central humidity control?
000000001
Tom Anderson
supply air temp, with each zone having a HW reheat coil to provide space
heating and avoid space subcooling. Yes, it is incongruent from an efficiency
perspective, but HVAC supports the process, even if efficiency takes a hit.
But modern designs minimize this waste by applying variable air volume, or by
rejection the heat absorbed by the cooling coil pulling moisture out of the
air into supply air downstream of cooling coil, thus reheating the cool dry
air.
These concepts for limited seasonal residential use are not practical. If it
were me, I would buy a good quality quiet portable dehumidifier, which
effectively rejects heat back into the space. for your reheat load. Or, get
fancy and control your AC off of interior humidity as well as temperature, and
install an economizer cycle using differential enthalpy to enable. A lot to
do for a residential system.
Or open a window when OA temp is 5F or less below interior. (poor mans
economizer cylce).
:-)
"Kirk A. Kerekes" wrote:
> I'm a DIY-intensive homeowner who monitors this group for ideas.
>
> We are currently in the planning stages for a new residence, to be built
> on our current property. Our current residence (which we designed and
> built) is sufficiently well insulated and sealed that a number of
> unintended side effects have revealed themselves -- the most prominent of
> which has been humidity control.
>
> We have had a _long_ and wet spring -- many days in the high '70s with 70%
> or higher exterior humidity. Because the house is well insulated and
> sealed, (we generally have to run the A/C until the outside temperature is
> in the 50's) the A/C barely runs, and the interior humidity rapidly climbs
> into the 80s. Importing outside air doesn't represent much of an
> improvement under these conditions, so we have been reduced to turning on
> the heat (which is independant of the A/C) to simulate a hot day, forcing
> the A/C to run longer and remove more humidity. With this ludicrous
> technique, we have managed to keep the humidity down into the 50s. (Last
> year we used a portable dehumidifier, but the noise persuaded us to go
> with a quieter method this year.)
>
> The weather appears to finally be turning summerlike, but this spring has
> convinced me that I need to find a way to incorporate automatic humidity
> removal into a central air system. It would _seem_ that it ought to be
> possible to incorporate a dehumidifier's "closed loop" inside the air
> path, but I have never heard of such an installation or device.
>
> Does such a widget or scheme exist for residential systems?
>
> --
> Kirk and Diane Kerekes/Red Gate Ranch
> X-Face by "Saving Face" <http://www.santafe.edu/~smfr/utils.html>
Neon John
"Kirk A. Kerekes" wrote:
>
> I'm a DIY-intensive homeowner who monitors this group for ideas.
Gonna assume this to be true.
>
> The weather appears to finally be turning summerlike, but this spring has
> convinced me that I need to find a way to incorporate automatic humidity
> removal into a central air system. It would _seem_ that it ought to be
> possible to incorporate a dehumidifier's "closed loop" inside the air
> path, but I have never heard of such an installation or device.
>
> Does such a widget or scheme exist for residential systems?
Two steps.
1)
Install another coil downstream of the evaporator and pipe the
liquid freon line to flow through it before reaching the expansion
device. This does two things. It reheats the air to lower its
humidity and it subcools the refrigerant, making your system more
efficient. The coil can be significantly smaller than the
evaporator - an auto condenser coil would work well. It need not
cover the whole duct and indeed can be suspended across the duct
with the material of your choice - wire, steel frame, etc.
2)
Install yet another coil downstream of the evaporator and pipe a
portion of the hot gas from the compressor through it. You will want
a hand valve to set the proportional hot gas flow and a refrigerant
solenoid so that this reheat flow can be controlled. This has the
same effect as your running your heat and indeed is the same way
humidifiers work. The air is first chilled to condense water out
and bring the dew point to approximately the evaporator temperature
and then the air is reheated to lower the humidity. This is vastly
more efficient than supplying reheat from some other source because
not only does it recover some of the heat absorbed by the
evaporator, it also lowers the load on the compressor (and thus the
energy use) by cooling the hot gas. This also functions as a
capacity control which dovetails nicely since the need of humidity
control is usually the highest when the cooling load is relatively
low.
You'll need a control system. The most basic would be a manual
switch to open the hot gas valve. When the house starts feeling
stuffy, just flip the switch. The next most basic would be a
humidistat to control the hot gas valve. The best system would
integrate the two functions. As cooling is called for, the AC would
operate with the hot gas valve open. it would close either when the
humidity reaches the desired setpoint OR when the heat load becomes
great enough that the ambient temperature rises to a second, higher
setpoint. This should be easily implemented with a multi-stage
thermostat such as the White-Rogers Digital Comfort Set II (~$100
wholesale with remote temp sensor).
Step 1 is a no-brainer. Aids humidity control and reduces operating
cost. If you'd like, you can include a bypass valve so that when
the heat load requires all the system's cooling, you can bypass the
coil. Probably not necessary unless your system is really
borderline.
John
--
John De Armond
johngd...@bellsouth.net
Neon John's Custom Neon
Cleveland, TN
"Bendin' Glass 'n Passin' Gas"
k.t.chan
The add on heat pipe can de-humid the air with the power of your air
conditioner.
Regards
K.T.Chan
"Kirk A. Kerekes" wrote:
> I'm a DIY-intensive homeowner who monitors this group for ideas.
>
> We are currently in the planning stages for a new residence, to be built
> on our current property. Our current residence (which we designed and
> built) is sufficiently well insulated and sealed that a number of
> unintended side effects have revealed themselves -- the most prominent of
> which has been humidity control.
>
> We have had a _long_ and wet spring -- many days in the high '70s with 70%
> or higher exterior humidity. Because the house is well insulated and
> sealed, (we generally have to run the A/C until the outside temperature is
> in the 50's) the A/C barely runs, and the interior humidity rapidly climbs
> into the 80s. Importing outside air doesn't represent much of an
> improvement under these conditions, so we have been reduced to turning on
> the heat (which is independant of the A/C) to simulate a hot day, forcing
> the A/C to run longer and remove more humidity. With this ludicrous
> technique, we have managed to keep the humidity down into the 50s. (Last
> year we used a portable dehumidifier, but the noise persuaded us to go
> with a quieter method this year.)
>
> The weather appears to finally be turning summerlike, but this spring has
> convinced me that I need to find a way to incorporate automatic humidity
> removal into a central air system. It would _seem_ that it ought to be
> possible to incorporate a dehumidifier's "closed loop" inside the air
> path, but I have never heard of such an installation or device.
>
> Does such a widget or scheme exist for residential systems?
>
David Laine
supply duct to act as a reheat coil. It can be triggered by a solenoid
valve and thermostat/humidistat. It must be sized to work with the
existing system. It will cost no more to operate in the long term, and
acts much like an off-the-shelf dehumidifier. Some local refrigeration
techs from the super-market arena should have no trouble with this
task.
Dave
In article <redgate-2706...@192.168.1.2>, Kirk A. Kerekes
<red...@tulsa.oklahoma.net> wrote:
|| I'm a DIY-intensive homeowner who monitors this group for ideas.
||
|| We are currently in the planning stages for a new residence, to be built
|| on our current property. Our current residence (which we designed and
|| built) is sufficiently well insulated and sealed that a number of
|| unintended side effects have revealed themselves -- the most prominent of
|| which has been humidity control.
|| Does such a widget or scheme exist for residential systems?
John Popelish
>
> I'm a DIY-intensive homeowner who monitors this group for ideas.
>
> We are currently in the planning stages for a new residence, to be built
> on our current property. Our current residence (which we designed and
> built) is sufficiently well insulated and sealed that a number of
> unintended side effects have revealed themselves -- the most prominent of
> which has been humidity control.
>
> or higher exterior humidity. Because the house is well insulated and
> sealed, (we generally have to run the A/C until the outside temperature is
> in the 50's) the A/C barely runs, and the interior humidity rapidly climbs
> into the 80s. Importing outside air doesn't represent much of an
> improvement under these conditions, so we have been reduced to turning on
> the heat (which is independant of the A/C) to simulate a hot day, forcing
> the A/C to run longer and remove more humidity. With this ludicrous
> technique, we have managed to keep the humidity down into the 50s. (Last
> year we used a portable dehumidifier, but the noise persuaded us to go
> with a quieter method this year.)
>
> The weather appears to finally be turning summerlike, but this spring has
> convinced me that I need to find a way to incorporate automatic humidity
> removal into a central air system. It would _seem_ that it ought to be
> possible to incorporate a dehumidifier's "closed loop" inside the air
> path, but I have never heard of such an installation or device.
>
This cooling while raising the humidity occurs when too much air passes
over the cooling coil. The air gets cooler, but the coil hardly gets
cool enough to reach the dew point temperature where it can condense
some water. You may be able to improve things by slowing the fan or
restricting the air over the coil. A more effective way may be to
bypass some air around the coil. Any of these methods allow the cooling
coil to reach a lower temperature and wring out more moisture. Then
this cooler air mixes with the warmer bypass or room air and you get
comfortably cool air with less total moisture. I am assuming that your
evaporator is set to allow the coil to reach 45 to 50 degrees to take a
lot of water out.
John Popelish
SkewedElf
Elf