14 m hull diameter, assuming single hull, and L/D of say 10 (ideal is 7 but no one is building that kind as far as i know 9-10 seems to be more common and that doesnt really add much drag) Means about 140 m in Length.
Submarine roughly have 3 kinds of "displacement" namely Surfaced which basically shows Pressure hull volume, Submerged which Surfaced+Ballast tank volume or ROB (Reserve of Buoyancy) and Envelope volume, which is Submerged + water in Free Flooding section.
If one read Capt Jackson's lecture of Submarine design. There is bit more into that :
NSC or Normal Surface Condition is basically the weight of the fixed equipment, structure etc in the submarine including variable ballast, consumables etc which to keep crew alive and submarine in equilibrium position.
Standard displacement is NSC+Fixed ballast. Fixed ballast or known as "Lead mine" is as name suggest lead blocks used to balance the volume provided by the pressure hull (Principles of flotation you want to keep the density of your sub = water, too low and you float, too heavy, you sink)
Submerged and envelope is basically what i described above.
14 x 130 m dimension provides about 21551 Cubic meter of volume. That is approximate for your Envelope displacement. As for the submerged displacement This typically 93% of the envelope, so 21551*0.93 = 20042 metric tonne Submerged.
Now what is Chinese consideration for ROB (Reserve of Buoyancy) ?. Which directly dictates the volume of the MBT (Main Ballast Tank) Historically Western powers e.g US have lowered the "standard" for ROB, Nowadays it's typically 10 % or less. Russians always go big due to their fear of mines about 32% and for Typhoon as they desire icebreaking capability, 48%.
If Russian consideration is taken then the MBT volume would be 20042*.32 = 6413 cubic meter. Thus leaving the Pressure hull volume which ideally should be same as the weight 20042-6413 = 13628 metric tonne for Surfaced displacement. If US/Western consideration is taken then the Surfaced displacement would be about 18000 metric tonne.