Timer controlled thermostat
 

But I don't mean your run of the mill programmable type.

Presently we are having very warm and humid days. The central air
conditioning handles this properly. Then late at night as the outside
temperature drops the system doesn't call for cooling as often. Once
again this is normal operation.

But during this time the humidity indoors rises. Very good chance the
interior temperature will be stable enough not to call again for air
conditioning for the remainder of the night. Net result being that
sticky feeling.

Wondering if it is possible to find a thermostat, or other computer
controlled device perhaps, that will instruct the air conditioner to
cycle say once every 15 minutes for a 1 minute duration. User
adjustable, to assist in controlling the relative humidity without running
for excessive amounts of time.

Anything like this exist?

Timer controlled thermostat
 

On Jul 11, 7:29 am, Jim wrote:
But I don't mean your run of the mill programmable type.

Presently we are having very warm and humid days. The central air
conditioning handles this properly. Then late at night as the outside
temperature drops the system doesn't call for cooling as often. Once
again this is normal operation.

But during this time the humidity indoors rises. Very good chance the
interior temperature will be stable enough not to call again for air
conditioning for the remainder of the night. Net result being that
sticky feeling.

Wondering if it is possible to find a thermostat, or other computer
controlled device perhaps, that will instruct the air conditioner to
cycle say once every 15 minutes for a 1 minute duration. User
adjustable, to assist in controlling the relative humidity without running
for excessive amounts of time.

Anything like this exist?

While Y'all are pondering Jim's question add this:

A programmable thermostat that allows a timer or cycle setting for the
circulation fan. I have a two story center hall colonial and of
course heat rises so upstairs is always warmer.

Timer controlled thermostat
 

"Jim" wrote in message
...
But I don't mean your run of the mill programmable type.

Presently we are having very warm and humid days. The central air
conditioning handles this properly. Then late at night as the outside
temperature drops the system doesn't call for cooling as often. Once
again this is normal operation.

But during this time the humidity indoors rises. Very good chance the
interior temperature will be stable enough not to call again for air
conditioning for the remainder of the night. Net result being that
sticky feeling.

Wondering if it is possible to find a thermostat, or other computer
controlled device perhaps, that will instruct the air conditioner to
cycle say once every 15 minutes for a 1 minute duration. User
adjustable, to assist in controlling the relative humidity without running
for excessive amounts of time.

Anything like this exist?


Running for such a short time wouldn't give the system a chance to remove
much humidity. It would be like having an AC unit too big for the house.

Is your house "leaky"? My system behaves like yours, but I don't notice
humidity building up. The lack of air movement is bothersome, though, after
the AC stops running at night. So, I have a quiet floor fan in the bedroom,
running on its lowest setting, pointed straight at the ceiling. The brand is
Vornado. Keeps the room very comfortable.

http://www.vornado.com/products/circulators/783b.htm

Timer controlled thermostat
 

Short cycling a ac wears it out. Bad idea.


"Jim" wrote in message
...
But I don't mean your run of the mill programmable type.

Presently we are having very warm and humid days. The central air
conditioning handles this properly. Then late at night as the outside
temperature drops the system doesn't call for cooling as often. Once
again this is normal operation.

But during this time the humidity indoors rises. Very good chance the
interior temperature will be stable enough not to call again for air
conditioning for the remainder of the night. Net result being that
sticky feeling.

Wondering if it is possible to find a thermostat, or other computer
controlled device perhaps, that will instruct the air conditioner to
cycle say once every 15 minutes for a 1 minute duration. User
adjustable, to assist in controlling the relative humidity without running
for excessive amounts of time.

Anything like this exist?

Timer controlled thermostat
 

Art wrote:
Short cycling a ac wears it out. Bad idea.


For the sake of clarification define short cycling? Only very hot days
it is not uncommon for my scroll compressor to run for say 90 minutes,
shut down, then come back on 10-15 minutes later.

Timer controlled thermostat
 

Jim wrote:
Presently we are having very warm and humid days. The central air
conditioning handles this properly. Then late at night as the outside
temperature drops the system doesn't call for cooling as often. Once
again this is normal operation.
But during this time the humidity indoors rises

you mention (not quoted above) every 15 min for 1 min which others have
already pointed out is a bad idea. however let me add that as an idea it is
not bad at all with proper timelimits.

I've seen several installations in s.florida where the thermostat maintained
a temp setpoint (as you mentioned) but humidity behaved erratically and it
was solved with a thermostat calling separately for low speed (variable
speed blowers) and stage1 (multi-stage system) for a given duration in
programmable timelimits

one such example was a dual compressor (2 ton & 4 ton) system where the VS
blower at very low speeds initiated the 2 ton compressor when humidity
setpoint (54%) was reached and it ran the system for 30 minutes and then
shut down. this was accomplished with a 24vac macromatic relay (timer
On/Off) tied into the stage1 (Y1) circuit from the thermostat RH% sensor
(DH). every time the DH 24vac relay opened, it sent a signal to the
macromatic On and this in turn ran to Y1 which activated the 2 ton
compressor, after 30 min (adjustable dial on the macromatic) the relay shut
down.

there are other types of macromatic relays, my personal favorites are the
interval On, interval Off where you can program the time duration on and
time duration off and the cycle repeats. thus you could have indoor temp at
77F while maintaining a precise 50% humidity and if the time interval
results in too little or too much cooling (likely not a problem with
variable speed blower and small stage1 compressor), it's simple and easy to
adjust

hope that helps

Timer controlled thermostat
 

On Wed, 11 Jul 2007 07:29:02 -0400, Jim wrote:

But I don't mean your run of the mill programmable type.

Please put what you mean in the text of the post. It's annoying to me
to have to guess what you are talking about, and then to have to hunt
for clues.

Presently we are having very warm and humid days. The central air
conditioning handles this properly. Then late at night as the outside
temperature drops the system doesn't call for cooling as often. Once
again this is normal operation.

But during this time the humidity indoors rises.

My words are only theory, not based on actual AC experience, or even
AC theory, but.... Why would the humidity rise? Did you take a steamy
shower, leave wet towels hanging on a towel bar, make spaghetti, boil
eggs, run the dishwasher, run the dryer with an indoor vent?

Or maybe there is an air leak with the outside. What I don't know is
if it is possible that the humidity would leak in faster than the
temperature. Maybe, but I don't know.

People perspire no matter what, but it's a lot slower if it is cool in
the house. How many people live in your house?

Very good chance the
interior temperature will be stable enough not to call again for air
conditioning for the remainder of the night. Net result being that
sticky feeling.

Wondering if it is possible to find a thermostat, or other computer
controlled device perhaps, that will instruct the air conditioner to
cycle say once every 15 minutes for a 1 minute duration. User

I don't think that would remove any more humitidy than it would cool
in so little time.

adjustable, to assist in controlling the relative humidity without running
for excessive amounts of time.

Anything like this exist?

Timer controlled thermostat
 

That sounds normal. A system that is too large for a house will turn on,
cool the house quickly and turn off quickly. Every turn on and turn off
shortens the life time of an ac. In a perfect world it would be sized to
run forever keeping the house at the right temperature and never turn off.
Of course the outside temperature is always changing so that a perfectly
sized ac system is impossible to design. That is why they have multistage
systems. In any case your thermostat idea is forcing it on and off often
and it would fail prematurely.


"Jim" wrote in message
...
Art wrote:
Short cycling a ac wears it out. Bad idea.


For the sake of clarification define short cycling? Only very hot days it
is not uncommon for my scroll compressor to run for say 90 minutes, shut
down, then come back on 10-15 minutes later.

Timer controlled thermostat
 

Art wrote:

That sounds normal. A system that is too large for a house will turn on,
cool the house quickly and turn off quickly. Every turn on and turn off
shortens the life time of an ac. In a perfect world it would be sized to
run forever keeping the house at the right temperature and never turn off.
Of course the outside temperature is always changing so that a perfectly
sized ac system is impossible to design. That is why they have multistage
systems. ...

Actually, while you are right that the reason for multistage systems
is so that the AC does not turn on and off as often, the major reason
that this cycling is undesirable is not AC lifetime, but energy efficiency
and humidity control.

When the AC turns on, you are spending energy for a while cooling down
you evaporator, ducts, etc. before you get to full efficiency. When you
turn on and turn off, you are blowing previously condensed moisture back
into your home.

Timer controlled thermostat
 

On Thu, 12 Jul 2007 00:20:23 GMT, M Q
wrote:

Art wrote:

That sounds normal. A system that is too large for a house will turn on,
cool the house quickly and turn off quickly. Every turn on and turn off
shortens the life time of an ac. In a perfect world it would be sized to
run forever keeping the house at the right temperature and never turn off.
Of course the outside temperature is always changing so that a perfectly
sized ac system is impossible to design. That is why they have multistage
systems. ...

Actually, while you are right that the reason for multistage systems
is so that the AC does not turn on and off as often, the major reason
that this cycling is undesirable is not AC lifetime, but energy efficiency
and humidity control.

When the AC turns on, you are spending energy for a while cooling down
you evaporator, ducts, etc. before you get to full efficiency.

Your reason below certainly makes sense, but I don't think this one
actually does so much.

When the evaportator, ducts etc. warm up between AC cycles, they are
sucking in heat from their surroundings. This cools the house, and
keeps the surroundings from warming the air when the AC is on.

And at he same time, the condenser is cooling down, which should make
the condenser more efficient until it warms up again.

When you
turn on and turn off, you are blowing previously condensed moisture back
into your home.

Yes, but I'm sure you mean some of it. Not the stuff that has drained
from the pan and gone into the sump or the condensate pump.