|
HVAC Discussions - Heating, ventilation and air conditioning.
|
|
|
|
If you were Registered and logged in, you could reply and use other advanced thread options
|
Posted by Todd H. on September 14, 2006, 4:01 pm
I've had a Carrier dealer discourage use of a variable speed motor
with my ductwork in a 15 year old home. As he explained, the
transitions from square duct to round can confuse the sensors in the
variable speed motor to cause it to ramp up to higher speeds
unnecessarily. Does this make sense? I ask because other dealers of
different equipment have not expressed this concern.
This led me to wonder how specifically Carrier variable speed motors
determine what speed to run at. What is the algorithm for speed
control--are there sensors put in the plenum, on-board sensors, are
they looking at temperature and inferring airflow from that, directly
measuring airflow, or. Are there fixed intervals involved like run at
X% for Y minutes, if tstat isn't satisfied ramp up to blah% for Z more
minutes, if not tstate, ramp up further? Or is airflow
involved/measured somehow?
Other dealers who've quoted have not expressed any concern with the
duct situation, even when directly asked. It's always possible they'd
love to sell a variable speed motor setup.
Of course, one of those dealers (a Frigidaire dealer) had no clue how
their variable speed motors worked and couldn't explain it other than
mentioning DIP switches for low and high speeds. Based on their
knowledge, I don't think I'll be using them I'm afraid.
A Ruud dealer explained that their variable speed sensed airflow
somehow (he said he wasn't sure precisely what was being mesured) but
did offer the anecdotal evidence that he had forgotten to change his
filter at his house once and the clue he had was that his variable
speed motor was running faster than normal due to the airflow
blockage.
Thanks for sharing and info you know on various manufacturer's
variable speed motor operation.
Best Regards,
--
Todd H.
http://www.toddh.net/
|
 
| |
Posted by Jake on September 14, 2006, 7:36 pm
Paul,
The guy asked some good questions that I've also asked here in some variety.
They deserve some answers, but I doubt he'll get them. The manufacturers
hold this information so close that it's ridiculous.
Now to Todd....
I'm a electrician and a controls engineer that has been around this NG
for a couple of years. My business has gotten more into the management
of small/medium HVAC systems for existing industrial & commercial
clients. I've learned a great deal about how HVAC systems work from the
contributors here.
That said... I'm going to tell you that the majority of VS systems out
there today are 'dumb', and take very little feedback from the
real-world into consideration during operation.
Airflow is a good example. It's usually extrapolated from a computation
of how much energy (amperage) the blower motor needs to operate at X
speed. This is done on-board at the motor... a expensive-to-replace
proposition that, as an engineer, I totally disagree with.
Some... better systems also will take readings from the refrigeration
circuit into consideration. Do a Google to learn more about how a
refrigeration circuit works.
Sensors might measure line temperatures or pressures at key points by
which things like airflow can be 'roughly' extrapolated.
Bottom line is... VS... by itself... does not gain you much efficiency.
How it effects the 'circuit' on the other hand... might yield great cost
savings. Remember, the biggest user of energy in your system is the
compressor and not the fan.
Jake
|
|
Posted by on September 14, 2006, 9:18 pm
Jake wrote:
> Remember, the biggest user of energy in your system is the
>compressor and not the fan.
>
>Jake
>
>
>
I would disagree with you.
The average leakage in a 15 yr old duct system ranges 30-45%.
people are delusional thinking they're getting 13 seer by buying
equipment but not replacing or sealing, sizing & insulating duct work.
|
|
Posted by Jake on September 14, 2006, 9:23 pm
>
> I would disagree with you.
>
> The average leakage in a 15 yr old duct system ranges 30-45%.
>
> people are delusional thinking they're getting 13 seer by buying
> equipment but not replacing or sealing, sizing & insulating duct work.
I might buy that... I'll take your word for it (-;.
On the other hand, I was talking strictly about the equipment and not
the system as a whole.
SO... is there a problem with VS in a duct-transitioned system the OP
described?
I'm not convinced of that... yet.
Jake
|
|
Posted by on September 14, 2006, 10:56 pm
Jake wrote:
>On the other hand, I was talking strictly about the equipment and not
>the system as a whole.
oh bs. you said system. system implies every component. :)
>
>SO... is there a problem with VS in a duct-transitioned system the OP
>described?
>
>I'm not convinced of that... yet.
it seems the problem exists only in the mind of that one carrier
dealer.
somehow, magically, VS motors work in every other similiar situation
for thousands if not millions of people.
>
>Jake
|
Page 1 of 5 1 2 3 > last >>
| Similar Threads | Posted | | do high-end residential heat pumps with variable speed air handlers truly vary the speed to control humidity? | May 9, 2007, 9:24 am |
| Trane Variable Speed Furnace | October 30, 2007, 11:20 pm |
| Tech question about variable speed compressors... | May 31, 2007, 12:57 pm |
| Furnaces with AFUE of over 90 percent: variable speed motors | November 1, 2006, 3:14 pm |
| Trane Variable Speed Air Handler - setting fan speeds | February 19, 2007, 9:51 am |
| Variable Speed residential motors ; too long a payback ?? | June 10, 2007, 12:58 pm |
| GE Fan Motor has low speed only | August 24, 2006, 2:00 am |
| HELP I need 2 new furnaces!! Single or dual 80% or 90% single or variable speed fan | September 10, 2006, 7:57 pm |
| Duct cleaning problems | December 1, 2007, 2:13 pm |
| Does duct size really matter when using ECM2 motor? | January 19, 2007, 11:14 pm |
|
|
|
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap