Diffrential pressure settings on chiller.

[ironmen]

Hi All,
Im working on a chill water system, and the set up is a diffrential pressure bypass and not sure about the DP.Can somebody advise me whats the normal diffrential pressure setting between main pipes of chilled water supply and return.Help appriciated.Thanks

[Mrdaikin]

Most chillers operate with a dp of 0.5bar

Do you have the old switch to see what this was set to?

Do u have any more detail on the chiller? Manufacturer, model etc?

[aramis]

It depends on the type of chiller and the action of the PD switch.

For example a chiller with a BPHE to control minimum flow is set at 0.2 bar.

[Brian_UK]

I don't think that OP is talking about a pressure switch but a differential pressure bypass valve.

The DP valve needs to be set to maintain the required minimum flow through the evaporator. These are often used when only two-port control valves have been installed instead of using three-port valves with balanced bypasses.

You either need to check the setting in accordance with the pump performance curve or be monitoring the evaporator flow rate at minimum demand.

[ironmen]

Hi guys,ive got constant chilled water pumps in this system controling on vsd and also two way valve on the terminal unit.ive got a diffrential pressure transducer installed in the main return and supply header to sense the diffrential pressure between them.ive got a two way motorised modulating valve installed for bypassing the chilled water from the supply chilled water pipe to the return to maintain the disigned diffrential pressure which i dont khow.Because as the coling demand is reduced,the control valves of some terminal unit are closed or partly closed ,system presuure will be built up and sense by the diffrential pressure set up,therefore the dpb controller will open the modulating valve to bypass excissive chilled water so that the original design diffrential pressure can be restore.because i dont khow the original setting on the dp how im gonna khow how to set it.help appriciated thanks.

[HVACRsaurus]

Hi there,

Differential pressure between system supply & return is more of an*arbitrary value, it is influenced by the system itself.

The important part of the circuit for Differential Pressure is the chiller, & it's the chiller design dp which will determine the system dp.*

1) Obtain the chiller design differential pressure information.

2) Set up instruments to measure chiller dp & system dp simultaneously.

3) Operate chiller pump & control position of bypass valves manually untill design chiller dp is achieved.

4) At the time chiller design dp is achieved, read measured value of system dp - this will be your value. Use this value to modulate the bypass valve in automatic control & monitor the chiller dp, tweak system dp setpoint if needed to maintain close to design dp across chiller.

Remember, if the system dp is increased - the chiller dp (& flowrate) will decrease, and vice versa.
*
Some systems that I have worked on required a system dp in the order of 100 Kpa, but by no means is it a rule.