Calculations of installation operating parameters every DeltaT=10°

I have a question,
when calculating the installation parameters, it is assumed that it will work, e.g. 75°/65°, i.e. ΔT = 10°
I understand that the assumption of 75° is quite logical and understandable because the stove will give as much as we want, but this return worries me.
When designing the installation, how do I know that there is a temperature drop of exactly 10°?
I have been designing my own installation for a long time, both on paper and in various programs, and always this assumption...

Can someone explain this to me? Or come closer to an explanation? I am inquisitive by nature

There are two issues here. One is transferring and giving energy to water. The formula from elementary school is E=m*c*ΔT. Therefore, in order to transport a lot of energy, we must either ensure a large flow of water "mass" (i.e. use large cross-sections or high flow rates) or a large difference in inlet and outlet temperatures. Thick pipe is expensive. Fast flow means noise and resistance (pump power). So from this point of view, it would be best to use a large "delta T", e.g. 85/30, and use thin pipes and a weak pump... Unfortunately, there is also a second factor, i.e. the power of the radiator as a radiator. It is approximately proportional to the difference between the average temperatures of the circulation and the air. This means that an 80/60 radiator at 20 degrees in the room has a 50-degree difference and some power P, while the same radiator at 60/30 has a 25-degree difference and only half the power! So, large delta T = larger and more expensive radiators. From the point of view of pure economics, it is necessary to calculate the minimum sum of the costs of pipes, pumps and radiators. In addition, there are also "comfort" factors - the lower the radiator supply temperature, the less convection and the better the climate.

Hello. ΔT 10°C results from the fact that you assume such power consumption by the radiator, i.e. its surface at 20°C air in time, that it will reduce the temperature of the return water by this value of 10°C, so you can also easily calculate the power delivered knowing what the flow is. water. each radiator catalog gives the power of the radiators at different ΔT and different temperatures, and you determine these parameters based on what type of furnace you have, its temperature and efficiency on water. and what heating solution you intend to use in the system. i.e. what parameters does your radiator need? temperature into temperature and the heating surface or radiator power. And by the way, it cuts; e.g. 85/30 and use thin pipes and a weak pump... Unfortunately, there is also a second factor, i.e. the power of the radiator as a radiator. It is approximately proportional to the difference between the average temperatures of the circulation and the air. That is, an 80/60 radiator at 20 degrees in the room has a 50-degree difference and some power P, while the same radiator at 60/30 has a 25-degree difference and only half the power,
small pipe diameter and weak pump mean low power! Moreover, 80/60 will not be a difference of 50°C [/b]

jack302 wrote:

Moreover, 80/60 will not be 50°C difference

Powering the radiator at 80/60 (i.e. with a circulation temperature difference of 20 degrees) gives an average radiator temperature of 70 degrees and a radiator-ambient difference (20) of 50 degrees. Buddy, forgive me for being honest, but if you don`t understand such basic concepts, don`t create confusion on the topic.

William Bonawentura wrote:

Unfortunately, there is also a second factor, i.e. the power of the radiator as a radiator. It is approximately proportional to the difference between the average temperatures of the circulation and the air. This means that an 80/60 radiator at 20 degrees in the room has a 50-degree difference and some power P, while the same radiator at 60/30 has a 25-degree difference and only half the power!

Okay, and I guess that explains the premise, let`s just say I get it :D

I will also ask if it is warmer outside and, for example, the calculated heat demand from 1000 W will drop to 500 W, i.e. Q will be equal to Q/2.
Then I understand that:
1) the calculated return temperature will be higher than the calculated one because the radiator will not cool down???

2) if there is a thermostat, it will reduce the flow rate ΔT will be further 10°C???

3) without a thermostat, the temperature in the room will increase and instead of 20° it will be, say, 23°

4) the furnace automation will reduce the supply temperature by a few degrees.

And the question is which (or maybe all) of my alleged statements are true?

seal78 wrote:

I will also ask if it is warmer outside and, for example, the calculated heat demand from 1000 W will drop to 500 W, i.e. Q will be equal to Q/2.
Then I understand that:
1) the calculated return temperature will be higher than the calculated one because the radiator will not cool down???

2) if there is a thermostat, it will reduce the flow rate ΔT will be further 10°C???

3) without a thermostat, the temperature in the room will increase and instead of 20° it will be, say, 23°

4) the furnace automation will reduce the supply temperature by a few degrees.

And the question is which (or maybe all) of my alleged statements are true?

Let`s start with the fact that the theory presented above concerns the case when the flow of the medium through the radiator delivers as much heat as the radiator is able to give off. When the thermostatic valves start operating, the flow is strongly dampened and, as a result, the average water temperature in the radiator drops significantly. This means that ΔT increases but the flow decreases significantly and ultimately the power output also decreases. Lowering the boiler outlet temperature (furnaces heat air, boilers heat water) is a completely separate topic (weather regulation). Certainly recommended for the hydraulic conditions of the installation. Point (3) is also true.

William Bonawentura wrote:

Let`s start with the fact that the theory presented above concerns the case when the flow of the medium through the radiator delivers as much heat as the radiator is able to give off. When the thermostatic valves start operating, the flow is strongly dampened and, as a result, the average water temperature in the radiator drops significantly. This means that ΔT increases but the flow decreases significantly and ultimately the power output also decreases.

The above is clear and understandable - thanks.

William Bonawentura wrote:

Lowering the boiler outlet temperature (furnaces heat air, boilers heat water) is a completely separate topic (weather regulation). Certainly recommended for the hydraulic conditions of the installation. Point (3) is also true.

Of course, it was supposed to be a boiler, not a furnace, I don`t use it every day and the terminology is there somewhere, but not always on demand :)

Can you expand on "recommended for hydraulic conditions"??
And how will such a reduction in the power supply affect the underfloor heating controlled by the mixer (with a stick sensor), in my opinion, as the supply temperature drops, the radiators are cooler, but the underfloor heating is still fed by the mixer at the set temperature of 45°. So it`s as if there has been no change. Is it supposed to be like this or should the boiler`s weather control be connected to the mixer control in some way?

Moderated By DonRomano:

The post was reported. Are these stamps in the title necessary? If not, please correct.

Generally, it is better if the supply temperature is reduced rather than the flow in the radiator. We have lower pump flow, noise in the valves.

William Bonawentura wrote:

We have lower pump flow, noise in the valves.

One sec,....
when the temperature is reduced?


EDIT.
Okay, OK, I got what I meant.

Friend, William Bonawentura, forgive me for being honest, but it`s clear that you don`t understand many things yourself, and you lecture others and, moreover, you write enigmatically. It`s obvious that the theory, even in an academic version, has no imagination. And arguing and raving about the fact that furnaces and boilers are different is usually just bullshit. .and there are so many factual errors .inferiority complex?
p.s. I`m quoting you
Generally, it is better if the supply temperature is reduced rather than the flow in the radiator. We have lower pump flow, noise in the valves.
I didn`t know that when the temperature decreases, the pump flow decreases and the noise in the valves decreases. What nonsense is this?!

Added after 3 [minutes]:

If you want to help, help, but don`t write such nonsense, my friend, because it would cause unnecessary confusion, isn`t that what you wrote?

jack302 wrote:

Friend, William Bonawentura, forgive me for being honest, but it`s clear that you don`t understand many things yourself, and you lecture others and, moreover, you write enigmatically.

I guess I have to write "in capital letters". If the installation operates with power lower than the design power, it is better to lower the supply temperature of the radiators than to maintain a constant temperature of the medium and strongly throttle the flow with valves. Now clear?

IT`S OBVIOUS FOR EVERYONE FROM THE VERY START, but you keep talking and talking about obvious topics all the time, you can`t admit it with dignity. When you explain something to someone, do it in such a way that it is clear to those who are not familiar with the topic and you are not. you can do it, maybe the knowledge is weak, but the message is worse. Regards

Moderated By DonRomano:

The post was reported.
Please correct errors and resolve disputes via PM.

Gentlemen, for the conditions selected by our colleague, i.e. -20, the radiator will be 70/60 dt 10`C. Now the installation is working.

Installation with standard radiator valves:
The installations are then qualitatively regulated, i.e. we reduce the temperature at a constant flow. Then the temperature difference remains quite constant, but we cannot lower the temperature too much because it will not heat the domestic hot water in the boiler or, what is more common now, we must maintain 60`C on the return to the boiler due to condensation and then we have to turn the valve on the radiator anyway because too hot in the rooms.

Installation with thermostats:
The installations are then regulated qualitatively and quantitatively, we change the temperature and flow. The thermostat itself adjusts the radiator parameters to the needs of the environment - it cannot regulate indefinitely, its possibilities are limited to the maximum radiator power that the radiator can achieve, i.e. if you have 65 in the installation and you need 75, the thermostat will not provide more flow to equalize the power demand. . It works great when there is a large radiator and limits its power to the needs, reducing the flow, and we regulate the quality because if the thermostat closes almost completely at 75, we lower it to 65 so that it opens 3/4. Moreover, the thermostat adapts to the individual needs of the room (in the past, this partially replaced the orifice).
In installations with thermostats, cooling is often greater than the assumed dt10`C on the radiator, but this strictly depends on the installation parameters.

In installations with thermostats, the flow is variable and may drop to the minimum, i.e. the flow through the hot water boiler and bathroom radiator (usually there is no thermostat).

Why is this happening?

Because when the installation is started and the temperature in the room is lowered, the installation operates at maximum efficiency, then when the temperature in the room reaches e.g. 20 (that is what we want), the thermostats will start to close to maintain the set temperature and the hydraulic system of the system will change. all you need to do now is open the window or door, it will blow harder on one side of the building, or the sun will shine on another side of the building and other all these factors will affect the operation of the thermostat and the operating parameters of the installation will change. The thermostat will work automatically on all these factors. In a regular installation, you have to turn off the radiators and set the boiler temperature every hour.

ad. 3 Yes


ad. 4 If the boiler is weather-controlled depending on the outside temperature.


Yes, extra.
There used to be temperature tables that determined the installation parameters depending on the outside temperature, and a number of additional tables were created taking into account sunlight exposure, wind strength, and others.

Therefore, the temperature of the installation is raised, e.g. by 3`C, and the regulation is left to the thermostat, which will later cope with changing conditions.