## Chiller condenser flow estimate

## Chiller condenser flow estimate

(OP)

I need to estimate the condenser water flow through a pair of TRANE Centravac water chillers (one 750-ton unit & one 1150-ton unit). I have data for % compressor load on both units and incoming/exiting cooling water temperatures, but no flow data. Can the flows across both chiller condensers be estimated from the information available?

Thanks in advance for your assistance.

Brad

Thanks in advance for your assistance.

Brad

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

The chilled water outlet temperature setpoint is 42°F.

Normal condenser water inlet tempeture setpoint is 78°F.

I do have delta-T's for both of those flows. Also, I have contacted the local TRANE rep for a copy of the differential pressure-to-flow conversion chart.

Here's a follow-up question. On some TRANE literature, I found this equation:

Tons = (GPM X delta-T X specific heat* X specific gravity*)/24

* = for fluids other than water.

QUESTION: Does this apply to the condenser flow as well as the chilled water flow? The TRANE tech didn't have an answer.

Thanks for all the help.

Brad

## RE: Chiller condenser flow estimate

GPM X 500 X delta-T (the '500' is just rounded from 8.33 lbs per gallon X 60 min per hour = 499.8

This gives you an accurate BTU per hour estimate for pretty much any situation involving water flow and temp change.

The '24' is 12,000 / 500.

Ton hours = USGPM X delta-T / 24

I do more heating than cooling, so I remember the first short-cut formula that takes water into BTU/hr. Then I can easily figure anything I need to, whether it's heating or cooling.

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

A cooling tower in the Arizona Desert 40% RH ,will need about

the half flow for Florida or other place with 95% RH.

So first get the tower flow

As an example : for a 200 TR chiller the condenser allowed flow could be from 300 GPM to 1200 GPM for the same chiller

Pardal

## RE: Chiller condenser flow estimate

Flow rate is dicted by chiller not the cooling tower. The tower is sized to reject the heat from the condenser water.

## RE: Chiller condenser flow estimate

Hi wj33

I must dissagree whit you :

On my "wood" desktop , I have four diferent proposal from 4 water tower vendors.

All they answer to my request to provide a tower to my chiller.

All them quote towers of diferents flow , because each tower dising as it's own heat tranfers coefficient.

Pardal

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

Pardal

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

Thanks for the info... I hadn't thought about the height difference. Upon checking the condenser, inlet & outlet P gauges are at the same height (but different instruments).

*Also, does anyone have the Pressure/Flow tables? My local TRANE rep. hasn't come through for me.

Thanks.

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

Literature Order Number = SYS-APM001-EN(October 2000)

File Number = PL-000-SYS-APM001-EN

Supersedes = CON-AM-21 (MAY 1987)

Stocking Location = La Crosse

www.trane.com

comfort@trane.com

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

You only need to do two procedures for your question:

1)Using a differential H2O pressure gauge purchased at any

instrumentation supply company,find out what the pressure differential of the supply & return is by attaching the ports to the the In & Out piping going to either the condenser or evaporator barrels.

2)(Simply obtain "COPIES" of both chillers' flow charts at your local Trane Parts Store...Make sure you have model & serial numbers of both chillers!)Multiply your pressure differential reading by 2.3 and the left side of your charts

will show you actual feet pressure and you will now be able to see the values for the gallons per minuite /Min-Max Ft. Pressure allowable by Trane standards on these charts.

## RE: Chiller condenser flow estimate

Thanks for the info! That's exactly what I was looking for.

## RE: Chiller condenser flow estimate

I have just joined the group and read your request regarding flow rates for evaporators and condensers. I have been in the chiller service and repair business for 20 plus years now. The questions that you have asked are common and easy to answer. I to have worked for Trane as a chiller tech for 10 years. I now evaluate and survey large chilled water plants and systems for performance and non-performance. Being in this position gives me the opporunity to see hundreds of facilties and at the same time see so many chillers that are running way outside the design conditions they were selected at. Many machines in the field today do not run at design conditions and for many reasons some good and some not so good.

I say all that to say this. If you know the tonnage you need for the evaporator then you have many choices as to what the flow rate and delta t could be. These two items are not selected based on what a chiller needs but are based on what the system needs mainly the coils that are being used. If the coils are selected for a wide delta t then the flow can be reduced or just the opposite. You also have to consider the pressure drop through any machine carefully because this will impact the pump horsepower needed to move the water. The formula that was mentioned by some of the other folks is the formula I use daily when calculating tonnage for systems that use water only. Tons=GPM*Delta T/24. If you know that one of the machines is in fact a 750 ton machine then you have to know what the temperature spread is going to be before you will know what the flow will be. Also bear in mind that if your are trying to determine the tower flow rate and the delta t on the condenser side there will be somewhere between 16 to 18 percent more heat being rejected at the tower! You have the heat of compression plus motor heat if it is semi-hermetic machine. There is another limiting factor to what the flow rate should be through a machine and that is the velocity of the water through the tubes. Typically the maximum is 11 feet per second and the minimum is around 3 feet per second.

This are given in the design info of most chiller manufactures.

Hope this helps.

Chiller Pro

## RE: Chiller condenser flow estimate

Gpm = (btu/hr)/(500 x t rise) = 13527 / (500x10) = 2.71 gpm per ton. The 750 ton chiller therfore will require 2.71 x 750 = 2033 gpm at 10 degrees TD. The gpm for the 1150 ton chiller can similarly be calculated. Actually it is usually possible to select electric chiller & cooling tower combinations that would work in the 2 to 3 gpm (note absorption chillers would require about 4.6 gpm/ton)range. But the minimum entering water temperature is always 85°F based on typically 78°F wb, (occassionally 80°F wb but selection will not be CTI certified). Typical is about 3 gpm per ton but we do design for the minimum, 2 gpm per ton if we want to save on cooling tower space (existing building limits available space) and pumping energy.

## RE: Chiller condenser flow estimate

## RE: Chiller condenser flow estimate

Brad