View Full Version : New Guy

ColdHam32

22-07-2013, 06:00 PM

I am relatively new at my current position of refrigeration engineer. This is a food plant using ammonia as a refrigerant. I have a couple of basics questions. First, I was curious to know how to calculate sensible and latent heat for a water chiller. It is a plate chiller with liquid overfeed of ammonia. Just curious on what equations and how to use them. Secondly I am trying to figure out how to do an energy and mass balance for my plant and am looking for examples or guidance. Any help would be appreciated. Thanks.

frank

22-07-2013, 07:30 PM

You need to do your calculations for the load to be cooled, not try and calculate for the chiller.

Once your cooling load is known, then you select the plant to handle the load.

Calculations include:

Product

Lighting

Infiltration

Occupancy

Machines (fork trucks etc)

Structure (building)

Once the load is known, then you divide it by the time cooling is required (t1 - t2) to find the nett cooling duty.

ColdHam32

22-07-2013, 10:19 PM

I already have the chillers in place and know the delta T for the water. I also know the conditions of the ammonia at inlet and suction. I am just curious as how to apply the equations.

Q=M*C*(T2-T1)

Q=M*Delta H

For latent heat is it the enthalpy of the ammonia or the water I am using in the calculation. It is the ammonia being vaporized, although this is a liquid overfeed, so I guess I am not sure how much latent cooling takes place in a flooded coil?

Magoo

23-07-2013, 06:09 AM

Best advise is get hold of a copy of " Principles of Refrigeration " by Roy Dossat easily available on line from Amazon.

frank

23-07-2013, 09:09 PM

OK...so you have the chiller and you know the dt.

lets assume that you have a 6K dt (water entering = +12C, leaving = +6C)

Without the flow rate of the water, how do you know the cooling capacity of the chiller?

Without the cooling capacity, how do you know how much product/air/equipment/structure/lighting/occupancy you can cool, and over what time?

ColdHam32

24-07-2013, 04:17 PM

The flow rate is 150GPM and the Delta T is 15 F. Using about 26 F liquid ammonia. It is a flooded coil however. I am questioning the latent heat that takes place? Do you use the ammonia or the water? If the ammonia, how much latent cooling takes place in a flooded coil? There is not as much evaporation taking place.

frank

24-07-2013, 10:46 PM

Do you have any experience in using Phycrometric charts http://en.wikipedia.org/wiki/Psychrometrics

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