UFH controlled by return temperature

[LukasV]

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? 

[JohnMo]

27 minutes ago, LukasV said:

will use a buffer tank, this will help me to disconnect the ASHP from UFH.

Ditch the idea you are over thinking it. Ditch the buffer, ditch the thermostat(s). You have taken zero account of floor inertia. Which can be huge. You can simply buffer excess energy in the floor, way more capacity than a water container buffer.

 

Simple - your heat pump already manages the return temp. But it needs to be directly connected. No mixers or additional pumps needed.

 

You set a WC curve to match your heat loss.  The compressor within you heat pump is started and stopped based on target flow temp, a delta T and therefore by default the return temperature is managed. The compressor starts based on return temp, stops based on flow temp control hysterisis.

 

A simple self regulating system is ASHP, WC, UFH manifold. You really don't need anything else. Your room gets solar gain, the floor stops giving out heat, continuous circulation moves the energy elsewhere in the house.

[Alan Ambrose]

Yeah agree - our present place takes a couple of days to get from cold to normal room temperature.

 

What’s your floor build up?

 

Interesting ideas though.

[LukasV]

On 17/11/2024 at 23:00, JohnMo said:

Ditch the idea you are over thinking it. Ditch the buffer, ditch the thermostat(s). You have taken zero account of floor inertia. Which can be huge. You can simply buffer excess energy in the floor, way more capacity than a water container buffer.

 

Simple - your heat pump already manages the return temp. But it needs to be directly connected. No mixers or additional pumps needed.

 

You set a WC curve to match your heat loss.  The compressor within you heat pump is started and stopped based on target flow temp, a delta T and therefore by default the return temperature is managed. The compressor starts based on return temp, stops based on flow temp control hysterisis.

 

A simple self regulating system is ASHP, WC, UFH manifold. You really don't need anything else. Your room gets solar gain, the floor stops giving out heat, continuous circulation moves the energy elsewhere in the house.

 

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?

 

 

[JohnMo]

18 minutes ago, LukasV said:

Can anyone help?

What are you asking? You have lost me. You seem to be trying hard to do something, but no idea what?

[SteamyTea]

I am struggling to follow all this.

 

You seem to want to heat in 'bursts' when the imported energy is cheapest and you also want to heat different rooms to different temperatures.

So if I understand your wants, you are looking at the best method to control it all, is that right?

[JohnMo]

8 hours ago, LukasV said:

That means that I will not be able to heat cca 6 hours every day.

So you need an oversized HP first. Needs to generate the heat demand for 24 hrs in maybe 14 hrs to have leeway.

 

Sunny day or not sunny days. Storage of energy floor is cheap it's also at a low temperature. Once house internal temp and floor temp match, zero heat is out into house. 

 

I would try to find a single thermostat that you can link to a price cap API. Or already had it built in. You place the thermostat in an average temp area say hall.  Ideally you want thick screed, and a 0.1 hysterisis thermostat. In cheap periods you up the thermostat demand temp say to 21, and more expensive times at 20.5 and super expensive set to 16.

 

No need to manage return temps, just keep it simple and understandable.

 

I would also assign an elevated temperature WC curve to heat pump running, this has two advantages less likely to overheat house, when running you get a slightly better CoP.

 

If your not very well insulated you plan wouldn't work full stop.

8 hours ago, LukasV said:

want to have in bathroom 24 degrees (other rooms should be 22

I found a well insulated you don't need anywhere near those temps. Comfort levels vary in the 0.1 degs scale. We find 20 is fine in the day, upto 20.2, then it's getting too warm. In the evening 20.5 to 21 is comfortable any hotter is just too hot.  

 

If you have a battery and smart meter, just get a simple time based tariff. Something like Cosy gives 3 cheap time periods, run house and HP on that. Simple very little cost difference and your wife/husband will not divorce you, when they have been cold all winter, because you wanted to save 50p a day on heating.

[Adrian Walker]

1 hour ago, SteamyTea said:

I am struggling to follow all this.

 

You seem to want to heat in 'bursts' when the imported energy is cheapest and you also want to heat different rooms to different temperatures.

So if I understand your wants, you are looking at the best method to control it all, is that right?

you’re over thinking and over engineering the problem. You want a uniform temperature everywhere. Do you have MVHR?

[Andehh]

OP basically wants to prioritise cheap rate power, which is erratic when you look at the spot rates only! So when the sun shines and wind blows on a winter day and the spot rate falls he wants to hammer the usage as much as possible.... But the following day when it's cloudy, still and cold and prices jump up.... The house coasts through without the ASHP Running. OP is just pushing it as far as he can through design, and whilst complicated if he pulls it off he will average cheap rates then anyone.

 

 

It's the future of smart homes and IOT (heating, fridges, EV etc) , with every appliances tracking prices and hammering cheap rates then coasting through peak rates as much as they can. Much smarter, more complicated but long term leverages renewable very well.... Everyone benefits (except OPEC....!!)

 

I can't advise OP, but we use tomato lifestyle and/or Octopus Cosy to sort of middle ground it. Their cheap periods will be aligned to statistical expectations of energy pricing and passing that in to customers. I then bias our energy usage to those cheap periods.

 

That's why our house, and every room being a thermostat controlled zone, is biased to hammer the ASHP and DHW during those cheap periods... And with my weather comp turned up, heating temps turned up and hotter DHW I lose efficiency/Cop, but I benefit more on the cheap rates.

Edited December 29, 2024 by Andehh

[LukasV]

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.

On 29/12/2024 at 07:56, SteamyTea said:

I am struggling to follow all this.

 

You seem to want to heat in 'bursts' when the imported energy is cheapest and you also want to heat different rooms to different temperatures.

So if I understand your wants, you are looking at the best method to control it all, is that right?

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.

 

On 29/12/2024 at 09:09, JohnMo said:

Sunny day or not sunny days. Storage of energy floor is cheap it's also at a low temperature. Once house internal temp and floor temp match, zero heat is out into house. 

 

I would try to find a single thermostat that you can link to a price cap API. Or already had it built in. You place the thermostat in an average temp area say hall.  Ideally you want thick screed, and a 0.1 hysterisis thermostat. In cheap periods you up the thermostat demand temp say to 21, and more expensive times at 20.5 and super expensive set to 16.

 

No need to manage return temps, just keep it simple and understandable.

 

I would also assign an elevated temperature WC curve to heat pump running, this has two advantages less likely to overheat house, when running you get a slightly better CoP.

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?

 

On 29/12/2024 at 09:38, Adrian Walker said:

you’re over thinking and over engineering the problem. You want a uniform temperature everywhere. Do you have MVHR?

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!!!!

 

Edited December 30, 2024 by LukasV

[Mike]

3 hours ago, LukasV said:

The house will be in passive standard or even better.

The Passivhaus standard was specifically set at a level that means that no conventional space heating system is required. The idea is that the cost saving by not installing space heating more-or-less pays for the cost of MVHR and other enhancements required to reach the standard (at least in Germany, where it originated).

 

In other words, you are overthinking. Just add an electrical heater - or at a blanked off conduit so you could add one later - in each bath / shower room. Or even embed some UFCH pipework for extra reassurance, but there should be no need to actually use it, so leave it unconnected.

 

[Adrian Walker]

8 hours ago, LukasV said:

No one wants uniform temperature in every room. Everyone wants the temperature that suits that room. 

 

 

That's not true at all.  Having a uniform temperature in every room is the best way to have a comfortable home. And UFH (with a slab floor) and MVHR is the best, and IMHO, the only way to achieve this.

[Andehh]

It's such personal preference, I prefer cooler bedrooms, warmer kitchen lounge and warm bathrooms.

 

We also designed a really special home, but it's a bastard for efficiency. Kitchen has huge glazing so needs extra heat, children's bedrooms have 4.5m ceilings with Mezzanines so don't heat up like the rest of the house. Other 1/3 of the house is normal.

 

Thermostats per room and hammering cheap periods using tomato lifestyle / cosy type means it all works well enough, and is still only £150 a month to run including daily dishwasher, washing drying machines etc. Also a large background usage due to so much IT and server etc.

 

 

[JohnMo]

Sorry this is just a load of waffle, stop trying so hard to save a few pence a day. To do what you want with a 6kW heat pump is a non starter. Flows sub 25 are a waste of time planning for because ashp don't go that low, min flow temperature is generally 25.

 

I will not be responding again to this thread as it's just making hard work of a simple problem. But my thoughts are.

 

3kW max heat required, install 6 to 8kW heat pump. Thick screed floor to buffer heat, charge floor with heat on a cheap tariff over night, charge batteries on same tariff. If required run ASHP on battery in evening. Ideally if you had around 25kW of battery you would never run out of cheap electric.

 

Problems you will have is defrosting of ASHP at 3-4 Deg and below, limiting power input. 

 

Different temps in different room, you embed more or less pipe.

[Gone West]

10 hours ago, LukasV said:

No one wants uniform temperature in every room.

What you mean is, you, don't want a uniform temperature in every room. I designed and built my own house, to better than minimum PH standards, which resulted in a uniform temperature throughout the house. It was very comfortable. I now live in an old stone bungalow, and have the whole house at the same temperature. I could never go back to the old, uncomfortable arrangement where walking from one room to another meant a change in temperature.

[jack]

I disagree with those who say all rooms need to be the same temperature in a Passivhaus class dwelling.

 

For example, it's generally fairly easy to maintain lower temperatures (during winter) in upstairs rooms. We have no heating in the bedrooms and it's naturally 2-3 degrees cooler upstairs than downstairs at this time of year.

 

The coldest ground floor room in our house is the TV room. It's the only room with carpet - the rest of the ground floor is polished concrete, which is much better at transferring heat.

 

As well as using different pipe spacing, you can throttle down the flow rate to rooms where you want less heat. You won't get massive temperature differences, but even a couple of degrees can be noticeable.

 

All that said, I agree with those who say you're overthinking it, especially as far as the challenges you think will arise out of using off-peak energy. Our slab temperature has varied by a total of 1.2 degrees over the last two months, with a typical daily fluctuation of about 0.2 degrees. That's with an extremely simple control setup in Loxone that doesn't even take into account outside temperature (the ASHP does weather compensation).

[marshian]

3 hours ago, JohnMo said:

Sorry this is just a load of waffle, stop trying so hard to save a few pence a day. To do what you want with a 6kW heat pump is a non starter. Flows sub 25 are a waste of time planning for because ashp don't go that low, min flow temperature is generally 25.

 

I will not be responding again to this thread as it's just making hard work of a simple problem.

 

I'm reminded of the ultimate race horse designed by a committee

 

 

Yes I know camel racing is a thing but that's not the point I'm making

[LukasV]

Thank you guys. Just a few words...

 

On 31/12/2024 at 03:02, Mike said:

The Passivhaus standard was specifically set at a level that means that no conventional space heating system is required. The idea is that the cost saving by not installing space heating more-or-less pays for the cost of MVHR and other enhancements required to reach the standard (at least in Germany, where it originated).

 

In other words, you are overthinking. Just add an electrical heater - or at a blanked off conduit so you could add one later - in each bath / shower room. Or even embed some UFCH pipework for extra reassurance, but there should be no need to actually use it, so leave it unconnected.

 

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...?

 

 

 

On 31/12/2024 at 08:56, JohnMo said:

Sorry this is just a load of waffle, stop trying so hard to save a few pence a day. To do what you want with a 6kW heat pump is a non starter. Flows sub 25 are a waste of time planning for because ashp don't go that low, min flow temperature is generally 25.

 

I will not be responding again to this thread as it's just making hard work of a simple problem. But my thoughts are.

 

3kW max heat required, install 6 to 8kW heat pump. Thick screed floor to buffer heat, charge floor with heat on a cheap tariff over night, charge batteries on same tariff. If required run ASHP on battery in evening. Ideally if you had around 25kW of battery you would never run out of cheap electric.

 

Problems you will have is defrosting of ASHP at 3-4 Deg and below, limiting power input. 

 

Different temps in different room, you embed more or less pipe.

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. 

 

 

On 31/12/2024 at 10:17, jack said:

I disagree with those who say all rooms need to be the same temperature in a Passivhaus class dwelling.

 

For example, it's generally fairly easy to maintain lower temperatures (during winter) in upstairs rooms. We have no heating in the bedrooms and it's naturally 2-3 degrees cooler upstairs than downstairs at this time of year.

 

The coldest ground floor room in our house is the TV room. It's the only room with carpet - the rest of the ground floor is polished concrete, which is much better at transferring heat.

 

As well as using different pipe spacing, you can throttle down the flow rate to rooms where you want less heat. You won't get massive temperature differences, but even a couple of degrees can be noticeable.

 

All that said, I agree with those who say you're overthinking it, especially as far as the challenges you think will arise out of using off-peak energy. Our slab temperature has varied by a total of 1.2 degrees over the last two months, with a typical daily fluctuation of about 0.2 degrees. That's with an extremely simple control setup in Loxone that doesn't even take into account outside temperature (the ASHP does weather compensation).

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.

[JohnMo]

53 minutes ago, LukasV said:

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?

There area few variables there. Mean flow temp sets the energy being input into the floor. As below 

Simple heat output graph for floor heating, you will have extend some of the number scales downwards. Just draw across from mean flow temp to pipe spacing to get W/m².

 

Room temp is just an output of kW input, kW consumed and how long you apply the energy for. But a heat pump is unlikely to run 24/7 even if you wanted it to. It will manage its self and cycle when energy demands is lower that energy output.

 

With a floor heating system you don't need a buffer.

 

Parts needed are manifold, pipe clips for pipe, eurocones for pipe to manifold coupling and a couple of isolation valves. You don't need mixers or pumps, do all direct from the heat pump. You don't need actuators you don't need a buffer. I spent less than £1k on UFH parts for a 192m² floor.

 

Running a single zone system, you get whatever room temps you want. By adjusting flow rates and how much pipe you bury in the floor. Set weather compensation up you don't need a thermostat, running a time of use tariff just use a 0.1 Deg thermostat to stop and start the heating, the 0.1 will limit under and over swings on temperature.

[jack]

21 hours ago, LukasV said:

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.

 

One of the Loxone relays is connected to the thermostat input of the ASHP.

 

The logic that controls the relay is driven off two temperature sensors: one on the surface of the slab underneath the kitchen island and the other behind a light switch in the upstairs landing. 

 

There's some simple logic that allows minor overheating downstairs during the cheap overnight period if the upstairs temp is too low.

 

Weather compensation is set on the ASHP.

 

I had grand plans to use weather forecasts and external temperatures as inputs to allow more heating to take place during the cheap period, but the current system works so well that I haven't been motivated to change since it was installed nine years ago.

[MikeSharp01]

2 hours ago, jack said:

it was installed nine years ago

Cripes is it nine years already?

[jack]

15 hours ago, MikeSharp01 said:

Cripes is it nine years already?

 

Yup. Knocked down at the end of 2014, moved in a few days before Christmas 2015.

 

Feels like the blink of an eye.

[LukasV]

On 31/01/2025 at 21:08, JohnMo said:

Room temp is just an output of kW input, kW consumed and how long you apply the energy for. But a heat pump is unlikely to run 24/7 even if you wanted it to. It will manage its self and cycle when energy demands is lower that energy output.

 

With a floor heating system you don't need a buffer.

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!

-------------------!!!!

[LukasV]

On 01/02/2025 at 17:45, jack said:

 

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?

[jack]

2 hours ago, LukasV said:

Thanks. So basically all the pipes are always fully opened and running. 

Yes.

 

2 hours ago, LukasV said:

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). 

 

The ASHP is expecting an on/off signal from a switch within a thermostat, which can be provided by the ASHP manufacturer or anyone else. In my system, the thermostat switch is replaced with a Loxone relay, and the temperature sensing part of the thermostat is replaced with temperature sensors connected to Loxone.

 

If I had only a single temperature sensor and programmed Loxone to provide only simple on/off controls based on whether the sensed temperature was above or below a temperature set point, Loxone would act exactly like a simple mechanical thermostat (albeit with less hysteresis).

 

2 hours ago, LukasV said:

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?

 

Sort of. I always planned to use Loxone, so it was always my plan to control the ASHP via Loxone. My ASHP came with a controller (for adjusting settings), but not a thermostat.

 

I wouldn't say I'm transferring data to the pump. All the pump sees is the switched signal telling it to heat or not heat the house. It doesn't know the house temperature or anything else about what's caused Loxone to change the relay state.

 

I still use the controller in my setup, for things like settings and the timer function. Loxone only takes care of the decision about when to heat.

 

I could in theory replace the controller with a modbus interface that would allow me to properly control the ASHP via Loxone. That would give me some useful extra flexibility, such as:

• Changing the heating curve depending on, e.g., electricity pricing and predicted exterior temperatures.
• Controlling hot water heating with more intelligence. For example, at the moment, I rely on the ASHP's controller to set periods for heating and hot water. The programming is extremely limited and it's a massive pain to change. With modbus, I could take complete control and do smart stuff like:
  • Keep more hot water on standby when there are more people in the house
  • Ensure that the ASHP doesn't start heating the hot water tank late in the evening, especially before the cheap rate kicks in, and instead waits until late in the cheap period to start, thereby ensuring maximum hot water is available first thing in the morning.

The modbus extension is several hundred quid though, and I'm not convinced it's plug and play. 

 

There are ways around some of these limitations. For example, I've thought about having a relay switch between the tank temperature sensor and a fixed value resistor to fool the ASHP into thinking the tank is cooler or hotter than it actually is. I could then better control when the ASHP starts a hot water heating cycle. I might get around to it eventually, but it's some way down the to-do list.

 

Despite the simplicity of the control system it keeps the ground floor of the house at a pretty constant temperature. This is the temperature of the slab under the kitchen island over the last three weeks:

 

 

The highest temperature is 22.1 °C  and the lowest is 20.3 °C.

 

The temperature upstairs (where there's no heating except for short period each morning in the bathrooms) is lower and does vary more with the external temperature. It varied between 17.3 °C and 18.8 °C over the same period.