Valves heat loss - multiplication factors

[mfqd13]

Some time ago, here in this forum i posted a thread asking about how to calulate heat loss from valves. At that time my problem was solved through a document that i attach (see page 6-8, Table 4).

I've used this values, but recently i used them once more and see some strange results and i looked into them a bit more and i concluded that this values turn the results of the heat loss calculations quite big. See example for heat loss in valve:

- Through heat transfer calculations i obtained a heat loss of 300 W/m2
- If my valve is DN150 and from the table mentioned above, the mult. factor is 3,85
- The new heat loss value is 1.115 W/m2

If i have several valves to isolate, the energy save is very very big and i'm starting to wonder if this mult. factors are correct???

I think that if i assume a equivalent area of a valve 1,2x greater than a pipe with the same length and diameter, and using the 1st value (300 W/m2), maybe it would be more reallistic....

Opinions please!!

 

[mfqd13]

Here is the attachment..sorry

 

[BigInch]

No insulation on the valves? Any on the pipe?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[mfqd13]

If you are asking about the pipe before and after the valve, yes it is insulated.

 

[kkala49]

I understand the valve has same heat loss as 3.84 ft of same diameter pipe. The external (uninsulated) surface of this piece of pipe is about 0.62 m2. If heat loss from pipe is 300 W/m2, heat loss from valve with same insulation would be 186 W.
Look into Engineering Sample Problem in the attachment; equivalent length may be more precise than multiplication factor written there.