Evaporative Condenser with HVAC CHiller ?

[kiranne]

Hello,

Anybody knows why you never see evaporative condenser with HVAC chiller, although they are more efficient then air cooled type or water cooled shell and tube type ?


Thanks

 

[freefallingbody]

Kiranne,

There is still a lot of money being made from inefficiency, thats why.

Evaporative condenser pads ( Celdek pads made by Munters) are common these days as an add on feature offered by manufacturers in coutries like India.

Most of the Ice plants, cold storages etc use Ammonia chillers with evaporative condensers.

I also wonder why its not common in typical air conditioning machines!

Regards

Dinesh

 

[RossABQ]

This is not a straight-forward question.

The total cost of ownership of an air-cooled machine tends to be less than that of water-cooled, until you get up to a total installed tonnage that justifies the additional maintenance costs of water cooling due to the better energy efficiency.

Cooling towers are high maintenance, more so when water is poor quality. I've seen tower systems that ran out of chemical feed for a week, and became so junked up that the repairs and cleaning costs far outweighed a year's energy savings (compared to air-cooled).

At some point (system tonnage) there may not be the physical space to have a bank of aircooled machines. In cold climates the potential for freezing adds other concerns on the water-cooled systems.

 

[lilliput1]

It is risky to pipe refrigerant through the building to an evaporative condenser.

 

[willard3]

snip
It is risky to pipe refrigerant through the building to an evaporative condenser.
snip

Good point........

 

[sterl]

People put in air cooled's cause:

They're cheap.

They don't load up a roof a whole lot.

They are largely of fairly shallow profile, so they are not architecturally objectionable.

They don't mold or ice film on the side of your building.

They don't care much which way the wind is blowing.

They don't pump steam.

The real question is why ever do a cooling tower instead of EC's?

The Refrig Pipe point is a good one, but there are big advantages to thermosyphon and similar heat transfer arrangements, and you really can't do that with CT water.

Duty cycle has a lot to do with it: a sizable 16 or 14 hour a day process thrives on EC's, cause there is no inherent thermal flywheel and the load doesn't tend to go near-zero.

 

[kiranne]

Thanks all for your answers.

All of the above are good points that explain most of the reasons why EC are not more widely used with HVAC chiller. As a result the chiller packages do not include the possibility of having an EC.

If you take the case of a chilled water chiller running wit R134a in an industrial facility in a country where frost is not an issue then :

-architectural considerations on an industrial site are not really a problem
- no fear of having freezing

In that case it is theorically possible to consider a EC, but chiller packages on the market don't propose this alternative, it would be either air cooler or else with cooling water.

I read in a fridge book that one of the reason is that for example if u take a centrif chilled water chiller, the refrigerant chosen will have a high specific volume which will make the condensing process in tubes not pratical. But looking at refrigerant's properties for example at 30 C R134 is 0.0265 m3/kg and ammonia is 0.111 m3/kg (both are vapour specific volume).
In this example Ammonia has a higher specific volume than R134a at this temperature. But EC functions often with ammonia so I don t understand the above reason.

 

[imok2]

The biggist problem I had with ECs is the water issue. They require a lot of attention to the cycles of concentration and chemistry and are not forgiving. There have been instances where I had to replace ECs for air cooled because the maintenance was unreliable. A well maintained EC is hands down a better system and a great energy saver IMHO.

 

[DrRTU]

Did you ever look at using one of these

http://www.aaonnet.com/LL_Evap.aspx

 

[sterl]

Specific volume is not really an issue: a relatively strange looking intensity unit, Volume Flow per (unit of heat transferred) leads to the circuiting criteria for any of the refrigerant-in-tube heat exchangers, and that unit will be considerably different for R-717 as opposed to R-134 due to the large latent of R-717.

So an evap condenser designed for ammonia will have considerably different circuit total lengths than one designed for R-134, as would an air cooled.

The control topic with an evaporative can get quite involved, especially if liquid line pressure is a substantial criteria. Control on water cooled is pretty simple, the regulators are on the water side and therefore relatively serviceable, and to a large extent on a circuit that does not sprawl or have alternate diversions for discharge gas, there will be no need for a high pressure receiver or other tolerance for swing in active refrigerant charge.

Excluding freezing from the design criteria: An evaporative installation will be more compact and involve less piping and less pump and fan HP in total than a water cooled. At large loads, and barring a use for "tempered" air off an air cooled condenser, the evaporative will be more compact and involve less total piping than an air cooled, once you reach the point where more than (2) air cooled's are required to balance the load.

The water treatment issue is a good one, though on an air conditioning load, a desuperheater will reduce both treatment and consumption costs. For a one on one arrangement, a cooling tower is easier to maintain and of itself not as sensitive as an EC to the accumulation of small amounts of scale; but if descaling involves tube cleanout on 3 or 4 shell and tube condensers, the effectiveness nod goes back to the EC.

 

[TXiceman]

One small company I worked for in Oklahoma built a line of evap condenser cooled water chillers with semi-hermetic screws. Pretty neat units and pretty good on power.

The problems have all been mentioned above and most can be adapted to or corrected. As for water treatment, it is a maintenance issue. Usually where you see poor water treatment, you will also see overall poor maintenance.

You can cut down on the vapor cloud in cooler weather by the addition of a desuperheating coil on the air outlet for the coil. Just heat the saturated air and get it away from the dew point. We built several units with the anti-fog coils as well as special low noise attenuation baffles on the air inlet and outlet.

For cold climates, you can use plate fins on the coils and run dry part of the year. Also indoor sumps to prevent winter freezing problems.

The one industry that really uses the EC approach is the food industry as they have the need for a lot of refrigeration and want to save on power.

Ken
KE5DFR

 

[marcoh]

Every time I have looked at evaporative condensers the outdoor plant has been located too far away from the chillers and traditional cooling towers have been used.

For large installations they do become very expensive and the only really saving is in reduced water usage.

 

[EddyC]

kirane,

Carrier makes the kind of chiller that you are talking about (indoor chiller to be used with outdoor evaporative condenser). I've seen it on their website. Please also note that some manufacturers also make evaporative chillers (Outdoor combined chiller/evaporative condenser unit).