REFRIGERATION REQUIREMENTS.
REFRIGERATION -- NECESSITIES -- ICE PLANTS -- NATURAL ICE -- CHILLING
-- QUANTITY REFRIGERATION TO PROVIDE -- SPACE PER TON MACHINE --
MACHINERY PER HEAD -- ICE COMPUTATION -- COMPRESSOR CAPACITY --
SUMMARY COMPUTATIONS -- LOW TEMPERATURE BRINE SYSTEM.
=Refrigeration.=--This word covers the “bugbear” and the “solace” of
the packers. No other one thing is of so much importance. Since the
abolishment of the use of chemicals, such as borax, boracic acid, etc.,
as a preventive or retardant in the propagation of bacilli during
the curing process, the packer’s sole dependence is refrigeration.
Consequently there has been considerable development and importance in
its use.
From the moment the animal is killed until the parts are disposed of,
refrigeration is a necessity. The proportion of freezing space to be
provided or hired at a commercial storage house is growing daily. In
many plants the total volume of freezer space approaches or exceeds,
that given over for moderate temperature storage purposes.
=Necessities.=--In the order of progress the first necessity for
refrigeration is the use of ice for chilling water for fats and meats.
Practically every packing house is now equipped with a small ice making
plant both for its use, and with commercial possibilities of selling
ice.
=Ice Plants.=--Ice plants are of various kinds:
(1) Common ice made from filtered water without processing.
(2) Raw water ice made from filtered or treated water, aerated or
agitated, while freezing.
(3) Distilled water ice made from condensed steam, reboiled.
(4) Plate ice, made from raw water in large plates and cut up into
blocks of convenient size.
In the production of distilled water there are various methods which
will not be treated upon here.
For the icing of cars and for ordinary cooling purposes ice made by
process No. 1 is amply good except, perhaps, if the water from which
the ice is made should not be clear, it may be necessary to use a
portion of the bottom of the cake for car icing purposes only.
=Natural Ice.=--The situation and climate has much to do with the
determination as to whether the packer can afford to harvest natural
ice for general use. For example, if the plant be situated in a
northern climate alongside a suitable stream adjacent to the plant,
the harvesting of ice and its storage can be afforded. However, if the
ice is stored at a remote point and teaming or car shipment of ice
is necessary, then the manufacturing plant will probably be the more
economical.
=Chilling.=--The chilling of the meat immediately after killing is
perhaps the most important function in the whole refrigerating process
and one that cannot have too much attention. In the matter of beef it
is the practice of the best operators to see to it that immediately
after the hide is removed the beef is placed in the coolers. At most it
should not be allowed to stand out in the open air to exceed half an
hour. Sheep and veal should be treated in the same manner. As for hogs
in some climates, such as latitude equal to Chicago or north thereof,
if space is available an open air hanging room is a valuable adjunct
where the animal can be air dried, depending upon seasons, from one
hour to over night. This feature also permits of increased slaughtering
during the winter season. It is a custom that can be abused, however,
by careless handling--resulting in sour meats.
=Quantity of Refrigeration to Provide.=--There are so many factors
which enter into the question of packing house refrigeration, and
so many details of construction and application of refrigerating
apparatus, that it is almost impossible to cover this subject
practically and intelligibly without devoting a volume to refrigeration
alone.
To give a fixed rule for packing house refrigeration, applicable to
all conditions, would be impossible, as much depends upon conditions
and surroundings, and the requirements would vary accordingly. For
instance, atmospheric conditions, quantity of space to be cooled,
temperature to be maintained, time for chilling, etc., these and
many other factors affecting the general results must be taken into
consideration and provided for, and as these vary, so will the
refrigeration requirements vary. A few ideas will be set out to assist
in the computation of the quantity of equipment to provide.
The capacity or size of the refrigerating equipment required for any
given plant is variable but can be reasonably closely computed by
assuming certain conditions.
=Space Per Ton Machine.=--Practice has demonstrated that one ton of
mechanical refrigerating effect duty, as rated by manufacturer used
continuously during a period of twenty-four hours will maintain at a
temperature of 33° to 38° F. from 7,000 to 12,000 cubic feet of storage
space. Conditions of exposure, insulation and outside temperature
affect this.
The minimum for beef storage coolers, the maximum for curing cellars.
The area of room or quantity of space enters into each of these
assumptions. If small rooms are used the unit to be assumed is smaller.
Concrete buildings are easier to control due to the stored cold in the
building mass of floors, columns and girders.
=Machinery Per Head.=--It is customary to figure that in addition
to that needed for cooling the space, one ton of refrigeration for
twenty-four hours would be required for either one of the following
items:
From fifteen to twenty-two hogs, average weight, 225 pounds.
From five to six head of cattle, average weight, 700 pounds.
About forty-five calves, average weight, 80 pounds.
From fifty to sixty-five sheep, average weight, 60 pounds.
=For Cooled Meats.=--For cold storage rooms, where meats which have
already been chilled or cooled are stored and held for a greater or
lesser period, the refrigeration requirements are not so great as in
chill and cooling rooms. The animal heat has been removed and the
meats cooled down to a low temperature, consequently but little more
refrigeration is required than that necessary to take care of the heat
leakage through the insulation, and possibly the recooling of the meat
through a range of a few degrees, when the meats may have gained a
little in temperature by exposure. Therefore it is estimated that one
ton of refrigerating duty will handle 12,000 cubic feet of curing or
storage space for temperature of 33° to 35° F.
=Freezer Space.=--As will be explained in the chapter relating to
refrigerating machine capacity, the capacity of a compressor very
rapidly decreases when operating under conditions necessary to produce
low freezer temperatures, and owing to the severe conditions imposed
it seems necessary to compute that one ton of refrigerating duty will
handle about 3,000 feet of freezer space.
=Ice Computations.=--Before the application of mechanical refrigeration
to packing house purposes, all artificial refrigeration was
accomplished by means of ice melting alone, and at that time the
packers computed ice melting requirements on a basis of cooling three
pounds of meat from 80° F. to as low as it could be cooled by ice
melting, for each pound of ice melted. While this rule undoubtedly was
the result of practical experience with well constructed coolers, and
was in no wise based upon theoretical or heat unit formulas, yet it
is interesting to note how close this old rule compares with modern
formulas of computing refrigeration. For example, the cooling of 100
head of hogs, averaging 250 pounds dressed, by the packer’s rule, would
require--
100 × 250
--------- = 8,333 pounds, or 4.16 tons ice melting.
3
And on a heat unit basis, cooling the same number and weight of hogs
from 80° to 32° F. would require--
100 × 250 × (80 - 32)
--------------------- = 4.166 tons refrigeration.
288,000
The above comparison shows that theory and practice approach very
closely to a common line, although in the calculation the factor of
specific heat of the meat is ignored, and in practice this may well be
left out, as specific heat of meats at various temperatures has by no
means been accurately established.
=Chilling Lard.=--The chilling of lard is a severe task on
refrigerating equipment owing to the very heavy duty imposed in a short
time. For example, with an eight-foot lard roll turning off 4,000
pounds per hour and changing the temperatures of the lard from 90° to
50° F. requires a very large compressor capacity per hour.
=Summary--Computations.=--Assuming the killing of 100 cattle and
250 hogs per day; making 10,000 pounds of lard, fifteen tons ice;
maintaining a freezer of 100,000 cubic feet and the small work
connected with the establishment:
For 100 cattle killed daily, and storage of 400 hanging, about 6,500
square feet area of cooler would be required; the height of this with
the lofts would be about twenty-two feet or a capacity of 143,000
cubic feet.
For 250 hogs daily or 750 total hanging, there would be required
3,000 square feet of floor area and a height of 18 feet or 54,000 cu.
ft.
The above number of hogs daily would also require a storage or cellar
capacity based upon one hundred pounds meat sent to cellar for a turn
over in sixty days equal to storing 1,500,000 pounds of product, or
15,000 to 20,000 square feet of floor area, requiring 200,000 cubic
feet of building space.
Ten thousand pounds lard daily in four hours running would require
the extraction of about two tons of duty, but by reason of the heat
transmission and the low temperature brine necessary would require
twelve tons duty while applied.
Fifteen tons daily ice making capacity requires about 30 tons
refrigerating duty, allowing for radiation and other losses.
A freezer capacity of 100,000 cubic feet which would store 1,500,000
pounds would not appear excessive. From known results this would
require about one ton refrigerating duty for 3,000 cubic feet of
space or thirty-five tons machine duty. We have then:
SUMMARY OF REFRIGERATION REQUIRED
Tons
143,000 cubic feet beef cooler space ÷ 10,000 14.3
100 cattle daily 500 pounds = 50,000 pounds
50,000 pounds meat chilled 70° or 70 B.t.u. per pound
50,000 × 70 = 3,500,000 ÷ 288,000 B.t.u. 12.2
54,000 cubic feet hog cooler space ÷ 10,000 5.4
250 hogs 180 pounds each = 45,000 pounds
45,000 × 70 ÷ 288,000 = 10.9
200,000 feet cellar space ÷ 12,000 16.6
15 tons ice × 2 tons refrigerating duty 30.0
10,000 pounds lard cooler 12.0
100,000 cubic feet freezer space 35.0
-----
Total tonnage refrigerating effect 136.4
=Low Temperature Brine System.=--The use of low temperature brine,
cooled by two stage compressors, a new development, is in the writer’s
opinion preferable to direct expansion. (See description of two stage
compression in Chapter IV.) A lineal foot of pipe filled with a liquid
like chilled brine seems to have greater heat absorbing power than the
same pipe filled with a light gas and consequently less piping can be
used.
_Preference Reasons._--Occasion arose to compare for a new large
installation the relative merits of direct expansion versus brine and
the following items suggested themselves:
(1) The direct expansion plant would require 150,000 lbs. ammonia in
excess of brine plant.
(2) There would be approximately 8,000 more joints to prevent leaking.
(3) Unavoidable ammonia leakage through rods, glands, valve stems,
compressor rods and purging would amount to at least $20,000 per year
based on experience with good practice.
(4) The installation by the same manufacturer estimated to cost 15%
more than a brine system.
(5) There would be no stored energy in the ammonia pipes as in brine
pipes should the refrigerating plant suspend operation temporarily.
(6) The compressor hazard from returning liquid and possible machine
wrecking with line breaks, ammonia losses, and danger to life.
(7) In case of extension or modification of piping, the difficulty with
ammonia pipes over brine is marked.
(8) In direct expansion plants the cooling effect is stopped
immediately when the compressor is stopped. It is required to operate
incessantly, or if speed be reduced the current is chiefly wasted in
resistance grids if electrically driven. Whereas in a brine plant the
compressors can be stopped several hours, the brine being circulated
rises in temperature but not sufficiently to vary room temperatures.
This is a great advantage, permitting keeping “off peaks” on commercial
electric lines and consequently earning lower rates.
(9) With an electrically driven compressor, speed control is fixed
within quite limited bounds and if direct expansion system is used
more power is purchased than needed for reasons already mentioned.
(10) The total cost for operating pumps and calcium taken collectively
will be far less than the uncontrollable ammonia leakage. The coil
attendants can be less skilled.
(11) Brine temperature 25 degrees below zero, Fahr., can be carried,
sufficiently low for all purposes. Rooms can not be controlled at as
exact temperatures with direct expansion as with brine, owing to its
sensitiveness.
(12) Lastly and very important, the complicated piping system to
carry several back pressures to produce varying temperatures and the
necessity of operating several compressor “ends” makes a complicated
installation of small units as against a simple system carrying one
temperature brine.
Plants of the character described usually operate on direct expansion,
require three sets of temperatures, three sets of suction pressures
and three sets of suction mains with various cross connections and
intricate pump-out arrangements. This necessitates multiplicity of
machines and connections to various cylinder ends.
Progressive authorities recognize the necessity of freezer storage
in meat plants. In combination pork and beef or pork plants, newer
installations will be made with far less curing space for sweet pickled
meats and far greater space for storing meats frozen either before or
after curing to the end of producing palatable meats, not salt soaked
and of inferior quality. There are slaughtering plants for export
where beef is shipped chilled or frozen, and mutton frozen. Some have
exclusive freezer buildings, others parts set aside for freezers.
One temperature brine is circulated, the temperature in the rooms
being governed by the quantity of pipe in service. In all instances,
sharp freezers, storage rooms and curing rooms are equipped with pipes
therein--and the chilling rooms for beef and pork closed coils or
spray, optional.
Shell and tube coolers have proven so fitting that no hesitancy need be
made about using them, and the possibility of freezing is negligible
with reasonable prudence. Tanks with submerged coils can be used, but
it prevents the saving made by using balanced brine pumping, on high
buildings, a quite material one.