Heat losses valves (heat network)

[Lora]

Hello,

I was interested in the thermal losses at 215 valves of a heat network (water heated by inceniration of urban wastes).

For my calculation, I followed the following procedure:
- calculation of the hi with the formula of Mac Adams I find about 4800 W / m²K (according to the flows).
- Depending on the thickness of the pipe: calculation of the overall exchange coefficient Ui with
λsteel = 45 W / mK and he = 25 W / m²K (I don't know if this value is correct: it is air that I need to be at 40 ° C with negligible ventilation).
- calculation of the heat exchanged at the wall for different water temperature depending on the time of year.
I considered a temperature in the valve chambers of 60 at 40 ° C.
60 ° C During 4 months
50 ° C During 3 months
40 ° C During 5 months

I find a thermal loss in the 215 valves of 441 198 KWh per year.

In a quotation requested, they calculated the hconvection of 11.13 W / m² ° C and the peeling with the emissivity coefficient of the steel and the Bolzamn constant and found a result of 2 629 812 KWh per year. While redoing their method I find a result of 328 732 KWh (with hiding = between 5 and 7 W / m²K following T of water.)

I think I do not take into account the losses in the slabs below which are the valve chambers. Do I have to calculate the temperature inside the rooms according to the outside temperature and the conductivity of the floor ????

thank you very much for your answer

[dedeleco]

Do I have to calculate the temperature inside the rooms according to the outside temperature and the conductivity of the floor ????

A priori this underground system heats the earth over years over several meters and so if the rooms are not ventilated strongly, my answer of general physicist is yes.
The losses will decrease with time, the years of heating the earth, in my opinion ..

It is also necessary to evaluate the actual ventilation leaks according to the closing of the plates or slabs of the rooms!
Not easy and so it would be good to test by measurement on a real system in operation, for months, even years, depending on the actual quality of replacement plates or slabs, because it is easy to mislead.
The valves could be insulated with a thick removable insulation ??
Or the rooms and slabs isolated, without thermal bridge ???