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| Does anyone know of a manufacturer who markets a superheat sensor that can
be installed permanently into a commercial or industrial AC system that can
lock out the compressor electrically if superheat is below or above safe
operational temperature? Thanks for info.
| |
| ..p.jm@see_my_sig_for_address.com 2005-10-15, 9:21 pm |
| On Sat, 15 Oct 2005 19:26:42 -0400, "Rick" <rarnold30@cox.net> wrote:
>Does anyone know of a manufacturer who markets a superheat sensor that can
>be installed permanently into a commercial or industrial AC system that can
>lock out the compressor electrically if superheat is below or above safe
>operational temperature? Thanks for info.
>
That would be a lot more complicated to make than you might
think.
Pressure transducer
Temp transducer
Internal refrigerant-specific logic
Application-specific adjustable
Must take itself out of the system when some OTHER control
takes the system down, IE, only in-circuit when the compressor is
running. Think about this one - you're gonna create short-cycling.
Must take itself out of circuit until system is within normal
operating range - which is what ? Another variable.
And yet that last one self-defeats the purpose of the device.
Think it through- an interesting idea, but not workable.
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/
Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
| |
|
| Thank you for your prompt and obviously educated reply, Paul. Let me mull
this over and I hope to clarify a response later.
<..p.jm@see_my_sig_for_address.com> wrote in message
news:f843l1t9uigsvg7r9casdonhbqqrbufa49@4ax.com...
> On Sat, 15 Oct 2005 19:26:42 -0400, "Rick" <rarnold30@cox.net> wrote:
>
>
> That would be a lot more complicated to make than you might
> think.
>
> Pressure transducer
> Temp transducer
> Internal refrigerant-specific logic
> Application-specific adjustable
>
> Must take itself out of the system when some OTHER control
> takes the system down, IE, only in-circuit when the compressor is
> running. Think about this one - you're gonna create short-cycling.
>
> Must take itself out of circuit until system is within normal
> operating range - which is what ? Another variable.
>
> And yet that last one self-defeats the purpose of the device.
>
> Think it through- an interesting idea, but not workable.
>
>
> Click here every day to feed an animal that needs you today !!!
>
> http://www.theanimalrescuesite.com/
>
> Paul ( pjm @ pobox . com ) - remove spaces to email me
> 'Some days, it's just not worth chewing through the restraints.'
> 'With sufficient thrust, pigs fly just fine.'
> HVAC/R program for Palm PDA's
> Free demo now available online http://pmilligan.net/palm/
| |
|
| ...p.jm@see_my_sig_for_address.com wrote:
> On Sat, 15 Oct 2005 19:26:42 -0400, "Rick" <rarnold30@cox.net> wrote:
>
Having worked up some SCADA packages (no control on superheat.. just
monitor) for industrial units... I'll comment with my limited expertise
here...
>
In a short answer... I've not seen anything like that (for all the
reasons Paul mentioned in his reply).
Being a controls nerd, the first question we always ask clients
requesting something like this is: Why do you want to do this? What
problem are you solving? What is the 'damage' you are trying to protect
against? Many units already have protection limit switches in them that
will STOP equipment before damage occurs...sometimes...
>
> That would be a lot more complicated to make than you might
> think.
>
> Pressure transducer
> Temp transducer
> Internal refrigerant-specific logic
> Application-specific adjustable
>
Off the cuff, depending on how fancy you wanted to go... about $3k minimum.
> Must take itself out of the system when some OTHER control
> takes the system down, IE, only in-circuit when the compressor is
> running. Think about this one - you're gonna create short-cycling.
Paul... how would this create short-cycling... high superheat or low
superheat more likely? I ask this in context of the compressor RUN
command or logic being on... I'd guess this relates to your comment
below re: "Normal operating range".
I'd just let the compressor come on-line... wait a minute or two for
things to stabilize and then switch-in.
>
> Must take itself out of circuit until system is within normal
> operating range - which is what ? Another variable.
>
> And yet that last one self-defeats the purpose of the device.
It would only 'self-defeat' on start-and-stop, wouldn't it? If you had
the necessary data available to the controller, it could calculate the
appropriate superheat 'window' couldn't it?
Jake
>
> Think it through- an interesting idea, but not workable.
>
>
> Click here every day to feed an animal that needs you today !!!
>
> http://www.theanimalrescuesite.com/
>
> Paul ( pjm @ pobox . com ) - remove spaces to email me
> 'Some days, it's just not worth chewing through the restraints.'
> 'With sufficient thrust, pigs fly just fine.'
> HVAC/R program for Palm PDA's
> Free demo now available online http://pmilligan.net/palm/
| |
|
|
Jake wrote:
[color=darkred]
> ..p.jm@see_my_sig_for_address.com wrote:
>
>
> Having worked up some SCADA packages (no control on superheat.. just
> monitor) for industrial units... I'll comment with my limited expertise
> here...
>
>
> In a short answer... I've not seen anything like that (for all the
> reasons Paul mentioned in his reply).
>
> Being a controls nerd, the first question we always ask clients
> requesting something like this is: Why do you want to do this? What
> problem are you solving? What is the 'damage' you are trying to protect
> against? Many units already have protection limit switches in them that
> will STOP equipment before damage occurs...sometimes...
>
>
> Off the cuff, depending on how fancy you wanted to go... about $3k minimum.
>
>
>
>
> Paul... how would this create short-cycling... high superheat or low
> superheat more likely? I ask this in context of the compressor RUN
> command or logic being on... I'd guess this relates to your comment
> below re: "Normal operating range".
>
> I'd just let the compressor come on-line... wait a minute or two for
> things to stabilize and then switch-in.
>
>
>
> It would only 'self-defeat' on start-and-stop, wouldn't it? If you had
> the necessary data available to the controller, it could calculate the
> appropriate superheat 'window' couldn't it?
>
>
> Jake
>
It's workable, but it probably isn't practical in most situations as a
retrofit system. The Flotronic system (Carrier) will shut down the
compressor on any out of range readings provided by its several
thermistors. The valid range is of course altered in real time in order
to accommodate startup and shutdown changes. Superheat is monitored by
two thermistors, one at the evap inlet the other in the compressor body,
measuring the superheat after the motor.
The Heatcraft Beacon system, which is extremely similar in operation to
the Flotronic system, may be offered as a retrofit package, I don't
really know. There are other companies that offer EXV upgrade kits, I've
looked at their web sites, but the OP can Google for those himself.
These systems go a bit beyond simple superheat monitoring though 
hvacrmedic
| |
|
| In article <Caudne6zK7mYNszeRVn-gw@centurytel.net>,
RP <no_mail_no_spam@yahoo.com> wrote:
> The Heatcraft Beacon system, which is extremely similar in operation to
> the Flotronic system, may be offered as a retrofit package, I don't
> really know.
Heatcraft tried a beta program for field retrofits but apparently it was
a disaster and aren't offering it or planning to.
--
Paul's cat got a furball and kept saying weasel's name.
*Hack* *Hack* *hack*
| |
| ..p.jm@see_my_sig_for_address.com 2005-10-16, 12:21 am |
| On Sun, 16 Oct 2005 00:49:20 GMT, Jake <jkelleyus@insightbb.com>
wrote:
>..p.jm@see_my_sig_for_address.com wrote:
>
>Having worked up some SCADA packages (no control on superheat.. just
>monitor) for industrial units... I'll comment with my limited expertise
>here...
>
>
>In a short answer... I've not seen anything like that (for all the
>reasons Paul mentioned in his reply).
>
>Being a controls nerd, the first question we always ask clients
>requesting something like this is: Why do you want to do this? What
>problem are you solving? What is the 'damage' you are trying to protect
>against? Many units already have protection limit switches in them that
>will STOP equipment before damage occurs...sometimes...
>
>
>Off the cuff, depending on how fancy you wanted to go... about $3k minimum.
>
>
>
>Paul... how would this create short-cycling... high superheat or low
>superheat more likely? I ask this in context of the compressor RUN
>command or logic being on... I'd guess this relates to your comment
>below re: "Normal operating range".
High SH would be the thing, IMO. You'd have to have it set up
as a 'one time and lock out'.
But then you have start-up to look at - SH is off the charts
high at first, so the control shuts off, so the compressor shuts off,
so the device resets itself on 'compressor off' as it must, but then
the compressor starts back up again ... etc etc.
It really would have to be part of a MUCH fancier setup, like
RP said, with all kinds of logic built in. To create a generic 'filed
install' version would be pretty impossible. Too many system
variables.
>
>I'd just let the compressor come on-line... wait a minute or two for
>things to stabilize and then switch-in.
What about pump-down ? :-)
>
>
>It would only 'self-defeat' on start-and-stop, wouldn't it? If you had
>the necessary data available to the controller, it could calculate the
>appropriate superheat 'window' couldn't it?
As above. You would have to allow in logic for every possible
LEGIT 'out of range' condition, and that is going to effectively be
machine-specific.
[color=darkred]
>
>
>Jake
>
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/
Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
| |
|
|
Bill wrote:
> In article <Caudne6zK7mYNszeRVn-gw@centurytel.net>,
> RP <no_mail_no_spam@yahoo.com> wrote:
>
>
>
>
> Heatcraft tried a beta program for field retrofits but apparently it was
> a disaster and aren't offering it or planning to.
And that doesn't hurt my feelings a bit. I think that I related the
story of my first encounter with Heatcraft here some time ago. The
system actually killed the compressor. One thermistor failed but the
system wasn't designed to lock out on that particular thermistor. It was
either the evap inlet or evap outlet sensor, don't recall which. The EXV
shut down and the discharge temp never went out of range. Hopefully
they've remedied this flaw. Not only that, but the sensors didn't hold
up very well, I actually ended up ordered a dozen of the bastards for
that one system and had used nearly all of them up in only a few years
time. Sad.
hvacrmedic
hvacrmedic
| |
| TURTLE 2005-10-16, 1:21 am |
|
"Bill" <bill@hvac2.com> wrote in message news:4351b50c_3@newsfeed.slurp.net...
> In article <Caudne6zK7mYNszeRVn-gw@centurytel.net>,
> RP <no_mail_no_spam@yahoo.com> wrote:
>
>
> Heatcraft tried a beta program for field retrofits but apparently it was
> a disaster and aren't offering it or planning to.
>
This is Turtle.
No Heatcraft should have not let you try to install this system to screw it up
and then after screwing it up , they told you they was stopping making it to not
let you install anymore.
TURTLE
| |
|
| RP wrote:
>
>
> Bill wrote:
>
>
>
> And that doesn't hurt my feelings a bit. I think that I related the
> story of my first encounter with Heatcraft here some time ago. The
> system actually killed the compressor. One thermistor failed but the
> system wasn't designed to lock out on that particular thermistor. It was
> either the evap inlet or evap outlet sensor, don't recall which. The EXV
> shut down and the discharge temp never went out of range. Hopefully
> they've remedied this flaw. Not only that, but the sensors didn't hold
> up very well, I actually ended up ordered a dozen of the bastards for
> that one system and had used nearly all of them up in only a few years
> time. Sad.
>
> hvacrmedic
>
>
>
> hvacrmedic
>
>
The 'killing' scenario is a excellent example of poor controls design, IMO.
Anytime.... ANYTIME... you are controlling real-world components that
would result in catastrophic failure of such requires that you use at
least dual sensors at critical points.
One of the first lessons you learn studying logic controllers is to
protect people first, equipment second, and then add the bells and
whistles necessary to achieve your desired result. With automated
control, the equipment must protect itself or all bets are off... the
controller is making decisions based on data that is incomplete or wrong.
Controllers are a great benefit when properly designed and
implemented... in most cases far outlasting the mechanical equipment the
system is controlling... but it has to be done right.
If you have to design a system with a 'critical' criteria sensor and can
only provide one... then the control should LO when the info looks bad..
that's easily done in software.
These guys should get some controls pros working on their problems....
Jake
| |
|
| In article <b7CdnXT5YY3cXczeRVn-gQ@centurytel.net>,
RP <no_mail_no_spam@yahoo.com> wrote:
>
> And that doesn't hurt my feelings a bit. I think that I related the
> story of my first encounter with Heatcraft here some time ago. The
> system actually killed the compressor. One thermistor failed but the
> system wasn't designed to lock out on that particular thermistor. It was
> either the evap inlet or evap outlet sensor, don't recall which. The EXV
> shut down and the discharge temp never went out of range. Hopefully
> they've remedied this flaw. Not only that, but the sensors didn't hold
> up very well, I actually ended up ordered a dozen of the bastards for
> that one system and had used nearly all of them up in only a few years
> time. Sad.
That sucks.
They have new, new sensors. Fourth generation? Seen them? I think they
are the white ones. Supposed to be a vast improvement and solve all the
problems.
I like the remote monitoring.
Have any names of who makes retrofit kits. Any down side to them?
--
Paul's cat got a furball and kept saying weasel's name.
*Hack* *Hack* *hack*
| |
| B-Hate-Me 2005-10-16, 9:21 am |
|
"Jake" <jkelleyus@insightbb.com> wrote in message
news:jsh4f.437950$x96.226636@attbi_s72...
> ..p.jm@see_my_sig_for_address.com wrote:
> Being a controls nerd, the first question we always ask clients requesting
> something like this is: Why do you want to do this? What problem are you
> solving? What is the 'damage' you are trying to protect against? Many
> units already have protection limit switches in them that will STOP
> equipment before damage occurs...sometimes...
I agree, there are off the shelf items that deal with the *effects* of both
low and high superheat.
| |
| TURTLE 2005-10-16, 8:21 pm |
|
"Bill" <bill@hvac2.com> wrote in message news:4351f4d5$1_5@newsfeed.slurp.net...
> In article <b7CdnXT5YY3cXczeRVn-gQ@centurytel.net>,
> RP <no_mail_no_spam@yahoo.com> wrote:
>
> That sucks.
> They have new, new sensors. Fourth generation? Seen them? I think they
> are the white ones. Supposed to be a vast improvement and solve all the
> problems.
> I like the remote monitoring.
> Have any names of who makes retrofit kits. Any down side to them?
>
This is Turtle.
Now if only some customer would trust you to install one ? They have to trust
you first.
TURTLE
| |
| refrigeration_man 2005-10-17, 9:21 pm |
| Maybe fuzzy logic could be applied here, probally expensive.
| |
| ..p.jm@see_my_sig_for_address.com 2005-10-17, 11:21 pm |
| On 17 Oct 2005 17:14:44 -0700, "refrigeration_man"
<refrigeration_man@msn.com> wrote:
>Maybe fuzzy logic could be applied here, probally expensive.
And maintain - all that constant shaving ...
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/
Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
| |
|
| ...p.jm@see_my_sig_for_address.com wrote:
> On 17 Oct 2005 17:14:44 -0700, "refrigeration_man"
> <refrigeration_man@msn.com> wrote:
>
>
>
>
> And maintain - all that constant shaving ...
>
Now that's funny!
Really... any decent PLC and HMI package properly programmed could get
you there... the HMI could allow the operator to set up their own
'rules' as they see fit..
As I like to say.... NOT expensive... just not too cheap!
Jake
>
> Click here every day to feed an animal that needs you today !!!
>
> http://www.theanimalrescuesite.com/
>
> Paul ( pjm @ pobox . com ) - remove spaces to email me
> 'Some days, it's just not worth chewing through the restraints.'
> 'With sufficient thrust, pigs fly just fine.'
> HVAC/R program for Palm PDA's
> Free demo now available online http://pmilligan.net/palm/
| |
|
|
Jake wrote:
> ..p.jm@see_my_sig_for_address.com wrote:
>
>
> Now that's funny!
>
> Really... any decent PLC and HMI package properly programmed could get
> you there... the HMI could allow the operator to set up their own
> 'rules' as they see fit..
>
> As I like to say.... NOT expensive... just not too cheap!
Differential thermostat with a time-delay bypass relay.
It can be done for under $120.
An example:
http://www.solairgen.com/PDF%20file....%20Control.pdf
hvacrmedic
[color=darkred]
| |
| ..p.jm@see_my_sig_for_address.com 2005-10-18, 2:21 am |
| On Mon, 17 Oct 2005 23:37:03 -0500, RP <no_mail_no_spam@yahoo.com>
wrote:
>
>
>Jake wrote:
>
>
>Differential thermostat with a time-delay bypass relay.
>It can be done for under $120.
>
>An example:
>
>http://www.solairgen.com/PDF%20file....%20Control.pdf
>
>hvacrmedic
OK, now 'splain me how it measures superheat.
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/
Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
| |
|
|
...p.jm@see_my_sig_for_address.com wrote:
> On Mon, 17 Oct 2005 23:37:03 -0500, RP <no_mail_no_spam@yahoo.com>
> wrote:
>
>
>
>
> OK, now 'splain me how it measures superheat.
One sensor at the evap inlet, the other at the evap outlet or suction
line or compressor or whatever. Depends upon what you're general plan is
hvacrmedic
>
>
> Click here every day to feed an animal that needs you today !!!
>
> http://www.theanimalrescuesite.com/
>
> Paul ( pjm @ pobox . com ) - remove spaces to email me
> 'Some days, it's just not worth chewing through the restraints.'
> 'With sufficient thrust, pigs fly just fine.'
> HVAC/R program for Palm PDA's
> Free demo now available online http://pmilligan.net/palm/
| |
| ..p.jm@see_my_sig_for_address.com 2005-10-18, 2:21 am |
| On Mon, 17 Oct 2005 23:54:13 -0500, RP <no_mail_no_spam@yahoo.com>
wrote:
>
>
>..p.jm@see_my_sig_for_address.com wrote:
>
>
>One sensor at the evap inlet, the other at the evap outlet or suction
>line or compressor or whatever. Depends upon what you're general plan is
OK - now 'splain me how it measures superheat.
Not TEMPERATURE ! SUPERHEAT ! :-)
Last I heard, that required a pressure reading .....
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/
Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
| |
|
|
...p.jm@see_my_sig_for_address.com wrote:
> On Mon, 17 Oct 2005 23:54:13 -0500, RP <no_mail_no_spam@yahoo.com>
> wrote:
>
>
>
>
> OK - now 'splain me how it measures superheat.
>
> Not TEMPERATURE ! SUPERHEAT ! :-)
>
> Last I heard, that required a pressure reading .....
Last I heard superheat was a difference in temperatures.
The suction pressure corresponds to SST, which can in turn be obtained
directly by measuring the temperature of the evap inlet. I don't even
pay attention to pressures on my gauges, I look at the inner green or
pink scale. It's all about temperatures, pressures are just incidental.
Gary Lloyd tried to impress this upon all of us at one time; by looking
at temps only you can work with any refrigerant without having to change
modes of thought and without changing methods.
hvacrmedic
>
>
> Click here every day to feed an animal that needs you today !!!
>
> http://www.theanimalrescuesite.com/
>
> Paul ( pjm @ pobox . com ) - remove spaces to email me
> 'Some days, it's just not worth chewing through the restraints.'
> 'With sufficient thrust, pigs fly just fine.'
> HVAC/R program for Palm PDA's
> Free demo now available online http://pmilligan.net/palm/
| |
| ..p.jm@see_my_sig_for_address.com 2005-10-18, 4:21 am |
| On Tue, 18 Oct 2005 00:11:11 -0500, RP <no_mail_no_spam@yahoo.com>
wrote:
>
>
>..p.jm@see_my_sig_for_address.com wrote:
>
>
>Last I heard superheat was a difference in temperatures.
One of which if obtained from a pressure reading.
>The suction pressure corresponds to SST, which can in turn be obtained
>directly by measuring the temperature of the evap inlet. I don't even
Say WHAT ????? Come on already, you know better than that
......
>pay attention to pressures on my gauges, I look at the inner green or
>pink scale. It's all about temperatures, pressures are just incidental.
So, you don't use gauges ? Just thermocouples ? Interesting
concept ..... not.
Why do you own gauges, then ? All you should need is a hose
and some thermocouples, right ?
Kinda like Weasel, except he doesn't have the thermocouples
.....
>Gary Lloyd tried to impress this upon all of us at one time; by looking
>at temps only you can work with any refrigerant without having to change
>modes of thought and without changing methods.
He NEVER said 'don't use pressures' and he NEVER said
'measuring superheat doesn't require a pressure reading'. nor does
anyone else in the industry.
As the person who converted his book to an ( updated & revised
by Gary in 2004 ) E-book, which is incorporated into HVACSUITE, I can
attest to this :-)
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/
Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
| |
|
|
...p.jm@see_my_sig_for_address.com wrote:
> On Tue, 18 Oct 2005 00:11:11 -0500, RP <no_mail_no_spam@yahoo.com>
> wrote:
>
>
>
>
> One of which if obtained from a pressure reading.
>
>
>
>
> Say WHAT ????? Come on already, you know better than that
> .....
>
>
>
>
> So, you don't use gauges ? Just thermocouples ? Interesting
> concept ..... not.
>
> Why do you own gauges, then ? All you should need is a hose
> and some thermocouples, right ?
>
> Kinda like Weasel, except he doesn't have the thermocouples
> ....
>
>
>
>
> He NEVER said 'don't use pressures' and he NEVER said
> 'measuring superheat doesn't require a pressure reading'. nor does
> anyone else in the industry.
>
> As the person who converted his book to an ( updated & revised
> by Gary in 2004 ) E-book, which is incorporated into HVACSUITE, I can
> attest to this :-)
Regardless of the content of his books, he most certainly did say as
much right here. Now as for measuring SST directly, you should probably
check with Heatcraft or Carrier, or anyone else on the planet marketing
EXV systems, because what I described is precisely, exactly, and
unambiguously, how they monitor superheat. There is no more accurate
way to derive SST (the temperature at which refrigerant boils at
saturation) than to measure the temperature of the boiling refrigerant
directly). This is more accurate than the pressure converted temperature
method that you think is required, since there is no pressure drop to
take into consideration when measuring the temperature directly.
Paul, I'm a bit surprised at your argument here, OTOH, I've learned a
thing or two in the past from you as well, so I guess it all works out
hvacrmedic
| |
| refrigeration_man 2005-10-18, 9:21 pm |
| Heatcraft's Beacon II uses a pressure transducer, evidently measuring
t.d. with sensors was not accurate enough.
| |
|
|
> Regardless of the content of his books, he most certainly did say as
> much right here. Now as for measuring SST directly, you should probably
> check with Heatcraft or Carrier, or anyone else on the planet marketing
> EXV systems, because what I described is precisely, exactly, and
> unambiguously, how they monitor superheat. There is no more accurate
> way to derive SST (the temperature at which refrigerant boils at
> saturation) than to measure the temperature of the boiling refrigerant
> directly). This is more accurate than the pressure converted temperature
> method that you think is required, since there is no pressure drop to
> take into consideration when measuring the temperature directly.
>
> Paul, I'm a bit surprised at your argument here, OTOH, I've learned a
> thing or two in the past from you as well, so I guess it all works out
>
> hvacrmedic
>
I would agree that a real, actual temperature would be more accurate....
the difficulty is getting it in a closed loop system. How is that
done...? Would you have the same problems with temp. gain/loss at your
RTD measuring point that you might see with 'pressure drops'... which I
believe would be less likely?
I looked at a Metasys project we have been working on interfacing with,
and I can indeed get pressures from a Carrier RTU or most chillers (not
all) from Carrier control packages for commercial equipment.
I'm not convinced that the direct temperature scheme is not more
accurate so much as it's more 'economically feasible' on a retrofit.
Any links you've got would be appreciated, RP.
Jake
| |
| ..p.jm@see_my_sig_for_address.com 2005-10-18, 11:21 pm |
| On Wed, 19 Oct 2005 00:52:54 GMT, Jake <jkelleyus@insightbb.com>
wrote:
>
>
>I would agree that a real, actual temperature would be more accurate....
Not for SST, it's not. Never, ever. your one and only 'most
accurate always' source for that is the Temp / press chart.
Which is different than the question RP posed. ( / answered
:-) ), which is 'We assume that the inlet represents saturation, and
that the surface we are measuring represents the actual internal
refrigerant temp, and thus can use it 'as if' converted from a
presssure reading.'
Flaw - the inlet often does NOT represent saturation. There
is an area of dynamic change there while sub-cool is gotten rid of,
and liquid flashes off. An inch or two one way or another can make a
several degree difference. While there is a theoretical point where
the SST is present ( after sub-cool is gone, before SH starts picking
up ), you don't KNOW where that point is ( hint - it ain't the
distributor , and it ain't the first inch of pipe after it ).
Flaw - the surface you are measuring often does NOT accurately
reflect the temperature of the refrigerant inside the pipe.
Flaw - at any time there is < 100 % pure liquid feed, it
becomes meaningless.
>the difficulty is getting it in a closed loop system. How is that
>done...? Would you have the same problems with temp. gain/loss at your
>RTD measuring point that you might see with 'pressure drops'... which I
>believe would be less likely?
>
>I looked at a Metasys project we have been working on interfacing with,
>and I can indeed get pressures from a Carrier RTU or most chillers (not
>all) from Carrier control packages for commercial equipment.
>
>I'm not convinced that the direct temperature scheme is not more
>accurate so much as it's more 'economically feasible' on a retrofit.
>
>Any links you've got would be appreciated, RP.
>
>Jake
>
>
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/
Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
| |
|
|
Jake wrote:
>
>
> I would agree that a real, actual temperature would be more accurate....
> the difficulty is getting it in a closed loop system. How is that
> done...? Would you have the same problems with temp. gain/loss at your
> RTD measuring point that you might see with 'pressure drops'... which I
> believe would be less likely?
>
> I looked at a Metasys project we have been working on interfacing with,
> and I can indeed get pressures from a Carrier RTU or most chillers (not
> all) from Carrier control packages for commercial equipment.
>
> I'm not convinced that the direct temperature scheme is not more
> accurate so much as it's more 'economically feasible' on a retrofit.
>
> Any links you've got would be appreciated, RP.
>
In the Beacon system the sensors are located in thermal wells. The
disadvantage of this is that on medium and low temp equipment ice forms
in the wells, which aren't sealed against moisture, and this can damage
the sensors with hydraulic pressure. (Don't take that as gospel, it's
just a theory that seemed to me to fit the facts). I assume that this is
the cause of Beacon's rampant sensor failure problem. On high temp
equipment, OTOH, sensors will typically last for several years at a
time. This has been my experience on Flotronic chillers, which I have
maintained several of over the years. The reason for the thermal well is
that thermistors aren't as responsive as pressure transducers, the heat
requires time to flow in and out of them. Even so, the EXV/EEV valve is
a fast acting valve, and because of this the electronic system is far
superior to standard TXV systems as far as maintaining desired
superheat, that is, when they are working correctly.
On the Flotronic systems the thermal wells actually extend into the
pipes, or surfaces that they are sensing, and they are sealed against
moisture. The sensors are also of a vastly superior quality to the
Beacon sensors. IMHO, if Heatcraft had upgraded the sensor situation on
the original Beacon system they would have had a superior product to the
newer pressure transducer system.
As for links, I searched EXV/EEV systems several years ago and ran
across a wealth of information. I've since reloaded windows several
times, so the bookmarks are long gone, as are the many pdf files that I
had downloaded. Try the key words EEV, EXV, superheat, thermistor, and
evaporator inlet, stepper.
hvacrmedic
| |
|
|
...p.jm@see_my_sig_for_address.com wrote:
> On Wed, 19 Oct 2005 00:52:54 GMT, Jake <jkelleyus@insightbb.com>
> wrote:
>
>
>
>
> Not for SST, it's not. Never, ever. your one and only 'most
> accurate always' source for that is the Temp / press chart.
>
> Which is different than the question RP posed. ( / answered
> :-) ), which is 'We assume that the inlet represents saturation, and
> that the surface we are measuring represents the actual internal
> refrigerant temp, and thus can use it 'as if' converted from a
> presssure reading.'
>
> Flaw - the inlet often does NOT represent saturation. There
> is an area of dynamic change there while sub-cool is gotten rid of,
> and liquid flashes off. An inch or two one way or another can make a
> several degree difference. While there is a theoretical point where
> the SST is present ( after sub-cool is gone, before SH starts picking
> up ), you don't KNOW where that point is ( hint - it ain't the
> distributor , and it ain't the first inch of pipe after it ).
>
> Flaw - the surface you are measuring often does NOT accurately
> reflect the temperature of the refrigerant inside the pipe.
>
> Flaw - at any time there is < 100 % pure liquid feed, it
> becomes meaningless.
Yes, that's all interesting, but doesn't seem to stop the engineers from
finding the sweet spot Typically, on systems designed for use with
the evap inlet thermistor, there is a substantial length of tubing
between the EXV and the evaporator coil. They have quite a few inches of
tubing *at* SST.
hvacrmedic
>
>
> Click here every day to feed an animal that needs you today !!!
>
> http://www.theanimalrescuesite.com/
>
> Paul ( pjm @ pobox . com ) - remove spaces to email me
> 'Some days, it's just not worth chewing through the restraints.'
> 'With sufficient thrust, pigs fly just fine.'
> HVAC/R program for Palm PDA's
> Free demo now available online http://pmilligan.net/palm/
| |
| Carolina Breeze HVAC 2005-10-19, 11:21 am |
|
"RP" <no_mail_no_spam@yahoo.com> wrote in message
news:HKSdnezCBIRtB8neRVn-rQ@centurytel.net...
>
>
> ..p.jm@see_my_sig_for_address.com wrote:
>
>
> Regardless of the content of his books, he most certainly did say as much
> right here. Now as for measuring SST directly, you should probably check
> with Heatcraft or Carrier, or anyone else on the planet marketing EXV
> systems, because what I described is precisely, exactly, and
> unambiguously, how they monitor superheat. There is no more accurate way
> to derive SST (the temperature at which refrigerant boils at saturation)
> than to measure the temperature of the boiling refrigerant directly). This
> is more accurate than the pressure converted temperature method that you
> think is required, since there is no pressure drop to take into
> consideration when measuring the temperature directly.
>
> Paul, I'm a bit surprised at your argument here, OTOH, I've learned a
> thing or two in the past from you as well, so I guess it all works out
>
> hvacrmedic
>
>
Umm...there are a couple of sets of "manifolds" that only use
thermocouples...have to find em and slap a link up.
>
>
>
| |
| ~^Johnny^~ 2005-10-26, 4:21 am |
| On Sat, 15 Oct 2005 19:26:42 -0400, "Rick" <rarnold30@cox.net> wrote:
>Does anyone know of a manufacturer who markets a superheat sensor that can
>be installed permanently into a commercial or industrial AC system that can
>lock out the compressor electrically if superheat is below or above safe
>operational temperature? Thanks for info.
>
Why? You've got accumulators...
--
-john
wide-open at throttle dot info
| |
| ~^Johnny^~ 2005-10-26, 4:21 am |
| On Sun, 16 Oct 2005 04:52:11 GMT, Jake <jkelleyus@insightbb.com>
wrote:
>These guys should get some controls pros working on their problems....
The trouble is, they are a bunch of control freaks.
--
-john
wide-open at throttle dot info
| |
| ~^Johnny^~ 2005-10-26, 4:21 am |
| On Tue, 25 Oct 2005 23:51:39 -0700, ~^Johnny^~
<nospam@gyrogearloose.com> wrote:
>On Sat, 15 Oct 2005 19:26:42 -0400, "Rick" <rarnold30@cox.net> wrote:
>
>
>Why? You've got accumulators...
I forgot about above. A CRO valve will take care of that problem.
It's high backpressure that will damage a hermetic compressor,
probably more so than a little liquid slopover. A high pressure
cutout, with manual rests, on the suction line, is all you need, as
afailsafe.
And for slopover, there's always the good old aspirating
accumulator. Works fine, lasts a long time.
--
-john
wide-open at throttle dot info
| |
|
|
"~^Johnny^~" <nospam@gyrogearloose.com> wrote in message
news:mlaul1p8mt01oc2st4q3gd3meghk186649@4ax.com...
On Tue, 25 Oct 2005 23:51:39 -0700, ~^Johnny^~
<nospam@gyrogearloose.com> wrote:
>On Sat, 15 Oct 2005 19:26:42 -0400, "Rick" <rarnold30@cox.net> wrote:
>
>
>Why? You've got accumulators...
I forgot about above. A CRO valve will take care of that problem.
It's high backpressure that will damage a hermetic compressor,
probably more so than a little liquid slopover. A high pressure
cutout, with manual rests, on the suction line, is all you need, as
afailsafe.
And for slopover, there's always the good old aspirating
accumulator. Works fine, lasts a long time.
--
-john
wide-open at throttle dot info
Just call Fred at Sporlan. He'll get you squared away.
ReRe
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