Chilled water free cooler control

[r.bartlett]

Gents

we are quoting out a small chiller and they want a free cooler. They showed one they already had elsewhere in the building.

I was thinking the chilled water return would flow back through the free cooler and it would be a simple case of turning the fan on when the temp drops to 10 C

However The free cooler there has a 3 port valve c/w a control panel arrangement.

Can anyone tell me the logic of this and if this set up is available 'off the shelf' so to speak

[frank]

I would assume that the 3 port valve is there to control the outlet water temp through various ambient conditions.

The parts are available 'off the shelf' from Electro Controls (although you have to purchase via one of their agents now)

http://www.electrocontrols.co.uk/

[r.bartlett]

I would assume that the 3 port valve is there to control the outlet water temp through various ambient conditions.

The parts are available 'off the shelf' from Electro Controls (although you have to purchase via one of their agents now)

http://www.electrocontrols.co.uk/


Thanks Frank

I'm more looking for the whole kit and caboddle. Valve control panel and cooler as a lump as I don't have much time to price out :confused:

[mad fridgie]

Gents

we are quoting out a small chiller and they want a free cooler. They showed one they already had elsewhere in the building.

I was thinking the chilled water return would flow back through the free cooler and it would be a simple case of turning the fan on when the temp drops to 10 C

However The free cooler there has a 3 port valve c/w a control panel arrangement.

Can anyone tell me the logic of this and if this set up is available 'off the shelf' so to speak
It could be a simple diversion valve, when free cooling is not available, water by passes the heat exchanger, and/or it could be being used as proportiainal mixing valve to control temperature, I think the best thing to do in this application is "cheat", if the client is happy with there present system, copy and understand it, make inprovements if you can.

[install monkey]

make sure the water circuit is dosed with glycol,the circulating pump runs constantly and a frost stat to open the 3 port valve to ensure flow though the cooler in frost conditions!!!

[frank]

Sorry Richard, I didn't realise you wanted the whole package.

Give these guys a ring. They appear to supply exactly what you are looking for.

I use them a lot for my coils.

http://www.hccoils.com/files/Catalogue%20-%20Dry%20Air%20Coolers%20HCL%20M%20NV%20NW%20V%20BV.pdf

[mad fridgie]

Without know the application, i would also look at going floating set, measuring return water temp and air temp. I would look at using a Seimens "Joker" controller (semi programable), if it is still called a Joker

[DTLarca]

I would be sure to have at least 20% ethylene glycol but preferrably 30%.

I didn't notice trace heating so perhaps they already have some percentage.

Compared to plain water 30% EG will have a freeze point of -14.1, system capacity of 97.3%, Power input of 99% and a pressure drop increase to 119%. That's all using the same pump.

Ordinarily we push the chilled fluid through the evaporator during mechanical cooling with an evaporator water side pressure drop of maybe 40kPa. Then for free cooling the water is drawn through the free cooling coil first then the evaporator with a total pressure drop of maybe 140kPa. The the free cooling coil demands an additional 100kPa from the pump - this means a larger pump. Depending on evap and coil designs of course.

You might want to simply add a low loss header to the return line just before the evaporator inlet. Then from this give the free cooling coil its own pump to be cycled with the availability of free cooling (ambient verus set-point) and then the free cooling fans are inverter driven from a free cooling leaving water temperature senser to have the same set point as the chiller.

Do not dare go without glycol if you go free cooling - you will freeze up even with a good indoors load if you have more winters like recent.

[Goober]

I would be sure to have at least 20% ethylene glycol but preferrably 30%.

I didn't notice trace heating so perhaps they already have some percentage.

Compared to plain water 30% EG will have a freeze point of -14.1, system capacity of 97.3%, Power input of 99% and a pressure drop increase to 119%. That's all using the same pump.

Ordinarily we push the chilled fluid through the evaporator during mechanical cooling with an evaporator water side pressure drop of maybe 40kPa. Then for free cooling the water is drawn through the free cooling coil first then the evaporator with a total pressure drop of maybe 140kPa. The the free cooling coil demands an additional 100kPa from the pump - this means a larger pump. Depending on evap and coil designs of course.

You might want to simply add a low loss header to the return line just before the evaporator inlet. Then from this give the free cooling coil its own pump to be cycled with the availability of free cooling (ambient verus set-point) and then the free cooling fans are inverter driven from a free cooling leaving water temperature senser to have the same set point as the chiller.

Do not dare go without glycol if you go free cooling - you will freeze up even with a good indoors load if you have more winters like recent.What the F?

[DTLarca]

What the F?

You're not familiar with free cooling systems and chilled water design principles?

Only after I posted my reply I realised the image, which I had looked at perhaps an hour before, in a hurrry, was not the system to be modified but was already a free cooling system itself and thus would not need trace heaters having glycol in it already and so I could not guess whether the system to be modified already had glycol.

But to maximise your annual free cooling savings you will, much of the year, have to supplement it with mechanical cooling which is standardly located inline and downstream of the freecooling - the colder the free cooling leaving temperatures the less loaded is the mechanical cooling :)

[r.bartlett]

I don't really understand the need for the dirverter valve.

If the return was piped through the free cooler and then into the chiller its fan would be set only run during outdoor temps of 10 deg and below.

if the concern is that it would over cool in harsh winters then a second stat could be fitted in the free cooler outlet set at 10 degrees so the fan would only run when

1 The outdoor temp is below 10 c
2 The outlet water temp of the Free cooler is above 10c (we need flow temp of 15 c)

that seems a simple logic.?

the addition of a 3 port valve c/w a programmer etc -which most of these seem to have- seems a bit excessive unless there I am missing something??

35% glycol is a given btw.

[DTLarca]

the addition of a 3 port valve c/w a programmer etc -which most of these seem to have- seems a bit excessive unless there I am missing something??


What you're saying makes sense but there is natural convection at the inactive free cooler to consider and the unnecessary pump power consumed during periods when free cooling is not possible.

[frank]

Without the diverter valve, there is no way of stopping the flow through the dry cooler, therefore, no control of the water temps.

Even without the fan operating, the coil and frame will equalise with the ambient temp so at really low outdoor temps, some cooling to the water flow will occur.

With the diverting valve in place and proper control, the circulating water can be prevented from entering the dry cooler (bypass) and so some form of outlet water temp control can be performed

[DTLarca]

Without the diverter valve, there is no way of stopping the flow through the dry cooler, therefore, no control of the water temps.

Even without the fan operating, the coil and frame will equalise with the ambient temp so at really low outdoor temps, some cooling to the water flow will occur.

With the diverting valve in place and proper control, the circulating water can be prevented from entering the dry cooler (bypass) and so some form of outlet water temp control can be performed

Indeed, I understand a TESCO store using dry coolers for their CO2 integral units was not charged with glycol because they thought that since with the integrals there would always be a few running at any time there should be no need to use glycol and stopping the fans will be enough unloading. 2008's cold winter caused the dry coolers to freeze up despite all this - the natural draft and the wind combined were enough to over-cool the water - and keep in mind this was meant as condenser water :)

A mistake that I or anyone else could easily have made - this is why I say "do not even think of taking a chance on the glycol side" - with free cooling or dry coolers, in the UK, always use glycol.

[VRVIII]

Hi Richard,

It might be worth considering a chiller with inbuilt free cooling, a few manufactures now produce these including Airdale: http://www.airedale.com/v2portal/page/portal/airedale_int/airedale_intProductDefault/airedale_int_com/products/level_3_airedale_content_019.