wrote:

On Aug 10, 9:24 am, "Smarty" wrote:


Nick,

If you "ignore Smarty" and use the original parallel combination of t-stat
and h-stat which was incorrectly recommended, you wind up with a system that
switches the a/c off as the humidity rises, and thus does exactly the
opposite of what is required.

My suggestion was (and is) to avoid adding an extra relay and power source
by choosing the correct type of control, namely, the Honeywell I recommended
or something equivalent to it. A parallel connection in this case will work
exactly as expected, namely to turn on the a/c when either the temperature
or the humidity level called for additional refrigeration.

I thus do not understand your recommendation to "ignore Smarty".

Could you please clarify? Thanks, Smarty

While everyone is engineering away, am I the only one wondering why
anyone would be worrying about a De-humidistat solution for a 110-115THI
outside environment, with the inside thermostat set to 70? In that
environment, any properly functioning AC system is going to run enough
(like all the time) to keep the temp under control that it will reduce
the humidity, without any help from a De-humidistat. And why you;d need
a set temp of 70 in that jungle environment is beyond me. When it's
humid and 85 outside, I set mine to about 76 and it feels nice and
cool. And that nowhere near the 115THI level.

There are high end thermostats that include humidity control, which is
what you want instead of some half assed glued together widget. But
I think they are targeted at systems that include a variable speed
blower. So, if the system gets close to the set temp, but the
humidity is still too high, it will run the blower at slow speed so it
takes more moisture out before reaching the desired temp. That makes
sense. Putting a De-humidistat in parallel with the thermostat does
not. How are you going to feel if the room temp goes down to 62 to
get the desired humidity?


Trader4, good point(s), in that situation, I would say the AC is too
oversized to achieve the application goals.
Also, if the lower blower speeds will achieve a tolerable CFM airflow,
one can use relays to change to a lower blower speed tap even with a
regular multiple speed motor. Where there are humidity problems the
Entire System Design has to address that problem to work properly.

In short, I think the OP is looking for a solution to a problem that
doesn't exist. (Right-On!)


At those temps, you are certainly correct!
Yes, in some applications they also slow the blower down until a %RH
setpoint is reached.
- udarrell

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