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21 Cards in this Set
- Front
- Back
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What is the safety factor for the total heat load? |
110% |
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How do you calculate transmission load? From finding k to getting U… Then Q=UATD |
(1) Find the conductivity coefficient (k) in the chart and divide it by the thickness in inches to find conductance (c) c=(k)/(inches) c=(1.10)/(0.75 in) c=1.47 BTU/(sq.ft. x F x hr) (2) R= 1/c R= 1/1.47 R= 0.68 (3) repeat for all materials in wall then add up all of the R values. (4) U= 1/R(total) U=1/(0.625+18.75+0.45) (4)U= 0.05 (5) get the total surface area (sq. Ft.) from the dimensions of the room for each wall 35x40x20ft (6) group the walls into ones where the delta T across the wall is the same. 70F inside, -20 outside, 55F under the floor) Total area with TD of 90F Roof + all walls = 4400 sq. Ft. Total area with TD of 15F Floor = 1400 sq ft (7) set up Q=UATD equations for both TD areas Q(TD(1))= (0.05)(4400 sq.ft.)(90F) Q(TD(2))= (0.05)(1400 sq.ft.)(15F) Q(total transmission)= Q(TD(2)) + Q(TD(1)) = 20,850 btu/hr Q(total per day)= 20,850 btu/hr x 24 hrs Q(total)= 500,400 BTU/Day |
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Not everything freezes at 32F!!! |
Yes |
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How do you calculate infiltration load? |
Q= (volume)(average air change)(service factor)(heat removed) A.k.a Q=(cubic feet)(table 8)(table 8 note)(table 9) Cubic feet = height x width x length Table 8 = take the volume and pick the highest number Ex. If 900 cu.Ft. @ 30F then either 15.3 or 13.5 air changes. Pick 15.3 (more is worse) Table 8 note= heavy = 2, medium = 1, light = 0.6. Pick the multiplier specified. Table 9 = with the outdoor air temp, relative humidity, and storage temp find the heat removed. Q=(1200 cu. Ft.) (17.5)(1)(1.7) Q=35,700 BTU/Day |
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How do you calculate product load if the load stays above its freezing point? |
There are 2 scenarios; either (1) the product starts warm and stays above the products freezing point or (2) the product starts warm and goes below the product freeze point. (1) if the product stays above its freeze point. (Table 10) then you need to do 2 equations (1.1) Q=m*c*delta T m=given in lbs c= sp ht is either above freezing or below freezing Choose above freezing value! Delta T= T2-T1 in F Q=m*c*deltaT Q=(1000lbs)(0.77)(90-39F) Q=39,270 btu/day (1.11) NOW!! If the load needs to be cooled in 7 hours then use the following steps: If there is no cool down time then skip 1.11!!! Divide by max hours (7hrs) 5,610.00 btu/hr Multiply by 24 hrs = 134,640 btu/day (1.2) Q=m*heat of respiration Only complete this step if the product is above the products freezing point AND has a heat of respiration m= tons (2000 lbs in 1 ton) Heat of Resp: see table 10, product and fridge temperature is needed to find BTU. Q= (0.5 tons)(2700 btu/day/ton) Q=1350 btu/day (1.3)And NOWWW!!!! Add: Q(product) and Q(respiration) ((134,640 btu/day)+(1350 btu/day)) Q(total product load) = 135,990 btu/day ————————- (2) the product drops below its freezing point. Then you will need to complete 3 equations No heat of respiration. |
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If the product moves below its freezing point? |
(2) if the product moves below its freeze point. (Table 10) then you need to do 3 equations (2.1) Q=m*c*delta T m=given in lbs c= sp ht is either above freezing or below freezing Choose above freezing value! Delta T= T2-T1 in F (2.2) Q=m*h m=lbs h=latent heat of fusion Q=(1000lbs)(100 btu/lb) Q=39,270 btu/day
(2.3) Q=m*c*delta T m=given in lbs c= sp ht is either above freezing or below freezing Choose below freezing value! Delta T= T2-T1 in F Q=m*c*deltaT Q=(1000lbs)(0.40)(29F- -10F) Q= 15,600 btu/day
Q(total)=Q(2.1)+ Q(2.2) + Q(2.3) |
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How do you calculate miscellaneous loads? |
Lightbulbs: section 15 3.41 btu/watt 2x 100 watt lightbulb for 12 hours Q(lights)= (2)(12 hrs)(100Wx3.41Btu/watt) Q(lights)= 8,184 btu/day Human Load: table 17 Find cooler temp and get BTU per person per hour Q(human) = (720 btu/hr/person at 50F)(2 people)(3 hrs a day) Q(human)= 4,320 Btu/day
Motor load: table 16 Go to table 16 find the motor btu/hr factor. If you have a 3 hp motor pick the larger btu number. Q(motor)= (3,700 btu/hr)(3hp motor)(3 motors)(18 hrs/day) Note: if you have a electric defrost then the fan motor run time will be 24Hr minus the defrost time. Electric defrost is 18hrs runtime so the fans will be running for 18hrs. —————— |
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What are enzymes? What temp kills them? |
Enzymes -Proteins that cause the decay of organic material. -Raising temperature greater than 170F kills most enzymes. -Lowering temperature does not kill enzymes, but slows the rate of enzymatic decay. |
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What are microorganisms? |
Microorganisms- Microscopic organisms that secrete enzymes that contribute to food decay. Bacteria - reproduce optimally between 75 - 85F -below 4 Celsius (39F) most bacteria become dormant and unable to reproduce. Yeasts - prefer temps between 55-85F -reproduction rate decreases as temps fall Molds - Can't tolerate high temps -can grow at temperatures approaching 32F -less active below freezing point -cease activity below 10F |
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Bacteria preferred temperatures? |
75-85F |
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Yeast preferred temperature? |
55-85 |
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Molds preferred temps? |
Cease activity below 10F |
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Correct fridge temps to limit food aging? |
Refrigerated Storage- Cooler temp must be 4 Celsius (40 Fahrenheit) or less) Seafood must be stored at 3.3 Celsius (38 Fahrenheit) or less Frozen food must be stored at -18 Celsius (0 Fahrenheit) or less. -10 Fahrenheit to keep ice cream solid (-23 Celsius) |
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Meat cooler evaps are push or pull? |
Push through |
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What temp should you store meat? Max? Low or high TD? |
Meats - Main concern is micro organisms -Store as close to 32F as possible. -Never exceed 40F -Dehydration is also a concern -Keep low TD -Use low velocity evaporator |
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What is the correct storage temperature for seafood? |
3.3C (38F) or less |
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How should you store fruits or veg? |
Fruits and vegetables - still alive - heat of respiration. -Need to breathe -holes in bags. -Very susceptible to surface dehydration - produce misters. |
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Mixed storage? |
Mixed Storage - Generally choose a lower relative humidity. Fish, potatoes and onion impart flavors to other foods especially dairy products, eggs, and nuts. |
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Milk and dairy storage? |
Milk and Dairy - Pasteurization (heating) kills bacteria, then milk is cooled again. -In Canada milk is heated to 72C for 16 seconds. |
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Freezing? Why freeze faster? |
Freezing - Freeze product as quickly after harvest as possible. -Faster freezing promotes smaller ice crystal formation and less damage to cell walls of food. -wrap tightly to prevent freezer burn (moisture sublimation) |
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What is sharp freezing? quick freezing? Immersion freezing? Contact freezing? Blast freezing? |
Freezing - Freeze product as quickly after harvest as possible. -Faster freezing promotes smaller ice crystal formation and less damage to cell walls of food. -wrap tightly to prevent freezer burn (moisture sublimation) Sharp Freezing - place product in a low temperature and allow to freeze slowly in still or low velocity air. Quick Freezing Used for fish and shrimp. evaporator) Immersion Freezing - Product is wrapped and immersed in a low temperature brine solution. Contact freezing - Product is placed on plates that freeze the product (plates are the Blast Freezing - Product is exposed to low temperature, high velocity air. You should avoid temperature fluctuations when storing products, this will result in ice crystal formation Com product. Ice cream is especially susceptible to ice crystal formation. |
