Scalable Chilled Water Plant?

If I understand your system correctly, it seems that you could add a 60-ton chiller, tower, and pump. The refrigerant should be a separate circuit from the existing chiller(s), but the chilled water would be in parallel. You might need some actuated valves to shut off chilled water to other zones than the critical gallery, during times of power outage.

I think you've got it. I don't have the room for an additional tower, thus the use of VFD's on everything, along with the 'modular' typ of chillers. I'm hoping to be able to turn down the tower fan to help match the condenser load from a single chiller.

Looking at two scenarious right now.

1) build a chiller 'plant' with 5 modular chillers of 60 tons each, running a separate secondary to the critical gallery ahu, with control valves shutting off the other secondary loop. When on Emergency power, only a single chiller would operate depending on the load. I'd try to maintain the primary chiller loop at a constant temp, and only run the critical zone secondary loop on emerg. power., letting the chiller controls stage additional chillers on or off as required by the load.

2) Use a separate chiller and loop on the critical gallery ahu. This approach would add pumps and make the Condenser water loop a parallel loop to the tower.

The tower is a BAC chiller, and i've been told by the rep that we could run the fan on a VFD along with the bypass to drop the capacity to match a single smaller chiller. I'm always 'suspicious' of rep information and was looking for some confirmation.

Id suggest forget the rep and speak to the techies at BAC.I would always check with the drive manufacturer when connecting existing kit to a VFD,due to subtle differences in motor characteristics and their suitability.

With regard to the capacity reduction of the system when emergency gens are connected I cannot grasp the revised system you are suggesting,a drawing or P&ID would be useful.

My initial suggestion would be to confirm the following:

1.Available power from emergency source,this will dictate whether d/x may be a more suitable option......another coil into an AHU isnt costly,especially when its only a fraction of the overall duty+You will benefit from more Kw cooling per Kw input.Refrigerant selection also important,R410A or similar good option at Te of 0C to 10C.Consider also integrating Copeland Digital scrolls,VFD control as standard,this technology can also be fitted in chillers as well as d/x.Aim for the maximum COP achievable and work back to confirm cooling capacity that can be provided.

2.What are the ambient extremes,is free cooling a likely option? Fitted on chillers it can save alot of energy.

3.Is the system providing ventilation as well as conditioning? If so,re-cycling during emergencies will also cut down the load considerably + reduce the humidity fluctuations from external air.

It all depends on how far you want to take it..........

My initial suggestion would be to confirm the following:

1.Available power from emergency source,this will dictate whether d/x may be a more suitable option......another coil into an AHU isnt costly,especially when its only a fraction of the overall duty+You will benefit from more Kw cooling per Kw input.Refrigerant selection also important,R410A or similar good option at Te of 0C to 10C.Consider also integrating Copeland Digital scrolls,VFD control as standard,this technology can also be fitted in chillers as well as d/x.Aim for the maximum COP achievable and work back to confirm cooling capacity that can be provided.

... I hadn't thought of adding a DX coil to the unit, but that is a possibility. Not sure where I can put the condensing unit.... but Thanks!

.... We'll be using the system power demand to help size the GenSet. So we've got whatever we need. Just trying to contain the size of the Gen Set.

2.What are the ambient extremes,is free cooling a likely option? Fitted on chillers it can save alot of energy.

....The museum is more interested in maintaining the contractually required criteria than in energy savings, at least in this one wing.

3.Is the system providing ventilation as well as conditioning? If so,re-cycling during emergencies will also cut down the load considerably + reduce the humidity fluctuations from external air.

.... Normally yes, but this is a 'Smithsonian" exhibit space, i.e. very tight humidity and temperature control. we're going with minimum required outside air at all times, with no o/a during emergency operation... 100% recycling.

thanks leon.. more to 'chew' on in my head!

I suspect that the tower on which the VFD is contemplated uses a centrifugal fan. Unless the VFD incorporates braking, slowing down the frequency may make the fan "overdrive" the VFD. Also, the motor will need to be inverter rated in the first place. In any case, be sure that the motor and VFD are properly matched.