Heat Load & Air Circulation NHB - Training 15.10.2013 - Delhi Himanshu Sheth
REFREGERATION CYCLE FOR POTATO COLD STORAGE www.alfalaval.com 2 www.helpman.com
Layout : Four Chamber Potato Cold Store www.alfalaval.com 3 www.helpman.com
OLD – BUNKER SYSTEM www.alfalaval.com 4 www.helpman.com
COIL ARRANGMENT - BUNKER www.alfalaval.com 5 www.helpman.com
NEW COLD STORAGE WITH AIR UNITS www.alfalaval.com 6 www.helpman.com
Fruit and vegetables keep on living, even during storage! Slide 7
Metabolism of vegetables and fruit after harvesting Oxygen Respiratory heat Carbon dioxide Water C 2 H 4 Transpiration www.alfalaval.com Slide 8 8 www.helpman.com
Respiratory heat • Depends on the product • Depends on the ambient temperature www.alfalaval.com Slide 9 9 www.helpman.com
Heat generation of various products Heat generation (kcal/t in 24 h) depending on the storage temperature (°C) 0 5 10 15 20 Potatoes 380 325 400 575 700 Apples 165 355 530 885 1,200 Tomatoes 320 425 750 1,450 1,875 White cabbage 340 475 700 1,125 2,250 Cucumbers 405 600 1,150 2,225 3,375 Asparagus 1,275 1,650 3,150 5,000 6,750 Chinese cabbage 1,100 1,680 3,480 5,600 8,500 Brussels sprouts 1,200 2,400 4,075 5,630 10,400 Mushrooms 2,400 3,200 5,100 9,800 12,800 Endives 2,480 4,000 5,450 7,300 11,000 www.alfalaval.com Slide 10 10 www.helpman.com
Quality requirements • It is essential to reduce respiration in order to maintain a high quality. • Once harvested, fruit and vegetables must therefore be stored as soon as possible at optimum temperature and humidity levels for the respective product. www.alfalaval.com Slide 11 11 www.helpman.com
Two types of storage • Short-term storage During short-term storage, several products may be kept together at comparatively high temperatures. • Long-term storage Long-term storage involves particularly high demands with regard to the air conditioning of the refrigeration system. Both the temperature and the air humidity must be adapted to the respective products. www.alfalaval.com Slide 12 12 www.helpman.com
Empirical values cold room evaporating temperature rel. air humidity temperature temperature difference measured values − 7 °C +1 °C 8 °C 85-92 % − 4 °C +1 °C 5 °C 92-94 % − 3 °C +1 °C 4 °C 97-98 % • The smaller the temperature difference, the lower the dehydration rate and the higher the air humidity. A temperature difference of 4 º C can only be achieved with an electronic expansion valve. • Caution: Make sure that the cooling capacity is designed to match this low temperature difference !!! www.alfalaval.com Slide 13 13 www.helpman.com
Heat to be extracted by the evaporator Field heat and packaging heat The product is stored at field temperature. The heat released is called field heat. The same applies to the packaging material. www.alfalaval.com Slide 14 14 www.helpman.com
Heat to be extracted by the evaporator Respiratory heat So-called respiration or dessimilation is associated with any living product and releases respiratory heat. Rules of thumb: – Lots of heat at high temperatures – Little heat at low temperatures – More or less heat depending on the type of product www.alfalaval.com Slide 15 15 www.helpman.com
Heat to be extracted by the evaporator Air exchange rate During air exchange, the entire air content of an empty cold room is exchanged and replaced by fresh air, an effect that is mainly caused by the opening of the cold room door. www.alfalaval.com Slide 16 16 www.helpman.com
Heat to be extracted by the evaporator Ventilation heat During ventilation, a certain air volume in the room is exchanged and replaced by fresh air from outside, which also introduces a certain amount of heat. At the same time, a certain amount of ventilation is to be expected if the cold room is not absolutely tight (e.g., if a door does not close tightly, or if one of the walls is permeable). Important: Permeability means heat supply! www.alfalaval.com Slide 17 17 www.helpman.com
Heat to be extracted by the evaportor Conduction heat entering through walls, ceilings, and floors. The difference between the inside and outside temperature causes a certain heat flow into the cold room. www.alfalaval.com Slide 18 18 www.helpman.com
Heat to be extracted by the evaporator Door heat The door is opened regularly to load products into the cooling cell, causing cold air to escape from the cold room and warm air to enter. www.alfalaval.com Slide 19 19 www.helpman.com
Heat to be extracted by the evaporator Fan motor heat The electrical power of the evaporator fan is converted into heat and must be removed. www.alfalaval.com Slide 20 20 www.helpman.com
Heat to be extracted by the evaporator Personnel and fork lift heat www.alfalaval.com Slide 21 21 www.helpman.com
Heat to be extractor by the evaporator Lighting Lights should be left on only as long as there are people in the cold room (e.g., during loading and unloading). www.alfalaval.com Slide 22 22 www.helpman.com
Heat to be extracted by the evaporator Fan motor heat Ventilation heat Lighting heat Conduction heat Personnel & fork lift heat Respiratory heat Field and packaging heat Door heat Air exchange www.alfalaval.com Slide 23 23 www.helpman.com
Potato Cold Store Chamber Volume 3.4 cu m/MT Design Conditions : Air Flow: Temperature 3 + 1 deg C Loading & Pull down 85 cmh/MT Relative Humidity 90 to 95 % Holding Around 50% Outdoor air change 2-6 air changes/day CO2 Level : During loading upto 4000 ppm During holding upto 2000 ppm Cooling Rate: For CIPC application: Cooling upto 10 Cooling upto 15 deg C in 24 deg C in 24 hours. hours. Cooling upto 3 + 1 deg C within 8 days. Cooling @ 0.5 deg C/day upto 11+1 degC. Typical operating conditions: Loading Rate: Air on 3 deg C 4 % at 25 deg C Air out 1 deg C 5 % at 20 deg C www.alfalaval.com Slide 24 24 (-)2 deg C Evaporating temp www.helpman.com
Determining size of the cold room The size of the cold room depends on: • The filling capacity • The air circulation system • Cold rooms should have a rectangular shape if possible (length-to-width ratio = 3:2) • The height of the room depends on the packaging. Reference: stacker height plus a clearance of at least 10% of the total room height. www.alfalaval.com Slide 25 25 www.helpman.com
Clearances 60 cm 25 cm Stacker height 525 cm Case height 75 cm www.alfalaval.com Slide 26 26 www.helpman.com
Clearance for sloping ceilings 35 cm 25 cm www.alfalaval.com Slide 27 27 www.helpman.com
Sample calculation for 250 t apples • Determining the size of the cold room – Stacking cases (wood, 60 kg) containing 300 kg apples – Dimensions l x w x h = 1 x 1.2 x 0.75 m • Number of cases – 250,000 kg : 300 kg per case = 840 cases • Stacking of cases – Stacked 7 cases high, the bottom level covers a floor space of 10 x 12 cases. – Space between cases = 5 cm – Space between walls = 10 cm www.alfalaval.com Slide 28 28 www.helpman.com
Dimensions of the cell • Length 12 x 1 = 12.00 m + 11 x 0.05 = 0.55 m + 2 x 0.10 = 0.20 m Inner length = 12.75 m • Width 10 x 1.2 = 12.00 m + 9 x 0.05 = 0.45 m + 2 x 0.10 = 0.20 m Inner width = 12.65 m • Height 7 x 0.75 = 5.25 m + min. 10% = 0.75 m Inner height = 6.00 m www.alfalaval.com Slide 29 29 www.helpman.com
Stacking plan for apple crates 10 5 1265 Dimensions in cm 5 100 1275 10 www.alfalaval.com Slide 30 30 www.helpman.com
Required cooling capacity 45 Respiratory heat loading 40 35 30 Field heat 25 20 Respiratory heat 15 Cooling capacity Lighting, fork lift, personnel Air exchange heat 10 Ventilator heat 5 Conduction heat kW 0 Day Loading 10 Long-term storage www.alfalaval.com Slide 31 31 www.helpman.com
ULO Principle (Ultra Low Oxygen) Relief valve Air CO 2 Scrubber N 2 generator N 2 Conversion of O 2 CO 2 O 2 to CO 2 ca 1% every 24 h CO 2 O 2 O 2 Air Vacuum safety valve O 2 & CO 2 analyser www.alfalaval.com Slide 32 32 www.helpman.com
Capacity / air volume ratio 50 kW 50 kW Sufficient air Insufficient air www.alfalaval.com Slide 33 33 www.helpman.com
Draw-through or blow-through air coolers Blow through Draw through +1 °C +1.2 °C -1 °C +1 °C -1.2 °C -1 °C Air in +1 °C Air out -1 °C Evaporating temp. -6 °C Surface 284 m 2 K value 24 Air temperature °C Air temperature °C +1.2 +1 TD air, motor side 0.2 °K +1 0 0 -1 -1 -1.2 -2 -3 -3 -4 -4 -5 -5 -6 -6 -7 -7 -8 -8 -9 -9 -10 ∆ T 1,2 = 7.2 K 5 K ∆ T 1,2 = 7 K 4.8 K LOG ∆ T = 6.03 LOG ∆ T = 5.83 Capacity = m 2 x K value x LOG ∆ T Capacity = m 2 x K value x LOG ∆ T = 284 x 24 x 6.03 = 284 x 24 x 5.83 = 41.1 kW = 39.8 kW www.alfalaval.com Slide 34 34 www.helpman.com
RH draw-through Air Coolers Air-off -1 °C 89 % RH +1 °C -1 °C www.alfalaval.com Slide 35 35 www.helpman.com
RH blow-through air coolers Air-off 0 °C 98 % RH (drawing: 89%) +1 °C -1 °C www.alfalaval.com Slide 36 36 www.helpman.com
Relative humidity as a function of DT1 DT1 = diff. Between air inlet and evaporating temperature. 100 95 90 Rel. humidity in % 85 80 75 70 4 5 6 7 8 9 10 11 12 DT1 in K www.alfalaval.com Slide 37 37 www.helpman.com
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