Optimal Length of Underfloor Heating Loop: 95-100m, 18x2 Pipe, Redesign Considerations, 16x2 & 120m

I wonder what the optimal length of the underfloor heating loop is.
Will the installation with 95 - 100 m loops made of 18x2 pipe work well for loops of similar length? Is it worth redesigning the installation so that the loops are shorter?
Most materials from underfloor heating system manufacturers recommend not to exceed 100 m for a 16x2 pipe and 120 m for 18x2. But what lengths are optimal?

What do you mean by optimal in this case?

If you give no more than 120m, the installation will be correct, i.e. you will get an even temperature distribution in a given loop. The point is that if you give shorter loops, you have more and more expensive ones, because more distributors, but it is possible to turn off specific parts of the floor. Question: what for?

By "optimal" I mean ensuring economical operation of the circulation pump and adapted to heat pump supply, i.e. operation with low supply and return temperature.
I quickly calculated for the largest room based on KISAN materials (http://www.is.pw.edu.pl/~zenon_spik/Ogrzew2/Pod%B3oga%20materia%B3y.pdf).
assumptions:
heat loss: Q = 1600 W
floor area: F = 50 m?
I calculate the approximate heat flux density: q = Q / F = 32 W / m?

flow temperature: t_z = 33 ° C
return temperature: t_p = 28 ° C
internal room temperature: t_i = 20.5 ° C
(the above assumptions result from the optimization of the installation for work with a heat pump - low temperature of the upper source)
I calculate the average temperature difference between the heating medium and the room temperature: t_śr = (t_z + t_p) / 2 - t_i = 10 K

The room will have a parquet floor or panels - I assume R? = 0.05 m?K / W
In table 6 there is no data for t_śr = 10 K, but approximating the data by regression method, I get the heat flux density values q at 32 W / m? for the pipe arrangement module a = 0.01 m.
I calculate the thermal efficiency from 1 mb of coil: q_l = qa = 3.23 W / m.
I calculate the coil length: l = Q / q_l = 495 m.
You can see that I need 5 loops of 99 m to cover the heat loss.

I calculate the water mass flow: G = 0.86 Q / ?t = 55 kg / h. From table 7 I read the water velocity and unit pressure drop. There is no data for 18 x 2 pipe, but for 16 x 2 and G = 54 kg / h we have: R = 23 Pa / m and w = 0.13 m / s, and for 20 x 2.25 and G = 54 kg / h we have: R = 5.2 Pa / m and w = 0.066 m / s so I estimate that these values will be: R = 10 Pa / m and w = 0.1 m / s.
I calculate the local resistances (assuming the coefficient of local resistances ? = 0.5 for a single coil knee, the number of about 60 knees per coil and the unit local resistance of the coil Z_1 = 5 Pa): Z = Z_1 ?? = 150 Pa.
I calculate the resistance of water flow through the coil: ?p = R l + Z = 1150 Pa.

The calculated value seems strangely small.
In addition, the recommended minimum water flow rate in the coil v = 0.15 m / s, and the calculation is 0.1 m / s.

What is wrong?

Manufacturers specify the maximum lengths according to their calculations.
Practice and good school requires loops up to 80 mb, all in equal sections.
6-8 mb / sq m depending on where the loops are laid (zones around balconies, bathrooms require more, the center of the room less).
Distributors with rotameters, of course, to see and be able to balance flows.
greetings

irus.m wrote:

Practice and good school requires loops up to 80 mb, all in equal sections.

I assume that the length of 80 meters refers to a 16x2 pipe, and for 18x2 it can be more. I'm right?
What does this value actually mean. Certainly, the resistance to flow through the loop (?p) is important, but is there anything else?

irus.m wrote:

Distributors, of course, with rotameters to see and be able to balance flows.

Only if at a flow rate of 54 dm? / h, i.e. 0.9 dm? / min, do the indicators show anything? Can you choose them for such small flows?

Greetings!