# What is a chiller differential pressure?

## What is a chiller differential pressure?

Differential Pressure Measurement Several instruments can be used to measure the differential pressure across a chiller. The differential pressure measured corresponds to the flow rate; the higher the flow, the higher the DP.

How do I know my DP setpoint?

The chilled or hot water building DP setpoint (DPsp) is set based on the following equation. DPsp = kcal *(GPM)2 +Pad (6) Here Pad is pressure added to the setpoint for control valves to be adjusted for the requirement of flow rate. The range of Pad is 1 psi to 2 psi based on our field experience.

### What should chilled water pressure be?

Generally, most chilled water systems operate at a pressure of around 10-12 bar. Some chilled water systems work at more than 16 bar of pressure but they rarely exceed 20 bar. High pressure chilled water systems usually use heat exchangers to reduce the pressure to below 20 bar.

How do you control a chilled water pump?

Control strategy: Enable primary chilled water pump when outside air temperature is above setpoint and at least 1 chilled water coil control valve is open to coil. Modulate (vary) the speed of the pump VFD to maintain a constant differential pressure. Enable chiller after flow is proven.

## What causes low differential pressure?

Differential pressure is used to determine if a pipeline has any clogs or contaminates as particles flow through orifices and filters. If part of the pipe gets clogged, it will cause a change in the pressure, which causes differential pressure to increase or decrease.

What is the purpose of a differential pressure switch?

A differential pressure switch is designed to sense a difference in pressure between two pressure sources in the plant for control purposes.

### What is DP setpoint?

The chilled water and hot water DP setpoint or return temperature setpoint or flow rate setpoint was a constant value or reset based on outside air temperature.

What does a chilled water bypass valve do?

The purpose of the chiller/heater system bypass is to prevent deadheading of the pumps when all of the internal unit valves go closed as well as allow temperature and differential pressure sensors to sense active flow.

## When WSE and Chiller are enabled the control speed is?

•When WSE and chiller(s) are enabled run 95% speed •When chiller is disabled control speed to maintain CHWST setpoint76 77 Summary In this seminar, you have learned how to

Which is more efficient running two VFD chillers or two fixed speed chillers?

Running two VFD chillers is more efficient until 35% load Running two fixed speed chillers always uses more energy 65 Cautionary Note Staging logic must limit possibility for surge operation for centrifugal chillers

### When to stage off a variable speed chiller?

•For primary-secondary systems w/o check valve in the common, start chiller to ensure Primary- flow > Secondary-flow •Stage off when measured load/flow indicates load is less than operating capacity less one chiller – be conservative to prevent short cycling 62 Staging Variable Speed Chillers 63 Part Load Chiller Performance w/ Zero ARI Tolerance

What are the optimum sequences of a chiller system?

26 Optimum Sequences All plants are different •Tower efficiency, approach •Chiller efficiency, unloading control •Pump efficiency, head, unloading control •Number of chillers, pumps, towers Too many independent variables •CT fan speed