System Efficiency at Partial Load
System Efficiency at Partial Load
(OP)
Greetings
I encountered this chilled water system that I believe is inefficient. I have attached a schematic. Your thoughts are highly appreciated.
Brief System Description:
The 40 storey building chilled water supply comes from a district cooling provider. The lower and upper halves of the building are separated into two closed loop circuits. Each circuit has a heat exchanger and variable pumping stations. The heat exchangers and pumps for the first circuit are in the 1st basement while the ones for the second circuit are in the 17th floor serving the upper half only.
The problem is that the upper circuit is served by the lower circuit; i.e., the lower closed loop circuit has two functions: 1) to distribute chilled the lower half of the building and 2) to serve as a 'primary' loop for the second circuit (the upper half of the building).
Say if the building cooling demand is in the upper floors, both circuit pumps will be loaded even if the lower floors are unoccupied. Say, in another case, the cooling demand is in the lower floors, water will be circuilated through the heat exchanger of the upper circuit which is connected in series and without a 3-way valve to bypass it (also an energy waster).
I think it will be much more efficient if the pumps and heat exchangers of the upper half are also moved to the 1st basement so there will be two separate circuits. There will be an additional cost for piping and a larger capacity pump set but there will also be savings in the form of a smaller heat exchanger (that used to serve both circuits/loops) and better energy usage.
Much obliged for any information.
I encountered this chilled water system that I believe is inefficient. I have attached a schematic. Your thoughts are highly appreciated.
Brief System Description:
The 40 storey building chilled water supply comes from a district cooling provider. The lower and upper halves of the building are separated into two closed loop circuits. Each circuit has a heat exchanger and variable pumping stations. The heat exchangers and pumps for the first circuit are in the 1st basement while the ones for the second circuit are in the 17th floor serving the upper half only.
The problem is that the upper circuit is served by the lower circuit; i.e., the lower closed loop circuit has two functions: 1) to distribute chilled the lower half of the building and 2) to serve as a 'primary' loop for the second circuit (the upper half of the building).
Say if the building cooling demand is in the upper floors, both circuit pumps will be loaded even if the lower floors are unoccupied. Say, in another case, the cooling demand is in the lower floors, water will be circuilated through the heat exchanger of the upper circuit which is connected in series and without a 3-way valve to bypass it (also an energy waster).
I think it will be much more efficient if the pumps and heat exchangers of the upper half are also moved to the 1st basement so there will be two separate circuits. There will be an additional cost for piping and a larger capacity pump set but there will also be savings in the form of a smaller heat exchanger (that used to serve both circuits/loops) and better energy usage.
Much obliged for any information.





RE: System Efficiency at Partial Load
issues of inefficiency are more general issues of fixed flow system than something completely related to this separation.
upper fan coils are seemingly designed to somewhat different temperature regime.
i can imagine that this solution was made to somewhat simplify construction issues for risers. changes you propose would require major refurbishment, and taking into account the issues mentioned - reducing static pressure, achieving constructability of risers.
RE: System Efficiency at Partial Load
However if the lower HX is sized to accommodate the lower loads as well as the upper HX, you can look at the upper HX as another load off the lower system. If the lower system varies pump speed to maintain a loop DP, a reduced lower building load will have the pumps ramp down and only produce enough to keep the upper HX happy; if the lower building load is low and the upper is high, the lower pumps will modulate as needed to keep the upper system satisfied…
In general, I don’t see a problem with this configuration as long as the lower HX is sized to accommodate the full building load.
RE: System Efficiency at Partial Load
Thank you
RE: System Efficiency at Partial Load
RE: System Efficiency at Partial Load
RE: System Efficiency at Partial Load
The other issue is 120 m long riser, which makes outrageous demands on construction. Halving riser length halves thermal expansion and all construction loads related to it. 60 m is already long enough, requires special solution for fixed points and hanging.
RE: System Efficiency at Partial Load
IBechir, two way. Have an end-of-loop minimum flow device (controlled or by circuit setter).
RE: System Efficiency at Partial Load
RE: System Efficiency at Partial Load
and you said the provider connection is variable, what control it?
RE: System Efficiency at Partial Load
RE: System Efficiency at Partial Load
RE: System Efficiency at Partial Load