Chiller & electric cooling ton-hour

[1952mike]

Hi all,

If I have this Co-Gen unit that can generate enough hot water to power a 600 ton absorbtion chiller and the system runs about 8000 hours a year, then what would equivalent "ton-hours" of electric cooling be?

I am guessing it would be 600 * 8000 = 4,800,000 ton-hour of electric cooling but I am not sure.
I am at a loss if there are inefficiencies (sp?) that I need to consider.

 

[Yorkman]

I usually see the term of ton hours used in conjuction with thermal storage. And it usually relates to how many tons of cooling capacity you have available based on, the pounds (tons) of ice storage multiplied by the hours the load is present. Or another way to put it. The load you have multiplied by the time the load is present = ton hours. Example 120 ton load for 11 hours = 1320 ton hours.
Running the value over a year run time does not take into the variations in load. The number your getting can be very misleading. Many times the load is broken into hourly values and added up to achieve the ton hour number.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int.

 

[Yorkman]

What temperature are you trying to achieve for your inlet combustion air for the turbines? About 6 years ago we took out two 1000 ton absorbers from a 275 Mega-watt co-gen plant in Colo. They were trying to get 47 - 49 degree combustion air. That required 37 - 38 degree chilled water @ 35% glycol, pretty tough for an absorber. They ended up installing 3; 1450 ton centrifugal chillers putting out 37 degree water, and are quite pleased with the result. The only small snag is the existing cooling towers are about maxed out when the wetbulb, drybulb, and demand all peak at the same time. They are considering putting in 5000 tons of dedicated tower so they can run lower condenser water temps for the chillers at peak loads.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int.

 

[1952mike]

The system is not a turbine, but couple of gas engines driving generators, and using exhaust gas & the jacket water heat to heat up absorbtion chiller's hot water circuit. The customer has this requirement that by running the system for 8000 hours a year & powering 600 ton chiller, we need to offset 4,800,000 ton-hour of electric cooling! Another word, if this chiller didn't exist, they would have spent 4,800,000 ton-hours of electrical energy to cool whatever they are cooling (or so I guess)!

Thanks
Mike

 

[quark]

Another word, if this chiller didn't exist, they would have spent 4,800,000 ton-hours of electrical energy to cool whatever they are cooling (or so I guess)!

No. There is nothing like 4,800,000 ton-hours of electrical energy. The coefficient performance of electrical prime moved refrigeration systems (for example vapor compression systems) have better COP than an absorption system. A 600 ton capacity centrifugal chiller will consume about 0.6 kW/ ton cooling at full load.

Though it may exist, ton-hr seems to be the most inconsistent unit (unlike kW-hr) I came across and can enhance already existing confusion about tons. It will be simple and prudent to use either btu/hr or kW and btu or kJ when you take up energy savings calculation.

 

[1952mike]

If I understand your comment correctly, the offset would be in the order of 4,800,000 * 0.6 = 2,880,000 ton-hour (or even half that amount 2,400,000) am I right?

Thanks
Mike

 

[MintJulep]

Ok, so this is an avoided cost calculation.

First of all, just because the chiller nameplate states "600 ton chiller" doesn't mean that it is running at rated capacity all of the time. Is this a process chiller, or space cooling?

1 ton = 12,000 BTU/hr

And 1 BTU/hr = .29 watts

However, if you put .29 watts into an electrically driven chiller you do not get 1 BTU of cooling out. You get more. You need to consider the coefficient of performance of the chiller.

So

Step 1: Figure out how many tons of cooling is really produced annually.

Step 2: Figure out what types of electrically driven chillers might be used in place of the existing system, and calculate how many kW-hr it would suck down to produce the same cooling calculated in step 1.

Step 3: Don't forget to consider the utility rate structure. (that is, the client's demand charges will go up too)