Piping thermal loss coefficient

Dear Paul

I want to assign a correct value to the parameter "Piping thermal loss coefficient". After reading the help and the Technical Manual I have some doubts:

• In the SAM Help it is said that "The coefficient specifies the number of thermal watts lost from the system per pipe surface area, square meter of aperture area and temperature difference between the fluid in the piping and the ambient air (dry bulb temperature)." I don't understand this sentence. What area is considered? The pipe surface area, the aperture area, both,…?

• As I read in the Technical Manual for the SAM Physical Trough Model, eq. 2.26, the piping thermal loss coefficient is used to calculate a HTF temperature drop. As I know how much the temperature drops, I would like to fix this temperature drop in the design point, but I don't know how SAM calculates the total piping surface area (if this area is the one applied in the formula), so I can't determine the correct value of the piping thermal loss coefficient. Can you explain me how I can know the value of the total piping surface area or how SAM estimate it?

Moreover, as I seen, it is only considered the hot outlet temperature drop, but it is a fact that also drops the cold inlet temperature drop. It is considered this drop in another thermal loss?

• I have estimated, with hand calculation, the pipe thermal loss as a coefficient of thermal power loss instead of temperature loss. Is there any way in SAM to define this power loss instead of temperature loss?

Best regards

Igor

Dear Igor,

For the physical trough model, SAM applies the coefficient to the calculated piping surface area for the headers, runners, and non-HCE piping (between receivers and cross-over piping). The trough reference manual explains how SAM calculates the dimensions of these pipes. The losses are calculated for both the hot and cold sides of the header and runner piping. The only way to adjust these losses is to change the piping thermal loss coefficient.

The description in Help is misleading, and I will correct it.

Best regards,
Paul.