Posted by Noon-Air on March 6, 2005, 10:37 pm
THis is why a correctly sized and installed system is so important. When in
doubt, if the load calc calls for a number of BTU cooling, its best to
actually look at the specs of the equipment componant combination and the
actual BTU capability of the equipment. When in doubt, I personally will
recommend a little bit smaller system maybe a 2 1/2 ton instead of a 3 ton,
if for nothing else but better humidity control. This also reinforces the
need for expantion valves and variable speed blowers currently only found on
the super high efficiency (high dollar) equipment.
Posted by Gymn Bob on March 6, 2005, 11:06 pm
I think that "smaller than calculated size is being lost for better logical
thinking these days. Although this is a good idea it ends up costing more to
run the system and less comfortable by the residents. Sure the humidity may
end up being lower but the residence may be overheated upstairs where the
sleeping areas are until 3:00 AM in the morning. This overworks the
compressor and lowers the comfort level or the occupants, not allowing them
to live the way they desire.
A little education and experience goes a long way with your customer base
also. In a hot/cold seasonal climate many people like to open their windows
when the air conditioner is not required. Suddenly one day the home becomes
overheated and before they realize it becomes almost 30C in the home. The
windows get shut and the A/C system goes on. The humidity is already in the
furniture and walls and the undersized system you have installed now takes
3-4 days to lower the humidity and the temperature. A customer tossing a
turning in a 28C home in the middle of the night because it is too hot is
not a happy customer and does not "spread the good word" about your
installation. I hear this complaint all the time in my area. The humidity is
the problem with a smaller unit.
Telling the customer to turn his unit on in May and off in December may do
the trick for many people but if you ever have guests over the human heat at
the party makes the guests ask "Can you turn the A/C on?" ... another happy
customer in front of all his/her friends the system allows the home to go up
The old paradigm will die hard but people are beginning to learn not to go
with the cheapest bidder because he undersized the compressor and A coils.
The lower humidity comfort idea is just a myth and not very acceptable to
most people after the bill is paid. It usually doesn't provide comfort in
the long run.
This may not apply to regions with more arid climates that don't endure
<bottom posting mess deleted>
Posted by Noon-Air on March 7, 2005, 12:08 am
thats assuming multiple floors, single system with no zoning...here the
lions share of homes are single story on a concrete slab with the furnace or
air handler in a hall closet, and ductwork in the attic.
There are only a couple of weeks here when folks can open their
windows....just about a week before Halloween, and then for about a week
just before Easter. Otherwise its either too hot, too humid, or too cold. We
do have 4 seasons here....December, January, February, and summer
You never heard of auto change-over programmable thermostats??
Not in this neck of the woods... the cheapest bidder just throws in whatever
size that was already there or the customer wants a bigger unit so he gets
it instead of correcting the problems with the complete system. Not unusual
to find where a hack has put a 5 ton package unit with flex duct running
under a house outside of the city limits where there is no license
requirement or code enforcement. I also run into a lot of "Its not cooling,
it needs more FREON". I recover almost twice as much refrigerent from new
customers overcharged systems, than what I sell.
So explain how cold and clammy equates to comfort??
BTW... what are *your* design parameters for you to corretly size a system??
Do you do a complete room-by-room heat load/loss analysis before you size
and install a heating and cooling system?? What type of systems do you
normally install?? zoned?? multi stage?? gas?? electric?? heat pumps??
Posted by Gymn Bob on March 7, 2005, 3:03 am
I have only been involved mostly with residential systems.
I rescued one home with a 60,000BTU furnace and a 2 ton unit installed. The
owner complained of the original installer coming out many times and taking
stupid air movement readings for registers. Then telling him they had to get
blinds for all the windows and to expect the upstairs to be 5-10C hotter
than the downstairs where the 6 foot long pipe runs over the central furnace
blasting cold air directly at the thermostat would shut the system down
early. This system never stopped going full blast until 3-4 am every day.
The unit cut in at about 11 am and never cycled until shut down again.
This is way 99% of the installers do it here. They take a bunch of
measurements of windows and ask about insulation and then look at the BTU of
the furnace. The measurements all go inthe garbage because they don't know
what to do with them. There are too many factors involved anyway. The
problem with this home was it had 3 floors exposed due south and had an
amazing amount of heat gain. 60KBTU for a 2500 sq. ft. home in Canada is
pretty small. So the guy puts in the 2 ton unit, based on the furnace BTU,
and it doesn't work.
We got him to rip it out and give the money back all except about $50 for
the wiring, breaker and unit service disconnect (required here). Then we
install a 2.5 ton unit with a 3 ton A coil (changing the orifice) and
reposition the A coil the correct way (had it in sideways making massive
turbulence). Customer is happy and it works great the way they want it. Uses
the setback thermostat to drop a degree at 3 am to circulate the air. Single
zone, no fancies needed. The hockey rink in the basement is open from 10
am - 10 pm each day though...LOL Hard to avoid that one with single zoners.
Oh yeah! The owner ended up about $00 cheaper for the larger unit when it
was all done.
As far as humidity goes if you oversize the unit it can become a problem
sure but I have seen heat pump units that are double the A/C requirements
and the problem isn't that great. Mind you the heat pump is undersized and
the backup heat needs to run regularly. Last thing I heard on these was
systems to adjust the BTU capacity season to season were being tried. Most
gave up on them after they all became maintenance nightmares that would cost
them more than a whole new gas furnace and weren't cost effective when
maintenance was considered.
Furnace size is definitely a good start but other factors have to be
considered. Some are only customer reports but the measurement system and
windows is only a joke anyway. You can't tell how well the insulation in the
walls was packed or carefully placed. Should I measure size and distance of
all the trees and pit them against average wind velocity measurements
too?...LOL Not for the $00 one makes on an installation. I don't like
working for minimum wage. Homes here run from insulbrick to R48 in the
ceilings depending on when they were built. There is a lot of leeway in the
Posted by Noon-Air on March 7, 2005, 3:29 am
Let me get this right... you do a complete system installation and only make
No wonder you can't do it right... you can't afford to, you'll go broke.