Rookie Question - COP for 1200 Ton Chiller

[toothless]

I am not a refrigeration guy, but I overheard an engineer in another section talking about purchasing another chiller for his section. The one he is getting consumes 935 kW to get 1200 tons of chilling. This is a COP of about 4.5. I'm no expert, but I am under the impression that a COP of 4.5 is NOT very good. What would be a decent COP for a 1200 ton chiller producing 39 F water?

I appreciate any info you could provide.

 

[krb]

By todays standard, for an HVAC application that is not very good. The higher the COP the better. But there are alot of variables that affect this number, so it is hard to say if this is good for that particular application or not. Another way to look at this is that equates to .78 kW/ton. For a new HVAC application, you can get a chiller to run at full load conditions around .6 kW/ton, some applications will be better, some worse. You may ask about some of the specifics to get a better understanding of the application (condenser water temps, refrigerant, brand, etc.) to determine if this is good or not.

KRB

 

[imok2]

The term Coefficient of Performance (COP) is simply the ratio of the cooling effect produced expressed in Btu/hr divided by the energy input expressed on the same basis. For an electric chiller at 0.6 kW/ton, this ratio is 12,000 Btu for a ton of cooling divided by the corresponding 0.6 kW energy input. The units of kW can best be thought of as kW hours per hour. Each kW is equivalent to 3,413 Btu, therefore 0.6 kW is 2,048 Btu. Therefore, a 0.6 kW/ton chiller is equivalent to a COP of 12,000 Btu/2,048 Btu, about 5.9 COP. Notice the term COP is dimensionless.

There is a short-cut formula to compute COP directly from any given kW/ton. Simply divide 3.516 by the chiller's kW/ton to derive COP. (3.516 comes from dividing 12,000 Btu by 3413 Btu per kWh). For example, 3.516/0.6 is the same ~ 5.9 COP as before. Be careful when comparing cooling system COPs to be sure exactly what is being included. A fair comparison includes the full heat rejection circuit as well.

 

[quark]

Your COP is coming out to be about 5.2 instead. 0.78kW/TR seems to be practically reasonable figure, on an average. If that is what the manufacturer promises at full load, then you have better chillers.

Like Imok2 suggested, it depends upon the lowest cooling water temperature available.

 

[HVAC68]

1200 tons = 4219 KW
With a 935KW power consumption, COP would be 4219/935 = 4.51.

Please note that the chilled water temperature - It's 39 deg F and not the standard 42 or 45 deg F that we use.

The COP is bound to be lower with a lower chilled water temperature.

Other variables which affect the COP are condenser water entering temperature (This must be is a water-cooled chiller), fouling factors (quality of water).

Having said all that, comparing COP at full load only is not the right solution. You need to find out at what capacity the chiller generally works for most number of hours in the year and do a SPLV calculation if possible. IPLV numbers may also give a better insight, though not very accurate and has its own detractors.

Judging a chiller solely by its COP value is definitely not the best method.

HVAC68

 

[Cooky]

I opened this thread, intending to contribute my experiences of chiller COP to the discussion.

Instead, I was too distracted with the use of metric AND imperial units to create a ratio!!

Please use either metric OR imperial units (preferably metric).

Sorry for the rant, but I had to say something.

Cooky

 

[toothless]

We used Fahrenheit (imperial), tons of refrigeration (imperial, I think), and kW (metric and imperial). Where is the confusion?

 

[ChrisConley]

One of the standard efficiency ratings for air conditioning is EER.

It took me forever to figure out that it was kW/Btu/hr.

It does make some sense as AC equipment is rated in Btu/hr and electricity is billed in kW - but the mixing of imperial and metric makes it hard to follow.

Besides EER can anyone think of any other 'mixed unit' numbers?

 

[quark]

Objection your honour!

TR is more metric than imperial, IMHO. There is a straight conversion of 1 ton ice to 1000 kgs of ice. Anyhow, that is a standard ratio (kW/TR) in this part of the world.

Chris!

Not many to my idea, but if liters are not metric, then unit of leakrate mbar.L/sec is a mixed unit of measurement.

 

[KiwiMace]

It is quite apparant that we from the non-american part of the world generously adopted the units; kW/RT, RT and EER in order to introduce transitional language into the US vocab and help the americans metrify. Well, what happened? =)

 

[walkes]

Quark,

My thoughts on one ton of refrigeration, one metric tonne of ice is 1000 kg. (2200 lbs), One ton of ice is 2000 lbs. I believe a ton of refrigeration is based on 2000lbs of ice.

 

[toothless]

The latent heat of fusion for water is 144 BTU/lb.

144 BTU/# * 2000 #/ton = 288,000 BTU

This energy over a 24 hour period is 1 TR.


30 years ago as a kid I was told America would switch to metric units. While I see some advantages to metric units (base 10), I am comfortable with English units. I can tell you that based on the progress we (America) made toward the metric system in the past 30 years, it will be a long time, probably never, that we will switch over.