Determine what pressure will be required

| January 29, 2015

In the 1800s, before the development of modern air-conditioning, it was proposed to cool air for buildings with the following procedure using a large piston–cylinder device [“John Gorrie: Pioneer of Cooling and Ice Making,” ASHRAE Journal 33, no. 1 (Jan. 1991)]:

1. Pull in a charge of outdoor air.

2. Compress it to a high pressure.

3. Cool the charge of air using outdoor air.

4. Expand it back to atmospheric pressure.

5. Discharge the charge of air into the space to be cooled.

Suppose the goal is to cool a room 6 m x10 m x 2.5 m. Outdoor air is at 30°C, and it has been determined that 10 air changes per hour supplied to the room at 10°C could provide adequate cooling. Do a preliminary design of the system and do calculations to see if it would be feasible. (You may make optimistic assumptions for the analysis.)

(a) Sketch the system showing how you will drive it and how step 3 will be accomplished.

(b) Determine what pressure will be required (step 2).

(c) Estimate (guess) how long step 3 will take and what size will be needed for the piston–cylinder to provide the required air changes and temperature.

(d) Determine the work required in step 2 for one cycle and per hour.

(e) Discuss any problems you see with the concept of your design. (Include discussion of any changes that may be required to offset optimistic assumptions.)

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Category: Coursework

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