We have our milestone next week to start some chillers. For that we need calculate output flow of chillers, but the flow transmitter is procurement stage. We have discharge pressure gauge. Can we calculate manually flow from discharge pressure? Or give me some idea to do this.

 

> We have discharge pressure gauge. Can we calculate manually flow from
> discharge pressure? Or give me some idea to do this.

Short answer is NO. But if you have one good differential pressure sensor then you can use it sequentially for each chiller. Is that sufficient for what you need to do?

The pressure on the discharge of chillers supplying the same header is so similar that it gives only a gross indication of whether there is the same flow to a factor of 3 or so.

Regards, 4-20 Camp

 

You can follow this link

http://www.madsci.org/posts/archives/2000-06/960600443.Eg.r.html and get some idea for your problem.

 

> We have our milestone next week to start some chillers. For that we need
> calculate output flow of chillers, but the flow transmitter is procurement
> stage. We have discharge pressure gauge. Can we calculate manually flow from
> discharge pressure? Or give me some idea to do this.

You can do it if these three conditions are fulfilled

(1) The pump is a constant speed type
(2) You have typical discharge value for the know delivery pressure
(3) Delivery pipe ID has not significantly changed

Assuming the known baseline flow is 500l/s for delivery pressure of 100mH2O. Then you can approximate the flow with acceptable accuracy as long as the delivery pressure lies between 95-105mH2O. The formula is as follows<pre>
Q_wtr = kH^0.5

k= 500/(100^0.5) = 50

Since your Q_wtr and H are known, you can solve for the unknown coefficient k, assuming k is constant. Then for any H, says 95<H<105m, use equation 1

Q_wtr = 50*H^0.5 (1)

E.g H= 98m

Q_wtr = 50*(98^0.5)

= 495 l/s

Note that in reality k is not exactly constant. That is why we have to limit applicable range +/- 5m from the known Q_wtr. </pre>
Thank you.

 

Ali... Power measurement is a very good way to monitor chiller performance, especially if you have the machine's flow curves!

Regards, Phil Corso

 

Dear Phil

I think using delivery pressure is better because it is the pressure that acts as a driving force to move water from one elevation to the other. If we use power consumption we may add one uncertainty, i.e. effect of pumping unit components efficiency degradation to the calculated discharge. E.g. if bearing friction loss increases the pumping unit may take the same amount of power but produces less pressure and eventually less discharge. Power measurement alone cannot account for this.

 

Install additional 2 - 3 gauges in discharge. this also would give you average differential pressure & it would be directly proportional to flow. this is only temporary situation solution.

Location of additional pressure gauges should be logical, where you get differential pressure & compare with the estimated DP

ANYNOMOUS