New Chiller Design
New Chiller Design
(OP)
A client has asked for a new chillled water plant for a medium sized building. Air cooled chiller feeding the chilled water plant will be sized at approximately 100 tons. This chiller will feed 5 or 6 separate chilled water air handling systems. I'm evaluating pros/cons of designing the system with 3-way valves or 2-way valves. If one were to go with 2-way valves would you recommend a VFD on the pump or just riding the pump curve. I'd like to get input from some of the smart folks out there about items to consider and what they would do in this situation. Thanks in advance for your help.





RE: New Chiller Design
Generally a centrifugal pump should not be run below 25% of the flow rate at BEP (i.e below safe minimum flow). If you reduce the speed of the pump, safe minimum flow also gets reduced.
You should tell us the maximum, minimum flow rates, static discharge head and total discharge head at full flow to get a better solution.
Regards,
RE: New Chiller Design
Tony
RE: New Chiller Design
RE: New Chiller Design
Imok2 - How much money are we really talking about saving in reality? Chiller electrical costs will remain essentially the same I believe so the main area we are saving energy cost is in pumping costs. The pump minimum threshold I think will be determined by chiller's minimum flow threshold as opposed to the pumps minimum flow threshold. Assume for example that a 100 ton chiller's minimum threshold is ~150 gpm versus full design flow of 240 gpm. Is the energy savings really that significant on a 5 hp to 7.5 hp motor? Please let me know your thoughts.
TFurst - You lost me on the Griswold flow controllers. If I have a two-way valve it's going to modulate based on a variable I'm trying to maintain (room temperature or supply air temperature or similar). I believe I just want to balance it initially so that my full design flow is obtained when the valve is full open. After the initial balancing it should modulate based on whatever variable it is attempting to satisfy. Let me know if I'm missing something. You also lost me on decoupling the system. If I create a bypass so that my chiller is always getting full design flow what have I accomplished? My pumping costs remain the same as the pump is always pumping the full design flow even though it's a 2 way system. Let me know what I'm missing. Thanks.
RE: New Chiller Design
HP = 7.5 x 746 watts/hp ~ 5600watts..now with a turn down of 50%
We know that the power consumed = Speed cubed so, with a 50% turndown we have 5600 watts x0.5 x 0.5 x0.5 = 700 watts.
Now the curve on a typical office building heat load looks like an IQ curve. (did i say that)! Anywhy, the pumps will be mostly in the 50 to 60% speed range. If you consider what you pay for a KW and the hours of operation .. well I leave it up to you.
RE: New Chiller Design
Tony
RE: New Chiller Design
You can learn more on a paper M150, titled design considerations of pump hydronic system at PDHonline.org.
RE: New Chiller Design