1. HVACR416 - Design Psychometrics Unit 35 Refrigeration & Air Conditioning Technology

2. Air Before you can grasp an understanding of Air Conditioning, and Heating design you must understand the properties of air.

3. Air Air changes with: o Changes in temperature o Changes in pressure o Changes in humidity o Changes in weight o Changes in content

4. Volume and Temperature Air changes volume with temperature. o There is a temperature / pressure relationship. o Virtually all substances expand as the temperature increases, and air is no exception.

5. Volume and temperature An example of this is to place a glass, upside down in a pan of water trapping the air inside of it. Gently heat the glass and you will see air bubbles push out from the bottom of the glass.

6. Volume and Temperature Formula for volume and temperature: V 1 T 1 --- = --- V 2 T 2 V1= original volume T1= original temperature V2 = new volume T2= new temperature

7. Volume and Temperature V 2 = V 1 (T 2 /T 1 ) So, the Volume after the temperature increase is the 1 st volume times the second temperature divided by the first temperature.

8. Absolute Temperature For any air calculations you must use absolute temperature. o Absolute Zero Temp = -460 degrees F For any air calculations you must use absolute pressure: o Psia = Gauge Pressure + 14.696

9. Volume and Pressure The volume of a constant weight of air will decrease with an increase of pressure. We can fit 1 pound of air in a ¼ of the space if the pressure is increased. Example: Nitrogen cylinder.

10. Volume and Pressure This increase of pressure must happen at a constant temperature. The formula’s for calculating this relationship is: (V 2 /V 1 ) = (P 1 /P 2 ) V 2 = V 1 (P 1 / P 2 ) P 2 = P 1 (V 1 / V 2 )

11. Volume, Pressure, and Temp Changes in volume with respect to both temperature and pressure can be found by calculating both individually. Example: Ten cubic feet of air at atmospheric pressure and a temperature of 85 degrees are to be compressed to a final pressure of 30 psig. The final temp is 125 deg. Find the volume.

12. Volume, Pressure, and Temp First find the change in volume with pressure: o V2 = V1 (P1/P2) o V2 = 10 (14.7 psia / 44.7 psia) o V2 = 3.29 cu. ft

13. Volume, Pressure, and Temp Next find the change based on temperature using the volume just found: V2 = V1 (T2 / T1) V2 = 3.29 (585 / 545) V2 = 3.53 cu. ft.

14. Volume, Pressure, and Temp The following formula can be used to calculate volume at any temp. and pressure. V = 0.37 ( T / P)

15. Comfort and Humidity Comfort o The properties of air determine our comfort.  Temperature  Humidity  Air Movement  Air Contamination

16. Comfort and Humidity Temperature affects the human body because of: o Body temperature (98.6 degrees) o The way the body adjusts to temperature changes - by sweating or shivering o The way the body gives off heat and absorbs heat is through the skin.

17. Heat Transfer There are four methods of heat transfer: o Evaporation - water evaporates from a surface and leaves the surface cold. o Conduction - heat transfers from one side of a substance to the other. o Convection - Heat is moved by the use of air or water. o Radiation - Radiation like sunlight warms an area.