LukasV

Thanks. So basically all the pipes are always fully opened and running. And what have you done is that instead of using the thermometers from the ASHP producer (I guess all ASHP producers offer thermometers to control the pump) you use the Loxone gadgets through which the Loxone starts/stops the ASHP or tell the pump how how is inside so the pump can modulate output (when possible by this model). Thus basically you could do the same with thermometer that would come with pump to control the pump... but you already have a Loxone and you didn‘t wanted another controllers so you are transferring the data to the pump through Loxone. Correct?

Thank you. I understand that. But that is about the maximal possible energy (maximal potential energy output) or so I guess. When the water flows constantly (no automatic turn-off by the heat pump) at some moment the slab will have the same temperature as the water... at that moment the slabs gets no more energy, no more heat. Same is it with heat/solar gains, at the moment when the sun shines on the floor the floor becomes so "hot" that the UFH can not give it any more energy and the water flows back at the same temperature or even at higher temperature ... that is the princip how UFH can transfer solar gains into other rooms. Of course there is always some heat loss thus the slab is always little bit cooler (or have some capacity for another energy) thus the UFH give to the slab some energy always (unless solar/inner gains). But this theory is about the fact that there is some strict limit at when no more heat goes from UFH to slab/house. And according to me (this is how I understand that) the limiting value is the Mean water temperature. just one more example: We have a room in total vacuum. No heat gain, no heat loss. There is a running UFH for a long time. Flow temp is 30, Return is 25. Thus mean is 27,5. I suppose that the whole slab, whole air, every wall, everything there have already reached the same temperature 27,5. The Flow is hotter thus it has the „strength“ to give some more heat to the slab. But at the same time the return is cooler thus the same amount (the temperature difference between flow/return and the surroundigs is the same) of heat is taken back to return flow thus there is null heat transfer into the room.... no matter what pipe distance is or how long the UFH will run. Correct? Then it means that.... no matter how "tight" (small distance) the pipes in the bathroom are (as suggested above) I will never be able to reach in bathroom temperature 25 when the mean water flow temperature for the house will be for example 22,5 (Flow 25, Return 20). And on the other hand when I would limit the mean to 22,5 then I could be sure that the house will never overshoot the temp 22,5 even without any other regulation (W-C, thermostat or so) so I could heat 24/7 with this setting and I could be sure that I always have 22,5... when less then the UFH heats more to reach it quickly again when more (solar gains) no heat transfer occurs until the temperature drops back again. ------------------ !!!! This is how I understand it. And that is also the reason why I wanted to use such a primitive and easy set-up with flow/return temp to control UFH. And now as I am thinking about it... it seems that I can use it though. I do not need to set the flow temp higher to compensate the heating pause. I could hold this setting. When the ASHP runs it has higher output into water than the house needs so the water in the buffer will heat up until whole volume reaches the requested 25. During that time the water circulates 25/20 and the house has 22,5. Then come the pause, ASHP stops, the water in tank gets colder and colder without heat source and with heat loss of the house until the ASHP starts again. During that time the UFH heat 25/20 too so the house is also 22,5. And I could also easily control overheating by the valve! At the moment when I will have a huge solar or inner or other gain it will have no impact on flow water temperature (it is fixed by mixing valve at 25) but the return will get hotter because less heat can go to slab/surrounding with these gains(thus also the mean goes higher which suggests that in some time the house would/could overshoot/overheat to new maximum given by new/higher mean). And exactly at that moment when the return water temp overcomes 20 will I switch the valve thus I will close the water inlet from buffer tank and only the water which is in UFH will circulate until the return temp drops again under 20. When it comes I open the valve again and I am heating again from the tank. I cannot store the solar gain in the buffer but it is not a problem. The heat from sun will be stored in slab/walls so no problem. Correct? Please say that I am correct! This is the solution that I was looking for. So easy. I need just one mixing valve, one closing valve, one circulating pump and one thermometer on the pipe. No weather control, no thermostat, nothing, only one temperature in the house the whole year. Except the fact the I will not be able to heat with it bathroom to higher temp so for morning/evening heat up I will need to use the some electric towel rail (or wet one preheated with coil from DHW), but that I can survive. Omg, that's it! -------------------!!!!

Thank you guys. Just a few words... Good idea but not workable.... You are missing few things... 1) Some way of heating is always necessary. At least here. 2) No one wants to live in a house that has air heating (sorry all you guys in the US, but comfort is something else) 3) Passive house setting have null influence on the cost of DHW production 4) Self-made wet UFH is one of the cheapest way (if not the cheapest at all) how to get a heating "source" Take all these for in one and you will find out the best result == cheap ASHP for DHW and wet UFH, no matter what the type of the house it is. A calculator from local supplier says complete material for UFH for me is less than 4000EUR. Cheap ASHP is also 4000EUR. Buffer/Storage tank with some features is 2000 EUR. With 10 000EUR + one day of my work and I have everything. Is it too much? What is cheaper...? I am sorry, the numbers were just an example. Thank for tip with pipes but please just a simple question... Flow 28, Return 23 (thus Mean 25,5), Pipe Spacing 15cm - can I ever reach room temperature 28? ..... Yes? / No? Flow 30, Return 25 (thus Mean 27,5), Pipe Spacing 30cm - can I ever reach room temperature 28? ..... Yes? / No? Flow 30, Return 25 (thus Mean 27,5), Pipe Spacing 15cm - can I ever reach room temperature 28? ..... Yes? / No? Flow 32, Return 27 (thus Mean 29,5), Pipe Spacing 30cm - can I ever reach room temperature 28? ...... Yes? / No? The question is/was ... which temperature sets the limit for maximal room temperature? Is it Flow temp? Or Mean temp? I thought that the limit is given through Mean temp, thus when from the tank goes Flow 26 and Return is 21 (Mean 23,5) to never overcome 23,5 in whatever room, then even when I put the pipes in bathrooms 5cm aside I will never reach the wanted 26 there for example...... Or is it Flow temp?, thus narrow pipe spacing can give me a chance to charge the bathroom more to reach 26 and to limit the rest of the house with wide piping space to lower temp? But I do not know this and I cannot find an answer. Thank you in advance. Thank you, everything looks like that I will/must go with Loxone too because obviously I will not be able to find out how to set the UFH pump to stop in time. I am just scared about its ability to drive an UFH. I used it at former home for everything but we had radiators so it was much easier to control radiator valves with it. Please, can you tell me little bit more about the setting which you use? ...I do not mean software settings but hardware... how do you control it? You have a Loxone "radiator" valve on the pipe to manifold or what? This could really help me and it could probably deal with my "problem" at all when I would know how to control it with Loxone. At their webpage they present it like to you a valve actuator for every loop which is unfortunately 1) terribly expensive 2) ineffective because I do not want to close the loops - I want them always open to distribute the heat over whole house.

Thank you everyone and I apologize. It was a hard day and I had a lot of thoughts to the topic that I tried to communicate. Probably worked it not good enough. Andehh hit the nail perfectly. I am not planning to build “old-fashioned” house but one that could be called “house of the future” (no it is not more expensive, one must just think about everything more thoroughly because the set-up is more complicated and no „standard solutions yet exist“). The house will be in passive standard or even better. Everything will run on electricity only. I will use cheap ASHP for heating and DHW. A big (as large as I can place) photovoltaic will supply the house, some Tesla and the battery (also big enough) and of course MVHR. Everything will be driven through some kind of AI controller (I will probably start with Loxone miniserver until appliances with Matter standard (https://en.m.wikipedia.org/wiki/Matter_(standard) will be available and able to incorporate other appliances (ASHP, A/C and so) that these days do not comply (at least the cheap ones that are good enough for my purpose and also cost efficient). I want to supply all these things with my own electricity from PV and I will buy electricity from supplier ONLY THEN when I am not able to supply enough amount myself and only then when it will be cheap (when there is oversupply on the market) In winter I cannot supply everything from PV so I must use also a market electricity thus I will run the heating and DHW only on low prices from SPOT (I must and want to do that to have an option to sell/trade the electricity) which are cca 16 hours a day. From that 16 hours I will need up to cca 4 hours to heat DHW with prospective 6kW ASHP (big family, lot of young kids that love bathing) thus only 12 hours a day is left for heating. And yes I need to heat in bursts to do that. I do not want to talk about „what is the optimal temperature in the house“ it is highly dependent on customs. What I want / would like is to have the possibility to have a higher temperature in bathroom. I do not care about my shower-time… something else are my kids who can spend an hour in bath playing (thus not sitting in hot water). I know and understand that it is not easy to reach different temperatures/zoning in passive house. Despite that I am looking for possibility how to reach that in bathrooms. I will use 6kW HP for a house where I expect heat loss cca 3-4kW at lowest temp. There will be also a 5-split A/C with heating possibility and a fireplace, thus I am save even in brutal winter. Normally everything will run on the HP only and the fireplace (for a mood purpose only) will help with heating DHW when used. A/C is ready for summer cooling when needed. I understand that the slab hat a huge capacity and I know that the heat flow will stop when the temperature match. What I am afraid of is the match "level". Let assume that I want 20 in rooms, to reach that I need flow water temp 23,5 (return 18,5) when heating 24/7. But I will heat only 12 hours a day. This means I must use flow temp 24,5 (twice as much heating strength). And what I have read is that the UFH have cca 6 hours delay. Let suppose I am heating 10-13, then DHW 13-17 (to have a DHW for bathing), then 20-08. Saying that the night heating is 12 hours... and during that time the temperature will probably overhshoot (in the time when I want lower time for a good sleep!). The setting will have no matter what also a buffer tank for a fireplace thus it makes no sense to heat the slab directly from the heat pump and overshoot the temp at night when I can heat the water in the tank a from the tank heat the UFH regularly 24/7. But to be able to do that I must be able to control the heating from tank. If I will not find some easy solution with return temp, I will use Loxone WC curve to control these valves. I just wanted to find some easier solution that need no other inteligence, just a return temp monitoring. I see no possibility that something like thermostat or so could lose such a problem. What I do not understand is what influences the highest possible temperature in a room (in my case bathroom). As I said I want to heat 24/7 from the buffer tank at the level to reach (let say, whatever) 22 in rooms but 24 in bathrooms. This means that I will use flow temp X with return flow Y. Let say 24,5 and 19,5. I can lean the UFH pipes in rooms with 30cm distance and in bathrooms with 10cm distance. The mean temp of UHF is then 22. All this means that in long time I will reach and hold 22 in rooms .... but will the lover distance in bathroom help to heat it up to 24? I do not think so... when the mean temp is 22 I see no possibility to reach 24 in bathroom even if the distance of pipes is lower than in rooms. So this means that I muss send to the UFH water with mean temp at least 24 (to reach 24 in bathroom) and I muss reduce the flow of heating water to rooms to compensate the higher mean water temp to get lower temp in rooms and probably also make the pipes distance bigger. correct? I understand where you aim. But no. I apologize but those are bullshits. No one wants uniform temperature in every room. Everyone wants the temperature that suits that room. Thus everyone wants to have a lowest temp at bedroom, moderate in living/kids rooms and highest in the bathroom. I understand that the better insulation the house has the more complicated it is to reach that. I am not overthinking I guess. I am just looking for the way how to reach it (as much as possible) in very well insulated house. I can accept the the rooms will have uniform temperature (even the bedroom - my wife will be happy and I can survive it) but I definitely want to find a way how to have higher temp at baths. And I know why I want it. I could use an electricity sourced radiator to overcome the standard temp during an evening. But this is inefficient and I would love to reach such a temp whole day, not just during the evening (I do not like to poop when my ass is freezing). So I am looking for a way how to do that with UHF. I am able to increase the overall temp of UHF temp to reach that or lay the pipes tight, what is necessary. And in other rooms I will compensate with flow rate to reach lower temp there. But I am not sure what is the best way. I hope it is clear now. I will use the buffer tank to heat 24/7 because it is better for me (and I am expecting invigoration of on/off pump in few years). The direct heating from HP to UFH driven by WC curve will not be able to reach stability I guess. The problem is how to controll the water that goes from buffer to UFH and how to set it to have a higher temp at bath than in living room. Any idea? Thanks!!!!

Well, this is not a regular system, this is something like miracle, something world-changing... unfortunately. Thank you John, I appreciate it. Unfortunately, I am afraid that I am not able to set a WC curve properly. ... It will be somehow "variable". I need/want to use SPOT prices for electricity. Saying that means it also that I cannot use electricity during peak prices, thus cca between 8-10 and 17-20. On the other hand I want to use as much as possible the price drop around noon. The household will run from the battery during the peak time, but not the heating/DHW, which should run on max during price drop. That means that I will not be able to heat cca 6 hours every day. I understand that the slab hat a really huge capacity... this is what I also want to use. But the ASHP (or other sources) are too much stupid (at least I think) to be able to compensate such a "blackout" everyday. Just imagine... on one day we can have 0 Celsius outside and cloudy .... I could lose something like 5x4,5kWh of heat from the house. On the other day we can have 0 Celsius outside too but sunny day... I would lose also 5x4,5 kWh of heat but would gain 5x5 kWh from sunshine. Then the peak price ends and I start heating again... it is still 0 outside but the pump gives to the house just the amount that is needed for 0 and do not compensate the loose from the last 5 hours (in the second example it stops heating sooner thanks to the higher return flow as I got more heat than lost). This could happen a week in row and I will get cold in the house. Basically the WC curve must be set to higher than needed so it would be able to compensate everyday's "blackout". Dealing with overheating is simple with the WC curve in ASHP - it will stop heating thanks to the higher return flow. Problem is (at least I think) to deal with the heat demand - because I am the one who set the demand through the WC curve. 1) I need the pump to run at maximum output around the noon (to have the best COP and use the cheapest electricity) - this cannot be done through the WC curve, I must store the energy somewhere (in the water/buffer tank or in the slab). 2) I need the pump to compensate the off-period during the peak-price-period, which is also not possible through the WC curve (or not easily done). I should set it higher and wait until the return flow stops the heating. But how high should I set it? Every grade above necessary minimum means a lose of COP... But (and on the first place) I cannot say how higher I should set it as it will be strongly dependent on the weather conditions (as said above). The house is good insulated (will be) at passive house standard thus I probably need just something like 1-3 grades above "normal" WC curve and it will be able to compensate everything during the day (6x4,5=27kWh lost in a day during blackout at lowest temp, with heating 18 hours means the need to compensate 1500W per hour == 1,25 Celsius of WC curve above "normal"). So this I could do with WC curve when I set it little bit higher than is necessary ...cca 1,25 above calculation should be enough ... the rest will do the sun and the internal gains and the return will stop it in time.... So we know now that anyway it is necessary to know the return flow temp when the ASHP must stop - the pump knows it and it should not be a problem to determine that also for other pumps. Unfortunately I do not have experience with ASHP so I do not know what the difference should be to stop the pump, but I can ask others or the manufacturer. Easily in such a scenario it is not important whether it will be the ASHP return temperature to stop heating or "another sensor return temperature" that stops the heating. This means the I get nothing from using the pump's software to regulate the heating. I can do it self and only thing that I need above is one sensor and one valve (and yes this function from the pump I will lose) which costs like nothing. We also know that I cannot use a pump software to boost the heating storage during lowest-price-period ... In any case I must override its setting and force the pump to run at max during that time. 3) The most important thing I did not mentioned ... which is a problem in 90% passive houses (thus every house in future) and will be problematic for a long time yet wenn the people will not think enough.... but I want to have a fireplace in that house. And to be able to enjoy the atmosphere I must use the fireplace with water-heat-exchanger anyway. Thus the buffer tank is nothing "more" for me, it will be there anyway. And I will happily use the heat stored there not only for DHW but also for heating, to use it in the best possible way. This all means that it is better/easier to store all the energy in that buffer tank than to boost the slab in the noon. It will also solve the problem 1) because I can use on/off pump and not to overpay (at least 2-3 time the on-off price) for the inverter and run the ASHP at maximal output during noon into water (or anytime I want it to run... which I can moderate according to electricity prices and actual COP - both easily to calculate). And also I can use the system that every WC moderated pump uses to stop heating (ie the return flow temperature) to disconnect the heating the UFH from the tank = thus to solve problem 2. Everything I need to such a perfect system is one sensor and one/two valve/s (plus one buffer tank that will be there in any case)... which costs not even 1% of the overpay for the inverter ASHP. Plus I need the know how of the manufacturer or owners of UFH/ASHP how to set it..... and that is what I am asking. ..... let say that the bathroom (8m2) have a heat loss 200W... UFH can have output 6-20W/K/m2 (according to centers)... and I want to have in bathroom 24 degrees (other rooms should be 22). This means that optimal for rest of the house is to have 25/19 (I cannot go lower than 25 with "my" ASHP). And now comes the question again. With 25/19 the highest temperature is 25 but the mean temperature is 22.... Am I able to heat the bathroom to 24???? I am willing to place the pipes even 1cm aside but will it help? IMHO the centers is important for the overall heating capacity (ie low-insulated houses to heat up the rooms) but the mean water temperature is important for the maximal possible temperature in the room. Thus now whether how tight are the UFH pipes, if I will let the the mean 22 (25 flow, 19 return) the room will not heat over 22. Thus I muss set the flow/return mean to at least 24 to heat bathroom to 24 and the rest of rooms must be adjusted with centers and flow to fall to 22. Correct? Or can I run even 25/19 with tightly leaning pipes to reach 24? .... what should be the return temp to stop heating... this should be something like constant from flow temp and every user/owner of ASHP should be able to answer this.... at which delta T from flow temperature stops the pump working? As what I know/read I suggest that delta T to stop pump is 5 degrees. Thus I can set the flow temperature to x (waiting for the bathroom/mean temp) and set the valve to disconnect heating at flow-5 temp. Then I would just need to adjust flows to other rooms to lower overall heating capacity and the system is done. Can anyone help?

Hi guys, I got a lot of info here to the possible system. I especially appreciate the infos about systems some of you which hold system perfectly tight with just one thermostat with tight hysteresis. But I got another game-changing idea. Unfortunately I am struggling because I cannot find a room/place, where to place that thermostat. Every single possible place, that I have thought about, seems that it can be unpredictably under strong influence of heat sources. I obviously must make the system somehow different. I will use a buffer tank, this will help me to disconnect the ASHP from UFH. I can charge the tank anytime I want, how much I want in advance (which will help me to ameliorate the electricity price spikes or outside temp drops.. And the UFH will be supplied with hot water from that buffer tank based on the needs of the house. Charging the tank is easy task with temperature measuring in the tank, the rest will do the ASHP self. But the house... ouch. 1) theoretically I could use weather compensated heating with a lot of thermometers (one in every room?) and apply a logic on them, that would work with mean/median temperature for example. Then I can have a chance to get something like real temperature/real house needs and regulate with low hysteresis like you do. At least, I hope so. But that would be also really really expensive solution and possibly unstable. 2) But I got another idea - I could set a flow temperature from the tank to UFH to a fixed value. I can calculate the highest UFH flow temp needed in cold winter and set it accordingly. With that flow temp I can heat all year around. What the problem is, is the fact that I muss find a correct timepoint when to stop heating from tank and just circulate the water that´s left in UFH to prevent overheating. I hoped I could use a return temperature - this represents the ability of the house to accept more heat (with the flow temperature fixed and aimed air temperature). ie. when the house is fully saturated for the aimed room temperature, the return will rise - and that can be the point when I could disconnected buffer from UHF, thus no more heat from buffer, just circulating UHF water. But WHAT is that correct return temperature that represents the full saturation?? Let`s assume I want a room temp 22, the mean water temp (mean of flow and return) must be 2 degrees higher to satisfy the house need in -12 degrees (heat loss 2600W, UFH with 200m2 heating area, ie with usual 6W /m2K must be mean temp at 24 to have a 22 room temp) and I would set the flow temp to 26. This means that when the flow is 26 and return is 22, then I am heating just enough to cover the actual heat loss. When I start the circulation, I could get something like flow 26, return 18, which in time gets to 26/22 and would go further until having 26/26 (then the home accepts no more heat and would be reaching to a room temp 26). I would prefer to get to 26/22 and then to make a little booster, then close the valve a let the UHF circulate until next heating period will come. So in that case I could stop heating at for example 26/24 and then wait some time (let say until next hour or until return drops enough). But that can be a solution for this situation, but I am looking for something universal. When the outside temperature is +10, I would need mean temperature only 0,8 above room, thus with 26 flow, I would need the return to be only 19,6. ie ((26+19,6)/2)=22,8 ie 0,8 above room. At that moment stopping the heating when the return temp reaches 24 or more could cause dramatical overheating. So what is the solution? How to set the expected return temp at which I need to close the heating from buffer? Ofc, I know the heat loss et every moment of outside temp thus I could stop it accordingly, but what if the calculation is not enough correct? Can I do it successfully with setting a fixed return temp too? Do I have a solution?.... An example: Flow temp is set to fixed 26, return temp to close the heating valve is set to 24, mean temp when the heating valve closes is 25. Requested room temp is 22. When outside is -12, the heat loss is 2400W, so this setting would need to heat 40 minutes in a hour to meat the heat loss (thus far enough). But it is strong winter. The morning temperature is really cold and hits -5 degrees but when the sunshine starts the outside temp goes quickly to 10 degrees. - It is 8:00 , outside is -5. Heat loss is 2100, I would need delta mean temp 1,6, instead of heating of 60 minutes I would need only 32 minutes to meet the house needs. At that moment, the return would be 20,6, but I will heat more until the return reaches 24 (which can happen anywhere between almost immediately and indefinitely according to house heat capacity and looses). But with simplicity I have boosted the house with cca 2000W more than needed. Because the diference was 25-20,6 = 4,4K - this was the maximal difference, the mean difference is 2,2K. UHF hat an output 1200W/K (over 200m2 area), thus 2640W total. The heat valve closes and waits until next command to open. - It is 9:00, system again opens the valve. Outside temperature is 0 degree. But between 8 and 9 the loss was only 1900W but I boosted 2640W, the return is still above 24, so the valve immediately closes and I am not heating anything, just circulating a hot water in UFH. - It is 10:00, system again opens the valve. Outside temperature is 5 degrees. For that temp I would need only 1400W heat output to meet needs which would need delta mean 1,1 thus heating only 21 minutes. But between 9:00 and 10:00 I lost "on average" another 1600W. Total between 8 and 10 is 3500W and at 8 I boosted only 2640W, thus the return temperature is bit under 24, the heating starts. The necessary heating to reach missing 860W is supplemented quickly and also quickly is reached return 24 because there is not a lot of capacity where to store the energy when the house again reaches equilibrium at 22 with outside temperature 5. Also the sun is up and starts shining inside, that shortens the next booster time again, same as do the family and friend coming inside to celebrate at birthday party or so. In next few hour the suns is making its job heating the house and until sunset no more heating is needed so every opening a valve will find out that the return is at least 24 and close the valve again immediately. With the sunset the return falls and the process comes again. ---- I understand that the numbers are not prefectly correct, the heating/loosing is continuous, not relying just on one temperature at the moment. I am just talking about the principle. That sounds reasonable and really good to me. For that system, I would need just one mixing valve that will keep the flow temp fixed at given temp, one sensor sensing the return temp, one valve disconnecting the UFH and buffer tank and one relay which every hour opens the valve and closes it again when the return temp reaches the preset temperature. The system is self-solving, self-healing, self-regulating. No matter what happens outside or in the house would complicate it. When the house is full of heat, it just closes heating quicker, when it is cold, it heats longer. It supply just enough to keep the temperature totally stabilized without needing anything other like thermostats, specialized weather compensing systems, outside sensors,.... just nothing. It seems so studiply easy that I must be missing something bc otherwise this system would be the best at the world and totaly universal at every house. So what I am missing, what is the problem? Of course the acting of the system is strongly dependent on the house type and its heat capacity - in a wood house the return will rise steadily, in accumulating house it will take its time. But at the end, during the time, it does not matter, the accumulating house will release the stored heat thus the return will have not a change to chill/fall quickly, but in wood house it will fall quickly because no heat is stored. Thus the difference would be just between the length or frequence of heating periods, but would work good in both of the extremes. Also the flow speed of water must be set at some fixed rate... probably somewhere in the middle of possible values. But still seems to me like an ultimate system. What am I missing? Please what do you think about it? Can I use it? How to make it better?

Fair enough, makes sense. Thank you everyone guys.

Hi, thank you for opinion, it is possible to keep things simple when they are simple or ... when you can not do the math. I know that there is a thought to run the UFH with thermostat with low hysteresis. Unfortunately, this is total nonsense. I am aware of that that @Jeremy Harris reached good control with it, but this way is nonsense and should be banned to advise to do this to anyone. Do the math. Heat pump lifespan is limited by "running hours" or "starts". In passive house the running hours are unimportant, we will be dead by the time it reach the maximum. But using a thermostat with low hysteresis (ie 0,1 deg) the only you will get is a cycling heat pump. It will start and stop every few minutes or seconds. No way to reasonably prevent this. And now the math ... regular passive house needs something around 8-10 MWh heating energy in a year, with heat pump it means something like 2,25-4 MWh of electricity per year... it is circa 225-400 Euro per year (contra 900 Euro with heating directly with electricity). But the pump cost is circa 10 000 Euro or more. So you need something like 15-20 years even to payoff the investment to the heat pump!! With the heat pump constantly cycling you will not get even half of that. This way of use makes no sense, it is better to heat the house with electricity directly and heat the water with heat pump boiler. But I need to use the UFH also for cooling in summer, otherwise I would need to use an A/C (cca 5000 Euro) so the investment cost for electrical (dry) UFH + heat pump boiler + A/C would be quit similar like the investment costs for wet UFH with heat pump which can do all of that in one device... but I cannot destroy it too soon. Beside that where should be the thermometer placed? In a hallway? I do not care about the temperature in hallway, I want to prevent overheating in living room meanwhile I heat the kids' rooms enough. As to the option 1),... how do you know that I need a temperature 30 to 35? Which one should I use when I heat 12 hours? When 14 hours? When 16 hours? Should I use the 35 also when I am roasting a goose for 12 hours? Any difference when we are out of house vs. when we are at home and kids are running in living room with dogs and TV playing whole the time or not? How long should I charge the floor this way? How should the fixed flow temp help? Why to heat with 30 both time when outside is -10 or +7? Yes, it is better to use a lower COP and heat the house with cheap price faster than maximize COP and heat with price going from 20 to 150 Euro, but how to use it? I can run the UFH on 42 (or so maximum) few hours a day (when the price is minimal) to charge the slab but that will cause an overheating. I can stop the charging the slab when the temperature in a few rooms reach the max. to prevent overheat. It could be a cost-efficient (not top but good) but again I will get in troubles... during the shutdown the whole family will be in living room, duck is roasting, TV is running, same like kids and dogs... the slab there is not discharging there but in other rooms is. Then the pump/UFH starts again with 35-42 inflow... The living room is reaching the top temp (despite the fact that I am the only one there now) but I can't stop heating because other rooms are still not heated enough. I am waiting for another representative room to call to stop heating. This takes another few hours and meanwhile the living room is overheated because the slab there had a lot of remaining energy and with inflow temperature 35-42 there is no way ho to stop discharging the heat into air there or even to revers a heat flow to other rooms. The comfort would be totally unstable and low. So how to deal with it?

Hi, I am new to this forum but not to the topic and as many of you I am thinking too "how to control the UFH". Here were some systems described that looked that they reached the comfort-efficiency, but, unfortunately, I would say that they lack energy-/cost-efficiency. Probably the best way how to easily reach a stable comfort and solid cost-effectivity is to use the pre-builded weather compensation curve and run the heating 24/7. After proper setting this curve deliver the exact necessary amount of heat and the inflow would have the lowest possible temperature (thus highest COP). Ofc the pump must be connected directly without any blender/buffer or so. ... so this is the way I would probably go. I do not think that it is a good idea to rely on weather forecast so I would use a temperature sensor to provide an accurate temperature instead of forecasted. As our passive house should be in modern style - cube with massive south facing glazing - I am a bit afraid of solar gains... to prevent overheating I would use a south sun-facing weather station. My idea is to use a weighted average from the sensor on the north and the weather station in the sun on south. I guess the temperature from the weather station should have weight about 1/3 - 1/2 (but I must run the numbers first to find out how many solar gains compared to heat loss expect). The weighted average would be the final temperature for the heating curve. Hopefully, this could be enough to keep the temperature stable. This is also a quite effective in terms of energy/cost, but not fully effective. It is much better to run 16 hours inflow at 28 degree instead of 24 hours of 25 degree (the COP will change minimally) but with the price for MWh 60 EUR instead of 150 EUR. With the electricity from spot market I need to let the pump run just something like 12-16 hours a day. And here is the problem... I do not know how to compensate the curve/inflow temperature. Everyday could be different. For example the pump can run 18 hours on Monday, 12hours on Tuesday and 16hours on Wednesday to heat only with a good price. But which inflow temperature do I need?? Let's say I can properly set the curve for 24/7 after which the inflow would be at 25 degree... but then I need to change it to higher to compensate (preheat and warm up) the time when the pump was stopped. .... I know the exact outside temperatures during the day, I know outside temperatures during shutdown and a day-before I know when and how long will the shutdown be... but I must calculate the inflow temperature that will be able to preheat the house before shutdown and warm up the house after the shutdown. How to do that? I do not think that PHPP can calculate the heat loss exactly, if it could, no one would need to titrate the curve... there are also another variables like wind speed, humidity and so. And I am definitively not able to exactly calculate solar and internal gains. Any gains or inaccurate calculation in 24/7 mode would stop the pump immediately as the reverse flow temperature rises so it would be self-controlling, but these gains during the shutdown cause only that the slab will remain with higher heat inside at the end of shutdown period and the subsequent warm up with "hotter" water will overheat the house. I could measure the heat (temperature) in the slab but I would need to do it in many rooms to get a good overview about the amount of heat there and yet it would be extremely difficult to calculate the correct need of heat to be added and according to it necessary inflow temperature. So this is probably not the way. Also except for the weather station in every room there will be a thermostat (the house will be driven by Loxone) so I could do that in the way that when the average temperature in few rooms hits some point I could stop the pump... maybe is this the way how to find out that the warm up is done? Unfortunately, the whole family in the living room during the shutdown would heat the slab there enough that in warm up period (until other rooms would be warmed up too) there would be overheated living room. So this way with thermostat feedback looks problematic too. It is quite problematic although I am now dealing only with weather control and shutdown period problems,.... to deal with internal gains all over the day would be total crazy - although I somehow believe that internal gains cannot be solved be heating anyway (I see the only way how to solve internal gains through MVHR/windows). I am on the way to abandon the shutdown and just buy a bigger battery. With the 24/7 mode I would need something like 2x4 hours "shutdown". With 4,5kW heat loss of the house and ASHP/GSHP it needs only something like 1,3-1,8 kWh per hour under the worst weather conditions ie something like 2x 6kWh electricity from battery (which can be restored immediately when price drops) to cover the most expensive periods of the day. That would be better than loose the comfort ie having cold or overheated house just to save a money. Does anyone have any idea how to solve it and how to find out correct inflow temperature please? Thanks