Choosing the working parameters for the cold storage system is very important because if you choose a reasonable and correct working mode, it will bring high economic efficiency, increased cold productivity while low power consumption. . The working mode of the refrigerating system is characterized by the following 4 temperature parameters:

- The boiling temperature of the solvent t0 (oC).

- Condensation temperature of the solvent tk.

- Excessive solvent temperature of the tql1 condenser and the temperature of the liquid medium before the tql2 throttle.

- Temperature of steam drawn to the compressor (over temperature) th.

The boiling temperature of the solvent t0

The boiling temperature of the solvent depends on the temperature of the cold storage unit stored. The boiling temperature of refrigerant used for design calculations can be obtained as follows:

t0 = tb - ∆t0 = -20 - 8 = -28oC

Inside

tb - storage temperature, 0C

∆t0 - temperature difference between the boiling temperature of refrigerant and the temperature of the air in the warehouse. For direct evaporating indoor units ∆t0 = 8 ÷ 13oC. Select ∆p0 = 8oC.

Condensation temperature tk

The condenser temperature depends on the temperature of the condenser cooling medium. Due to the choice of a water-cooled condenser:

tk = + ∆tk = 33+ 5 = 380C

Inside:

- is the temperature of the water coming out of the condenser, 0 ° C

∆tk - is the required condensing temperature difference, usually taken from 3 ÷ 5oC.

Choosing the condenser temperature difference is actually the best economical problem for the cheapest cost of a cold unit. If the condenser temperature difference is small, the condenser temperature will be low, the capacity increases, the power consumption is small but the water consumption is much and the water cost increases. I choose ∆tk = 5oC.

The water temperature out of the condenser can be determined by the formula:

tw2 = tw1 + ∆tw = 28 + 5 = 330C

Inside:

tw1 - is the water inlet temperature, 0C

∆tw - is the temperature difference of water in and out of the condenser, usually taken from 2 ÷ 60C. I choose

Due to geological conditions in Soc Trang, the temperature of groundwater is about 370C, so groundwater is pumped to the storage tank and treated by pre-cooling by air. Water after cooling the condenser about 280C.

Steam temperature

As the temperature of the solvent vapor prior to entering the compressor, it is always greater than the boiling point of the medium.

To ensure that the suction compressor is not liquid, a liquid separator is arranged and must ensure that the steam drawn into the compressor is necessarily superheated. The temperature of the superheated is different for each type of compressor and for different types of media. With ammonia solvent, the steam temperature is 5 ÷ 150C higher than the boiling temperature. This means that the suction steam superheater ∆th = 5 ÷ 150K can ensure safety for the machine to work. Select ∆th = 80C.

We have: th = -28 + 8 = -200C

Ammonia air overheating can be achieved by the following:

- Overheating steam is absorbed right inside the indoor unit when using heat expansion valves.

- Overheating due to cold loss in the pipeline from the evaporator to the compressor.

The temperature is too cold

The lower the cold temperature, the greater the cold yield. Therefore, people try to bring the too cold the temperature down as low as possible.

The liquid overcooling in the cycle that we calculate here will be done as follows: part of the condenser has a tql1 temperature and then most of it gets too cold in the coils. The medium has a tql2 temperature.

In the condenser we choose is a horizontal shell tube condenser, the temperature too cold when passing through the reverse heat exchanger is still 3 ÷ 50C higher than the input water temperature. Select ∆t = 50C.

tql1 = t5 = tw1 + ∆t = 28 + 5 = 330C

Water is fed into the condenser, the overcooling is done in the condenser by allowing the liquid level to flood some of the bottom pipes of the condenser in the cluster condenser. The water supplied to the condenser will go through these pipes first to be too cold or liquid then onto the upper pipes to condense the solvent.

The liquid after the condenser liquid will be divided into two parts: a small part will be throttled to cool low-range compressed steam, the majority of the solvent will be too cold in the medium. After coming out of the average, there will be temperature and be sent to throttle into the indoor unit (based on experience):

tql2 = t6 = ttg + 50C = 50C