the radiators doesn't do much more than switching on or off.
  • The maximum reachable temperature is usually around 19.5 °C in Kanthaus. It slightly changes depending on the outdoor temperature though.
  • It's good for the system to run continuously rather than to be frequently switched on and off. Hence it is normal and wanted that the heatpump outside is working all the time.
  • It needs a minimum water flow through the radiators to work at all. This means at least 6 radiators need to be turned on all the time.
  • It can be very expensive if it doesn't run efficient, so there is a lot of focus on keeping the efficiency of the system high.

:page_with_curl: Default settings

as of 2024-01-10

  • heating water target temperature: between 30 and 40 °C
    • consequence: the radiators can never be hotter than this
    • more advanced mechanics regulate the exact heating water temperature automatically (see details below in 'Advanced information')
  • between 7 am and 8 pm day mode is activated, then we heat to:
    • 18.7 °C if the outside temperature is at or below -6 °C
    • 20 °C if the outside temperature is at or above 10 °C
  • between 8 pm and 7 am night mode is activated, then we heat to:
    • 18.5 °C
  • the target temperatures are evaluated using the Piano Room and the Main Office
    • the mean temperature of both rooms combined over the last 5 minutes is the figure used
    • conesquence: if (one of) those rooms get colder, the whole house will be heated more and the other way around

:house: Room heatability

We purposefully do not heat all rooms in Kanthaus.

The rooms which are warm by default in Winter are:

  • Snack Kitchen
  • Main Office
  • Main Kitchen
  • Dining Room
  • Elephant Room
  • Piano Room
  • Bathroom

Additionally, when there are enough people to justify it, we usually also heat:

  • Fansipan
  • Silent Office

If someone is in need of a warm private room, the best choice for that is definitely:

  • The Lantern

Also K-20-3 is very well heatable, but uses a completely decoupled heating solution.

To keep the efficiency of the system high, we actively decided that badly heatable rooms stay cold(er). A room is badly heatable if:

  • the radiator is too small for the specific room
  • it is surrounded by cold walls (including floor and ceiling)

Here's an incomplete list of those rooms:

  • The Private (6 cold walls)
  • Hipster Room (6 cold walls)
  • Sleep Kitchen (6 cold walls)
  • Ex Food Storage (6 cold walls)
  • Freeshop Lounge (6 cold walls)
  • Cloud Room (4 cold walls)
  • Dragon Room (5 cold walls)

To determine yourself if a room is well or badly heatable, please refer to the expfloorer and analyze the room's location in the house. Keep in mind that K18 is completely cold, while WR9 is mostly heated.

:bath: Domestic hot water (aka DHW)

The heat pump is also responsible for domestic hot water ('DHW') being available in the Main Bathroom, the Main Kitchen and the Snack Kitchen. We have a DHW tank in K20-B water room for that purpose. When full and freshly heated, it holds 200 liters of 52°C water.

The heat is transferred without the two liquids touching.

Heating up DHW and water for radiators is not possible at the same time!

Usually the heat pump switches to water mode once a day at some point when it's sunny. If the hot water tank is empty, however, it immediately starts heating it up again.

The process of heating up DHW takes 30 to 90 minutes depending on how warm the water in the tank was to begin with.

Details of DHW heating

To heat the DHW, the heating water which otherwise would go through the radiators is redirected and its' target temperature adapted. A DHW tank is specifically designed to have passages for heating water than can give off heat to the DHW without touching it.

When DHW is used, cold water flows into the tank from below. The hot water on top can still be used, because different temperature layers form in the tank. The thermometer to check the DHW's temperature is on the upper side of the tank so that the reheating doesn't start too early. When the temperature of the DHW falls below 39 °C on the top, then the heat pump will switch to water mode automatically and start heating the tank to the target temperature of 52 °C again.

The start of the heating process will mix the layers of different temperature water and first make it colder overall. Meaning: If you're taking a shower and the hot water seems to not be so hot anymore, you better finish quickly.


A known problem in domestic water systems are legionella bacteria which cause lung diseases. They only die above 60 - 70 °C, but there are other ways to get rid of them. To avoid chlorine, we went for physical removal, which means to create enough throughput of water to basically wash them away. When they don't have the time to settle down and form bigger populations they're nothing to worry about.

:question: Troubleshooting

A radiator is not getting warm, although the heating system should be running?

  • Is it warm outside? Maybe the heating system turned off temporarily during nighttime?
  • Try another radiator in another room, preferably on the other side of the house or in the other house
    • If successful, a part of the heating system might be turned off at the valves in K20-B-old-heating-room or K22-b-event-storage. Find people who might be working on the heating system before turning it back on.

If both are not successful, go to the heating system control panel in K20-1 hallway.

  • It does not show anything?

    • Locate the heating systems fuse in the main electricity fuse box in the electricity room in the basement
    • When you open the right panel of the heat pump outside (losen 4 screws, push it down, yes, push it down harder!) there are also 2 fuses at the top.
  • It shows an error?

    • H62: Too many radiators are turned off so the heat pump could not satisfy its minimum water flow. Turn on some more radiators and make sure that nobody can turn them off (e.g. by removing the thermostat to have it fully on)
    • H70: Check the fuse "heater" in the main electricity box on the bottom right
    • H74: Maybe the house bus node controlling the heating system had a problem? Press the "On" button and watch it for 5 minutes, if it reappears, disable "Optional PCB connectivity" in the installer menu to make it completely autonomous again.

I really want to heat a badly heatable/cold room/ I need to heat a room quickly.

  • Use an electric space heater ("Heizlüfter").
  • Isn't this very expensive?
    • Yes (60 cents per hour), but adjusting the heating system so this is possible without the electric heater is more expensive all the time and this scenario should not occur often.

I would like to permanently use a badly heatable room. What do I need to do?

  • Install fans underneath the raiator for better heat distribution
  • Install a bigger radiator
  • If this need is really there for many rooms, we might want to increase the whole heating systems temperatures, this increases the heating cost about 2.5 percent per degree (+ the increased heating cost for the rooms getting warmer of 6% per degree of room temperature)
  • Generally it would be preferable to rather find a better heatable room instead.

The heat pump is annoyingly loud, can we do something?

  • Depends. Is it a certain time or mode of operation? We can always have it operate on lower power for some hours, where it will then be more silent. Communicate your wish :-)

:construction_worker: Advanced information

Our heat pump is a Panasonic Aquarea T-Cap 12 kW WH-MXC12H9E8.

:wrench: Required maintenance

In K20-B water room, there are two filters that should be cleaned regularly (e.g. at least once per heating season):

  • Spirotap MB3 (The "big" thing in the return line on the bottom)
    • Turn off the heat pump, so the pump is not running
    • Pull down black magnetic cap
    • Get a bucket, put it underneath the exhaust in the bottom
    • Use the cap to turn the knob
    • Leave it open for a second, it will immediately get rinsed
    • Careful: water comes out with high pressure! Don't let the cap slide off the knob!
    • Put black magnetic cap back on, turn heat pump back on
  • Superfilter (The ball valve with the black handle on the bottem)
    • Turn black handle until it reaches closing position
    • Unscrew cap and get the filter out
    • It's quite hidden inside, find it by feeling with your finger
    • Take it out and rinse it, use a (tooth)brush to get it really clean
    • Put it back in - no need to let it dry
    • Close cap again and open black handle

The outside unit in the garden also has a filter, but it seems to be fine without maintenance after 2 winters.

:eyes: Additional layers of control

Because of some shortcomings in the controller of the heat pump itself, it is additionally monitored and controlled by a House Bus node, a Heishamon and a selfmade heating controller script.

There is some unwanted redundancy, complexity and inflexibility in this setup that might be addressed at some point in the future, but for now it's functional as it is.

If you want access to these additional layers because you are technically adept and interested in helping out with managing and improving the system, talk to Tilmann. He will be happy about it. :blush:

House Bus integration

The House Bus node is a piece of hardware and software. The physical part is installed in K20-B water room and the digital part, which is running on it, is recorded in Matthias' github.

Its' purpose is to allow reading all status from the heat pump, the heat meter and the electric counter, and to then write the data in InfluxDB. From there we can import it into (Grafana)[]. and use it to e.g. debug and understand the heat pump's behaviour better.

The info made visible by the House Bus node is:

  • heating water temperature
  • power usage
  • heat generation
  • water flow
  • DHW mode or heating mode
  • outside temperature
  • compressor power consumption
  • many small details which not even Tilmann uses or understands

The House Bus node is a new generation coming from our other nodes as it uses upgraded uavcan v1 and an arduino base stack.

Heishamon interface

Heishamon is a small piece of open-source software and hardware to monitor and control the heatpump. It is located in the K20-B water room and is connected to WiFi.

It also emulates the Optional PCB thus is able to set the SG ready signals and demand control.

Heishamon is used to adjust the water target temperatures, with the aim to keep room temperatures consistent and use more of our own solar power.

This probably is something the House Bus node is capable of, too, but at the time it seemed easier to set up a new system than to modify the existing one.


A heating controller script called is running on the Kanthaus server. It is additionally stored in the git repo heating_control, although the version in there might not be fully up-to-date.

It maintains comfortable temperatures in the house while minimizing energy usage. It does this by reading room temperature sensor data provided by the House Bus system from InfluxDB and adjusting the heating water target temperature via Heishamon. Also, it can switch the heating on or off based on temperature thresholds.

Additionally, the program determines the amount of available solar power and makes use of it by raising temperatures to store heat in the house.

The program also triggers DHW re-heating if conditions are good, for example if the house is warm enough and there's solar power available.

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