advanced hvac question

[Ben J. Gromicko]

Calculating air flow through a duct system is dependent on the static pressure

a) More pressure inside the system will cause air flow out the register to decrease

b) The static pressure requirements for the duct designer are listed on the furnace data plate

c) Static pressure is generally measured by water column inch

d) Answers b and c are correct

[David C. Macy]

The answer is D

Static pressure is the force that moves air through
the duct system. It is measured in water column
inches. Total pressure is velocity pressure + static
pressure. To understand static pressure suppose
the air handler fan pushes air into the duct system.
When the air fills the space it creates pressure and
the pressure forces the air out through the branch
ducts and then through openings (supply
registers). The air moving out of the registers is
the velocity pressure and the pressure remaining is

the static pressure.

[Charley L. Bottger]

I thought we were going to have a advance question that is elementary

[jallcroft]

You have a 30’LX20’WX10’H room. The room already has a 30,000 BTU natural gas water heater in it pulling combustion air from the room. What is the largest BTU high efficiency natural gas furnace you can install in this room before the room is considered a confined space?

a) 120,000 BTU
b) 90,000 BTU
c) 60,000 BTU
d) None of the above.

[Ben J. Gromicko]

I'll bite. Assuming the furnace does not have a 2-pipe system with dedicated combustion air from outside, I'll say "almost B" (89,999 BTU).

[Jae Williams]

Originally Posted by cbottger

I thought we were going to have a advance question that is elementary

"Elementary" is different things to different people...

I know some who went throught elementary school in 5 years...I was there until I was 32...

[David A. Andersen]

You were just dodging the draft Jae!

[jallcroft]

Originally Posted by bgromicko

I'll bite. Assuming the furnace does not have a 2-pipe system with dedicated combustion air from outside, I'll say "almost B" (89,999 BTU).

Yeah, it was a bit of a trick question... Wonder how much efficiency is lost from a 90+ if the combustion air is drawn from the conditioned space?!?!

[jallcroft]

Alright, here is another,

The condensate from a running AC system is:

a) Slightly basic.
b) A neutral 7 on the PH scale.
c) Very acidic.
d) Has a PH close to orange juice.