Is pumping away from chillers technically okay?

[nuuvox000]

I'm working on a remodel project where they're redoing most of their hydronic piping in the building but keeping the existing pumps and chillers. In their current setup the pumps are pumping away from the chillers. The piping is on the roof and has aluminum jacketing so it would be expensive to redo this piping configuration. Is it okay to keep it this way? Would I just have to make sure the pressure is high enough in the closed system? This is on a 13 story building and the pumps and chillers are on the roof. Thanks in advance.

 

[TugboatEng]

It complicates your NPSH estimate.

Heat exchangers have convoluted flow paths with many sites turbulence can occur at. Under suction conditions this turbulence can cause cavitation and erosion in the heat exchangers.

 

[immsk]

I see no issues with this.

 

[LittleInch]

A diagram would help but from your description yes, you just need to maintain enough pressure in the chillers to prevent vacuum conditions.

If it works now then there is no reason why it shouldn't in the future, even if it is a little strange.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EnergyProfessional]

I fyou keep both chillers and pumps and it works, then it should be fine. Obvioulsy confirm it actually works fine and if you do other hydraulic changes to the system it may be different....

IF you installed a new chiller, I'd consult with that manufacturer.

 

[nuuvox000]

Yeah, that's some of the issue is they've never had a system that works well in the building (heating or cooling). They fired their maintenance guy that had been there for years so we have no way to ask specifics. The non-engineers just say that it's never worked great but they don't have any details. The current piping in the building is full of gunk and almost closed off in some places, the fan coils never had circuit setters or strainers, there's a lot of issues. We're doing new fan coils and new piping so I think I'll be able to solve most of their issues; I've just never had chillers on the suction end of the pumps so I'm a bit worried about that. These are all existing chillers but I'm going to check their manuals and see if they say anything about it.

I attached a preliminary schematic that I put together. Happy to take any feedback.

 

[BronYrAur]

Based on the location of the expansion tank, you are still pumping towards the chillers....they are just at the end of the loop.

Can I assume that you have very low delta-T with this system?

 

[nuuvox000]

Oh, I didn't realize that. It's 55 deg F return and 45 deg F supply.

 

[lilliput1]

To be ok the following must be met: the NPSH at the pump inlet must be greater than the pump minimum NPSH requirement; air in the piping must be automatically vented by automatic air vents located at all high points of piping; the expansion tank initial pressure must be set such that minimum 10 ft height of water pressure would be available at the highest point of piping in the building to allow automatic venting of air in the piping.

 

[SAK9]

The pump away from chiller configuration is used in installations where the plant room is at the ground level of a high rise building. If you put the pumps ahead of the chiller s in such an installation the pressure exerted on chiller tube will be static height + pump outlet pressure. This is a determination that needs to be made in consultation with the vendor.

In a closed loop circulation system NPSH has no relevance(assuming you do not have a globe valve at the pump suction).Therefore I do not see any issues with the pump being located on the chiller discharge side but make sure all flow throttling is done at the pump outlet.