Refrigeration tubing is measured in OD and ¼ OD is .192 in. ID. Many
home built systems make the mistake of using tubing that is too large
in their systems. All refrigeration compressors require a return
suction gas temperature of from 60 to 90 degrees F. for compressor
cooling. Compressors also rely on a reasonable gas velocity through
the system to return the oil. You could get by with 5/16 OD tubing,
but I would not run the system set to a very low temperatures.
You are correct about tube damage in the box, there must be some type
of a guard to protect it.
I ounce did a system for a crab fisherman in Alaska and he put a live
fish inside that punch a hole in the refrigerant tubing.
When you want variable capacity with the BD50 in the case of your
purposed system I would use a OX Danfoss orifice. Yes, I know the OX
is a 1500 btu orifice but as soon as it sees the cool return gas it
will adjust down.
You should have my latest Do It Yourself Book revised in 2000. And the
book you just ordered 12/24 volt Refrigeration Manual covers changes
in DC refrigeration up to 2004. I believed that revising the original
book every five years was good enough. Today with the changes in the
industry and the high cost of service I felt I should find another way
to communicate more often than five years. Book revisions, service
bulletins and typical repairs would cost too much so I elected to use
my web site as a way that book owners and others can keep up to date
with what is new in boat refrigeration. Glen if you don't find all
you need in the design section of the new book please use the new
refrigeration forum on my web site to ask your questions.
http://www.kollmann-marine.com.
Glenn Ashmore wrote in message news:vW5Uc.29891$Jo1.23863@lakeread01...
#2 is the idea I am leaning towards. I have room to mount an air cooled
BD50 directly below the box with plenty of ventilation.
Couple of things still have me stalled. I would like to use .192" ID
stainless tube which should stand up better to bumps with cans and
corrosion but the thermal conductivity is a lot lower than copper. I
could compensate by going to .335" ID but that might slow down the
refrigerant to much to push the oil through. Think I will stick with
.192" and adjust the expansion valve and compressor speed.
The other thing is probably that I am not reading the charts right but I
can't figure out which orifice to use in the Danfoss expansion valve.
They all look to large for the BD50.
BTW, have you revised the DIY book? I have about worn my copy and the
Calder book out. :-)
Richard Kollmann wrote:
Glen, there are three proven way to build the system you are looking
for:
1. Install a full length stainless steel holding plate in an insulated
box, it can be used as a dry box or a wet box. See picture on front
page of my web site, this box's holding plate is connected to a
Danfoss BD2.5 compressor. The purpose of the plate in this cooler is
to act as a flywheel affect of energy when warm product is put in the
box.
2. The same insulated box can be cooled by a plain copper tube coil
attached to interior wall. When I did fish hold box designs I used
stainless tubing with tubing above and below the water.
3. Either one of the above concepts can be used with an existing large
refrigeration system by splitting the refrigerant flow.
I have system #1 in one of my boats and system #3 in the other.
Glen here is a concept using a Danfoss BD50 air cooled condensing
unit, and 50 ft. of ¼ inch tubing as an evaporator coil, A receiver
and expansion valve instead of a capillary tube.
This combination in a drink cooler with a 30 degree evaporator
temperature might deliver 790 btu. Per hour. ( Danfoss ASHRAE
Capacity chart with compressor running at 3500 rpm ). I would also
install a manual speed selector switch to adjust compressor speed for
current box demand.
From the author of books on boat refrigeration
http://www.kollmann-marine.com