HVAC - Why Not Constant Volume
HVAC - Why Not Constant Volume
(OP)
I'm new to HVAC and thermodynamics in general, and am struggling with something pretty basic. All the examples I've seen with the the psychometric chart imply the cooling and heating process of a environment is constant pressure. Even for a house, why isn't constant volume more accurate?
I'm assuming it is because of air infiltration/leakage? If this is the case, then how does one go about determining how much infiltration will occur? Do you normally use a rule of thumb?
I'm assuming it is because of air infiltration/leakage? If this is the case, then how does one go about determining how much infiltration will occur? Do you normally use a rule of thumb?





RE: HVAC - Why Not Constant Volume
RE: HVAC - Why Not Constant Volume
RE: HVAC - Why Not Constant Volume
RE: HVAC - Why Not Constant Volume
RE: HVAC - Why Not Constant Volume
The saturation pressure of moist air is a function of temperature only. Refer the two formulae on pg 1.2 of your 2009 Fundamentals.
In practice the localised ambient pressures on a building vary considerably due to wind and stack effect, but this is often transient and otherwise averages out. Deliberate mechanical pressurisation is insignificant.
RE: HVAC - Why Not Constant Volume
RE: HVAC - Why Not Constant Volume
RE: HVAC - Why Not Constant Volume
In hydrodynamics, it is hard to reach assumption how acceptable error from simplifications is, but once you have quantifiable results, mostly as combination of theory and long-time observations - than new technical field is open.
Most of air handling works in range up to 700-800 Pa, and up to 1000 Pa air can still be assumed to be incompressible (like water), which enables much of simplifications.