【 Weak current college 】 selection of prefabricated cold storage and current problems

Summary description of the selection of prefabricated cold storage and its total cooling load calculation, insulation thickness of prefabricated, evaporator and rational allocation of the refrigeration unit. And introduction of a "machine" shock absorbers "in refrigeration units installed in the application.
Keyword (s) total fabricated cold storage, refrigeration load, thermal insulation thickness, evaporator, machine tool shock absorber.

I. preface
Prefabricated cold storage is developed a fast and easy Assembly of refrigeration equipment, it and compared to traditional civil cold store has the following advantages:
1. heat insulation layer for polyurethane, thermal conductivity as 0.02kcal/m.h. ℃; insulation for poly styrene, thermal conductivity as 0.034kcal/m? h? ° c. Such materials waterproof performance, low water absorption, the outside covered with plastic coated Panel, makes its vapor permeation resistance H → ∞. Therefore, good heat insulation and moisture-proof waterproof performance. Use the range from-50 to + 100 ℃.
2. light weight, easily worn-out, flame-resistant properties.
3. high compressive strength, good seismic performance.
4. the combination of flexible, easy to install, or configure according to user needs and refrigeration units and system control components.

II. selection of prefabricated cold storage:
Currently on the market usually prefabricated cold store Interior and exterior, its selection criteria are as follows:
1. cold storage, the ambient temperature and humidity: temperature to + 35 ° c; relative humidity is 80%.
2. the freezer set temperature within: L-refrigerator: + 5 ~-5 ° c; D-cold storage:-5 to-20 ° c; J-cold storage:-25 ° c
3. Enter Library food temperature: L-30℃ cold storage: +,-,-D J: + 15 ° c cold storage.
4. cold storage stack cargo effective volume for the nominal volume of 69%, the storage of fruits and vegetables is then multiplied by the correction factor for 0.8.
5. the daily purchase of cold storage effective volume of 8 to 10%.
6. refrigerator work factor 50 ~ 70%.

3. cold storage total refrigeration load determination:
1. refrigeration storage tonnage: G = (σ V. r-η)/1000 (t) (1)
2. daily stock quantity: Gj = 0.1.G (kg) (2)
3. cargo cooling consumption: Q1 = Gj? C (t1-tn) (kcal/h) (3)
4. the library door cooling consumption: Q2 = △ I? V? n/24 (kcal/h) (4)
5. loading personnel cooling consumption: Q3 = q? nr (kcal/h) (5)
6. interior lighting cooling consumption: Q4 (the negligible)
7. cold storage building envelope of heat:
Q5＝Q5a+Q5b+Q5c　　　　　　　　　　　　　　(kcal/h)(6)
Type: Q5a = 1.6? (λ/δ)? Fa?　(tw-tn) (kcal/h) (6-1)
Q5b＝1.3?（λ/δ）?Fb?　　　　(tw-tn) (kcal/h) (6-2)
(The above two-in option is not multiplied by the correction factor)
Q5c＝（λ/δ）?Fc? (tw-tn) (kcal/h) (6-3)
8. cold theory cooling consumption:
Qm＝Q1+Q2+Q3+Q5　　　　　　　　　　　　　(kcal/h)(7)
9. total cooling consumption: Q0 = 1.1? Qm (kcal/h) (8)
More in:
V--cold nominal volume (m3)
R--food or goods in the calculation of severe (kg/m3)
Η--cold storage volume utilization factor within
Tn--cold temperature (℃)
T1--food into the library of temperature (℃)
C--food or goods, specific heat (kcal/kg? ° c)
△ J--cold storage and external air enthalpy difference (kcal/m3)
Η--24 hours cold storage doors opening times
Q--each cold store operator within the unit of time of cooling consumption (kcal/h)
Nr-a-cold storage in the number of operators
F--cold storage building envelope of the heat transfer area (m2)
F＝Fa+Fb+Fc
-In-the-envelope materials for thermal conductivity (kcal/m? h? ° c)
Δ--retaining structure materials (prefabricated) of thickness (m)
Tw--freezer-calculation of temperature (℃)
Q5a--cold roof surface cooling consumption (kcal/h)
Q5b--cold around the walls of cooling consumption (kcal/h)
Q5c--cold floor of cooling consumption (kcal/h)

IV. cold storage in the calculation of the area of evaporator:
Evaporation area: Fz = Qo/(K? ¡÷ t) (m2) (9)
Type: K--evaporator heat transfer coefficient (kcal/m2? h? ° c)
¡÷ T--cold storage of internal and external temperature (℃)
5. insulation thickness precast slab calculations of experience:
Insulation thickness: δ = (tw-tn)/8 × 20 (mm) (10)
Polyurethane rigid foam thermal conductivity into = 0.025 (kcal/m2? h? ° c)

6. now assembled cold inventoryIn question:
1 insulation thickness precast slab lack of serialization:
Current market sales of fabricated cold storage, manufacturers in the production, whether high or low temperature requirements of libraries use the thickness of 100 mm of polyurethane insulation prefabricated panels, which will correspondingly cause cold storage library on insulation capacity is insufficient, cold consumption seriously and many other issues. To this end, we are available from the insulation thickness of prefabricated experience-analysis visible: cold storage insulation thickness (δ) is the temperature inside the cold store itself (tw-tn) proportional to the temperature inside the library, depending on the set requirements, insulation thickness meets the design criteria, cold storage of heat insulation performance is good, the outside world through its envelope into cold storage in the thermal load on the small, and energy consumption and refrigerator with low coefficient; on the contrary, the freezer set temperature in the lower Gallery body insulation performance will drastically declined, and the resultant cooling loads and energy consumption increases, refrigerator, work factor exacerbates the cooler itself mechanical wear and unit weight increase of cold storage expenses. To my experience, if the insulation thickness corresponding increase 25%, the envelope of heat flux from 10 (kcal/h m2?) down to 8.5 (kcal/h m2?), perimeter guarding incoming heat will reduce the 17-18%, thus, manufacturers in the production of precast reinforced concrete prefabricated insulation of cold storage configuration, you should take into account the temperature on the cold storage and external thermal insulation thickness requirements, depending on the library temperature requirements for configuring different thickness of insulation prefabricated panels to meet the cooling process requirements.
2 evaporator evaporation area of unreasonable configuration:
Library in the evaporator evaporation area in configuration and actual refrigeration process a big gap between the technical requirements. According to some prefabricated cold storage field observations, the evaporator evaporation area only 75% should be configured. We know, in the cold evaporator configuration, on the basis of their design temperature for the thermal load calculation to determine the evaporator evaporation area, and then under refrigeration technology requirements. If you do not press the design requirements of reasonable configuration evaporator and blindly reduced evaporator configuration area will make the flat area of refrigerating factor significantly decreased and refrigeration load increases, the energy efficiency ratio significantly lower, resulting in declining slowly in the temperature cold storage, refrigerator work factor towards increased operating costs increase, and so called negative factors, therefore, in the design selection of evaporator refrigerating plants should be the best heat temperature difference to select Configuration area of the evaporator.
3 refrigeration units of unreasonable configuration:
Some manufacturers on the production of prefabricated cold store refrigeration units are configured, not according to the library design cooling load calculation of total and its envelope insulation thickness, etc for reasonable configuration, but to add refrigeration unit number of the means to meet library demands for fast cooling down inside. To 4-type assembled cold BZL-3× as an example, the Library 4 meters long, 3 meters wide, high 2.7 m, net capacity within 28.723 cubic meters, equipped with 2 2F6.3 series refrigeration units and 2 independent group of snake-like optical tube evaporator, the unit with an independent evaporator consists of a complete refrigeration systems for refrigeration. Under cold storage machine loading diagram analysis shows (see Figure 1): the cold Chamber machine load of about 140 (W/m3), the total load is 4021.22 (W) (3458.25kcal), according to the above data, the library selection 1 2F6.3 series refrigeration units (standard refrigeration capacity 4000kcal/h) will also be able to meet the technological requirements of refrigeration (up to-15 ° c to-18 ° c), therefore, in the library on multiple distribution 1 2F6.3 series refrigeration units are redundant, and you will waste a lot of energy and increasing the unit cost of maintenance.
We all know, in the refrigeration system, evaporation temperature and evaporation pressure each other to function, they are and the temperature of a body by cooling and refrigerating capacity, heat area (mainly refers to the evaporator) and compressor capacity, and several other conditions, if one of the conditions change, refrigeration system of evaporation temperature and evaporation pressure will change accordingly. In 4-type assembled cold BZL-3×, evaporation area has not changed, but its refrigerator capacity but increase twice, this enables the evaporator of evaporation and compressor suction volume not adapted (evaporation Vo significantly less than the compressor suction volume Vh), i.e., V0 page〈 Vh, evaporation pressure Po and evaporation temperature to a sharp decline, heat transfer, thermal ¡÷ t temperature inside the cold store but difficult, due to the evaporation temperature too low, then the compressor performance indicators, economic indicators deteriorated.

VII. refrigeration units install machine shock absorber's recommendations:
Traditional refrigeration units installed, usually on the basis of the concrete pre-embedded, then install it. The above installation methods generally require a duration is long, and the unit and the concrete foundation for rigid contact, seismic performance is poor. The author according to years of practical experience, recommend a "machine" shock absorbers ", to address past refrigeration units in use of vibration problems. The product uses a large amount of oil damping rubber, takes full advantage of damping rubber absorbs vibration performance, has excellent shock absorbing, vibration isolation and noise reduction, and easy to install, and can save a lot of Foundation construction cost and time. Practice shows that the use of machine tools, due to the shock absorber unit vibration refrigerator parts damaged, refrigeration piping interface fault rupture and loose, etc.