Underfloor heating with fireplace: keep floor warm or let cool for lower gas usage?

Question

Hello everyone, I'm new to the forum and I have one question. I have underfloor heating throughout the house, gas powered. Area about 110m. ground floor and first floor. In the guest room, I have a thermoregulator installed that controls the ambient temperature. I also have a fireplace in...

szymonjasiu · Answer

It's better to keep it on all the time than to turn it off and take breaks.
If you have a properly made system, your underfloor heating should have weather control - you can use the automation to change the heating curve in the periods when you use the fireplace.
If your system does not have weather control (implementation unacceptable at today's prices of energy carriers) - you have limited adjustment possibilities (thermostatic heads - read the necessary gymnastics at least 2 times a day for you)
The controller with the mixing valve, actuator, and sensors costs from 0.9 k, so it can even be installed in a solid fuel boiler.

If you only have underfloor heating, your controller should have a capillary filled with concrete in the floor and measure the temperature there.

Regards

Grzegorz Siemienowicz · Answer

Interesting.... how did you calculate it. And what does the fireplace have to do with the outside temperature according to which the weather forecast is controlled? Can you explain it to yourself first and then to others in the topic? P.S You sign as MSc. so .....

szymonjasiu · Answer

I do not have to calculate anything, the floor system is characterized by high inertia - it is better to reduce the temperature of the medium and not allow the floor to cool down. This is a matter of course for the heating industry.

So when Freddie76 is burning in the fireplace, then the regulator can disconnect the floor heating and the floor will start to cool down. So it's better to heat all the time by lowering the parameter than to turn off the system completely. In one of the threads you write "Hi, he does not understand that maintaining a constant temperature is not the same as heating up to temperature in a short time" so you probably understand what these systems are all about?

Having the appropriate knowledge, you can get weather control for underfloor heating even by burning in a solid-burning boiler or a fireplace with a water jacket. This is elementary knowledge for the heating industry - I'm surprised that such a simple system raises questions for a specialist like you. Maybe it's time to learn something (basics) or stick to your industry? (a question for you).

A properly made system has weather control for the low-temperature circuit (underfloor heating), and if there is such a high-temperature circuit (radiators). If a car electrician takes care of such a system and assembles the components "how's it going", then strange flowers and questions come out later. Most of the older installers install mixing systems with a thermostatic head and ask the investor to increase or decrease the temperature of the medium manually depending on the external temperature - read that the user is responsible for weather control. It ends up setting the factor higher than it needs, and all potential savings go to waste.

As a MSc. I will be happy to teach you the basics of selecting devices and automation for these systems. In short, it's never too late to learn. Maybe I can learn something from you too. I am waiting for constructive conclusions and ideas for the main plot.

Grzegorz Siemienowicz · Answer

1) The amount of heat loss is ...... linearly proportional to the temperature difference. It follows that a warmer room will radiate more heat than a cooler room. Is not it obvious.
2) If there is another source of heat in the room, the automation should correct the underfloor heating so that there is no increase in temperature and thus an increase in heat loss. (point 1) ;
3) In most cases, it is not necessary to maintain a constant temperature throughout the day and there it is worth (for savings) to temporarily lower the temperature. Problems arise with underfloor heating due to its inertia and not due to economy;
4) I will start talking about weather control if you know what impact the following has on the heat collection from the building in windless weather:
a) lowering the temperature by 5°C;
b) maintaining the same temperature but rainfall and wind 5 m/s;
c) wind 15 m/s.
Until then, our considerations about the weather are pointless (mine takes into account temperature, precipitation and wind).
5) Only in heating devices where the efficiency is inversely proportional to the temperature of the central heating medium (heat pumps, condensing boilers) there is a (limited) sense in using the weather forecast. In solid-burning boilers and older-type gas boilers, the weather indicator is an unnecessary gadget that harms and does not help. You should know this very well and ..... above all, know why it is so.

szymonjasiu · Answer

ad 1,2,3.
I see that you share my opinion from the first statement - that is, it is better to heat the floor constantly, but with a reduced parameter to avoid inertia. This solution is more advantageous than intermittent heating. In addition to inertia, economy is also a plus. It is better to warm up the building by 3 degrees than to warm up from the beginning.

ad.4,5
They are definitely not linear relationships!
Even the simplest weather controller constantly measures the temperature outside and the temperature in the room, based on these parameters it selects the temperature of the medium flowing in the floor heating system.
A good controller, if it cannot raise the temperature to the one requested by the user for a certain period of time, will shift the heating curve in parallel to obtain the desired effect (times of controllers on/off are probably coming to an end).

The environmental factors you write about will never be noticed by the potential user. The designer and installer should make the system in such a way that it meets the assumptions in wind, frost, snow and rain.

There is a basic criterion that you haven't mentioned or COMFORT.

In your opinion, the floor should have a constant temperature both at -15 and +10 outside? As part of gymnastics, do you think the user should spin the thermostatic head experimentally with each temperature change?

So it makes sense to use such systems in solid fuel boilers.
If the heat source is not particularly controllable, it is enough to add a buffer - to store heat during combustion at high efficiency, and then use the slow cutting through weather control.
Today's systems are often built from multiple heat sources, then weather control also increases comfort.
Even with a traditional gas boiler, I prefer a weather control system + thermostatic heads to a boiler + on/off controller system. Of course, we are talking about a building, not a 40 m2 apartment.

I don't know how it looks in your industry - I mostly run condensing boilers. Even when modernizing, it is worth preparing a system with weather control, each boiler will have to be replaced, and everything indicates that the one with the highest efficiency at the lowest heat load. I know these dependencies very well. Larger buildings, even with a solid fuel boiler, have weather control. You say it doesn't make sense, yet designers and contractors build these systems that way.
As a curiosity, I will tell you that to each Termet boiler it is enough to add an external sensor for PLN 70 (even to an open chamber for 1.8 k) and you can already use the weather-controlled system.

Please correct spelling mistakes
mod - mirzo

Grzegorz Siemienowicz · Answer

You write about four different temperatures that are not and do not have to be related to each other or are related to get benefits (sometimes apparent).
Most traditional boilers have the highest efficiency at nominal power and not at the minimum, i.e. at a specific temperature and flow rate in the combustion chamber. (this is T1).
In most traditional boilers, the exchanger is a concurrent system and this determines it.
In solid-burning boilers, the size of the furnace and air intake, etc., etc.
The temperature of the CO medium (T2) depends on:
a) power at which the boiler operates;
b) exchanger efficiency;
c) flow rate of the CO agent and its temperature.
There is also a mixer in the floorstanders that lowers and regulates the temperature T2a.
T3 is the room temperature - we set it. We can obtain it both when we have a lower or higher temperature T2 (depends on the surface of the heat exchanger (radiator or floor), temperature and operation time. For radiators, thermostatic heads are used (should be for economic reasons).
The external temperature T4 is theoretically needed to set the lowest central heating temperature (e.g. in condensing boilers) to obtain the highest efficiency and still be able to heat the house.
And here is the paradox:
It is impossible to economically heat a house with the lowest temperature.
Between the efficiency for 50/30 and 60/40 temperatures there is a difference of .... 1.5% for a monthly gas consumption of 300m?, it is currently PLN 9 per month
but ......
a) in the case of 50/30, the CO factor is pumped much longer when using room regulators than in the case of 60/40, and the operation of the pump (electricity consumption) eats up all the savings because the cost of non-stop work is PLN 30 per month, i.e. if by increasing the temperature in the condensing boiler with 50/30 to 60/40 we will reduce the operation time of the central heating pump by 50%, it will pay off anyway :!:

heat with a higher temperature;
b) it is impossible to temporarily lower the temperature because the time of additional heating is .... very long. This forces uneconomic heating with a constant temperature around the clock.
All "heating curves" in gas condensing boilers are linear and controlled by linear temperature sensors. Offset and slope steepness are set.
Auto-adaptation protects only against cooling down of the house. It is a few simple lines of code in the boiler micro-controller program.

P.S
Everything I write:
a) I know and understand the principle of operation;
b) I have the knowledge to convert it and simulate it theoretically;
c) I checked at least some of them in practice.

szymonjasiu · Answer

One of your statements contradicts the other. The outside temperature is not constant! So the temperature that the current weather forecast counts for is also not constant. It is uneconomical to heat with a constant temperature around the clock. Heating curves will not allow such a case as you describe. Imagine February +8 in the day and -5 in the night do you think the weather will choose a constant temperature? The rule here is very simple: Good automation selects the temperature of the heating medium in order to achieve the set temperature in the building. After reaching it, it does not turn off the heating, but it lowers the temperature of the medium, waiting for the building to gradually cool down! If the temperature inside drops by the set value, the whole process starts again. And so on... Isn't it simple? According to you, unfortunately, it looks different, you say that it is impossible to limit the factor in time because the reheating time will be long. Maybe someone with experience can chime in here? Since you write that you know the principle of operation, why don't you answer the question of the founder of the thread Freddie76. It asks whether to let the floor cool down or not? His whole house has underfloor heating. I replied that in my opinion you should leave the floor on all the time, but lower the factor for the time of heating with the fireplace, if there is a need for it. I will add that the creator of the thread has a condensing boiler. I look forward to constructive requests and your feedback regarding the question in the main thread. You describe a lot of theoretical foundations and obvious things, e.g. about a mixer in underfloor heating. This is obvious even to a layman in the subject of underfloor heating. Whereas control This mixer causes problems for most installers. They assemble ready-made systems of well-known companies that have manual control. In practice, the user initially changes the temperature in the mixer, then leaves it higher than necessary. This is the installers bug I'm pointing out. I propose weather control with this mixer. The cost of the controller, valve, actuator, and sensors is currently 0.9-1.3k, so the expense is relatively small compared to the potential benefits. Of course, you can use solutions dedicated to individual boilers. A decent pump can consume less energy per month than you state. Congratulations on your theoretical knowledge if you are able to calculate it all. After four semesters of mathematics (University of Technology) and three semesters of thermodynamics (classes, lectures, laboratories), I would not be able to cope with such a challenge. I heard during training in the field of automation that leading manufacturers of controllers are not able to calculate heating curves knowing the parameters that you provide - are selected experimentally. So I see that you have a bright future ahead of you in theoretical matters. However, when it comes to practice, it is sometimes worth opening your eyes to economical and proven solutions. Take into account that there are ready mixer + weather forecast systems in the commercial offer at a catalog price of about 4k. However, if no one asks about such solutions in the warehouse where you buy them, then such a product is only available in the catalogue. Again, I stand by my opinion: If the entire building has floor heating (and in addition a condensing boiler - this is the case), the best solution will be weather-controlled floor heating. Comfort and savings. And that's about it. Please correct spelling errors mod - mirzo

mirrzo · Answer

All condensing boilers, or their vast majority, are equipped with electronic circulation pumps, so your arguments are useless here. However, you don't know the subject. Added after 20 [minutes]: Yes, I agree 100%

Grzegorz Siemienowicz · Answer

You still misunderstand.
1) The weather sensor affects only and exclusively the temperature of the CH factor leaving the boiler.
2) The temperature in the room is controlled based on the temperature sensor in the room and not the outdoor temperature sensor :!:

.
Underfloor heating catalog . It is the regulators controlled by temperature sensors in the rooms that select how much CO factor should be taken from the central heating system to achieve and maintain the temperature in the room. For them, it does not matter whether the medium has a temperature of 45 or 55 °C.
After all, probably everyone knows (should) that in order to maintain the temperature in the room, as much energy as escapes must be supplied.
The formula for energy in this case is simple:
Q=m*c*?T
and according to this formula, the temperature controllers in the room will select the amount of CO factor that will be needed.
It is only in order to improve the efficiency of the condensing boiler (improve energy recovery from flue gases) that the temperature of the CO medium is reduced.
Reducing the power and temperature of the CO medium in older type gas boilers is harmful and reduces the efficiency of the system same as in solid fuel boilers. This is because they are completely different efficiency charts
If anyone has doubts, let the fireplace with a water jacket heat at the current temperatures with the temperature of CO in the fireplace jacket at 40 ° C.
I hope this is clear to everyone.
If, as it is written in the subject, the fireplace fires up, the automatic control of the CO factor supply should automatically limit the CO factor supply to the heating in this room so as not to exceed the set value set on the thermostat.
Mirzo :
Explain to everyone:
1) What is an electronic pump;
2) Why are they used;
3) How and on the basis of what factors it is controlled.
I hope this doesn't overwhelm you.

P.S
I was also taught thermodynamics and mathematics at PW (labs, exercises and lectures) I passed without any problems and you can see that I know something else

.

szymonjasiu · Answer

1. The temperature in the room should be constant regardless of external factors 2. As for uncontrollable solid-fuel boilers, I wrote that it is enough to add a buffer. The main thread concerns the condensing boiler - I still don't know what the theory specialist's opinion is on the main topic of this thread. As for solid fuel boilers, it is clear to everyone in the industry that condensation in these devices must be avoided. 3. Your lecturers should be proud of you. From what I remember from the training in the field of weather automation Honeywell and Kromschneider were not able to mathematically calculate the heating curves - they selected these curves experimentally. And yet I see that everything can be counted, only the appropriate theoretical arguments are enough - congratulations on your knowledge. You have embarrassed serious corporations ...

Grzegorz Siemienowicz · Answer

In one of the threads, I described in detail how to determine the heating curve for a heated object due to the external temperature. It could easily be calculated but ..... construction is the field where there is a very large imperfection of workmanship. The biggest problem is thermal bridges, which are not foreseen in the design of the facility. A safety factor is established for them and therefore the power of the heating devices is increased in the project. P.S I also wrote that all heating curves are useless because they are controlled only on the basis of the outdoor temperature sensor and do not take into account the wind, precipitation and air humidity, i.e. other factors that often have a greater impact on heat loss through the building than the temperature itself. Anyone can empirically verify that these factors are no less important for heat dissipation than the change in outside temperature. Therefore, the savings resulting from the change of curve 1 to curve 2 are immeasurable and are supposed to improve the well-being of the owner-clicker, who can boast that he has something to click on.

mirrzo · Answer

genius Have you thought it over? Do you know how a drizzle or downpour or snowflakes affect the sensor's temperature measurement? At IMGW, thermometers for temperature measurement are placed in booths. Just to avoid other factors affecting the correct measurement. The sensor housing is just such a booth. You can do the experiment if you are inquisitive. Besides, you're confusing two concepts here: temperature measurement by an outdoor temperature sensor and heat loss through the building.

Grzegorz Siemienowicz · Answer

You are increasingly convincing me that you have no idea how a condensing boiler works and why temperature reduction is used. Therefore, I do not know how training and qualified service technicians are conducted. In the heating curve, the lowest possible temperature of the central heating medium is selected, at which the central heating system is able to balance the heat losses of the heated object. This is used to recover as much energy as possible from the condensation And that's the whole definition The outside temperature is only one of the factors affecting the rate at which an object loses heat If you have any doubts, contact an engineer constructing a condensing boiler to explain it to you pathologically.

mirrzo · Answer

Here you are right that it is one of the factors, but I still insist on the thesis: It is the room regulator that gives the signal for the boiler to work, if the noise of the wind blows the heat out of the building, and the outdoor temperature sensor indicates how much the boiler should be heated to supplement the lack of this heat. It's simple, isn't it I have. It turns on, it's warm, you pay for gas. And so around

Freddie76 · Answer

Well, you talked and I still don't know whether it's better to keep the floor warm while heating with a fireplace or let it cool down. What will be the difference in gas consumption during keeping warm and heating after cooling down.

szymonjasiu · Answer

I already answered you earlier - it's better to keep the temperature.
You can temporarily limit the parameter of the factor in the room that the fireplace heats up (controllable head is needed on these circuits or another solution).
Better to hold than let it cool.

Regards

mirrzo · Answer

I also think it's better to support the floor. This is due to its high inertia. Today you warm it, and only tomorrow you start to feel it. Today you finished warming it, tomorrow it starts to get cold. Briefly.
And how long do you heat with a fireplace during the day?

Freddie76 · Answer

It happened that the temperature was higher than the set temperature all day because of the fireplace heating.

Grzegorz Siemienowicz · Answer

It will use less gas when machine will turn off floor heating. The paradox is that the automatic machine should cut off the floor heating itself, after all, it is controlled by the temperature sensor in the room I don't understand why you don't.

mirrzo · Answer

I do not know what boiler and regulator it is, but there are many solutions that allow you to turn off the thermostat function in them, e.g. for the time of burning in the fireplace. What about the rest of the rooms? I didn't read how you heat them (Freddie76): fireplace with DGP?

saskia · Answer

The rest of the rooms are really important.
If the adjacent (door) rooms have radiators, we will never control the floor heating properly.

With electric floorboards, double thermostats are also used, one sensor in the floor and the other on the wall.
A few posts above, you discussed the control of the underfloor heating, whether it is better to keep heating continuously or intermittently, so I think both sides are right.
By using a double room thermostat with a sensor on the wall and floor, too low medium temperatures (improvement of boiler efficiency) and continuous operation of the boiler can be avoided, and excessive cooling of the floor (inertia) can be avoided.
I know from personal experience that few use double thermostats, especially in water floor tiles (basic error, in my opinion).

Added after 9 [minutes]:

The whole thing with a double thermostat also works so that we can independently set the floor temperature (screed or other material), we can set the room temperature, the temperature of the heating medium on the mixer and the temperature of the boiler (the most economical one).
Changes in the room cooling time only change the boiler operation time between breaks, nothing else.
The weather forecast then slightly affects the operation of the boiler, so it can be eliminated.

Added after 9 [minutes]:

Flooring with a fireplace, as many have already mentioned, works best with a buffer.
Control errors and overheating of the system are then avoided and the heating operation is extended after the fireplace goes out

szymonjasiu · Answer

We are constantly digging into the subject of the room in which there is a fireplace, or the neighboring ones that the fireplace affects. The floor loops in the mentioned rooms should be properly controlled - the rest of the system (the whole house is only a floor floor) works unchanged.

So I propose once again to reduce the parameter of the factor in these rooms to prevent the floor from cooling down. This can be done by various methods - manually on the heads (cheapest) - or automatically - controllable heads. Alternatively, another solution on the mixer. It should be remembered that the costs of advanced solutions may exceed the potential profits.
If comfort is the main criterion and costs play a lesser role, each loop in the circuit can be controlled separately. Such automation is recommended for heat pumps, then + 5% on the investment is not a big difference.

So think about whether you really need to interfere with your system while smoking, or maybe just move the environmental sensor (boiler controller) to another room (consider wireless) so that it is not affected by the fireplace.
Turning off the floor heating system completely during these periods is the worst solution.

Regards

Underfloor heating with fireplace: keep floor warm or let cool for lower gas usage?

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