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Join Date: May 2011
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### Cogen Efficiency with HVAC?

06/12/2012 1:47 AM

I am having a confusion in calculating the overall cycle efficiency of Cogen plant with kets see exhaust chiller..

- suppose we are producing 2000 TR and 3000 KWe. I am considering to convert TR into KWth and then add into KWe

= (TR in KWth+KWe)/ (Fuel in KWth).

Should we add in the FUEL KWth + the heat rejected in the chiller during chilling ?

= (TR in KWth+KWe)/ (Fuel in KWth + Heat rejected in the chiller Kwth).

or we should not consider the TR as the excat KWth?

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#1

### Re: Cogen Efficiency with HVAC?

06/12/2012 10:06 AM

Intuitively, the first calculation makes more sense.

Treat the areas separately. Chiller calculations produce a coefficient of performance, not an efficiency, and require a generated power stream in order to perform the chilling. No power, no chilling.

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#4

### Re: Cogen Efficiency with HVAC?

06/13/2012 12:37 AM

Thanks for the reply. I case of chiller the TR in KWth is usually energy output into the whole system. Bt at what expense in terms of KWth?

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#2

### Re: Cogen Efficiency with HVAC?

06/12/2012 11:35 PM

What are expansions for KWth & KWe?

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#3

### Re: Cogen Efficiency with HVAC?

06/12/2012 11:54 PM

Refrigeration machine is reverse heat engine. I n heat engines efficiency which is the ratio of heat input to work out is used whereas in refrigeration machines term COP which is the ratio of net refrigeration effect to the work input. 1. T.R= 12000 btu/hr or 3000 kcal/hr. .

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#5

### Re: Cogen Efficiency with HVAC?

06/13/2012 1:12 AM

The straightforward approach is to look at equivalent energy displaced divided by the energy input.

The generator creates a certain amount of electricity that displaces purchased electricity.

The thermally-driven chiller also displaces a certain amount of electricity (use a reasonable value, one that is easily purchased, like 0.6 kWe per 12,000 BTU (or 3.51 kWth) to determine the displaced electricity that would have been purchased which was provided from the thermal output.

You can only count the "waste" thermal of the chiller IF you are using it for some beneficial use that can be quantified- like displacing some thermal load that would have required some defined input which will not happen.

For simplicity, convert the input thermal to electrical equivalents as well and calculate the efficiency as a simple output divided by input.

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#6

### Re: Cogen Efficiency with HVAC?

06/14/2012 9:15 AM

WOW .. Thats Great.. Thanks a lot .. I got the concept... iTs now managable Overall efficiency ....:) thanks a lot