I wish to use a single large compressor to service 3 cold plates and 3 air
conditioning evaporators, but I am not a refrigeration expert, so if my
thinking is incorrect please let me know. Each one of these (users) will
have their own mechanical temperature controlled evaporator valve. I assume
the compressor should be cycled by head pressure with an overtemp sensor for
safety. I would like to use a salt water cooled condensor on the high
pressure side and a freon gas that changes state around -40 C. Please
advise. Do I need an accumulator of some description on either side? If so,
what? Each one of the users have 3/8" in/out tubes. How do I size the
compressor? Any tips or books on this subject would be welcome.
Steve

"Steve Lusardi" fired this volley in
:

I would like to use a
salt water cooled condensor on the high pressure side and a freon gas
that changes state around -40 C. Please advise. Do I need an
accumulator of some description on either side?

Yep, you need an accumulator (fairly large one) on the high-pressure
side, and that's a good place to put the head-pressure switch.

However, I'd recommend a refrigerant that changes state at about -40F.

LLoyd

On Mon, 25 Aug 2008 14:23:14 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

SNIP

However, I'd recommend a refrigerant that changes state at about -40F.

LLoyd


Yeah, that would be much better than the -40 C stuff, and besides it's
easier to get..

Steve Lusardi wrote:
I wish to use a single large compressor to service 3 cold plates and 3 air
conditioning evaporators, but I am not a refrigeration expert, so if my
thinking is incorrect please let me know. Each one of these (users) will
have their own mechanical temperature controlled evaporator valve. I assume
the compressor should be cycled by head pressure with an overtemp sensor for
safety. I would like to use a salt water cooled condensor on the high
pressure side and a freon gas that changes state around -40 C. Please
advise. Do I need an accumulator of some description on either side? If so,
what? Each one of the users have 3/8" in/out tubes. How do I size the
compressor? Any tips or books on this subject would be welcome.
Steve



You can't realy cycle the compressor off in an application like this.
When the compressor is off, the liquid in the evaporator continues to
evaporate, and very quickly the low-side pressure rises. Then, ALL the
evaporators stop working. With thermostatically-controlled metering
valves regulating the temperature of the separate evaporators, you can
probably run the compressor all the time (except for fault conditions)
and as long as the accumulator has sufficient volume, it should all
regulate itself pretty well. The compressor will unload when there's
little gas coming in. Are you really trying to achieve -40 (C or F,
doesn't matter) with a single stage? That is quite pushing it. R-22
will do it, but at low pressure, so a larger compressor and evaporators
will be needed.

You can't size the compressor until you know the heat flow. Knowing the
tube size is nearly worthless. You need orifices in the expansion
valves to prevent slugging the liquid in the evaporator all into the
compressor at once. These set the maximum capacity per evaporator.

Jon

In article ,
Brian Lawson wrote:

On Mon, 25 Aug 2008 14:23:14 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

SNIP

However, I'd recommend a refrigerant that changes state at about -40F.

LLoyd


Yeah, that would be much better than the -40 C stuff, and besides it's
easier to get..

Ooooh, sneaky _and_ ornery; I like that in a person.

"Steve Lusardi" wrote:
I wish to use a single large compressor to service 3 cold plates and 3 air
conditioning evaporators, but I am not a refrigeration expert, so if my
thinking is incorrect please let me know. Each one of these (users) will
have their own mechanical temperature controlled evaporator valve. I assume
the compressor should be cycled by head pressure with an overtemp sensor
for safety. I would like to use a salt water cooled condensor on the high
pressure side and a freon gas that changes state around -40 C. Please
advise. Do I need an accumulator of some description on either side? If so,
what? Each one of the users have 3/8" in/out tubes. How do I size the
compressor? Any tips or books on this subject would be welcome.

I'd probably crosspost a request to alt.hvac; those guys are very helpful
when someone who isn't a trained hvac technician asks a question. Be sure
and tell them you are a homowner, and that you have a done a few DIY
projects (like a fence and a water faucet) in the past so they know you
would be capable of the work.

Jon

I'd probably crosspost a request to alt.hvac; those guys are very helpful
when someone who isn't a trained hvac technician asks a question. *Be sure
and tell them you are a homowner, and that you have a done a few DIY
projects (like a fence and a water faucet) in the past so they know you
would be capable of the work. *

Jon

Jon you are a mean person, hvac guys hate anyone to touch an a/c
without a licence, especially a homeowner. They really wish this to
become a death penalty crime. This group will chew him up if he does
this, a bunch of arrogant (*&^%$) people there.

Scott

wrote:
I'd probably crosspost a request to alt.hvac; those guys are very
helpful when someone who isn't a trained hvac technician asks a
question. Be sure and tell them you are a homowner, and that you
have a done a few DIY projects (like a fence and a water faucet) in
the past so they know you would be capable of the work.

Jon

Jon you are a mean person, hvac guys hate anyone to touch an a/c
without a licence, especially a homeowner. They really wish this to
become a death penalty crime. This group will chew him up if he does
this, a bunch of arrogant (*&^%$) people there.

Scott

Half the problem is they think the refrigeration cycle is some kind of
arcane magic . The other half is most of the sheeple think so too .
--
Snag
killer of sacred cows at any opportunity

Jon,
Good info. The cold plates I have bought are used units and they all have
the expansion valves with them. I have assumed they also have integral spray
orifices. I suppose I could apply compressed air to determine approximate
flow rates. How else would I test these, as they are not able to be
disassembled? The cold plates are used marine units and I want to use them
for a freezer, not a refrigerator, hence the -40 requirement. I am aware of
the requirement to change the medium in the cold plate itself in order to
reduce the temperature of the state change. The goal is to freeze the plates
down once a day or less when in use. How do I estimate the heat load? The
cold plates are aproximately 24" x 18" x 4".
Steve

"Jon Elson" wrote in message
...


Steve Lusardi wrote:
I wish to use a single large compressor to service 3 cold plates and 3
air conditioning evaporators, but I am not a refrigeration expert, so if
my thinking is incorrect please let me know. Each one of these (users)
will have their own mechanical temperature controlled evaporator valve. I
assume the compressor should be cycled by head pressure with an overtemp
sensor for safety. I would like to use a salt water cooled condensor on
the high pressure side and a freon gas that changes state around -40 C.
Please advise. Do I need an accumulator of some description on either
side? If so, what? Each one of the users have 3/8" in/out tubes. How do I
size the compressor? Any tips or books on this subject would be welcome.
Steve

You can't realy cycle the compressor off in an application like this. When
the compressor is off, the liquid in the evaporator continues to
evaporate, and very quickly the low-side pressure rises. Then, ALL the
evaporators stop working. With thermostatically-controlled metering
valves regulating the temperature of the separate evaporators, you can
probably run the compressor all the time (except for fault conditions) and
as long as the accumulator has sufficient volume, it should all regulate
itself pretty well. The compressor will unload when there's little gas
coming in. Are you really trying to achieve -40 (C or F, doesn't matter)
with a single stage? That is quite pushing it. R-22 will do it, but at
low pressure, so a larger compressor and evaporators will be needed.

You can't size the compressor until you know the heat flow. Knowing the
tube size is nearly worthless. You need orifices in the expansion valves
to prevent slugging the liquid in the evaporator all into the compressor
at once. These set the maximum capacity per evaporator.

Jon

In article ,
says...
Jon,
Good info. The cold plates I have bought are used units and they all have
the expansion valves with them. I have assumed they also have integral spray
orifices. I suppose I could apply compressed air to determine approximate
flow rates. How else would I test these, as they are not able to be
disassembled? The cold plates are used marine units and I want to use them
for a freezer, not a refrigerator, hence the -40 requirement. I am aware of
the requirement to change the medium in the cold plate itself in order to
reduce the temperature of the state change. The goal is to freeze the plates
down once a day or less when in use. How do I estimate the heat load? The
cold plates are aproximately 24" x 18" x 4".
Steve

"Jon Elson" wrote in message
...


Steve Lusardi wrote:
I wish to use a single large compressor to service 3 cold plates and 3
air conditioning evaporators, but I am not a refrigeration expert, so if
my thinking is incorrect please let me know. Each one of these (users)
will have their own mechanical temperature controlled evaporator valve. I
assume the compressor should be cycled by head pressure with an overtemp
sensor for safety. I would like to use a salt water cooled condensor on
the high pressure side and a freon gas that changes state around -40 C.
Please advise. Do I need an accumulator of some description on either
side? If so, what? Each one of the users have 3/8" in/out tubes. How do I
size the compressor? Any tips or books on this subject would be welcome.
Steve


Somehow I get the idea that you are building a "boat installation" in
which case try to lay your hands on a book named Refrigeration for
Pleasureboats: Installation, Maintenance and Repair by Nigel Calder.

It gives you methods and formula to calculate heat and insulation
values, condenser water flow, cold plate area and everything else you
need to design and build a refrigeration system for a boat.

Even tells you how to build your own condenser using either copper or
Cupro-nickle tubing.

--
Cheers,

Bruce in Bangkok

Steve Lusardi wrote:
Jon,
Good info. The cold plates I have bought are used units and they all have
the expansion valves with them. I have assumed they also have integral spray
orifices.
Yes, they should. The orifice size should be able to be looked
up from the part number. Also, thermostatic expansion valves
have to have the same refrigerant in the sensing bulb as is used
in the system.
I suppose I could apply compressed air to determine approximate
flow rates. How else would I test these, as they are not able to be
disassembled? The cold plates are used marine units and I want to use them
for a freezer, not a refrigerator, hence the -40 requirement. I am aware of
the requirement to change the medium in the cold plate itself in order to
reduce the temperature of the state change. The goal is to freeze the plates
down once a day or less when in use. How do I estimate the heat load? The
cold plates are aproximately 24" x 18" x 4".
What are you cooling? Just the plates? A tank of brine?
Making a block of ice?

It gets messy. What is the starting temp of the plates when you
begin to cool them? Will you be cooling only one at a time?
Would you be keeping one or more plates cold while starting the
cool-down process on a warm plate? That's the worst-case
scenario. To calculate the heat load, you need to know the
surface area of the tubing, and the thermal conductivity of the
heat source to the cold plate. If you are hanging the plates in
mid air and cooling the air in a room, the heat flow is very
low. If the cold plates are attached to metal walls or immersed
in circulating brine, the heat flow is maybe 100x higher. You
really aren't telling us enough to give you any help.

Anyway, to get to -40 C (or F) you need an evaporator pressure
(suction, low-side) of 105 kPa absolute, or just barely above
atmospheric pressure. This will cut the performance of the
evaporator, as well as making the compressor work a lot harder.

Jon

Jon,
Effectively, I am building an old fashioned ice box and these plates will be
atached to the walls of the well insulated box. The air flow inside the box
would be convective, just like in your freezer at home. All the plates would
be in parallel. These cold plates are holding plates and I suspect they are
filled with brine, as they were probably used as a refrigerator. In order to
use these plates in a freezer efficiently, the solution will have to be
changed to one that changes state at a lower temperature. You stated that
the expansion valve must have the same freon on both sides of the diaphragm.
I hadn't thought of that, but it makes sense. I know I must use the most
appropriate freon for the task, which means that I will have to buy new
expansion valves to match that choice. Good info. I understand the
difficulty in calculating the heat load, but I don't think the ice box
itself has much to do with it. I would think the volume of the cooled fluid
medium is the 90% answer. The rate that medium has in warming up is not very
relevent, because the system will not be operating then. It is also
unreasonable to think that these holding plates will freeze solid at he same
time, but if each has its own control valve it shoudn't matter.
Steve

"Jon Elson" wrote in message
...
Steve Lusardi wrote:
Jon,
Good info. The cold plates I have bought are used units and they all have
the expansion valves with them. I have assumed they also have integral
spray orifices.
Yes, they should. The orifice size should be able to be looked up from
the part number. Also, thermostatic expansion valves have to have the
same refrigerant in the sensing bulb as is used in the system.
I suppose I could apply compressed air to determine approximate
flow rates. How else would I test these, as they are not able to be
disassembled? The cold plates are used marine units and I want to use
them for a freezer, not a refrigerator, hence the -40 requirement. I am
aware of the requirement to change the medium in the cold plate itself in
order to reduce the temperature of the state change. The goal is to
freeze the plates down once a day or less when in use. How do I estimate
the heat load? The cold plates are aproximately 24" x 18" x 4".
What are you cooling? Just the plates? A tank of brine? Making a block
of ice?

It gets messy. What is the starting temp of the plates when you begin to
cool them? Will you be cooling only one at a time? Would you be keeping
one or more plates cold while starting the cool-down process on a warm
plate? That's the worst-case scenario. To calculate the heat load, you
need to know the surface area of the tubing, and the thermal conductivity
of the heat source to the cold plate. If you are hanging the plates in
mid air and cooling the air in a room, the heat flow is very low. If the
cold plates are attached to metal walls or immersed in circulating brine,
the heat flow is maybe 100x higher. You really aren't telling us enough
to give you any help.

Anyway, to get to -40 C (or F) you need an evaporator pressure (suction,
low-side) of 105 kPa absolute, or just barely above atmospheric pressure.
This will cut the performance of the evaporator, as well as making the
compressor work a lot harder.

Jon

Bruce,
Good assumption, that is exactly what I'm building and effectively what I'm
looking for is a simple reliable design that fits my requirements. I see
this as a good example of spiral developement philosophy. The more I learn,
the more I know, the more I learn etc. That book is a good tip. It certainly
can't hurt. Thanks.
Steve

"Bruce in Bangkok" wrote in message
...
In article ,
says...
Jon,
Good info. The cold plates I have bought are used units and they all have
the expansion valves with them. I have assumed they also have integral
spray
orifices. I suppose I could apply compressed air to determine approximate
flow rates. How else would I test these, as they are not able to be
disassembled? The cold plates are used marine units and I want to use
them
for a freezer, not a refrigerator, hence the -40 requirement. I am aware
of
the requirement to change the medium in the cold plate itself in order to
reduce the temperature of the state change. The goal is to freeze the
plates
down once a day or less when in use. How do I estimate the heat load? The
cold plates are aproximately 24" x 18" x 4".
Steve

"Jon Elson" wrote in message
...


Steve Lusardi wrote:
I wish to use a single large compressor to service 3 cold plates and 3
air conditioning evaporators, but I am not a refrigeration expert, so
if
my thinking is incorrect please let me know. Each one of these (users)
will have their own mechanical temperature controlled evaporator
valve. I
assume the compressor should be cycled by head pressure with an
overtemp
sensor for safety. I would like to use a salt water cooled condensor
on
the high pressure side and a freon gas that changes state around -40
C.
Please advise. Do I need an accumulator of some description on either
side? If so, what? Each one of the users have 3/8" in/out tubes. How
do I
size the compressor? Any tips or books on this subject would be
welcome.
Steve


Somehow I get the idea that you are building a "boat installation" in
which case try to lay your hands on a book named Refrigeration for
Pleasureboats: Installation, Maintenance and Repair by Nigel Calder.

It gives you methods and formula to calculate heat and insulation
values, condenser water flow, cold plate area and everything else you
need to design and build a refrigeration system for a boat.

Even tells you how to build your own condenser using either copper or
Cupro-nickle tubing.

--
Cheers,

Bruce in Bangkok

Scott,
You are correct with your assessment!
Steve
wrote in message
...

I'd probably crosspost a request to alt.hvac; those guys are very helpful
when someone who isn't a trained hvac technician asks a question. Be sure
and tell them you are a homowner, and that you have a done a few DIY
projects (like a fence and a water faucet) in the past so they know you
would be capable of the work.

Jon

Jon you are a mean person, hvac guys hate anyone to touch an a/c
without a licence, especially a homeowner. They really wish this to
become a death penalty crime. This group will chew him up if he does
this, a bunch of arrogant (*&^%$) people there.

Scott

Jon Elson fired this volley in
:


You can't realy cycle the compressor off in an application like
this.
When the compressor is off, the liquid in the evaporator continues
to
evaporate, and very quickly the low-side pressure rises. Then, ALL
the evaporators stop working. With thermostatically-controlled
metering valves regulating the temperature of the separate
evaporators, you can probably run the compressor all the time
(except
for fault conditions) and as long as the accumulator has sufficient
volume, it should all regulate itself pretty well. The compressor
will unload when there's little gas coming in. Are you really
trying
to achieve -40 (C or F, doesn't matter) with a single stage? That
is
quite pushing it. R-22 will do it, but at low pressure, so a larger
compressor and evaporators will be needed.

You can't size the compressor until you know the heat flow. Knowing
the tube size is nearly worthless. You need orifices in the
expansion
valves to prevent slugging the liquid in the evaporator all into the
compressor at once. These set the maximum capacity per evaporator.

Jon

Jon, I agree with most of what you said, but it's not true about
cycling the compressor. That's what accumulators (high liquid and low
gas) are for. Think about the automotive CCOT systems. They don't
have expansion valves at all, but still cycle the compressor, based
upon the high-side pressure at the accumulator.


Now, I'll agree that you may need some pretty large low-side capacity
to keep the low-side pressure low enough, but it certainly can be - is
- done that way on many systems.

It's not a simple setup in terms of design criteria, but it's simple
mechanically.

I wholeheartedly agree that -40 is a tough spec.

LLoyd

fired this volley in
news:1d295d6f-e8bf-4bc5-9503-
:


Jon you are a mean person, hvac guys hate anyone to touch an a/c
without a licence, especially a homeowner. They really wish this to
become a death penalty crime. This group will chew him up if he
does
this, a bunch of arrogant (*&^%$) people there.

Scott


Agreed. Most of them are there to pet their own egos.

LLoyd

the compressor should be cycled by head pressure with an overtemp sensor
for safety. I would like to use a salt water cooled condensor on the high
pressure side and a freon gas that changes state around -40 C. Please

I'm not an expert, other than maintaining my 2000 bushel cooler for 20
years, but a good choice for low temperature freon is R-502. its used for
freezers. Hold on to your shorts when you buy some.

Karl

Lloyd,
These holding plates are filled with a fluid medium and they are around 18"
x 24" x 4" . How much high side and low side tankage would be enough in
cubic inches to self regulate do you think?
Steve

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
Jon Elson fired this volley in
:


You can't realy cycle the compressor off in an application like
this.
When the compressor is off, the liquid in the evaporator continues
to
evaporate, and very quickly the low-side pressure rises. Then, ALL
the evaporators stop working. With thermostatically-controlled
metering valves regulating the temperature of the separate
evaporators, you can probably run the compressor all the time
(except
for fault conditions) and as long as the accumulator has sufficient
volume, it should all regulate itself pretty well. The compressor
will unload when there's little gas coming in. Are you really
trying
to achieve -40 (C or F, doesn't matter) with a single stage? That
is
quite pushing it. R-22 will do it, but at low pressure, so a larger
compressor and evaporators will be needed.

You can't size the compressor until you know the heat flow. Knowing
the tube size is nearly worthless. You need orifices in the
expansion
valves to prevent slugging the liquid in the evaporator all into the
compressor at once. These set the maximum capacity per evaporator.

Jon

Jon, I agree with most of what you said, but it's not true about
cycling the compressor. That's what accumulators (high liquid and low
gas) are for. Think about the automotive CCOT systems. They don't
have expansion valves at all, but still cycle the compressor, based
upon the high-side pressure at the accumulator.


Now, I'll agree that you may need some pretty large low-side capacity
to keep the low-side pressure low enough, but it certainly can be - is
- done that way on many systems.

It's not a simple setup in terms of design criteria, but it's simple
mechanically.

I wholeheartedly agree that -40 is a tough spec.

LLoyd

Bruce,
I ordered the book. It is $65. Must be good. Had to buy a used one. It is
out of print.
Steve

"Bruce in Bangkok" wrote in message
...
In article ,
says...
Jon,
Good info. The cold plates I have bought are used units and they all have
the expansion valves with them. I have assumed they also have integral
spray
orifices. I suppose I could apply compressed air to determine approximate
flow rates. How else would I test these, as they are not able to be
disassembled? The cold plates are used marine units and I want to use
them
for a freezer, not a refrigerator, hence the -40 requirement. I am aware
of
the requirement to change the medium in the cold plate itself in order to
reduce the temperature of the state change. The goal is to freeze the
plates
down once a day or less when in use. How do I estimate the heat load? The
cold plates are aproximately 24" x 18" x 4".
Steve

"Jon Elson" wrote in message
...


Steve Lusardi wrote:
I wish to use a single large compressor to service 3 cold plates and 3
air conditioning evaporators, but I am not a refrigeration expert, so
if
my thinking is incorrect please let me know. Each one of these (users)
will have their own mechanical temperature controlled evaporator
valve. I
assume the compressor should be cycled by head pressure with an
overtemp
sensor for safety. I would like to use a salt water cooled condensor
on
the high pressure side and a freon gas that changes state around -40
C.
Please advise. Do I need an accumulator of some description on either
side? If so, what? Each one of the users have 3/8" in/out tubes. How
do I
size the compressor? Any tips or books on this subject would be
welcome.
Steve


Somehow I get the idea that you are building a "boat installation" in
which case try to lay your hands on a book named Refrigeration for
Pleasureboats: Installation, Maintenance and Repair by Nigel Calder.

It gives you methods and formula to calculate heat and insulation
values, condenser water flow, cold plate area and everything else you
need to design and build a refrigeration system for a boat.

Even tells you how to build your own condenser using either copper or
Cupro-nickle tubing.

--
Cheers,

Bruce in Bangkok

On Aug 25, 1:51 pm, "Steve Lusardi" wrote:
I wish to use a single large compressor to service 3 cold plates and 3 air
conditioning evaporators, but I am not a refrigeration expert, so if my
thinking is incorrect please let me know. Each one of these (users) will
have their own mechanical temperature controlled evaporator valve. I assume
the compressor should be cycled by head pressure with an overtemp sensor for
safety. I would like to use a salt water cooled condensor on the high
pressure side and a freon gas that changes state around -40 C. Please
advise. Do I need an accumulator of some description on either side? If so,
what? Each one of the users have 3/8" in/out tubes. How do I size the
compressor? Any tips or books on this subject would be welcome.
Steve

No, the compressor should NOT be cycled on head pressure, only safety
devices for over pressure and under pressure should be used for head
pressure.
Also it can be done mixing air conditioning and refrigeration/freezer
evaporators in one system, but you will need many more controls and
mechanical systems. You want to have 2 compressors and keep the air
conditioning separate from your cold plate application. This is
because what ever working fluid you use (R22/502/134A) the evaporator
boiling point is a function of suction pressure. For freezer
applications, you will cause the air condition coils to freeze, or for
air conditioning you will never get the cold plates to freeze.
If you are hell bent on this, you will need to control the input
refrigerant to the evaporators with electric solenoid valves, I assume
you have a 12 volt battery system on your boat, I've seen 12 volt
valves. Also I assume you are connecting the compressor(s) to a
diesel engine. The output of the condenser will go into a receiver
(not an accumulator). There are suction accumulators, which are used
to prevent liquid slugging into the compressor. To control air
conditioning suction pressure on such a system (one compressor) you
will need to use pilot operated suction valves for the air
conditioning evaporators, in the output of the evaporator so the
suction pressure will not be at the same pressure as the cold plates.

The last time I was sailing on a Moorings bare boat charter, the cold
plate system was replaced with a +12 compressor, and this worked so
much better then the cold plate of previous sails, it would keep ice
cream frozen, where the cold plate would totally defrost between
engine recharge cycles, or be one frozen mass of sh*t.
ignator

In article ,
says...
Bruce,
I ordered the book. It is $65. Must be good. Had to buy a used one. It is
out of print.
Steve


I think you'll find it worth the money. It takes you from wanting to
have a fridge through each and every step in sizing, design, building,
measuring heat loss, cooling requirements depending on water
temperature. Just about everything you have been asking about. There is
even a step by step overhaul section on most common compressors.

And, the guy is a good enough writer that you can almost read the book
for entertainment. He has also written a book on electrical systems that
is interesting and factual.

The author has been living aboard and cruising for quite a few years now
so everything he recommends is based on experience and I found both the
refrigeration and the electrical books worth paying for.

--
Cheers,

Bruce in Bangkok

"Steve Lusardi" fired this volley in
:

Lloyd,
These holding plates are filled with a fluid medium and they are
around 18" x 24" x 4" . How much high side and low side tankage
would
be enough in cubic inches to self regulate do you think?
Steve

That's not nearly enough information. You need to know the heat load
at pretty much all operating conditions. You also need to know the
condensor operating conditions. For a job of this nature, I doubt
you'll ever gather enough good info to do it.

Lacking that information, and doing it simply by 'overkill', you'll
have to follow Jon's advice, and keep the compressor running any time
either TEV is open.

You can do that by adding a low-side switch that monitors the
evaporators' exit pressure, and turning on the compressor any time it
goes higher than your desired preset.

LLoyd

On Aug 26, 7:24 am, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:
"Steve Lusardi" fired this volley :



Lloyd,
These holding plates are filled with a fluid medium and they are
around 18" x 24" x 4" . How much high side and low side tankage
would
be enough in cubic inches to self regulate do you think?
Steve

That's not nearly enough information. You need to know the heat load
at pretty much all operating conditions. You also need to know the
condensor operating conditions. For a job of this nature, I doubt
you'll ever gather enough good info to do it.

Lacking that information, and doing it simply by 'overkill', you'll
have to follow Jon's advice, and keep the compressor running any time
either TEV is open.

You can do that by adding a low-side switch that monitors the
evaporators' exit pressure, and turning on the compressor any time it
goes higher than your desired preset.

LLoyd

The problem is that air conditioning suction pressure needs to be much
higher then freezer suction pressure. As indicated in my post
something like a POA valve is needed so the air conditioning
evaporators operate at a higher pressure then the freezer
evaporators. You still can use thermostatic expansion valves to
control a constant super heat of the refrigerant in each evaporator.

I have not worked this industry since 1977, but my recommendation is
to keep the two systems separate down to dual compressors, and
condensers. Each sized for the application, and operating
temperatures.
ignator

That is really good info....... thank you. I think you are correct about
keeping the systems separate. Combining them will create far too much
complexity. I have made the same observation of cold plate performance that
you have, but I think that is because of the use of brine as the storage
medium for a freezer applications. Its state change is far too warm to be
efficient. There are far better solutions for cold storage capacity, hence,
the -40 degree requirement.
Steve

"ignator" wrote in message
...
On Aug 25, 1:51 pm, "Steve Lusardi" wrote:
I wish to use a single large compressor to service 3 cold plates and 3
air
conditioning evaporators, but I am not a refrigeration expert, so if my
thinking is incorrect please let me know. Each one of these (users) will
have their own mechanical temperature controlled evaporator valve. I
assume
the compressor should be cycled by head pressure with an overtemp sensor
for
safety. I would like to use a salt water cooled condensor on the high
pressure side and a freon gas that changes state around -40 C. Please
advise. Do I need an accumulator of some description on either side? If
so,
what? Each one of the users have 3/8" in/out tubes. How do I size the
compressor? Any tips or books on this subject would be welcome.
Steve

No, the compressor should NOT be cycled on head pressure, only safety
devices for over pressure and under pressure should be used for head
pressure.
Also it can be done mixing air conditioning and refrigeration/freezer
evaporators in one system, but you will need many more controls and
mechanical systems. You want to have 2 compressors and keep the air
conditioning separate from your cold plate application. This is
because what ever working fluid you use (R22/502/134A) the evaporator
boiling point is a function of suction pressure. For freezer
applications, you will cause the air condition coils to freeze, or for
air conditioning you will never get the cold plates to freeze.
If you are hell bent on this, you will need to control the input
refrigerant to the evaporators with electric solenoid valves, I assume
you have a 12 volt battery system on your boat, I've seen 12 volt
valves. Also I assume you are connecting the compressor(s) to a
diesel engine. The output of the condenser will go into a receiver
(not an accumulator). There are suction accumulators, which are used
to prevent liquid slugging into the compressor. To control air
conditioning suction pressure on such a system (one compressor) you
will need to use pilot operated suction valves for the air
conditioning evaporators, in the output of the evaporator so the
suction pressure will not be at the same pressure as the cold plates.

The last time I was sailing on a Moorings bare boat charter, the cold
plate system was replaced with a +12 compressor, and this worked so
much better then the cold plate of previous sails, it would keep ice
cream frozen, where the cold plate would totally defrost between
engine recharge cycles, or be one frozen mass of sh*t.
ignator

On Tue, 26 Aug 2008 05:04:22 -0700 (PDT), ignator
wrote:
On Aug 25, 1:51 pm, "Steve Lusardi" wrote:

I wish to use a single large compressor to service 3 cold plates and 3 air
conditioning evaporators, but I am not a refrigeration expert, so if my
thinking is incorrect please let me know.

Not necessarily incorrect, but new technologies available might
require a rethink on how you accomplish the task. There's always more
than one way to do it, and the alternatives may be better than "that's
how we always did it."

"Don't raise the drawbridge, lower the river."

Each one of these (users) will
have their own mechanical temperature controlled evaporator valve. I assume
the compressor should be cycled by head pressure with an overtemp sensor for
safety. I would like to use a salt water cooled condensor on the high
pressure side and a freon gas that changes state around -40 C. Please
advise. Do I need an accumulator of some description on either side? If so,
what? Each one of the users have 3/8" in/out tubes. How do I size the
compressor? Any tips or books on this subject would be welcome.
Steve

No, the compressor should NOT be cycled on head pressure, only safety
devices for over pressure and under pressure should be used for head
pressure.
Also it can be done mixing air conditioning and refrigeration/freezer
evaporators in one system, but you will need many more controls and
mechanical systems. You want to have 2 compressors and keep the air
conditioning separate from your cold plate application. This is
because what ever working fluid you use (R22/502/134A) the evaporator
boiling point is a function of suction pressure. For freezer
applications, you will cause the air condition coils to freeze, or for
air conditioning you will never get the cold plates to freeze.

I've seen these big built-up "one compressor" refrigeration systems
at supermarkets, and they certainly can be made to work. But consider
what happens when that one compressor blows up, or that one massive
refrigerant system springs a leak - now you have no refrigeration for
the entire boat, and the Chief starts sweating.

Supermarkets can call the local refrigeration service company and
have a tech on site in an hour who knows that system inside and out,
and with full access to parts and supplies from the local supply
house. If you are out in mid ocean...

And supermarkets usually put all the freezers on one combined system
and refrigerators on the other, just to simplify the controls.
Otherwise they have to start adding check valves and suction
regulation everywhere. And it's best to unload the compressor and let
it run rather than constant starts and stops - but then you get into
run-time wear, and since you have to make your own the power is a lot
more expensive on a boat than a building...

Consider that these big systems always have a problem keeping the
refrigeration oil in the compressor - it gets carried out into the big
accumulator and all the low spots of the lines, and unless you put oil
traps and return lines everywhere it never gets back. Then the
compressor dies from oil starvation - see "What happens when the one
compressor fails" above.

You will be fighting this forever with oil traps and oil makeup
tanks and crankcase controls. And trying to keep the velocities in
all the return lines right, and getting the slopes and falls right,
placing P-traps everywhere to get the oil moving back - and then the
boat goes up on plane and all the working angles change...

You do need at least a small accumulator on the compressor suction
side as a trap to protect against slugging - gases compress, liquids
don't, and you don't want to test the anti-slugging feature on the
compressor head too often or it can break the springs. Then refer to
"What happens when the one compressor fails" above.

If you are hell bent on this, you will need to control the input
refrigerant to the evaporators with electric solenoid valves, I assume
you have a 12 volt battery system on your boat, I've seen 12 volt
valves. Also I assume you are connecting the compressor(s) to a
diesel engine. The output of the condenser will go into a receiver
(not an accumulator). There are suction accumulators, which are used
to prevent liquid slugging into the compressor. To control air
conditioning suction pressure on such a system (one compressor) you
will need to use pilot operated suction valves for the air
conditioning evaporators, in the output of the evaporator so the
suction pressure will not be at the same pressure as the cold plates.

The last time I was sailing on a Moorings bare boat charter, the cold
plate system was replaced with a +12 compressor, and this worked so
much better then the cold plate of previous sails, it would keep ice
cream frozen, where the cold plate would totally defrost between
engine recharge cycles, or be one frozen mass of sh*t.
ignator

This was my thought too - Danfoss (http://compressors.danfoss.com)
makes the BD Series 1/20 HP and 1/12 HP hermetic brushless motor
compressors that run on 12V or 24V internally, and they have several
control boxes to run them on 12/24V battery systems OR variable
voltage solar or wind systems OR auto-changeover between 120VAC/240VAC
world voltages and 12/24 VDC. And the control boxes have integrated
temperature controls - just add a thermistor in the conditioned space
and an adjustment rheostat.

Even one control box specifically to control EMI/RFI radiation that
could rip the navigation and radar systems on a ship to heck.

And if there is enough demand, I'll bet they could build them bigger
without too much trouble. 1/2 HP or even 1 HP isn't out of the
question for 12VDC battery supplied systems.

It will be a HECK of a lot simpler to make separate systems that run
continually from a deep-cycle battery bank, and each one optimized to
it's task - freezer, refrigerator, ice-maker, live-well chiller, etc.

And a whole lot simpler to circulate low pressure condenser water
around the ship to separate small heat exchangers at each
refrigeration device, rather than high pressure refrigerant.

And it WINS hands down on KISS simplicity and redundancy - if one
refrigerator fails, you just move everything to the three others that
still work. If your battery bank goes flat, start the generator set
and they all switch to 120V.

For space cooling in the cabins, consider either a "Mini-Split"
refrigeration based heat-pump separate from the freezers (if you plan
to run the gen-set or inverters 24/7), or ducted fan coil units and
circulating chilled/heated water from the engine room. Keep all the
refrigeration in one compact spot, and you could use a large ice-bank
tank low in the ship (they are heavy!) to shut down the gen-set at
night.

Heat is easy, I'll bet you have lots of excess heat when those two
big main propulsion diesels are running - and when they aren't use the
same tankless hot water heater you have for the showers. Or an
RV-style forced air propane furnace. Many ways, all depends.

-- Bruce --

Steve Lusardi wrote:
Jon,
Effectively, I am building an old fashioned ice box and these plates will be
atached to the walls of the well insulated box. The air flow inside the box
would be convective, just like in your freezer at home. All the plates would
be in parallel. These cold plates are holding plates and I suspect they are
filled with brine, as they were probably used as a refrigerator. In order to
use these plates in a freezer efficiently, the solution will have to be
changed to one that changes state at a lower temperature. You stated that
the expansion valve must have the same freon on both sides of the diaphragm.
I hadn't thought of that, but it makes sense. I know I must use the most
appropriate freon for the task, which means that I will have to buy new
expansion valves to match that choice.
They CAN be refilled, but that's not for the amateur.
Good info. I understand the
difficulty in calculating the heat load, but I don't think the ice box
itself has much to do with it. I would think the volume of the cooled fluid
medium is the 90% answer. The rate that medium has in warming up is not very
relevent, because the system will not be operating then. It is also
unreasonable to think that these holding plates will freeze solid at he same
time, but if each has its own control valve it shoudn't matter.
Steve
OK, I gather the compressor will only be run a couple times a
day, and the brine (or whatever state-change fluid) needs to
keep it cold between runs? Is that the basic idea?

Very concentrated brine can probably be made up with something
like calcium chloride that will freeze out at some really low
temperature. I don't know if you can get to -40, but definitely
well below 0 F. The cooling capacity of these brines drops as
the water content drops, though. Oh, yeah, litium bromide would
definitely work! But, it might be way too hazardous to use near
food. If there was any leakage, you'd get REALLY mellow on all
that lithium.

Anyway, I'm not a pro at this, but I think you will have real
trouble making it to -40 with an R-22 system and any appreciable
heat load. It will eventually get there if you can keep the
doors shut, and there aren't any air leaks.

One other thing I discovered some years ago is that some foam
insulations get saturated with ice. You know this has happened
when a chunk of foam suddenly weighs about 40 Lbs! It is HELL
to get the water back out of the foam, too.

Jon

Steve Lusardi wrote:
That is really good info....... thank you. I think you are correct about
keeping the systems separate. Combining them will create far too much
complexity.
Absolutely. This will NEVER work with any efficiency. You'd
need to have suction throttling valves on the air cond
evaporators, or the'd raise the suction pressure preventing the
freezer from ever getting cold. Suction throttling valves are
used in cars to prevent freezing the evaporator, but having very
heavy throttling will MASSIVELY reduce compressor capacity.
You'd end up using a 10 Hp compressor to get 1/2 Hp worth of
comfort air conditioning - it would be a collosal disaster.

They actually make DIFFERENT compressors for different
temperature differentials, or expressing it a different way,
specific suction pressures. For many refrigerants that are used
in different services, like R-22, you will find low, medium and
high-pressure compressors, meant for freezer, refrigerator and
air cond use, respectively. If you use a low-pressure
compressor for AC, it will overload due to the much higher
volume of gas pouring into it. If you use a high-pressure
compressor for a freezer, it will not develop rated power as it
is not getting as much gas in as it was designed for.
I have made the same observation of cold plate performance that
you have, but I think that is because of the use of brine as the storage
medium for a freezer applications. Its state change is far too warm to be
efficient. There are far better solutions for cold storage capacity, hence,
the -40 degree requirement.
Don't confuse freezing temperature with heat capacity. They are
totally different. You want the most heat of solidification per
volume, but maybe most H.O.S. by weight should suffice.

Jon

In article ,
says...
That is really good info....... thank you. I think you are correct about
keeping the systems separate. Combining them will create far too much
complexity. I have made the same observation of cold plate performance that
you have, but I think that is because of the use of brine as the storage
medium for a freezer applications. Its state change is far too warm to be
efficient. There are far better solutions for cold storage capacity, hence,
the -40 degree requirement.
Steve


I have the idea that I heard somewhere that the preferred liquid for the
cold plates was a mixture of ethylene glycol rather then "brine". I
believe that the reason is that by mixing water and E.G. you can control
the freezing point which is pretty much what you are trying to do.

--
Cheers,

Bruce in Bangkok

On Tue, 26 Aug 2008 13:45:53 +0200, "Steve Lusardi"
wrote:

snip
I ordered the book. It is $65. Must be good. Had to buy a used one. It is
out of print.
Steve

Steve, they must have saw you coming on this one. Just in
case the deal falls through and you can try again take a
look at this search:

http://www.abebooks.com/servlet/Sear...+Pleasureboats

There were several new copies for under $20 when I visited.

An even better place to go looking for the best price is
he

http://www.bookfinder.com/

Give these places a whirl next time you need an odd book

--
Leon Fisk
Grand Rapids MI/Zone 5b
Remove no.spam for email

Bruce,
No, it is cold storage capacity by volume, as Jon alluded to (HOS) and there
have been several very successful solutions developed recently for the
transport of human organs from donor to recipient, which work much better
than the conventional fluids like brine and ethylene glycol. These mediums
require the -40 temperature to freeze.
Steve

"Bruce in Bangkok" wrote in message
...
In article ,
says...
That is really good info....... thank you. I think you are correct about
keeping the systems separate. Combining them will create far too much
complexity. I have made the same observation of cold plate performance
that
you have, but I think that is because of the use of brine as the storage
medium for a freezer applications. Its state change is far too warm to be
efficient. There are far better solutions for cold storage capacity,
hence,
the -40 degree requirement.
Steve


I have the idea that I heard somewhere that the preferred liquid for the
cold plates was a mixture of ethylene glycol rather then "brine". I
believe that the reason is that by mixing water and E.G. you can control
the freezing point which is pretty much what you are trying to do.

--
Cheers,

Bruce in Bangkok

On Wed, 27 Aug 2008 14:42:54 -0400, with neither quill nor qualm, Leon
Fisk quickly quoth:

On Tue, 26 Aug 2008 13:45:53 +0200, "Steve Lusardi"
wrote:

snip
I ordered the book. It is $65. Must be good. Had to buy a used one. It is
out of print.
Steve

Steve, they must have saw you coming on this one. Just in
case the deal falls through and you can try again take a
look at this search:

http://www.abebooks.com/servlet/Sear...+Pleasureboats

There were several new copies for under $20 when I visited.

An even better place to go looking for the best price is
he

http://www.bookfinder.com/

Give these places a whirl next time you need an odd book

Don't forget www.ISBN.nu and www.ebay.com . I get lots of 1-cent books
shipping for $2.36, the total price essentially covering Media Mail
s/h on eBay (and Amazon $4 total.)

--
Smokey the Bear's rules for fire safety should apply to government:
Keep it small, keep it in a confined area, and keep an eye on it.
--John Stossel in _Myths, Lies, and Downright Stupidity_

In article ,
says...
Bruce,
No, it is cold storage capacity by volume, as Jon alluded to (HOS) and there
have been several very successful solutions developed recently for the
transport of human organs from donor to recipient, which work much better
than the conventional fluids like brine and ethylene glycol. These mediums
require the -40 temperature to freeze.
Steve

Can you expand on this a bit as my understanding of eutectic systems has
always been that you "freeze", or at least get slushy, a medium
contained in the plates. The temperature at which the medium "freezes"
is controlled in part to match the capacity of the compressor. The
volume/mass and initial temperature of the plates then keeps the
interior of the fridge below a desired temperature for a period of time
depending on the mass of the plate/medium and insulation value of the
container (ignoring the number of times you open the door for the
moment).

I'm not arguing but trying to correct my understanding if it is not
correct.






"Bruce in Bangkok" wrote in message
...
In article ,
says...
That is really good info....... thank you. I think you are correct about
keeping the systems separate. Combining them will create far too much
complexity. I have made the same observation of cold plate performance
that
you have, but I think that is because of the use of brine as the storage
medium for a freezer applications. Its state change is far too warm to be
efficient. There are far better solutions for cold storage capacity,
hence,
the -40 degree requirement.
Steve


I have the idea that I heard somewhere that the preferred liquid for the
cold plates was a mixture of ethylene glycol rather then "brine". I
believe that the reason is that by mixing water and E.G. you can control
the freezing point which is pretty much what you are trying to do.

--
Cheers,

Bruce in Bangkok




--
Cheers,

Bruce in Bangkok

On Aug 28, 3:14 am, Bruce in Bangkok wrote:
In article ,
says...

Bruce,
No, it is cold storage capacity by volume, as Jon alluded to (HOS) and there
have been several very successful solutions developed recently for the
transport of human organs from donor to recipient, which work much better
than the conventional fluids like brine and ethylene glycol. These mediums
require the -40 temperature to freeze.
Steve

Can you expand on this a bit as my understanding of eutectic systems has
always been that you "freeze", or at least get slushy, a medium
contained in the plates. The temperature at which the medium "freezes"
is controlled in part to match the capacity of the compressor. The
volume/mass and initial temperature of the plates then keeps the
interior of the fridge below a desired temperature for a period of time
depending on the mass of the plate/medium and insulation value of the
container (ignoring the number of times you open the door for the
moment).

I'm not arguing but trying to correct my understanding if it is not
correct.

Cheers,

Bruce in Bangkok

It is the phase change i.e. latent heat of fusion (freezing) that is
where the energy is stored in the the cold plate. The working fluid
needs to have a very large latent heat, BTU/lb.mass, and not have a
strange shape change that destroys the container. I have no idea what
that fluid is in cold plates. Water alone has 144 BTU/lb. latent
heat, just how much better can you get by adding salts or glycol? It
must change phase to store and retrieve this energy.
ignator

ignator writes:

Water alone has 144 BTU/lb. latent
heat, just how much better can you get by adding salts or glycol? It
must change phase to store and retrieve this energy.

My constant sermon.

Refrigeration only happens effectively when you have intimate thermal
contact with a phase-changing medium. Brines or other fluid mediums cannot
work as well, because their temperatures rise as they absorb heat, and heat
transfer efficiency is all about delta T.

Homebrewers with jockey boxes will never accept that drained ice works
better than a water/ice bath, though.

I just brought home a 1944 copy of Audell's "Refrigeration and Air
Conditioning Guide". That ought to be fun reading this winter.
Lots of chapters dealing with marine and commercial units, drinking water
coolers, brine systems, and even soda fountain equipment, but no mention of
automotive as it hadn't been done yet.
Makes me want to restore and old cooling tower. Remember those scenic
wonders? I know where two are still standing.
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty

On Fri, 29 Aug 2008 08:23:35 -0700, "Stupendous Man"
wrote:

I just brought home a 1944 copy of Audell's "Refrigeration and Air
Conditioning Guide". That ought to be fun reading this winter.
Lots of chapters dealing with marine and commercial units, drinking water
coolers, brine systems, and even soda fountain equipment, but no mention of
automotive as it hadn't been done yet.
Makes me want to restore and old cooling tower. Remember those scenic
wonders? I know where two are still standing.

Automotive had to have been done before 1944, but it would still be
somewhere between the "Laboratory Prototype" and "Very expensive and
not widely used - which would bring down the cost but we can't get the
ball rolling" stage. The only place you would need it back then is
the President's bulletproof limousine or other armored car - everyone
else can roll down the windows.

The sticking points were probably weight, added horsepower needs in
the days when you didn't have a lot to spare, added electrical needs
in the days of the DC generator and 6-volt system that was pretty well
maxed out already, and the high pressure rubber hoses to put it all
together, coming up with a synthetic rubber that would keep the
refrigerant on the inside long term.

Water cooled condensers (cooling towers) are still made new and in
use, but mostly in commercial settings where they have an on-site
maintenance staff. The reason they don't get used more is that added
energy efficiency also comes with a lot more maintenance work - you
have to clean and descale it, and drain and refill, and keep the
chemistry right and the fill valve from sticking, and occasionally
rebuild it.

They've got some nifty small fiberglass units, but even though the
outer shell doesn't rust and/or corrode the guts still do...

-- Bruce --

Bruce L. Bergman wrote:
On Fri, 29 Aug 2008 08:23:35 -0700, "Stupendous Man"
wrote:

I just brought home a 1944 copy of Audell's "Refrigeration and Air
Conditioning Guide". That ought to be fun reading this winter.
Lots of chapters dealing with marine and commercial units, drinking water
coolers, brine systems, and even soda fountain equipment, but no mention of
automotive as it hadn't been done yet.
Makes me want to restore and old cooling tower. Remember those scenic
wonders? I know where two are still standing.

Automotive had to have been done before 1944, but it would still be
somewhere between the "Laboratory Prototype" and "Very expensive and
not widely used - which would bring down the cost but we can't get the
ball rolling" stage. The only place you would need it back then is
the President's bulletproof limousine or other armored car - everyone
else can roll down the windows.

Or something like this....

http://img.photobucket.com/albums/v4...2/aircondi.jpg

Stupendous Man writes:

... but no mention of automotive as it hadn't been done yet.

R12 mobile refrigeration was developed in the 1930s and used in WWII.

On Fri, 29 Aug 2008 11:35:34 -0700, Jim Stewart
wrote:

Bruce L. Bergman wrote:
On Fri, 29 Aug 2008 08:23:35 -0700, "Stupendous Man"
wrote:

I just brought home a 1944 copy of Audell's "Refrigeration and Air
Conditioning Guide". That ought to be fun reading this winter.
Lots of chapters dealing with marine and commercial units, drinking water
coolers, brine systems, and even soda fountain equipment, but no mention of
automotive as it hadn't been done yet.
Makes me want to restore and old cooling tower. Remember those scenic
wonders? I know where two are still standing.

Automotive had to have been done before 1944, but it would still be
somewhere between the "Laboratory Prototype" and "Very expensive and
not widely used - which would bring down the cost but we can't get the
ball rolling" stage. The only place you would need it back then is
the President's bulletproof limousine or other armored car - everyone
else can roll down the windows.

Or something like this....

http://img.photobucket.com/albums/v4...2/aircondi.jpg

Hey, if it works... Looks like someone's 'Last Resort' residence.

Any idea what the white and green "Book" logo on the trunk is? I've
seen that around a few times.

-- Bruce --

"Richard J Kinch" wrote in message
. ..
Stupendous Man writes:

... but no mention of automotive as it hadn't been done yet.

R12 mobile refrigeration was developed in the 1930s and used in WWII.

I once saw a 1940 Packard on a used car lot that had a large evaporator
mounted under the rear package shelf. It had a large V-twin compressor and
it all appeared to be factory installed. I think several of the luxury car
manufacturers were starting to offer air conditioning about that time. It
seems to me that Nash was the first to offer it in the lower price cars,
around 1952 as I recall. I have owned a 1954 Packard, a 1955 Cadillac, and
a 1957 Olds convertible, all with factory air conditioning. It seemed very
common at that time in the desert southwest US.

I saw a mid-fifties Chrysler which had the condenser lying nearly horizontal
under the front bumper pan. It was also unusual in that it used R-22
refrigerant.

Don Young