District Cooling - criteria for a unit pressure drop (Pa/m) and speed
District Cooling - criteria for a unit pressure drop (Pa/m) and speed
(OP)
Dear all,
I would kindly ask for your assistance please regarding sizing pipelines for district cooling system, please.
I have been looking for criteria that have to be met in order to size district cooling systems with parameters supply 7C and return 12C. Terrain configuration allows both downstream and upstream flow with total lenght of 4 km.
From ASHRAE 2005 Habdbook, I understand that this question is not that straightforward. While for larger diameters criterion is water velocity, for smaller pipe diamteres is unit pressure drop. Generally, water velocities above 3.0 m/s are undesirable.
My concerns. ....
1) Generally, what unit pressure drop should be selected for calculations (Pa/m)?
2) What is the range for small pipe diamaters and that of big pipeline diameters.
3) In urban environment it makes sense to consider noise in pipes due to high velocities but is it of big importance if pipelines are installed on "virgin" land.
Some extracts from my calculations and what would you select taken into consideration the cost of pipes and above criteria.
Parameters: 7/12C, NP6 bar, Absolute roughness 0.02mm
Results:
38 320kW....DN800...w=3.57m/s....R=42Pa/m
33 20kW...DN700...w=4.68m/s....R=80.5Pa/m
6 000kW...DN350...w=3.0m/s....R=88.1Pa/m
500kW...DN125...w=1.7m/s....R=106.3Pa/m
I would kindly ask for your assistance please regarding sizing pipelines for district cooling system, please.
I have been looking for criteria that have to be met in order to size district cooling systems with parameters supply 7C and return 12C. Terrain configuration allows both downstream and upstream flow with total lenght of 4 km.
From ASHRAE 2005 Habdbook, I understand that this question is not that straightforward. While for larger diameters criterion is water velocity, for smaller pipe diamteres is unit pressure drop. Generally, water velocities above 3.0 m/s are undesirable.
My concerns. ....
1) Generally, what unit pressure drop should be selected for calculations (Pa/m)?
2) What is the range for small pipe diamaters and that of big pipeline diameters.
3) In urban environment it makes sense to consider noise in pipes due to high velocities but is it of big importance if pipelines are installed on "virgin" land.
Some extracts from my calculations and what would you select taken into consideration the cost of pipes and above criteria.
Parameters: 7/12C, NP6 bar, Absolute roughness 0.02mm
Results:
38 320kW....DN800...w=3.57m/s....R=42Pa/m
33 20kW...DN700...w=4.68m/s....R=80.5Pa/m
6 000kW...DN350...w=3.0m/s....R=88.1Pa/m
500kW...DN125...w=1.7m/s....R=106.3Pa/m





RE: District Cooling - criteria for a unit pressure drop (Pa/m) and speed
I doubt very much that noise will be a factor. The pressure drop in city water mains will typically be much higher than you'd design for for a chilled water system, and I'm not aware of anybody being able to detect any noise from the water mains, let alone at level that would trigger complaints. Inside buildings of course, velocity noise is another matter.
Velocity, pressure drop, and flow are all linked. If you run a higher pressure drop, the velocity increases, but you can use smaller lines for the same flow. Now you're into pumping cost considerations. The higher delta-P, the more horsepower you'll need. This means both a higher first cost, and an ongoing operational cost.
Seriously consider checking out the IDEA people. I haven't worked in that business for a number of years, but I'd bet that the design info and actual running plant data available will be well worth the price of joining.
RE: District Cooling - criteria for a unit pressure drop (Pa/m) and speed
RE: District Cooling - criteria for a unit pressure drop (Pa/m) and speed
HVAC68
RE: District Cooling - criteria for a unit pressure drop (Pa/m) and speed
3m/s is not hard and fast. You can go for higher velocities if the pipesize is big. I like the suggestion by TBP. In the absence of any help, I would just select the break even point of pipe cost vs power consumption.
You should consider heat gained by chilled water in the 4km piping. Otherwise, if the dT at chilled water generation system is 5C, you may end up with some trouble.
RE: District Cooling - criteria for a unit pressure drop (Pa/m) and speed
Upsizing the pipes to allow for future flow will reduce pumping costs as well.
RE: District Cooling - criteria for a unit pressure drop (Pa/m) and speed
quark.....
In case of pre-insulated pipelines, heat transfer through casing and insulation is very low (cca. 3%) and thus; almost negligible.
Thanks Sasa