Subject: Re: Now, how do I tune it ? ( was Re: Freon Breakdown )

From: [email-masked] (TMETHOD)
Date: 5 Oct 1995 19:50:22 -0400

In article <[email-masked]>, [email-masked] (paul
milligan) writes:

>	At this time, I plan on a 1:1.5 ratio on the pneumatic relay, so
>that a 0 - 20 # change out of the prop controller results in 0 - 30 to
>the HGBV, giving me a max evap of 55 + 30 = 85#, in other words each
>1# change from the prop controller raises ( or lowers ) my evap pressure
>1 1/2 #.  Also, my max pneumatic pressure will never be able to exceed my

>suction pressure, so the next leak will be freon out, not air in !
>
>

What's wrong with this picture? Paul, I have read this paragraph over and
over and there is something wrong with the logic (last sentence in
particular), but I can't quite put my finger on it. Maybe I'm missing
something. Is the ratio adjustable on the HGBV? Doesn't the pneumatic
pressure have to exceed the evap pressure in order to open it? Talk to me.

Gary

================================================
Everything should be made as simple as possible, but not simpler
     -Albert Einstein-

Gary R. Lloyd CMS
TECH Method Training
HVACR Trouble Shooting Books/Software
Tel 313-671-0188  Fax 313-676-9262

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From: [email-masked] (paul milligan)
Date: 6 Oct 1995 21:33:03 GMT

In article <[email-masked]>,
   [email-masked] (TMETHOD) wrote:
~~>In article <[email-masked]>, [email-masked] (paul
~~>milligan) writes:
~~>
~~>>	At this time, I plan on a 1:1.5 ratio on the pneumatic relay, so
~~>>that a 0 - 20 # change out of the prop controller results in 0 - 30 to
~~>>the HGBV, giving me a max evap of 55 + 30 = 85#, in other words each
~~>>1# change from the prop controller raises ( or lowers ) my evap pressure
~~>>1 1/2 #.  Also, my max pneumatic pressure will never be able to exceed my
~~>
~~>>suction pressure, so the next leak will be freon out, not air in !
~~>
~~>What's wrong with this picture? Paul, I have read this paragraph over and
~~>over and there is something wrong with the logic (last sentence in
~~>particular), but I can't quite put my finger on it. Maybe I'm missing
~~>something. Is the ratio adjustable on the HGBV? Doesn't the pneumatic
~~>pressure have to exceed the evap pressure in order to open it? Talk to me.

	Not sure what you're seeing...The pressure of the control air feeding
the HGBV is variable 0 - 80.  The response of the HGBV is not
adjustable, but the minimum evap pressure is.  There's a spring inside,
with an adjusting stem, much like TXV, such that spring pressure plus
pneumatic pressure = total pressure, thus the spring is doing most of the
work of overcoming system pressure, and the pneumatic rides 'on top' of it.

	Assuming I set the minimum pressure spring ( via the stem )to 55#,
at 0 # pneumatic I have 55 # evap, at 1 # pneumatic I have ( 55 + 1 = 56 )
back, etc.  The ratio question comes in where the standard RH sensor feeds
the standard proportional band controller, with reverse action output, and
I have to determine how much of a change in sensor pressure ( varying in 
10ths of lbs ) will result in what proportional span of the output ( 0 - 20),
which will then be ratio-relayed at a 1 : 1.5 factor ( as I'm thinking right
now, anyway :~)  ), such that actual control to the HGBV is at a span of
0 - 30 ( over the minimum set).

	To rephrase my question - let's say my RH sensor says the RH is 1%
too low ( set at 60%, reading 59% ).  How do I think about how much I have
to change my evap pressure to let 1% RH more through the system ?  And
what does it mean in terms of evap pressure ?  Raise the back too high, and
the RH will overshoot considerably.  Don't raise it enough, and the RH will
remain too low.  Keep in mind that there is electric reheat coming in to
deal with the Dry Bulb effect of the system when it over-cools, I'm only
trying to worry about latent.  As I see it, what I'm trying to accomplish by
changing evap pressure is to manipulate the SHR around a desired dew point,
in terms of final RH output. 

	So, how can I predict evap pressure vs SHR vs RH ?

	Interesting question, eh ?  :~)

Paul

_________________________________________________________
No Disclaimer needed - This is my own PPP account, and my
employer doesn't care what I think anyway !  :~)
_________________________________________________________

http://www.elitesoft.com/sci.hvac/ is the home page of
sci.engr.heat-vent-ac

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From: [email-masked] (TMETHOD)
Date: 7 Oct 1995 00:04:55 -0400

In article <[email-masked]>, [email-masked] (paul

>0 - 30 ( over the minimum set).

If this is the case then how could the HGBV have leaked air into the
system with a minimum setting of 68# spring pressure?

Gary

===========================================
I pretend to work. They pretend to pay me. I pretend to eat.
     -Anonymous Soviet Citizen-

Gary R. Lloyd CMS
TECH Method Training

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From: [email-masked] (TMETHOD)
Date: 7 Oct 1995 10:17:10 -0400

In article <[email-masked]>, [email-masked] (paul
milligan) writes:

>
>In article <[email-masked]>,
>~~>>now, anyway :~)  ), such that actual control to the HGBV is at a span
of
>~~>>0 - 30 ( over the minimum set).
>~~>
>~~>If this is the case then how could the HGBV have leaked air into the
>~~>system with a minimum setting of 68# spring pressure?
>~~>
>
>	Previous set-up, as I inherited it, was resulting in the system
>running at 80 - 110 # pneumatic, which is probably what broke the
>diaphragm in the HGBV.
>
>

Duh...I think I'm beginning to get the picture. The HGBV was subjected to
an unregulated air supply (80-110#). A call for bypass resulted in the
HGBV being driven to it's full open position and then some, thus exceeding
the maximum operating pressure of the device. BTW, what is the max
pressure of the HGBV? Do you plan on installing a regulator in it's air
supply or are you counting on the multiplier to protect it (a very risky
proposition, IMHO)? 

Will 85# evaporator pressure be enough to achieve the desired result? Not
being an engineer, and given the complexity of this system, the variables
would seem overwhelming. My unscientific approach would be to subject the
HGBV to something slightly less than its max pressure rating as a starting
point, and then gradually reduce it from there. Perhaps the engineers out
there have a better way.

Gary

Gary R. Lloyd CMS
TECH Method Training

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From: [email-masked] (paul milligan)
Date: 7 Oct 1995 11:32:50 GMT

~~>>now, anyway :~)  ), such that actual control to the HGBV is at a span of
~~>>0 - 30 ( over the minimum set).
~~>
~~>If this is the case then how could the HGBV have leaked air into the
~~>system with a minimum setting of 68# spring pressure?
~~>

---

From: [email-masked]
Date: 8 Oct 1995 14:58:25 GMT

>running at 80 - 110 # pneumatic, which is probably what broke the

Paul, an 80 - 110 psig pneumatic would not normally harm the diaphragm
of your HGBV.  In fact, 200 psig shouldn't be much of a problem.

If the pneumatic signal is cycling the valve open and closed frequently,
that's another story.  The signal would then be, in effect, life
cycling the valve.

I suspect moisture in the air being used is causing rust to form in
the valve above the diaphragm, and the rust is causing the diaphragm
to fail.

Andy Schoen
[email-masked]