Putting to rest the "undersize coil for humidity removal" argument
Jason
in Dallas who either 1) understands that purposely using a "mismatch" with a
smaller coil than is indicated by the BTUH rating of the condenser will
remove latent heat (humidity) better; and, 2) that using a 2.5 ton coil with
a 3 or even 3.5 ton condenser is okay and will not cause the planets to
collide.
Here is a link to possibly the best collection of papers on the subject:
http://www.centralcityair.com/Documents/EngData00.htm
James
Im in montreal
Last summer we removed a hp22 311 with a cvp 10 41 coil A very large coil
made for the ec10 furnace.
We replaced it with a HS29 030 with a c 23 31 coil.
Guess what the complaint is? Too much humidity.
Both systems used the same furnace a half horse direct drive.
Both a basically the same seer rating
So how does this work??
oh.and take a look at the web reference you showed.
Data engeneered by computer program.....not by actual operation.
Ok so lets say we put in a five ton system with a three tone coil, like the
data shows. Ya realy think it will work?
Oh...another thing in the computer data, they list 2000 cfm coming from a
1/2 horse motor. Maybe if there was no duct work involved or the ducts took
up more room then the house.
If this is Lennox data, a Q3/4 motor is a 1/2 horse. Q3/4 indicting
tonnage. Q5 is a 3/4 horse. So in two areas your web reference is false.
Makes me wonder about the rest.
I like slower air flow over a larger coil.
Heat pumps work better and quieter.
Cooling removes more humidity.
I cant see a 5 ton heat pump witha 1/2 horse motor with a three ton coil.
Unless you want to change alot of compressers
thanks
James
"Jason" <no...@nowhere.com> wrote in message
news:aNPKa.567$sg2...@newssvr31.news.prodigy.com...
bill
<ja...@nothanks.com> wrote:
>
> I cant see a 5 ton heat pump witha 1/2 horse motor with a three ton coil.
>
> Unless you want to change alot of compressers
>
> thanks
> James
The pages are also part of a Texas contractors site. The dude is either
advertising or lying.
TAB Dude
bill
@ Netzero. net) Remove spaces to reply> wrote:
> I understand - just don't live in Dallas.
What if he has a load of 37,860.
Arthur
larger evap coil, slowing the air volume, & orficing the amount of gas into
the coil one could get that type of result, (guess I have to put on my
thinking cap & I hope it is placed correctly). But the sizes and other areas
come into play & one should know what they are doing. Mostly the unit is
selected by BTU capacity vs the Manual J Load, ARI rates matched systems and
each rated system bears a cost to the manufacturer. So there are a lot of
things that must be looked at and weighed to obtain the results you are
referring to. Usually the load & unit done correctly (with design
temperatures) will take care of this. In Miami with older people a
undersized unit (causing it to run more) took care of humidity problems but
again you have to balance all of that.
Website residential info www.arthurhewett.com & www.thingsanditems.com
Arthur
"Jason" <no...@nowhere.com> wrote in message
news:aNPKa.567$sg2...@newssvr31.news.prodigy.com...
TURTLE
This is Turtle.
Jason, they may understand more than you think you are not catching on to
what they are telling you. In my younger years in the HVAC business we would
do like you say and undersize the evaperator coil 1/2 ton to get more
moisture out of the air. Then came along seer rating and the government
getting in the hvac business and made all the manufactors have real btu
ratings and seer ratings. Then now days if you do this in a climate that may
be having the customer running the equipment in weather below 70 degree
ambiant. The evaperator coil will freeze up like a block of ice. If you do
it now days you will have to log up the condenser coil with freon to slow
the condenser down to a point of lesser ton to let it run in weather less
than 70 degrees. This is very hard on your equipment and is not recommended
at all and even by the Hacks. I have only done this one time in the last 20
years and it was for a furneral home where they had 3 - 5 ton splits taking
care of the place and they would not run it till it was 100+ degrees out
side and would automaticly cut off at temp.s below 100+ degrees ambiant. The
forth unit was back up on 100+ degree weather for the place was manual J
well but in 100+ weather the run time would be 110% of the time to keep up.
When it cut in it would start pulling moisture out of the air too but was
just for running in 100+ degree ambiant. If it stays 100+degrees outside the
missmatch will be fine but not at lower temps. We had the extra unit on the
outdoor thermostat to cut in at 100 degree and cut it's self out at 95
degrees ambiant. When it was 100+ degree ouitside it would be 135 degrees on
the roof area and this unit worked very well in that kind of weather.
Now to tell you what you really need to do here to get high moisture
removeing ability here.
First ) Get you a good hvac people / company and have them run a real and
very correct Manual J on your home and also a manual D for the duct work to
be installed. Tell the fellow to run it very close to exactly what is to be
calculated on. Take the tonage and heating ability and use those exact
figures as to the equipment but don't round up but round down on tonage and
have the freon level set by super heat or charting method. Have everything
exactly as it says to the manual J calculations but round down and not up.
Second ) Have you a Humitistat install with the thermostat to keep the
cooling running until the humitity is right and also the temperature of the
home is right. You can control the humitity and the temperature as you want
it. Now if your Manual J calculation are on the money you will not need the
humitistat for it will control the humitity very well without other
controls.
Your ideal that you have from the 1970's does not work well now a days but
only in certian conditions. If the contractors that your talking to was not
in the business in the 1960 to 1970 they will not be aware of the old
methods or ways thing was done.
TURTLE
Stormin Mormon
.coil the OVERSIZES always boss My
.area more has it way That
--
Christopher A. Young
Learn more about Jesus
www.lds.org
www.mormons.org
.
.
"Jason" <no...@nowhere.com> wrote in message
news:aNPKa.567$sg2...@newssvr31.news.prodigy.com...
kjpro
"Stormin Mormon" <cayo...@hotmail.com> wrote in message
news:3efcc...@news.athenanews.com...
> .backwards it have might I
>
> .coil the OVERSIZES always boss My
>
> .area more has it way That
>
>
> --
>
> Christopher A. Young
I
s
a
y
y
o
u
'
r
e
c
o
r
r
e
c
t
!
!
!
kjpro
:-)
ps Spell check that!!! lol
REL
time on the unit and the result will be better humidity control. when
you oversize it, you have too short of a run time and you have high
humidity problems.
the other rich
kjpro
efficiency and de-humidification is what he is saying.
Are you saying this is NOT correct??
kjpro
EX. man J says 33,000 btu.........so use a 2.5 ton and a 3 ton coil. (for
more surface area)
"REL" <rl...@hotmail.com> wrote in message
news:3efdda7b...@news.earthlink.net...
REL
use the 2.5 MATCHED set and have increased run times due to
undersizing.
the other rich
GetOut, Inc.
I got an idea, why don't you find someone who can install a properly sized:
A - Carrier ComfortHeat system with variable indoor fan with a
Thermidistat(combo t'stat/hum'stat) for humidity control
B - Trane Texas ComfortSystem with variable indoor fan with a thermostat and
humidistat for humidity control
C - Amana system with variable speed indoor fan with a thermostat and
humidistat for humidity control.
D - Any other brand of equipment with variable speed indoor fan that has a
de-humidity input to slow down the fan speed until desired humidity level is
reached with a thermostat and humidistat for humidity control
My home in central GA.(one of the most hot and humid places on the planet or
a least it seems, certainly comparable to Dallas) has a 39,800 btu load at
98 f. It is equipped with a 3.5-ton Amana RHF heat pump, Amana VariSpeed
blower(5-ton) set at 1500 cfm nom. and 4-ton TXV coil, Carrier 6 -zone
ComfortZone. I use a separate humidistat(located in the RA duct to both
control de-humid mode in summer and a AprilAire 760 humidifier in the
winter. It produces 41,500 btu at 15.2 SEER
I maintain <50% RH all summer long, my old heat pump(came with the house)
was a 3-ton REAM(Rheem) with a 3.5-ton REAM(Rheem) ahu and coil. I charted
a full week before the retrofit and it maintained 55-57% RH.
As always, my opinions are just my opinions,
Tim
Jason
sized:
humidistat)
Uh, because what you described would cost about ten grand more than just
replacing my coil and I'd be old and grey before I ever broke even on that
one. Hell, I'll probably be moving up to a bigegr house within 5 years
anyway and as it is my current system is fine, but since I need a new coil
anway I want it sized right for my application.
My house isn't even worth $200K, and my electricity bill plus gas average
out to $150 total over a 12-month span and we keep the house COLD during the
summer since we like it that way. A new coil will help efficiency out since
the oild one looks like a shag carpet, and a completely new system just
doesn't make sense. I'll also be adding a TXV which will help efficiency as
well.
Your solution would work, but a bit of overkill for my home.
Richard
For greater moisture removal use a 'larger coil' and 'lower airflow'.
Adjust airflow, as nearly as possible, to provide the SST as before
(i.e. under the same ID/OD conditions). This will provide the same load
on the compressor as before, thus preventing compressor damage due to
overload, (the total system capacity or 'load' remains unchanged). The
latent heat removal capacity will be, more or less, increased in
proportion to coil size, due to
1) greater coil area at the same SST
2) lower air velocity through the coil.
Greater efficiency usually results as well from this alteration.
The original thinking of some was that the larger coil would 'reduce'
moisture removal and thus less btu's would have to be removed in order
to drop the indoor temp to some desired point. At least that is the
story told to me by years ago when I questioned this practice. However
that conclusion is exactly wrong. Once the moisture in the space is
removed to a greater degree by the lower cfm system, then less btu's are
thereafter required to maintain the same given temp in the space,
moreover the temp on this less humid space can be run higher than
before, and at the same time provide greater comfort to the occupants
(ceiling fans suggested). Double whammy here, greater comfort, less
expense. Doesn't provide as much cost savings over the higher cfm
systems in leaky houses though. Good double or triple pane windows will
pay for themselves easily in terms of infiltration control and the
insulating factor that they provide.
Your 'smaller' coil won't be the way to go, you'll reduce SST thus
causing frequent freeze-ups, moreover you won't gain that much, if any,
in terms of moisture removal (A given volume of air won't be in contact
with the coil as long, thus you'll get the same air/coil behavior as
increased cfm, which is a decreases moisture removal) IOW these factors
will cancel one another and thus the effect that you're after. If you
then 'increase' cfm to raise SST back up out of the freeze-zone, then
you get even more bypassing thus even less moisture removal capacity.
We had this discussion last summer, at length.
hvacrmedic
Geo Man
First, in a refrigerated walk in we had a customer complain that the cooler was too dry. It had a
small evaporator with a TXV. We increased the evaporator size by 30 percent with a TXV. The humidity
increased dramatically.
Secondly, it seems that your discussion has to be separated into two sections. The first is
evaporators with a fixed orifice and the second is an evaporator with a TXV. Both systems will
result in different results, they must. Your charge with a fixed orifice will change dramatically
and affect the compressor much more than a TXV will.
I guess what I'm trying to say is, the TXV system charge will not vary that much where the FCCV
will. The results are vastly different BTU capacity on the system, both latent and sensible.
When I get the chance I will look up some ARI figures on this subject.
Rich
"GetOut, Inc." <geto...@cox.net> wrote in message news:8n7La.32367$VQ6.10647@lakeread01...
Richard
Geo Man wrote:
>
> Well, I am of a different opinion than many here.
>
> First, in a refrigerated walk in we had a customer complain that the cooler was too dry. It had a
> small evaporator with a TXV. We increased the evaporator size by 30 percent with a TXV. The humidity
> increased dramatically.
>
> Secondly, it seems that your discussion has to be separated into two sections. The first is
> evaporators with a fixed orifice and the second is an evaporator with a TXV. Both systems will
> result in different results, they must. Your charge with a fixed orifice will change dramatically
> and affect the compressor much more than a TXV will.
>
> I guess what I'm trying to say is, the TXV system charge will not vary that much where the FCCV
> will. The results are vastly different BTU capacity on the system, both latent and sensible.
>
> When I get the chance I will look up some ARI figures on this subject.
>
> Rich
Run-time is a pertinent factor. If you oversized the capacity with the
larger coil, then run-time was reduced. Also if the cfm was also
increased when the coil size was, then this also contributes to less
moisture removal. If you had dropped cfm such that SST was the same as
before (i.e. with the smaller coil), then you will definitely have
reduced RH in the space, no way around it.
hvacrmedic