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• Using the ControlBox to for smart heating control

  Anton Verburg • 02/26/2025 at 15:54 • 0 comments

  Its nice to have a high-quality control device, but its even nicer to use it to control your house. In this log I want to showcase how we use the ControlBox in our own house.
  

  During the renovation of our house, we had to supply a calculation of the heat dissipation in our house to apply for the permits. I found a very useful example of such a calculation, made by Steven van Lier. The original calculation can still be found here. We converted this calculation to represent our own case, and we added some calculations to estimate what kind of heat sources we would need in different use cases to heat our house. It gave us a nice overview of what is required, and why. Our own variant of this calculation is available here.

  Finally I created a schematic to supply an overview of how the different heat-supplying and heat-buffering devices in our house are inter-connected. The schematic is available here.

  I think we did some less-conventional things to reduce energy consumption.

  • We use a small heat-pump water boiler (input power 400 Watt) to supply heated tap water.
  • We have a heat exchange between the tap water boiler and the two hot-water buffer boilers in the attic.
  • We can provide heat from the heat-pump to those buffer boilers, but we can also bring back heat from the buffer boilers to the tap water.
  • As we also have a vacuum-tube heat collector on the roof of the house, we are able to switch the (electricity consuming) heat pump off in summer time; in this period hot water is provided by the heat collector.
  • In winter time, the heat transfer will be directed in the other direction; the heat pump and the heat collector will both heat the hot water buffers.
  • Using those hot-water buffers we are able to lower the temperature at night, while we still have comfortable temperatures when the day starts.
  • Because the heat pump we use is a air-to-water heat pump, we also use it to ventilate our house.  By supplying the heat pump with the relative warm ventilation airflow, the efficiency of the heat pump increases.

  In order to regulate & coordinate all those tasks, the ControlBox is used. The ControlBox will:
  

  • Read all temperature sensors t_x.
  • Switch valve A, B and C. Use 24VAC for safety reasons
  • Switch the motors on floor heater distribution group
  • Control the flow of pump p₁ and p₄ via PWM signal.
  • Switch all pumps on/off
  • Check via internet outdoor temperature & weather forecast

  With the input of the temperature sensors the ControlBox can:

  • Verify if there is a request for heat on 1st floor (living room/kitchen) is (t₁₄).
  • Verify if there is a request for heat on the 2nd floor (t₁₃).
  • Calculate the amount of heat dissipation of the house (t₈ en t₉)
  • Check if wood stove is burning:
    t₁₅ will go high: switch off floor heating. If delta between t₁₅ and t₁₆ gets too large switch p₁ on.
  • Balance and regulate the heat in the heat-buffer boiler, tap water boiler and solar collector (t₁ to t₇ , t₁₀ to t₁₂ and t₁₈).

  With pump p₃ and valve a, b and c heat can be exchanged from the heat buffers to the tap water boiler or vice versa. Direction of the heat flow can be regulated with valve a and c. In winter time, the heat buffers can be heated by the heat collector, the heat pump and the wood stove. In summer time, the heat collectors can heat also the tap water, and the heat pump can be left off.

  Pump p₄ brings heat from the heatcollector to the buffer boiler. The PWM pump is regulated with a PID controller
  that regulates the delta between t₁ and t₁₈.  The switch-on moment is defined by monitoring the cumulative amount
  of energy that has been harvested by electrical solar panels since the last time it was switched off.

  Pump p₂ en p₅ are switched off when not in use .

  Heat transfer from wood stove to heat buffer boilers will basically happen via natural circulation (thermosyphon).
  This will ensure a safe flow independent from pumps, hardware or software (ensuring safety).
  If temperature of t₁₅ gets too high, pump p₁ can be switched on to cool down the...

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• Typical design decissions

  Anton Verburg • 12/07/2024 at 16:19 • 0 comments

  So what decisions did I make during the design of the ControlBox, and why?

  
  Well, when building hardware a lot of decisions have to be made. During the development of this piece of hardware, I always tried to choose the most-robust option. So here we go:

  • For mains outputs, we selected panasonic AQG22105 solid state relays with integrated snubber circuit and zero-crossing detection.
    • The disadvantages of electromechanical relays are their slow response
      time, high maintenance, and limited functionality. They are prone to wear and tear, contact erosion, and mechanical failures. So we wanted to use solid state relays.
    • According to the datasheet it should be able to supply up to 2A. But when testing the fuses, it was proven that a fast fuse of 2A would break the switch, so we decided to limit the current to 1.5A.
    • Utilizing the integrated snubber circuit and zero-cross detection, unexpected current peaks and other harmful signals are omitted.

  • For the 24VAC outputs, I had the following reasons:

    • This 24VAC is typically consumed by installation devices in an environment where leakage is possible. Think about the thermal wax valves of the radiant floor heating, but also 24VAC zone valves exist. The reason why these devices do not work on mains power, is safety. Imagine what happens if water is leaking over your 230VAC powered devices....

    • 24VAC thermal wax valves are very common, and can be bought anywhere on the world.

    • An unforeseen benefit of using the 24VAC devices is the connector space on the board; because the lower voltage, a smaller distance between the pins is allowed. And that allows denser connectors, so that we can put more IO on a smaller footprint.

    • Switches for 24AC are cheaper than those for 230VAC as well.

    • During my search for controlling the thermal wax valves I also saw that you can control them with 24VDC. But when I continued my search, I concluded that a 24VDC power supply is always more expensive than an on-board mains-to-24AC transformer.

  • Reading the 1-wire (temperature) sensors happens via two DS2482S-100 drivers. They are robust, and they have a function that enables to provide parasitic sensors with power via a push-up FET.
  • You might have asked yourself the question:
    • Why a RS482 half duplex port?
      The reason is simple; I have seen several devices utilizing such a port. An example is our own GoodWe solar panel transformer, or the Hewalex heat pump. And as our idea was to combine all available hardware via Home Assitant, in order to make the smartest possible decisions, we needed an RS485 port.
    • Why 2kW LED strip outputs?
      Just because it's fun. We had the idea to provide some kind of 'anti-theft' light around our house. Because we where preparing the renovation, we had the freedom to plan it like we preferred. And because I had done some nice projects with LED lights before, I thought 'well, it would be nice to put that around our house too'. And that's why I integrated it. When bringing this device to the public, I have considered to leave it out. But as the component costs are not that large compared to the rest of the unit, they are still there.
    • Why the RPi 5 + NVMe solid state disk?
      The raspberry pi is a common used hardware platform for Home Assistant, and can be easily installed with Home Assistant Operating System. This will give you all benefits of Home Assistant, including automatic system maintenance via the supervisor, and easy installation of the HACS. In future, the raspberry pi can easily be swapped for a faster or better single-board computer. The only disadvantage of the raspberry Pi till now was that it runs from an SD card. As internally Home Assistant uses database software, this is not a stable solution. But from version 5 this is solved; the pi can now run on a fast NVMe solid state disk, that contains a good controller to prevent the disk from corruption.
    • Why do you prefer wired connections? The newest wireless protocols are good, isn't it?
      Well, the newer protocols are getting better. But I have seen too...

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