CV UFH & warm water supply system for a tiny house

29 Jan 2023
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Hi all,

I'm new in here. So I'm working on a tiny house for myself and currently designing the CV & warm water supply system. I'm an engineer myself, but CV, electrical and plumbing are not my core expertises, so I was trying to seek for a professional advice here in the Netherlands where I'm going to build my tiny house, but unfortunately to no success. Most of the self-employed people from this field here are installateurs, and are not qualified enough to provide a professional feedback on the overall system design. And bigger companies work in such a way that you make a request, give them your address and they will come up with a proposal for a gas boiler, UFH etc. Which is not my case.

So long story short, I'm looking for some feedback from experienced people for my DIY system design: if the overall logic is sound, if the placement of the components is correct and so on. Separately I would like to emphasize the UFH system design and ask for a feedback for it, especially the wiring diagram. In the P&ID I provided a simplified wiring scheme and I know that I did not follow the accepted convention with color codes, live (L), neutral (N) terminal indications and so on, but as I said I'm not that experienced in this and so far it's just a concept - for me it's important first to check if the operation philosophy as I want to implement it is feasible, and if so, then I will definitely dive in the details and develop a more detailed wiring diagram myself or will ask for it from a professional.

So some motivation behind the developed design and the desired behaviour of the system:

1. The house is completely off-grid (power, water, sewer, everything). The main water supply is rain water collection system that will store the collected water in a tank and a main supply pump station p-1 (pump+membrane hydro accumulator) that will keep the pressure in the supply line at the setpoint (say 5 bar) by means of a pressure switch/flow sensor/controller, i.e. all standard stuff.

2. The main warm water supply for heating and water utilities is provided by a PV boiler (2 in the P&ID). So basically what I can do with my off-grid PV power system (which is out of the scope of this review) is to program the controller to supply the surplus PV power when the batteries are full (e.g. above 95% setpoint) to power the electric DC boiler. In such a way, I kind of store the excess solar power in the form of heat, which otherwise would be wasted.

3. Now imagine that the solar power is insufficient to provide the desired water temperature because several showers were used in a short time, not enough sun and so on. In that case (say if hot water temperature T<55C setpoint) the diverging valve v-9 will direct the water via a backup propane tankless water heater (1 in the P&ID) where it will be heated up to the heater's setpoint temperature (something like 60C). The same is done by the valve v-8 for a heating contour.

4. Finally the UFH system. My idea is to have 2 separate independent zones, each with its own circuit, electric actuator and a thermostat. So if at least one thermostat communicates that the temperature is less than the current setpoint temperature, the circulation pump of the pump group will be started and the corresponding actuators on the manifold block will be adjusted. The startup of the pump group circulation pump will trigger the tankless propane heater by creating enough flow rate (minimum activation flow rate is 2l/min), so there's no need to wire the tankless propane boiler to the wiring center. By the way another side question about the electric circuit actuators, so from what I understood there are 12/24Vdc and 230V (110V in the US?) actuators? And 12/24Vdc are kind of slow, so if I want to have a more dynamic response I rather go with 230V actuators, but their power consumption is probably considerably higher? So I have no exact choice regarding this yet.

5. The bathroom towel radiator is connected to the same manifold as the UFH. My idea is to put a manual actuator on the manifold, which will be normally open and regulate the temperature of the radiator by a manual regulator installed on the radiator itself.

6. Finally the last criteria is of course to have the system efficient, and I'm not that worried about the thermal efficiency, perhaps that's not the best system, but given the limitations of the power capacity of an off-grid system I'm very keen on having low electric consumption. It would not be nice if the controls would constantly tweak and power all the actuators, valves, pumps etc.

Some other remarks:

You can see that the mixing valve of the pump group is electric with a feedback loop from the downstream temperature sensor/transmitter. I'm not sure if that would be the case, t.b.h I'm thinking to have a thermostatic mixing valve instead, unless there some really significant advantages of an electric mixing valve that I'm not aware of. If anybody can share their thoughts on that, I would also appreciate that.

What is also missing in my UFH system is a flow rate control valve, like in this video. Again, not entirely aware of the criticality of not having it, so if somebody could shed some light on it then it would be nice.

Finally there are other system components as you will find it in the P&ID, like an UV lamp with an integrated flow sensor, that will automatically switch on and off once a flow of >~1.5l/min is detected on the cold water supply line to kitchen and bathroom faucets. Also a recycling line with all required components, that will periodically recycle the warm water supply line, to keep it above certain setpoint temperature (water is precious in the off-grid house and we don't want to waste it to the sink until warm water will come from the tap haha). So feel free to provide any feedback regarding these components as well, however those are not critical to me. Also if there are any other questions and/or remarks regarding placement of the components (like expansion vessels, dirt separators etc.) or missing components, then please let me know! :)

Besides the P&ID, I also attached a document I've drawn up a while ago, that summarised the design philosophy and contains some operation scenario examples. Not all components are present there and the layout is slightly different, but by looking at the examples it may give you a better idea of how I want to operate the system.

Please start throwing stones of unbearable criticism at me and proof my concept is a complete garbage :D


  • warming_system_B05.pdf
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  • heating_TH_B04.pdf
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also what i noticed already now, is that probably I will plumb the towel rail radiator differently, in order to make it independent from the heating contour and to be able to use it in times when the heating system is not used. Probably plumb it to the warm water supply contour, but didn't wrap my head around how to make it sound...
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