Low Water Flow in Evaporator

The term "balancing valve" could be ambiguous here. There are various ways in which 3-way diverting or mixing valves can be advantageous, but an existing system vs proposed system piping diagram would be helpful.

On our hot water circulating system an adjustable pressure relief bypass valve was added at the very end of the hot water loop to provide a flow from supply to return above a set point. This was to prevent zone valve blowouts as well as provide a minimum flow.

The similar chilled water system had a manual bypass valve just inside the building from the chiller between the supply and return to provide a minimum flow however I would recommend a pressure regulated bypass valve as flow pressure changes with number of zone valves calling. Obviously care must be taken to maintain pressure at the end of the loop and perhaps like the hot water system the end of the loop would be the preferred location for such a bypass valve.

Just what I have seen.

Norm

Dear aruna,

No machine gives of its best when short-cycling, and as there will be an excessive number of operations of the motor control gear whether electronic soft start or contactor it will inevitably shorten the working life of the machine as a whole. Clearly it is desirable to investigate why the evaporator circuit is experiencing an inadequate flow, either load changes have reduced the demand since commissioning or there are problems with the pump(s).Perhaps alterations have been made which are permitting a large proportion of the circulating water to return without passing through any effective load ie, via over-sized 3-port valves.

A check on the DP across the evaporator should reveal what the actual flow is, as would a check of the pump head being generated.

If you are happy with the general flow conditions you could consider transferring the control sensor from the flow side to the return side of the chiller. This does carry an increased risk of freeze up so a police stat should remain in the flow side 'pocket' set at say 35F. By adopting the revised sensor location you will generally find an increased temperature differential is achieved plus a reduced cycling frequency.

Energy transfer is therefore increased and better control achieved.

I would still question the load-side conditions as the current situation is unfavourable. Beyond that you might consider setting up a flow share arrangement between the chillers to avoid circulating the dead second machine and therefore concentrating all the available flow onto the duty chiller; a butterfly type valve and actuator is a compact and low cost solution. You would configure the two machines in a lead/standby arrangement with automatic selection on an hours-run and/or lead-trip basis.

Hope this helps,

Massey.

GA Massey!!!

A couple of other things to consider. Trane chiller barrels will remain efficient up to 3 pounds DP if there is substantial load to keep it above or at 3 pounds. If it drops below that you will trip on low refrigerant temps or the freeze stats will drop you out. This is where you need to be sure that the existing piping is adequate enough to supply a proper return to the chillier when the zones go into by pass.

As stated in the first post by Tornado a piping diagram would be helpful.

SO

What is the barrel DP?

What is the approach?

What is entering Condenser water temperature, needs to be no lower than 80 degrees?

What are the actual readings at the pumps and do they meet required flow and head parameters?

When this unit was commissioned did somebody leave a 2x4 inside the return line?

Sorry guys had to mention that since I have pulled a couple of 2x4 out of the return and supply lines.

If everything checks out maybe the new unit is oversized for the application. The next attack would be on the CONDENSER side. Install a butterfly valve on the condenser barrel inlet to maintain proper head pressure. Or if it is DX install fan cycling controls on the condenser to maintain proper head pressure. This will also bring system pressures up allowing the system to run.

Or a speed drive on your cooling tower.

Good luck!

hi aruna its Karthik working in Research & Development in Pricol - Automotive Engineering,,,,,,,

i find your problem and this may due to the poor insulation over there and similar thing is did u use any exchanger,,,,, need little bit clarity yar,,,,,,,,,,,,,,,,,,

I would start with the obvious:

-Has this set up worked properly to date?

-Have there been changes to the system load?

-When was the last time the chiller barrel tubes were inspected and cleaned?

-Are you maintaining the quality of the chilled and condenser water?

-Is the water flow for the chillers in parallel?

With the delta "T" through the chiller barrel, it appears that you have very little load.

Ah yes

The first question is.........whats changed?

I am sure you must have got a fair idea of this problem from the answers posted. You can check rating charts of the chiller from the manufactures technical details which gives the loading rates in heat units per unit area of the surface of the chiller refrigerant tubes for a range of Mean Effective Temperature Difference ( METD) between the chilled water temperature entering and leaving the chiller and the chiller refrigerant temperature.

Yes we could check the charts but without site data and as builts the chart data really can not be considered as a fix but rather a good story.

Besides if we take all the information from the poster, then check the charts and do the fix the poster would be disappointed. It is much more fun to have the suggestions to move in the right direction and discover the fix yourself.

Talk to these people, either over the 'phone or face-to-face.