My goal here is to - first and foremost - identify all the fans, including their positions, in my own workstation and then all alternatives that can work as drop-in replacements. The HP Z820 seems to be able to use the exact same fans as the newer Z840 and vice versa. A number of these fans should work in the Z600/Z400-series and the older Z800. I cannot confirm this, however, as I don't have a Z800 so my main focus will be on the Z820.
Why bother with this? Delta fans, for example, have a good reputation but are unfortunately known to be noisy so owners with those might be interested in the quieter Nidec options - especially if you do audio work and need a quieter system. Those of us with Nidec fans might be interested in replacing them with Delta's for other reasons - perhaps the better longevity, price and availability are deciding factors. I wanted to document the cooling fans to make things easier for people who want to do the replacement themselves so having the exact model information should keep your workstation within HP's specifications (CFM, RPM etc.). The fan numbering scheme i use in the images is arbitrary. I think information about alternative fans to those i happen to have is somewhat complete but I have no way of knowing if I've identified all variants HP has used in these workstations. I don't have all modifier numbers yet but I will update this post when/if I do.
Update: I went with the option of replacing the entire shroud because the combined shipping costs and rarity of some fans was making things difficult. I got a great deal on eBay on a brand new shroud for the dual cpu option.
The Shroud
The Case
The Powersupply
FAN1, FAN2 & FAN4
Dimensions: 60mm (Blower-style) 4-pin
Model: Delta BUB0712HF
Modifier number: -BE04
HP P/N: 670051-001 REV 1
FAN3
Note: The AVC fan in my shroud doesn't seem to have a HP product number which suggests that the generic model might have the same pinout. I did manage to find the PN from other sources, however.
Dimensions: 60*60*25mm 4-pin PWMModel: AVC DS06025B12U
Modifier number: P063
HP P/N: 670050-001 Rev.A
Alternative Delta Model
Dimensions: 60*60*25mm 4-pin PWM
Model: Delta AFB0612EH
Modifier number: ??
HP P/N: ?? (PN Required for HP OEM model)
FAN5, FAN6, FAN9 & FAN10
Note: The Nidec fans are rated at ~38db while Delta's are around ~45-49db and both run at 3800 RPM. Some sources suggest the Nidec fans use sleeve bearings while others that it's a ball bearing - I'm pretty sure they're sleeve bearing. The 92mm Nidec's have a MTBF of 45.000h which is nearly equal to the 50.000h you are likely to get from the Delta. I could not find the specifications for these exact OEM fans so these are my best guesses based on the specifications of the non-OEM equivalents of the Nidec and Delta fans. In other words, I cannot guarantee the above statements about the bearing, MTBF and noise profile to be 100% correct.
Dimensions: 92*92*25mm 4-pinModel: Nidec T92T12MS3A7-57A03
Modifier number: 2223G
HP P/N: 647113-001 REVA (or REVB)
Alternative Delta Model
Dimensions: 92*92*25mm 4-pin
Model: Delta QUR0912VH
Modifier number: -AK59
HP P/N: 647113-001 REV 0A
Alternative Nidec Model (New revision that should work)
Dimensions: 92*92*25mm 4-pin
Model: Nidec FAN A T92T12MS3A7-57A03
Modifier number: ??
HP P/N: 644315-001 REVB
Alternative Delta Model (Used in Z800 that should work)
Dimensions: 92*92*25mm 4-pin
Model: Delta QUR0912VH
Modifier number: -8C2T
HP P/N: 468763-001
FAN7 & FAN8
Note: FAN7 & FAN8 come as a pair with wires going to the same proprietary 6-pin connector
Dimensions: Dual 92*92*25mm fans to one 6-pinModel: Nidec FAN B T92T12MS3A7-57A03
Modifier number: 2429H F4 / 4X30H G4
HP P/N: 644315-001 REVB
Alternative Delta Model
Dimensions: Dual 92*92*25mm fans to one 6-pin
Model: Delta QUR0912VH
Modifier number: -BL3H
HP P/N: 644315-001 REV 0B (or 0A)
FAN11 & FAN12
Note: The powersupply contains two identical Delta fans of the below model, these were found in the 1125W PSU and are likely also to be found in the less powerful 800W PSU. Given that Delta built these power supplies I seriously doubt any other fan manufacturers are used.
Dimensions: 80*80*25mm 4-pinModel: Delta QUR0812SH
Modifier number: -HE00
HP P/N: None