for a regular house HVAC system (Fu
for a regular house HVAC system (Fu
(OP)
for a regular house HVAC system (Furnace and AC unit), is the external static pressure the same in both heating and cooling modes? in my understanding the answer is No.
I mean can we say the furnace fan is 1600 cfm @ 0.5" for heating and 1600 cfm @0.5" for cooling.
I mean can we say the furnace fan is 1600 cfm @ 0.5" for heating and 1600 cfm @0.5" for cooling.





RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
And as you know when we calculate fan pressure we use index circuit ( the circuit having the highest pressure drop), is this circuit the same in heating and cooling mode? ( most house supply outlets have different cfm in heating than in cooling, if we say the outlet number 9 (100 cfm for heating and 75 cfm for cooling) is the index outlet, is it the same in winter and summer.
Wet coil usually have about 0.3 inWG pressure drop for coil only.
RE: for a regular house HVAC system (Fu
B.E.
You are judged not by what you know, but by what you can do.
RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
The grilles get adjusted by the HO so don’t sweat that. The only way to get the system to match the calculated is with 100% room by room zoning and then this will not fix all cases.
RE: for a regular house HVAC system (Fu
Looks like a single unit to do both modes; assume ductwork is not changing, no VAV boxes in ductwork I assume (not unless it is very big house).
Unless you want to analyze things to the nth degree the pressure losses of 1600 CFM through a given duct system will be the same regardless of whether it is in heating or cooling mode. Just look at your ductulator, it's not like we have different ductulators for different air temperatures.
This discussion seams to have gotten hung up on CFM requirements between heating and cooling and which is greater. And when one runs load calculations, I agree, there will be differences, what I will contend is for a residential unit it does not matter which mode requires more. I say this because it is extremely rare to find a residential unit that changes the fan speed based on the heating/cooling mode. What is important is that the unit is able to provide the maximum required CFM through the ductwork.
RE: for a regular house HVAC system (Fu
dbill74, my concern is about using the same cfm at the same pressure loss for heating and cooling for a regular small house with simple furnace, AC unit, and simple duct design, is it right in theory to say this furnace fan give 1600 cfm @ 0.5" in heating and 1600 cfm @0.5" in cooling.?
RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
No, it's not right.
If you are "rating" a piece of equipment you are (or should be) rating it in accordance with an established standard. Without citing the standard no one will ever know the conditions used to establish the rating, and the numbers are effectively meaningless.
RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
Because you stated "in theory" the answer is NO. Go look up the properties of moist air at different states (temperature, RH and pressure), if know anything about fluid mechanics that search result should be enough.
But as Willard said, the difference is small enough that "in practice" the answer is YES.
RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
Correct. On an evaporator wet coils (in cooling) have much higher pressure drops than dry coils (in heating).
As an example: I am currently looking at the cut sheet for a basic 4 ton nominal goodman residential unitary split DC evaporator (CAPF4860). At 1600 CFM the coil has a dry pressure drop of 0.220" w.c.; when the coil is wet with condensation that number jumps to 0.355" w.c.
RE: for a regular house HVAC system (Fu
RE: for a regular house HVAC system (Fu
They all agree.
What else do you expect?
RE: for a regular house HVAC system (Fu