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rlara
27-01-2014, 09:02 AM
Hello,

I am an electrical engineer and very new in designing refrigeration system. Now I am calculating / designing cold rooms in a high rise building which requires water-cooled condensing units. My questions are these:

1. In the specification, it was mentioned that the water cooled units should be suitable for connection to the central chilled water system operating at 6 deg C flow, and return temperature as required.

I supposed that the return temperature calculated will be the same temperature of water inlet for the condensing units. If this so, is there any rule of thumb or at least formula how to calculate it?


2. Since this is in high rise building (and the cold rooms are located in the basement), I would like to know where the condensing units should be located / installed.
It was mentioned in the specification as "locate remote from cold storage rooms, on roof".I am not sure if this means like it should be installed on roof top of the building. If so, my doubt is the riser pipe would be too much.

Please help me with this. And thank you in advance.

frank
27-01-2014, 09:58 AM
1. In the specification, it was mentioned that the water cooled units should be suitable for connection to the central chilled water system operating at 6 deg C flow, and return temperature as required.

With a +6C entering temperature onto the water cooled condenser, the return (exiting) temperature will be dependant on the water flow rate and the amount of heat absorbed.

The formula for calculating this is:

Q = mass flow x sensible heat co-efficient x temperature difference (Q = m c dt)

Where

Q = Capacity of the condensing unit in kW
m = mass flow of cooling water in kg/s
c = 4.19kj/kg for pure water
dt = Temperature 1 - Temperature 2