chiller efficiency 1

[tuerca]

I'm looking for a good paper out there that outlines clearly the relationship between variable chiller flow and its direct effect on efficiency (i.e. kw/ton). The machine in question is a centrifugal 415 ton chiller with manufacturer's stated efficiency of 0.65 kW/ton. Thanks in advance!

 

I can try to obtain some literature for you. It would be helpful if you can reply with the chiller manufacturers name and model number and refrigerant (ie 11, 123).

I assume you are asking about a variable speed centrifugal chiller and the relationship between refrigerant flow capacity and chiller efficiency in kw/ton?

The .65 kw/ton you mentioned is a fairly efficient chiller and is right there with the newest machines which have ratings in the .58 & .59 kw/ton range. You must realize, that the specified kw/ton indicated in the manufacturers literature is that specific chiller, under a specified load, and at pure design conditions (chilled temp/flow - condenser temp/flow), and furthermore with specific electrical characteristics.

Generally, if you do the electrical math calculating rated tons vs actual voltage/amps/power factor or kw, you'll find out that the math usually doesn't add up. This is caused by the actual electrical characteritics and power factor being different from the ones tested or used by the manufacturer.

What this is summarizing, is that all parameters have to be at the precise and exact optimum characteristics for the specified kw/ton to actually exist on the job site. The real truth is, that your chiller efficiency would have been calculated the same as how all manufacturers do, and you just have to compare this efficiency from one to another.

If your question is just asking at what percent load and chilled/condenser conditions can I operate to obtain the maximum efficiency, this information can be determined in many ways - info from manufacturers data or calculating actual chiller gpm and delta t to obtain actual tonage at different percentages of load and measuring amperage at each of those load conditions as well. This will give you actual job site efficiency at each of the percentages of load where the readings were taken. In order to do this however, you must have fairly accurate tools to measure the chiller/cooler pressure drop to obtain gpm, an accurate thermometer to measure delta temperature across chiller/cooler, then calculate actual tons. to measure the amperage, either use the chiller display if its micro proccessor based or a good amp meter. from these readings, you can calcualte where the best efficiency is being achieved. The condenser flow should be at design gpm (somewhere around 1200 to 1250 gpm) and the condenser water inlet temp should be at 85 degrees. It is important that you have 85 degree condenser water for the testing because in the summer months, 85 degree condenser is at or around the best achievable temperature. Of course, this condition changes with your geological location.

Chiller efficiency increases with decrease in condenser water temperature. The condenser water temperature can be manipulated to increase chiller efficiency. You have to be a little carefull however that you dont run the temperature too cold to cause chiller problems (when you can get it there depending on ambient conditions), or definately not to the point where you waste cooling tower fan horse power trying to get the condenser water down to an unachievable temperature. There are controls on the market or can be built that look at ambient wet and dry bulb conditions to deterimine the achievable condenser water temperature. From this determination, a condenser fan set point is developed and controlled for, without wasting fan power, and getting the best out of your tower and efficincy out of your chiller.

I hope this can be of help to you,

Steve

 

[bumpjones]

If you are examining your chiller efficency in order to reduce your electrical bill another place to look is the condenser water pump. It is possible to reduce the pumping power required by reducing the flowrate of the condenser water. This reduces the pumping power required for the condenser water but it at the same time reduces your chiller efficency. The chiller uses more power but the condenser water pump uses less and the overall effect is to reduce the total power used, lowering your electical usage. Trane has written a short paper explaining the process. If you can't get one from Trane let me know and I will send you a copy. Good luck.

 

[leelock]

the answers you want have been debated in papers
on the trane.com and york.com website, where trane
is proposing 2usgpm/ton for condenser water flow,
and york is refuting it.
also note that at ari conditions of 44degF and
85degF, the latest trane centrifugal chillers
are inching towards 0.48kw/ton. we were already
using 0.54kw/ton units from york in the mid 1980s.

rgds
leelock

 

Leelock, 23 months ago, two 700 ton York YT R123 chillers were installed on one of our jobs. They are rated at .59 kw/ton (54-44 / 85-95). We have also recently changed out a of couple of 300 ton Carrier's, installed in the late 80's, which were rated at 1.0 kw/ton. Any comments?

 

[leelock]

re the 2 x 700tr yorks, at standard ari
conditions at this size range york can
get to 0.53kw/ton or thereabouts.
trane could get to about 0.48kw/ton.
however depending on the wet bulb in
your region it might make sense to have
inverters fitted for the compressors, in
which case i think york has the edge in
annual efficiency.

rgds
leelock

 

[arzelan]

Sir/madam,
Im looking for some answer to the problem i got right now. Im replacing old chiller with motor rating l/p kw= 375kw ton=402..=Ikw/ton =0.7
New chiller motor rating l/p kw=206kw, ton=350..=Ikw/ton 0.59.
can someone help me to find out how much i save in dollar term & KWH and how do you work it out? .
Thank you.(needed help very fast).

 

[bumpjones]

Your kw/ton doesn't add up for your present chiller 375/402=.93, so I can't use your numbers for the cost savings estimate but I can tell you how I figure the savings. First you must estimate the time weighted average load on your chiller in tons. You can calculate that by the temperature difference across the evaporator. Then multiply the load in tons times the kw/ton and then multiply that by the cost of your electical power. Do this for the old chiller and the new chiller and the difference will be the cost savings. Need more help let me know.

 

[arzelan]

G'day bumpjones,
Sorry i make a booboo on my last question i posted.
I should have put down 280/402=0.7kw.The 375 was the motor Horse power. Can you please help me on this again.
Thank you so much for your help.

 

[arzelan]

Dear Expert,
I need someone to tell me if there's any problem with the RH in the room if i increase the delta T by 1 degeed.At the moment the chiller is operating on delta T (4) which i think it's abit low, with ambeint tempt at 31c.Is the flow too fast or what? the leaving tempt from chiller is 5.9c and the entering is 9.7c, the condenser is 34c rtn, 28.7c supply.Any idea i can use? flowrate is 69.5 l/s

2.AHU (1) entering 8c, leaving 9c what can happen here? do we have choked coil or flow too fast?

Thank you