Whenever liquid and vapor coexist in a closed vessel, they will be at saturation. This concept comes into play when a condenser discharges into a receiver. The liquid refrigerant often leaves the condenser with some subcooling. However, once in the receiver, liquid and vapor will coexist in a closed vessel, so they will be at saturation - some of the subcooled liquid will evaporate to cool the remainder, and all subcooling will be lost.
Looking at a refrigerant table, 135 psig is 150 psia, which corresponds to a saturation temperature of 47F. If the actual temperature is 59F, the vapor is superheated.
3. The value of the superheat/subcooling is:
The saturation temperature from a refrigerant table is 47F. Superheat is actual temperature (59F) minus saturation temperature (47F) or 12F.
4. A conference room has a latent load of 2550 BTUH and must be maintained at 76F with a relative humidity no greater than 55%. The adjacent spaces are maintained at 52% rh. The air quantity that must be drawn in from the adjacent spaces and exhausted from the conference room to keep the conference room rh below 55% is:
Design specific humidity in the conference room (76F/55% rh) is 0.0106 lb/lb. Specific humidity in the adjacent area is (76F/52% rh) is 0.0100 lb/lb. As the slightly dryer air from adjacent spaces enters the conference room, it can pick up moisture. The applicable formula is BTUHl = 4840 * CFM * Δlb/lb. Rearranging, solving, rounding, and choosing the closest answer, CFM = 2550/(4840 * (0.0106-0.0100)) = 850.
5. A system has 16,000 CFM of return air leaving the space at 76F db/50% rh. The return air plenum heat gain is 44 MBH. The dry bulb temperature entering the mixing box is:
Return air entering the plenum picks up the heat gain in the plenum on its way to the mixing box. The applicable formula is BTUHs = 1.1 * CFM * ΔT. Rearranging and solving, ΔT = 44,000/(1.1*16,000) = 2.5F. The air temperature leaving the plenum is 76 + 2.5 = 78.5F