a. where the ductwork is (i.e. is the supply duct in the space being conditioned)
b. How humid is the air in the space.
c. Is the air being recirculated.
d. How important are the running costs
e. How long is the ductwork run.
f. Do you need additional acoustic insulation (Break out and break in)
etc
Some people recommend insulating supply ductwork to prevent condensation on the outer skin.
We do it for energy costs and condensation prevention, although contractors trying to save a few quid(sorry pounds or dollars) seem to get away with it.
Insulation works out at about £10/m2 which isn't a lot compared to the whole installation.
Also, if you run cold ductwork in voids, the heat in the void warms the supply air and you don't achieve the desired cooling rate.
Also, if you are recirculating the air (to save money), it can also be beneficial to insulate. We had a situation where the return air passed through a very warm duct and picked up heat which we had to cool down even further therefore costing more money.
When speaking of duct loses, you need to consider Location, Location, Location. If in a conditioned space, then I would say no, duct insulation is not required because of thermal regain which underpins any discussion of where ducts should be located within the facility. The higher the thermal regain factor, the better the location. .The best places for ducts are in spaces that are intentionally heated, or that retain lost heat exceptionally well. If ducts are located within the conditioned space, any lost heat or cooling is not really lost (although it may be necessary to rebalance the system to attain proper distribution within the facility. All other duct locations have regain factors ranging from 30% down to essentially zero, and should be insulated.To the extent that thermal regain occurs, duct energy losses are reduced.
